The purpose of this Environment Agency project is to maintain the protection from flood risk for homes and businesses along the Ouse Washes.
What are the Ouse Washes?
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.
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.
What work is required to maintain the Ouse Washes?
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 the Environment Agency 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.
The existing bank protects surrounding areas from flood water stored in the reservoir. A 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 work is taking place?
The Environment Agency 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).
This work is taking place over 4 summers (2017, 2018, 2019 and 2020). Due to the overwintering and breeding bird population found on the Washes, there is a narrow timeframe to do any work on the banks, from mid-July to end of October each year.
You can find out about the latest progress of the project through the link below: