Appendix H: Cost of compaction - Defra, UK - Science …sciencesearch.defra.gov.uk/Document.aspx?Document=10138... · Web viewThe cost of soil degradation in England and Wales Appendix

The cost of soil degradation in England and Wales

Appendix H: Cost of compaction

Water Industry costs A review of water industry costs was not able to ascertain the extent to which additional capital and operating costs are directly attributable to soil degradation1. Although data are available from OFWAT for the costs for nitrate removal, pesticide removal and reduction of turbidity in England and Wales, it is not possible to derive a breakdown of how much of this expenditure specifically relates to soil degradation.

Ofwat reports2 that from 1992-93 to 2009-10 over £1bn (2009-10 prices) has been spent on water treatment assets and processes to comply with the pesticides parameters, and just over £400m (2009-10 prices) on water treatment assets and processes to comply with the nitrate parameter under quality enhancement programme. This equates to an average spend of about £90m/year in 2010 prices. Although not all of this is due to soil degradation, it is known that the processes of erosion and compaction exacerbate the transport of nutrients to water.

According to OFWAT3 during the period 2005 -10, the water industry made £2.02bn capital investment and committed an extra £29m/year operating costs on its drinking water quality programme. About 6-8 % of these costs were associated with the aforementioned items, including removal of discoloration from drinking water that is often linked in some way to land management and the degradation of soils.

For the period 2010-154, OFWAT has separated its drinking water (£1.1bn capex, £11m/year opex) and environmental (£3.4 bn, £56m/year opex) programmes. Of the former, about 15% (about £150 capex) could be linked to land and soil management. Of the latter, actions to meet the Water Framework Directive’s objectives (about £120m capex) are, amongst other things, linked to the reduction of diffuse pollution from farmland with implications for soil management. In broad terms it appears, that an additional capital spend of about £150m /year and about £5m /year extra operating costs are potentially associated with soil management, over and above current capex and opex expenditures.

Seventeen water companies have included a total of about 100 catchment management schemes in their business plans for AMP5 (2010-15). These provide for action or investigation at the catchment level to address deteriorating raw water quality, rather than pursuing traditional, capital-intensive treatment solutions. The proposed industry expenditure was £52m capital expenditure for 2010-15, and £9m operating expenditure per annum from 2014-15 (2007-08 prices). These schemes cover all catchment management proposals and therefore are not solely as a result of soil degradation, but some specifically address run off and pollution from farm land.

Box 1: Case study. Upstream Thinking – South West Water – joining up land, soil and water management in practice

Climate change and pressures for intensive agriculture are affecting the quality and quantity of our raw water supplies collected in reservoirs and abstracted from rivers. South West Water (SSW) promoted two series of actions from 2006 to 2009 to develop responses to this based on moorland restoration on Exmoor and reducing soil loss and pollution from farms and has now developed a long term response which is being implemented.

1 OFWAT , 2011. Water Company Returns to OFWAT http://www.ofwat.gov.uk/regulating/junereturn/jrlatestdata/2 Ofwat 2011, in responses to data request3 OFWAT (2004) Future water and sewerage charges 2005-10:Final determinations . Period review 2004. Office for Water Services, Birmingham http://www.ofwat.gov.uk/pricereview/pr04/det_pr_fd04.pdf4 OFWAT (2009) Future water and sewerage charges 2010-15: Final determinations. Period review 2009. Office for Water Services, Birmingham http://www.ofwat.gov.uk/pricereview/pr09phase3/det_pr09_finalfull.pdf

Draft report Page 1 Cranfield University

http://www.ofwat.gov.uk/pricereview/pr04/det_pr_fd04.pdf

Ditch construction and drainage schemes in the past improved the land for agricultural purposes, but loss of natural water storage has led to significant erosion, carbon dioxide release from drying peat, biodiversity loss and increased downstream flood risks. A restoration project was started on Exmoor in 2003 by Exmoor National Park Authority and South West Water provided additional funding from 2006 onwards. To date over 320 hectares of moorland have been restored with a wide range of hydrological and environmental benefits. Changes in grazing yields are offset by support payments from Natural England to the landowners involved. The Environment Agency is providing an extensive hydrological investigation to confirm the benefits.

A group of 15 farms were improved above one of our most damaged reservoirs, Upper Tamar Lake near Bude. Similar techniques were undertaken to those of the England Catchment Sensitive Farming Delivery Initiative, with funds mainly provided by the Tubney Charitable Trust, to reduce soil erosion, loss of manures and damage caused by the access of stock to watercourses. Water quality below the farms is observed to be better quality than the water above, as farms were not losing their soil and fertilizer to streams and rivers in or beside their land. It is reported that farm productivity and incomes have been raised - both essential for food production and ensuring a viable future for farming.

Current risks: erosion and river pollution

A more extensive programme of changes to uplands and farmed land was promoted in the last Period Review (PR09) with support from all regulators, Ofwat and Consumer Council for Water. A 3,000 hectare restoration on Exmoor, a 110 hectare trial on Dartmoor and seven catchment scale farmland improvements above key intakes and reservoirs are underway. £0.7m is being spent on 15 two-year catchment investigations to develop further schemes for inclusion in the PR14 Business Plan. This programme of water quality and quantity protection is branded as ‘Upstream Thinking’. SSW owns carries out this work on third party property by negotiation with owners and tenants. According to SSW Clean raw surface water costs 20% less to treat than water with heavy sediment loads and if deteriorating water quality can be stopped it will delay or avoid costly longer-term water treatment upgrading. When assessed over 30 years in line with Ofwat’s instructions for PR09, the programme is estimated to offer a benefit to cost ratio of 65:1 or better. Thus water users are offered the prospect of lower bill increases and ‘soft engineering’ for flood protection, which complements essential conventional defences for urban areas and water treatment works adjacent to rivers.

The current improvement programme for moorland and catchments raises £8.1m for local projects to restore the natural water storage ability of uplands and limit the damage to rivers from farmland from 2010 to 2015. These projects are included in the South West River Basin Management Plan as they will contribute to ‘Good Status’ delivery for the Water Framework Directive. Moorland restoration offers carbon capture at about 12 tonnes CO2/hectare/year while farmers are being encouraged to create wetlands and biodiversity areas with the Woodland Trust’s support. The cost to our water customers is an additional 65p on bills by 2015, compared to a customers’ willingness-to-pay identified in PR09 of £2.40 for additional environmental projects. Our delivery partners are Rivers and Wildlife Trusts and others with a network of local experts and volunteers able and willing to identify risks and engage landowners in remedial action.

Acknowledgment: Martin Ross: Environmental Manager, South West Water. [email protected]

Since it was difficult to determine from water industry data, what proportion of cost related specifically linked to different forms of soil degradation, and in this case, from compaction, the costs were estimated from first principles as described in the following section.


Estimating on-site costs of soil compactionThe cost of compaction was considered to include: the onsite cost of agricultural and forestry yield decline caused by impaired rooting medium and water holding capacity, the extra draught power associated with ploughing and cultivation operations, and the cost of losing applied N, P, and K because of extra runoff. The off-site costs included the impact of N and P in the water environment and the environmental burdens associated with increased soil tillage and the additional use and loss of N and P caused by compaction.

The degree and severity of compaction varies according to land use and soil type. In order to calculate the area of headlands, tramlines and general field areas that might be subject to compaction, a GIS layer of field size from the rural payments agency was sampled across the different areas of land use developed during the categorisation of land cover and soil type (Appendix 1). This provided data on the relative size of fields, which was then used to adjust the mean national field size of 12 hectares reported to be the average field size by the North East Biodiversity Forum 5. The assumptions regarding field sizes, field rectangularity, tramline width and tillage width from which the estimates of compaction were derived are show in Table 1.

