Wandle Half Tide Weir Removal

Wandle Half Tide Weir Removal

Client: Land & Water Services

Designer: Crouch Waterfall

Duration: August 2016 - July 2017

The River Wandle joins the River Thames on the Tideway and runs about 9 miles long throughout the southwest of London. A defunct half-tide weir that existed at the junction of the Wandle and the River Thames was hindering the river’s natural flow and biodiversity. With support from The Environment Agency, the Marine Management Organisation, and the Port of London Authority, the half-tide weir was set for demoltion to improve water flow, water quality, and restore lost wildlife habitats.

Land & Water were awarded the contract for demolition of the weir and the subsequent dredging works to clear the river upstream of the weir. There was concern that the weir had been supporting the retaining walls on either side of the river and that these could move during and post demolition.

R L Geotechnical Ltd. were contracted by Land & Water, after referral from Crouch Waterfall, to design and implement a monitoring scheme to monitor the retaining walls on either side of the weir prior to, during, and post demoltion for a period of up to 12 months. 

Liquid levelling cells and tilt meters were installed on the concrete mass retaining wall on the east side of the weir to monitor settlement/heave and tilt. In addition a number of vibrating wire crack-meters were installed to monitor existing cracks in the wall. Submersible tilt-meters were installed on the sheet pile retaining wall on the west side of the weir to monitor tilt of the wall. Data from the tilt-meters on the west bank was sent via a radio link to a central datalogger located on the east bank. Data was then sent via GPRS to the web-based monitoring software. As well as e-mail alerts, there was also a visual alarm on site to alert the site team of excessive movement.

In addition to the automated instrumentation above, prisms and survey targets were installed at the locations of the instrumentation to allow for a manual monitoring survey to be undertaken to verify the automated readings.

The installation was tricky and had to be undertaken by boat in line with the tides. There was also a lack of a permanent power source for the majority of the monitoring period, meaning that everything had to be powered by battery which was changed monthly.

Check out the ‘Customer Success Story‘ on the RST Insruments website!

Links: Land & Water, Crouch Waterfall, Liquid Levelling Cells, Tilt-Meters, Crack-Meters, Wireless, Demolition, Conservation