Llys Marl, Llandudno Junctionbeechdevelopmentsplanning.co.uk/wp-content/uploads/2017/...Waterco Ltd, Eden Court, Lon Parcwr Business Park, Ruthin, Denbighshire LL15 1NJ Tel: 01824

Waterco Ltd, Eden Court, Lon Parcwr Business Park, Ruthin, Denbighshire LL15 1NJ

Tel: 01824 702220 Email: [email protected] Web: www.waterco.co.uk

w10278-170518-FCA and Drainage Strategy

Llys Marl, Llandudno Junction

Flood Consequences Assessment & Drainage Strategy

May 2017

mailto:[email protected]

http://www.waterco.co.uk/

Llys Marl, Llandudno Junction FCA & Drainage Strategy


DOCUMENT VERIFICATION RECORD

CLIENT: Beech Developments (NW) Ltd

SCHEME: Proposed residential development at Llys Marl, Llandudno Junction – Flood Consequences Assessment and Drainage Strategy.

INSTRUCTION: The instruction to carry out this Flood Consequences Assessment and Drainage Strategy was received from Mr John Gardiner of Beech Developments (NW) Ltd

DOCUMENT REVIEW & APPROVAL

AUTHOR: Sally Pettit

CHECKER: Jordan Jones BSc (Hons) MCIWEM

APPROVER: Aled Williams BSc (Hons) MCIWEM

ISSUE HISTORY

ISSUE DATE COMMENTS

18/05/2017 First issue



Contents

Introduction .......................................................................................................................................... 1

Existing Conditions ................................................................................................................................ 1

Development Proposals ........................................................................................................................ 3

Flood Zone Category and Policy Context .............................................................................................. 3

Consultation .......................................................................................................................................... 6

Sources of Flooding and Probability ..................................................................................................... 7

Surface Water Management ............................................................................................................... 10

Water Quality ...................................................................................................................................... 13

Maintenance ....................................................................................................................................... 14

Foul Drainage ...................................................................................................................................... 15

Conclusions ......................................................................................................................................... 17

Recommendations .............................................................................................................................. 17

Appendices

Appendix A – Location Plan & Aerial Image

Appendix B – Topographical Survey

Appendix C – Drainage Survey, Sewer Plan, & DCWW Correspondence

Appendix D – Proposed Layout Plan

Appendix E – Flood Maps & NRW Correspondence

Appendix F – MicroDrainage Runoff and Volume Estimates

Appendix G – Maintenance Schedules


w10278-170518-FCA and Drainage Strategy 1

Introduction

Waterco Consultants have been instructed to prepare a Flood Consequences Assessment (FCA) and

Drainage Strategy in respect of a proposed residential development at Llys Marl, Marl Lane,

Llandudno Junction, LL31 9HB.

The purpose of this report is to outline the potential flood risk to the site, the impact of the

proposed development on flood risk elsewhere, and the proposed measures which could be

incorporated to mitigate the identified flood risk. This report has been prepared in accordance with

the guidance contained in Planning Policy Wales (PPW) and Technical Advice Note 15 (TAN15):

Development and Flood Risk.

This report has been prepared in consultation with Natural Resources Wales (NRW) and Dŵr Cymru

Welsh Water (DCWW).

Existing Conditions

The site is located north of Llandudno Junction at National Grid reference: 279591E 378984N. The

site currently comprises undeveloped agricultural land and covers an area of approximately

1.91hectares. A location plan and an aerial image are included in Appendix A.

The site is bordered by agricultural land to the north, a small wooded strip with the A470 (road)

beyond to the east, Marl Lane and residential properties to the south and residential properties

(Woodlands housing estate) to the west. Access is provided from Marl Lane to the south.

Local Topography

A Topographical Survey has been undertaken by Angle Surveys Ltd in October 2016 and is included

in Appendix B. The Topographical Survey shows that the site generally slopes from north-west to

south-east. Site levels fall sharply towards the A470 east of the site. A topographical high point of

23.71metres Above Ordnance Datum (m AOD) is identified in the north-western corner of the site. A

topographical low point of 10.06m AOD is identified along the eastern boundary.

Ground Conditions

The British Geological Survey (BGS) online mapping (1:50,000 scale) indicates that the site is

underlain by superficial deposits of Devensian Till, generally comprising Diamicton. The superficial



deposits are identified as being underlain by the Nantglyn Flags Formation comprising mudstone and

siltstone.

A Site Investigation (SI) was undertaken by Evans Wolfenden Partnership Ltd in March 2017 (project

reference EWP 6169). The fieldwork involved 17 machine excavated trial pits with depths varying

down to a maximum of 2.8m below ground level (bgl). The underlying strata comprised of stiff silty

clay from 0.3m bgl to 0.7m bgl with firm compact grey / green / brown clay below 0.7m bgl.

Groundwater seepage was encountered within the trial pits at the interface between the stiff silty

clay and the firm compact clay.

Soakaway tests were undertaken and given the impermeable nature of the strata, water levels did

not reduce.

Local Drainage

The DCWW sewer plan (Appendix C) shows that there are no public sewers crossing the site. The

sewer plan identifies a 225mm public combined sewer flowing east within Marl Lane. There is also a

300mm public surface water sewer and a 150mm private (subject to Section 104 adoption

agreement) surface water sewer in Marl Lane flowing east. The surface water sewers discharge to

the Afon Wydden approximately 55m east of the site. The Woodlands housing estate east of the site

is served by a separate foul and surface water drainage system. Surface water flows are discharged

to the 300mm public surface water sewer in Marl Lane. Foul flows are discharged to the 225mm

public combined sewer in Marl Lane.

The sewer plans also identify a 225mm public combined sewer flowing south adjacent to the A470

east of the site.

A drainage survey of the public sewer system south of the site has been undertaken by Invek Surveys

in March 2017 (see Appendix C). Invek Surveys also surveyed the connectivity of the highway

drainage system within Marl Lane adjacent to, and west of the site.

As shown by the Invek Survey, public surface water sewer manhole SH79786850 located

immediately south of the site has a cover level of 13.63m AOD and an invert level of 12.49m AOD.

There are no manholes associated with the 225mm public combined sewer in Marl Lane

immediately south of the site. However, a lamp-hole (SH79785805) on the public combined sewer in

Marl Lane south of the site has a cover level of 12.1m AOD an invert level of 9.66m AOD.



A survey of the highway gullies along Marl Lane shows that highway gullies immediately south of the

site are drained to the 150mm private surface water sewer. All highway gullies upstream of the

Junction of Marl Lane and Victoria Drive (180m west of the site) up to the Junction of Marl Lane and

Pentywyn Road (580m west of the site) are drained to the public combined sewer in Marl Lane.

Development Proposals

The proposed development is for 52 dwellings with associated driveways, gardens, access roads and

public open space. The proposed development will introduce hardstanding in the form of buildings

and roads. Hardstanding will comprise approximately 7,750m2 or 40.6% of the total site area. The

remaining permeable areas will occupy 11,350m2 or 59.4% of the total site area. A proposed

development plan is included in Appendix D.

Flood Zone Category and Policy Context

Flood Zone Category

The Welsh Government Development Advice Map included in Appendix E shows that the

developable area of the site is located within Flood Zone A - an area considered to be at little or no

risk of fluvial or tidal flooding, with a less than 0.1% (1 in 1000) annual probability of flooding. The

eastern boundary of the site lies within Flood Zone C1 - an area at flood risk with a greater than 0.1%

annual probability of flooding, however is served by significant infrastructure including flood

defences.

The Natural Resources Wales (NRW) ‘Flood Map for Planning’ included in Appendix E, shows that the

developable area of the site is located outside of the extreme flood extent (Flood Zone 1), meaning it

has a less than 0.1% annual probability of flooding from rivers or the sea. The eastern boundary lies

within the defended Flood Zone 2 - an area considered to be at risk of fluvial flooding with between

a 1% (1 in 100) and 0.1% annual probability, however benefits from the protection offered by flood

defences.



Development Vulnerability Classification

The proposed residential development is considered to be ‘highly vulnerable’ development in

accordance with Figure 2 of the Welsh Government’s Technical Advice Note 15 – Development and

Flood Risk (TAN15).

TAN15 states that highly vulnerable development is appropriate within Flood Zone A. No residential

dwellings, roads or gardens are proposed within the Flood Zone C1 extent.

Local Policy

The Conwy County Borough Council Local Development Plan 2007 – 2022 was adopted in October

2013 and is the current development plan for the County. The Local Development Plan contains the

following policies relating to flood risk and drainage:

Policy DP/3 – PROMOTING DESIGN QUALITY AND REDUCING CRIME

1. All new development will be of high quality, sustainable design which provides usable,

safe, durable and adaptable places, and protects local character and distinctiveness of the

Plan Area’s built historic and natural environment. The Council will require development

to:

….f) Provide sustainable urban drainage systems to limit waste water and water pollution and reduce

flood risk in line with national guidance and Policy NTE/8 – ‘Sustainable Drainage Systems’

POLICY NTE/6 – ENERGY EFFICIENCY AND RENEWABLE TECHNOLOGIES IN NEW DEVELOPMENT

The efficient use and conservation of natural resources are essential to the overall quality of life

within the Plan Area and to support wider social and economic sustainability objectives. The Council

will:

….c) Ensure that all new developments incorporate the principles of sustainable design such as:

….rain water harvesting, energy efficiency, sustainable drainage….



POLICY NTE/8 – SUSTAINABLE DRAINAGE SYSTEMS

1. The use of Sustainable Drainage Systems will be required wherever reasonably practicable

with preference for on site disposal and where satisfactory arrangements can be put in

place for the long term maintenance of those systems. Where this is not proposed a

developer will need to justify that discharge is necessary and is adequately controlled.

2. Subsequent preference for surface water drainage will be for:

a) Drainage to a surface water (river, lake etc.) subject to appropriate treatment and

attenuation;

b) Drainage to surface water sewer;

c) Drainage to combined sewer.

3. The developer must demonstrate that higher preference drainage options are unfeasible

before proposing less sustainable options.

POLICY NTE/9 – FOUL DRAINAGE

1. Foul drainage to an adopted sewer should be provided wherever possible, in compliance

with Welsh Ministers Build Standards which are effective from October 2012. The

development of sites where drainage to a public sewer is not feasible will only be permitted if

proposed alternative facilities are considered adequate and would not pose an unacceptable

risk to the quality or quantity of ground or surface water or pollution of local watercourses or

sites of biodiversity importance.

2. Development proposals which include vehicle parking and other hard surface areas used by

vehicles must include measures such as trapped gullies and petrol / oil interceptors or other

suitable methods of pollution control to safeguard against pollution of the water

environment.

POLICY NTE/10 – WATER CONSERVATION

All development should incorporate water conservation measures where practicable and conform to

BREEAM standards promoting water conservation, efficiency measures and utilize SUDS techniques.

Development proposals greater than 1000m2 or 10 dwellings should be accompanied by a Water

Conservation Strategy.



Consultation

A developer enquiry was submitted to DCWW by the developer prior to commencement of this

Drainage Strategy. The DCWW developer enquiry highlighted that the proposed development has

potential to overload the public foul / combined sewer system. As such, a Hydraulic Modelling

Assessment of the sewer system was undertaken by DCWW in August 2015 to establish the impact

of development foul flows on the public foul / combined sewer system and to identify any solutions

to resolve any potential detriment caused by the development.

The DCWW Hydraulic Modelling Assessment identifies two potential solutions to mitigate

development foul flows:

Solution 1: Construction of online storage in two locations within the sewer network

(upsizing of x2 manholes on the 225m public combined sewer adjacent to, and within the

A470 east of the site; and upsizing of storage at the Marl Drive Sewage Pumping Station

(SPS);

Solution 2: The removal of 0.084ha (840m²) of impermeable drainage area from the

combined sewer system upstream of Marl Drive SPS / Combined Sewer Overflow (CSO).

Following completion of the DCWW Hydraulic Modelling Assessment, further consultation was

undertaken with DCWW regarding an alternative surface water removal scheme. The alternative

surface water removal scheme, local to the site, is to remove connectivity of highway gullies within

Marl Lane from the public combined sewer. New connections from highway gullies within Marl Lane

will be made to the public surface water sewer (which discharges to watercourse). A new length of

surface water sewer within Marl Lane will be required.

Correspondence with DCWW dated 9th May 2017 (Appendix C) states that:

‘Your e-mail confirms a solution can be achieved, based on the principle of the surface water removal

scheme, and provided that surface water from a contributing drainage area of 0.084ha is removed,

the principle of connecting foul flows into the public combined sewer system would be considered

acceptable. Accordingly, in respect of any forthcoming planning application, it is recommended that

an accompanying proposed drainage strategy is formulated to address the proposed surface water

removal scheme including your calculations which equate to an area of 0.084ha and evidence from

your recent CCTV survey that confirms the connectivity of highway gullies’



Further correspondence from DCWW dated 4th May 2017 (Appendix C) in relation to surface water

discharge from the proposed development states:

‘having had an opportunity to review our exchange of e-mails below and your accompanying Ground

Investigation Report (attached), namely Section 7.7 and Appendix C regarding soakaway tests, I am

satisfied that you’ve investigated and exhausted alternative drainage options under Part H of

Building Regulations and would therefore accept discharge into the public surface water sewer at an

attenuated rate. Accordingly, in respect of any future planning application submission, please accept

this e-mail as an agreement in principle to allow for communication of surface water into the said

public sewer through an attenuation device that discharges at a rate not exceeding 5 l/s.’

Pre-application advice was sought from NRW with a response included in Appendix E. NRW state

that:

‘As you may be aware the area suffered from a significant flood event in June 1993. Following the

event our predecessors carried out a flood alleviation scheme for the main river (Afon Wydden) in

Llandudno Junction. Although the scheme at the time was designed to provide a certain standard of

protection it is highly likely that the standard today would have been reduced.

We would expect Welsh Water to demonstrate that any new direct outfalls to the watercourse will

not increase flood risk from the river Wydden for a range of annual exceedance probability events.

We are at an early stage of developing a hydraulic model for the Wydden which will include various

input points; unfortunately we cannot provide a date as to when the model would be available’.

Sources of Flooding and Probability

Fluvial

The nearest watercourse is the Afon Wydden which is located approximately 50m east of the site

and beyond the A470. Afon Wydden flows south in this location. There is an unnamed tributary of

the Afon Wydden located approximately 180m north of the site. This watercourse flows east in this

location and discharges into the Afon Wydden approximately 185m north-east of the site. There are

no other watercourses in the immediate vicinity of the site.

As stated by NRW, the area (Llandudno Junction) suffered from a significant flood event in June

1993. However, there are no records of flooding affecting the site.



A review of topographic levels shows that the Afon Wydden is situated at approximately 10m AOD.

The Flood Zone C1 extent reaches a level between 10m AOD and 12m AOD. The developable area of

the site is situated outside of the Flood Zone C1 extent (0.1% annual probability extent) and at a

minimum level of approximately 14m AOD. Any potential flooding from the Afon Wydden will

therefore not affect the site.

Site levels slope steeply at the eastern boundary. To form a development platform, an element of

ground levelling will be undertaken. To facilitate this, a retaining wall will be established near the

eastern boundary of the site. The proposed wall will be located outside of the Flood Zone C1 extent

and will not result in a loss of floodplain storage.

It can therefore be concluded that the developable area of the site is at very low risk of fluvial

flooding.

Tidal

The developable area of the site will be situated at a minimum of 14m AOD and is significantly above

sea level. Therefore the site is not at risk of tidal flooding.

Surface Water

Surface water flooding occurs when rainwater does not drain away through the normal drainage

system or soak into the ground. It is usually associated with high intensity rainfall events, but can

also occur with lower intensity rainfall or melting snow where the ground is saturated, frozen or

developed, resulting in overland flow and ponding in depressions in topography. Surface water

flooding can occur anywhere without warning. However, flow paths can be determined by

consideration of contours and relative levels.

The NRW ‘Flood Map for Surface Water’ map (Appendix E) shows that the developable area of the

site is at very low risk of surface water flooding, meaning it has a less than 0.1% annual probability of

flooding. Low land immediately east of the site is shown at high risk of surface water flooding,

meaning it has a greater than 3.3% annual probability of flooding.

Any potential surface water flooding arising at or near to the site would be directed south-east,

away from the site, following the local topography.

It can be concluded that the risk of surface water flooding is low.



Sewer Flooding

Flooding from sewers can occur when a sewer is overwhelmed by heavy rainfall, becomes blocked, is

damaged, or is of inadequate capacity. Flooding is mostly applicable to combined and surface water

sewers.

There are no records of sewer flooding at or in the immediate vicinity of the site. However it is

acknowledged by DCWW that the downstream sewer network has capacity issues.

Any potential flooding arising from the sewers in Marl Lane to the south of the site would be

directed south-east, away from the site, following the local topography. As shown on the

Topographical Survey (Appendix B), site levels rise steeply above adjacent road levels. As such, any

potential sewer flooding would not reach the site.

It can be concluded that the risk of sewer flooding is low.

Groundwater Flooding

Groundwater flooding occurs when water levels underneath the ground rise above normal levels.

Prolonged heavy rainfall soaks into the ground and can cause the ground to become saturated. This

results in rising groundwater levels which leads to flooding above ground.

The PFRA contains no records of groundwater flooding at the site. Based on the elevations of the site

above any local watercourse, it can be concluded that the risk of groundwater flooding is low. This is

confirmed by the Site Investigation (Evans Wolfenden Partnership Ltd, March 2017) which did not

encounter any significant groundwater issues within the trial pits.

Artificial Sources of Flooding

There are no canals in the immediate vicinity of the site.

The NRW Reservoirs Flood Map (Appendix E) shows that the site is not at risk of flooding from

reservoirs. Land immediately east of the site is shown at risk of flooding associated with a failure of

the Afon Wydden flood alleviation scheme. The flood risk is derived from failure of a flood storage

area along the Afon Wydden approximately 50m east of the site. The Afon Wydden flood storage

area is maintained by NRW who are responsible for its maintenance.



Summary of Potential Flooding

It can be concluded that the risk of flooding to the developable area of the site is very low. No flood

mitigation measures are considered necessary for the development. However, in accordance with

Building Regulations, finished floor levels should be set 150mm above surrounding ground levels.

Surface Water Management

The site is undeveloped and considered to be greenfield. The site is not currently served by a formal

drainage system.

In accordance with TAN15, new development should not create additional runoff when compared

with the undeveloped situation.

In order to ensure no increase in surface water runoff as a result of the development, the runoff rate

will be controlled and sustainable drainage systems used to accommodate the 1 in 100 year plus

30% Climate Change (CC) storm event.

Greenfield runoff rates have been estimated using the FEH (Flood Estimation Handbook) method

within MicroDrainage and are included within Appendix F. The existing QBAR (equivalent to the 1 in

2 year event) runoff rate is 3.9 l/s. It should be noted that the FEH data indicates a low soil

percentage runoff value for the sub-catchment which in turn results in a low runoff rate. Given the

underlying clay found during the Site Investigation, it is likely that the site specific soil percentage

runoff value would be higher.

DCWW have confirmed in correspondence (Appendix C) that they would accept a discharge rate of 5

l/s to the public surface water sewer system.

Attenuation Storage

In order to achieve a discharge rate of 5 l/s, attenuation storage will be required. A storage estimate

is included in Appendix F. An estimated storage volume of 468m³ will be required to accommodate

the 1 in 100 year plus 30% Climate Change (CC) event. An estimated storage volume of 223m³ will be

required to accommodate the 1 in 30 year event. The storage estimates are based on storage within

a tank or pond structure, an impermeable drainage area of 0.775ha, a design head of 1m and

hydro-brake flow control.



The storage estimates are provided for indicative purposes and should be verified at the detailed

design stage.

Discharge Method

In accordance with Part H of the Building Regulations, the following hierarchy of surface water

disposal methods should be applied: infiltration (soakaways); watercourse; sewer.

Infiltration

The first consideration for the disposal of surface water is infiltration (soakaways and permeable

surfaces). As stated in the preceding sections, the underlying strata comprises of stiff silty clay from

0.3m bgl to 0.7m bgl with firm compact grey / green / brown clay below 0.7m bgl. Soakaway tests

were undertaken and given the impermeable nature of the strata, water levels did not reduce.

It can therefore be concluded that infiltration techniques (soakaways) will not be a feasible option.

Watercourse

The next consideration for surface water discharge is to watercourse. The nearest watercourse is

the Afon Wydden which is located 50m east of the site and beyond the A470.

A direct connection to Afon Wydden would require crossing third party land and laying a new pipe

beneath Marl Lane and the A470. To avoid forming a new outfall to the Afon Wydden and causing

significant disruption on the A470, a connection to Afon Wydden should be made via the existing

300mm public surface water sewer located within Marl Lane south of the site.

Sewer

As discussed above, a connection to watercourse via the 300mm public surface water sewer in Marl

Lane appears a feasible option. A connection to this sewer at a rate of 5 l/s has been agreed in

principle with DCWW.

Public surface water manhole SH79786850 located immediately south of the site has a cover level of

13.63m AOD and an invert level of 12.49m AOD. The minimum proposed site level is approximately

14m AOD. As such, a gravity connection can be achieved subject to utilising a shallow feature for

attenuation storage.



Sustainable Drainage Systems

Attenuation storage should be provided in the form of Sustainable Drainage Systems (SuDS) where

practical. The following SuDS options have been considered:

Soakaways

As described above, soakaways are not feasible due to the impermeable strata. This has been

confirmed through infiltration testing.

Swales, detention basins and ponds

The development plans do not include provision for an above ground attenuation feature such as a

pond or basin. However, there is potential to utilise a pond or basin as an above ground attenuation

feature. A pond or basin could be located within the area of public open space in the topographically

lower south-eastern extent of the site.

However, an above open surface water attenuation feature such as a pond or basin presents a

significant safety risk; the hazards and appropriate mitigation should be considered at the detailed

design stage. Safety risks are particularly prudent in this instance given that a children’s play area is

proposed within the area of public open space.

Rainwater Harvesting

The attenuation benefits provided through the use of rainwater harvesting are considered to be

limited, and would only be realised when the tanks were not full. However, rainwater harvesting

techniques could be incorporated within the final design.

Green Roofs

Green roofs are not identified on the development plans. Given the nature of the proposed

development, the significant additional cost involved in installing and maintaining green roofs and

the additional works required to allow for the additional loading on the buildings, green roofs are

not considered a practical option. The benefits achieved through installing a green roof would be

disproportionate to the significant ongoing maintenance and construction costs involved.

Porous / Permeable Paving

Permeable paving could be incorporated within private roads and driveways. Private roads and

driveways occupy approximately 4,250m². Storage would be provided within a lined sub-grade

material prior to controlled release to the receiving sewer. The provision of storage within the sub-



grade material would only be feasible in areas with a proposed gradient of <1 in 20 as detailed

within CIRIA RP992/28 (Design Assessment Checklists for Permeable/Porous Pavement). Site

gradients should be confirmed at the detailed design stage. The amount of storage provided within

permeable paving is subject to sub-grade depth and gradient. The use of permeable paving will be

considered at the detailed design stage.

Underground Attenuation Tanks

Storage could be provided within an underground attenuation tank or within oversized pipes.

Sufficient space for an underground tank is provided beneath the area of public open space in the

lower south-eastern extent of the site. Oversized pipes could be located beneath the access roads.

Concept Surface Water Drainage Scheme

Surface water will be discharged to the 300mm public surface water sewer located south of the site

within Marl Lane at a rate of 5 l/s. The connection has been agreed in principle by DCWW. Surface

water run off up to the 1 in 100 year plus 30% CC event will be attenuated on site through provision

of an attenuation tank (modular storage) located within the area of public open space. Oversized

pipes could also be provided beneath the access road.

The proposed surface water drainage scheme will ensure no increase in runoff over the lifetime of

the development. The proposed development will therefore not increase flood risk elsewhere.

Exceedance Event

The proposed drainage system will be sized to accommodate the 1 in 100 year plus 30% CC event

below ground. During an exceedance event, flows should be permitted to create temporary shallow

depth flooding within the area of public open space. Finished floor levels will be set at a minimum of

150mm above surrounding ground levels ensuring exceedance flooding will not affect the building.

Water Quality

In accordance with the CIRIA C753 publication ‘The SuDS Manual’ (2015), residential roofs have a

‘very low’ pollution hazard level. Individual property driveways and low traffic roads have a ‘low’

pollution hazard level. Table 1 overleaf shows the pollution hazard indices for each land use.



Table 1 – Pollution Hazard Indices

Land Use Pollution

Hazard Level

Total Suspended

Solids (TSS) Metals Hydrocarbons

Residential roofs Very Low 0.2 0.2 0.05

Individual property

driveways,

residential car

parks and low

traffic roads

Low 0.5 0.4 0.4

Table extract taken from the CIRIA C753 publication ‘The SuDS Manual’ – Table 26.2

* Indices values range from 0-1.

There is potential for runoff to be directed to a pond, detention basin or permeable paving. Table 2

below shows the pollution mitigation offered by these features.

Table 2 – SuDS Mitigation Indices

Mitigation Indices

Type of SuDS Total Suspended

Solids (TSS) Metals Hydrocarbons

Permeable

Pavement 0.7 0.6 0.7

Detention Basin

0.5 0.5 0.6

Pond 0.7 0.7 0.5

Table extract taken from the CIRIA C753 publication ‘The SuDS Manual’ – Table 26.3

It can be concluded that a pond, detention basin and / or permeable paving provide sufficient

treatment. Where attenuation is provided in a below ground attenuation tank or within oversized

pipes, treatment could be provided by a suitably sized separator.

Maintenance

Maintenance of drainage features accommodating runoff up to and including the 1 in 100 year plus

30% CC event will be the responsibility of the site owner. Maintenance can be arranged through

appointment of a site management company.



Maintenance of oversized pipes accommodating runoff up to and including the 1 in 30 year event

can be offered for adoption to Welsh Water who would then be responsible for their maintenance.

Maintenance schedules for a pond, detention basin, permeable paving and an attenuation tank are

included in Appendix G. The maintenance schedules detail the maintenance requirements and

frequency.

Foul Drainage

DCWW have confirmed through a Hydraulic Modelling Assessment that proposed development foul

flows have potential to cause detriment to the public foul / combined sewer network downstream of

the site.

The DCWW Hydraulic Modelling Assessment identifies two potential solutions to mitigate

development foul flows:

Solution 1: Construction of online storage in two locations within the sewer network

(upsizing of x2 manholes on the 225m public combined sewer adjacent to and within the

A470 east of the site; and upsizing of storage at the Marl Drive Sewage Pumping Station

(SPS)

Solution 2: The removal of 0.084ha (840m²) of impermeable drainage area from the public

combined sewer system upstream of Marl Drive SPS / Combined Sewer Overflow (CSO).

Further investigation has been undertaken by Waterco Consultants and the client to formulate a

viable surface water removal scheme local to the site to offset development foul flows.

Invek Surveys were instructed to undertake a survey to establish the connectivity of the highway

gullies along Marl Lane. As shown on the Invek Survey (Appendix C), highway gullies along a 310m

stretch of Marl Lane, from the junction of Marl Lane and Victoria Drive and the junction of Marl Lane

and Pentywyn Road are draining to the public combined sewer. Assuming a uniform road width of

6.5m, an approximate road surface area of 2,105m² is drained to the public combined sewer.

