Added 21/7/2009

From: Attfield, Kerry [mailto:kerry.attfield@environment-agency.gov.uk]
Sent: 14 July 2009 16:08
To:
Cc: Hill, Doug
Subject: Dredging of the Thames

I apologise for the delay in responding to your query on dredging of the Thames, however I only received the final report from our Consultants, Halcrow, yesterday.

The study was undertaken to determine whether available river bed surveys of the Thames from Hurley to Teddington taken between 1994 to 2008, shows that these reaches of the river are naturally changing. The initial results show that these reaches are naturally morphologically dynamic and net annual changes in bed volumes in each of the 15 reaches are significant. For the period of available data most reaches have shown net erosion, with changes in reach bed volume tending to be related to river flow, with net erosion tending to occur over periods of high flow, and net deposition tending to occur over periods of low river flows. Short term variations in bed profiles may be masked by the longer time periods between some surveys. For reaches where data is available at more frequent intervals (Old Windsor, Bell Weir and Penton Hook) significant variations in channel bed levels have been recorded from year to year. I have attached some PDF files indicating both flows and bathymetric surveys for all three reaches over specific time periods, with a note on how to read the data. 

Based on these results it appears that dredging of the River Thames is not necessary as a long term flood-risk solution. However we will continue to monitor changes in the river bed to further understand any future need for dredging.

Regards