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Transcript
Innovative methods of soil erosion control Royal Society of Chemistry 21st January 2013 Jane Rickson Professor of Soil Erosion and Conservation National Soil Resources Institute (NSRI) School of Applied Sciences Cranfield University Outline of the talk • Attitudes to soil • The role of soil chemistry Soil erosion in Ross on Wye, 2009 • The importance of soil • Threats to soil resources • Soil protection - Innovative and practical solutions • Geotextiles for soil erosion control • Concluding thoughts 1. Attitudes to soil • “….And what do you do for a living?” • Soil’s poor “PR”: • ‘mud’ used in a figurative sense meaning worthless or polluting (16th century) • ‘mudslinging’ • ‘drag his name through the mud’ • ‘His (her) name is mud / Mudd’ • ‘stick in the mud’ • Connotations of the word “soil” http://www.visualthesaurus.com/app/view 1. Attitudes to soil • Cultural context • Soil science (more later) ….and the arts 1. Attitudes to soil “The thin layer of soil covering the earth's surface represents the difference between survival and extinction for most terrestrial life.” From: Doran, J.W. and T.B. Parkin. 1994. Defining and assessing soil quality. In J.W. Doran, D. C. Coleman, D.F. Bezdicek and B.A. Stewart (eds.), Defining Soil Quality for a Sustainable Environment. Soil Science Society of America. 2. The role of soil chemistry • Soil chemical properties • • • • Carbon Nutrients Trace elements pH • Chemical processes in soils • Carbon and nutrient cycling • Carbon storage • Gaseous emissions (greenhouse gases etc) 2. The role of soil chemistry The Carbon Cycle http://www.gfdl.noaa.gov/anthropogenic-carbon-cycle 2. The role of soil chemistry http://www.tececo.com/sustainability.role_soil_sequestration.php The Soil Carbon Cycle 3. The importance of soil 1. Can 9 million people be fed [and housed and transported] equitably, healthily and sustainably? 2. Can we cope with future demands for water? 3. Can we provide enough energy to supply the growing population coming out of poverty? 4. Can we mitigate and adapt to climate change? 5. Can we do all of this and reverse declining biodiversity and loss of ecosystems Sir John Beddington, Chief Scientific Advisor to HM Government, Foresight Report; “The Perfect Storm” 3. The importance of soil 1. Can 9 million people be fed [and housed and transported] equitably, healthily and sustainably? Can soil address these challenges? 2. Can we cope with future demands for water? 3. Can we provide enough energy to supply the growing population coming out of poverty? 4. Can we mitigate and adapt to climate change? 5. Can we do all of this and reverse declining biodiversity and loss of ecosystems Sir John Beddington (Chief Scientific Advisor to HM Government) “The Perfect Storm” 3. The importance of soil • Soil provides vital ecosystems goods and services (or “functions”) Ecosystem service Examples Provisioning of material goods and services Agricultural production (food, fibre, fodder, fuel) Water storage and supplies Land for development (residential, industry, infrastructure) Regulation of ecosystem processes Flood control (water storage) Carbon storage (CO2 emissions: mitigate climate change) Cultural, non-material services Landscape aesthetic Recreation / amenity, protection of heritage Supporting services Habitats, biodiversity Soil formation • Sustainability (economic, environmental and social pillars) • Human health and wellbeing (Millennium Ecosystem Assessment) • Individuals’ and national economic status 3. The importance of soil 1. Can 9 million people be fed [and housed and transported] equitably, healthily and sustainably? Soil has a role in addressing these challenges…however……. 2. Can we cope with future demands for water? 3. Can we provide enough energy to supply the growing population coming out of poverty? 4. Can we mitigate and adapt to climate change? 5. Can we do all of this and reverse declining biodiversity and loss of ecosystems 4. Threats to soils and their functions • As identified in the EU Thematic Strategy for Soil Protection (2006) • • • • • • • • • Soil erosion* Compaction Loss of organic matter Surface sealing Contamination Loss of biodiversity Salinisation Acidification Landslides 4. Threats to soils and their functions “Soil degradation involves both the physical loss (erosion) and the reduction in quality of topsoil, associated with nutrient decline and contamination. It affects soil quality for agriculture and has implications for the urban environment, pollution and flooding. Currently, 2.2 million tonnes of topsoil is eroded annually in the UK and over 17% of arable land shows signs of erosion. This POSTnote examines the…challenges and opportunities for soils in a changing climate. These include the potential for using degraded and polluted soils in the built environment for brownfield redevelopment as well as the possibility of using soils to mitigate carbon emissions.” 