The foul mitigation proposal is to re-direct highway drainage from the public combined sewer and

into the public surface water sewer within Marl Lane. This will result in highway drainage being

directed to the Afon Wydden via an existing surface water sewer, rather than to the public combined

sewer. As agreed with DCWW, a contributing drainage area of 840m² (840m² of road surface) will



need to be removed from the public combined sewer network. To achieve the foul mitigation

proposal, the surface water sewer within Marl Lane will need to be extended west within Marl Lane

to facilitate connections from highway gullies.

Correspondence from DCWW (Appendix C) sets out an agreement in principle to the foul mitigation

scheme. DCWW state that:

‘Your e-mail confirms a solution can be achieved, based on the principle of the surface water removal

scheme, and provided that surface water from a contributing drainage area of 0.084ha is removed,

the principle of connecting foul flows into the public combined sewer system would be considered

acceptable.’

Once a contributing drainage area of 840m² has been removed from the public combined sewer, a

foul connection from the site should be made to the public combined sewer in Marl Lane. The Invek

Survey did not find any public combined sewer manholes within Marl Lane immediately south of the

site. However a lamp-hole with an invert level of 9.66m AOD was identified. A gravity connection to

the public combined sewer in Marl Lane therefore appears feasible. A new connection may require a

new manhole chamber within the highway.



Conclusions

The proposed development is for 52 dwellings with associated driveways, gardens, access roads and

public open space.

The developable area of the site is located within Flood Zone A on the Welsh Government

Development Advice Map – an area considered to be at little or no risk of fluvial or tidal flooding,

with a less than 0.1% (1 in 1000) annual probability of flooding.

The flood risk from all sources is considered to be low. The minimum level in the developable area of

the site is 14m AOD and at least 2m above the Flood Zone C1 extent (1 in 1000 annual probability

flood extent) associated with the Afon Wydden.

The proposed development will introduce impermeable area in the form of buildings and roads. The

increase in impermeable area will increase surface water runoff rates. In order to ensure the

increase in surface water runoff will not increase flood risk elsewhere, flow control will be used and

attenuation will be provided to accommodate the 1 in 100 year plus 30% climate change event.

Soakaway testing has confirmed that the site is not suitable for the use of soakaways. As such,

surface water runoff will be discharged to the Afon Wydden via the 300mm public surface water

sewer in Marl Lane. An agreement to connect to the surface water sewer in Marl Lane has been

established with Welsh Water. The required discharge rate is 5 l/s.

In order to achieve a discharge rate of 5 l/s, attenuation will be provided on site. Attenuation could

be provided in the form of a below ground attenuation tank beneath the area of public open space.

Welsh Water, through a Hydraulic Modelling Assessment, state that the proposed development foul

flows have potential to cause detriment to the public combined / foul sewer network. A foul

mitigation strategy has been agreed in principle with Welsh Water whereby:

Development foul flows will be permitted to drain to the public combined sewer in Marl Lane

provided that surface water runoff from a contributing area of 840m² will be removed from the

public combined sewer network. This will be achieved by re-routing highway gullies in Marl Lane

from the public combined sewer and into the public surface water sewer.

Recommendations

1) Submit this report to the Local Planning Authority in support of the planning application.



Appendix A – Location Plan & Aerial Image

DATE:31/01/2017

PLOT NAME:w10278-Location_Plan

REV:-

DRAWN:RCL

CHECKED:AW

APPROVED:VG

PLOT SCALE @ A3:

(UNLESS STATED OTHERWISE)1:5,000

PLOT STATUS:FINAL

PLOT TITLE:

LOCATION PLAN

SCHEME:

LLYS MARL,LLANDUDNO JUNCTION

CLIENT:

BEECH DEVELOPMENTS (NW) LTD

LEGENDSite BoundaryWatercourses / Water Bodies

0 100 200 300 400 50050m

NOTES:1) ALL DIMENSIONS ARE IN METRES AND ALL LEVELS IN METRESABOVE ORDNANCE DATUM UNLESS STATED OTHERWISE±

CONTAINS OS DATA © CROWN COPYRIGHT (2017)

Waterco LtdEden Court, Ruthin, LL15 1NJ

01824 702220www.waterco.co.uk

DATE:31/01/2017

PLOT NAME:w10278-Aerial_Plan

REV:-

DRAWN:RCL

CHECKED:AW

APPROVED:VG

PLOT SCALE @ A3:


PLOT STATUS:FINAL

PLOT TITLE:

AERIAL PLAN

SCHEME:


CLIENT:


LEGENDSite Boundary

0 100 200 300 400 50050m


CONTAINS OS DATA © CROWN COPYRIGHT (2017)BASEMAP: WORLD IMAGERY. SOURCES: ESRI, DIGITALGLOBE, GEOEYE, I-CUBED, EARTHSTAR GEOGRAPHICS, CNES/AIRBUS DS, USDA, USGS, AEX, GETMAPPING, AEROGRID, IGN, IGP, SWISSTOPO, GIS USER COMMUNITY





Appendix B – Topographical Survey

LP

LP

LP

LP

IC

A

Z

B

378850N 378850N

378900N 378900N

378950N 378950N

379000N 379000N

379050N 379050N

379100N 379100N

279500E

279500E

279550E

279550E

279600E

279600E

279650E

279650E

279700E

279700E

10.91

11.09

11.34

11.62

12.26

12.7012.81

13.1413.23

13.5013.60

13.99

14.1714.26

14.41

14.71

15.05

15.46

15.87

15.93

16.13

16.31

16.64

17.03

17 06

17.15

16.7516 69

16 35

16.44

16.08

15.69

15.80

15 73

15 27

15.18

14.78

14.88

14 85

14.3814.28

14.39

14.0513.97

13.89

13.41

13.51

14.08

13.73

13.89

13.02

13.13

12.49 12.6012.28

12.19

12.17

12.02

12.02

11.82

11.92

11.70

11.8211.58

11.46

11.26

11.39

11.11

11.23

10.81

11.04

11.76

12.14

12.14

11.83

12.19

12.78

13.45

14.04

14.36

14.71

15.04

15.51

16.17

16.42

16.69

17.07

17.32

16.97

16.54

16.02

15.99

15.33

15.09

14.62

14.11

13.01

13.45

15 00

14 63

14.28

13.54

13 00

11 84

11 42

11 2011 06

10 94

10 82

26.54

22.65

10.81

12.53

11.99

11.44

12.14 12

.0012

.11 11.

86

11.97

11.56

11.66

11.3911

.49

11.201

1.0510.92

10.83

10.74

10.84

10.24

10.63

11.53

12.06

12.69

12.80

12.90

12.75 12 76

10.95

11.1511.19

10.91

11 60

11 9511 77

11 95

11 91

12.85

12.28

11.70

11.43

11.07

10.90

11.27

10.83

10.87

10.92

10.87

10.59

10.43

10.25

10.13

10.09

10 71

10.06

10.88

10.91

10.26

10.22

10.95

11.00

10.66

10.45

11.23

11.24

10.97

10.93

11.23

11.41

11.42

11.53

11.36

11.07

11.21

11.37

11.69

11.72

10.04

10.01

9.92

9.88

9.81

9.81

9.97

9.97

10.12

14.6415.75

23.00

22.65

21.93

15.40

15.02

14.91

14.72

14.61

14.61

14.48

14.36

14.33

13.7011.96

11.49

11.28

11.06

10.94

10.71

10.57

10.38

10.37

10.45

10.30

10.45

10.23

10.21

10.06

9.98

10.27

10.56

23.77

26.53

26.28

26.93

28.87

29.11

29.97

30.49

31.02

31.89

27.46

26.92

23.36

27.64

12.59

13.09

11.45

11.39

12.99 10.76

21.71 20.06 17.56

23.71

21.55

20.86

19.90

19.07

18.48

17.88

17.19

16.21

15.83

15.76

15.77

FH

NP

NP

SV

RS

SIGN

BOX

BIN

RIDGE

EAVES

NP

RS/LP

RS

MKR

1.8

WPR 1.4MH2 x MKRS

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

EAVES

EAVES

EAVES

RIDGE

KTARMAC

FRENCH DRAIN

GRASS

TREES/ HEDGE

HEDGE/ BOTTOM OF BANK

GRASS

K

DK

K K

TARMAC

TREES/ HEDGE

GRASS

IC CL

UTLG

K

IC CL

UTL

GIC CL

UTL

MARL DRIVE

DK

TAR

TAR

LONG GRASS

O/H CANO

PY

O/H CANOPY

O/H CANOPY

WPR 1.4MH

GRASS

GRASS TAR

WOODLAND/ DENSE OVERGROWTH




KERB LINE SHOWN FOR ILLUSTRATIVE PURPOSES ONLY

IC CL

UTL

DK

K

K

UTL

G

IC CL

IC CL

IC CL

IC CL

ICs UTL

IC CL UTL

K

FOOTPATH

FOOTPATH

FOOTPATH

KISSING GATE

KISSING GATE

WALL

SIGN

INACCESSIBLEFOOTPATH

FOOTPATH

INACCESSIBLE

TREE CANOPY/ OVERGROWTH

TOP OF GRASS BANK

WOODLAND

WPR 1.4MH

GRASS

G

A470

TO LLANDUDNO

TREE

O/H CANOPY

POST AND WIRE 1.

2MH

CHAIN LINK 1.4MH

GARDENS

LONG GRASS

FENCE DILAP.

FENCE DILAP.

11.00

11.00

11.00

15.00

15.00

15.00

17.00

17.00

17.00

16.00

16.00

16.00

22.00

12.00

12.00

12.00

14.00

14.00

14.00

13.00

13.00

13.00

18.00

18.00

21.00

20.00

19.00

19.00

10.00

DK

GIVE WAY

279450E

279450E

279750E

279750E

RS

LONG

Reproduction in whole or part is prohibited without the prior permission of Angle Surveys Limited.

Grid - Related to OSGB36 (National Grid) derived from GNSS

EAST NORTH HEIGHT DESCRIPTION

Angle Surveys LimitedPlasEirias Business Centre

Abergele RoadColwyn BayLL29 8BF

+44(0)1492 850050www.anglesurveys.co.uk

[email protected]

Project

TOPOGRAPHICAL SURVEYThe Woodlands, Marl Drive

Llandudno JunctionClient

Reference No Drawing No Scale

96/BD/2971 001Survey Stations

Levels - Related to Ordnance Survey Datum derived from GNSS

STATIONS

Revision No: -\ Topographical Survey October 2016

Revisions/ Notes

BolBS

BollardsBus stop

BT British Telecom ICCPS Concrete paving slabsCATV Cable television IC

DR DrainElec Electric ICEP Electric poleER Earth rod

FP Fence postFB Flower BedG GullyGP Gate PostH/C Harcore

IC Inspection cover

KO Kerb outletLB Letter boxLP Lamp postMkr Utility marker

MP Mile postNP Name plate

PO PostPM Parking MeterRE Rodding EyeRS Road signRW Retaining WallSP Soil pipeST Stop tapStay Cable stayTCB Telephone call box

TL Threshold LevelTP Telephone poleTar Tarmacadam

FH Fire Hydrant

VP Vent pipe

WM Water meterWO Water outletUTL Unable to lift

W Water coverK Kerb

DK Drop kerb

O/H OverheadO/G Overgrown

FL 5.55 Floor Level

WL Water level

FENCE ANNOTATIONBW Barb wireWP Wooden panelCI Corrugated iron

CPWP Concrete post Wooden PanelHR Hand railIR Iron railing

CL Chain link

PR Post and railPW Post and wireSF Security fence

PC Post and chain

WPR Wooden Post and Rail

Fence/ Height

Gate

O/H Canopy

Foilage

Survey Control stationCoordinated point

Surveyed point

Spot Level

Legend

A12.28

WP 1.0MH

All critical dimension to be checked on site

Further investigation may be needed to show the full extent of the drainage on site

1:500Scale Factor

1.0000

HMP Hazard Marker Posts

Beech Developments (NW) Ltd,Warwick House,Riverside Business Park,Benarth Road,Conwy, LL32 8UB

Only trees with a bole diameter of 300mm or greater have been surveyed

Groups of trees are shown as a canopy symbol

Fences shown on the survey do not necessary represent legal boundaries

Pipe sizes are approximation only

A 279608.837 378877.218 13.553

B 279648.112 378841.168 11.247

Z 279600.458 379039.656 17.689

Road Nail

Road Nail

Wooden Peg



Appendix C – Drainage Survey, Sewer Plan, & DCWW Correspondence

Owner

New Stamp

VC 2

25 m

m.

VC 375 m

m.

VC 2

25 m

m.

VC 150 m

m.

MDPE 100 mm.

VC 225 mm.

VC 300 mm.

VC 2

25 m

m.VC

225

mm.

VC 2

25 m

m.

VC 2

25 m

m.

VC 225 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 1

50 m

m.

VC 2

25 m

m.

VC 225 mm.

VC 225 mm.

VC 1

50 m

m.

VC 150 mm.

VC 1

50 m

m.

VC 150 mm.

VC 150 mm.

VC 1

50 m

m.VC 150 mm.

VC 1

50 m

m.

VC 150 mm.

VC 225 mm.

VC 150 mm.

VC 225 mm.

VC 2

25 m

m.

VC 2

25 m

m.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 2

25 m

m.

VC 225 mm.

VC 225 mm.

VC 150 mm.

VC 2

25 m

m.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 150 mm.

VC 150 mm.

VC 2

25 m

m.

VC 225 mm.

VC 225 mm.

VC 150 mm.

VC 150 mm.

VC 225 mm.

VC 2

25 m

m.

VC 225 mm.

VC 150

mm.

VC 225 mm.

VC 225 mm.

VC 150 mm.

VC 2

25 m

m.

VC 150 mm.

VC 225 mm.

CONC 600 mm.

VC 225 mm.

VC 150 m

m.

CONC 1050 mm.

VC 225 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 225 mm.

VC 2

25 m

m.

VC 225 mm.

VC 2

25 m

m.

VC 2

25 m

m.VC

225

mm.

VC 225 mm.

CONC 600 mm.

CONC 900 mm.

