Broadland Fens Site Hydrology Assessment

Feb 2013

Broadland Fens Site Hydrology Assesment and WETMEC Development

ELP Team

Kirsty Spencer and Jonny Stone

Broads Authority Team

Sue Stephenson and Andrea Kelly

Prepared for

Broads Authority

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Name Position Signature

Author Kirsty Spencer Senior Ecologist

Co-Author Jonny Stone Senior Ecologist

Approved by Mike Hill Fisheries and Ecology

Manager

This report was prepared by OHES Environmental Ltd (OHES) solely for use by the Broads Authority (BA). This

report is not addressed to and may not be relied upon by any person or entity other than the Broads Authority

for any purpose without the prior written permission of the Broads Authority. OHES, its directors, employees

and affiliated companies accept no responsibility or liability for reliance upon or use of this report (whether or

not permitted) other than by the Broads Authority for the purposes for which it was originally commissioned

and prepared. In producing this report, OHES may have relied upon information provided by others. The

completeness or accuracy of this information is therefore not guaranteed by OHES.

(This page has been left blank intentionally)

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CONTENTS

Summary 7

1. Introduction 9 1.1 Project Background 9 1.2 Aims of this Study 9

2. Review of existing hydrological datasets held by the Broads Authority 10 2.1 Sources of information 10 2.2 Methodology 10 2.3 Results 12

2.3.1 Hydrological parameter: Regional RoC data 12 2.3.2 Hydrological parameter: Regional conductivity logging points 18 2.3.3 Hydrological parameter: Site specific conductivity monitoring 24 2.3.4 Hydrological parameter: Conductivity monitoring of river water 31 2.3.5 Hydrological parameter: Tidal data 35 2.3.6 Hydrological parameter: River water quality data 38 2.3.7 Hydrological parameter: Rainfall data 44 2.3.8 Supporting information 49

3. Production of a site-based summary spreadsheet of hydrological data 57

4. Assessment of selected sites using a WETMEC approach 58 4.1 General methodology 58 4.2 Trial site assessment 59

4.2.1 Ebb and Flow Marshes 59 4.2.2 Hall Fen 69 4.2.3 Mrs Myhills Marsh, Catfield Common and Lings Hill 79

5. Conclusions 94

6. References 96

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Summary

The Broads Authority is in the process of conducting and commissioning a number of studies with the overall aim of assessing current and future hydrological functioning in Broadland fen habitat. The purpose of this report is to assess data currently held by the BA on site hydrology and construct a spreadsheet which lists all hydrological data available by site. A second aim of the study is to use the available hydrological data to consider a number of sites within the WETMECS framework (Wetland Water Supply Mechanism).

The datasets interrogated were limited to those already held by the Broads Authority and those easily obtainable from the Environment Agency during the life of the study. The first suite of datasets relates purely to hydrological parameters, including sources such as: Review of Consents (RoC) data, regional and site specific conductivity monitoring, water quality data and tidal data. The second suite of datasets contains supporting information which is relevant to the hydrological functioning of fen sites or reflects hydrological conditions. It includes sources such as: the Fen Vegetation Survey, The Fen Audit, The Fen invertebrate Survey and Appendix 3A of the report by Wheeler, Shaw and Tanner (2009) on sites where WETMEC types have been identified.

The study acknowledges that gauging the usefulness of each dataset will depend on the end use. Four key uses are identified;

• The formation of a conceptual hydrological model (such as the WETMEC framework). In this case, water level data from dipwells and boreholes are considered to be the most useful hydrological information held by the BA. However, site-specific conductivity monitoring is also considered to be very valuable.

• The assessment of fen condition (e.g. whether water levels and water quality is appropriate for maintaining features of high ecological importance). Once again, dipwell, gaugeboard and borehole data are all of importance, but conductivity monitoring from a range of sources is of increased significance.

• The prediction of future environmental changes. Where frequency and impact of tidal incursions is the main issue; conductivity data, climate data and tide data are all valuable resources. Where risk from abstraction is the issue; dipwell and borehole data are of particular value. Where climate change is the key concern; river and tide levels alongside data from weather stations is of key importance.

• The measurement of changes to site management (such as the effect of constructing a new sluice or re-routing surface waters). In this respect, much of the data currently held by the BA is not designed for this use and therefore has limited value. However, dipwell, gaugeboard and borehole data would still be moderately useful.

Several potential uses of the existing datasets are described in detail and include:

• Using water level data to assess fen condition.

• Using regional conductivity monitoring to inform the formation of a conceptual hydrological model.

• Using regional conductivity monitoring in aiding assessment of best fen condition.

• Using conductivity data to predict the extent of brackish water incursion within Broadland sites.

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Three trial sites were chosen for WETMEC assessment, based on the resources available within this project. Sites were chosen to reflect different river catchments, different landscape situations and differences in available data held by the BA. The three sites were as follows: i) Ebb and Flow Marshes, ii) Hall Fen, and iii) Mrs Myhills Marsh, Catfield Common and Lings Hill.

For each site, all available BA data was compiled to build up a picture of site characteristics and highlight any uncertainties. Wheeler, Shaw and Tanner’s report (2009) was then used to work through each WETMEC unit to find the best match for the site.

The process of classifying sites within the WETMEC framework was felt to be an extremely useful one. Not only does it provide a means of exploring the similarities and vulnerabilities between sites through the use of standardised terms, but it also requires an holistic approach to assessing the hydrological functioning of a site. It therefore brings together various sources of information which may have existed about a site for some time, and which in themselves may not be conclusive, but when brought together form a clearer picture.

A valuable dataset used in all three trial sites for WETMEC assessment was found to be EA RoC data (from dipwells, gaugeboards and boreholes). However the usefulness of this data was somewhat limited by the absence of marsh height data (Lidar or otherwise) so that it was not possible to gauge whether the water table was, for example, 10cm below ground level (bgl) or 50cm bgl. The Fen Vegetation Survey proved a key alternative means of gauging wetness within a site, and possible water sources, by the use of Ellenberg Indicator Values. These values gave a clue to long-term conditions within the site and, where real data was also present, often reflected the raw data surprisingly well. Conductivity monitoring data also proved extremely useful at some sites so that the influence of the river could be assessed. However, EA conductivity data is very dependent on the placement of the monitoring point, as is highlighted by the BA site specific conductivity monitoring and the Ellenberg Indicator Values for Salt.

The remainder of useful data came from the direct observations of staff or surveyors after visiting the site (either in the form of notes within the Fen Audit, or from the memories of Fen Vegetation surveyors). However, it is strongly believed that direct communication with those members of staff who manage the site would have facilitated this process and, in some cases, have been a more reliable source of information. A further piece of information which was found to limit application of the WETMEC framework was the absence of soil surface details. Collection of this data would not need to be a detailed set of information but merely a walkover survey recording the condition of the peat surface during a typical summer.

In conclusion, it is believed that the BA hold a considerable set of useful data which, where water level and vegetation data exist (together with the input of site staff) would be sufficient to classify a large majority of broadland sites using the WETMEC classification. Sites without water level data but with vegetation data may still be able to be broadly classified but would have a greater level of uncertainty until water level data could be obtained.

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1. Introduction

1.1 Project Background

The Broads Authority is in the process of conducting and commissioning a number of studies with the overall aim of assessing current and future hydrological functioning in Broadland fen habitat. The aims of the suite of studies are to:

• Assess actions required on a site by site basis to determine what needs to be done on these sites to bring them into best fen condition in the Broads by using the site data in the Fen Ecological Study (combining Fen Audit assessment and the site hydrology where available)

• Assess data on site hydrology and assess a number of sites using WETMECS.

• Produce a clear summary of any problems, issues or constraints limiting best fen condition and recommend restoration and management projects required to address these.

• Provide a framework for assessing biodiversity value and vulnerability risk from climate change.

1.2 Aims of the Study

The purpose of this report is to realise the second of the overall aims. In particular, to:

• Identify and assess the usefulness of existing datasets held by the BA relating to water quality, water levels and other hydrological studies pertinent to fen hydrology.

• Produce a site-based spreadsheet listing available hydrological data (for all fen sites).

• Assess three selected sites using a WETMECS approach.

• Document the process used during the WETMECS trial and the uses of data available.

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2. Review of existing hydrological datasets held by the Broads

Authority

2.1 Sources of information

For the purposes of this study, the datasets interrogated were limited to those already held by the Broads Authority and those easily obtainable from the Environment Agency during the life of the study. The first suite of datasets relates purely to hydrological parameters and includes: - Regional hydro-geological data commissioned by the EA and collected primarily for

Review of Consents (RoC). - Regional conductivity logging points (source: EA). - Site conductivity monitoring of selected sites (source: BA). - Conductivity monitoring of river water on the Bure and Ant (source: EA). - Tidal data on the River Thurne and Bure (source: EA). - River water quality data (source: EA). - Rainfall data (source: EA). The second suite of datasets contains supporting information which is relevant to the hydrological functioning of fen sites, or reflects hydrological conditions. It includes: - WETMECS data (source: Wheeler, Shaw and Tanner, 2009). - National Vegetation Classification (source: BA Fen Vegetation Survey). - Invertebrate data (source: BA). - The Fen Audit Database (source: BA). - Data from the Broadland Headwaters Peat Survey 2010 (source: BA). - Data from Broads Peat Database (source: BA). It is likely that several other very relevant datasets are held by organisations such as Natural

England, Norfolk and Suffolk Wildlife Trust and the University of Sheffield. Though it was not

possible to incorporate such datasets into this study (due to time constraints), it is intended

that this data will be added to the summary spreadsheet as it becomes available to the

Broads Authority.

2.2 Methodology Information on each dataset is presented in three ways. The first section describes the

coverage of the dataset. The second section describes the content and availability of the

data (for example, the length of the monitoring period, the frequency of monitoring and the

variables recorded). The third section describes the potential uses of the dataset. However

it is noted that, with the objective in mind of “Assessing current and future hydrological

functioning in Broadland fen habitat”, there are several different ways in which the

hydrological data can be considered;

Firstly, it’s use in the formation of a conceptual model of how the site hydrology

currently operates. This can be approached through a number of techniques, such as

construction of a water balance or application of the Wetland Water Supply Mechanism

classification (WETMECS) developed by Wheeler, Shaw and Tanner (2009). Where such a

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model exists, it provides a means of assessing the importance of groundwater, rainwater,

drainage of surface waters, the importance of flooding and adjacent land uses etc. and

therefore forms a baseline for predicting the effects of changes to these water resources.

Secondly, hydrological data can be used in improving understanding of how site hydrology

relates to the fen condition. In particular, whether water levels and water quality on a site

is appropriate for maintaining fen plant, invertebrate and mammal communities of high

ecological importance.

Thirdly, hydrological data can be used in the prediction of future environmental changes

such as increased tidal incursion, increased river flooding, changes in rainfall and

evapotranspiration rates, and increased abstraction of groundwater.

Lastly, the data can be considered in terms of its use in measuring changes to site

management, either to counteract external influences or improve fen condition (for

example, in measuring the effect of constructing a new sluice or re-routing surface water).

In the following sections, the usefulness of each dataset will be analysed with these four uses

in mind.

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2.3 Results 2.3.1 Hydrological parameters – Regional RoC data

2.3.1.1 Coverage

Figure 1: Location of RoC stations monitored by the Environment Agency

Contains Ordnance Survey Data. © Crown copyright and database right (2011).

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Dipwell data is available within 31 of the 113 fen sites, with a further 19 sites showing

dipwells within 500m of the site boundary1. The Ant catchment has the best resource of

dipwell data, usually in the form of a row of dipwells running at right angles to the river.

However, there appears to be an absence of dipwells within Sutton High Fen, Sutton Wood

Farm Marsh and Snipe Marsh in particular. The Thurne catchment is well resourced around

Hickling Broad but no dipwells occur within Horsey Mere or Compartment 14/04-16.

Dipwells are less frequent within the Bure catchment, for example around sites such as

Ranworth, Horning Marsh Farm, Hoverton Marshes and Dobbs Beck. The Yare catchment

is well resourced around Strumpshaw, Buckenham and parts of Surlingham, but gaps are

present within Surlingham Broad, Bargate and the upper reaches of the Yare. No dipwells

were present within the Muckfleet catchment and dipwell data within Rond compartments is

extremely rare.

Gaugeboard data is available within 38 of the 113 fen sites, with a further 19 sites showing

gaugeboards within 500m of the site boundary1. Catchments for the Rivers Ant, Thurne,

Bure and Yare all have modest but scattered numbers of gaugeboards, but the Muckfleet and

Waveney catchments contain very few monitoring points of this kind. Within all of the

catchments, the majority of gaugeboards are located within the fens, and are a measure of

internal ditch water levels. However, due to the open connections which often exist

between fen sites and the Rivers Bure and Yare, several of these gaugeboards also represent

river water level data2.

Borehole data is available within only 16 of the 113 fen sites, with a further 14 sites showing

boreholes within 500m of the site boundary1. Their distribution typically involves clusters

around a few key sites (such as Smallburgh, Broad fen and Catfield in the Ant catchment,

Potter Heigham and Mrs Myhills Marsh in the Thurne catchment, Crostwick Marshes and

Upton Fen in the Bure catchment, and Limpenhoe Marsh and Poplar Farm on the Yare).

Outside of these key sites, a scattering of individual boreholes occur around residential

property.

2.3.1.2 Description of content and availability

This dataset consists of water table readings from a network of dipwells, gaugeboards and

boreholes. The majority of monitoring points are levelled in to Ordnance Datum, though

this is not always the case. Datasets typically start in 2006/07 and show monthly readings up

to the end of 2009. They therefore represent three years of data, which includes a

particularly wet year with a very wet summer (2007), an average year (2008) and an

especially dry year due to a very dry autumn (2009)3.

Eighty of the points are dipwells, three of which are not yet surveyed into Ordnance Datum.

The typical dipwell depth ranges from 0.75 to 2m bgl (below ground level) and data is logged

by Diver and/or Baro loggers. Forty eight of the monitoring points are gaugeboards, 6 of

which have not been levelled into Ordnance Datum. Gaugeboards are typically either 1 or

1 Excluding those dipwells which occur on the opposite side of a river or main watercourse. 2 Within the summary spreadsheet, a comment is provided within the cell where river water levels are based on internal ditch levels with an open connection. 3 Based on monthly rainfall data for Lowestoft over a ten year period.