Table 1. The estimates of field sizes, field rectangularity, tramline width and tillage width used to estimate in field compaction

Arable Extensive

Arable Intensive

Grassland Improved

Grassland unimproved Horticulture

Relative size (%) 101.3 137.9 80.3 112.2 167.1Assumed average field size (ha) 12Fields per km2 (n) 8.23 6.04 10.38 7.43 4.99Headland (m) 15 15 12 12 15Tramline width (m) 24 24 24Tramline compaction zone (m) 0.4 0.4 0.4Tillage width (m) 2.25 2.25 2.25Tillage compaction width (m) 0.4 0.4 0.4Field ratio: width 2 2 2 2 2Length 5 5 5 5 5Average field area (ha) 12.15 16.54 9.64 13.46 20.05Field width (m) 220 257 196.34 232.03 283.18Field length (m) 551 643 491 580 708Total headland compaction (m) 6,614 7,717 4,712 5,569 8,495Headland compaction (%) 5.44% 4.66% 4.89% 4.14% 4.24%Tramline runs per field (n) 9.19 10.72 11.80Tramline compaction (m/field) 3830 5257.00 6399Tramline compaction (%) 3.15% 3.18% 3.19%Tillage runs per field (n) 97.98 1143 126Tillage compaction (m/field) 40849 56075 68260Tillage compaction (%) 33.62% 33.90% 34.05%Total area of compaction reduction (%) 42.22% 41.74% 41.48%

The proportion of each field that would be subject to headland, tramline and general field compaction was calculated from the data in Table 1. The areas and yield decline associated with each type of compaction was estimated by using literature 6 7 8 and personal communication (Professor D. Godwin and Dr T. Chamen) and are shown for headlands in Table 2, for tramlines, in Table 3, and for the general field area, in Table 4.

The impact of compaction on crop yields was generally assumed to be greatest on clays and lowest on silt for headland and general field compaction due to the shape of the individual particles making up the soils (personal communication, Professor D Godwin). Tramlines developed for field operations during crop growth were assumed to totally inhibit crop growth and 33% of this cost was assumed to

5 North East Biodiversity Forum: http://www.nebiodiversity.org.uk/biodiversity/habitats/farmland/cerealmargins/default.asp6 Defra project BD23047 Defra project BD50018 Chamon, T., (2006). Controlled traffic’ farming: Literature review and appraisal of potential use in the U.K. Research Review No. 59. Submitted to the Home Grown Cereals Authority


be associated with managing compaction risk. The integrated yield and risk level associated with these different sources of compaction are shown in Table 5.

Table 2. The estimates: a) the headland area at risk of compaction, and; b) associated yield loss on the compacted area

a) Headland area at risk (%) SoilscapesLand use Clay Silt Sand PeatUrbanHorticulture 4.24% 4.24% 4.24% 4.24%Arable intensive 4.66% 4.66% 4.66% 4.66%Arable extensive 5.44% 5.44% 5.44% 5.44%Grassland improved 4.89% 4.89% 4.89% 4.89%Grassland unimproved 4.14% 4.14% 4.14% 4.14%Rough grasslandForestryWoodlandWildscape b) Yield loss on headland area (%) SoilscapesLand use Clay Silt Sand PeatUrbanHorticulture 18% 2% 10% 2%Arable intensive 13% 6% 9% 6%Arable extensive 10% 5% 7% 5%Grassland improved 13% 2% 5% 2%Grassland unimproved 13% 2% 5% 2%Rough grasslandForestryWoodlandWildscape

Table 3. The estimates: a) the tramline area at risk of compaction, and; b) associated yield loss on the compacted area

a) Tramline area at risk (%) SoilscapesLand use Clay Silt Sand PeatUrban Horticulture 3.19% 3.19% 3.19% 3.19%Arable intensive 3.18% 3.18% 3.18% 3.18%Arable extensive 3.15% 3.15% 3.15% 3.15%Grassland improved Grassland unimproved Rough grassland Forestry Woodland Wildscape b) Yield loss on tramline area (%) SoilscapesLand use Clay Silt Sand PeatUrban Horticulture 100% 100% 100% 100%Arable intensive 100% 100% 100% 100%Arable extensive 100% 100% 100% 100%Grassland improved Grassland unimproved Rough grassland Forestry Woodland Wildscape


Table 4. The estimates: a) the general field area at risk of compaction, and; b) associated yield loss on the compacted area a) General field area area at risk (%) SoilscapesLand use Clay Silt Sand PeatUrban Horticulture 34.05% 34.05% 34.05% 34.05%Arable intensive 33.90% 33.90% 33.90% 33.90%Arable extensive 33.62% 33.62% 33.62% 33.62%Grassland improved 33.82% 33.82% 33.82% 33.82%Grassland unimproved 34.08% 34.08% 34.08% 34.08%Rough grassland Forestry Woodland Wildscape b) Yield loss on general field area (%) SoilscapesLand use Clay Silt Sand PeatUrban Horticulture 2% 1% 0% 2%Arable intensive 1% 1% 1% 1%Arable extensive 1% 1% 1% 1%Grassland improved 1% 1% 0% 1%Grassland unimproved 1% 1% 0% 1%Rough grassland Forestry Woodland Wildscape

Table 5. The estimates: a) the headland area at risk of compaction, and; b) associated yield loss on the compacted area A) Total area at risk (%) SoilscapesLand use Clay Silt Sand PeatUrban 0% 0% 0% 0%Horticulture 41% 41% 41% 41%Arable intensive 42% 42% 42% 42%Arable extensive 42% 42% 42% 42%Grassland improved 39% 39% 39% 39%Grassland unimproved 38% 38% 38% 38%Rough grassland 0% 0% 0% 0%Forestry 0% 0% 0% 0%Woodland 0% 0% 0% 0%Wildscape 0% 0% 0% 0%

c) Yield loss on compacted area (%) SoilscapesLand use Clay Silt Sand PeatUrban 0% 0% 0% 0%Horticulture 6% 4% 3% 6%Arable intensive 5% 4% 4% 3%Arable extensive 5% 4% 4% 4%Grassland improved 3% 1% 0% 2%Grassland unimproved 3% 1% 0% 2%Rough grassland 0% 0% 0% 0%Forestry 0% 0% 0% 0%Woodland 0% 0% 0% 0%Wildscape 0% 0% 0% 0%

Ploughing and cultivating compacted land requires extra draught power. This was calculated as a penalty on the draught power that is used in tillage operations. The mean size of tractors sold in 2010


was 120 HP9. The per hour running cost of a tractor of this size is given as £10.41 h -1 in fuel and oil costs and the price per litre of diesel is given as £0.42. Assuming that most of the hourly cost is for diesel, a tractor of this horse power consumes about 24.8 l h -1 of diesel. However, tractors used for tillage operations tend to be larger. A size of 200 HP was assumed as the typical size for tractors used in tillage operations and the per hour running costs were estimated from the data in Nix 10 by scaling up the per HP fuel requirements for a 120 HP tractor to a 200 HP tractor, assuming that the per HP fuel consumption would be identical for both sizes. From this, it was estimated that the hourly consumption of a 200 HP tractor was 29.7 l h-1 of diesel.

The times required for tillage operations assumed to be affected by compaction, such as ploughing, cultivation, and seed bed preparation were taken Nix11 and the total fuel consumption and fuel costs per hectare derived from the estimate of the hourly fuel requirement of a 200 HP tractor (Table 6).

As noted above, it was assumed that the extra fuel consumption caused by compaction was already implicit within the hourly operating cost in such farm data. The additional penalty for tillage operations is given in Table 7.