4. Threats to soils and their functions Example: Soil erosion in England & Wales &W Typical erosion rate range (t ha-1 year-1) Land use affected Exported off field Wind erosion Tillage erosion Co-extraction with root crops and farm machinery Water 0.1 – 2.0 0.1 – 10.0 0.1 – 5.0 0.1 – 15.0 Arable Arable Arable, pasture, upland No Yes Yes Arable, upland, some pasture Yes Comparison of the magnitude of soil loss for different erosion processes (Owens et al., 2006). N.B. Rate of soil formation ≈ 1 t ha-1 year-1 (Verheijen et al., 2009) 4. Threats to soils and their functions Estimated annual costs of soil erosion to UK economy in £million (2000 prices) £ million % contribution from agriculture Soil organic loss, leading to carbon dioxide loss 74 95% On-farm costs (additional fertilisers, etc.) 8 100% Accidents/stream channels (i.e. off-site costs mainly related to clean-up operations) 8.2 95% Effects on flooding 115 14% TOTAL ANNUAL COST (£ million) 205 Source: Environment Agency 2002. Agriculture and natural resources: benefits, costs and potential solutions. Bristol. What can be done? 5. Innovative and practical solutions Engineering measures Field structures Terraces Storm water drains Cut off channels Lined waterways 5. Innovative and practical solutions Soil management measures Use of tillage and cultivation practices direction of tillage operations residue management conservation tillage (minimum till, zero till) Use of soil amendments Soil conditioners Organic matter additions 5. Innovative and practical solutions Agronomic measures The use of vegetation and simulated vegetation • Mulches • Geotextiles “Bioengineering” practices Geotextiles • Definition: “a permeable textile materials, used with foundation, soil, rock, earth or any geotechnical engineering related material”. • Not a new technique • ancient Egypt - use of cotton to reinforce building materials • use in civil engineering increased in 1960s • availability of cheap, synthetic textiles • rapid urban and infrastructural development and expansion • implications for world trade and economic development Geotextile applications • Applications • Separation • Filtration • Drainage • Soil reinforcement / slope stability enhancement • Soil erosion control* • Vegetation management Total global geotextile market ≈ 1000 million m2 per annum (2000 data) Geotextiles for soil erosion control • Fibres used • woven • non-woven • knitted • Structure of geotextiles: • • • • Mats Webs Grids Sheets • Two or three dimensional • Natural versus synthetic • Buried or surface laid Geotextiles for soil erosion control: Natural products • Materials • • • • • • • • • • • wood fibre / straw coir jute Others: cotton, wool, paper, sisal, banana leaves?! bio- / light degradable environmentally friendly organic matter available nutrients aesthetics costs – see later temporary other, 3% jute, 15% coir, 22% wood fibre / straw, 60% Geotextiles for soil erosion control: Synthetic products • Materials • polypropylene, nylon, polyester, polyamide, polyethylene • permanent • resist acids, alkalis, microbiological activity • may interact with vegetation to provide composite methods of soil erosion control (synergy?) • aesthetics • costs – see later • chemical lobby on Standards Committees Geotextiles for soil erosion control • Surface laid products • simulate canopy and stem effects of vegetation • protect against surface erosion processes by • intercepting rainfall • storing rainfall • imparting roughness to flow • reducing flow velocity – infiltration – reduced detachment and transport capacity of flow Geotextiles for soil erosion control • Buried products • simulate root effect • additional tensile strength added to soil matrix • encourages infiltration through the loose, unconsolidated backfill Geotextiles for soil erosion control Product name Material Characteristics Weight Type (g m-2) Area of geotextile (%) Buried / Surface installation 1 Enkamat (Surface) 3D nylon mesh 265 60 Geomat S 2 Enkamat (Buried) 3D nylon mesh 265 60 Geomat B 3 Geojute 100% jute woven mesh 500 54 Bionet S 4 Bachbettgewebe 100% coir woven mesh 700 58 Bionet S 5 Fine geojute 100% jute woven mesh (fine) 292 80 Bionet S 6 Enviromat Wood chips in a photodegradable synthetic mesh 450 94 Biomat S 7 Tensarmat 3D Polypropylene mat 450 38 Geomat B Geotextile costs installation time (hrs/ha) * $’000 / ha** $ / m2** min max min max jute woven 38 1.48 1.73 14.8 17.3 straw blanket 38 1.98 2.59 19.8 25.9 coconut fibre blanket 38 3.2 3.5 32.0 35.0 coconut fibre mesh 38 7.4 8.2 74.0 82.0 straw/coconut fibre blanket 38 2.5 3 25.0 30.0 wood fibre blanket 38 1.98 2.59 19.8 25.9 curled wood fibre blanket 38 1.98 2.59 19.8 25.9 biodegradable fibres with synthetic netting 38 7.4 8.9 74.0 89.0 synthetic fibre with synthetic netting 96 8.4 9.9 84.0 99.0 bonded synthetic fibres 96 11.1 13.6 111.0 135.00 *assumes a 2 person crew. **cost data from Caltrans Erosion Control Manual (Draft), Training materials 2003) Global markets for erosion control geotextiles natural erosion control products* synthetic erosion control products total erosion control product market Region Consumption (Mm²) (%) Consumption (Mm²) (%) Consumption (Mm²) (%) North America 57 66 44 51 101 58 Western Europe 17 20 35 40 52 30 World residual Totals 12 86 14 100 8 87 9 100 20 173 12 100 Annual growth rate estimated at 8.5% Legislative context driving the expansion of geotextile markets in Europe • Water Framework Directive • ‘good ecological status’ • Draft Soil Framework Directive • • • • Erosion is a “major threat to soil resources Areas at risk Risk reduction targets Incentives / fines • Sustainable Urban Drainage (SUDs) Geotextiles for soil erosion control • Evaluating geotextiles for erosion control • How do these products work? Geotextiles for soil erosion control High rainfall intensity, Clay as % of control High rainfall intensity, Sand as % of control Low rainfall intensity, Clay as % of control Low rainfall intensity, Sand as % of control 160 Soil loss as % of control 140 120 100 80 60 40 20 0 control 34 geojute fine geojute enviramat natural fibre products bachbett enkamat s enkamat b tensarmat synthetic products 6.Correlation Validation of between resultsgeotextile properties and erosion control effectiveness coefficients (soil loss; as measured when rainfall and runoff processes are combined) Correlation with erosion control effectiveness Significance of correlation Area of geotextile (%) -0.8723 p<0.05 Depth of flow (mm) -0.8302 p<0.05 -0.7095 p<0.05 Water holding capacity (%) -0.8369 p<0.05 Weight (g m-2) -0.7189 p<0.05 Wet weight as % after 24 hours -0.8419 p<0.05 Wet weight as % after 48 hours -0.5990 p<0.10 Cost ($ m-2) 0.2970 NS Flow velocity (m s-1) -0.0681 NS Mean yarn diameter (mm) -0.4667 NS Tensile strength (kN m-1) 0.2939 NS Thickness (mm) 0.3730 NS Geotextile property Manning’s roughness coefficient (n) / Geotextile Induced Roughness Source: Rickson, 2000 35 Geotextiles for soil erosion control • This work has also identified the salient properties of erosion control geotextiles: • % cover • water holding capacity • geotextile induced roughness • % weight when wet • depth of flow ponded • Can be used by designers and manufacturers to make more effective products • Can help specifiers / contractors select most effective products Geotextiles for soil erosion control • As well as control of erosion, geotextiles can be used to enhance vegetation establishment and growth. This is achieved by: • Control of erosion (of soil + seeds, fertilisers and seedlings) • Modifying site microclimatic conditions • Temperature • Moisture content • Light interception • Improving soil properties • Nutrients • Organic matter (5 t/ha - jute?? - do we need less top soil then?) • Soil structure Case study: Cobrey Farms, Herefordshire Case study: Cobrey Farms Images c/o Dr Rob Simmons, NSRI Grassed waterway specifications with and without a geotextile lining (Manning equation) Without a geotextile lining Water Slope Depth* way o () (m) Section 1 5.06 0.049 2 5.06 0.049 3 3.92 0.059 4 2.51 0.083 Total *plus 20% freeboard. Width (m) 11.8 29.1 38.2 62.5 Area 2 (m ) 224 873 2032 4180 7309 With a geotextile lining Depth* (m) Width (m) Area 2 (m ) 0.08 0.08 0.097 0.136 5.23 12.8 16.8 27.5 116 384 893 1839 3232 Geotextiles for soil erosion control • The use of geotextiles in erosion control and slope stabilisation Immediate erosion control Long term synergistic effects with establishing vegetation Use of sustainable resources Use of biodegradable, environmentally friendly products May contribute organic matter, C, nutrients May encourage microbiological activity in the soil Increasing data base on geotextile effectiveness in controlling sediment Site aesthetics Relevance to markets? Technical performance alone is not enough….. • Sustainability procurement by end users / specifiers • Public and private agencies: • Governments • Highway Agencies • Civil engineering contractors • Supermarkets • Agricultural producers • Impacts on ecosystem goods and services (Millennium Development Goals) • Environmental Impact Assessments throughout the supply chain Relevance to markets? Technical performance alone is not enough….. Environmental Impact Statement for the application of jute geotextiles Area of impact Description of impact Geographical level of issue importance* I Human Beings e.g. farmer livelihoods Flora & fauna e.g. impact of jute production on fauna Soil & Geology e.g. control of soil loss Water e.g. reduction in sedimentation and flooding risks N R D Impact Nature** L *I = International; N = National; R = Regional; D = District; L = Local **ST = short term; LT = long term; R = Reversible; IR = Irreversible Significance Mitigation measures 6. Conclusions • Geotextiles are effective at controlling soil erosion and establishing vegetation • Understanding geotextile properties is critical (including chemical properties?) • Laboratory trials need more field validation • Effect of changing weather patterns? • Technical performance alone is not enough • Demand for erosion control geotextiles is likely to expand Concluding thought….. “The nation that destroys its soil destroys itself” Franklin D Roosevelt Thank you for your attention Any questions?