VC 150 mm.

VC 150 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 150 mm.

uPVC

150

mm.

VC 2

25 m

m.

VC 225 m

m.

VC 2

25 m

m.

VC 225 mm.

VC 375 mm.

VC 300 mm. VC 300 mm.

VC 150 mm.

VC 225 mm.

VC 225 mm.

VC 225 mm.

VC 2

25 m

m.

VC 1

50 m

m.

VC 1

50 m

m.VC 150 mm.

VC 225 m

m.

VC 150 mm.

VC 150 mm.

VC 150

mm.

VC 150 mm.

CONC 600 mm.

VC 375 mm.

VC 225 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 225 mm.

CONC 1200 mm.

VC 225 mm.

CONC 600 mm.

VC 150

mm.

VC 150 mm.

VC 150

mm.

VC 150 mm.

CONC 105

0 mm.

CONC 1

050 mm

.VC 300 mm.

VC 300 mm.

VC 300 mm.

VC 225 mm.

VC 225 mm.

VC 1

50 m

m.

VC 225 mm.

VC 225 mm.

VC 375 mm.

VC 225 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 900 mm.

CONC 1050 mm.

CONC 1050 mm.

CONC 1050 mm.

VC 150 mm.

VC 100 mm.

VC 150 mm.

VC 1

50 m

m.

VC 1

00 m

m.

CONC 750 mm.VC 150 mm.

VC 150 mm.

VC 100 mm.

VC 100 mm.

VC 150 mm.

VC 150 mm.

VC 150 mm.

VC 100 mm.

VC 100 mm.

VC 100 mm.

VC 100 mm.

VC 1

00 m

m.

VC 100 mm.

VC 100 mm.VC 1

00 m

m.VC

100

mm.

VC 1

00 m

m.VC

100

mm.

VC 100 mm.

VC 150 mm.

VC 150 mm.VC

150 mm

.

VC 150 mm.

CI 100 mm. uP

VC 150 mm.

VC 150 mm. VC 150 mm.

VC 150 mm.

VC 150 mm.VC 150 mm.

VC 150 mm.

CONC 450 mm.CONC 450 mm.

CONC 450 mm.

CONC 450 mm.

VC 225 mm.

CONC 450 mm.

CONC 450 mm.

CONC 450 mm.

CONC 450 mm.

CONC 450 mm.

CONC 450 mm.

VC 150 mm.

S 104 S 104S 104

S 104S 104

S 104S 104

S 10

4

S 104 S 104

S 104S 104

S 104S 104

S 10

4

S 104

S 104S 104

S 104

S 104

S 104

S 104S 104

S 104S 104

S 104

S 104S 104

S 104S 104

S 104

S 10

4

S 104

S 104 S 104S 104

S 104

S 104

S 104

S 104

S 104 S 104

S 104S 1

04

S 104

S 104S 104

B

A

A

A

B

B

B

B

B

B

BB

B

B

B

A

A

BB

B

B

BB

A

B

B

B

B

BB

B

B

B

B

B

B

B

B

BB

B

B

B

B

BB

BB

B

B

B

B

B

BB B

B

B

B

B

B

B

B

B

BB

BB

B

SH79782403

SH79783403

SH79784401

SH79794006

SH79785909

SH79784902

SH79794002

SH79794007

SH79794008

SH79784906

SH79784907SH79784908

SH79784910

SH79794004

SH79794005

SH79784905

SH79784505

SH79784507

SH79790208

SH79790209

SH79780601

SH79780602

SH79780701

SH79784506

SH79783504

SH79784509

SH79783803

SH79783804

SH79783805

SH79783806

SH79783807

SH79783901

SH79783902

SH79783903

SH79783904

SH79780802

SH79780902

SH79782605

SH79781501

SH79781502

SH79781601SH79781602SH79781603

SH79781604 SH79781605

SH79781606

SH79781608SH79781607

SH79781609SH79781610

SH79781701

SH79781702

SH79781703SH79781704

SH79781705

SH79781706SH79781707

SH79781708

SH79781801SH79781802

SH79781901

SH79781902

SH79781903

SH79781904

SH79782501

SH79782502

SH79782503

SH79782504

SH79782505 SH79782506

SH79782601SH79782602

SH79782603SH79782604

SH79782606

SH79782801SH79782802

SH79782803

SH79782804

SH79782901

SH79782902

SH79782903SH79782904

SH79782906

SH79782907

SH79782908

SH78789502

SH78789503

SH78789504

SH79782909

SH79782910

SH79782912

SH79782913

SH79783502

SH79783501

SH79783601SH79783602

SH79783701

SH79783702

SH79783703

SH79783704

SH79783801

SH79784501

SH79784503

SH79784601

SH79784701

SH79784703

SH79780501

SH79780502

SH79780503

SH79790204

SH79790206

SH79794003

SH79794001

SH79793001SH79793002

SH79783908 SH79784909

SH79783905

SH79783906

SH79783907

SH79794009

SH79784911

SH79785907

SH79784912

SH79790207

SH79783503

SH79784508

SH797902

05

SH79783404

SH79790106

SH78799103

SH79790105

SH79790104SH79790203

SH78799201

SH78799102

SH78799101

SH79790102

SH79790101

SH79790202

SH79790201

SH79794401

SH79784504

SH79792001

SH79791002

SH79790103

SH79791001

SH79785403

SH79785404 SH79786401

SH79786402

SH79787410SH79787411

SH79787415SH79787416 SH79787422

SH79787423

SH79787432SH79787433

SH79787435

SH79787421

SH79787420

SH79788407SH79787414

SH79786405 SH79789410SH79789409SH79789401

SH79795002

SH79787604

SH79787504 SH79787506SH79787507SH79787508SH79787505

SH79787503

SH79787502

SH79785901

SH79787509

SH79787605

SH79786703

SH79785902

SH79785908SH79785904

SH79785905

SH79785906

SH79786611

SH79787601

SH79787551

SH79788501

SH79785501

SH79785502 SH79785503

SH79785504

SH79795401

SH79795301

SH79795201

SH79787602

SH79786504

SH79786502

SH79786501

SH79786503

SH79796002

SH79786802

SH79786804

SH79786803

5802

SH79796101

SH79785803

SH79785804

SH79786801

SH79785801

SH79786901

SH79796001

SH79787501

SH79787603SH79786602

SH79786603

SH79786604

SH79786605

SH79785606

SH797865

05

SH79786607

SH79787510

SH79787511

SH79787512

SH79787513

SH79785505

SH79786507

SH79786618

SH79786702

SH79786613

SH79786614

SH79786506

SH79786615

SH79786616

SH79786617

SH79785506

SH79786601

SH79786619

SH79786620

SH79786621

SH79786622

SH79786623

SH79786705

SH79786704

SH79786612

SH79786701

SH79785601

SH79795001

SH79786609

SH79786608

SH79785602

SH79786610

SH79780901

SH79784602

SH79783802

SH79780703

SH79784901

SH79780801

SH79785903

SH79785805

SH78799205SH78799206

SH78799207

SH78799208SH78799209SH78799210

SH78799211 SH78799212SH78799213

SH79790210SH79790211 SH79790212

SH79790213 SH79790214

SH79790215

SH79790216

SH79790218SH79790219

SH79790220

SH79790221

SH79790222

SH78799223SH79790223

SH79790244 SH79790245

SH79790246SH79790250

SH79790251

SH79790252

SH79790253SH79790254

SH79790255

SH79790256

SH79790257SH79790258

SH79790259

SH79790261

SH79790262

SH79790263

SH79790264SH78799265SH78799266

SH78799267

SH78799268

SH78799225

SH78799226

SH78799227

SH78799228

SH78799229

SH78799231

SH78799232

SH78799233

SH78799234

SH78799235

SH78799236

SH78799237

SH78799238 SH78799239

SH78799240

SH78799241

SH78799242 SH78799243

SH79790260

SH79790265

SH79790266

SH79790267

SH7979

0268

SH79790269

SH79790299

SH79790271

SH79790272

SH79790273SH79790274

SH79790275

SH79790276SH79790277

SH79790278

SH7979

0280

SH79790281

SH79790282

SH79790283

SH7979

0284

SH78799202

SH78799230

SH79783426SH79783432

SH79783534SH79783535

SH79784805

SH79784806

SH79784915

SH79784914SH79784916

SH79784917

SH79784918

SH79785918

SH79785818

SH79784807SH79784808

SH79784919

SH79784920

SH79784921

SH79784922

SH79784923

SH79784924

SH79784925

SH79784926

SH79784927SH79784928

SH79784829

SH79784830SH79784831

SH79783832

SH79784833

SH79784834

SH79784835

SH79784836

SH79784837 SH79784838SH79784839

SH79784840

SH79784841

SH79784710

SH79784711

SH79784712

SH79784713

SH79784714

SH79785715

SH79785816

SH79785817

SH79785819

SH79784842

SH79784843

SH79784844

SH79784845

SH79784846

SH79784847SH79783848

SH79784849

SH79784850

SH79785851

SH79785852

SH79785953

SH79785854SH79784855SH79784856 SH79785857

SH79784858

SH79784959SH79785960

SH79782611SH79782612

SH79788502

SH78799105

SH78799109

SH78799113

SH78799115

SH78799116

SH78799117

SH78799119

SH78799120SH78799121

SH78799122

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SH79790110SH79790111

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SH79790115SH78799127

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SH79790120 SH79790121

SH79790125

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SH79782905

SH79782914SH79782915

SH79782704

SH79782705

SH79780750

SH79780751

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SH79781850

SH79781851SH79781852SH79781853

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SH78799365SH78799366

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SH79784605SH79784606

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7 MAES GLAGARAGES 9

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9 CWM ESTY9 CWM ESTY

9 DOL HUDO9 DOL HUDO

93 VICTORI93 VICTORI

99 VICTORI99 VICTORI

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c 43.39i 40.74

c 43.73i 40.78

c 44.84i 40.94

c 43.01i 41.17

c 33.12

c 34.68

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c 25.16

c 43.21i 40.71 c 42.99

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i 41.58 i 40.7

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i 42.3

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i 43.4

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i 44.55

i 45.08

i 44.96

i 45.2i 45.6

i 45.85

i 44.64i 43.9 i 43.29i 45

i 45.75 i 43.5

i 43.47i 44.13

i 44.28 i 43.65

i 42.22

i 42.5

i 42.09

i 42.09

i 41.94 i 41.62

i 42.25i 41.95

i 42.41i 42.25

i 42.4

i 42.58i 42.53

i 41.96i 42.23i 42.6

i 42.4i 42.15

i 41.7

i 44.98

i 43.61

i 45.65

i 45.59

i 44.4

i 45.85

i 43.58

i 43.87

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i 42.13

i 42.84i 42.95

i 43.87

i 42.33

i 42.9

i 42.32

i 41.56i 41.76

i 41.65

i 42.4i 41.38i 42.2

i 41.81

i 42.2

i 43.55i 41.45

i 43.28

i 41.3i 42.5i 42.5

SH79784502

SH79787606

SH79786902

SH79787750

outfall

6

259MARL LANE

366MEADOWS LLANDUDNO JUNC

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w10278, Llys Marl, Marl Lane

Dwr Cymru Cyf gives this information as to the position of its underground apparatus by way of general guidance only on thestrict understanding that it is based on the best information available and no warranty as to its correctness is relied upon in the event of excavations or other works made in the vicinity of the Company’sapparatus and any onus of locating the apparatus before carrying out any excavations rests entirely on you. It must be understoodthat the furnishing of the information is entirely without prejudice to the provision of the New Roads and Streetworks Act 1991 and ofthe Company’s right to be compensated for any damage to its apparatus.Service pipes are not generally shown but their presence should be anticipated.

EXACT LOCATIONS OF ALL APPARATUS TO BE DETERMINED ON SITE.

Reproduced by permission of Ordnance Survey on behalf ofHMSO. © Crown copyright and database right 2008.

All rights reserved.Ordnance Survey License number 100019534.

Printed on:Printed by:

1:1,250Map scale:

Notes:

LEGEND(Representative of most common features)

Map Ref: 279591,378984

AM28/03/2017

Private Sewer Transfer

Inspection ChamberLateral Drain

Whilst every reasonable effort has been taken to correctly record the pipe material of DCWW assets, there is a possibility that in some cases, pipe material (other than Asbestos Cement or Pitch Fibre) may be found to be asbestos cement (AC) or Pitch Fibre (PF) . It is therefore advisable that the possible presence of AC or PF pipes be anticipated and considered as part of any risk assessment prior to excavation

1

Aled Williams

From: Jones Sion <[email protected]>Sent: Tuesday, May 9, 2017 2:47 PMTo: Aled WilliamsCc: Jones-Hughes HenrySubject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction

Hi Aled, Thanks for your response. Your e‐mail confirms a solution can be achieved, based on the principle of the surface water removal scheme, and provided that surface water from a contributing drainage area of 0.084ha is removed, the principle of connecting foul flows into the public combined sewer system would be considered acceptable. Accordingly, in respect of any forthcoming planning application, it is recommended that an accompanying proposed drainage strategy is formulated to address the proposed surface water removal scheme including your calculations which equate to an area of 0.084ha and evidence from your recent CCTV survey that confirms the connectivity of highway gullies. Prior to any planning application, however, I would also remind there is now a mandatory legislative requirement as of 1st August 2016 to undertake pre‐application consultation with all ‘Specialist Consultees’, including Welsh Water, in respect of any major developments as outlined in the Town & Country Planning (Development Management Procedure) (Wales) (Amendment) Order 2016. Please note this is separate to Welsh Water’s formal pre‐planning service – which is non‐statutory and was previously subject of PPA0000551 – and entails due process and submission of relevant forms i.e. Schedule 1C – Article 2D Notice; a substantive response would be required within 28 days from the date of the notice, as per the requirements of Article 2E. This statutory pre‐application consultation exercise would offer an opportunity for consultees to comment on the draft planning application submission and at this stage it would be useful to provide a copy of the draft drainage strategy. This is effectively a frontloading exercise that should ease the application process and on the proviso that the strategy includes the relevant evidence base, it should overcome any request for pre‐commencement conditions as part of our consultation response. On this subject, and from our previous correspondences below, I trust that pre‐planning consultation is or has also been undertaken with the Trunk Roads Agency and NRW in regards to discharging into the Afon Wydden. I hope this information is of assistance and look forward to hearing back from you in regards to the above. Regards, Siôn

Siôn Jones

Development Control Officer | Developer Services | Dwr Cymru Welsh Water

Linea | Cardiff | CF3 0LT | T: 0800 917 2652| www.dwrcymru.com

We will respond to your email as soon as possible but you should allow up to 10 working days to receive a response. For most of the services we offer we set out the timescales that we work to on our Developer Services section of our website. Just follow this link http://www.dwrcymru.com/en/Developer‐Services.aspx and select the service you require where you will find more information and guidance notes which should assist you. If you cannot find the information you are looking for then please call us on 0800 917 2652 as we can normally deal with any questions you have during the call. If we’ve gone the extra mile to provide you with excellent service, let us know. You can nominate an individual or team for a Diolch award through our website.