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2m in height and are occasionally accompanied by a stilling well. The gaugeboards are logged

by a combination of EC Diver, Diver and Baro or Metrolog. Fifty four of the points are

boreholes, 7 of which have not been levelled into Ordnance Datum. The range of depth is

considerable, with some as shallow as 1m and others more than 50m deep (plumbed depth).

However the majority of boreholes are 5 to 25m deep. Boreholes are logged using either a

Metrolog or Diver (with occasional Baro).

RoC data is held by the EA and is only available by requesting datasets for specific

monitoring points in relation to sites under investigation.

2.3.1.3 Potential uses Formation of a conceptual hydrological model.

The regional RoC data provides an extremely valuable resource in this respect. For

example, when classifying a site into WETMEC types, information on typical summer and

winter water levels are necessary. Though an idea of the range of fluctuation can be

obtained anecdotally through site staff observations, ideally it should be sourced from an

objective dataset of actual measurements. It is probably no coincidence that virtually all of

the Broadland WETMEC sites trialled by Wheeler, Shaw and Tanner in the 2009 report are

located on sites where there is at least some water level data available.

The dipwell and borehole data is particularly useful in identifying the influence of

groundwater, as well as a measurement of actual water levels within the marsh (which may

not necessarily be the same as ditch water levels due to variations in soil permeability).

Gaugeboard data, though of very limited use in recording groundwater influence, is much

more valuable in recording how surface waters are managed within the site and how they

interact with river water (as long as river levels are also available and both are related to

Ordnance Datum). Thus those sites with both dipwell/borehole and gaugeboard data will

allow for the best understanding of site hydrology, dipwell data alone is also extremely

valuable, while gaugeboard data alone is of value on sites likely to be influenced by river

inputs.

In all cases, however, the main weakness of this dataset is that it still requires knowledge of

the surface water management of the site (including main direction of flow, location of water

control structures and presence of footdrains). Otherwise the water levels recorded in one

marsh could be assumed to apply to an adjacent marsh, without knowing that it is connected

to a different ditch network or is held at a different ditch water level. This information

clearly already exists in the experiences of site staff but in many cases may not have been

recorded and stored at a central location. A further weakness identified by Wheeler, Shaw

and Tanner is that dipwell and borehole data alone will not take into account the existing

“top-layer controls” (such as surface peat condition) affecting the site and therefore suggests

simple stratigraphic surveys should be made alongside monitoring installations to aid

interpretation.

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Accompanying datasets needed for maximum use: Lidar, vegetation, map of surface-water management.

If these datasets were available (and in most cases they are) WETMEC classification is likely to be

possible in at least another 14 sites within Broadland.

Advantage to continuing monitoring: low

Advantage to setting up new monitoring: high

Assessing fen condition.

The Regional RoC data is also potentially valuable in assessing the fen condition of a site,

particularly with regard to vegetation communities. Box 1 gives an example of how water

level data can be used to highlight plant communities which may be outside of their observed

range of water level preferences. Dipwell data is the most valuable in this respect because it

is a measure of water table depth and therefore does not necessarily require Lidar data to

establish the depth from marsh surface (so long as information on the top of casing in

relation to the marsh surface is provided). However gaugeboard data is also of some use as

long as Lidar data and basic soil information is available.

There are several potential weaknesses in this method of condition assessment. Firstly, it

depends on understanding how the surface hydrology is managed, which should be

straightforward to establish. Secondly, it is reliant on accurate topographic data because the

majority of fen species may only have an optimal water level range of 20-50cm, so unless

data is accurate results could be misleading. This can be achieved through selective ground-

truthing across a range of sites and then calibration of the Lidar data to take into account

factors such as peat shrinkage (although ground-truthing may show that Lidar data is

sufficiently accurate without calibration).

A further weakness is the amount that is known about the requirements of rare species and

their tolerances. For some species, we can be fairly confident in their optimal water level

requirements but for others only broad estimates of observed ranges are available.

However, in this respect, the additional information provided by the RoC data (when

coupled with vegetation data gathered during the Fen Ecological Survey, 2009) may help to

improve that knowledge (see Box 1) and achieve a better definition of what best fen

condition would be.

Accompanying datasets needed for maximum use: Lidar, vegetation, map of surface-water management.

If these datasets were available (and in most cases they are) fen condition analysis could be performed

across at least 10 sites in the Ant, 7 in the Bure, 6 in the Thurne, 10 in the Yare and 3 in the Waveney

catchments. In each catchment, dipwells occur in close proximity to M22, M24, S24, S25, S4, S2 and

S26, with some catchments also holding dipwells in M13, S14, M23, MG10, S27, S5, S6, M25, S28,

OV27, OV26 and several of the new sub-communities proposed in the Fen Vegetation Survey (2009).

Advantage to continuing monitoring: high

Advantage to setting up new monitoring: high but ideally needs to be coupled with permanent vegetation

monitoring plots

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BOX 1: Using water level data to assess fen condition

Much useful research has been published on the observed water level ranges of wetland plant

communities and individual species, which can be helpful in illustrating the effects of water level

change upon wetland vegetation. The data available through RoC monitoring points, when combined

with vegetation and levels data (such as Lidar), would allow for very useful analysis of whether those

conditions are being met within a set of sites and thus flag up areas “potentially” at risk. However it

is important to note that the response of plants to water levels can be strongly influenced by other

environmental factors, in particular availability of nutrients and base-richness, but also competition

from other species and concentration of reduced toxins such as Fe2+ (Wheeler, Shaw and Tanner,

2009). Therefore threshold water level values for individual species, though useful, can be misleading

and must be viewed with some caution. Instead, the aim should be to build on the “observed” ranges

within which each community currently exists.

Figure 1.2 illustrates the kind of analysis which is possible, namely the range in water levels the

existing communities at Pashford Poors Fen may require in order to persist (based on their current

location within the fen and observed published water levels for those NVC communities). The green

lines show the ditch winter water level range at the time of survey (and therefore summer levels are

likely to be considerably lower). The blocks of colour show the preferred water level range of the

plant communities present (using topographic data and published water level preferences). In this

example, it shows that much of the fen-meadow vegetation is outside of its ideal water level range.

These remnant communities are predicted to continue degrading in floristic value unless water levels

are raised (ideally to the red line in some areas). In contrast, the Phragmites swamp communities are

currently within acceptable water levels.

Figure 1.2 : Range in Water Level Requirements of Existing Communities at Pashford.

Similarly, where the vegetation is clearly in good condition, the water level data represents a valuable

resource in expanding our understanding of the water level requirements of wetland communities and

species. Clearly this data is not as accurate as those sites where dipwells are set up alongside

permanent vegetation monitoring and therefore can only be taken as an indication of condition.

Furthermore, they should not be considered in isolation, but alongside other variables such as soil

type, fertility and competition. However, it is likely that useful data can still be extrapolated from this

data source.

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Predicting effects of future environmental change.

The most obvious application is the use of dipwell and borehole data in measuring the effects

of groundwater abstraction (although this would need to be coupled with rainfall data to be

effective). In such a circumstance, there are considerable advantages to having dipwell data

before an abstraction begins. A second application is the use of dipwells and gaugeboards in

monitoring how water levels on the marsh have changed in relation to, for example, lower

rainfall and higher evapotransipration rates (though this would only be relevant to those sites

where the main water supply mechanism is surface-water and/or direct rainfall).

There is also a remote possibility that dipwells and gaugeboards could also be useful in

understanding the extent of the influence of tidal surges, particularly when coupled with

conductivity readings. For example, if a tidal surge occurs when rainfall is low, any increase

in on-site water levels could be linked to river input. However, as dipwells and gaugeboards

are only monitored monthly, the chances of such an event being recorded are very slight and

would therefore not be statistically significant. As there are other more effective ways of

measuring this impact, the use of dipwell data for this purpose is not considered further.

Accompanying datasets needed for maximum use: rainfall and evapotranspiration data, vegetation data,

river level data, geological data

This data is available for some sections of broadland, but a longer period of monitoring would be

required before reliable predictions could be made.

Advantages to continuing monitoring: high if further abstraction is likely, moderate if rain water-fed sites

are present.

Advantages to setting up new monitoring: high if abstraction likely, moderate if rain-fed sites are present.

Monitoring impact of changes to management.

Lastly, there is the use of RoC data in monitoring the impact of changes to surface-water

management. In this respect, gaugeboard and dipwell data are equally useful sources of

water level information and are helpful if measures such as new sluices, changing sources of

water supply or constructing bunds are planned. It is also invaluable data when compiling a

Water Level Management Plan. Monthly readings are sufficient for such a purpose but will

require the continuation of RoC monitoring points. However, the RoC monitoring points

were not set up for this purpose and therefore their locations may not be ideal for

monitoring this kind in many cases.

Accompanying datasets needed for maximum use: surface-water management, rainfall data.

This data is appropriate for this use in some sections of broadland, but a longer period of monitoring

would be required to establish if significant changes have occurred. It may also be redundant if no

alterations are planned.

Advantages to continuing monitoring: moderate if changes to management are likely

Advantages to setting up new monitoring: high if changes to management are likely

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2.3.2 Hydrological parameters – Regional conductivity logging points

2.3.2.1 Coverage

Figure 2: Location of conductivity logging points monitored by the Environment Agency


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The majority of conductivity monitoring points are located in the Ant catchment (10 points), the Thurne catchment (9 points) and the Yare catchment (13 points). Six points are also monitored within the Bure catchment but no monitoring points are located within the Waveney or Muckfleet. Each monitoring point coincides with a gaugeboard which has been levelled to Ordnance Datum.


The dataset consists of hourly readings over slightly different timespans depending on the individual monitoring point. Within the Ant catchment, data typically runs from June 2006 to July 2010, but some of the data is either unconfirmed or appears suspect. In the Bure valley, data runs from June 2007 to May 2010, and the majority of readings having been confirmed as reliable. Within the Yare valley, data typically runs from August 2006 to June 2010. The majority of readings are unconfirmed by EA but do not appear to be suspect. In the Thurne valley, data runs from July 2006 to July 2010, with all readings unconfirmed and several months missing data.

Regional conductivity monitoring data is held and owned by the EA, with a copy of all

monitoring point data held by the BA.

2.3.2.3 Potential uses

Formation of a conceptual hydrological model.

This dataset provides useful supporting information when forming a conceptual hydrological model of a site because it represents clear evidence of whether a site is being affected by brackish water incursion during tidal surges. If there is a significant relationship between river conductivity readings and conductivity readings within the site, it can be extrapolated that river water is an important water supply mechanism and thus be assigned one of the appropriate WETMEC types. Box 2 illustrates how the data could be applied. BOX 2: Using regional conductivity monitoring to inform formation of a conceptual hydrological model. The data available through the EA conductivity monitoring points, when combined with a surface water management map and river salinity monitoring, would provide an indication of sites which are likely to receive significant volumes of river water. For example, monitoring point TG31/647 is located within an internal ditch to the east of Ranworth Broad. River salinity monitoring suggests that a major peak in river salinity occurred in November/December 2007, during the time that TG31/647 was monitored. However, because this monitoring point shows no significant increase in conductivity over this time period it could be inferred that river water does not significantly contribute to the hydrological operation of this area. In contrast, if there had been a significant relationship between the two datasets, it would suggest when river levels are sufficiently high water will enter the site. It could then be compared to rainfall data to establish whether there is a pattern to the ingress of river waters (for example, does river water become a more important water supply mechanism to the site during summer/autumn).

Unfortunately, unlike the site-specific conductivity dataset (see section 2.3.3) monitoring points are too infrequent to gauge how far across a site river water may penetrate and therefore there would still need to be a personal judgement of the extent of the relevant WETMEC unit. Furthermore, on some sites it may already be obvious to site staff that river water enters the site and therefore analysis of the regional conductivity points to inform the conceptual model may be unnecessary.

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Accompanying datasets needed for maximum use: River salinity data, map of surface-water management,

rainfall data.

If these datasets were available (and in most cases they are) it could assist WETMEC classification in

at least another 7 sites within Broadland.


Advantage to setting up new monitoring: low (because there are more effective ways of obtaining the

same information)


Regional conductivity monitoring points will not be of use in assessing fen condition in terms

of whether water levels are appropriate to the vegetation communities present, but does

have a use in gauging whether water quality may be an issue in attaining best fen condition.

Not only because, in the same way as shown above, the conductivity dataset may provide

evidence of river water inputs and therefore exposure to waters of a different pH, nutrient

level or salinity, but more importantly in assessing the response of fen communities to

increases in conductivity. Conductivity readings of this kind, when combined with a

conceptual hydrological model and vegetation data, provide a broad method of comparing

the different conditions in which fen communities are currently found. The dataset could

therefore contribute to an improved understanding of what observed concentrations of salts

may be suitable when a site is at best fen condition (see Box 3).

Accompanying datasets needed for maximum use: Vegetation, map of surface-water management, a

conceptual hydrological model, river salinity monitoring.

If these datasets were available (and in most cases coverage is scattered) fen condition analysis in

relation to conductivity could be performed across at least 10 sites, with the potential (if more

WETMECs were available and the Regional conductivity dataset was combined with the BA site-

specific dataset) to conduct such vegetation analysis over approximately 25 sites across the Ant, Bure,

Thurne and Yare (though only approximately half of these contain invertebrate samples).

Advantage to continuing monitoring: high in the short-term, with the potential to be less important if

analysis shows key species exist which are good indicators of change.

Advantage to setting up new monitoring: high, particularly in close proximity to those communities of

high ecological importance which are not covered by existing monitoring points, or on rivers

currently missed by monitoring (i.e. Waveney and Muckfleet).

