SRA Annual Report 2019-20: River Sowy – King’s Sedgemoor Drain (KSD) enhancements

The River Sowy is used by the Environment Agency to take excess water away from the River Parrett near Aller. Water flows into the Sowy through the Monk’s Leaze Clyse sluice, goes down via Beer Wall to King’s Sedgemoor Drain near Greylake, then re-joins the Parrett at Dunball.

During the floods of 2013-14, after Monk’s Leaze Clyse was opened fully, flood waters fell 80 centimetres in two days. No other single act had such a dramatic effect. It was described by one senior officer as being “like magic”. In the latest wet winter of 2019-20, the Sowy again helped to take pressure off the Parrett and allow for earlier and longer pumping.

The Sowy is a man-made river (see below).

It was conceived as a Parrett Flood Relief Channel after downpours deluged 50,000 acres of Somerset (including Taunton) in October 1960.

Curry Moor Pumping Station and the Somerset floods of 1960.

The first plan in 1961 was for a channel that could carry 30 cubic metres of water per second into a widened KSD. After long arguments about cost, the Sowy was scaled back to 17 cubic metres per second (cumecs). Work started in 1969, and took three years.

However – though the Sowy was built smaller than first suggested – all associated sluices or bridges were built or modified so they could deal with 30 cumecs and the system could be made larger once funding was available in future. Somerset Rivers Authority is now picking up the possibilities left to us all by an earlier generation.

Aller Drove Bridge is one of the structures deliberately built bigger so as to leave possibilities open for the future.

Providing more capacity in the Sowy-KSD system, so that it can be used more effectively, is a key aim of Somerset’s 20 Year Flood Action Plan, which is overseen by the SRA. Sowy-KSD works in recent years have included the creation of new river channels under the A372 at Beer Wall along with tilting weirs, the installation of a new water level control gate near Chedzoy, the removal of obstructive masonry from under Dunball Old Bridge, which carries A38 traffic southbound, and de-silting of bridges at Parchey and Dunball.

All these works are part of a programme to reduce flood risks across 150 square miles. Now, as back in the 1960s, the intent is to reduce the risks of flooding – particularly summer flooding – for moors upstream of Langport and some lower roads, and for moors west of the Parrett. Doing this will help to protect people, homes, farms, businesses, land and infrastructure.

Activities during 2019-20

Designers have been fine-tuning plans for increasing the capacity of key parts of the Sowy and KSD through work in these rivers’ channels and on their banks. Works on a first phase of channel improvements are now planned for the second half of 2020.

In early 2020, discussions were held with individual landowners who will be affected, for example because access to their land will be required.

Three drop-in sessions for the public were held in mid-February, in Westonzoyland, Othery and Aller village halls. Dozens of people attended, including the Chair of the Environment Agency Emma Howard Boyd. Ms Howard Boyd met SRA Chair Cllr David Hall and Vice-Chair Tony Bradford of the Parrett Internal Drainage Board (IDB).

Emma Howard Boyd talking to Cllr David Hall (centre) and Tony Bradford.

Sowy-KSD works are being delivered for the SRA by the Environment Agency, working closely with partners including Natural England and Somerset Drainage Boards Consortium. The SRA is using Growth Deal funding from the Heart of the South West Local Enterprise Partnership and money put specially aside from local council tax.

The Sowy and KSD run through environmentally sensitive areas protected by law. It is essential to make sure that no damage occurs to the designated sites of the Somerset Levels & Moors Special Protection Area and Somerset Levels & Moors Ramsar. It is also vital to mitigate any detrimental impacts that works might have on nearby areas that are valuable for wildlife, particularly birds feeding in splashy conditions over the winter.

A very fine balance has to be achieved between keeping more water in river channels and keeping wetlands at the right level of wetness.

More about what partners intend to do over the next two years can be read in this report’s next section on the SRA’s Strategic Approach to Mitigation.

One action is that dozens of water level control structures are to be replaced or refurbished at the Moorlinch and Westmoor Raised Water Level Areas and Egypt’s Clyse.

View from track of black membranes fixed on banks near a water control structure on Westmoor that needs improvement works. — A membrane fitted to keep water voles away from a water level control structure on Westmoor.

In March 2020, membranes were fitted near 39 of these structures so as – temporarily – to stop vegetation growing and deter water voles. It is against the law to harm water voles, so it is vital to keep them out of harm’s way until works have been completed later in the year.

The sensitive nature of the area means that Sowy-KSD works will be undertaken in stages, so that impacts can be checked and water level management practices amended as need be to maintain environmental features.

Further works on the Sowy-KSD system are being designed by the Environment Agency for the SRA, for example channel smoothing at Dunball. This is a difficult site to access and work at safely. The team’s aim is to overcome various complex problems and find a scheme that is deliverable and affordable.