Before you print please think about the ENVIRONMENT

2

From: Aled Williams [mailto:[email protected]] Sent: 04 May 2017 15:57 To: Jones Sion <[email protected]> Cc: Jones‐Hughes Henry <Henry.Jones‐[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction

******** External Mail ******** Hi Sion, Many thanks for your reply and for confirming the discharge rate for surface water flows. Based on your email it appears that the principle of the surface water removal scheme to offset development foul flows is acceptable in principle subject to removing a contributing area of 0.084ha from the combined system. With reference to the impermeable area of 0.084 ha, we note that the modelling report suggests that this would equate to a road length of 130m (assuming a 6.5m wide road). A review of the attached gully connectivity survey shows that highway gullies are draining to the public combined sewer along a road length of approximately 380m. We will therefore be able to remove the required 0.084ha contributing area from the combined system. For confirmation and agreement in principle, please could you confirm that development foul flows can drain to the public combined sewer system provided that surface water from a contributing drainage area of 0.084ha is removed from the combined sewer. Surface water removal would be in the form of disconnecting highway gullies from the public combined sewer in Marl Lane and connecting them into the public surface water sewer (which discharges to a watercourse). Kind Regards,

Aled Williams BSc (Hons) MCIWEM Senior Environmental Consultant 01824 702220

Ruthin - Chester - Manchester - Hyderabad Assessment, Modelling, Design

For email confidentiality, limitations and company details please see our disclaimer webpage. Registered in Wales under company no. 3577754. Waterco Ltd, Eden Court, Ruthin LL15 1NJ

From: Jones Sion [mailto:[email protected]] Sent: Thursday, May 4, 2017 3:07 PM To: Aled Williams Cc: Jones-Hughes Henry Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Good Afternoon Aled, Thanks for your previous e‐mails. Firstly, in respect of your e‐mail last Wednesday (26th), I apologise for any confusion caused as you rightly highlight that the off‐site surface water removal scheme would not be subject to the hierarchical approach set out under Part H of Building Regulations and therefore would not require infiltration testing to support a scheme for soakaways.

3

Notwithstanding this, having discussed the matter with our modelling team and referred back to the original Hydraulic Modelling Report, it was brought to my attention that the surface water removal scheme solution (Section 6.2) would require removal of 0.084 ha of impermeable area upstream of Marl Drive CSO; your previous e‐mail, dated 6th April, identified a scheme for the removal of approx. 213sqm. I communicated your calculations to the modelling team who reiterated that 0.084 ha of impermeable area would be required to mitigate the detriment predicted by the additional development flows and hence the scheme (equating to 0.0213ha) falls significantly short to satisfy the HMA requirement. I am happy to review any additional information should you wish to revert back to me on the matter, for example I note that the survey identified connectivity of a number of other highway gullies along Marl Lane. You mentioned scope for a meeting in your previous e‐mail but unfortunately, being based in our Linea office in Cardiff, this isn’t something I would be able to arrange and therefore would be grateful to continue the dialogue in e‐mail correspondences. In the meantime, having had an opportunity to review our exchange of e‐mails below and your accompanying Ground Investigation Report (attached), namely Section 7.7 and Appendix C regarding soakaway tests, I am satisfied that you’ve investigated and exhausted alternative drainage options under Part H of Building Regulations and would therefore accept discharge into the public surface water sewer at an attenuated rate. Accordingly, in respect of any future planning application submission, please accept this e‐mail as an agreement in principle to allow for communication of surface water into the said public sewer through an attenuation device that discharges at a rate not exceeding 5 l/s. I trust this information is of assistance. Regards, Siôn

Siôn Jones





From: Aled Williams [mailto:[email protected]] Sent: 27 April 2017 14:18 To: Jones Sion <[email protected]> Cc: Jones‐Hughes Henry <Henry.Jones‐[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction

******** External Mail ******** Hi Sion, Further to my below email, I am now pleased to attach the requested ground investigation report for the Llys Marl / Woodlands site. See section 7.7 for conclusions regarding soakaway tests. With the attached evidence, please advise if you are now in a position to agree a surface water connection in principle to the public surface water sewer from the proposed development site. I also look forward to hearing back from you in regards to the proposed foul mitigation strategy.

4

Kind Regards,




From: Aled Williams Sent: Wednesday, April 26, 2017 5:13 PM To: Jones Sion Cc: Jones-Hughes Henry Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Hi Sion, Many thanks for your reply. In regards to infiltration testing, I understand that this would be required prior to agreeing discharge to the public surface water sewer from the proposed development. The developer will arrange for these to be undertaken on site as part of the planning process. However, please could you explain why infiltration testing would be required to support a surface water removal scheme for flows currently entering the public combined sewer. Our proposal is for off‐site works within a public highway (diverting highway gullies from the public combined to a surface water sewer) approximately 180m from the site. This is not somewhere that we can realistically look at introducing soakaways. If necessary, I am happy to meet at your Bodelwyddan office to discuss the scheme further. Kind Regards,




5

From: Jones Sion [mailto:[email protected]] Sent: Wednesday, April 26, 2017 2:25 PM To: Aled Williams Cc: Jones-Hughes Henry Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Good Afternoon Aled, Apologies for the delay in my response, I only had an opportunity to issue the information contained in your proposed surface water removal scheme below to the modelling team on my return from leave last week, but will chase on the matter. Based on the information set out below I would envisage a positive outcome, particularly the scope for further SW removal options from the Junction of Marl Lane and Victoria Drive up to the Junction with Pentwyn Road, but will revert to feedback from the modelling team to confirm if the calculations and area identified would be sufficient. Apologies for the delay and I will report back at the earliest possible opportunity. In the meantime, however, I acknowledge that the proposed SW removal scheme seeks disposal into the public surface water sewer but there is still the matter of infiltration testing as part of your evidence base to establish any principle to agree a SW connection. Can you update me on the results of these tests please? Regards, Siôn

Siôn Jones






******** External Mail ******** Hi Sion, Please could you let me know if you have had an opportunity to review my email below. We require a response as soon as possible. Kind Regards,


6



From: Jones Sion [mailto:[email protected]] Sent: Friday, April 7, 2017 5:27 PM To: Aled Williams Cc: Jones-Hughes Henry Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Hi Aled, Apologies, I haven’t had an opportunity to respond or review the information submitted in any great detail and I will be on annual leave next week, returning Tuesday 18th, but will endeavour to respond with feedback in the week following. This is a matter I will need to research in a bit more detail based on the attached and your e‐mail below. Please do not hesitate to call me in the week following Easter (WC 18th). Regards, Siôn

Siôn Jones





Please note I will be on annual leave during the week commencing Monday 10th, returning on Tuesday 18th. If you require assistance in my absence I would kindly request that you e‐mail your enquiry to Developer Services at [email protected] or telephone 0800 917 2652.


******** External Mail ******** Hi Sion,

7

Further to discussions regarding the Llys Marl site and following review of the Welsh Water Hydraulic Modelling Report we have looked into a scheme for surface water removal from the public combined sewer system to offset development foul flows. Solution 2 within the HMR details a scheme for surface water removal. However, we have identified a surface water removal scheme local to the site which will be more cost effective. Our proposal is based upon the removal of highway drainage from the public combined sewer system within Marl Lane. I attach an Invek survey showing the connectivity of the highway drainage (gullies) along the length of Marl Lane. The survey shows that highway gullies south of the site are drained to a private 150mm surface water sewer (assumed to be subject to S104 adoption agreement) which serves the recent Llys Onen development south of Marl Lane. This sewer discharges to watercourse. Highway gullies further north‐west along Marl Lane are shown to discharge to the public combined sewer system. Proposal Our proposal is to remove highway gullies from the combined system in Marl Lane and re‐direct them into the surface water sewer (which discharges to watercourse). The HMR indicates that the average foul flow to be generated from the development is 0.417 l/s. Applying a peaking factor (x6 +10%) gives a peak foul flow rate of 2.75 l/s (for a 70 dwelling scheme). 54 properties will likely be proposed in the final planning stage and as such the peak flow of 2.75 l/s is a conservative rate. The surface water removal scheme therefore needs to remove 2.75 l/s from the combined sewer to offset foul flows. Using the rational method to calculate rainfall runoff from the road, a drainage area of 210m² would need to be removed from the combined system to offset development peak foul flows (2.75 l/s). This is based on a rainfall intensity of 47.11mm over a 6 hour duration 1 in 30 year rainfall event. Removal of gullies G19 and G20 shown on the attached ‘Marl Lane Gully Connectivity – 2’ plot would remove a contributing drainage area of approximately 213m² and would offset development foul flows. A new length of sewer of approximately 50m would be required to connect the highway gullies to the 150mm surface water sewer in Marl Lane. Please could you advise on the acceptability of the above proposal to Welsh Water and also the acceptability of the use of 1 in 30 year rainfall data within our calculations. I trust the above provides a less intrusive and cost effective solution than suggested within the HMR and also identifies potential further surface water removal options to Welsh Water (highway drainage from the Junction of Marl Lane and Victoria Drive up to the Junction with Pentwyn Road is all drained to the public combined system). Kind Regards,



8


From: Jones Sion [mailto:[email protected]] Sent: Thursday, March 30, 2017 3:27 PM To: Aled Williams Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Good Afternoon Aled, Thanks for your e‐mail and apologies for the delay in my response, I haven’t had an opportunity to chase on the matter of point of connection with the preceding Development Control Officer or Modelling Team but will do so this afternoon. In the meantime, in respect of your e‐mail below, I appreciate that you have already undertaken extensive research into alternative options for disposal of surface water which is evidently comprehensive including the recent survey work undertaken by Invek. However as per my previous e‐mail, and in reference to the hierarchy set out under Part H of Building Regulations, I would reinforce that the results of infiltration testing will need to be provided upfront as an evidence base before the principle of a connection to the public surface water sewer can be agreed. I appreciate this is your intention regardless but only on receipt of this evidence would we be able to progress discussions regarding an acceptable discharge rate into the sewer. Notwithstanding this, the attached documents accompanying your e‐mail gives assurance that a low discharge rate can be achieved on this site and we would welcome the information that supports this calculation. I appreciate this doesn’t expand a great deal on my last e‐mail but will happily discuss and review any further information in future correspondences. Regards, Siôn

Siôn Jones





From: Aled Williams [mailto:[email protected]] Sent: 22 March 2017 09:49 To: Jones Sion <[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction

******** External Mail ******** Hi Sion, Thank you for your email.

9

In regards to the surface water connection, whilst we don’t have infiltration test results, we have recently received a survey (undertaken by Invek) of the sewers and highway drainage in Marl Lane. Please find a drainage layout and chamber details attached. The survey shows that there is a 300mm public surface water sewer (serving the Woodlands estate) and a 150mm private surface water sewer (which serves the recent Bryn Marl estate) in Marl Lane. Both sewers drain to the Afon Wydden. The highway drainage along Marl Lane is connecting to the 150mm private surface water sewer which discharges to the Afon Wydden. There are no land drainage features in this area. Given that nearby residential developments are drained to the Afon Wydden it would appear quite conclusive that soakaway drainage is not feasible in the area. However we understand that you will require this. Based on the above evidence, and in order for us to inform our Drainage Strategy which will support the planning application, please could you advise on a suitable discharge rate for a connection to the public surface water sewer (on the provision that infiltration testing will be provided and show that soakaways are not feasible). I attach greenfield runoff calculations based on FEH data for information. I look forward to hearing back from you. Kind Regards,




From: Jones Sion [mailto:[email protected]] Sent: Tuesday, March 21, 2017 5:39 PM To: Aled Williams Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Hi Aled, Thank you for your e‐mail and apologies for the delay in my reply, I was out of the office in North Wales for a number of days last week and playing catch up on e‐mails. The Hydraulic Modelling Report associated with the Woodlands / Llys Marl site in Llandudno Junction was before my time but, in respect of your query on the point of connection, I will discuss the matter with the preceding Development Control Officer for this area and the Modelling Team and report back to you at the earliest opportunity thereafter. In the meantime, with regards to your query regarding surface water, I would highlight that the results of infiltration testing will need to be provided upfront as an evidence base before the principle of a connection to the public surface water sewer can be agreed. Also, have you explored alternative land drainage features and/or highway drainage systems? On this point, are you also liaising with the Trunk Roads Agency? If all avenues are exhausted and

10

you are minded to connect into the surface water sewer line there would also be a need to ascertain that the line is functional and its size which I would suggest entail a CCTV survey. On receipt of all this information, I will review and report back on the principle of a connection and a suitable discharge rate accordingly which of course would be informed by your interaction with NRW regarding discharging further flows into the Afon Wydden. I appreciate this is a wealth of information, and may not be the response sought for, but would welcome any further evidence which you may wish to submit my way for further review. Regards, Siôn

Siôn Jones





From: Aled Williams [mailto:[email protected]] Sent: 15 March 2017 13:52 To: Jones Sion <[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction

******** External Mail ******** Hi Sion, In relation to the Woodlands / Llys Marl site in Llandudno Junction and the attached associated Hydraulic Modelling Report (HMR), is there any movement on the point of connection to the combined sewer system suggested within the HMR? The HMR suggests a point of connection south‐east of the site within a verge adjacent to the roundabout on the A470. The preferred point of connection would be to the sewer in Marl Lane immediately south of the site i.e. where the proposed site access will be. In terms of commissioning any modelling updates, the client is currently exploring the potential of a localised scheme for surface water removal from the combined sewer. Should these investigations be inconclusive we will be in touch regarding modelling updates. I also look forward to hearing back from you in regards to a connection to the public surface water sewer as discussed in the below email chain. Kind Regards,


11



From: Jones Sion [mailto:[email protected]] Sent: Tuesday, February 28, 2017 4:46 PM To: Aled Williams Cc: Jones-Hughes Henry Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Good Afternoon Aled, Thank you for your e‐mail and apologies for the delay in my response. If you could keep me posted as and when you have been given confirmation from your client that would be appreciated. In the meantime, I will liaise with Henry in regards to the attached and respond via this in a separate e‐mail. I’m sorry I haven’t had a chance to review this but will take the opportunity to also liaise with my colleagues from network operations regarding the existing public surface water sewer and its capacity to accommodate a connection. I’ll report back on this in due course; please do not hesitate to contact me on the number below in the meantime. Regards, Siôn

Siôn Jones




Developer Services have an on‐line service at www.dwrcymru.com. Here you can find all the services available, complete application forms and also make payments. If you have a quotation you can pay for this on‐line or alternatively by telephoning 0800 917 2652 using a credit/debit card. If we’ve gone the extra mile to provide you with excellent service, let us know. You can nominate an individual or team for a Diolch award through our website.