Table 6. Estimates of fuel requirements (l ha-1) and fuel costs (£ ha-1) required for soil tillage operations potentially affected by compaction

Crop Ploughing/cultivation time (h ha-1)Total fuel required (l ha-

1)Total fuel cost (£ ha-

1)Winter wheat 1.4 34.7 14.6Spring barley 1.4 34.7 14.6Winter oilseed rape 1.6 39.7 16.7Peas 3 74.4 31.3Winter beans 1.4 34.7 14.6Sugar beet 4.6 114.0 47.9Potatoes 7.9 195.8 82.3Carrots 7.9 195.8 82.3Onions 4.6 114.0 47.9Forage maize 1.4 34.7 14.6Lettuce 1.4 34.7 14.6Celery 1.4 34.7 14.6Leeks 1.4 34.7 14.6

Table 7. The assumed additional power requirements (% of total requirement) for tilling compacted soils

Extra power requirement (% total requirement) SoilscapesLand use Clay Silt Sand PeatUrban Horticulture 87% 60% 29% 29%Arable intensive 87% 60% 29% 29%Arable extensive 87% 60% 29% 29%Grassland improved Grassland unimproved 29% 60% Rough grassland 29% 60% Forestry 29% 60% Woodland Wildscape

An additional cost of compaction is in terms of the additional losses of nutrients from compaction induced runoff and in the case of N, of compaction gaseous emissions. The loss of nutrients, (especially of N which is highly mobile) varies by soil, management and the form of the applied

9 Nix, J. (2011). The farm management pocketbook. 41st edition. 10 Nix, J. (2011). The farm management pocketbook. 41st edition. 11 Nix, J. (2011). The farm management pocketbook. 41st edition.


nutrient. Here the loss for N for wheat as developed by Williams et al12 was assumed to be representative of typical losses across the different agricultural landscapes in England and Wales. In this, 62% of N applied in fertiliser is considered to be used by the crop, or fixed by the soil. Of the 38% that is considered to be lost, 34% is considered to be leached whilst 66% is considered to be denitrified, 5% as N2O, 7% as NH3, and 55% as N2. In the case of both P and K, 96% of the applied nutrient is considered to be used by the plant or fixed by the soil, whilst 4% is considered to be emitted to the water environment.

Table 8. Assumptions regarding typical losses of N as applied to wheat and developed from (Williams et a13)

Losses of N Proportion of totalProportion used by crop or fixed in soil 62.0%Proportion emitted to water and air 38.0%

Of the proportion emitted to water and air:Proportion leached 34.0%Proportion denitrified 66.0%

Of the proportion denitrified:Proportion emitted as N20 4.0%Proportion emitted as NH3 7.0%Proportion emitted as N2 55.0%

The rates of additional loss of N, P, and K caused by compaction (Table 9) were assumed to act only on the fraction of the nutrient already being lost (i.e. the 38% for N and the 4% for P and K) rather than on the total application rate of these nutrients, and estimated only for that proportion of the field considered to be at risk of compaction (Table 5a).

The use of diesel and fertilisers is associated with a range of environmental burdens. The value for diesel includes the CO2e involved in producing and using diesel, whilst the values for CO2e include only the values for producing N, P, and K 14. The environmental burdens were calculated in relation to the additional use of diesel and nutrients that were assumed to be needed to compensate for the effects of compaction.

Table 9. The assumed applied nutrient loss (% of total applied) from the compacted portion of land

N, P, K loss because of compaction (%) SoilscapesLand use Clay Silt Sand PeatUrban Horticulture 20% 11% 2% 20%Arable intensive 20% 11% 2% 20%Arable extensive 20% 11% 2% 20%Grassland improved 20% 11% 2% 20%Grassland unimproved 20% 11% 2% 20%Rough grassland Forestry Woodland Wildscape

12 Williams, A.G., Audsley, E. and Sandars, D.L. (2006) Determining the environmental burdens and resource use in the production of agricultural and horticultural commodities. Main Report. Defra Research Project IS0205. Bedford: Cranfield University and Defra. Available on www.agrilca.org and www.defra.gov.uk13 Williams, A.G., Audsley, E. and Sandars, D.L. (2006) Determining the environmental burdens and resource use in the production of agricultural and horticultural commodities. Main Report. Defra Research Project IS0205. Bedford: Cranfield University and Defra. Available on www.agrilca.org and www.defra.gov.uk14 Williams, A.G., Audsley, E. and Sandars, D.L. (2006) Determining the environmental burdens and resource use in the production of agricultural and horticultural commodities. Main Report. Defra Research Project IS0205. Bedford: Cranfield University and Defra. Available on www.agrilca.org and www.defra.gov.uk


The GWP of production of diesel, N, P, and K is shown in Table 10. The cost of these impacts in the water environment has already been outlined in Appendix F. The use of N fertiliser is associated with a burden to the atmosphere in terms of N2O and NH3. The ratio of the molecular weights of fertiliser N, N2O, and NH3 were used to convert the additional loss of N fertiliser to N2O (ratio 1 to 3.14) and NH3 (ratio: 1 to 1.21).

Table 10. The global warming potential of diesel combustion and N, P, and K application

GWP burden of diesel (kg C02e l-1 diesel) 3.10GWP burden of N (kg C02e kg-1 N) 5.00GWP burden of P (kg C02e kg-1 P) 1.00GWP burden of K (kg C02e kg-1 K) 0.50

ResultsThe cost of compaction induced production lossThe total area of agricultural land suffering from some degree of compaction, based on the previous assumptions outline in Table 2 to Table 4, was 3.9 million ha, approximately 28% of the total land area of England and Wales and 38% of the area of agricultural land in England and Wales. The majority of this was associated with extensive arable production and intensive grassland on clayey soils.

The total yield penalty attributable to compaction was calculated to be £162.7 million per year mostly on clayey soils. On a per hectare scale, the cost was estimated to be £11.7 ha -1 with the highest per hectare yield penalty costs associated with horticulture and intensive arable production (Table 12).

Table 11. Area in each landuse/soil type category at risk of compaction.

Total areas at risk within categories (ha) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 10,729 7,614 6,349 531 25,223Arable intensive 72,143 34,949 41,460 3,437 151,989Arable extensive 1,148,190 229,177 326,955 19,840 1,724,162Grassland improved 890,389 179,119 225,623 49,997 1,345,128Grassland unimproved 280,326 47,123 80,105 204,614 612,169Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 2,401,778 497,982 680,491 278,419 3,858,670

Table 12. The estimated cost of compaction induced productivity loss.

Total E&W productivity loss due to compaction (£) Soilscapes

Land use Clay Silt Sand Peat Urban - - - - -

Horticulture 11,413,696 4,022,727 5,054,035 280,525 20,770,983

Arable intensive 15,835,219 5,619,211 8,168,907 840,948 30,464,284

Arable extensive 59,771,796 7,136,408 9,575,184 568,034 77,051,422

Grassland improved 25,082,491 681,136 1,849,468 167,901 27,780,996

Grassland unimproved 4,733,433 110,148 384,842 373,758 5,602,181

Rough grassland - - - - -

Forestry - - - - -

Woodland - - - - -

Wildscape - - - - -

116,836,634 17,569,631 25,032,436 2,231,166 161,669,867


Total E&W productivity loss due to compaction in total area (£ ha-1) Soilscapes

Land use Clay Silt Sand Peat Urban 0 0 0 0 -Horticulture 441 219 330 219 341.6Arable intensive 92 67 82 102 83.7Arable extensive 22 13 12 12 18.9Grassland improved 11 1 3 1 8.0Grassland unimproved 6 1 2 1 3.5Rough grassland 0 0 0 0 -Forestry 0 0 0 0 -Woodland 0 0 0 0 -Wildscape 0 0 0 0 -

14.3 10.5 9.3 1.6 11.6

The cost of additional diesel useThe increased use of diesel because of additional draught requirements for tillage operations was estimated to be £17.5 million. Whilst the main cost of this was associated with intensive and extensive arable production, the highest per hectare cost was in intensive arable production, especially on clays and silts (Table 13).