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BOX 3: Use of conductivity monitoring in aiding assessment of best fen condition

Currently, published data on observed water conductivity within wetland vegetation exists for some

plant communities (e.g. M13, M22, M24 and S24 in WETMEC report), while other communities have

relatively little data. However, it may be possible to further this knowledge by using a combination

of conductivity data (from regional EA monitoring points and BA site-specific points), the relevant

vegetation data (from the Fen Vegetation Survey, 2009) and site WETMECS. Profiles could be

constructed which analyse those areas falling within WETMEC types affected by river water. The

profiles would describe the kinds of NVC communities found, the ecological value of those

communities (i.e. were they species-rich examples containing rarer fen plants), and the variations in

conductivity recorded in the water supplying those communities.

Furthermore, Ellenberg Indicator values for Salt tolerance could be generated from the existing Fen

Vegetation Survey to compare analysis of vegetation response to the actual conductivity readings.

The results of the Fen Vegetation Survey generated such indicator values for Broadland communities

as a whole (using summary tables), but did not generate them based on individual quadrat data.

Therefore, where actual conductivity data is available, there is a means to test the reliability of the

Indicator values and establish whether they could be used to record environmental change instead

of/or complimentary to direct conductivity monitoring. Figure 3.1 shows an example of the kind of

output which may be possible from this kind of analysis.

Figure 3.1

The results are likely to be indicative only (because the datasets used will not have been set up for

this specific purpose and there may be several limitations in the data available). However it could

provide useful additional insight into, for example, which S24 sub-communities (including new sub-

communities proposed in the Fen Vegetation Survey) currently exist in sites prone to brackish water

incursions. Such a study should ideally be performed in conjunction with work categorising the risk

and intensity of increased conductivity within Broadland sites (see Box 4) once the results of the

river modelling by BESL have been generated. Thus providing the possibility of predicting which

communities are likely to be sustainable (in conductivity terms) at each site under future conditions.

In combining conductivity data with vegetation data and WETMEC classification, it may be possible to

identify key species which could act as indicators of change (a process which has already begun with

22

regard to invertebrates – Telfer, 2010). Such key indicators could then, for example, be incorporated

within condition assessment surveys or speed the re-survey of permanent monitoring plots to

monitor the effects of brackish incursion within Broadland plant communities.

A similar process of analysis may be possible using the Fen Invertebrate Survey results, though the

sample size will be smaller and therefore less reliable. Furthermore, the mobile nature of

invertebrate species is likely to complicate the analysis of conductivity and species data, so that it may

be more successful to link conductivity with vegetation and then vegetation to invertebrate

communities.


A key use of the regional conductivity monitoring however is in predicting future

environmental changes, particularly as a direct measurement of saline incursion. All the

monitoring points provide very useful information on actual effects observed during tidal

surges and should therefore be incorporated into any modelling of the effects of future tidal

events. The data is particularly useful because it includes a mixture of river and internal

ditch sampling points, but would need to be combined with several other datasets to

optimise its use. It should be noted that the data is far less useful than site-specific

conductivity monitoring because there is typically only one sampling point at each site.

However, once the relationship between a site and its vulnerability to brackish water

incursion had been established, one sampling point of this kind would in many cases be

sufficient to continue observing the environmental conditions and confirming the validity of

any predictive models without the expense of a series of sampling points at each site.

Regional conductivity data may also be useful supporting data in assessments of the impact of

climate change because changes in river and internal ditch conductivity will be affected by

changes in rainfall and evapotranspiration. However, such climate changes are already

expected to have been taken into account within BESL river modelling of conductivity.

This kind of data will also provide additional information in assessments of the impact of

abstraction, because it is indicative of changes to water supply mechanisms within a site. For

example, if a site receives both groundwater and river water and, due to an abstraction

upstream, groundwater input is reduced, conductivity levels within internal ditch water can

be expected to rise in line with that recorded within river water. However, such data is

only indicative and would need to be considered alongside several other variables (for

example, the distribution of acid-sulphate soils).

Accompanying datasets needed for maximum use: rainfall and evapotranspiration data, tide data, river

conductivity data.

This data is available for some sections of broadland, but a longer period of monitoring would be

required before reliable predictions could be made.

Advantages to continuing monitoring: high

Advantages to setting up new monitoring: high

23


Regional conductivity monitoring is only likely to be of use in gauging the impact of

management changes if those changes relate to alterations in the water supply mechanism.

Furthermore, those points would need to continue to be monitored in the future to obtain

any indication of change and are unlikely to be located in the optimum position to record

such change. This use of the data is therefore very limited but would provide useful

supportive information within site Water Quality Management Plans.

Accompanying datasets needed for maximum use: surface-water management, rainfall data, river

conductivity

Advantages to continuing monitoring: low

Advantages to setting up new monitoring: moderate if changes are planned to a site’s water supply

mechanism.

24

2.3.3 Hydrological parameters – Site-specific conductivity monitoring

2.3.3.1 Coverage

Figure 3: Location of site-specific conductivity points monitored by the Broads Authority


25

2.3.3.2 Description of content and availability Conductivity readings were taken by BA staff at the six trial sites between December 2003 and April 2008. The timing of sampling was largely chosen to fit in with site visits already planned for site maintenance. However, some visits were made when it was felt extreme weather/river levels had been experienced. At each site, samples were taken from each of the main dykes, a selection of side dykes and at least one river sample. The data is held by the Broads Authority.



This dataset, like the regional conductivity monitoring, provides useful supporting information when forming a conceptual hydrological model of a site because it represents evidence of whether a site is receiving significant inputs of river water. Furthermore, several conductivity monitoring points occur within each site, so that it is possible to estimate how far across a site river water may penetrate. However, this kind of data is not essential in the classification of a site in WETMEC terms and would not justify the cost of implementing such sampling widely within Broadland sites.

Accompanying datasets needed for maximum use: Map of surface-water management, vegetation data,

dipwell or gaugeboard data, Lidar data.

However, as 3 of the 6 sites where conductivity monitoring has taken place already have WETMEC

classification, the use of the existing data set for further conceptual modelling is very limited.


Advantage to setting up new monitoring: low


Like regional conductivity monitoring, site-specific conductivity data will be of use in gauging

whether water quality may be an issue in attaining best fen condition, not only by providing

evidence of river water incursion (and exposure to nutrient-rich waters) but more

importantly in assessing the observed levels of conductivity within existing plant

communities. As Box 3 discusses (page 20), conductivity readings of this kind, when

combined with a conceptual hydrological model and vegetation data, provide a means of

comparing the different conditions in which fen communities are currently found. The

dataset could therefore contribute to an improved understanding of what kind of

conductivity levels may be suitable for a site in best fen condition.

Site-specific conductivity data has the advantage over regional data in that there are a

greater number of sampling points across a site, thus better reflecting geographical variations

in conductivity. Figure 4 illustrates how this increased coverage of sampling points would

enable a better comparison with the vegetation samples recorded during the Fen Vegetation

Survey. However regional conductivity is recorded every 15 minutes and therefore is more

representative over time. It would be useful for any study using these two data sets to

correlate the data and evaluate which is the more useful/representative measure.

26

Figure 4: Showing Reedham Marsh monitoring points and average conductivity readings against and NVC communities found.

27

Accompanying datasets needed for maximum use: Vegetation, map of surface-water management, a

conceptual hydrological model, regional conductivity monitoring.

If these datasets were available (and in most cases coverage is scattered) fen condition analysis in

relation to conductivity could be performed across 6 sites, with the potential (if more WETMECs

were available and the data was combined with the regional conductivity dataset) to conduct such

vegetation analysis over approximately 25 sites across the Ant, Bure, Thurne and Yare (though only

approximately half of these contain invertebrate samples).

Advantage to continuing monitoring: high in the short-term, with the potential to be less important if

analysis shows key species exist which are good indicators of change.

Advantage to setting up new monitoring: high, particularly in close proximity to those communities of

high ecological importance which are not covered by existing monitoring points, or on rivers

currently missed by site-specific monitoring (i.e. Yare, Thurne, Waveney and Muckfleet).


The primary use of the site-specific conductivity monitoring is in predicting future

environmental changes, particularly as a direct measurement of brackish water incursion.

The recent study analysing the results of site-specific monitoring (OHES, 2011) showed that

this type of monitoring is very effective at showing where peaks in river conductivity

currently affect the internal ditch network. Figure 5 is an example of the results generated

from this kind of data set (using data from Catfield Fen) and illustrates results obtained

during a peak in river conductivity. In this example, the data has highlighted the different

water supply mechanisms operating within the site (i.e. surface water run-off and possibly

groundwater are the key sources for the north east of the fen and river water is a major

source for the south of the fen).

The study found that sites monitored in this way fell into three categories:

1. Sites typically beyond the effect of brackish water incursion from rivers.

2. Sites directly affected by brackish river water, with a highly predictable response in ditch

conductivity.

3. Sites which appear to be affected by brackish water incursion during extreme tidal

surges but which have unresolved additional factors.

Clearly, once this data is coupled with the river modelling currently underway at BESL, it will

be possible to predict with a high level of confidence how conductivity on sites which fall

into categories 1 and 2 will change in response to future climate change and tidal surges.

Furthermore, any neighbouring sites sharing similar WETMEC types to the six monitored

sites may respond in a similar fashion (depending on surface water management). However,

there is a need for more sites to be monitored in this way (i.e. site-specific conductivity

monitoring) in order to accurately predict the effect of brackish water incursion on rivers

where no such monitoring has taken place (i.e. the Thurne, Yare, Muckfleet and Waveney).

28

Figure 5: Site specific conductivity monitoring at Catfield Fen during a peak in

river conductivity.

As the Salinity Report states, such monitoring would not necessarily need to be at the same

frequency as has been used on the six sites, but would need to include three or four

examples per site of each of the circumstances below:

- Occasions when samples are taken from the entire ditch network, coinciding with

peaks in river conductivity.

- Occasions when samples are taken from the entire ditch network, several days after

peaks in river conductivity have occurred.

- Occasions when samples are taken from the entire ditch network, during typical

environmental conditions (i.e. typical rainfall, typical river conductivity, no extreme

tidal surges).

Obtaining such data could be achievable within a single year. Some analysis is possible

without this additional data (see Box 4) but the accuracy of any predictions on certain rivers

and sites will be limited by the absence of such data.

Site-specific conductivity data may also be useful supporting data in assessments of the

impact of climate change because changes in ditch conductivity will be affected by changes in

rainfall and evapotranspiration. However, such climate changes are already expected to have

been taken into account within BESL river modelling of conductivity.

29

BOX 4: Using conductivity data to predict the extent of brackish water incursion within

Broadland sites.

In conjunction with the river conductivity modelling currently being undertaken by BESL (which it is

hoped will generate predictions of the future extent and intensity of brackish water incursion within

Broadland rivers) modelling of the effects on internal ditch networks could be generated utilising a

combination of the site-specific conductivity monitoring, the regional conductivity monitoring, surface

water management maps and conceptual hydrological site models (e.g. WETMECS). Such a model

would not necessarily require detailed hydrological modelling using specialist software (and indeed,

the number of unknown variables may make use of such software rather problematic) but could be

constructed using a combination of Excel spreadsheets and GIS software.

The obvious locations for trialling this kind of study would be the Ant and Bure, which contain the

greatest number of conductivity monitoring points and for which several WETMEC classifications

have already been performed. The work would require the WETMEC classification of the remaining

XX sites (is data available to do this? And how long would it take), data output from the BESL

modelling (due in XXX), and the conductivity data sets (all of which are already held by BA). The

objective of the project would be to categorise the level of risk of future brackish water incursion

within Broadland sites.

This study could run simultaneously with new site-specific conductivity monitoring on key sites of

other Broadland rivers, so that modelling could take place in phases as funding and data becomes

available.

A limitation of this kind of study is that it will only be able to categorise the risk (and possibly

intensity) of increased conductivity within Broadland sites. It will not be able to predict what effect

this will have on the vegetation and other communities currently found on sites. For such an effect to

be established, a greater understanding of the relationship and occurrence of plant communities in

relation to conductivity would need to be established (see Box 3).

As with regional conductivity monitoring, site-specific monitoring of conductivity will also

provide additional information in assessments of the impact of abstraction, because it is

indicative of changes to water supply mechanisms within a site. However, once again, such

data is only indicative and would need to be considered alongside several other variables

(such as rainfall and soil type).

Accompanying datasets needed for maximum use: river conductivity data and modelling, conceptual

hydrological models (e.g. WETMECS), vegetation data, regional conductivity data.

The majority of datasets exist for some sections of the Rivers Ant and Bure, with data on river

modelling due in 2011. However further conductivity monitoring will be needed before reliable

predictions can be made across all Broadland sites and rivers.

Advantages to continuing monitoring: moderate, but will not require the same frequency of sampling

points or events in order to be effective.

Advantages to setting up new monitoring: high, particularly on the Yare, Thurne, Muckfleet and Waveney


Site-specific conductivity monitoring is only likely to be of use in gauging the impact of

management changes if those changes relate to an alteration in the water supply mechanisms

of that site (e.g. increasing the input of river water). Furthermore, those points would need

30

to continue to be monitored in the future to obtain any indication of change. This use of the

data is therefore somewhat limited but would provide useful supportive information within

site Water Quality Management Plans.


conductivity


Advantages to setting up new monitoring: moderate only if changes are planned to a site’s surface water

management which may lead to increased river water.

31

2.3.4 Hydrological parameters – Conductivity monitoring of river water

2.3.4.1 Coverage

Figure 6: Location of river salinity points monitored by the Environment Agency


32

Coverage is limited to the Rivers Ant (at Barton Broad outflow) and Bure (at two points within Ranworth Broad, one within Decoy Broad and one at Acle).


The River Ant salinity data is recorded monthly from January 2003 – January 2005, then again from March 2007 – November 2008. On the River Bure, conductivity values are recorded from Ranworth Broad every month from May 1995 – February 1997, then again in August 2003 – March 2010. Occasional field measurements were also taken in 1999 and 2002. Conductivity values (in µS/cm) are accompanied by a series of other water quality parameters (such as pH, temperature, Nitrogen (in various forms), Phosphorus (in various forms), Calcium, Chlorophyll and various metals. The same parameters are recorded from Decoy Broad, with conductivity measured every 1-2 months from April 1983 - February 1990, then monthly from February 1990 – July 1995. A few measurements were also recorded in 2005 but there no longer appears to be a regular monitoring point here. Hourly conductivity values were also logged from Acle, during April 1995 – April 2008, and then every 15minutes from May 2008 – October 2010. Data is held by the Environment Agency, with a copy held by the Broads Authority (except any data gathered after October 2010).