From: Aled Williams [mailto:[email protected]] Sent: 21 February 2017 16:32 To: Jones Sion <[email protected]> Cc: Jones‐Hughes Henry <Henry.Jones‐[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction

******** External Mail ******** Hi Sion, Thank you for this. We are awaiting client confirmation in regards to obtaining the modelling quote. Please can you advise when we can expect a response to the attached email. I believe Henry has passed this onto you.

12

Kind Regards,




From: Jones Sion [mailto:[email protected]] Sent: Tuesday, February 7, 2017 3:27 PM To: Aled Williams Cc: Jones-Hughes Henry Subject: RE: w10278 - Llys Marl, Marl Lane, Llandudno Junction Good Afternoon Aled, Following on from my e‐mail last week, I’ve been informed by our modelling team that the model would need to be re‐run in respect of the 54 proposed units and I’m advised that a fee of £250+VAT (£300.00) is required in order to obtain a detailed quotation to re‐run the modelling and develop any subsequent solutions. A payment can be made by phone or online (Ref: 6999999995) or alternatively, should you wish to pay for this fee via BACS, please see attached our bank details accordingly. Regards, Siôn

Siôn Jones





From: Jones Sion Sent: 01 February 2017 09:39 To: Aled Williams <[email protected]> Cc: Jones‐Hughes Henry <Henry.Jones‐[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction Good Morning Aled,

13

Following on from Henry’s e‐mail yesterday, I have been in contact with our modelling team and will report back shortly to confirm if any associated costs are required in order to re‐run the model. Regards, Siôn

Siôn Jones





From: Jones‐Hughes Henry Sent: 31 January 2017 16:14 To: Aled Williams <[email protected]> Cc: Jones Sion <[email protected]> Subject: RE: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction Hi Aled Ive passed your email onto the development control officer for the Conwy area, Sion Jones. He will contact you in due course. Just a few points to mention on this one.

The modelling team may require a fee to re‐run the model if property numbers have changed. Sion will check this for you.

In terms of the surface water drainage, before we can consider a connection into the surface water sewer, it would have to be demonstrated that it would not be feasible to connect directly to a watercourse. We would also want to see that infiltration doesn’t work on‐site. I believe that the source of the watercourse on the other side of the road to the A470 is on the development side of this road.

Regards Henry

Henry Jones‐Hughes


PO Box 3146 | Cardiff | CF30 0EH | T: 0800 9172652| F: 02920 740472 | Ext. 65813 If we’ve gone the extra mile to provide you with excellent service, let us know. You can nominate an individual or team for a Diolch award through our website

From: Aled Williams [mailto:[email protected]] Sent: 31 January 2017 15:54 To: Jones‐Hughes Henry <Henry.Jones‐[email protected]> Subject: w10278 ‐ Llys Marl, Marl Lane, Llandudno Junction

******** External Mail ******** Proposed residential development at Llys Marl, Marl Lane, Llandudno Junction.

14

Good afternoon Henry, DCWW have previously been contacted regarding the above site (also known as Woodlands) and a hydraulic modelling assessment was undertaken in August 2015. Foul flows The HMR gives solutions to resolve the detriment caused by the development. The favoured solution includes online storage by replacing two existing manholes with two 2.4m diameter manholes (providing 16m³ of storage) along with upsizing existing storage at the Marl Drive CSO by 11m³. Following the completion of the HMR the development proposals have changed with 54 dwellings proposed, rather than the 70 assessed in the HMA. Please find a layout plan attached. Based on the values given in the HMR (2.6 people per household and 180 litres per head per day) the reduction in dwellings could lead to a 7.49m³ reduction in foul flows over one day. Please advise if the reduction in foul flows has potential to reduce the required mitigating volumes, especially at the CSO (given the potential third party land issues identified with providing 11m³ at the CSO). We understand that this may need to be evidenced through additional modelling, therefore please advise on the associated costs if necessary. Surface water The site is separated from the nearest watercourse (the Afon Wydden) by the A470. In order to make a connection to this watercourse, and to avoid making a new connection crossing under the A470, please advise if we can make a connection to the public surface water sewer in Marl Lane, south of the site. Discharge would be at a greenfield rate of 5 l/s and only required should soakaways not be feasible. Please don’t hesitate to contact me if you have any questions. Kind Regards,






Appendix D – Proposed Layout Plan

01

A4

ME

TER S

GSVP

rwp

rwp

SVP

G

SP

WP

rwp

rwp

MET ERS

GSVP

rwp

rwp

rwp

rwp

SVP

G

SP

P3

DQ3 DQ3

GA

RA

GE

GA

RA

GE

SELFCLOSING

GATEBOW TOP RAILINGS

LITTER BIN AND

SEATING

LITTER BIN AND

SEATING

CALG

AR

Y M

OD

ULA

R TO

WER

CITY JUNIOR SWING

ELE

PHA

NT

SPR

ING

ER

CH

ICKE

N

SPR

ING

ER

EQ

UIP

PE

D P

LAY

SPA

CE

SELFCLOSING

GATE

0402 03

METERS

G

SVP

rwp

rwp

rwp

rwp

SVP

G

SP

P3

GA

RA

GE

F2

ME

TERS

SVP

G

rwp

rwp

SVP

G

rwp

ME

TERS

rwp

G

G

rwp

EFEFF2

A4

MET ERS

G

SVP

rwp

rwp

SVP

G

SP

WP

rwp

rwp

G3

1212A 14

15 16 1718/19

GA

RA

GE

H3

SVP

G

METERS

rwp

SVPMETE

RS

SHOWER

SHOWER

rwp

rwp

rwp

G

EF

EF

32

48

45

50

46

44

4043

28

35

30

WO

OD

LAND

S

WO

OD

LAND

S

17

24

1412

27

35 to 43

34

MARL LANE

20

StaPpg

EXISTING RIG

HT OF W

AY SHOW

N

IN B

LACK

LP

LP

LP

LP

IC

A

Z

B

279550E

279600E

279650E

2279700E

10.91

11.09

11.34

11.62

12.26

12.7012.81

13.1413.23

13.5013.60

13.99

14.1714.26

14.41

14.71

15.05

15.46

15.87

15.93

16.13

16.31

16.64

17.03

17 06

17.15

16.7516 69

16 35

16.44

16.08

15.69

15.80

15 73

15 27

15.18

14.78

14.88

14 85

14.3814.28

14.39

14.0513.97

13.89

13.41

13.51

14.08

13.73

13.89

13.02

13.13

12.49 12.6012.28

12.19

12.17

12.02

12.02

11.82

11.92

11.70

11.8211.58

11.46

11.26

11.39

11.11

11.2311.04

11.76

12.14

12.14

11.83

12.19

12.78

13.45

14.04

14.36

14.71

15.04

15.51

16.17

16.42

16.69

17.07

17.32

16.97

16.54

16.02

15.99

15.33

15.09

14.62

14.11

13.01

13.45

15 00

14 63

14.28

13.54

13 00

11 84

11 42

11 2011 06

10 94

26.54

22.65

10

12.53

11.44

12.14 12

.0012

.11 11.

86

11.97

11.56

11.66

11.3911

.49

11.201

1.0510.92

10.83

10.74

10.84

10.24

10.63

11.53

12.06

12.69

12.80

12.90

12.75 12 76

10.95

11.1511.19

10.91

11 60

11 9511 77

11 95

11 91

12.85

12.28

11.70

11.43

11.07

10.90

11.27

10.83

10.87

10.92

10.87

10.59

10.43

10.25

10.13

10.09

10 71

10.06

10.88

10.91

10.26

10.22

10.95

11.00

10.66

10.45

11.23

11.24

10.97

10.93

11.23

11.41

11.42

11.53

11.36

11.07

11.21

11.37

11.69

11.72

10.04

10.01

9.92

9.88

9.81

9.81

9.97

9.97

10.12

14.6415.75

23.00

22.65

21.93

15.40

15.02

14.91

14.72

14.61

14.61

14.48

14.36

14.33

13.70

11.96

11.49

11.28

11.06

10.94

10.71

10.57

10.38

10.37

10.45

10.30

10.45

10.23

10.21

10.06

9.98

10.27

10.56

23.77

26.53

26.28

26.93

28.87

29.11

29.97

30.49

31.02

31.89

27.46

26.92

23.36

27.64

12.59

13.09

11.45

11.39

12.99 10.76

21.71 20.06 17.56

23.71

21.55

20.86

19.90

19.07

18.48

17.88

17.19

16.21

15.83

15.76

15.77

FH

NP

NP

SV

RS

SIGN

BOX

BIN

RIDGE

EAVES

NP

RS/LP

RS

MKR

1.8

WPR 1.4MH2 x MKRS

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

RIDGE

EAVES

EAVES

EAVES

RIDGE

KTA

FRENCHGRA

TREES

HEDGE/ BOTTOM OF BANK

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K

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IC CL

UTL

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MARL DRIVE

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KERB LINE SHOWN FOR ILLUSTRATIVE PURPOSES ONLY

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11.00

11.00

11.00

15.00

15.00

15.00

17.00

17.00

17.00

16.00

16.00

16.00

22.00

12.00

12.00

12.00

14.00

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13.00

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15.125

15.250

15.375

15.500

15.625

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15.875

16.000

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1 IN 45

beechdevelopments

LLYS MARL

DQ 2 APARTMENT

D APARTMENTS

F2 HOUSEF3 HOUSE

A3 HOUSES

H3 HOUSES

2 No

2 No

4 No6 No

7 No

10 No

TOTAL 52 No

SITE CONCEPT PLAN

Scale : 1:500 @ A2MARCH 2016

DRAWING TITLE

DRAWING NO REVISIONBD/LM/ PL1

PLANNING LAYOUT

~

LLYS MARLLLANDUDNO JUNCTION

P3 HOUSEA4 HOUSES

4 No5 No

N3 HOUSE 6 No

DQR 3 BED HOUSE 2 No

G3 HOUSE 4 No



Appendix E – Flood Maps & NRW Correspondence

DATE:31/01/2017

PLOT NAME:w10278-TAN15_FloodMap

REV:-

DRAWN:RCL

CHECKED:AW

APPROVED:VG

PLOT SCALE @ A3:


PLOT STATUS:FINAL

PLOT TITLE:

WELSH GOVERNMENTDEVELOPMENT ADVICE MAP

SCHEME:


CLIENT:


LEGENDSite BoundaryZone BZone C1Zone C2

0 100 200 300 400 50050m

JANUARY 2017


CONTAINS OS DATA © CROWN COPYRIGHT (2017)WG TAN 15 DEVELOPMENT AND FLOOD RISK DEVELOPMENT ADVICE MAP DOWNLOADED FROM THE LLE GEO-PORTAL



DATE:23/03/2017

PLOT NAME:w10278-NRW_FloodMap

REV:-

DRAWN:RCL

CHECKED:AW

APPROVED:VG

PLOT SCALE @ A3:


PLOT STATUS:FINAL

PLOT TITLE:

NRW FLOOD MAP FOR PLANNING

SCHEME:


CLIENT:


LEGENDSite BoundaryNRW Flood DefencesAreas Benefitting from DefencesNRW Flood Zone 2NRW Flood Zone 3

0 100 200 300 400 50050m

JANUARY 2017


CONTAINS NATURAL RESOURCES WALES INFORMATION © NATURAL RESOURCES WALES AND DATABASE RIGHT. ALL RIGHTS RESERVED. SOME FEATURES OF THIS INFORMATION ARE BASED ON DIGITAL SPATIAL DATA LICENCED FROM THE CENTRE FOR ECOLOGY AND HYDROLOGY © NERC (CEH). DEFRA, MET OFFICE AND DARDRIVERS AGENCY © CROWN COPYRIGHT. © CRANFIELD UNIVERSITY. © JAMES HUTTON INSTITUTE. CONTAINS OS DATA © CROWN COPYRIGHT AND DATABASE RIGHT 2015. LAND AND PROPERTY SERVICES © CROWN COPYRIGHT AND DATABASE RIGHT. CONTAINS OS DATA © CROWN COPYRIGHT (2017)