Table 13. The estimated cost of compaction induced productivity loss.

Total E&W additional cost of diesel penalty (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - - Horticulture 87,118.6

4 29,877.0

0 41,553.1

0 2,083.4

7 160,632

Arable intensive 2,080,937.12

522,192.83

1,085,534.64

67,082.13 3,755,747

Arable extensive 9,873,207.07

1,047,267.95

2,553,745.93

86,093.29 13,560,314

Grassland improved - - - - - Grassland unimproved

- - - - -

Rough grassland - - - - - Forestry - - - - - Woodland - - - - - Wildscape - - - - -

12,041,263 1,599,338 3,680,834 155,259 17,476,693 E&W additional diesel (£ ha-1) Soilscapes

Land use Clay Silt Sand Peat Urban 0.0 0.0 0.0 0.0 0.0Horticulture 3.4 1.6 2.7 1.6 2.6Arable intensive 12.0 6.2 10.9 8.1 10.3Arable extensive 3.6 1.9 3.3 1.8 3.3Grassland improved 0.0 0.0 0.0 0.0 0.0Grassland unimproved

0.0 0.0 0.0 0.00.0

Rough grassland 0.0 0.0 0.0 0.0 0.0Forestry 0.0 0.0 0.0 0.0 0.0Woodland 0.0 0.0 0.0 0.0 0.0Wildscape 0.0 0.0 0.0 0.0 0.0

1.5 1.0 1.4 0.1 1.3


The cost of additional nutrients lostThe estimated cost of nutrients applied and lost because of compaction was estimated to be £23 million for N (£1.6 ha-1) (Table 14), £0.7 million for P (£0.05 ha-1) (Table 15), and £1.8 million for K (£0.07 ha-1) for England and Wales (Table 16). Again, most of this was associated with extensive arable systems and improved grassland on clay soils.

Table 14. The estimated cost of compaction induced N loss.

Total E&W N loss cost due to compaction (£) Soilscapes Land use Clay Silt Sand Peat TotalUrban - - - - - Horticulture 52,238 3,708 15,456 259 71,66

0 Arable intensive 265,649 14,355 95,030 2,124 377,159 Arable extensive 8,130,657 152,683 1,049,744 13,423 9,346,507 Grassland improved 10,030,778 200,740 1,260,886 54,828 11,547,231 Grassland unimproved 1,343,328 23,690 181,223 76,747 1,624,988 Rough grassland - - - - - Forestry - - - - - Woodland - - - - - Wildscape - - - - - 19,822,651 395,174 2,602,339 147,381 22,967,545 Average E&W N loss cost due to compaction (£ ha-1 category area) Soilscapes Land use Clay Silt Sand Peat Urban 0.0 0.0 0.0 0.0 -Horticulture 2.0 0.2 1.0 0.2 1.2Arable intensive 1.5 0.2 1.0 0.3 1.0Arable extensive 3.0 0.3 1.4 0.3 2.3Grassland improved 4.4 0.4 2.2 0.4 3.3Grassland unimproved 1.8 0.2 0.9 0.1 1.0Rough grassland 0.0 0.0 0.0 0.0 -Forestry 0.0 0.0 0.0 0.0 -Woodland 0.0 0.0 0.0 0.0 -Wildscape 0.0 0.0 0.0 0.0 -

2.4 0.2 1.0 0.1 1.6

Table 15. The estimated cost of compaction induced P loss.

Total E&W P loss cost due to compaction (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -

Horticulture 4,377 311 1,295 22 6,005

Arable intensive 34,329 1,791 11,339 236 47,695 Arable extensive 260,063 5,140 35,433 450 301,086 Grassland improved 211,839 4,239 26,629 1,158 243,865Grassland unimproved 55,388 977 7,472 3,164 67,002 Rough grassland - - - - -

Forestry - - - - -

Woodland - - - - -

Wildscape - - - - -

565,997 12,458 82,167 5,030 665,651 Average E&W P loss cost due to compaction (£ ha-1 category area) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -

Horticulture 0.17 0.02 0.08 0.02 0.10

Arable intensive 0.20 0.02 0.11 0.03 0.13

Arable extensive 0.10 0.01 0.05 0.01 0.07

Grassland improved 0.09 0.01 0.05 0.01 0.07

Grassland unimproved 0.08 0.01 0.04 0.01 0.04


Rough grassland - - - - -

Forestry - - - - -

Woodland - - - - -

Wildscape - - - - -

0.07 0.01 0.03 0.00 0.05

Table 16. The estimated cost of compaction induced K loss.

Total E&W K loss cost due to compaction (£) Soilscapes

Land use Clay Silt Sand Peat Urban - - - - -Horticulture 4 0 1 0 6Arable intensive 72 4 24 1 101Arable extensive 420 9 65 1 495Grassland improved 796 16 100 4 916Grassland unimproved 193 3 26 11 234Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 1,486 32 217 17 1,751 Average E&W K loss cost due to compaction (£ ha-1 category area) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 0.08 0.01 0.04 0.01 0.05Arable intensive 0.22 0.02 0.13 0.03 0.14Arable extensive 0.08 0.01 0.04 0.01 0.06Grassland improved 0.18 0.02 0.09 0.02 0.14Grassland unimproved 0.14 0.01 0.06 0.01 0.08Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - -

0.09 0.01 0.04 0.01 0.07

The off-site cost of soil compaction

The greenhouse gas impact of compactionThe use of additional resources such as diesel and nutrients to compensate for the effects of compaction has costs in terms of greenhouse gas emission and impacts on the water environment. Using the cost defined in Appendix C, the GHG cost of the extra diesel used in cultivation was estimated to be £6.6 million, most of this associated with extensive arable systems on clayey soils (Table 17). The GHG impact of the estimated use of applied N, P, and K lost because of compaction was calculated to be £9.4 million for N, £0.5 million for P and £0.4 million for K (Table 17).

Table 17. The estimated cost of compaction induced K loss.

GHG cost of diesel penalty (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 32,793.95 11,246.56 15,641.78 784.28 60,467Arable intensive 783,324.19 196,568.30 408,626.25 25,251.63 1,413,770Arable extensive 3,716,557.23 394,221.58 961,302.93 32,407.97 5,104,490


Grassland improved - - - - -Grassland unimproved - - - - -Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 4,532,675 602,036 1,385,571 58,444 6,578,727 GHG cost of increased N loss (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 21,485.00 1,524.86 6,356.88 106.34 29,473Arable intensive 109,258.94 5,904.01 39,085.08 873.70 155,122Arable extensive 3,344,060.53 62,796.95 431,749.73 5,520.87 3,844,128Grassland improved 4,125,561.97 82,562.27 518,590.10 22,550.13 4,749,264Grassland unimproved 552,498.01 9,743.32 74,535.26 31,565.22 668,342Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 8,152,864 162,531 1,070,317 60,616 9,446,329

GHG cost of increased P loss (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 328.29 23.30 97.13 1.62 450Arable intensive 2,574.69 134.32 850.41 17.68 3,577Arable extensive 19,504.73 385.51 2,657.44 33.74 22,581Grassland improved 15,887.92 317.95 1,997.14 86.84 18,290Grassland unimproved 4,154.12 73.26 560.42 237.33 5,025Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 42,450 934 6,163 377 49,924

GHG cost of increased K loss (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 105.78 7.51 31.30 0.52 145Arable intensive 1,834.04 97.06 618.95 13.25 2,563Arable extensive 10,707.56 228.52 1,660.20 19.24 12,616Grassland improved 20,301.22 406.28 2,551.90 110.97 23,370Grassland unimproved 4,933.02 86.99 665.49 281.83 5,967Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 37,882 826 5,528 426 44,662

Impact of nutrients losses in emissions to water and airThe estimated off-site costs for N and P in the water environment have been given in Appendix C. The damage cost of N to rivers and canals and transitional waters was estimated to be approximately £2.0 and £0.1 million respectively, mostly from extensive arable and intensive grassland production on clays (Table 18). The cost of N in drinking water was £2.2 million (Table 18). The cost of P in lakes was estimated to be £1.4 million, again, mostly associated with extensive arable and intensive grassland production on clays (Table 19).


