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

• The importance of soil

• Threats to soil resources

• Soil protection - Innovative and practical solutions

• Geotextiles for soil erosion control

• Concluding thoughts

Soil erosion in Ross on Wye, 2009

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 The Soil Carbon Cycle

http://www.tececo.com/sustainability.role_soil_sequestration.php

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?

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”

Can soil address these challenges?

3. The importance of soil

• Soil provides vital ecosystems goods and services (or “functions”)

• Sustainability (economic, environmental and social pillars) • Human health and wellbeing (Millennium Ecosystem Assessment) • Individuals’ and national economic status

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

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

Soil has a role in addressing these challenges…however…….

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

Wind erosion Tillage erosion

Co-extraction with root crops and farm machinery

Water

Typical erosion rate range (t ha-1 year-1)

0.1 – 2.0 0.1 – 10.0 0.1 – 5.0 0.1 – 15.0

Land use affected

Arable, upland, some

pasture

Arable Arable Arable, pasture, upland

Exported off field Yes No Yes 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)

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.

4. Threats to soils and their functions

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

• 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

Geotextiles for soil erosion control: Natural products

wood fibre / straw, 60%

coir, 22%

jute, 15%

other, 3%

• 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: Synthetic products

• 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

28

• Buried products

• simulate root effect

• additional tensile strength added to soil matrix

• encourages infiltration through the loose, unconsolidated backfill

Geotextiles for soil erosion control

Geotextiles for soil erosion control

Product name Material Characteristics Weight

(g m-2)

Area of

geotextile

(%)

Type 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) * $ / m2** $’000 / ha**

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 12 14 8 9 20 12

Totals 86 100 87 100 173 100

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)

• Evaluating geotextiles for erosion control

• How do these products work?

Geotextiles for soil erosion control

34

Geotextiles for soil erosion control

0

20

40

60

80

100

120

140

160

control geojute fine geojute enviramat bachbett enkamat s enkamat b tensarmat

So

il lo

ss a

s %

of

co

ntr

ol

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

natural fibre products synthetic products

6. Validation of results

Geotextile property 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

Manning’s roughness coefficient (n) /

Geotextile Induced Roughness -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

Correlation coefficients between geotextile properties and erosion control effectiveness (soil loss; as measured when rainfall and runoff processes are combined)

35 Source: Rickson, 2000

• 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

Geotextiles for soil erosion control

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 With a geotextile lining

Water

way

Section

Slope

(o)

Depth*

(m) Width (m)

Area

(m2)

Depth* (m) Width

(m)

Area

(m2)

1 5.06 0.049 11.8 224 0.08 5.23 116

2 5.06 0.049 29.1 873 0.08 12.8 384

3 3.92 0.059 38.2 2032 0.097 16.8 893

4 2.51 0.083 62.5 4180 0.136 27.5 1839

Total 7309 3232

*plus 20% freeboard.

• 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

Geotextiles for soil erosion control

• 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…..

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*

Impact Nature** Signifi-cance

Mitigation measures

I N R D L

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

*I = International; N = National; R = Regional; D = District; L = Local

**ST = short term; LT = long term; R = Reversible; IR = Irreversible

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?