18

1614

12

20

10

22

24

8

26

1010

10

12

8

0 50 10025m

PLOT SCALE @ A3: 1:1,500

DATE:17/05/2017

PLOT NAME:w10278-NRW_SW

REV:-

DRAWN:IJ

CHECKED:AW

APPROVED:VG

PLOT SCALE @ A3:


PLOT STATUS:DRAFT / FINAL

PLOT TITLE:

SCHEME:


CLIENT:


LEGENDSite BoundaryHigh Risk (3.33% AEP Event)Medium Risk (1.0% AEP Event)Low Risk (0.1% AEP Event)

0 100 200 300 400 50050m


NRW FLOOD MAP FORSURFACE WATER

MAY 2017

www.waterco.co.uk

CONTAINS NATURAL RESOURCES WALES INFORMATION © NATURAL RESOURCES WALES AND DATABASE RIGHT. ALL RIGHTS RESERVED. SOME FEATURES OF THIS INFORMATION ARE BASED ON DIGITAL SPATIAL DATA LICENCED FROM THE CENTRE FOR ECOLOGY AND HYDROLOGY © NERC (CEH). DEFRA, MET OFFICE AND DARDRIVERS AGENCY © CROWN COPYRIGHT. © CRANFIELD UNIVERSITY. © JAMES HUTTON INSTITUTE. CONTAINS OS DATA © CROWN COPYRIGHT AND DATABASE RIGHT 2015. LAND AND PROPERTY SERVICES © CROWN COPYRIGHT AND DATABASE RIGHT. CONTAINS OS DATA © CROWN COPYRIGHT (2017)

Ceir rhestr lawn o delerau ac amondau yn https://naturalresources.wales/rhybuddsafonol neu drwy gysylltu ag [email protected]. A full list of terms and condiitions is available from the https://naturalresources.wales/StandardNotice or by contacting [email protected] © Crown copyright and database rights 2017 Ordnance Survey 100019741. Geological Mapping: British Geological Survey ©NERC. Centre for Ecology & Hydrology © NERC (CEH). Defra and Met Office © Crown copyright. © Cranfield University. © James Hutton Institute. Land & Property Services © Crown copyright and database right.

1:

17/05/2017

Dyddiad / Date

Reservoirs

5,001

Map Perygl Llifogydd / Flood Risk Map

Graddfa / Scale

0.13

Kilometers

0.3

British_National_Grid

00.3

Allwedd / Map Key

Reservoir Depths

0 - 0.3m

0.3 - 2.0m

Greater than 2.0m

Tŷ Cambria 29 Heol Casnewydd Caerdydd CF24 0TP

Cambria House 29 Newport Road Cardiff CF24 0TP Croesewir gohebiaeth yn y Gymraeg a’r Saesneg Correspondence welcomed in Welsh and English

23/03/2017 Dear Aled Williams, PROPOSAL: Scheme for the removal of highway drainage (surface water runoff) from

the public combined sewer system LOCATION: Along Marl Lane, Llandudno Junction Thank you for consulting Natural Resources Wales about the above proposed development at pre-application stage. This response is to the enquiry regarding advice specifically on flood risk. Please note that our comments are without prejudice to any comments we may wish to make when consulted on any subsequent planning application or permit (either at pre-application or application stage) for the proposed development. At that time there may be new information available which we will need to take into account in making a formal response. Flood Risk As you may be aware the area suffered from a significant flood event in June 1993. Following the event our predecessors carried out a flood alleviation scheme for the main river (Afon Wydden) in Llandudno Junction. Although the scheme at the time was designed to provide a certain standard of protection it is highly likely that the standard today would have been reduced. We would expect Welsh Water to demonstrate that any new direct outfalls to the watercourse will not increase flood risk from the river Wydden for a range of annual exceedance probability events. We are at an early stage of developing a hydraulic model for the Wydden which will include various input points; unfortunately we cannot provide a date as to when the model would be available. Due to the status of the watercourse, any new structures/outfalls into the watercourse will be subject to Flood Risk Activity Permit as per the Environmental Permitting Regulations 2016. The existing outfall from the area discharges upstream of the Meadows estate and the BT flood storage area. Should you wish to discuss the above, please contact Iwan on 03000 653783/ [email protected] Please do not hesitate to contact us if we can be of any further assistance to you. Our comments above only relate specifically to matters related to your enquiry, i.e. the flood risk aspects of your proposal. We have not considered potential effects of other matters in relation to our remit that we may have concerns with, when providing our response to the local planning authority. “Natural Resources Wales and Planning Consultations” (March 2015) which is published

Ein cyf/Our ref: CAS-30433-W2Z9

Ebost/Email: [email protected] Ffôn/Phone: 03000 65 4682



www.naturalresourceswales.gov.uk www.cyfoethnaturiolcymru.gov.uk Page 2 of 2

on our website: (https://naturalresources.wales/planning-and-development includes a checklist of areas where we will provide comment. You should also be advised that, in addition to planning permission, it is your responsibility to ensure that you secure all other permits/consents relevant to your development. Yn gywir / yours faithfully

Siôn M Williams Siôn M. Williams

Ymgynghorydd Cynllunio Datblygu / Development Planning Advisor

Cyfoeth Naturiol Cymru / Natural Resources Wales

https://naturalresources.wales/planning-and-development



Appendix F – MicroDrainage Runoff and Volume Estimates

Waterco Ltd Page 1Eden Court w10278 - Marl LaneLon Parcwr Business Park Llanduno JunctionDenbighshire LL15 1NJ Greenfield RunoffDate 31-01-2017 09:54 Designed by Johanne.WilliamsFile Checked by Aled WilliamsXP Solutions Source Control 2016.1

FEH Mean Annual Flood

©1982-2016 XP Solutions

Input

Site Location SAAR (mm) 782 SPRHOST 32.300 FARL 1.000Area (ha) 1.913 URBEXT (1990) 0.0000 BFIHOST 0.519

Results

QMED Rural (l/s) 3.9 QMED Urban (l/s) 3.9

Waterco Ltd Page 1

Eden Court w10278

Lon Parcwr Business Park LLys Marl

Denbighshire LL15 1NJ Llandudno Jct

Date 17/05/17 Designed by SJP

File 1 in 30 year.srcx Checked by AW

XP Solutions Source Control 2016.1

Summary of Results for 30 year Return Period


Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Volume

(m³)

Status

15 min Summer 9.485 0.485 5.0 108.7 O K30 min Summer 9.580 0.580 5.0 129.9 O K60 min Summer 9.684 0.684 5.0 153.2 O K120 min Summer 9.782 0.782 5.0 175.3 Flood Risk180 min Summer 9.828 0.828 5.0 185.6 Flood Risk240 min Summer 9.850 0.850 5.0 190.5 Flood Risk360 min Summer 9.860 0.860 5.0 192.7 Flood Risk480 min Summer 9.858 0.858 5.0 192.2 Flood Risk600 min Summer 9.851 0.851 5.0 190.6 Flood Risk720 min Summer 9.841 0.841 5.0 188.4 Flood Risk960 min Summer 9.830 0.830 5.0 186.0 Flood Risk1440 min Summer 9.793 0.793 5.0 177.7 Flood Risk2160 min Summer 9.722 0.722 5.0 161.7 Flood Risk2880 min Summer 9.634 0.634 5.0 142.1 O K4320 min Summer 9.397 0.397 5.0 89.0 O K5760 min Summer 9.258 0.258 5.0 57.8 O K7200 min Summer 9.178 0.178 4.8 39.9 O K8640 min Summer 9.134 0.134 4.5 30.0 O K10080 min Summer 9.114 0.114 4.2 25.6 O K

15 min Winter 9.546 0.546 5.0 122.3 O K30 min Winter 9.655 0.655 5.0 146.6 O K

Storm

Event

Rain

(mm/hr)

Flooded

Volume

(m³)

Discharge

Volume

(m³)

Time-Peak

(mins)

15 min Summer 78.390 0.0 113.8 2630 min Summer 47.441 0.0 137.6 4060 min Summer 28.711 0.0 166.8 68120 min Summer 17.376 0.0 201.9 126180 min Summer 12.953 0.0 225.8 184240 min Summer 10.516 0.0 244.4 242360 min Summer 7.839 0.0 273.3 330480 min Summer 6.364 0.0 295.8 390600 min Summer 5.414 0.0 314.6 456720 min Summer 4.744 0.0 330.8 522960 min Summer 3.901 0.0 362.6 6621440 min Summer 2.960 0.0 412.8 9442160 min Summer 2.246 0.0 469.9 13642880 min Summer 1.847 0.0 515.2 17684320 min Summer 1.340 0.0 560.8 24645760 min Summer 1.068 0.0 595.7 31207200 min Summer 0.895 0.0 624.2 37608640 min Summer 0.775 0.0 648.5 441610080 min Summer 0.686 0.0 669.8 5144

15 min Winter 78.390 0.0 127.4 2630 min Winter 47.441 0.0 154.1 40

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Summary of Results for 30 year Return Period


Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Volume

(m³)

Status

60 min Winter 9.772 0.772 5.0 172.9 Flood Risk120 min Winter 9.887 0.887 5.0 198.7 Flood Risk180 min Winter 9.944 0.944 5.0 211.5 Flood Risk240 min Winter 9.975 0.975 5.0 218.3 Flood Risk360 min Winter 9.995 0.995 5.0 222.8 Flood Risk480 min Winter 9.988 0.988 5.0 221.2 Flood Risk600 min Winter 9.977 0.977 5.0 219.0 Flood Risk720 min Winter 9.963 0.963 5.0 215.8 Flood Risk960 min Winter 9.942 0.942 5.0 211.0 Flood Risk1440 min Winter 9.874 0.874 5.0 195.8 Flood Risk2160 min Winter 9.750 0.750 5.0 167.9 Flood Risk2880 min Winter 9.587 0.587 5.0 131.4 O K4320 min Winter 9.273 0.273 5.0 61.3 O K5760 min Winter 9.145 0.145 4.6 32.4 O K7200 min Winter 9.108 0.108 4.0 24.3 O K8640 min Winter 9.094 0.094 3.5 21.0 O K10080 min Winter 9.084 0.084 3.1 18.8 O K

Storm

Event

Rain

(mm/hr)

Flooded

Volume

(m³)

Discharge

Volume

(m³)

Time-Peak

(mins)

60 min Winter 28.711 0.0 186.8 68120 min Winter 17.376 0.0 226.1 124180 min Winter 12.953 0.0 252.9 180240 min Winter 10.516 0.0 273.7 238360 min Winter 7.839 0.0 306.1 346480 min Winter 6.364 0.0 331.3 442600 min Winter 5.414 0.0 352.3 478720 min Winter 4.744 0.0 370.5 556960 min Winter 3.901 0.0 406.2 7121440 min Winter 2.960 0.0 462.2 10222160 min Winter 2.246 0.0 526.3 14722880 min Winter 1.847 0.0 577.0 18804320 min Winter 1.340 0.0 628.3 25085760 min Winter 1.068 0.0 667.2 31047200 min Winter 0.895 0.0 699.1 36808640 min Winter 0.775 0.0 726.3 440810080 min Winter 0.686 0.0 750.2 5136

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Rainfall Details


Rainfall Model FEH D3 (1km) 0.311 Cv (Winter) 0.840Return Period (years) 30 E (1km) 0.300 Shortest Storm (mins) 15

Site Location F (1km) 2.342 Longest Storm (mins) 10080C (1km) -0.030 Summer Storms Yes Climate Change % +0D1 (1km) 0.377 Winter Storms YesD2 (1km) 0.421 Cv (Summer) 0.750

Time Area Diagram

Total Area (ha) 0.775

Time

From:

(mins)

To:

Area

(ha)

Time

From:

(mins)

To:

Area

(ha)

Time

From:

(mins)

To:

Area

(ha)

0 4 0.258 4 8 0.258 8 12 0.258

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Model Details


Storage is Online Cover Level (m) 10.000

Tank or Pond Structure

Invert Level (m) 9.000

Depth (m) Area (m²) Depth (m) Area (m²)

0.000 224.0 1.000 224.0

Hydro-Brake Optimum® Outflow Control

Unit Reference MD-SHE-0105-5000-1000-5000Design Head (m) 1.000

Design Flow (l/s) 5.0Flush-Flo™ CalculatedObjective Minimise upstream storage

Application SurfaceSump Available YesDiameter (mm) 105

Invert Level (m) 8.995Minimum Outlet Pipe Diameter (mm) 150Suggested Manhole Diameter (mm) 1200

Control Points Head (m) Flow (l/s)

Design Point (Calculated) 1.000 5.0Flush-Flo™ 0.296 5.0Kick-Flo® 0.637 4.1

Mean Flow over Head Range - 4.3

The hydrological calculations have been based on the Head/Discharge relationship for theHydro-Brake Optimum® as specified. Should another type of control device other than aHydro-Brake Optimum® be utilised then these storage routing calculations will beinvalidated

Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s)

0.100 3.6 1.200 5.4 3.000 8.4 7.000 12.50.200 4.8 1.400 5.8 3.500 9.0 7.500 12.90.300 5.0 1.600 6.2 4.000 9.6 8.000 13.30.400 4.9 1.800 6.6 4.500 10.1 8.500 13.70.500 4.7 2.000 6.9 5.000 10.6 9.000 14.10.600 4.3 2.200 7.2 5.500 11.1 9.500 14.50.800 4.5 2.400 7.5 6.000 11.61.000 5.0 2.600 7.8 6.500 12.1

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Event: 240 min Winter


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File 1 in 100 year +30%CC.srcx Checked by AW


Summary of Results for 100 year Return Period (+30%)


Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Volume

(m³)

