SRA Annual Report 2024-25: River Sowy – King’s Sedgemoor Drain Enhancements Scheme 2024-25
During 2024-25, the Parrett Internal Drainage Board (IDB) worked on plans for completing Phase 1 of the SRA’s major River Sowy – King’s Sedgemoor Drain (KSD) Enhancements Scheme. The IDB’s project team focused on the two main tasks still needing to be done, firstly improving Chedzoy Tilting Weir and KSD Back Ditch outfall, secondly raising up to 1.8 kilometres of the left bank of the KSD.
Outfalls
The project team reviewed designs originally commissioned by the Environment Agency, fully inspected both structures, agreed some revisions to save money and ease construction, and got the necessary approvals (a complex process) for works to start at the end of April 2025. At Back Ditch, replacing both headwalls and installing a tidal flap. At Chedzoy, replacing a culvert, inlet headwall, and tilting weir, with a new outfall with tidal flap and raising an existing Public Right of Way to achieve a level defence line along this stretch of the KSD.
King’s Sedgemoor Drain (KSD)
After doing a ground investigation and a topographic survey, the team modelled different ways of getting sections of the left bank up to the required height, again to save money and ease construction, and began getting the necessary approvals (again, a complex process to ensure compliance with relevant laws). Put simply, the plan now is to excavate material from the landward side of the bank, and put enough of this material on top of the bank to allow for settling and consolidation. Thus, large volumes of material will not need to be dumpered in from further afield at far greater cost and environmental impact. The team is hoping to get works underway and completed in the second half of 2025.
Background
The River Sowy is also known as the Parrett Flood Relief Channel. It was created between 1969 and 1972, to take excess water away from the River Parrett near Aller, downstream of Langport. Water flows into the Sowy through a sluice called Monk’s Leaze Clyse near Combe north-west of Langport. It goes down via Beer Wall beneath the A372 near Othery to King’s Sedgemoor Drain (KSD) near Greylake, then it re-joins the Parrett through Dunball Sluice, 22km (13.5 miles) after it went through Monk’s Leaze Clyse.
Improving the Sowy-KSD system was a top target in Somerset’s 20 Year Flood Action Plan, published in 2014. The SRA has been funding works since 2016. The main aim of Phase 1 Enhancements has been to increase the amount of water that can flow, in a controlled way, through the Sowy-KSD system, and thereby help to reduce flood risks for homes, businesses and roads across 150 square miles of the Somerset Levels and Moors.
SRA partners have also needed to ensure that legally-protected wetlands of international importance are not made less wet, because of more water being kept in river channels. For example, around 100 water level management control structures have been upgraded. These help to maintain and improve habitats.