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TESTING PROGRAMME
Following discussions with the Environment Agency, it was decided to put earlier plans for a temporary dam at Green Lane on hold, whilst we instead pursue an alternative testing programme using piezometers (boreholes) to measure ground water levels and test the permeability of the ground adjacent to the stream.
Eleven 4-5 metre deep piezometers have been installed along the main route and monitoring has commenced using a purpose built reel and sensor device. During the installation of the boreholes the contractor Costain Geotechnical Services extracted soil samples using special 1- metre long plastic lined steel cutting tubes, which were then removed for analysis to confirm the make up of the ground adjoining the stream (the geology of the Thames Valley typically comprises layers of chalk, gravel, sand and clay).
The boreholes are now being used by volunteer members to capture and chart the movement in ground water and stream levels in the area over time. The Environment Agency is also supplying us with data from its boreholes to the north of Maidenhead, plus information on pumping rates from the various licenced extractions in the area. Finally Readng University is kindly providing us with daily rainfall data for Maidenhead to allow us to better understand the linkages between rainfall, ground water and stream levels along the waterways route.
River bed samples have in addition been taken for analysis and a programme of Falling Head tests was undertaken for us by Costains, to measure the actual permeability of the ground in the vicinity of each borehole as part of the overall water supply assessment. Depending on the results of these and other tests we will then be able to judge whether lining of parts of the channel will be needed, to reduce water losses through the bed.
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