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Little Waltham: River Restoration Project

Little Waltham: River Restoration Project | Essex Rivers Hub
Date: 2015
Project Lead: Essex Wildlife Trust

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Project Partners: Environment Agency
Funding: Catchment Restoration Fund

This project was completed in March 2015 and was the first, Healthy Headwaters Catchment restoration funded project to be successfully completed. It is now used as an exemplar site to promote the multi-benefits of river restoration projects including correct riparian management, flood alleviation and creation of new habitat for the benefit of biodiversity.

This project built upon the work undertaken by the walkover surveys in 2012, where a number of issues affecting the river were identified. These included a large culvert with water of unknown origin feeding directly into the River Chelmer, a drying wet woodland reducing habitat diversity and affecting water quality into the river and crucially a lack of connection to the surrounding floodplain and a lack of features within the river channel.

There are also a number of Meta issues facing the River Chelmer as a whole; this water body is currently classed as being in poor condition under the Water Framework Directive and failing for a number of reasons including phosphates, hydro morphology and dissolved oxygen. Therefore any solution had to take into account both the overall factors affecting the river and the water body and the aims and aspirations of the reserve. After a period of consultancy with the Environment Agency and after hiring APEM Ltd to conduct a site survey an ambitious scheme was designed that would contribute to WFD targets and improve the nature reserve.

This involved connecting the existing culvert and drain to three new stilling ponds, a new back channel, installing a new sluice to control water levels coming into the back channel and creating a new backwater bay. This was combined with installing a new sluice to control water levels in the wet woodland and to raise water levels by around 2 to 3ft.

It is hoped that these will enhance the river by intercepting the water coming out of the culvert and filtering it through the stilling ponds and the back channel. These will remove phosphates and nitrates before entering the main river Chelmer. The back channel and back channel bay will also provide a refuge for fish fry during times of high flow. Both the wet woodland and the new back channel will also increase the amount of riparian habitat along the corridor and promote new and exciting species to colonise.

Once the final designs were agreed upon the project was put through an exhaustive planning and consenting procedure. This is a necessary and vital part of the project. It allowed us to identify a conflict with any potential Archaeology on site, working with the Public rights of way officer to maintain public access and manage the interface between the public and works and most importantly liaise with the Environment Agency in order to ensure that the works do not interfere with any flooding issues and are still able to maintain the flows in the river in times of drought.

Earthworks commenced in September 2014. Initial excavations began focused around the back channel and lasted about a week and involved the movement of around 3000 cubic metres of spoil, which was deposited on a nearby dry hill. This was then spread and reseeded using a clay seed mix. The back channel runs for around 280 metres and has a 40cm fall, meaning it is 40cm lower at the river end than the top end. This allows the water to fall in the right direction and allows the far end to be permanently submerged.

The final element of the earthworks in this area was to then connect the new back channel with the three ponds, the culvert and the river, setting the correct levels for the bunds and allowing water to traverse through. Each pond is separated from each other by a bund which has been set at a certain height to slow water up and allow silt to drop out of the water column. As they approach the back channel the heights of the bunds get progressively lower but above the height of the base of the back channel, keeping water flowing in one direction. The last stage was then to connect to the river with a sluice set at the correct level, as determined by the consenting and planning process.
Once the back channel was complete, attention turned to the wet woodland in the north of the site. This was a fairly simple intervention; the level of the sluice was set to bring water up and over the height of the ditch bank. Raising the water height in the woodland and securing it against drying out in the summer months. In conjunction with this there was some scraping of the adjacent field surface to encourage further expansion of the wet woodland. This was then backed up with planting of alder and willows to kick start an expansion of the woodland, and increasing the overall size by around 0.5ha. Finally this area was fenced off to prevent cattle grazing in the area and allow the development of scrub on the edge of the wetter area.

The site is now fully open and accessible to the public and it is well worth a visit all year around. Depending on the recent weather conditions the channel can be full of water or down to a mere trickle. The ponds are normally full of water as is the back channel bay. Since completion there has also been planting of 8 black poplars along the back channel, this is one of the rarest tree species in the UK and are a real addition to the reserve.

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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.