River Bank Protection W Pol Tm WT's Fact Sheet

7/30/2019 River Bank Protection W Pol Tm WT's Fact Sheet

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River Bank ProtectionWorking with nature to prevent and control bank erosion

Protecting Wildlife for the Future

Water Policy Team : Fact Sheet 4

Introduction

Rivers are dynamic ecosystems meandering andchanging course within the floodplain. Banks areconstantly being eroded and are reformed inareas where silt is deposited. In their naturalstate rivers form green arteries within ourcountryside, providing both habitat for riverspecies and corridors for movements of wetlandspecies. Rivers, particularly those in the UKlowlands, are not usually free to follow theirnatural course. Engineering techniques have beenused to alter the course of rivers, for bank

protection and to protect land and property fromflooding. To prevent erosion in the 20th century,engineering solutions typically involved cladding asloping soil bank with hard materials including:

rip-rap (largebolders)

concrete blocks orprecast concreteunits

metal sheet piling

gabions (wire

mesh cages withtightly packedstones)

These attempts toprevent erosion ofriver banks canrarely offer a long-term solution, sincethey do nothing toaddress the causes

of erosion. Hardengineering solutions have reduced the

distribution and abundance of species. Inaddition, they can contribute to erosion furtherdownstream by channelling water downstream ata faster rate.

Causes of Erosion

Overgrazing - If allowed unrestricted access tobanks, livestock, in particular cattle, can breakdown the banks causing silting in the channel.

Mismanagement of bankside trees - If trees areallowed to shade out all other vegetation theycan reduce habitat diversity. The river can

undercut the trees root system causing thetrees to become unstable, eventually falling intothe water. A toppled tree causes local erosionproducing a "tear point" which can lead toerosion moving further down the river bank.

Recreation - Rivers and wetlands are verypopular sites for visitors. Irresponsible driving ofpowerboats can cause waves (boatwash) thaterode banks and undercut trees. Many publicpaths run alongside rivers. However, heavyuse of a footpath may damage the surface andsurrounding plants, leading to erosion.

Poaching of banks by overgrazing is a major cause of bank erosion.

CAUTIONSome bare muddy river bank areas can harbour rareinvertebrates and muddy poached areas can be arefuge for plant species such as tri-lobed water-crowfoot (Ranunculus tripartitus).

Earth cliffs can offer an ideal habitat for burrow-nestingbirds such as kingfisher (Alcedo atthis) or sand martin(Riparia riparia). Therefore, such habitats should be leftwherever possible provided they are safe and causing

no other environmental damage.

Before carrying out any river channel modificationconsult with your local planning authority to ascertain ifpermission is required. In addition, it may be

necessary to obtain Environment Agency permission forany works affecting river beds and banks in Englandand Wales. The Rivers Agency should also beconsulted for works in the river channel in NothernIreland and the landowner in Scotland.

Hard revetment provides no bank side ormarginal habitat.


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Preventing Erosion

Addressing the causes of erosion is the only long-term solution to the problem of erosion.

Reducing Recreational PressureZoning of uses to reduce disturbance, can allowthe public to enjoy the river while protectingvulnerable sites. Paths and car parks should besited away from critical areas and moving thecourse of an eroding path may be the only long-term solution. To reduce boatwash, encourage thelocal navigation authority to impose and enforcespeed limits.

Exclude Livestock

Plants can protect against erosion. Fencing an

area to permanently exclude livestock ortemporarily exclude them during vulnerable timesof the year can reduce erosion. In some areas,reducing the stocking densities may allow grazingall year round. In many cases, simply fencinglivestock away from a badly poached bank (bankeroded by hooves) is sufficient to allow marginalvegetation to recover.

The Way of Nature

It is now possible to use engineering techniquesthat work with the natural stabilising forces of treesand plant roots. Roots bind the soil in the bankand vegetation reduces the erosive forces ofwater. Plants are able to adapt to changingconditions and can provide long-term, low cost

bank reinforcement. Allowing vegetation torecover may have the added benefit of naturallynarrowing over-widened channels, which in turnraises water-levels

Using vegetation to support and protect the bankis advantageous because it:

improves wildlife habitat

improves fish spawning habitats

is easily achieved

offers long-term protection

integrates into other protection schemes has low capital costs

integrates into the landscape better than hardengineering methods

Trees, Stakes or Poles

The presence of well-managed trees can reduceriver bank erosion by as much as 90 per cent.Willows are useful when planted as green stakes

driven into the toe of the bank for protection andback-filled with suitable material. The new shootswill continue to reinforce the surface soil and bindthe material used to build up the bank.