Table 18. The estimated cost of compaction-induced N emitted to water

Cost of N in rivers and lakes (£)Soilscapes

Land use Clay Silt Sand Peat

Urban - - - - -Horticulture 4,612.11 327.34 1,364.61 22.83 6,327Arable intensive 23,454.25 1,267.39 8,390.26 187.55 33,299Arable extensive 717,858.33 13,480.41 92,682.27 1,185.15 825,206Grassland improved 885,620.64 17,723.37 111,324.01 4,840.76 1,019,509Grassland unimproved 118,602.91 2,091.57 16,000.24 6,776.00 143,471Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 1,750,148 34,890 229,761 13,012 2,027,812 Cost f N in transitional waters (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 254.96 18.10 75.43 1.26 350Arable intensive 1,296.54 70.06 463.81 10.37 1,841Arable extensive 39,682.85 745.19 5,123.43 65.51 45,617Grassland improved 48,956.67 979.74 6,153.94 267.59 56,358Grassland unimproved 6,556.31 115.62 884.49 374.57 7,931Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 96,747 1,929 12,701 719 112,096 Cost of N in drinking water (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 4,927.23 349.70 1,457.84 24.39 6,759Arable intensive 25,056.72 1,353.99 8,963.51 200.37 35,575Arable extensive 766,904.55 14,401.43 99,014.60 1,266.12 881,587Grassland improved 946,128.88 18,934.28 118,930.00 5,171.50 1,089,165Grassland unimproved 126,706.21 2,234.47 17,093.42 7,238.96 153,273Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - -

1,869,724 37,274 245,459 13,901 2,166,358

Table 19. The estimated cost of compaction induced P emitted to water

Cost of P in freshwater lakes (£) Soilscapes

Land use Clay Silt Sand Peat Urban - - - - -Horticulture 9,057.04 642.81 2,679.76 44.83 12,424Arable intensive 71,031.14 3,705.58 23,461.21 487.64 98,686Arable extensive 538,101.10 10,635.53 73,314.08 930.86 622,982Grassland improved 438,319.54 8,771.81 55,097.51 2,395.83 504,585Grassland unimproved 114,604.85 2,021.06 15,460.87 6,547.58 138,634Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - -

1,171,114 25,777 170,013 10,407 1,377,311


The cost of additional N emissions to air were substantially larger then for water, particularly for that portion of the N denitrified as N2O, a GHG with a potency that is 311 times that of CO2. The total cost for N2O was estimated to be £73.6 million (Table 20), despite the relatively small quantity of applied fertiliser N being converted to N2O (Table 9). The cost of that portion of N converted to NH3, an air pollutant, was substantially smaller, at £3.5 million (Table 22).

Table 20. The estimated cost of compaction induced N emitted to air as N2O

GHG cost of N as NO2 (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 167,460.24 11,885.21 49,547.35 828.82 229,722Arable intensive 851,595.40 46,017.51 304,640.25 6,809.85 1,209,063Arable extensive 26,064,563.19 489,457.37 3,365,180.72 43,031.25 29,962,233Grassland improved 32,155,808.70 643,513.90 4,042,039.40 175,762.18 37,017,124Grassland unimproved 4,306,327.32 75,942.25 580,949.10 246,028.36 5,209,247Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 63,545,755 1,266,816 8,342,357 472,460 73,627,388

Table 21. The estimated cost of compaction induced N emitted to air as NH3

GHG cost of N as NH3 (£) Soilscapes Land use Clay Silt Sand Peat Urban - - - - -Horticulture 7,865.56 558.24 2,327.22 38.93 10,790Arable intensive 39,999.18 2,161.43 14,308.86 319.86 56,789Arable extensive 1,224,244.63 22,989.66 158,061.52 2,021.16 1,407,317Grassland improved 1,510,348.59 30,225.65 189,853.37 8,255.50 1,738,683Grassland unimproved 202,266.89 3,566.98 27,287.00 11,555.88 244,677Rough grassland - - - - -Forestry - - - - -Woodland - - - - -Wildscape - - - - - 2,984,725 59,502 391,838 22,191 3,458,256

Soil compaction and flooding Land use and management can affect the hydrological characteristics of the landscape and the propensity to generate floods, especially in the rural context that is dominated by agriculturally managed land. Generally, the greater the intensity of agricultural land use, the greater is the runoff of rain water from farmland and the greater the speed at which it is discharged into water courses (Evans, 199015; Niehoff et al., 200216; Naef et al., 200217; Boardman, 200318; Bronstert, 200319; Hall et al., 200320; O’Connell et al., 200421; Pfister et al., 200422).

15 Evans, R. 1990. Soil erosion: its impact on the English and Welsh landscape since woodland clearance. In: J. Boardman, I. D. L. Foster and J. A. Dearing (eds) Soil erosion on agricultural land. Chichester, England, John Wiley & Sons: 231-254.16 Niehoff, D., Fritsch, U., and Bronstert, A. 2002. Land-use impacts on storm-runoff generation: scenarios of land-use change and simulation of hydrological response in a meso-scale catchment in SW-Germany. Journal of Hydrology 267: 80-93.17 Naef, F., S. Scherrer and M. Weiler (2002). A process based assessment of the potential to reduce flood runoff by land use change. Journal of Hydrology 267: 74-79.18 Boardman, J. 2003. Soil erosion and flooding on the eastern South Downs, southern England, 1976-2001. Transactions of the Institute of British Geographers 28: 176-196.19 Bronstert, A. 2003. Floods and climate change: interactions and impacts. Risk Analysis 23(3).


Runoff generation involves two main processes: overland flow generation and flow connectivity (Posthumus et al., 200823). Rain falling on land will either infiltrate into the soil or flow over the land, depending on the intensity of the rainfall, the permeability of the soil and how wet the soil is at the start of the event (antecedent wetness). The less rain that infiltrates, the greater the volume of overland flow.

The probability of runoff from farmland varies according to land use and related management practices associated with differences in the degree of crop cover and the condition of soils as determined by the intensity of soil cultivations, use of heavy field machinery and stocking densities of livestock on grassland.

While it is possible to produce general estimates of the proportion of rainfall that is likely to run off for given soils types, land cover and antecedent soil wetness (Table 22), it is difficult to produce general estimates of contribution to reduce flood flows because these are very context specific.

Table 22.: Relative probability of runoff and soil erosion of various land uses (after Armstrong et al., 1990)24

Least Risk Forestry / WoodlandPermanent PastureSpring CerealsAutumn CerealsShort Term Grass Ley

Greatest Risk Sugar Beet / Maize/ Potatoes / Horticultural Crops

The way that land is managed can influence flow connectivity, that is the speed with which overland and infiltrated water reaches the main watercourses and rivers. Surface water can flow quickly downhill along compacted surfaces, plough lines, tyre tracks, ‘tramlines’ (repeat field travel lines) and farm tracks into water courses. Large fields and long hillslopes, with few boundary features such as trees and hedgerows, tend to increase the rates of flow into water courses (Posthumus et al., 2008)25.