Where this dataset can be combined with site-specific or Regional EA conductivity monitoring, it aids the formation of a conceptual hydrological model, because it measures the extent to which river waters enter a site. However, such data is currently rather limited. In other respects, this dataset is not informative in constructing site-specific hydrological models (such as WETMECs).

Accompanying datasets needed for maximum use: site-specific or EA conductivity monitoring, map of

surface-water management, rainfall data.

If these datasets were available (and in most cases they are not) confidence in site WETMEC

classification is likely to be improved along sites within the Ant and Bure (but only if river monitoring

continues).

Advantage to continuing monitoring: moderate if combined with other conductivity monitoring.

Advantage to setting up new monitoring: moderate if combined with other conductivity monitoring


In an extension to the above, river conductivity monitoring when combined with other

conductivity data would aid the assessment of the likely fen condition, both in terms of

brackish water incursion but also as an indicator of nutrient enrichment of river water onto

the site. This is outlined further in section 2.3.2.3.

33

Accompanying datasets needed for maximum use: Site-specific or EA conductivity monitoring, a

conceptual hydrological model, vegetation, map of surface-water management.

If these datasets were available (and in most cases site-specific monitoring and conceptual models is

the limiting factors) fen condition analysis comparing known river water input with existing plant

communities could be performed across a handful of sites in the Ant and Bure.

Advantage to continuing monitoring: moderate only if combined with other conductivity monitoring

and/or formation of a conceptual hydrological model.

Advantage to setting up new monitoring or additional rivers: moderate but needs to be coupled with other

conductivity monitoring or conceptual hydrological models (ideally both)


Where this dataset is most valuable is in the prediction of future environmental changes,

specifically the relationship between freshwater and brackish inputs along the river. The

current dataset can be used not only to identify the extent to which saline incursion has

occurred within the Ant and Bure, but also in the prediction of how far future brackish

incursions may reach within the rivers. Hydrological river modelling of this kind has been

commissioned by the Broads Authority and is being performed by BESL (estimated

completion date). However the limitation in this data is that, in isolation it can only predict

future effects within the river and not within the sites themselves. In order to predict

brackish incursion into individual sites, either site-specific monitoring or a conceptual

hydrological model would first be needed (ideally both).

As with regional conductivity monitoring, river monitoring of conductivity will also provide

supportive information in assessments of the impact of abstraction, because river

conductivity will be needed to assess the extent of changes to river water input within a site.

However, once again, such data is only indicative and provides little insight without several

other data sets being available.

Accompanying datasets needed for maximum use: rainfall and possibly evapotranspiration data, tide data,

river level data.

This data is generally available for large sections of the Ant and Bure catchments, but there are

significant gaps in certain datasets within the Thurne, Muckfleet, Yare and Waveney catchments.

Advantages to continuing monitoring: high in order to confirm the validity of predictions or amend if

necessary.

Advantages to setting up new monitoring: high on those rivers which currently lack river conductivity

monitoring.


River conductivity monitoring will generally be of little use in assessing the effect of changes

to surface-water management within sites. In this respect, site-specific conductivity

monitoring or modelling reflecting conceptual hydrology and brackish incursion will be much

more accurate. However, river conductivity monitoring near those sites which are exposed

34

to river waters would be useful background information if sites require a Water Quality

Management Plan. Monthly readings are sufficient for such a purpose but will require the

continuation of the EA river monitoring points.

Accompanying datasets needed for maximum use: surface-water management, site-specific monitoring

points or conceptual hydrological model and saline incursion model.

This data is currently unavailable but may become available in the foreseeable future.

Advantages to continuing monitoring: moderate (because most of the accompanying information needed

will only become available in the future)

Advantages to setting up new monitoring: moderate (because no river salinity data appears to exist for

certain catchments).

35

2.3.5 Hydrological parameters – Tidal data

2.3.5.1 Coverage

Figure 7: Location of tidal points monitored by the Environment Agency


36


Tide data was only available from Hickling Broad (on the River Thurne) and Ranworth Broad (on the River Bure). The Hickling data consists of daily water level readings (to Ordnance datum) during January 1997 to January 2010, with most months showing a complete dataset of good reliability. The Ranworth data consists of daily water level readings (to Ordnance datum) during August 1996 to January 2010, with most months showing a complete dataset of good reliability. Data is held by the Environment Agency, with a copy held by the Broads Authority (except any data gathered after January 2010).



In essence, the two sets of tide data represent two additional points where river water

levels have been recorded but include a greater level of detail than was recorded in the RoC

gaugeboard data (which was only recorded monthly). Therefore, on sites which may be

vulnerable to input from river waters, and where internal ditch water level readings also

exist, tide data can be of some use in establishing the extent of river incursions and

therefore which WETMEC type is appropriate. However, because tide data is only available

for two locations, its usefulness is limited to supporting classification only of those few sites

in the neighbouring area which do not already have a WETMEC study.

Accompanying datasets needed for maximum use: Lidar, vegetation, map of surface-water management,

gaugeboard data.

If these datasets were available WETMEC classification is likely to be assisted in several sites along the

Rivers Thurne and Bure.

Advantage to continuing monitoring: moderate

Advantage to setting up new monitoring: high on rivers which do not have tidal monitoring


Like RoC gaugeboard data, tide data can be useful in the identification of existing plant

communities which may be outside of their preferred water level range. The frequency of

recording (daily) is particularly useful because it allows an assessment of what water levels

occur in both extreme and typical conditions, and the duration that a plant community may

be outside of its typical water level range. Furthermore, though water levels are only

recorded at two locations, any tidal fluctuation seen at Ranworth and Hickling can be

presumed to have also occurred in sites downstream. Thus the usefulness of the data

extends further than the immediate sampling points. However, in order to be useful, tide

data must be analysed alongside Lidar data, basic soil data, vegetation data, a conceptual

hydrological model and (ideally) gaugeboard or dipwell data (see Box 1 for details).

37

Accompanying datasets needed for maximum use: Lidar, vegetation, map of surface-water management

(or conceptual hydrological model), dipwell or gaugeboard data.

If these datasets were available (and in some cases they are) fen condition analysis could be assisted

on sites within the Thurne and Bure.




One application of tide data is in measuring the effects of tidal surges and climate change as a

whole. Such data, though very limited in terms of the number of sampling points, is useful in

river conductivity modelling (for example, currently underway by BESL), particularly where it

coincides with conductivity monitoring. Because the tide data is recorded daily, the

likelihood of capturing surge events is much higher than in, for example, RoC data.

Tide data is unlikely to be of much use in assessing groundwater abstraction because very

significant abstractions would be needed before they significantly affected river levels and it

would be harder to prove a relationship between the two because of the many other

variables which could cause reductions in river water levels.

Accompanying datasets needed for maximum use: rainfall and evapotranspiration data, other river level

data, river conductivity monitoring

This data is available for some sections of the Rivers Thurne and Bure.

Advantages to continuing monitoring: high in order to confirm predictions of climate change and tidal

incursions

Advantages to setting up new monitoring: high on rivers which do not have daily water level monitoring.


Tide data will have very limited use in assessing the impact of surface-water management

changes and are only likely to be of use if those changes relate to increased input of river

water. The location of tide monitoring points is also unlikely to be ideal for such monitoring

and therefore it is considered that installation of an internal gaugeboard would be a much

more effective approach. However, where tidal data exists it should be taken into account

within any neighbouring site Water Level Management Plans.


conductivity


Advantages to setting up new monitoring: low

38

2.3.6 Hydrological parameters – River water quality data

2.3.6.1 Coverage

Figure 8: Location of river water quality points monitored by the Environment Agency


39

River water quality data is available within 1km distance at 41 of the 113 fen sites, with a

further 16 sites showing data within 2km of the site boundary. The Ant catchment has the

best resource of river water quality data, but the Waveney and Bure also have several

monitoring points. The Thurne and Muckfleet are the only rivers to have no such

monitoring points along their length. There is also a significant absence of data from the

lower reaches of the Rivers Yare and Bure.


River water quality data is freely available on the internet (www.environment-agency.gov.uk)

and is split into Biological, Chemical and Nutrient parameters. The published data series

typically runs from 1990 to 2009.

Biological monitoring includes sampling of macro-invertebrates, with samples graded to

reflect the range of species expected in the river if it was not polluted. Samples are

collected two times every third year. Grades are as follows:

Table 1: Environment Agency Grades assigned during Biological Assessment of Rivers

Classification Description

A - very good Biology similar to that expected for an unpolluted river

B - good Biology is a little short of an unpolluted river

C - fairly good Biology worse than expected for unpolluted river

D - fair A range of pollution tolerant species present

E - poor Biology restricted to pollution tolerant species

F - bad Biology limited to a small number of species very tolerant of pollution

Chemical parameters include ammonia, biochemical oxygen demand (BOD) and dissolved

oxygen (DO). Results are recorded in mg/l and percentage saturation, then compared with

limits set for each of the grades listed below. Grades are assigned according to the lowest

grade achieved in any of the three tests (e.g. if the site gets a grade A for ammonia and

dissolved oxygen but a grade B for BOD, the overall grade given will be B). Samples are

collected 12 times a year at regular intervals along the river.

Table 2: Environment Agency Grades assigned during Chemical Assessment of Rivers

Classification Likely uses and characteristics *

A - very good All abstractions, Very good salmonid fisheries, Cyprinid fisheries, Natural ecosystems

B - good All abstractions, Very good salmonid fisheries, Cyprinid fisheries, Ecosystems at or close to natural

40

C - fairly good Potable supply after advanced treatment, Other abstractions, Good cyprinid fisheries, Natural ecosystems, or those corresponding to good cyprinid fisheries

D - fair Potable supply after advanced treatment, Other abstractions, Fair cyprinid fisheries, Impacted ecosystems

E - poor Low grade abstraction for industry, Fish absent or sporadically present, vulnerable to pollution **, Impoverished ecosystems **

F - bad Very polluted rivers which may cause nuisance, Severely restricted ecosystems

*providing other standards are met **where the grade is caused by discharges of organic pollution

Nutrient parameters include nitrate and orthophosphate are recorded in mg/l. Grades are

assigned in the following manner. Samples are collected 12 times a year at regular intervals

along the river.

Table 3: Environment Agency Grades assigned during Nutrient Assessment of Rivers

Classification for phosphate

Grade limit (mgP/I) average Description

1 0.02 Very low

2 0.06 Low

3 0.1 Moderate

4 0.2 High

5 1.0 Very high

6 >1.0 Excessively high

Classification for nitrate

Grade limit (mg NO3/I) average Description

1 5 Very low

2 10 Low

3 20 Moderately low

4 30 Moderate

5 40 High

6 >40 Very high

41



The river water quality data set is not particularly useful in the construction of a hydrological

site model. Firstly it does not include parameters such as pH or conductivity which might

provide particular insight into a site’s connection with the river. Secondly river data ideally

needs corresponding site data (measuring the same variables) in order to be of any use in

formation of the model. In most cases, this kind of site data is not available. Thus the data

set has very limited value in this respect.

Accompanying datasets needed for maximum use: Site water quality monitoring of the same parameters,

Lidar, vegetation, map of surface-water management, gaugeboard data.

Data sets such as comparable site water quality monitoring are not available in the majority of cases.




In contrast, river water quality data can be useful in predicting fen condition and how that

condition may change (for example by changing the water supply mechanism of a site).

Several of the quintessential Broadland plant communities are not generally found in areas

with a high nutrient status (e.g. M13 and M24). Therefore, if it is known that river water is a

significant water supply mechanism within a site, and the river water quality data set shows

that river to be eutrophic or even hypertrophic, it can be extrapolated that the condition of

any existing communities of this kind will decline.

However, in order to predict such a situation between vegetation and river water quality, it

is essential that either a reliable conceptual hydrological model of the site is formed, or

water quality monitoring has taken place on the site itself. Without such a model/data, it

will be difficult to tell the importance of river water and therefore the affect its nutrient

status will have. Furthermore, fen condition will not only be affected by the nutrient status

of the water but also by other key variables such as the management regime (e.g. is it

grazed/mown), the soil conditions and the water table height. This may be the reason why

Wheeler, Shaw and Cook (1992) found overall fertility of soil samples (using phytometric

response) to be more reliable than water and soil chemical measurements.

The river water quality data set therefore provides some valuable information in those sites

affected by river water, which should be taken into consideration when assessing the

sustainability of vulnerable plant communities. However, it is not suitable for independent

detailed comparison with individual vegetation data (for example to test the relationship

between existing plant communities within certain WETMEC types and nutrient levels of

river water) because of the number of other key variables which could not easily be taken

into account.

42

Accompanying datasets needed for maximum use: A conceptual hydrological model or on-site water

quality monitoring, vegetation data, soil fertility data

If these datasets were available (currently on most sites they are not) fen condition analysis could be

assisted on sites within the River Ant, Waveney and upper reaches of the Bure and Yare.




This water quality data set is of little use in predicting the extent of brackish water incursion

due to the absence of conductivity readings. Similarly, it is poorly suited to assessing the

effects of groundwater abstraction or changes in rainfall/evapotranspiration because it does

not include parameters such as pH and is not keyed into specific sites.

It does, of course, provide a means of broadly monitoring changes in eutrophication of river

waters which will in turn affect some Broadland sites. Whether this data could be used as a

predictive tool is more debatable. Nutrient models of river catchments are relatively

straightforward to construct (provided information such as observed monthly Total

Nitrogen and Total Phosphorus, aerial photographs showing land-use, population census

data and sewage outputs, livestock numbers/distribution and rainfall data are available).

Once a model has been constructed, it can be used to identify which sources are likely to be

generating the most nutrients and test scenarios (such as; how would concentrations of TN

and TP change if X number of fields were turned over to wetland, or how nutrient

concentrations would change if sewage treatment methods were improved). However, the

current river water quality data set is not appropriate to the formation of such a model.

Firstly it only records Nitrate and Organophosphate rather than TN and TP. Secondly the

sampling has not been of sufficient frequency to confidently gauge an observed total nutrient

load. Thirdly it is not accompanied by flow data or continuous water level monitoring. It is

possible that this data is being monitored by the EA, but no such data was available for this

study.

