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Chelmer Valley Local Nature Reserve: Phase One

Chelmer Valley Local Nature Reserve: Phase One | Essex Rivers Hub
Date: 2015
Project Lead: Essex Wildlife Trust

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Project Partners: Environment Agency
Funding: Environment Agency, CRF

The Chelmer Valley Nature Reserve is a small local nature reserve that runs through the centre of Chelmsford; it incorporates a number of habitats including some relic fen meadows and wet woodland but also a large amount of amenity grassland.

A key feature of this Local Nature Reserve is the River Chelmer which runs through the park for around 2.5km before heading into Chelmsford City Centre.

The river is heavily impounded and is characterised by slow flows and historically has been deepened, widened and dredged leading to poor floristic diversity. The aim of this project was to attempt to reverse this by introducing faster flowing water, providing edge habitat and reconnecting the floodplain.

Existing site character

We achieved this by putting in a number of interventions, including bank reprofiling. In the case of the project at Chelmer Valley Local Nature Reserve, this meant forming and creating five berms out of historical dredgings. The soil is then placed into the main river bank and compacted using an excavator, to approximately a third of the channel.

The main purpose of these berms was to improve local flow velocity. This has a number of benefits for the river; the sped up flow prevents silt from settling on the riverbed and exposes gravels. These exposed gravels and faster flowing columns of water are the most biodiverse areas in the river providing great habitat for insects and fish, especially fish fry.

In addition to constricting the flow and revealing gravels; these features also provide a number of other benefits. They provide an interface between the water environment and the terrestrial environment, allowing flora and other interesting flowers to develop, offering habitat for a wide range of invertebrates both aquatic and terrestrial.

As a final complementary feature, the bank reprofiling also reconnects the floodplain, allowing floodwater to be stored in the floodplain away from houses and property. Historical management of the site means that a lot of water is funnelled down the river at the same time until it hits a hard object when it hits the hard object such as a sluice or a weir it backs up, this means that rivers can sometimes flood. By allowing water onto the floodplain higher up the catchment it prevents the water getting to the structure quite so quickly and can reduce flooding. Also by storing water in the floodplain it also means that we are hopeful of creating new habitat, in this case, a mosaic of wetlands and fen meadows.

The project was undertaken in March 2017, with the earthworks lasting about a week. Within four months the berms and bank re-profiling had completely vegetated over and had completely stabilised to provide new habitat.

Forming the berms

The new features form a new bankside, gently sloped and reduce the channel by about a third. This makes the channel narrower and the flow quicker. There is no need to bring in vegetation as the natural seed bank will quickly establish and bind the new feature together. Angles and length vary depending on what the characteristics of the site are. In locations like here at Chelmer Valley LNR, these solutions are quick, simple and easy ways to establish some flow dynamics. Perhaps more suitable than woody debris in these locations due to depth of the channel and width of the channel which would offer some logistical challenges to installing woody debris.

Within four months the berms and bank re-profiling had completely vegetated and had stabilised to provide new habitat.

This project was funded by the Catchment Partnership Action fund and was undertaken by the Essex Wildlife trust in partnership with the Environment Agency on behalf of the Combined Essex Catchment Partnership (Essex Rivers Hub).

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The topics below represent the pressures that many waterbodies in the Combined Essex catchment face. They have been divided into six main categories, but it is quite often that these categories can overlap as pressures relate to each other.

Diffuse pollution occurs as water moves across the land or through the ground and picks pollutants. These pollutants can come from a variety of places, including urban and field run off. The pollutants that enter the river can range from sediment to toxins to excess nutrients, meaning that diffuse pollution can cause a whole range of different issues. The variety in these pressure groups means that it is something that can be quite difficult to tackle. It requires groups of people, business and stakeholders to work together in order to solve this problem.

Fish should be able to travel up and down a river freely, allowing them to move and breed in the most suitable habitats for them. It is important that fish populations do not become isolated, as this makes them more susceptible to disease and puts pressure on their survival. Unfortunately, there are often many barriers along rivers that prevent fish from being able to migrate up and down stream. Where barriers have been identified, they will be seen as a ‘pressure’ on a waterbody. Thankfully, there are many solutions now that can be put in place to aid fish passage, even over large barriers.

The flow in a river can vary greatly throughout the year as rainfall and run off can have an effect. This is a natural process. It is when flow is impacted by non-natural processes that it can cause problems. Sometimes, water can be intercepted or removed from a system; this will reduce the flow, therefore changing the habitat conditions. Some species are happy in high energy rivers. This means that when flow is reduced, these species will no longer survive. The opposite of this can occur when excess water is entering a river, for example through increased runoff. Low energy systems then become high energy and displace the species that live there.

A species that is not meant to be found in a particular area is known as an invasive species. Invasive species can be from a different habitat or a different country altogether. Most of the invasive species that we find on our rivers have come from other countries – plants that people have imported for their gardens or animals that have been released for food or by animal rights activists. Control of invasive species requires a lot of time and effort. We are fortunate that we do have a range of methods to manage most of the invasive species that cause havoc on our rivers, but there are still some which we are still struggling to control.

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