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Project LeaderEnvironment AgencyProject PartnersGreen CorridorLondon Borough of Richmond-upon-ThamesLondon Borough of HounslowEnvironment AgencyLondon Wildlife TrustFriends of the River Crane Environment (FORCE)Kneller GardensMoormead ParkNorthcote Nature ReserveTidal Crane AssociationFunding SourcesEnvironment AgencyProject Budgetcirca £15,000Project TimescaleNov 2017 - November 2018

Lower River Crane Flow Improvements

The tilting weir at Mereway Road in Twickenham is designed to regulate the water level in the lower Duke of Northumberland's River (DNR), due to a historic arrangement that keeps the river at an almost constant level. As a result, water flowing down the lower River Crane is controlled as well, resulting in very little water being diverted during dry spells.

The Crane Valley Partnership’s catchment plan highlights the need for ‘Increased and more variable flow throughout the River Crane, Duke of Northumberland’s and Longford Rivers’, to be achieved in part by implementing an ‘improved water level management scheme for the lower River Crane involving all relevant stakeholders’. The impact of the diversion of flows down the DNR on flows in the River Crane is a particular concern.

As part of the Environment Agency's hydrological investigation in support of the partnership’s aims and in recognition of its concerns, the weir was lowered on 18 October 2016 for a one-day test, to allow more water to flow down the River Crane. This was done in two stages: a first lowering at 11:00 and a second at 14:00. The weir was then returned to automatic operation at 16:00. See the photos below for before and after comparisons on the day.

The report discussing the results is available to download.

Mereway Weir before lowering
Mereway Weir after lowering
Mereway weir from downstream on River Crane before (photo on left) & during test (photo on right)

Mereway Weir before lowering
Mereway Weir after lowering
River Crane near Twickenham station before (photo on left) & during test (photo on right)

Next phase

Based on studies so far there is no expectation that these changes in flows will negatively impact the Duke of Northumberland’s River. However, we have planned a one year test to investigate this further, starting on 29 November 2017. The purpose of the test is to identify the impact of improving flows in the lower River Crane on local water abstractions, ecology of the Duke of Northumberland’s River and ecology of the lower River Crane. If the test proves to be successful the weir will remain at the lower operational level.

This project is running alongside the Crane Valley Partnership’s Vision for an improved landscape along the River Crane from Kneller Gardens to Cole Park Island.

What will we monitor during the test?

Real time river level monitoring will be carried out at the Environment Agency gauging stations and Mereway Weir. If the levels fall outside the set limits an automatic notification will be sent allowing the Agency to act accordingly. Real time river levels can be viewed at gauge map.

In addition to river level monitoring, we will observe water depth and velocity (flow speed) at multiple sites along the Duke of Northumberland’s River and Lower River Crane each month. We will monitor the ecology through habitat, fish and invertebrate surveys alongside fixed point photographs.

What effect will changing the weir settings have on flood risk?

The change of settings will allow more water down the lower River Crane at medium and low flows, diverting it from the Duke of Northumberland’s River. At very high flows the weir automatically lowers to allow as much water through as possible (as is currently the case), this will not be changed. Therefore, the test will not alter the current flood risk on either river.