Little Waltham: River Restoration Project

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.