In the UK, studies on the impacts of agricultural land management and flooding (O’Connell et al., 2004, 200726; EA, 200827) concluded that there is evidence of a link between land and soil management and flood generation at the farm and small sub-catchment scale (<10km2) – apparent for example in the incidence of local ‘muddy’ floods (e.g. Boardman, 2003b)28.

There is limited firm evidence, however, to confirm the relationship between land use, soil condition and flood generation for more extreme events at the catchment scale (O’Connell et al, 200729).

20 Hall, J.W., Evans, E.P., Penning-Rowsell, E.C., Sayers, P.B., Thorne, C.R., and Saul, A.J. 2003. Quantified scenarios analysis of drivers and impacts of changing flood risk in England and Wales: 2030 - 2100. Environmental Hazards 5: 51-65.21 O'Connell, P.E., Beven, K.J., Carney, J.N., Clements, R.O., Ewen, J., Fowler, H., Harris, G.L., Hollis, J., Morris, J., O'Donnell, G.M., Packman, J.C., Parkin, A., Quinn, P.F. Rose, S.C., Shepherd M., and Tellier, S. 2004. Review of impacts of rural land use and management on flood generation. R&D Technical Report FD2114. London, DEFRA22 Pfister, L., Kwadijk, J., Musy, A., Bronstert, A., and Hoffmann, L. 2004. Climate change, land use change and runoff prediction in the Rhine-Meuse basins. River Research and Applications 20: 229-241.23 Posthumus, H., Hewett, C.J.M., Morris, J., Quinn, P.F. 2008. Agricultural land use and flood risk management: engaging with stakeholders in North Yorkshire. Agricultural Water Management 95: 787-79824 Armstrong, A.C., Davies, D.B. and Castle, D.A. (1990). Soil Management and the Control of Erosion on Agricultural Land. John Wiley and Sons Ltd., Chichester, UK.25 Posthumus, et al, 2008. Op cit.26 O’Connell, E., Ewen, J., O’Donnell, G., and Quinn, P. (2007) Is there a link between agricultural land-use management and flooding? Hydrology and Earth Systems Science 11:97-107.27 Environment Agency 2008. Delivery of Making Space for Water- HA6 Catchment Scale Land-Use Management & HA7 Land Management Practices. Environment Agency, Bristol.28 Boardman, J., Evans, R., and Ford, J. 2003. Muddy floods on the South Downs, southern England: problem and responses. Environmental Science & Policy 6: 69-8329 O’Connell, et al, (2007) op cit


Similarly, Beven et al. (2008)30 could not identify a clear relationship between observed changes in land management and river flows. Year to year variability in weather, however, makes it difficult directly to attribute changes in the patterns of flows to changes in land use change. Furthermore, understanding the relationship between land use and flood generation is confounded by seasonal effects (some land management changes may only impact on flood flows at certain times of year) and the effects of other changes in the catchment (such as modifications to channel characteristics).

Catchment-scale modelling has indicated that changing land management practices tends to have a greater impact on small and medium events than on large events (Environment Agency, 200831; Salazar et al., 200932). However, although the magnitude of flood peaks may not be greatly reduced, the delay of the flood peaks may be enough to give longer flood warning times. As a result, it is a widely held view that agricultural intensification has been associated with increased flood probability, and that appropriate land management to “retain water in the landscape” could contribute to flood risk mitigation.

The challenge here is to determine the extent to which the condition of soils themselves affects the run off from farm land with propensity to generate flooding and flood damage costs.

The Costs of Flooding

Urban areas Flooding has become more problematic in England and Wales 33, with the annual cost of flooding in excess of £1.4bn. A further £1bn per year is spent on flood risk management34 35. Currently about 550,000 households are at serious risk of flooding36, that is more often than a 1.3% chance in any one year. A further 5 million properties exposed to moderate to low probability of flooding (between 0.5% and 1.3% chance of flooding each year). Climate change, however, could increase their exposure to higher levels of flood risk37. The greatest share of total annual flood costs is borne by urban households and businesses, evident in the profile of the 2007 floods in England which resulted in estimated economic costs of £3.2 billion38. The Foresight Future Flooding Project39 identified a possible increase in river and coastal flood annual damage costs by 2080 of £17-23 billion in 2010 prices under future consumption oriented scenarios in the absence of additional measures to control flood risk.

Data, methods and guidance are available to support the economic appraisal of flood risks ,40. There is comprehensive guidance on flood estimation costs for urban areas, covering residential, business

30 Beven, K. Romanowicz, R., Young, P., Holman, I.P., Posthumus, H., Morris, J., Rose, S., O’Connell, E., and Ewen, J. 2008. An event classification approach to the identification of hydrological change. Defra Flood and Coastal Management Conference. Manchester, 1-3 July 200831 Environment Agency 2008 opcit32 Salazar, S., Francés, F., Komma, J., Blöschl, G., Blume, T., Franke, T. and Bronstert, A. 2009. Efficiency of non-structural mitigation measures: “room for the river” and “retaining water in the landscape”. In Flood Risk Management: Research and Practice. Samuels et al. (eds). Taylor & Francis Group. London.33 Pitt, M. 2008. Learning Lessons from the 2007 Floods. Cabinet Office, London.34 Environment Agency, 2009a Flooding in England, Environment Agency, Bristol 35 Environment Agency, 2009b Flooding in Wales, Environment Agency, Cardiff36 Foresight Flood and Coastal Defence. 2004. http://www.bis.gov.uk/foresight/our-work/projects/published-projects/flood-and-coastal-defence, 37 Environment Agency, 2009c Investing for the Future. Flood and Coastal Risk Management in England, Environment Agency, Bristol38 Chatterton J., Viavattene, C., Morris, J., Penning-Rowsell, E., and Tapsell, S. (2010) The Costs of the Summer 2007 Floods in England. Science Project SC070039. Environment Agency. http://publications.environment-agency.gov.uk/pdf/SCHO1109BRJA-e-e.pdf39 Foresight Flood and Coastal Defence. 2004. http://www.bis.gov.uk/foresight/our-work/projects/published-projects/flood-and-coastal-defence40 Defra. 2009. Appraisal of Flood and Coastal Erosion Risk Management. Department for Environment, Food and Rural Affairs, London. http://www.defra.gov.uk/environment/flooding/documents/policy/guidance/erosion-manage.pdf. For Scotland see: http://www.scotland.gov.uk/Topics/Environment/Water/Flooding, and Flood Risk Management (Scotland) Act 2009: http://www.legislation.gov.uk/asp/2009/6/pdfs/asp_20090006_en.pdf


http://www.scotland.gov.uk/Topics/Environment/Water/Flooding

http://www.defra.gov.uk/environment/flooding/documents/policy/guidance/erosion-manage.pdf

http://www.bis.gov.uk/foresight/our-work/projects/published-projects/flood-and-coastal-defence


and infrastructure41. Average annual damage costs to residential properties, usually the major category of flood damage costs, vary according to standards of protection and flood warning lead times. For example, a property protected against the 1 in 100 year flood event (ie with a 1% annual probability of flooding) has an equivalent annual flood damage cost of £76 without flood warning. The cost of flood damage to commercial and industrial property and infrastructure depend on the type and size of premises and facilities affected.

Direct intangible impacts on flood victims include stress and health risks. A survey of households 42 showed a weighted average willingness to pay of £200/household per year to avoid the intangible costs associated with 1% per year chance of flooding, equivalent to a present value sum of about £5000 over 50 years. Evidence from the 2007 floods suggests this is probably an underestimate 43. This equates to a willingness to pay to avoid intangible costs of £110 million/year for the 550,000 households in England and Wales at serious risk of flooding.

