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Geology and hydrogeology ... …

Report No. SRL/FP/004.1 (10/05/2006)

E, one to remove fish, another for dry-working? Was Lake E drained via Lake F or not? There seems to be conflicting evidence. Also, is it actually the case that the water level in Lake F was unaffected or not (and indeed, whose recollection of an event(s) a number of years ago is correct?) It is worth pointing out that, if the draining took place during the angling close season, there may have been no complaint from the angling alliance. There are eyewitness reports36 that Lake M (Orchard Pool) dried up when they drained H/I, as did all the surrounding ditches, which suggests a strong likelihood that draining a lake, such as Lake E, has the potential to affect groundwater levels over a wide area. BUT the big question is, if Lake E is drained to prepare for bunding to receive PFA from Didcot, will Lake F be affected? Without more research I do not think we know the definite answer to

that question and must still fear for irreparable ecological damage to Lake F.

However,

we are left with a converse question.

If Lake E was indeed drained directly to the Thames

(not via Lake F) and if indeed the water level in Lake F was maintained level, why was that? The worrying answer is that Lake F may be spring us to the next question.

at a fed.

satisfactory This brings

On whether springs exist in the vicinity of Radley Lakes and whether such springs can damage the sealing efficiency of the clay bund of existing and proposed PFA dumps.

This addresses the question of whether or not there are springs at Radley. If there are, then this could explain why draining Lake E in the past might have had little affect on Lake F. What other evidence is there for springs at Radley? First, we know that springs can be formed at any faulting in the Corrallian Rag, a layer of predominantly limestone (often shelly, as at Headington) which underlies the Kimmeridge Clay. (Such springs occur along a line of villages from Iffley to Otmoor and Beckley and springs in north and west Abingdon (fed by pressure from Boars Hill and perhaps Lodge Hill) may also be related to faulting in t h e C o r r a l l i a n R a g . ) . ) A l s o t h e r e a r e s p r i n g s e v e n c l o s e r t o R a d l e y . T h e r e i s a l i n e o f s p r i n g s a l o n g t h e n o r t h e r n p a r t o f L o n g m e a d L a k e ( a b o u t 1 k m t o t h e W e s t o f L a k e E ) 3 7 . A n d t h e r e a r e s p r i n g s a t A b b e y F i s h p o n d s ( a b o u t 5 0 0 m t o t h e N o r t h w e s t o f L a k e E An additional spring is visible at the western end of Barton Lane, where it emerges from the ground and flows under the Sustrans National Cycleway and into Longmead Lake. Secondly, divers who did a survey on behalf of Save Radley Lakes reported coldwater upwellings in Lake F, suggesting water entering from below, but this is not proven. Thirdly is the search for an explanation for the apparent leakage from Lakes H/I at Radley ) 3 8 . ( e v i d e n c e , t h e o b s e r v a t i o n o f p o l l u t e d w a t e r s o u t h o f L a k e M a n d o f c o n t a m i n a t i o n o f b o r e h o l e s a m p l e s t o t h e s o u t h o f L a k e s H / I 4 ) . U n d e r g r o u n d s p r i n g s c a n o c c u r a n y w within the gravel – and their presence is revealed only by excavation. If there were springs beneath Lakes H/I, there would be damage to the sealing ability of its clay bund. Springs cannot be capped by covering with a few feet of clay. The hydraulic pressure driving a spring will typically be of sufficient force to penetrate any weaknesses in or under the sealing layers, and will erode those layers, probably quite rapidly, in the process. Evidence of springs under the sealing layers might be the appearance of excessive or unexplained h e r e g r o u n d w a t e r o r w a t e r l o g g i n g i n t h e a r e a s i m m e d i a t e l y o u t s i d e t h e b u n d s w h e r e t h e s p r i n g w a t e r i s l e a k i n g t o . S u c h a r e a s d o o c c u r 4 . I f a s p r i n g w e r e t o b r e a k t h r o u g h i n t o t h e P F A w i t h i n t h e l a k e a b o v e , i t w o u l d e r o d e v o i d s w i t h i n i t , p o s s i b l y c a u s i n g i n s t a b i l i t y o f t h e l a y e r s a b o v e ( a n e x p l a n a t i o n o f D r E e l e s s w a l l o w h o l e s 4 p e r h a p s ? ) . A n o t h e r o b s e r v a which might be consistent with the spring hypothesis is that Npower have found that the t i o n

36

Eeles R M G, pers. comm.

37

Eeles R M G pers. comm.

38

White M, pers. comm.

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© SAVE RADLEY LAKES 2006

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