Accompanying datasets needed for maximum use: rainfall and evapotranspiration data, flow data or

continuous river water level monitoring, catchment characteristics (such as land-use), site specific

water quality monitoring or a conceptual hydrological model.

This data does not currently appear to be available within Broadland.

Advantages to continuing monitoring: high in order to monitor changes in eutrophication

Advantages to setting up new monitoring: high on rivers which do not have river water quality

monitoring.


River water quality monitoring will generally be of little use in assessing the effect of changes

to surface-water management unless site-specific water quality monitoring also takes place

or a conceptual hydrological model exits of the extent to which river water will have an

influence on the site. However, river water quality monitoring near those sites which are

exposed to river waters would be useful background information if sites require a Water

43

Quality Management Plan. Monthly readings are sufficient for such a purpose but will

require the continuation of the EA river monitoring points.

Accompanying datasets needed for maximum use: surface-water management, site-specific monitoring

points or conceptual hydrological model.

This data is currently only available on a few sites within Broadland.

Advantages to continuing monitoring: moderate (because most of the accompanying information needed

will only become available in the future)

Advantages to setting up new monitoring: moderate (because no river water quality data appears to exist

for certain catchments).

44

2.3.7 Hydrological parameters – Rainfall data

2.3.7.1 Coverage

Figure 9: Location of weather stations


45

Only two EA stations are located within the Norfolk Broads (at Acle and Barton Hall), with two other outlying stations at North Walsham and Buxton Dudwick. Free historic data from the Met Office is also available at www.metoffice.gov.uk/climate/uk/stationdata for Lowestoft.


The data consists of telemetered values every 15 minutes or manual readings with daily totals). Data recording began in 1980 (at Barton Hall), 1998 (at Acle), 1996 (at North Walsham) and 1994 (at Buxton Dudwick). Historic data for Lowestoft consists of monthly totals since 1914. Data is held by the EA and Met Office but can be made available to the BA on request.



Rainfall data is primarily useful in the formation of a water balance model, which can be for a

particular site or the river catchment as a whole. Typically for a detailed model, it would

also need to be accompanied by flow data, evapotranspriation data and dipwell data in order

that a conceptual model can be constructed which would indicate the importance of water

sources (rainfall, surface-water run-off, groundwater etc). To construct such a model for an

individual site, rainfall data would need to be calibrated using several stations (as there are

often issues with continuity and length of datasets). Furthermore, if the site is within 1 or 2

miles off the coast, significant changes in rainfall but also humidity and temperatures are

likely, making inland station data less useful. Such models are notoriously complicated to

construct and their accuracy will be very dependent on the quality and quantity of the data.

In many cases it is almost as costly (and less accurate) to try and calibrate/estimate

rainfall/ET values from free datasets than it is to buy the data from the Met Office. As a

consequence, detailed water balance models are generally costly to perform and would not

be a viable option on the majority of Broadland sites.

In contrast, the WETMEC approach does not necessarily require climate or flow data to

identify water supply mechanisms (though dipwell data is still a key source of information).

Where rainfall data is available alongside dipwell or gaugeboard data, it can help to identify

the importance of groundwater (because if water levels remain relatively unchanged during

low rainfall periods, groundwater is likely to be playing a significant role). For this purpose,

the data available from EA and Lowestoft stations would probably be sufficient for most sites

(as only broad trends are needed).

It should be noted that a WETMEC classification will not be able to estimate quantities of

water supplied from each source, as would be possible with a water balance model.

However, it can still highlight where changes in the water supply mechanism may affect the

existing communities found. Therefore it is likely that in most cases, a WETMEC approach

would be much more appropriate to the level of detail needed to understand broadland sites

sufficiently to ensure their sustainability.

46

Accompanying datasets needed for maximum use: Evapotranspiration data, temperature data, dipwell

data, flow data, surface-water management.

Such datasets are not currently available for the majority of broadland sites.




Though rainfall is a key parameter in the sustainability of some wetland communities (such as

the Sphagnum-Dryopteris variant listed within the Fen Vegetation survey) detailed rainfall

data is of little value without a clear understanding of the relationship between fen

communities and water sources (e.g. are they primarily groundwater fed, surface-water fed

etc.). In this respect, it is the conceptual hydrological model which is of importance rather

than the individual rainfall data. However, such individual data will become useful in

estimating how future climate change may affect a site (see section below).

Accompanying datasets needed for maximum use: Conceptual hydrological model, vegetation.

Only 4 sites combine existing WETMEC classification with close proximity to a climate station (within

2km). For all other sites climate data would either need to be calibrated with respect to the area, or

purchased from the Met Office, or new stations set up.




Where this dataset is of key importance is in the prediction of future environmental

changes, in particular regarding reductions in water supply from rainwater sources and the

sustainability of abstraction based on changes in rainfall. When combined with regional

predictions of future climate change, and conceptual models of those sites dependent on rain

fed sources, it should be possible to highlight those sites most at risk from water supply

shortages. In some cases, it may be possible to replace the supply with other suitable

sources while in other cases it may mark the decline of wetland communities in that area.

This kind of prediction would be most accurate if water balance models were in place for

groups of sites. However this is likely to be impractical in most cases due to cost

implications.

Accompanying datasets needed for maximum use: climate predictions for the area, conceptual

hydrological model and vegetation data.

Advantages to continuing monitoring: high in order to confirm the validity of predictions or amend if

necessary.

Advantages to setting up new monitoring: moderate within those areas which currently lack climate

stations. Alternatively, Met Office data could be bought if required in the future.

47


Rainfall data could be of use when monitoring the impact of management changes if, for

example, a change in the surface water management coincided with a reduction in site

wetness, because such a reduction may be due simply to low rainfall that year and therefore

only temporary. For such purposes, the free data available from the EA and Met Office

should be sufficient to identify general trends (e.g. was it a drier than average summer?).

Rainfall data is also useful supporting information to include within any site Water Level

Management Plans (for which monthly totals are usually sufficient), particularly when

accompanied by gaugeboard or dipwell data.

Accompanying datasets needed for maximum use: surface-water management map or conceptual

hydrological model, dipwell or gaugeboard data.

These datasets exist on scattered locations throughout the Broads, with the main limiting factor being

the location of dipwells/gaugeboards in places appropriate to the management change.

Advantages to continuing monitoring: high (because most of the assessment will be based on future

events)

Advantages to setting up new monitoring: moderate (because data will be more representative of the site

the closer it is to that site).

In summary, each dataset varies in its worth depending on the end use intended. Table 4 broadly

assigns a score for how useful each dataset appears to be given the above review. However, it

should be noted that this is a very crude method of ranking datasets and is only intended to give a

guide of which datasets are most valuable.

48

Table 4: Broad ranking of the importance of hydrological datasets held by the BA

Dipwell Gaugeboard Borehole Regional salinity

Site-specific salinity

River conductivity

Tide levels

River Water Quality

Rainfall

Conceptual model

*** ** *** * ** * * - * or ****4

Fen condition *** ** or *** *** ** or ***

*** * ** ** *

Future environmental changes:

Climate influence

** ** ** * * ** *** * ***

Tidal influence

** *** *** **** **** **** **** - ***

Abstraction **** * **** * * ** - - *** Changes to site management

** ** * * * * * * **

*=supportive, **=moderate use, ***=key parameter, ****=critical

4 Essential if constructing a water balance model, otherwise of little use

49

2.3.8 Supporting information The following sections represent a brief review of additional supporting information which could be of use in establishing the hydrological elements of broadland sites. However, the scope of the project does not allow for detailed discussion of the nature of the data or its applications.

2.3.8.1 WETMEC data

Thirty three of the fen sites in Broadland have been classified using the WETMECs approach

(see Figure 10). Details of each WETMEC type are given in the Wheeler, Shaw and Tanner

report (2009), some of which include:

• Summary characteristics

• Concept and description

• Situation and surface relief

• Substratum

• Water Supply mechanisms

• Ecological characteristics

• Naturalness

• Conservation value

• Vulnerability

Appendix 3A of the WETMEC report contains the ecohydrological site accounts for East

Anglia, including many broadland compartments. Each account (which may contain several

“sites” as they are known within this report) lists the WETMECs types believed to occur

within the study area, a description of the study area and its vegetation, a description of

what is known about the substratum and method of water supply and a summary

conclusion. The report states:

“The WETMECs listed for each site are based on the data samples available and do not necessarily

include all of the WETMECs that occur. Nonetheless, in most sites the list is likely to include the

main WETMECs. As some of the samples used in the data analyses are quite ‘old’ (see Appendix 2)

it is possible that some WETMECs no longer occur at certain sites (mainly in consequence of drying,

but sometimes of restoration initiatives). Where this is known, or thought likely, to be the case, it is

indicated in the text.”

The level of detail within each site account varies considerably, no doubt largely as a result

of the supporting information available. Some sites, such as Catfield, have been subject to

considerable study, including ecohydrological investigations (Wheeler, Shaw and Tanner,

2009). For other sites, such as Decoy Carr, relatively little is known and the descriptions

are necessarily brief.

The accounts are based on a wide range of datasets only some of which are currently

available to the BA. They include a number of datasets from the FENBASE database5.

5 Held and maintained at the University of Sheffield (and including vegetation data from an extensive list of

wetland studies – see report for more details).

50

Figure 10: Location of sites which have received WETMEC classification


51

The advantage of this dataset is that it provides an holistic approach to assessing the

hydrological functioning of a site, and a means of exploring how sites share similar

characteristics and vulnerabilities. In working through the process of applying the WETMEC

framework to a site, a range of information sources are brought together in ways which may

not previously have been attempted and, as a result, can significantly improve the

understanding of the key issues involved. This is discussed further in section 4.

As with any classification system, there are some limitations, which are discussed in detail in

the report. There are also a number of recommendations provided in the same document

discussing how the WETMEC framework could be further developed, including suggestions

such as; i) creation of a practical field handbook to assist in the identification and description

of wetlands, ii) establishment of an expert panel to resolve any conflicts between the

different user groups in relation to conservation objectives for wetland sites, and iii)

inclusion of further wetland types from other regions.

2.3.8.2 Fen Vegetation Survey data

This survey was commissioned by the Broads Authority and Natural England and conducted

by OHES (known at the time as ELP) over a period of 5 years. It included a comprehensive

survey of all major fen sites within the broads using the National Vegetation Classification

(NVC). In total, 7038 samples of vegetation were recorded in approximately 1750ha of fen

(see Figure 11). The results of the survey include a description of the floristics of all of the

vegetation types identified and their matching with reference NVC types. It proposes a

number of new broadland communities and sub-communities, which are described in detail.

The survey data also includes measurements of sample characteristics such as open water

percentage cover, sward height, scrub percentage cover and plant litter percentage cover, as

well as individual site descriptions and management observations.

In terms of hydrological functioning, this dataset provides a key source of information on the

condition of the fen and the characteristics which are affecting community development

(such as water quality and supply). Linking this dataset to other monitored environmental

data such as water level information would further our understanding of community

requirements and best practice management of the fen resource.

The applications of this dataset also go beyond simple analysis of individual species presence

or absence by the application of analyses such as Ellenberg’s Indicator Values (for salinity,

fertility, reaction (i.e. pH), light and moisture). The Ellenberg values (Hill et al 1999) are a

numerical rating given to each plant species according to its place on the spectrum of each

determinant. So, for salinity, saltmarsh species have a high salinity value, freshwater marsh

species a low one. A total score can be calculated for each sample, indicating how brackish

the conditions are where the sample was recorded. Mapping these scores then gives an

indication of the distribution of brackish fen types. Such maps allow a geographical

appreciation of distribution of habitat factors, always understanding these values are inferred

from the vegetation and not measured directly. Light levels are perhaps least useful as it

largely reflects stature of the vegetation, itself moderated by management.

52

Figure 11: Location of samples taken during the Fen Vegetation Survey


53

The results of such analysis, though circumstantial, often provide a long-term view of site

characteristics and are often corroborated by known environmental changes in the Broads

through other monitoring methods. An example of their application is provided in section 4.

2.3.8.3 Fen Invertebrate Survey data

This dataset was gathered in 2007 to 2009, at the same time as the Fen Vegetation Survey. It includes samples taken in 28 Broadland sites, typically with one or two samples per site (see Figure 12). The data includes lists of species, many of which show preferences for wetland environments. In this respect, the database provides a useful resource for broadly identifying where hydrological conditions are suitable for desirable species, and it would be useful to better understand how this fits within the WETMEC framework (in the same way that some plant communities have been identified within the WETMEC report). However, the necessarily reduced sample numbers within this survey compared to the Fen Vegetation Survey, make the information less useful with respect to understanding a site’s hydrological functioning at the current time.

2.3.8.4 Fen Audit data

The Fen Audit consists of a spreadsheet listing all Broadland compartments, which were assessed in 2002-3 (see Figure 13). Information includes a broad habitat description of the compartment, compartment area (and proportion of open fen), current management information, information on access and any other observations. Though this database does not have many applications in a hydrological sense, it does sporadically provide observations of flooding frequency, general peat condition and past management which assist in the background understanding of how a site operates as a whole. The presence of such information in a spreadsheet format is often surprisingly useful and very easy to access, though it would be even more useful in a hydrological sense if it consistently included a description of areas prone to flooding, the presence of key water control structures and the condition of the peat).

2.3.8.5 The Peat Resource Survey data

For the purposes of this project, two sources of information are included here. Firstly, the Broads Authority hold information from several sources known as the Broads Peat Database, the coverage for which has been transferred to GIS and was available to this project. It shows the main distribution of peat within all 6 river catchments, which is useful background information when attempting to understand the hydrological functioning of a site. However, detailed information on what other data is provided within the Broads Peat Database was not available during this project.

The second source is the Broadland Headwaters Peat Survey of 2010 (undertaken by OHES), which includes samples from approximately 10 sites within the Ant, Thurne and Bure catchments. Though this second source holds useful information on the peat condition from direct augering, the location of samples are all outside of the main fen compartments identified BA for inclusion within this project.

54

Figure 12: Location of samples taken during the Fen Invertebrate Survey


55

Figure 12: Location of sites included within the Fen Audit, 2002-3.


56

Figure 12: Location of sites included within the Braodland Headwaters Peat Survey and the Broads Peat Database


57

3. Production of a site-based summary spreadsheet of hydrological data

The Fen Hydrology Database consists of 113 sites (with each site containing several

compartments). Those compartments listed contain either wholly fen communities or a large

proportion of fen with some woodland/scrub present also. The database is provided digitally on

CD. For each site, a tick box is provided on whether information is available from the BA on the

following areas:

- Fen Audit

- Fen Vegetation Survey

- Year of Vegetation Survey

- Dipwell data within the site (plus details of the relevant codes)

- Dipwell data within 500m of the site (plus details of the relevant codes)

- Gaugeboard data within the site (plus details of the relevant codes)

- Gaugeboard data within 500m of the site (plus details of the relevant codes)

- Borehole data within the site (plus details of the relevant codes)

- Borehole data within 500m of the site (plus details of the relevant codes)

- River level data within <1km of the site

- River level data within 1-2km of the site

- BA conductivity monitoring within the site

- EA conductivity monitoring within the site (plus details of the relevant codes)

- River water quality data within <1km of the site

- River water quality data within 1-2km of the site

- WETMEC classification

- The Peat Survey of 2010

- The Peat Distribution Map

The database has been used for the following trial WETMEC classification (see section 4).

58

4. Assessment of selected sites using a WETMEC approach

4.1 General Methodology

Three trial sites were chosen for WETMEC classification, based on the resources available within

this project. Sites were chosen to reflect different river catchments, different landscape situations

and differences in available data held by the BA. The three sites were as follows:

1. Ebb and Flow Marshes (compartments 25/4-9); Situated on the north side of the River Bure.

This site was chosen because the BA hold detailed conductivity data for this site as well as

gaugeboard and dipwell. The site was also believed to be potentially complex in hydrological

terms but had not previously been assessed using the WETMEC approach.

2. Hall Fen (compartments 08/15-24); Situated on the west bank of the River Ant. This site

was chosen because it appeared to be relatively straightforward in hydrological terms and

the BA held some dipwell, gaugeboard and borehole data for the site, as well as conductivity

data. This site had not been previously classified using a WETMEC approach but was close

to Reedham Marsh (which has been classified by Bryan Wheeler).

3. Mrs Myhills Marsh, Catfield Common and Lings Hill (compartments: 11/11-15); Situated on

the northern bank of the River Thurne. This site was chosen because it was believed to

contain a range of water supply mechanisms and the BA already held data from several

dipwells, gaugeboards and boreholes in the area (as well as some conductivity data). The

site has previously undergone WETMEC classification by Bryan Wheeler, during which

process a greater variety of data was available than purely BA held data. Hickling therefore

presented an ideal opportunity to see how closely the two classifications compared given

their different data resources.

For each site, all available BA data was compiled to build up a picture of site characteristics and

highlight any uncertainties. The WETMEC report was then used to work through each WETMEC

unit to find the best match for the site. As the WETMEC types relate to landscape situation (e.g.

Valley head sites, floodplains etc.) many of the types could be dismissed quickly, typically leaving 3 or

4 types as contenders for a unit match. These types were then worked through in detail to pick out

key characteristics which would pinpoint the best WETMEC match.

Section 4.2 provides the detail behind each site classification and the uncertainties encountered.

Section 4.3 summaries which datasets were of most use and whether any key sources of data were

missing which would prevent the wide scale application of a WETMEC approach in the Broads.

59

4.2 Trial Site Assessment

4.2.1 Ebb and Flow Marshes

4.2.1.1 Existing data

The following data sources were available from the BA for this site:

- BA Fen Audit & ditch network sketch

- BA Responses to Fen Management Study

- Dipwell and Gaugeboard data from the EA Roc database

- BA Fen Vegetation Survey (2007)

- River water quality data from the EA website

- BA Site specific conductivity monitoring

- EA conductivity monitoring

- BA Peat Distribution map

- Rainfall data for Lowestoft from the Met Office

The Fen Audit identified that the site has undergone scrub clearance in 2004 and consists largely of

reed dominated or mixed fen. The notes state that commercial sedge is cut from the north of

compartment 8 and commercial reed used to be cut from compartment 9. The audit also highlights

that compartment 8 can get very wet with pools and wet woodland to the south. The sketch of the

ditch network provided as part of the BA salinity study (OHES, 2011) shows river water can enter

the site via two open connections (see Appendix X). Some of the internal ditches have become

overgrown and some have recently had pipes inserted to improve flow onto the sedge beds.

The BA Responses to Fen Management Study also used Ebb and Flow Marshes as one of the

example sites. In the site characteristics text it states that the vegetation communities found here

span a range of pH values, and that wetness and nutrient status within the site is extremely variable.

The substrate is described as fen peat over estuarine clays and Norwich Crag, with more than 50%

of the site thought to have undergone cutting for peat. It suggests that the site characteristics most

closely correspond to WETMECs type 6e: Wet SW Percolation Quag.

Three dipwells and one gaugeboard are present on Ebb and Flow Marshes (see Figure 13).

Monthly data for these monitoring points typically runs from February 2007 to April 2011and is

presented in Figure 14. It shows that water levels within Compartment 7 fluctuate seasonally by

approximately 45cm, with;

- mean winter water levels of 0.50mAOD,

- mean spring water levels of 0.43mAOD,

- mean summer water levels of 0.36mAOD and

- mean autumn water levels of 0.47mAOD.

Some of the peaks and troughs visible within Figure 14 coincide with extremes of rainfall

experienced (for example, high rainfall in July 2007 has led to higher than average water levels on the

site for this time of year, while little rainfall in the Spring of 2007 led to low water levels in the

ditch). However, the majority of peaks in water levels appear to coincide with tidal surges (for

example in January and December of 2007, February-March of 2008 and November 2008).

60

Figure 13: EA RoC datasets available for Ebb and Flow Marshes.


Figure 14: Water levels recorded in dipwells and gaugeboards at Ebb and Flow

Marshes (source EA RoC data).

61

As the conductivity data in the following paragraph will show, only some of the internal ditches

reflect this increase in river conductivity levels.

Unfortunately, though the data here provides us with water levels to Ordnance Datum, with

some information of how these levels relate to the top of the dipwell casing, it does not specify

what the marsh height is at these points. Therefore we can only crudely estimate what the

depth of the water table below ground level may be, based on the assumption that most dipwells

are approximately 40cm high. If this were the case, the marsh height within compartment 7

would be around 1.1mAOD, making the mean water table between 60-75cm bgl.

Lidar data may be able to clarify this uncertainty, but it was not available during the course of the

project. Furthermore, there is some uncertainty as to the accuracy of Lidar data in wetland

situations. This is due to a combination of variables, but main causes of inaccuracy include peat

shrinkage (due to drainage) and a wide range of vegetation heights (which make correction of

lidar data difficult). In our experience, Lidar data differs from actual land heights (taken using

DGPS) by 20-40cm in reedbeds and drained peatlands, but can be inaccurate by as much as

70cm in unusual vegetation types.

The Fen vegetation survey classifies the fen vegetation nearest to the river as various forms of

S26 Phragmites-Urtica community, with S4 Phragmites swamp also occurring close to the river

and in compartment 9 (where commercial reed cutting used to take place and the area is known

to be very wet). S24d Typical sub-community was found throughout the whole site. However,

more localised distributions included the Cladium sub-community of S24 (f) occurring mainly in

the northern half of the site, while S24g Myrica gale sub-community occurred mainly in the

south. A small stand of Sphagnum-Dryopteris dominated fen (BS5) occurred in compartment 7

(see Figure 14).

The compartment descriptions provided in the report identify a hollow in compartment 5 (near

Q10) and wetter areas in compartment 6 (where scrub clearance has taken place) and

compartment 8. However it should be noted that the vegetation survey of this site took place in

the summer of 2007, when greater amounts of rainfall would have made the site wetter than

normal.

62

Figure 14: Fen Vegetation Survey (200X) results for Ebb and Flow Marshes (Key to

all NVC communities presented in Appendix X).

© Crown Copyright. All rights reserved. Broads Authority (2011).

Simple calculations of the Ellenberg Indicator Values based on individual quadrat data were

undertaken for Ebb and Flow Marshes to try and establish what typical water levels might be for

the fen. Figure 15 shows the Moisture Indicator Values (with 10 representing aquatic conditions

and 1 representing very dry conditions). The dotted line shows where open water was

recorded during the Fen Vegetation Survey.

It indicates that species favouring very wet conditions occur in several areas; firstly in

compartments 8 and 9 (where conditions are likely to be wet all year round), secondly along the

edge of the highland in compartment 6 (where conditions are likely to be seasonally wet but

with some hollows remaining wet all year round), and thirdly in a large area within the centre of

the marsh. There is a slight difference between the distribution of open water and the Ellenberg

moisture indicator values within the central area, which is believed to be the result of excessive

rainfall in 2007 making the area appear wetter than the indicator values would suggest normally

occurs. Thus it has been interpreted that this central area is also only seasonally wet during

normal conditions.

Drier conditions are clearly shown by the yellow and green shading, which coincide with those

areas of Sphagnum-Dryopteris vegetation and W2b woodland. These areas will therefore

primarily be rainwater-fed due to their elevation above the surrounding fen surface.

63

Figure 15: Ellenberg Indicator Values for Moisture (calculated from individual

quadrats recorded during the Fen Vegetation

Survey).

64

Calculations of the Nitrogen Indicator Values are shown in Figure 16. The highest values are

recorded around the river edge and along the edges of internal ditches which have a close link

to river water. All of compartment 9 shows relatively high nitrogen indicator values which

suggests a strong link to river waters. However, the central area of Ebb and Flow Marshes, has

low to very low Nitrogen Indicator Values, which may help to explain the high ecological value

of the site. This data would suggest that river water does not penetrate beyond the main

internal ditch to any significant degree.

The higher values in the north of the site may be the result of surface water run-off from

neighbouring farmland, but appear to be very localised.

Figure 16: Ellenberg Indicator Values for Nitrogen (calculated from individual

quadrats recorded during the Fen Vegetation Survey).

65

Figure 17 shows the Reaction Indicator Values for quadrats within Ebb and Flow Marshes. It

highlights the concentration of plant species preferring acidic conditions within compartment 7

(in the south). It also suggests a few areas to the north are beginning to show a preference for

more acidic conditions, which may be the result of hydroseral succession towards more W2

woodland.

Figure 17: Ellenberg Indicator Values for Reaction (calculated from individual


66

Figure 18 shows the Salt Indicator Values for quadrats within Ebb and Flow Marshes. It clearly

illustrates that the majority of the marsh received relatively low salt indicator values, despite the

open river connection. The exceptions are the vegetation found around the perimeter of the

river and in compartment 9 (due to the dominance of reed).

Figure 18: Ellenberg Indicator Values for Salt (calculated from individual quadrats

recorded during the Fen Vegetation Survey).

River water quality data from the EA website is only available from the confluence of the River

Bure and Ant (though data for each river are provided). It shows that the River Bure is Grade 3

for Nitrogen (Moderately Low) and Grade 2 for Phosphorus (Low).

Two types of conductivity data are available for this site. The BA data showed that saline

incursions during tidal surges do affect the margins of the site (as shown in Figure 19), during a

surge in September 2004) but tend not to penetrate into its centre. The report suggests that,

due to recent restoration works (such as improvements to water movement on and off the

sedge beds via an extended pipe network) it can be assumed that any saline river events can also

penetrate deep into the fen vegetation. However the Ellenberg Indicator values and EA

67

conductivity monitoring point do not corroborate this assumption (though it may be possible

that the vegetation has not as yet adjusted to the new pipe network).

High conductivity was recorded by BA staff both during dry months and months of average

rainfall. Furthermore, peat conductivity results produced by Parmenter (which are restricted to

the northern half of the site) show samples fell into the ‘Very High’ category (>1000 KS/cm). It

is therefore likely that higher than average conductivity values recorded from the central area of

this site are more a reflection of background soil properties than recent river water ingress.

The EA conductivity monitoring point at 662 runs for the period between June 2007 and April

2010. The data shows somewhat variable conductivity readings between 1530 - 2923µS, with an

average value of 1922µS and standard deviation of 226µS. However, as the BA site specific

conductivity readings show, the EA conductivity measuring point lies within an area where salt

levels are generally beyond the influence of saline incursions, in all but the most extreme

examples (such as November 2007).

Figure 19: Conductivity values recorded by BA staff in September 2004.

Ebb and Flow Marshes also appears within the Peat distribution map and therefore is likely to

represent a significant depth of peat.

4.2.1.2 Ebb and Flow Marsh Conclusions

The available data suggests that Ebb and Flow Marshes consists of combinations of the following

WETMEC groups:

68

- 6d Swamped surface water percolation surface

- 6e Wet surface water percolation quag

- 6c Surface water percolation ‘boils’

- 6f Surface water percolation water fringe

Figure 20 shows the approximate locations of these types.

Initial identification of WETMEC 6 Surface water percolation floodplains was apparent from the

position of the site in relation to the river (i.e. floodplain), the topography of the site (typically

flat), the absence of apparent groundwater input (dipwells show seasonal fluctuation in water

levels), the wetness of the site throughout the year, and the nature of the peat (typically soft or

buoyant).

Further separation of the site into sub-types was more complicated. The majority of the site

appears to be either 6d or 6e. The 6d sub-unit is stated to occur in poorly drained areas which

remain wet for much of the year but where the vegetation is ‘grounded’. They can be isolated

from watercourses and dykes, and occur on spongy but not obviously buoyant peat. 6d has a

mean summer water level of -4cm bgl (below ground level). This classification is therefore most

appropriate for those parts of Ebb and Flow Marshes for which the internal ditch network has

become overgrown (such as in the south of compartment 7) or in areas of compartment 6.

The sub-unit 6e is differentiated from 6d by its buoyant surface, which is summer-wet and

typically occupies former turf ponds. 6e has a mean summer water level 12.5cm agl (above

ground level) and best matches the wettest parts of the site (such as in compartments 8, 9 and

parts of 6 and 7). However, without a walkover of the site to record the peat condition (i.e.

buoyant or grounded) during typical summer conditions, it is not possible to map the

distribution of these two types in Figure 20.

