Geology and hydrogeology ... …
Report No. SRL/FP/004.1 (10/05/2006)
Page 2-3 On Kimmeridge Clay:
“The clay will also provide an effective hydraulic barrier between ……and the underlying Corallian Limestones”.
Only if it is rather thick (for example, the 30 m erroneously assumed by Npower) and if it has an uninterrupted structure. Since Npower knows neither of these and have totally neglected fossils, palaeo-channels and faulting in the ragstone, this is, at best, a guess and, at worst, a lie.
Page 2-4 Aquifer properties.
Taking the height of the groundwater surface (51.1 to 52.44m) there is a variation of 1.34 m across the site. That produces a gradient of at least 2.6x10-3 m/m whereas the value quoted on the same page is 1x10-3 m/m, a factor 2.6 different. This is an important error, used later on page 2-15, to discuss the magnitude of the groundwater flow.
“The capacity of [the] drainage system need only be small…
In fact, so small that if we assume a flow speed of 3 m/s during a 1 in 1 year flood event, the cross sectional area need only be 0.042 m2. Even if this ditch is 1 km long and we ignore the fact that some of it already exists, its total volume will be less than 100 cubic metres. If we allow for slower flows and some spare capacity, this volume will still lie below 1000 cu m. BUT on page 2-9 it is stated that the ditch
“…will provide a small additional flood storage volume in the area…which will be connected to the River Thames floodplain.”
This additional volume is too small to matter. At under 1000 cu m it must be compared with the loss of 100,000 cu m of floodplain lost by bunding Lake E. This comment is almost a joke, but it is presented seriously. It is actually serious, because it shows that although npower state that Lake E is not in the floodplain, they secretly believe that it might be – as indeed it is!
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© SAVE RADLEY LAKES 2006