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Chelmer Valley Local Nature Reserve: Phase Two

Chelmer Valley Local Nature Reserve: Phase Two | Essex Rivers Hub
Date: 2017
Project Lead: Essex Wildlife Trust

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Project Partners: Environment Agency
Funding: Essex County Council, Environment Agency

This project builds on the original project at Chelmer Valley Local Nature Reserve undertaken in 2015, by installing some new scrapes, installing a further berm to improve local flow velocity, and putting in an additional fish refuge, at an area just north of Chelmer Valley Bridge. The project was undertaken in early 2017 and the aim of the project was to improve the overall riparian habitat quality but also it will help to store and attenuate flood water.

The first intervention was to reprofile the bankside and create a new berm feature. This area of the river is characterised by slow, sluggish flows which means silt can drop out of the water, smothering gravels and allowing choking weeds to develop. Therefore to introduce some faster flowing water and expose these gravels would enable the river to manage itself, introducing gravel and a column of oxygenated water and benefit the wildlife found in this reach and wider afield.

The difference between before and after is remarkable. We have already seen turbulent water typical of faster-flowing columns of water indicating that this is already having an effect on the local flow velocities.

Via the process of creating the berm the bankside has been lowered, this also has benefits to wildlife as it means that silt is settled outside of the river and it also increases the connectivity of the floodplain, allowing this section of river to behave in a more natural fashion and aid the creation of natural riparian habitat including wet meadows and wet woodland.

A major part of this intervention was to create four new scrapes or ponds. Scrapes are shallow seasonally flooded areas of land which are incredibly vital and valuable to wildlife. The aim of the scrapes is to create a mosaic of wetland habitats that are flooded in the winter and stay wet into summer, for the benefit of wildlife. They also store and attenuate floodwater, especially during the summer months.

The scrapes are connected to the river via an existing ditch network, which should enable them to be seasonally flooded and thus benefit the wildlife of the River Chelmer. The scrapes were created using an excavator. The average depth of the scrape was the same as the existing ditches on the site.

The final intervention was the fish refuge, fish populations in the Chelmer are declining. Partly as a result of the number of interventions on the Chelmer which prevent natural fish movements. Fish refuges work by providing a place out of the main flow, especially during high flow events where fish, especially young fish can sit out flooding incidents and avoid being washed downstream, helping to maintain fish populations in this area.

It is still early days for this project, but all the bare areas have been reseeded with a low maintenance meadow mix which should hopefully produce a nice varied sward. The final aim for this project is to plant trees which will be the last piece of the jigsaw in creating this mosaic of wetland habitats.

Thanks must go to Luke Bristow at Essex County Council and the Environment agency for funding this project.

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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.

Many of our rivers have been heavily modified over the years as rivers have been used for a wide range of purposes. Physical modification is one of the biggest factors that causes our rivers to be unhealthy. The issues that it can cause range from reducing habitat, preventing migration of mobile species, and even have an effect on the water quality. Where structures and modifications are no longer in use or necessary, they should be removed to allow the river to regain its natural state. Unfortunately, this action is not always taken which means that many of our rivers are over straightened and contain redundant structures. It is possible to return a lot of our rivers to their natural state, through one off projects, but in other cases it is not possible as the river has been changed to protect assets or manage flooding. It is recognised that some modifications cannot be removed without having severe negative impacts both socially and economically.

This is pollution that comes from a single identifiable source. The pollution entering the river could include a whole range of pollutants. Some point source pollution is known about and licences, for example sewage treatment works. Other sources are not licensed, and therefore work needs to be done with landowners to fix the problems that are allowing the pollution to enter the river. Point source pollution is more easily controlled than diffuse pollution as it often only takes one management approach to solve the issue.