Policy paper

Somerset Levels and Moors: reducing the risk of flooding

Updated 5 December 2023

Applies to England

Background

The Somerset Levels and Moors lie between the Quantock and Mendip hills in central Somerset. Much of the area has been historically drained for agricultural and residential purposes. The area is cut in 2 by the Polden Hills which run parallel with the Mendip Hills further to the north.

The north of the Polden Hills is drained by the Rivers Axe and Brue. The southern area of the Polden Hills is drained by the River Parrett.

The Levels and Moors are one of the lowest areas in the UK; 18% of Somerset lies below average tide level. The area extends to over 60,000 hectares and is very flat. Records of flooding in this area go back as far as the 1600s.

In early 2014, the Somerset Levels and Moors communities experienced widespread flooding, particularly within the Parrett and Tone river catchments. The Environment Agency estimated there were 100 million cubic metres of floodwater covering an area of 65 square kilometres. Residents of Northmoor had to leave their homes at the height of the flood and many communities were cut off by floodwater. Following this, investments were made, and a trigger point plan was created.

In 2023, a major incident was declared due to flooding. The guidance set out in the trigger point plan was followed and few properties experienced flooding.

Actions the Environment Agency take when flooding is forecast

We operate 21 permanent pumping stations across Somerset and can provide large additional mobile pumps when needed. It is normal for permanent pumps to be operating during winter when rainfall tends to be higher. This does not mean that there is an increased risk of flooding.

When rainfall is prolonged and heavy, we can use more pumps to control water levels to reduce the risk of flooding. This approach is based on trigger points.

We review and update the trigger points when necessary. We did this throughout 2023.

There are 3 criteria we check against. We these are met we will fulfil our commitment to increase pumping capacity by deploying mobile pumps at key locations.

These criteria are:

• flooding of a specific road
• the cumulative total rain forecast for the next 3 to 5 days must be 100 millimetres (or greater)
• moor levels will be rising at 50 millimetres per hour or more

If all 3 criteria are met we will provide one or more temporary mobile pumps. Most of the temporary pumps are used to add capacity to our permanent pumping stations. The exception is the provision of mobile pumps at Dunball Sluice. This provision is to allow pumping from the Kings Sedgemoor Drain during periods of tide locking. The pumping stations are set to operate automatically according to water levels in the rhynes draining the moors.

These pumps cannot operate if:

• the receiving river is full
• when spillways are operating
• when riverbanks are overflowing

The local triggers

This section explains what the local triggers are.

The flooding of New Road, between West Lyng and North Curry

The Northmoor, Saltmoor and Currymoor triggers are interlinked. Water levels on Currymoor rise when Hookbridge Spillway runs, spilling water from the River Tone into Currymoor. At this point, Currymoor pumping station cannot operate as the River Tone is full. Cuts Road floods first, and then New Road (between West Lyng and North Curry).

The local trigger point for Northmoor, Saltmoor and Currymoor, is when the Currymoor Main Drain as measured at Currymoor pumping station, reaches 5.80m.   We may then start installing temporary pumps in advance of likely increases in water levels in Northmoor and Saltmoor.

Flooding of the Muchelney to Long Load road

When flooding is predicted, all inlets to the moor at Huish Episcopi are closed manually and water continues through the river systems. The permanent pumps at Huish Episcopi pumping station will continue to operate automatically until the River Yeo, measured at Huish Episcopi pumping station reaches 8.20m. At this point, Huish Episcopi pumping station cannot operate as the River Yeo is full. Flooding will eventually render the roads between Langport, Muchelney and Long Load impassable.

We will consider and agree the need for temporary pumps when the level on the moors is above that at which the Muchelney to Long Load road floods. We will put these pumps in place ready for when river levels drop below 8.20m and pumping can begin again.

Flooding of the Long Sutton road

When flooding is predicted, all inlets to the moor are closed manually and water continues through the river systems. The permanent pumps at Long Load pumping station will continue to operate until the River Yeo reaches 8.80m. At this point, Long Load pumping station cannot operate as the River Yeo is full.

The Long Sutton road floods when levels in the moor exceed a certain level. At this point we will consider and agree the need for temporary pumps. These pumps will be in place ready for pumping to start when river levels drop below 8.80m.

Flooding of the lowest road in Middlezoy

When flooding is predicted all inlets to the moor are closed manually and water continues through the river systems. We will operate Westonzoyland pumping station when the lowest field floods.

The local trigger point for Westonzoyland is when the lowest road in Middlezoy floods. We will then install an additional mobile pump at the pumping station . All pumps operate on all but the highest tides.

Note, we cannot provide additional pumps at Lakewall.

Flooding of the lowest part of the Westover Trading Estate

When flooding is predicted, all inlets to the moor are closed manually and water continues to flow through the river systems. Westover pumping station operates automatically until the River Parrett reaches 8.05m. At this point, Westover pumping station cannot operate as the River Parrett is full.

The moor level may exceed the lowest part of the access road to the Westover Trading Estate. At this point, we will consider and agree the need for temporary pumps.

These pumps will be in place and ready to operate when river levels drop below 8.05m and pumping may restart.

Flooding of lowest roads at West Sedgemoor

West Sedgemoor pumping station operates automatically until the River Parrett reaches a level of 7.50m and Beasley’s Spillway runs.

We will consider and agree the need for temporary pumps when the lowest road is on the threshold of flooding. We will put these in place ready for when river levels drop below 7.50m.

Monksleaze

At Monksleaze the local trigger is not the flooding of a local road.

When flooding is predicted, Oath Lock is opened. Monksleaze Clyce is also partially opened to lower river levels in the River Parrett and allow pumping to continue upstream of Langport.

We will close Monksleaze Clyce when Allermoor and Beasley’s Spillways start to run. If Monksleaze Clyce is opened while spillways are running, flood risk in the Sowy system may increase.

When the River Parrett levels are declining and spillways are predicted to stop running, we will open Monksleaze Clyce incrementally. This gives us better control of flows within the Sowy Flood Relief Channel.

Work carried out to reduce the risk of flooding

Following the flood event in 2013/14, significant investment has been made to reduce flood risk to properties and infrastructure.

This includes:

• Somerset Levels and Moors Flood Action Plan that lead to the formation of the Somerset Rivers Authority
• road raising between Muchelney and Drayton to make sure the village is accessible in a flood
• new control structures at Beer Wall to make sure the A372 road does not flood
• dredging of the Parrett and Tone to make sure they flow freely
• annual maintenance of the dredged sections to make sure the rivers continue to flow freely
• new flood alleviation schemes at Westonzoyland and Aller
• repairs to damaged flood banks
• improvements to some existing flood alleviation schemes which were damaged or overtopped

The Bridgwater Tidal Barrier scheme

We are working with Somerset Council on the Bridgwater Tidal Barrier project. 

The tidal barrier will be constructed across the River Parrett north of Bridgwater. It will have gates that can be closed to prevent high water levels from travelling upstream.

The scheme will better protect at least 11,300 homes and 1,500 businesses from the risk of tidal flooding in Somerset.