Ouse Washes Section 10 Works information page

Closes 31 Mar 2020

Opened 13 Jun 2019

Overview

diagram of the Ouse WashesAerial view of the Ouse Washes flooded

The purpose of this page is to provide information on how the Environment Agency maintains the protection from flood risk for homes and businesses along the Ouse Washes and how it complies with the Reservoirs Act 1975.

The Ouse Washes is defined, under current legislation, as a ‘large raised reservoir’ more commonly known as Ouse Washes Flood Storage Reservoir. It is approximately 33km (22 miles) long and 1.7km (0.5 mile) wide providing about 2,000 hectares (5,000 acres) of land between the banks and it's in Cambridgeshire. The Dutch Engineer ‘Sir Cornelius Vermuyden’ originally constructed it in 1653 for the purpose of draining the fens. It is designed to store floodwater that would otherwise cause overtopping of riverbanks. 

 

diagram of Ouse WashesDiagram of Ouse Washes - click to enlarge image

Over time the Washes has evolved into an important area for a variety of species and subsequently received local, national and international conservation status. It is also important from an agricultural aspect and is heavily grazed during the summer. This grazing serves a dual purpose, it facilitates the management of the Washes by controlling vegetation and maintaining the effective transfer of floodwater; it also acts as an effective technique to manage the grassland habitats of the Washes, providing best conditions for the vast array of bird species visiting the area.

A qualified civil engineer completed an inspection in 2013 and recommended a number of Measures in the Interests of Safety under Section 10 (6) of the Act. These resulted in a project to raise the Middle Level Barrier Bank to address changes to the bank crest level caused by settlement.

The Middle Level Barrier Bank is lower where the Welney Wash road crosses into the Ouse Washes Flood Storage Reservoir. This low spot reduces the safety and stability of the bank and increases the flood risk to the communities. Historically we have created a temporary flood barrier across the Welney Wash road using large sand bags. Installing large sand bags is costly in terms of labour and waste, as the sand bags cannot be reused. We have investigated alternative solutions which will be simpler to install and we can store and reuse.

aerial view of the Ouse Washe and Welney Wash road floodedAerial view of the Ouse Washes and the Welney Wash road flooded

Our objectives

Our objective is to maintain the high level of flood protection we provide to communities living near the Ouse Washes.

The existing bank protects surrounding areas from flood water stored in the reservoir. Our recent assessment of the bank height shows that flood water could overtop the bank at isolated locations in the equivalent of a 1% probability event.

Overtopping could lead to erosion and subsequent collapse of the bank. Under the Reservoirs Act 1975 the Middle Level Barrier Bank needs to be safe for a 0.1% probability event. Where communities are immediately adjacent to the bank, the Middle Level Barrier Bank needs to be safe for a 0.01% probability event.

What are we doing?

We are raising the Middle Level Barrier Bank between Earith and Welmore Lake Sluice. Other associated works include building barrier works at Welney, a new wall at Welches Dam Pumping Station, extending a retaining wall at Sutton Gault, and decommissioning the Black Sluice culvert (near Earith).

We are doing the construction works over 4 summers (2017, 2018, 2019 and 2020). We have allowed for a further year to establish the new grass cover (2021). Due to the overwintering and breeding bird population found on the Washes, there is a narrow timeframe for us to do any work on the banks, from mid-July to end of October each year.

placement of reinforcement gridPlacement of the reinforcement grid

Year 3 (2019) works

Over the winter we have been finalising the detailed design for the structures and the next phase of works on the Middle Level Barrier Bank. We’ve been doing winter inspection surveys, maintenance, vegetation clearance, and environmental surveys to prepare for the rest of the works.

We start preparation works from 1 July 2019 for the main bank works to start on the 15 July. We are importing clay material from local quarries to raise the crest level of the Middle Level Barrier Bank between Mepal and Welney.

More information on the routes of the construction work on the newsletter attached.

We are organising two public drop-ins in June to provide information on this year's works - see more information at the bottom of the page.

bank worksBank works

Public footpaths

The grass is important on the reservoir bank. As the grass grows, the roots help to stabilise the bank and reduce erosion. We use a mixture of different seeds to get a variety of different grass species.

 Over the winter and spring months we regularly inspected the banks and grass growth on sections of work that we had completed. The grass is growing and the footpath diversions will stay in place until there is sufficient cover on the bank.trial banks by Welney Sluice
Trial banks by Welney Sluice

RSPB reserve bird hides

We will need to remove the bird hides to the south of Welches Dam this summer (2019), so that we can raise the bank. We will install new bird hides and they will be ready for use during the winter of 2019/20. However, the footpath along the top of the bank will remain closed until the grass has grown.

bird life on the WashesBird life on the bank

Welney Wash road barrier construction

We have sourced the demountable barrier option that will be bespoke to Welney which we will store and deploy from the Environment Agency's Ely compound. We will build a short textured concrete abutment wall either side of the road for the temporary defence to join.  We will install a concrete plinth across the highway for the barrier to be attached to whilst it is in use.

example of a demountable barrierExample of demountable barrier

Next steps

The Welney Wash road barrier wall construction will start in Summer 2020.

We will be providing more information on this in the coming months, so keep checking this page for updates.

For further information contacts us via the Public Liaison Officer on 07534 457348

Events

Audiences

  • IDBs
  • Local authorities
  • District and parish councils
  • Environmental bodies
  • Land owners
  • Farming associations
  • Drainage associations
  • RFCCs
  • Elected representatives, including MPs

Interests

  • Flood management