2018 – April Advances

Slowly, some results from HS2’s massive ground investigation programme are becoming public. Revisions to the British Geological Society’s maps in 1992 enabled a huge step forward in appreciating the geology of the Chilterns and the Misbourne valley. Understanding of the various chalk strata has evolved subsequently with work by, particularly, Dr Haydon Bailey. Some of the local detail came from the very boreholes that we now use for our monthly study of groundwater levels. Now the HS2 investigation has confirmed the extremely fractured nature of the chalk to a significant depth between Amersham and Chalfont St Peter; extending even deeper at the crucial Chalfont St Giles crossing point than that advised to, and ignored by, the Parliamentary Select Committees. The new data also identifies a number of faults, and other features, not previously mapped although suspected. These significant discontinuities to the simple, basically three layer, picture we have used before undoubtedly complicate the easy explanation of the enigmatic flow patterns that we have attempted and will warrant further study. Perhaps suffice to say the risks to future flow in the river and stability of the ground above the tunnel appear greater even than expected and remain to be mitigated. We must rely on the Environment Agency to ensure appropriate measures are implemented – in my view including environmentally sensitive buried lining to the river for at least 500m at each crossing point.

Meanwhile, also slowly, the river is recovering from the severe drought of last year, which saw the first period of no-flow at Amersham Church since 2006, (previous was 1997, when the river was dry along its whole course). People continue to express amazement that recent rainfall has not brought continuous flow but, in fact, groundwater levels are still below average for the time of year – approximately 2m below through the Chalfonts, though much healthier further upstream.

One problem with being retired is that there is never enough time to fit everything in. We have attempted a couple of work days this year but each time were dissuaded form going ahead by sub-zero temperatures – there was one day when 3 of our keenest expressed disappointment that I wasn’t happy to venture out in the falling snow! There is no doubt much to do – so many hands required – but recently the calendar has had no gaps. Particular tasks include clearing the way to join up the flow at the Recycling Centre with that below Bottom House Farm Lane; to clear though the woods downstream; and the annual onslaught on the leat though to Mill Lane. Please let me know if you can join us for some rewarding spring cleaning at work parties on Saturday 28th April morning 9.30 am), or afternoon (1.45 pm) shifts and/or Wednesday morning (10.00 am) on 2nd May.

As usual, I will send further details to those who contact me. If you suspect I may not have it, please let me know your shoe size so I can sort appropriate waders. (I will address the issues of GDPR in a future letter!) I’m still (slightly) optimistic that we can get flow to Chalfont St Giles in May.

Finally, are you able to offer part of a garage or shed or similar to store all our waders, tools, bags etc. – we only need approximately 10 cubic metres? Our present, very convenient facility in next door’s garage won’t be available for many more months.

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