Status

15 min Summer 9.467 0.467 5.0 219.0 O K30 min Summer 9.547 0.547 5.0 256.6 O K60 min Summer 9.637 0.637 5.0 298.6 O K120 min Summer 9.730 0.730 5.0 342.3 Flood Risk180 min Summer 9.782 0.782 5.0 366.6 Flood Risk240 min Summer 9.814 0.814 5.0 381.9 Flood Risk360 min Summer 9.850 0.850 5.0 398.7 Flood Risk480 min Summer 9.864 0.864 5.0 405.3 Flood Risk600 min Summer 9.866 0.866 5.0 406.1 Flood Risk720 min Summer 9.861 0.861 5.0 403.9 Flood Risk960 min Summer 9.862 0.862 5.0 404.4 Flood Risk1440 min Summer 9.851 0.851 5.0 399.0 Flood Risk2160 min Summer 9.819 0.819 5.0 383.9 Flood Risk2880 min Summer 9.780 0.780 5.0 365.6 Flood Risk4320 min Summer 9.635 0.635 5.0 298.0 O K5760 min Summer 9.489 0.489 5.0 229.1 O K7200 min Summer 9.379 0.379 5.0 178.0 O K8640 min Summer 9.296 0.296 5.0 138.8 O K10080 min Summer 9.235 0.235 4.9 110.1 O K

15 min Winter 9.524 0.524 5.0 245.9 O K30 min Winter 9.615 0.615 5.0 288.5 O K

Storm

Event

Rain

(mm/hr)

Flooded

Volume

(m³)

Discharge

Volume

(m³)

Time-Peak

(mins)

15 min Summer 154.375 0.0 219.4 2630 min Summer 91.094 0.0 258.4 4160 min Summer 53.754 0.0 311.6 70120 min Summer 31.719 0.0 367.5 128180 min Summer 23.298 0.0 404.6 188240 min Summer 18.717 0.0 433.2 246360 min Summer 13.748 0.0 476.9 364480 min Summer 11.045 0.0 510.4 482600 min Summer 9.320 0.0 537.9 600720 min Summer 8.112 0.0 561.3 674960 min Summer 6.600 0.0 607.2 7901440 min Summer 4.935 0.0 672.6 10482160 min Summer 3.690 0.0 771.9 14722880 min Summer 3.002 0.0 837.2 18844320 min Summer 2.147 0.0 896.8 27285760 min Summer 1.692 0.0 944.1 34087200 min Summer 1.407 0.0 981.3 41128640 min Summer 1.210 0.0 1012.8 476010080 min Summer 1.065 0.0 1039.3 5448

15 min Winter 154.375 0.0 245.5 2630 min Winter 91.094 0.0 288.5 41

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Summary of Results for 100 year Return Period (+30%)


Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Volume

(m³)

Status

60 min Winter 9.716 0.716 5.0 335.9 Flood Risk120 min Winter 9.823 0.823 5.0 385.9 Flood Risk180 min Winter 9.883 0.883 5.0 414.2 Flood Risk240 min Winter 9.922 0.922 5.0 432.6 Flood Risk360 min Winter 9.968 0.968 5.0 454.0 Flood Risk480 min Winter 9.989 0.989 5.0 463.9 Flood Risk600 min Winter 9.997 0.997 5.0 467.4 Flood Risk720 min Winter 9.996 0.996 5.0 466.9 Flood Risk960 min Winter 9.994 0.994 5.0 466.3 Flood Risk1440 min Winter 9.976 0.976 5.0 457.6 Flood Risk2160 min Winter 9.925 0.925 5.0 433.7 Flood Risk2880 min Winter 9.861 0.861 5.0 403.8 Flood Risk4320 min Winter 9.651 0.651 5.0 305.2 O K5760 min Winter 9.429 0.429 5.0 201.2 O K7200 min Winter 9.284 0.284 5.0 133.3 O K8640 min Winter 9.193 0.193 4.8 90.7 O K10080 min Winter 9.140 0.140 4.6 65.8 O K

Storm

Event

Rain

(mm/hr)

Flooded

Volume

(m³)

Discharge

Volume

(m³)

Time-Peak

(mins)

60 min Winter 53.754 0.0 348.8 70120 min Winter 31.719 0.0 411.3 126180 min Winter 23.298 0.0 452.9 184240 min Winter 18.717 0.0 484.9 242360 min Winter 13.748 0.0 533.6 358480 min Winter 11.045 0.0 570.9 470600 min Winter 9.320 0.0 601.4 582720 min Winter 8.112 0.0 627.3 690960 min Winter 6.600 0.0 677.2 8921440 min Winter 4.935 0.0 734.5 11142160 min Winter 3.690 0.0 864.6 15842880 min Winter 3.002 0.0 937.4 20484320 min Winter 2.147 0.0 1004.0 29445760 min Winter 1.692 0.0 1057.5 35847200 min Winter 1.407 0.0 1099.3 42488640 min Winter 1.210 0.0 1134.3 484010080 min Winter 1.065 0.0 1164.4 5440

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Rainfall Details


Rainfall Model FEH D3 (1km) 0.311 Cv (Winter) 0.840Return Period (years) 100 E (1km) 0.300 Shortest Storm (mins) 15

Site Location F (1km) 2.342 Longest Storm (mins) 10080C (1km) -0.030 Summer Storms Yes Climate Change % +30D1 (1km) 0.377 Winter Storms YesD2 (1km) 0.421 Cv (Summer) 0.750

Time Area Diagram

Total Area (ha) 0.775

Time

From:

(mins)

To:

Area

(ha)

Time

From:

(mins)

To:

Area

(ha)

Time

From:

(mins)

To:

Area

(ha)

0 4 0.258 4 8 0.258 8 12 0.258

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Model Details


Storage is Online Cover Level (m) 10.000

Tank or Pond Structure

Invert Level (m) 9.000

Depth (m) Area (m²) Depth (m) Area (m²)

0.000 469.0 1.000 469.0

Hydro-Brake Optimum® Outflow Control

Unit Reference MD-SHE-0105-5000-1000-5000Design Head (m) 1.000

Design Flow (l/s) 5.0Flush-Flo™ CalculatedObjective Minimise upstream storage

Application SurfaceSump Available YesDiameter (mm) 105

Invert Level (m) 8.995Minimum Outlet Pipe Diameter (mm) 150Suggested Manhole Diameter (mm) 1200

Control Points Head (m) Flow (l/s)

Design Point (Calculated) 1.000 5.0Flush-Flo™ 0.296 5.0Kick-Flo® 0.637 4.1

Mean Flow over Head Range - 4.3

The hydrological calculations have been based on the Head/Discharge relationship for theHydro-Brake Optimum® as specified. Should another type of control device other than aHydro-Brake Optimum® be utilised then these storage routing calculations will beinvalidated

Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s)

0.100 3.6 1.200 5.4 3.000 8.4 7.000 12.50.200 4.8 1.400 5.8 3.500 9.0 7.500 12.90.300 5.0 1.600 6.2 4.000 9.6 8.000 13.30.400 4.9 1.800 6.6 4.500 10.1 8.500 13.70.500 4.7 2.000 6.9 5.000 10.6 9.000 14.10.600 4.3 2.200 7.2 5.500 11.1 9.500 14.50.800 4.5 2.400 7.5 6.000 11.61.000 5.0 2.600 7.8 6.500 12.1

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Appendix G – Maintenance Schedules

SuDS Maintenance Schedule

File Ref: G - Detention Basin -SuDS Maintenance

Operation and Maintenance Requirements for Detention Basins

Ref. Table 22.1 CIRIA C753 ‘The SuDS Manual’

Maintenance Schedule Required Action

Typical Frequency

Regular maintenance

Remove litter and debris Monthly

Cut grass-for spillways and access routes Monthly (during growing season), or as required

Cut grass - meadow grass in and around basin

Half yearly (spring - before nesting season, and autumn)

Manage other vegetation and remove nuisance plants

Monthly (at start, then as required)

Inspect inlets, outlets and overflows for blockages, and clear if required. Monthly

Inspect banksides. structures. pipework etc. for evidence of physical damage Monthly

Inspect inlets and facility surface for silt accumulation. Establish appropriate silt removal frequencies.

Monthly (for first year), then annually or as required

Check any penstocks and other mechanical devices Annually

Tidy all dead growth before start of growing season Annually

Remove sediment from inlets, outlet and forebays Annually (or as required)

Manage wetland plants in outlet pool – where provided

Annually (as set out in Chapter 23)

Occasional maintenance

Reseed- areas of poor vegetation growth As required Prune and trim any trees and remove cuttings Every 2 years. or as required

Remove sediment from inlets, outlets. forebays and main basin when required

Every 5 years. or as required (likely to be minimal requirements where effective upstream source control is provided)

Remedial actions

Repair erosion or other damage by reseeding or re-turfing As required

Realignment of rip-rap As required Repair/rehabilitation of inlets, outlets and overflows As required

Relevel uneven surfaces and reinstate design levels As required


File Ref: G - Detention Basin -SuDS Maintenance

The maintenance requirements detailed above are to be undertaken by the site owner

Name: ……………………………………………….

Position: ……………………………………………….

Date: ………………………………………………. Signed on behalf of site owner ……………………………………………….


File Ref: G - Permeable Paving - SuDS Maintenance

Ref. Table 20.15, CIRIA C753 ‘The SuDS Manual

Maintenance Schedule

Required Action Typical Frequency

Regular maintenance

Brushing and vacuuming (standard cosmetic sweep over whole surface)

Once a year, after autumn leaf fall, or reduced frequency as required, based on site-specific observations of clogging or manufacturer’s recommendations – pay particular attention to areas where water runs onto pervious surface from adjacent impermeable areas as this area is most likely to collect the most sediment

Occasional maintenance

Stabilise and move contributing and adjacent areas As required

Removal of weeds or management using glyphospate applied directly into the weeds by an applicator rather than spraying

As required – once per year on less frequently used pavements

Remedial actions

Remediate any landscaping which, through vegetation maintenance or soil slip, has been raised to within 50mm of the level or the paving

As required

Rehabilitation of surface and upper substructure by remedial sweeping

Every 10 to 15 years or as required (if infiltration performance is reduced due to significant clogging)

Monitoring

Inspect for evidence of poor operation and / or weed growth – if required, take remedial action

Three-monthly, 48hr after large storms in first six months

Inspect silt accumulation rates and establish appropriate brushing frequencies

Annually

Monitor inspection chambers Annually

Operation and Maintenance Requirements for Permeable Paving


File Ref: G - Permeable Paving - SuDS Maintenance

The maintenance requirements detailed above are to be undertaken by the site owner.

Name: ……………………………………………….

Position: ……………………………………………….

Date: ………………………………………………. Signed on behalf Of the site owner ……………………………………………….


File Ref: G - Ponds and Wetlands -SuDS Maintenance

Operation and Maintenance Requirements for Ponds and Wetlands

Ref. Table 23.1 CIRIA C753 ‘The SuDS Manual’

Maintenance Schedule Required Action

Typical Frequency

Regular maintenance

Remove litter and debris Monthly (or as required)

Cut the grass – public areas Monthly (during growing season), or as required

Inspect marginal and bankside vegetation and remove nuisance plants (for first 3 years)

Monthly (at start, then as required)

Inspect inlets, outlets, banksides, structures, pipework etc for evidence of blockage, and / or physical damage.

Monthly

Inspect water body for signs of poor water quality Monthly (May – October)

Inspect silt accumulation rates in any forebay and in main body of the pond and establish appropriate removal frequencies; undertake contamination testing once some build-up has occurred, to inform management and disposal options.

Half yearly

Check any mechanical devices e.g. penstocks Half yearly

Hand cut submerged and emergent aquatic plants (at minimum of 0.1m above pond base; include max 25% of pond surface)

Annually

Remove 25% of bank vegetation from water’s edge to a minimum of 1m above water level

Annually

Remove sediment from any forebay Every 1 – 5 years, or as required

Remove sediment and planting from one quadrant of the main body of ponds without sediment forebays

Every 5 years, or as required

Occasional maintenance Remove sediment from the main body of big ponds when pool volume is reduced by 20%

With effective pre-treatment, this will only be required rarely, e.g. 25-50 years

Remedial actions

Repair erosion or other damage As required Replant where necessary As required Aerate pond when signs of eutrophication are detected As required

Realign rip-rap or repair other damage As required Repair/rehabilitate of Inlets, outlets and overflows As required


File Ref: G - Ponds and Wetlands -SuDS Maintenance

The maintenance requirements detailed above are to be undertaken by the site owner

Name: ……………………………………………….

Position: ……………………………………………….

Date: ………………………………………………. Signed on behalf of site owner ……………………………………………….


File Ref: Tank - SuDS Maintenance

Operation and Maintenance Requirements for Attenuation Storage

Tanks

Ref. Table 21.3, CIRIA C753 ‘The SuDS Manual’

The maintenance requirements detailed above are to be undertaken by the site owner.

Name: ……………………………………………….

Position: ……………………………………………….

Date: ………………………………………………. Signed on behalf Of the site owner ……………………………………………….

Maintenance Schedule

Required Action Typical Frequency

Regular maintenance

Inspect and identify any areas that are not operating correctly. If required, take remedial action

Monthly for 3 months, then annually

Remove debris from the catchment surface (where it may cause risks to performance) Monthly

For systems where rainfall infiltrates into the tank from above, check surface of filter for blockage by sediment, algae or other matter; remove and replace surface infiltration medium as necessary

Annually

Remove sediment from pre-treatment structures and/ or internal forebays Annually, or as required

Remedial actions Repair/rehabilitate inlets, outlet, overflows and vents As required

Monitoring

Inspect/check all inlets, outlets, vents and overflows to ensure that they are in good condition and operating as designed

Annually

Survey inside of tank for sediment build-up and remove If necessary

Every 5 years or as required

Documents

Llys Marl, Llandudno Junctionbeechdevelopmentsplanning.co.uk/wp-content/uploads/2017/...Waterco Ltd, Eden Court, Lon Parcwr Business Park, Ruthin, Denbighshire LL15 1NJ Tel: 01824