PROJECT TOPSOIL – LAYER BROOK AND ABBERTON RESERVOIR
Essex & Suffolk Water, who own and manage Abberton Reservoir, have noticed a rapid reduction in the abundance of submerged plant life in the reservoir close to where Layer Brook flows in. Investigations have so far failed to explain the loss of plant life but have identified an increased build-up of sediment from Layer Brook.
The Topsoil project aims to bring greater certainty to the sources and effects of sedimentation in the reservoir. Take a look on Google Maps
Abberton reservoir is not only an important public water supply within Essex, it is also an important wildlife site and has been designated as a Site of Special Scientific Interest (SSSI) for overwintering birds.
The suspicion is that sedimentation in the reservoir is reducing the areas available for aquatic plants to grow. If true then this is an important issue as a lack of plant life will reduce the food availability for the wildfowl that use this site and make it such an important SSSI.
Keeping soil in fields
An important aspect of this project is to keeping soil on arable fields and out of watercourses.
Sediment is what soil is called once it enters the water system. Valuable soil is continually being lost from arable fields, which is bad for farmers and bad for the environment. It is said that soil 1mm of soil takes around 1000 years to develop, so keeping it where it can be used to grow crops and provide valuable habitat is common sense!
Studies have shown that the top few inches of soil are the most valuable growing medium, therefore losing this is not good news for achieving good yields. Farmers routinely add various substances to the soil to help improve crops, which is increasingly expensive. It is better for the farmer to ensure their money stays on the land where it can improve crops rather than in the water system where nutrients and pesticides become pollutants.
Topsoil Project in Layer Brook
The Topsoil Project will determine where sediment entering Layer Brook is coming from, and the best methods to reduce the amount entering the reservoir. This a three-year project; we are currently in the first year and will use various methods to try to identify the sources of sediment. These are likely to include:
Walking the brook to identify potential areas where sediment is entering the brook from the land;
Measuring sediment levels directly using turbidity meters;
Surveying the catchment area over several months to see what happens to sediment under various weather conditions;
Sediment fingerprinting and Signal Crayfish – CSI Essex!
We are excited to have two MSc students from the University of East Anglia (UEA) working with us on this project. They will be using a method called ‘sediment fingerprinting’ to determine the sources of sediment. They will also calculate the number of the invasive Signal Crayfish present in the brook and reservoir to determine what, if any, impact they are having.
Signal crayfish burrow into banks to live and breed and the non-native Signal crayfish are prolific breeders! It is possible that if they are in Layer Brook in high enough numbers their burrowing and scuttling could be releasing sediment into the water column. This is in addition to the fact that Signal crayfish are significantly larger and better breeders than our native White-clawed crayfish, out competing them for space and food. So in high numbers they can impact on water quality, fish, invertebrates AND vegetation abundance.
Reducing sediment in Layer Brook – practical solutions.
Once the sources of sediment are determined we can then work with landowners to put measures in place to reduce the amount entering the brook. This could include small scale changes to ditch management or buffer strip creation (areas of unmanaged vegetation along the edges of rivers and ditches to prevent water from the arable fields running directly into the watercourses).
Slowing the flow, trapping sediment
We plan to look at areas where water could be stored for a period of time before entering the river, rather than quickly running off the land directly into the brook or ditches. By allowing the water to slowly filter through the ground, this will give the sediment time to drop out and remain on the land, allowing the water to return to the river containing fewer soil particles. These areas are often created by constructing a bund (a low wall of soil) at the edge of a field so that the water accumulates where previously it would have run directly into the water course. These areas are usually very wet and do not produce a good crop so the impact on the farmer’s yields can be minimal.
Left to right: Buffer strip: between field and river; interceptor pond: land runoff drains into the pond, remains long enough for sediment to drop out then flows into the water course; bund: under constructed within a ditch, this slows the flow and allows sediment to drop out; Swale: vegetated ditch where runoff can collect and slowly filter through the ground into the ground water; Silt trap: a shallow pool connected to a ditch that stores land drainage. Both above features slow the water so that sediment is able to drop out and remain on the land.
Changes to the river
We may also make changes within the brook itself. This would involve constructing silt traps. These are small barriers in the channel made of woody material that slows the flow of water allowing any sediment being carried to become trapped within the structure. These structures also create great habitats for fish and invertebrates so will also improve the biodiversity of the river. Silt traps will only be positioned where they do not increase risk of flooding to buildings or land not designated for this purpose.
The mostly likely outcome is that we will utilise several of the measures above to reduce the sediment levels with Layer Brook and ultimately Abberton Reservoir. We will keep you updated on our progress throughout the project. Click here to sign up to our email alerts.
Left to right: Berm; a ‘shelve’ feature within the river that restricts the channel when water levels are low, this speeds up flows, which helps to deposit sediment behind the berm meaning less is transported downstream; Large Woody Debris, this is similar to the berm in that it restricts the channel capacity, speeding up flows and allowing sediment to be deposited or trapped within the wood. Both this feature also create great habitat for fish and invertebrates.
Funding for Topsoil
Topsoil is a collaborative project involving partners throughout Northern Europe from Germany, Denmark, Holland, Belgium and of course the UK. The partnership is looking at various ways to protect the ‘topsoil’ that is vitally important in providing crops for food, biofuel and animal feed, water for drinking and the environment.
Essex and Suffolk Rivers Trust have secured a budget of €220,000 of funding from the European Union (Interreg) as a partner in a three-year project called Topsoil. This means we will receive up to 50% of this total as long as we can find the other 50% from funders in the UK.
We are grateful to our supporters Essex & Suffolk Water, and Environment Agency for valuable matched funding.
If you or your organisation wishes to support this project, or any of our other work, then please contact us. We urgently need to secure funding for years 2 and 3 of Topsoil so please do get in touch.