Willow stakes simply planted on the bank, quicklybuild root systems to bind the soil together andprovide food for water voles in winter and diversityfor wetland species. Try to use locally availablenative willow. Willows that are regularly managedwill provide plenty of healthy willow stakes thatcan be used to protect other areas.

Fencingout

livestockcan allow

marginalvegetation to

establish.

Boating speed restrictions and zoning recreational activity, can reduce recreational

pressures on waterways.

Soft engineering structures work with nature to counteract erosion.


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Spiling

This is a variationon the use ofwillow bundlesbut here 7.5cmdiameter stakesare driven into the

bank and liveosier willowwithies are wovenbetween them.The bank is thenback-filled withsuitable material.The growing osierwillows providebankreinforcement andare readilycolonised bywildlife. Thistechnique is moredifficult thanfaggoting butuses lessmaterial. It ismost suitable forthe protection ofsteep banks.

FaggotsUsually made from osier willow, poplar or hazel,these comprise brushwood or brashings ofapproximately 2.5cm diameter in bundles of 35-40cm across. They are bound together with wireor woven together and then held in place by poles.

They will encourage the accumulation of silt andvegetation roots will bind the newly accumulatedsilt to the bank. Faggot mattresses can be formedby staking a loose spread of willow and faggots.

Hurdles

If a small portion of gently sloping bank is eroding,hazel wattle hurdles (approx 1.8m square) can befixed to an eroding bank with stakes. This allowsthe vegetation to recover by temporarily protectingthe bank. The hurdle will not grow, and will slowlyrot, leaving a cover of vegetation to bind the bank.

The rotting hurdles provide habitat for beetles,fungi and many other species which feed onrotting wood.

Geotextiles

A geotextile is a mesh made from man-made ornatural materials, which can be designed tobiodegrade over time. Geotextiles can be openmeshes, grids or three-dimensional honeycombs.All these geotextile structures can be used toretain soil to a set shape (profile) at the toe of thebank until plants establish and consolidate thebank. If water voles are present when using

geotextiles, it is essential to ensure that burrowentrances are not blocked when back-filling behinda reinforcing structure. Geotextiles are mostsuccessful when combined with vegetationplanting and when they follow the natural contoursof the bank.

Willow can be coppiced providing a sustainable

supply of willow stems for bank protection.

Hazel hurdles can be used to repair the damage done by overgrazing, but erosion

will continue if the cause is not dealt with by fencing livestock or reducing stockingdensities.

Faggots provide a

flexible tool for bankprotection.


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Tall Wetland and Bankside Plants

Tall wetland plants that have leaves and/or stemsabove the water are known as emergent plants.Emergent plants such as common reed and reedcanary-grass can be used to help protect banks.Both plant species have a dense root structure

and tall leafy growth which helps to bind the bankand reduce wave action/erosive power of thewater. Silt is trapped around the vegetation, whichhelps build the bank.

A mixture of grasses, scrub and trees with a fringeof marginal emergent and wetland plants is likelyto provide the best protection from erosion. Inaddition to providing strong erosion prevention,this rich mixture of marginal and bankside(riparian) plants has other advantages which arelisted as follows.

Reeds, tall grasses and herbs will help toprovide cover, food and nesting sites for a widerange of wildlife for wetland birds.

Emergent plants provide ideal habitats foremerging insects such as dragonflies anddamselflies.

Many wetland plants flower, creating attractive,visually pleasing fringes along river banks.

Underwater tree roots can provide spawningareas for coarse fish.

Low branches and tree roots can provide refugefor fish from predators and flood flows.

Trees and shrubs can shade the water edges,providing a cooler water area in mid-summer aswell as reducing the growth of aquatic algae.

Invertebrates living in the marginal plants andfalling from trees can provide food for fish andother invertebrates.


The Water Policy Team is supported by Severn Trent Water Plc, Biffaward and The Waterways Trust.Written and published by The Wildlife Trusts Water Policy Team 2001

Information & Advice

Further information on river bank protection can be found in:

Understanding River Bank Erosion. The EnvironmentAgency (1998).

Policy and Practice for the Protection of Floodplains.Environment Agency (1997).

The New Rivers and Wildlife Handbook. RSPB, NRA andThe Wildlife Trusts (1994).

For further information on the conservation of waterand wetlands species and habitats please visit:

www.wildlifetrusts.og

Photos - Purple-loosestrife & Boating The Wildlife Trusts; all other photographs Dr Nick Giles

River Bank Protection W Pol Tm WT's Fact Sheet

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