Estimated weighted average annual damage (WAD) costs for residential properties by standards of protection and flood warning lead times (£/residence. 2010 prices) are given in Table 23 based on Penning Rowsell et al (2005) and updated to 2010 prices.

Table 23. Estimated weighted average annual flood damage (WAD) costs for given standards of protection.

Standard of protection Residences Non residencesyears £/property £/property

5 3490 977210 1772 496150 354 991

100 88 248200 36 100

Note: estimates show WAD for properties protected to the given standard. Residences - WAD based on Penning-Rowsell (2005, updated to 2010 prices) for flood without warning , plus 12% extra car damage and temp accommodation costs based on 2007 flood event costs (Chatterton et al, 2009). Non residential/business premises based on ratio of residential: business costs of 1: 2.8 (from Chatterton et al, 2009).

The cost estimates in Table 23 were shown to be consistent with the cost recorded in the severe 2007 floods in England44. Damage to 60,000 residences averaged £24,000/property, with a further £2,900/property due to vehicles and temporary accommodation ( an extra 12%) . Damage to 8,000 business premises averaged £55,000/business, plus an additional £20,000/business in lost or disrupted activity (an extra 40%). Damage and disruption to critical infrastructure and services was £674 million. The ratio between costs of the combined damage to households and businesses and the total damage costs of the event was about 1: 1.5.

Agricultural areas Flood generated on farmland can also impact on other farmed areas. Agricultural land is afforded a lower protection against flooding than urban land. Agricultural land is sometimes used to store water in preference to flooding of urban areas.

The cost of a flood event on agricultural land varies mainly according to land use and time of year, ranging from negligible costs for winter flooding of extensive grassland in winter to over £5,000/ha for summer flooding of vegetable crops45. Frequent flooding (and prolonged soil wetness) is associated

41 Penning-Rowsell E, Johnson C, Tunstall S, Tapsell S, Morris J, Chatterton J, and Green C, (2005) The Benefits of Flood and Coastal Risk Management, A Manual of Assessment Techniques. Flood Hazard Research Centre, Middlesex University, Enfield, London.42 RPA and FHRC et al., 2004. The Appraisal of Human Related Intangible Impacts of Flooding. R&D Technical Report FD2004/TR. Defra, London43 Foresight Flood and Coastal Defence. 2004. http://www.bis.gov.uk/foresight/our-work/projects/published-projects/flood-and-coastal-defence, 44 Chatterton et al, 2010. opcit




with lower value cropping, such that flood damage costs are lower. Almost 90% of agricultural flood costs related to damage to crops and grassland.

According to Defra, there are about 1,336,000 ha of agricultural at risk of flooding in England and Wales, of which 62 % are liable to flooding by rivers only, 23 % by sea only and 15% by both. About 421,500 ha currently benefit from flood defences in England and Wales (of which 70,000 ha (17%of total) are grade 1 and 2), and 424,000 benefit from coastal defences (of which 158,000 ha (37%) are grade 1 and 2). About 1,280,000 ha in England and Wales also benefit from pumped drainage to avoid either flooding or waterlogging, over 90% of which is used for agriculture, and a third of it in the Anglian region.

An assessment of land use, estimated flood damage costs, and flood return period in years for defended and undefended areas in England and Wales (Table B2) shows that flood defence reduces expected annual damage costs from river flooding by £5.2 million, and from coastal flooding by £117.7 million46. These costs are small compared with the costs of flooding in the urban sector.

Table 24. Expected annual damages of flooding on agricultural land in protected and unprotected areas in England and Wales

Expected Annual Damage with defences (£ million)

Expected Annual Damage without defences (£ million)

River Coastal River CoastalEngland 4.25 6.47 9.26 117.3Wales 0.87 1.27 1.08 8.25

Source: Roca et al, 201047

Estimating changes in flood damage costs attributable to soil condition

It is known that land use can affect run off and flood generation from farm land, and that this relationship varies according to soil type, and hence soilscape. In particular, as discussed earlier, the probability of erosion and compaction that can cause run off are strongly correlated with soilscape. It may be possible therefore to link soil condition to flood generation and hence costs of flooding.

For this purpose, operating at the broadscale, the following approach (Figure AA) was used to assess the likely impact of changes in soil condition on flood damage costs:

A catchment flood management tool48, developed by JBA consultants and Cranfield University, containing information on catchment flood areas, land cover and soil (HOST) classes, was used to assess the impact of changes in soil condition on relative changes in the mean depth of run off (mm) from land for given return period events.

The Flood Estimation Handbook49 was used to determine ‘catchment descriptors’ for selected catchments that were then fed into the Revised Flood Handbook (ReFH) Rainfall run off method 50. This enabled estimates of changes in run off to be converted to relative changes in peak flows for given return period events. For the purpose here, this is interpreted as a % change in the probability of an event of a given magnitude, eg a change in the probability of the 100 year event.

Information was derived from the National Flood Risk Assessment (NaFRA) Data Base on the number and type of properties at exposed to given return period flood events (eg for the 100 year flood).45 Posthumus, H., Morris, J., Hess, T., Neville, D., Philips, E. and Baylis, A., 2009. Impacts of the summer 2007 floods on agriculture in England, Journal of Flood Risk Management, 2009: 1-8.46 Roca, M., Bast, H., Panzeri, M, Hess, T., and Sayers, P. (2010). Developing the evidence nase to describe the flood and coastal erosion risk to agricultural land in England and Wales. Defra R&D Technical Report, FD2634/TR, May 2010. HR Wallingford Ltd, Wallingford.47 Roca et al, 2010 op cit48 Environment Agency. 2009. Land Management CFMP Tool – User Guide, Environment Agency. Bristol 49 Institute of Hydrology. 1999. Flood Estimation Handbook , inst Hydrology, Wallingford, 28850 Institute of Hydrology. REFH Rainfall Run off Method CD ROM,


Estimates of relative changes in the probability of events of a given magnitude were combined with information on the costs of an event to determine a change in flood damage. In this way changes in soil condition were linked to changes in flood damage.

This process has not been completed in time for reporting here due to data management problems, although it is anticipated that this will be carried out in due course51.

For the moment, a simplistic assessment is made while further work is underway.

.

Soilscapes: host class and

land cover

Climate zone∆ Soil

condition

∆ Depth of runoffmm (Qn)

Catchment hydrograph

Flood damage£/unit property

∆ Flood ‘depth’Qn

∆ Flood damage £/Qn

∆ Properties at risk

Figure 1. Approach to estimating the link between soils condition associated with compaction and flood damage costs using the catchment

The catchment flood management tool was used to explore the implications of changes in soil condition on run off with potential to cause flooding. Error: Reference source not found (and supporting notes) shows scenarios of soil condition. Assuming current scenario of land is ‘fair’, alternative scenarios assuming a switch to ‘poor’ and a switch to ‘good’ respectively were run for the non-urban areas within the policy areas of each of the catchment flood management plan areas. Table 26 shows the change in the depth of run-off weighted area based on soilscapes (land cover and soil type) on 8.9 million ha for which data are available (of an estimated 13.7 million ha of total catchment areas). A switch to good soil management suggests a reduction in the average depth of runoff (mm) of about 10% for median annual flood and about 7% reduction for the 75 year return period rainfall event that is associated with the threshold for serious risk to property. A further reduction in soil condition to poor would result in an increase of about 7.5% in average runoff depth for the median rainfall event, and about 5% for the Q75 precipitation event. The range good to poor indicates an 11% -12% change in runoff depth.