Figure 20: Estimated WETMEC types found at Ebb and Flow Marshes.


69

Sub-unit 6c is typically associated with areas fed by precipitation and have a mean summer water

level of -16.6cm bgl, which fits those drier parts of compartment 7. Sub-unit 6c is stated as

having a sub-surface water level all year round due to a buoyant or quaking surface, but none of

the existing data could confirm if this is the case at Ebb and Flow. However, 6c is also typically

dominated by Sphagnum sp. and occurs on acidic surfaces which can consolidate to permit

colonisation of birch woodland. 6c is transitional to WETMEC 3 Buoyant Weakly Minerotrophic

Surfaces (‘transitional bogs’). It is therefore considered to be the best fit for the drier parts of

Compartment 7.

Finally, there are one or two areas which may fall into 6f where very wet conditions were

recorded around the perimeter of pools (such as occurs in the south of compartment 8). Once

again 6f is linked to buoyant surfaces but which are encroaching directly upon open water

bodies. Mean summer water levels for 6f are -1.8cm bgl and can consist of S2 and S4 swamp (as

occurs here). However, confirmation of this sub-unit would require a site-visit or site-staff

knowledge of the buoyant nature of the vegetation in these areas.

4.2.2 Hall Fen



- BA Fen Audit

- Dipwell and Gaugeboard data from the EA Roc database

- BA Fen Vegetation Survey

- River water quality data from the EA website


- BA Peat Distribution map


The Fen Audit identified that the site had once been used as grazing marsh (in the 1950’s and

that approximately half of the site (the area nearest the river) is still cut commercially for reed.

The notes also indicate a sluice is present on the site which controls river input but that much of

the site remains very wet. The notes refer to old drains and ponds being particularly unstable

(especially when water is lying on the site).

Three dipwells, one gaugeboard and one borehole6 are present on Hall Fen (see Figure 21).

Monthly data for these monitoring points typically runs from July 2006 to October 2010 and is

presented in Figure 22. It shows that water levels within Compartment 15 fluctuate seasonally

by approximately 40cm, with;

6 The borehole dataset was not available during the project.

70

Figure 21: EA RoC datasets available for Hall Fen.


Figure 22: Water levels recorded in dipwells and gaugeboards at Hall Fen (source

EA RoC data).

71





The peaks and troughs visible within Figure 22 generally coincide with varying amounts of rainfall

experienced (for example, low rainfall occurred in July 2006, April 2007 and July 2008, while high

rainfall occurred in June 2007 and December 2009). In contrast, some peaks appear to coincide

more with tidal surge events. However, as the conductivity data in the following paragraph will

show, this is not related to an increase in ditch conductivity levels and therefore is presumed to

be the result of rainwater and land drainage runoff being unable to exit the site via the sluice due

to high river water levels, rather than ingress of river water.

Once again, the data here provides us with water levels to Ordnance Datum, with some

information of how these levels relate to the top of the dipwell casing, but does not specify what

the marsh height is at these points. Crude estimates, based on the assumption that most

dipwells are approximately 40cm high, suggest the marsh height within compartment 15 would

be around 0.9 to 1.0mAOD, making the mean water table between 50-70cm bgl. This is

contrary to several other sources of information suggesting the site is wetter than this and

therefore makes the accuracy of estimating ground height based on arbitrary dipwell heights

debatable.

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The Fen vegetation survey illustrated that the majority of the fen nearest to the river consisted of

forms of S4 Phragmites swamp or Intermediate S24-S25 tall herb fen (see Figure 23). A small area of

S14c was identified around open water within compartment 16 and occasional small patches of M22

or S26 were also recorded. In the western compartments, S4 was still present in some areas, but

Intermediate S24-S25 vegetation was much more abundant. Occasional patches of S27b, S14c, M22a

and BS3 were also recorded. The compartment descriptions provided in the report give a broad

picture of the vegetation present, but highlight that low-growing vegetation containing Carex

rostrata and Parnassia palustris are present in several compartments. It refers to recent turf ponds

containing simple swamp stands, some of which are the result of scrub clearance.

Figure 23: Fen Vegetation Survey results for Hall Fen (Key to all NVC communities

presented in Appendix 1).


73

Simple calculations of the Ellenberg Indicator Values based on individual quadrat data were

undertaken for Hall Fen to try and establish what typical water levels might be for the fen.

Figure 24 shows the Moisture Indicator Values. It clearly indicates that species favouring very

wet conditions occur in a strip of land adjacent to the river, and around several turf ponds (of

varying ages) within the heart of the fen. For these species to persist it is likely that very wet

conditions are maintained throughout the year. The majority of the remaining fen still contains

species able to tolerate wet conditions, though these seem to decrease in frequency towards the

far west of the site (in what was previously carr).



74

Calculations of the Nitrogen Indicator Values are shown in Figure 25. Interestingly, the higher

values (representing more eutrophic species preferences) occur in the same areas as the high

moisture values. This may suggest these areas share a water source which is higher in nitrogen,

such as river water, whereas other parts of the fen are more isolated from the ditch network

and are therefore supplied by more mesotrophic rainwater. It appears from the OS maps and

aerials that a number of internal ditches are no longer actively maintained, though these may still

be permitting lateral sub-surface flow of water across the site in compartments 19, 20, 22 and

24. Other compartments, such as 15 appear to have very few internal ditches which may explain

the lower nitrogen and moisture indicator values in some areas.



75

Figure 26 shows the Reaction Indicator Values for quadrats within Hall Fen and suggests that

conditions are generally circum-neutral. Unlike Ebb and Flow Marshes, no acidic conditions

were indicated by the Ellenberg Values. Similarly, no highly calcareous conditions were

suggested by the species present.



76

Figure 27 shows the Salt Indicator Values for quadrats within Hall Fen. From this map, the

vegetation around the margins the river appear to exhibit a greater salt tolerance in terms of

species composition. This would be consistent with tidal incursions which may have occurred in

the past within this area. Other areas receiving high salt indicator values coincide with those

areas marked out in Figure 24 as wetter.



River water quality data from the EA website shows this section of the River Ant to have very

low nitrogen and phosphate levels, though the data suggests levels have been higher in the past.

The EA conductivity monitoring point at 608a only exists for a short period of time between July

2007 and March 2009. The data shows fairly high but constant conductivity readings between

2336 - 2720µS. However, as the Ellenberg indicator values for salt show, the conductivity

measuring point lies within an area where salt levels are generally higher than occur in the

majority of the fen to the west.

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When this conductivity data is compared with conductivity levels within the River Ant (recorded

from the outfall of Barton Broad) it is clear that peaks in conductivity in the river (due to tidal

surges) do not appear to reach Hall Fen (see Figure 28).

Figure 28: Conductivity readings from Hall Fen and the outfall of Barton Broad

(source: EA).

Hall Fen also appears within the Peat distribution map and therefore is likely to represent a

significant depth of peat.

4.2.2.2 Hall Fen Conclusions

The available data suggests that Hall Fen consists of combinations of the following WETMEC

groups:

- 5c Winter-flooded floodplain

- An intermediate unit of 5d Floodplain Sump and 6a Solid surface-water percolation surfaces

- 6d Swamped surface water percolation surfaces


Initial identification of types 5 and 6 was clear-cut due to the basic characteristics of the site; i)

having a water supply source of rainwater and land drainage (with very little apparent

groundwater input), ii) close proximity to a river and a topography reflecting a floodplain

situation, iii) the pattern of seasonal flooding and iv) the presence of a substantial layer of peat.

Further division into sub-unit 5c was fairly straightforward and was indicated by the location of

the unit from the river, the suggestion from vegetation data that the area is wet during winter

but mostly dry in the summer, and evidence that the peat here is mostly firm and therefore of

78

low permeability. Sub-unit 5c has a mean summer water level of -17.5cm, which is consistent

with the absence of open water recorded in these areas during the Fen Vegetation Survey

(despite rainfall being high that summer).

Figure 29: Estimated WETMEC types found at Hall Fen.


Classification of the wetter depressions away from the river into either 5d or 6a was more

complicated, mainly because there is considerable overlap in the features of these two sub-types.

Both can appear in conjunction with 5c and both can appear in old peat workings. One aid to

separation of these two sub-types is that 5d tends to have a greater fluctuation in water levels,

with a mean summer water level in 5d of -15cm and 6a of -12.3cm. Unfortunately, BA do not

hold water level data for these depressions. A further aid to separation is that sub-unit 6a

usually has a less dense top-layer of peat (and thus a greater permeability) but data on peat

condition was also not held by the BA.

However, it could be argued that, as these sub-types hold so many similarities, and have similar

vulnerabilities, it is not essential to separate them.

Identification of sub-unit 6d is based on the very small amounts of evidence (i.e. the field

surveyor’s memory) that the vegetation does not appear to rise and fall with the water table but

appears to be high all year round. This is partly indicated by the Ellenberg moisture values and

open water recorded during the Fen Vegetation Survey, and partly inferred by the area being

commercially cropped and therefore presumably maintained at a high water level for much of

the year. Though this area next to the river also has some affinities to 5d, the peat in this area is

79

believed to be spongy but not buoyant (from the surveyor’s memory) and therefore more

permeable. However, evidence of tests within the ronds on Reedham Marshes to the immediate

south of Hall Fen (WETMEC report) showed that the river bank itself remains a relatively

impermeable barrier, and this is also presumed to be the case for Hall Fen.

WETMEC classification has been performed previously on the neighbouring Reedham Marshes

(WETMEC report), and was consulted once the above classification had been made. At

Reedham Marshes the following types were identified:

- 5c: Winter-Flooded Floodplain (ronds and areas of undug peat)

- 6b: Grounded SW Percolation Quag

- 6c: SW Percolation ‘Boils’

- 6d: Swamped SW Percolation Surface

- 6e: ‘Wet’ SW Percolation Quag

The distribution map of these types at Reedham is not presented in the WETMEC report, but

the extention of some of these types into Hall Fen seems highly likely.

4.2.3 Mrs Myhills, Catfield Common and Lings Hill (compartments 11-15)



- BA Fen Audit

- BA Responses to Fen Management Study

- Dipwell, Gaugeboard and Borehole data from the EA Roc database

- BA Fen Vegetation Survey (2005 & 2008)


- EA Tidal data


The Fen Audit records that compartment 11 (Catfield Common) is commercially cut for sedge

and has a heathy edge where the fen meets the upland. The other compartments all exhibit

winter flooding and are managed through summer grazing. Those compartments at Mrs Myhills

Marsh (14 and 15) are stated to have more scrub and ‘holes’. The Responses to Fen

Management Study does not cover Catfield Common but shows that Mrs Myhills has undergone

considerable scrub control in recent years but still contains large areas of scrub.

Six dipwells, three gaugeboards and three boreholes are present on Compartments 11-15 (see

Figure 30).

80

Figure 30: EA RoC datasets available for Mrs Myhills, Catfield Common and Lings

Hill.


Monthly data for these monitoring points typically runs from July 2006 to April 2011 and is

presented in Figures 31 and 32. Figure 31 shows that water levels within Compartments 14 and

15 (Mrs Myhills) fluctuate seasonally by approximately 30cm per monitoring point, with;





Here water level fluctuations are clearly very localised, falling from dipwell 11 (at the west of the

transect) to dipwell 11a (in the centre) and then rising again by dipwell 11b (at the eastern end

of the transect). However, the peaks and troughs of all three dipwells generally correspond

closely with each other (especially between 11 and 11a). Dipwells 11 and 11a are, on the whole,

comparable to the water levels within the perimeter ditch but the graph shows several occasions

when ditch water levels experience higher readings (such as in January 2007, October 2009 or

June 2010) which do not correspond with the dipwell data. This could be the result of several

causes, such as additional water being supplied by Catfield Dyke which does not reach into Mrs

Myhills, or an increase in run-off from the upland which is bypassing the dipwells. Either way it is

likely that there are several parts of Mrs Myhills which are isolated from the ditch network.

Figure 32 shows that water levels fluctuate by approximately 35cm in the dipwells and 35-50cm

in the ditches of compartments 11 to 13. Mean summer water levels are as follows:



81



The dipwells broadly follow similar trend lines and have identical mean annual water levels

(0.45m AOD). The gaugeboard data is sometimes higher than dipwell data (such as in January

2007 and December 2007) but mean annual water levels are much the same (between 0.43 and

0.45m AOD), including Catfield Dyke itself.

Once again, due to the absence of land height data we can only crudely estimate that marsh

height in Mrs Myhills is approximately 1.07-1.27mAOD and in Lings Hill is approximately

1.03mAOD (based on the assumption that most dipwells are approximately 40cm high). If this

were the case, the mean summer water table within Mrs Myhills would be 64-84cm bgl, and

64cm bgl in Lings Hill.

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Figure 31: Water levels recorded in dipwells and gaugeboards at Mrs Myhills (source EA RoC data).

83

Figure 32: Water levels recorded in dipwells and gaugeboards of Catfield Common and Lings Hill (source EA RoC data).

84

The borehole data for Mrs Myhills is shown in Figure 33. At the nearest borehole to the fen

(10), the mean annual water level is 1.23mAOD. Seasonal fluctuations are as follows:





Borehole 10b has the lowest water levels, which suggests a fall in the water table towards

Catfield Dyke. These borehole water levels are approximately 60-70cm higher than the

dipwells, which are only 120m away. Therefore, assuming the levelling in of the monitoring

points is accurate; this suggests a strong groundwater influence may be affecting Mrs Myhills,

particularly if the rough approximation of marsh height at 1.07 to 1.27m AOD is correct.

Figure 33: Water levels recorded in boreholes near Mrs Myhills Marsh.

85

The Fen vegetation survey shows the vegetation within Mrs Myhills consists of M25b (M.caerulea-

P.erecta mire) and an intermediate between S27b (C.rostrata-P.palustris fen) and M5 (C.rostrata-

Sphagnum squarrosum mire). The compartment description states recent clearance has occurred on

the drier, more acidic peat on the western margin of Compartment 15. It identifies the pond as

having S13 (Typha angustifolia swamp) and S4 (Phragmites swamp) communities.