These order of impacts of changes in run off were similar in magnitude to those based on a detailed application of the method by Hess et al 52 using data from about 518 CFMP policy units. They found that a switch from the fair scenario (as per Table 25) to a scenario comprising an increase in good to 50% and 0% land in the poor category (everything else the same) reduced runoff depth by 5% or less in most areas

51 This is being undertaken as part of an MSc Thesis project at Cranfield University52 Hess, T.M., Holman, I.P., Rose, S.C., Rosolova, Z., Parrott, A., (2010) Estimating the impact of rural land management changes on catchment runoff generation in England and Wales. Hydrological Processes. 24:1357–1368.


using the method to estimate the impact of soil management on base flow, Homan et al 2009 53 showed that similar changes in soil management had the effect of increasing the Base Flow Index by up to 10% in most catchments. Maintaining base flows are particularly important for securing river water quality and related freshwater services, including habitats. This is especially so under conditions of climate change.

It seems reasonable here, given the purposes, to use the switch from fair to good soil management scenarios to estimate the implications of soil degradation for runoff and potential flooding. The implications for base flow, though important, are not considered here, but their importance is recognised.

Table 25. Assumed scenarios for soil condition associated with run off from rural land

% of land area by soil conditionScenario modal soil condition Excellent Good Fair Poor Very PoorPoor 10 10 20 40 20Fair 10 20 40 20 10Good 20 40 20 10 0

Notes: Excellent: good top soils and upper sub soil structure to minimise surface runoff and transmission from field, eg grass strips, hedges, conservation tillage. Good; good soil structure plus some activities to reduce run off (eg conservation tillage). Fair : some evidence of soil structural degradation such as compaction, or practices that increase runoff eg tramlines across contour, long unchecked hillslopes, fine bare seed beds. Poor: evidence of poor structure such as compaction by machinery or animals under wet conditions leading to run off and unchecked transmission of runoff from fields. Very Poor: extensive structural damage associated with compaction and/or erosion and high and uncontrolled transmission of run off to water courses. (after Holman et al, 2011. Hess et al,2010).

Table 26 Estimated percentage changes in the average depth of runoff (mm) in catchment flood management plan areas for given scenarios of soil condition by given rainfall return period events (Q years)

Qmed Q5 Q10 Q50 Q75 Q100 Change in soil condition from fair to good scenario -9.86 -8.71 -7.75 -6.65 -6.49 -6.39 Change in soil condition from fair to poor scenario 7.48 6.74 5.97 5.00 4.83 4.72

Sensitivity analysis using the catchment tool showed that the impact of soil on condition on runoff tends to be greater for more intensively farmed areas (Error: Reference source not found).

Table 27. Broadscale changes in median run off depth (mm) from rural land associated with changes in soil condition for given soilscapes

Catchment land cover

Typical soil types Estimated % change in the mean Q75 year annual run off depth (mm) associated with a change in soil condition scenario

Poor to fair Fair to good Poor to goodExtensive arable Mixed mainly clay loams

and sandy clays +/-3% +/-5% +/-10%

Intensive arable Non–clay: silts, sands and peats

+/-5% +/-7% +/-15%

Grassland Clays +/-3% +/-7% +/-10%

The assessment here suggest that, under present practices, the probability of compaction of agricultural soils, that account for about 75% of the landscape is likely to be high, especially on arable

53 Holman, I.P., Hess, T.M. and Rose, S.C. (2011) A broad-scale assessment of the effect of improved soil management on catchment Baseflow Index. Hydrological Processes 25(16) 2563-2572.


cropping on predominantly clay soils, intensive root cropping and heavily stocked grasslands. A crude estimate is that soil degradation could account for between 3% and 10% increase in the depth of run off for the representative 75 year event (the commonly used threshold for serious property flooding) across a range of soilscapes, with a central estimate of 7% used here.

As referred above, current estimated total national flood costs to properties are about £1.4 bn with an additional £1 bn spent on flood risk management per year: a total of £2.4 bn.

If it is assumed that this order of increase in run off occurs for all return period rainfall events, and that this leads to an equivalent increase in the probability of flooding at the catchment scale, flood damage costs could increase by between £72m and £240m per year, with a central estimate of £168m/year (based on a 7% increase in flood risk). It is noted that the approach adopted here specifically attributes changes in flooding to changes in soil condition (for given land uses). Some agricultural land uses are known to be associated with more rapid run off than others, as referred to earlier. The estimate here of £168 million compares with the estimate by the Environment Agency (2002)54 that attributed about 14% of flood events and direct flood damage costs (£1.4 bn per year) with run-off from farm land, producing an estimate of about £200 million per year (£336 million if all £2.4 bn flood damage and management costs are assumed).

At the time of writing a more detailed assessment is being carried out as indicated above.

Summary of compaction induced costsA summary of the physical results, and the on-site and off-site costs are shown in Table 28. The total area of the unsealed landuse/soil type categories was 13.9 million ha, of which approximately 28% or 3.9 million ha was estimated to be affected by compaction. Overall, the estimated on-site impacts of £204 million were smaller than the off-site costs of £273 million. The cost associated with lost productivity was relatively large (£162 million), although other losses such as N losses (£23 million), and additional draught power requirements (£17 million) were also large. The main off-site costs were associated with flooding and flood damage and the emission of N2O from the additional compaction-induced fertiliser N loss.

Table 28. Summary of compaction induced costs (£)

Physical data Total Category areas (ha) 13,928,575 Total areas at risk within categories (ha) 3,858,670 Proportion at risk (%) 28% Additional diesel use (l yr-1) 41,611,174 Fertiliser N loss (t yr-1) 37,044 Fertiliser P loss (t yr-1) 979 Fertiliser K loss (t yr-1) 1,751 On-site costs Total E&W cost of additional diesel penalty (£) 17,476,693 E&W additional diesel in risk area (£ ha-1) 4.53 E&W additional diesel (£ ha-1) 1.25 Total E&W productivity loss due to compaction (£) 161,669,867 E&W productivity loss due to compaction in risk area (£ ha-1) 41.9

Total E&W productivity loss due to compaction in total area (£ ha-

1) 11.6

54 Environment Agency. 2002. Agriculture and Natural Resources: Benefits, Costs and Potential Solutions, Environment Agency, Bristol.


Total E&W N loss cost due to compaction (£) 22,967,545.4 Average E&W N loss cost due to compaction (£ ha-1 risk area) 6.0

Average E&W N loss cost due to compaction (£ ha-1 category

area) 1.6 Total E&W P loss cost due to compaction (£) 665,651 Average E&W P loss cost due to compaction (£ ha-1 risk area) 0.17

Average E&W P loss cost due to compaction (£ ha-1 category

area) 0.05 Total E&W K loss cost due to compaction (£) 910,747 Average E&W K loss cost due to compaction (£ ha-1 risk area) 0

Average E&W P loss cost due to compaction (£ ha-1 category

area) 0.07 Off-site costs Cost of N in rivers and lakes (£) 2,027,812 Cost f N in transitional waters (£) 112,096 Cost of N in drinking water (£) 2,166,358 Cost of P in freshwater lakes (£) 1,377,311 GHG cost of diesel penalty (£) 6,578,727 GHG cost of increased N loss (£) 9,446,329

GHG cost of increased P loss (£) 49,924 GHG cost of increased K loss (£) 44,662

GHG cost of diesel penalty (£) 6,578,727 GHG cost of N as NO2 (£) 73,627,388 GHG cost of N as NH3 (£) 3,458,256 Flooding (£) 168,000,000 Total costs Total onsite cost 203,690,504 Total offsite cost 273,467,590


Documents

Appendix H: Cost of compaction - Defra, UK - Science …sciencesearch.defra.gov.uk/Document.aspx?Document=10138... · Web viewThe cost of soil degradation in England and Wales Appendix