The vegetation of Catfield Common and Lings Hill consists mainly of mixtures of S24 Phragmites-

Peucedanum) and S25 (Phragmites-Eupatorium) fen, with very limited areas of pure S24b (Glyceria

sub-community) or S25c (Cladium sub-community). Various stands with affinities to S2 (Cladium

swamp) occur, particularly in Catfield Common, but also across the central parts of Lings Hill. Small

areas of M22a (Juncus-Cirsium fen-meadow) and S4 were also recorded close to the dykes in Lings

Hill. The compartment description notes that the perimeter of compartment 12 is marked by raised

ground and that compartment 13 has species-poor reed where water levels were at or above the

marsh surface.

Figure 34: Fen Vegetation Survey (200X) results for Compartments 11/11-15 (Key

to all NVC communities presented in Appendix 1).


86

Calculations of the Ellenberg Indicator Values based on individual quadrat data were undertaken

for Mrs Myhills, Catfield Common and Lings Hill to try and establish what typical water levels

might be for the fen. Figure 35 shows the Moisture Indicator Values. It suggests the wettest

areas are the southern and eastern boundaries of Lings Hill and the central area of compartment

12. Several localised spots of open water were also recorded from Catfield Common but the

lower Moisture Indicator Values found here suggest this may have been temporary ponded

rainwater due to a more impermeable surface. At Mrs Myhills, it appears that a strip of wetter

vegetation occurs running from the old pool eastwards towards the broad. The area to the

west and south of the pool appear to be much drier and would therefore be at least summer

dry.



87

Calculations of the Nitrogen Indicator Values are shown in Figure 36. The majority of Lings Hill

and Catfield Common show relatively low Nitrogen Indicator values, with only a few higher

readings around the margins of the dykes. This suggests that nutrient rich river water does not

penetrate into the heart of the compartments (though no river water quality data was available

from the EA for this area). Mrs Myhills shows the lowest nitrogen indicator values, which

suggests a particularly oligotrophic source of water supplies this area. Interestingly, the old lake

and wettest fen to the east appear to have higher nitrogen values than the rest of the fen. In

contrast, the perched areas of more acidic vegetation to the west of the pool are especially

oligotrophic, presumably due to rainwater being the primary water source here.



88

Figure 37 shows the Reaction Indicator Values and suggests that conditions across most of Lings

Hill are generally circum-neutral to calcareous. The exceptions of vegetation with more acidic

preferences coincide with either drier parts of the compartments (near Catfield Dyke) or areas

on the southern edge of the compartments. These areas are in some cases very wet and the

slightly more acidic preferences shown in the vegetation may be the result of seepage water

through the sands of the surrounding upland fringe. As expected, Mrs Myhills also shows the

highest reaction indicator values due to its situation on the edge of the upland and drier nature.

These areas correspond with the presence of Sphagnum sp but also extend into the wetter parts

of the marsh



89

Figure 38 shows the Salt Indicator Values for quadrats within Mrs Myhills, Catfield Common and

Lings Hill. It shows low values throughout Catfield Common and Lings Hill, with a slight

increase in values towards the Hickling Broad. Mrs Myhills shows very low values and appears

to be beyond the reach of brackish river water.



The EA conductivity monitoring point at 15,15a, 17 and 18 typically run for intermittent periods

only and the data recorded is “unconfirmed”. In Catfield Dykes, the levels range from 1500 to

6000µS/cm, with an average value of 2837µS/cm over the survey period (SD=1202µS).

Conductivity values in the side ditches range from 1100 to 4180 µS/cm in ditch 17 (dividing

Compartment 23 from 13) and 1720 to 5660 µS/cm at point 15a (dividing Lings Hill from

Catfield Common). Average values for point 17 are 2660µS/cm (SD=856 µS/cm), and for point

15a are 3295 µS/cm (SD=996 µS/cm).

These values are all above Water Framework Directive targets for freshwater waterbodies (i.e.

<1000 µS/cm) and are undoubtedly the result of high conductivity values in Hickling Broad itself.

Tidal data held by the EA shows water levels in the broad fluctuate considerably (see Figure 39)

and, if the data is correct, underwent a considerable rise in 1997. These values, combined with

the Ellenberg Indicator Values for Salt, would suggest brackish water can freely enter the internal

90

ditches at certain times of year and that in some areas, such as compartment 12, these is

affecting the vegetation present. However it does not appear to have adversely affected the

vegetation within Mrs Myhills Marsh or Catfield Common (where there are very few internal

ditches).

Figure 39: Water level readings from Hickling Broad (source: EA).

Compartments 11 to 15 all appear outside of the peat distribution map and therefore the peat

depth in these areas is not known within the available BA datasets.

4.3.3.2 Mrs Myhills Marsh, Catfield Common and Lings Hill Conclusions

The available data suggests that Hall Fen consists of combinations of the following WETMEC

groups:

- 6b Grounded surface water percolation quag

- 6c Surface water percolation ‘boils’

- 6d Swamped surface water percolation surfaces

- 13b Seepage percolation quag

- 13c Seepage percolation water fringe


This trial site has proved the most challenging of the three undertaken for this project, because

of the range of conditions found across the 5 compartments. Classification of Lings Hill and

Catfield Common was fairly straightforward due to its situation within a floodplain, the influence

of surface waters, the wet conditions for much of the year and local shallow depressions within

a generally flat topography. Lings Hill compartments are classified here as generally 6d, where

91

Figure 40: Estimated WETMEC types found at Mrs Myhills Marsh, Catfield Common

and Lings Hill.


poor drainage and shallow depressions combine with high water levels to ensure the area is wet

all year round. Some of the compartments are partially isolated from the dykes by

embankments which is in keeping with this sub-unit. Furthermore, one of the distinguishing

features of 6d is the condiction of the peat surface, which from surveyor recollection was

generally soft but not buoyant (Fen Vegetation Surveyor K. Spencer).

The presence of 6c within Lings Hill is less clear. Such areas are known to occur on the

northern side of Catfield Dyke around the edges of woodland/scrub and the presence of

vegetation indicating lower reaction values and moisture levels (e.g. in compartment 13 next to

Catfield Dyke, where scrub is also present) would suggest 6c may be forming here too.

However this has not reached a state where species such as Sphagnum and Dryopteris have

established.

Catfield Common appears to be slightly drier than Lings Hill, with surface water still present in

some areas but believed to be the result of ponded-back precipitation. Here the vegetation is

largely isolated from watercourses and largely dries out in summer, with corresponding firmer

peat surfaces. These characteristics fit well with 6b.

Classification of Mrs Myhills Marsh is less clear but the high water levels recorded in nearby

boreholes suggest groundwater plays a much more significant role here. Without levels data, it

is difficult to be certain, but it appears likely that the pool has a large groundwater component

and from surveyor memory has a buoyant surface which is wet all year round (Fen Vegetation

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Surveyor J.Stone). This buoyant surface extends towards the east, where large proportions of

open water where present during the Fen Vegetation Survey. J. Stone also observed some

suspect water quality issues, namely in signs of the formation of ‘flock’ within the waterbody.

This is believed to be the result of calcium and phosphorus locking together. These

characteristics are believed to best fit 13c.

Around this very wet fringe, lies an area which is still summer wet but not flooded due to a

buoyant surface. The occurrence of the area in conjunction with 13c and on the edge of

floodplain margins, together with the presence of M5 and S27 communities and the likelihood of

groundwater input suggests WETMEC unit 13b. However, the presence of other distinguishing

features for 13b, such as thick deposits of marl and peat, are not known using the BA data

available.

Consideration of types 10 Permanent Seepage slopes and 11 Intermitent and Part-Drained

Seepages were also considered for Mrs Myhills but were concluded to most likely occur outside

of the area surveyed. They are presumed to occur in close proximity to both Mrs Myhills Marsh

and the southern boundary of Lings Hill but are generally associated with more sloping ground

around the valleysides and are not listed as containing M5 or S27 communities.

4.3.3.3 Comparison with published WETMEC classification

When the WETMEC report (Wheeler, Shaw and Tanner, 2009) was consulted to assess how

closely the conclusions in this report (using only BA held data) compared to the conclusions of

Bryan Wheeler et al. the types identified were as follows (note that Wheeler’s results relate to a

considerably larger geographical area than was studied here, as shown in Figure 41):

- 5c: Winter-Flooded Floodplain

- 6b: Grounded SW Percolation Quag;

- 6c: SW Percolation ‘Boils’;

- 6d: Swamped SW Percolation Surface.

- 6e: ‘Wet’ SW Percolation Quag;

- 6f: SW Percolation Water Fringe

The data within Appendix 3A of the report confirms that Catfield Common has relatively deep

and solid peat and that Mrs Myhills Marsh has very shallow peat in some areas. The report

states:

“It is possible that groundwater discharge may be of some local importance in some locations

adjoining the upland margin, e.g. Mrs Myhill’s Marsh, but there is no known evidence for this and

the underling clay may act as an effective aquitard”.

The conclusion of Appendix 3A is:

“Primarily a surface-water fed system. The Broad may recharge the underlying Crag but may

possibly also receive some groundwater inputs at certain times of the year (summer). Some

marginal fen locations may also receive localised groundwater inputs, but the importance of this

is not known. The water is slightly brackish”.

It therefore broadly confirms the conclusions of this study but does not refer to any areas within

Mrs Myhills as 13b or c (though groundwater inputs are mentioned in the above text). It is

93

unclear whether this is due to a different set of data being available under this study (for

example EA RoC data and Vegetation data) or whether it is due to mis-classification under this

study. Appendix 3A does not provide distribution maps of the WETMEC types identified and

therefore cannot be directly compared with this study.

Figure 41: Area classified using WETMEC approach by Bryan Wheeler et al (shown

by the green line).

94

5. Conclusions

The study acknowledges that gauging the usefulness of each dataset will depend on the end use. Of the four main uses identified, the following datasets were found to be of key importance:

• The formation of a conceptual hydrological model (such as the WETMEC framework). In this case, water level data from dipwells and boreholes are considered to be the most useful hydrological information held by the BA. However, site-specific conductivity monitoring is also considered to be very valuable.

• The assessment of fen condition (e.g. whether water levels and water quality is appropriate for maintaining features of high ecological importance). Once again, dipwell, gaugeboard and borehole data are all of importance, but conductivity monitoring from a range of sources is of increased significance.

• The prediction of future environmental changes. Where frequency and impact of tidal incursions is the main issue; conductivity data, climate data and tide data are all valuable resources. Where risk from abstraction is the issue; dipwell and borehole data are of particular value. Where climate change is the key concern; river and tide levels alongside data from weather stations is of key importance.

• The measurement of changes to site management (such as the effect of constructing a new sluice or re-routing surface waters). In this respect, much of the data current held by the BA is not designed for this use and therefore has limited value. However, dipwell, gaugeboard and borehole data would still be moderately useful.

However, it is also felt that other non-hydrological datasets held by the BA hold a surprising

amount of information which can provide valuable background data to any hydrological site

assessment.

A key dataset used in WETMEC assessment of all three trial sites was EA RoC data on water

levels (from dipwells, gaugeboards and boreholes) which gave a valuable picture of water level

fluctuations throughout the year. Borehole data was especially useful, though for two out of the

three trial sites was not available. However the usefulness of the EA RoC data was somewhat

limited by the absence of marsh height data (Lidar or otherwise) so that it was not possible to

gauge whether the water table was, for example, -10cm bgl or -50cm bgl. The Fen Vegetation

Survey proved a key alternative means of gauging wetness within a site, and possible water

sources, by the use of Ellenberg Indicator Values. These values gave a clue to long-term

conditions within the site and, where real data was also present, often reflected the raw data

surprisingly well. This information was particularly useful when combined with data on the

percentage cover of open water recorded during the Fen vegetation survey.

Conductivity monitoring data also proved extremely useful at some sites (e.g. Hall Fen and Ebb

and Flow Marshes) so that the influence of the river could be assessed. However, EA

conductivity data is very dependent on the placement of the monitoring point, as is highlighted by

the BA site specific conductivity monitoring and the Ellenberg Indicator Values for Salt.

95

The remainder of useful data came out of the direct observations of staff or surveyors after

visiting the site (either in the form of notes within the Fen Audit, or from the memories of Fen

Vegetation surveyors). However, it is strongly believed that direct communication with those

members of staff who manage the site would have facilitated this process and been a more

reliable source of information.

A further piece of information which was found to limit classification was the absence of soil and

marsh surface details. For example, at Ebb and Flow Marshes the division of the site into sub-

types is largely dependent on whether the vegetation mat is buoyant or grounded – data which

currently only exists in the experience of site staff. Collection of this would not need to be a

detailed set of information but merely access to Lidar information and a walkover survey

recording the condition of the peat surface during a typical summer, or a discussion with site

staff.

In conclusion, it is believed that the BA hold a considerable set of useful data which, where water

level, and vegetation data exist (together with the input of site staff) would be sufficient to classify

a large majority of broadland sites using the WETMEC classification. Sites without water level

data but with vegetation data may still be able to be broadly classified but would have a greater

level of uncertainty until water level data could be obtained.

.

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6. References

• ELP (2010b) Peat Resource Contract. Report to the Broads Authority, Norwich

• Hill, MO, Mountford, JO, Roy, DB and Bunce, RGH (1999) Ellenberg’s Indicator Values for

British Plants. Technical Annex to Volume 2 of the ECOFACT Research Report Series. ITE/DETR.

• OHES (2010). Vegetation Responses to Management at Five Broadland Fen Sites: a pilot

study. Broads Authority, Norwich.

• OHES (2011). Analysis of Salinity Data from 2003-2008. Broads Authority, Norwich.

• OHES (2011). Fen Plant Communities of Broadland; Results of a comprehensive survey

2005-9. Broads Authority & Natural England, Norwich.

• Wheeler, B., Shaw, S. & Tanner, K. (2009). A Wetland Framework for Impact Assessment at

Statutory Sites in England and Wales. Environment Agency, Bristol.

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Appendix 1: Legend for Fen Vegetation Survey Communities

98

Documents

Broadland Fens Site Hydrology Assessment