MRA: March Media

 

 

 
Our little river has been punching well above its weight in the news and social media forums recently with the lead articles being mainly about sewer overflows in Chalfont St Peter and groundwater flooding in Chalfont St Giles – (not forgetting the CStG pond liner!).   It has been fun trying to correct some of the wilder ideas and engaging with press, councillors, MP’s, Thameswater and others in the search for future improvements.
 
  • No, the Misbourne has not ‘broken its banks and flooded Chalfont St Peter” : it doesn’t!   (For a short length from the constraint and local low spot by the Vic Wotton bridge some flow takes a short detour down the footpath and back into the river from the car park before reaching the Greyhound; otherwise its doing a pretty good job,)
 
  • Similarly, the situation at Chalfont St Giles and further up the valley is due to very high groundwater levels – see sketches and charts below.  Observers will have noticed standing water in Stone Meadow long before it joined up with the river to show a common level across the valley.
 
  • Yes, the water pouring out from Affinity’s works in Mill Lane, CStG is groundwater, not a leak or sewage discharge.  
 
  • No, the closing of the small abstraction borehole at those works will not have had a significant effect on the flow in the river – talking in order of 1%.
 
  • Yes, the fact that manholes and sewers along the valley are submerged, or have cracks and leaks below the water table, inevitably means that enormous quantities of groundwater enter the system. which eventually overflow where others are feeding in – as outside the Greyhound and Yaprak in Chalfont St Peter.  Without the enormous pumping and tankering operation, all this would would have found its way into the river.  In 2001, I think it was actually pumped into the river avoiding High Street closure but incurring unacceptable pollution and more widespread unpleasantness.  Latest information is that some pressure grouting to seal leaky manholes is in hand as and when possible and relining some of the trunk sewer itself is being investigated.  Good news, except we have been pressing for this for more than 10 years and patching may not suffice.  A new parallel sewer seems unlikely .
 
  • It may have been “the wettest February in 256 years” in Thameswater’s area, or perhaps more likely in England as a whole.  However, even with 29 days, I’m not sure that last month earned that claim across our catchment. In any case, January 2014, for instance, was over an inch wetter and, at Heathrow for instance 1951 was a much wetter February.   In the 12 months to 1st March this year, the Chalfonts had 944 mm of rain – exceptionally high – but not greater than 966 in 2001 (without a leap-year!).  Yes, “exceptional” but not “unprecedented”.  
 
  • Of course, there is much muttering regarding HS2 impacts
    • We understand that water used for the actual tunnel and vent shaft constructon is sent down the tunnel for treatment, by-passing the Misbourne.
    • But the size of the scar at, for instance the Great Missenden works immediately begs the question asking where does the run-off from the sites now go when before there was grass and trees.  Trish (“MRA North”) and Chiltern Society have been vigorously ensuring the various consent conditions are strictly observed and discharges into the Misbourne or the overloaded stage system are eliminated.
    • More interesting is the continuing debate about the effect that building two enormous tunnels through the aquifer might have on cross flows within it.  Will water be dammed behind and forced up and over?  ……. or given slopes off both the tunnels and the groundwater levels, will it be displaced along the line of the tunnel to flow under? The answer depends on many factors – the natural GWL at any time, the line of flow compared to the line of the tunnel and the actual type and condition of the chalk along the way.  This long running debate is definitely not over but, to date, it does not seem possible to prove any effect, or to rule out the possibility.  It is interesting but possibly totally unrelated that the groundwater levels in the lower part of the catchment – HS2 tunnel country – are noticeably more extraordinary than those above Great Missenden.
 
  • Undoubtedly, there have been large increases in housing since the trunk sewer and main sewers were installed 70 years ago.  We have to accept that, technically, if fully watertight, the load is still within their design capacity so we have to be careful with that argument but they are not watertight.  Paved gardens and illegal downpipe connections are also an issue.
 
Many businesses and a few homes have had, and continue to have, really challenging times.  Those local pubs, restaurants and shops  that have lost significant takings really need our support and will be delighted to see you.  Nevertheless, upstream of the Chalfonts, and away from the media, it seems that the general feeling has been that it’s good to see the Misbourne flowing well along it full length and no major concerns have been raised.
 
 
March.jpeg         Summer.jpeg
 
 
The graph below shows average of all GWL’s along the valley for the exceptional years 2000-2001 and 2013-2014, together with the minimum average, average and maximum averages for the past 30 years against the progress of 2023-20234 to 1st March.  “Exceptional but not unprecedented”, though heavy rain continuing into March.
 
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These similar plots below for individual locations e.g. Chalfont St Peter and Mayortone Manor (Wendover Dean) suggest recent months rainfall has had a noticeably more significant effect through the Chalfonts than at the top of the valley.  Locally more extreme rain storms???, HS2???, Differing response from the different chalk strata along the valley??? – Comments please!
 
 
image.pngPicture 3.jpeg
 
With the focus on the sewerage issues and local flooding, little attention has been given to the continuing unfolding disaster of the 2020 “Improvement works” downstream of Amersham by-pass where the river has escaped from both the artificial bund of the wetland area and from the leat in which it quietly ran for possibly centuries and is now redefining its route down the South Bucks Way to rejoin its ancient course downstream of Quarrendion Mill.  In the long term, it is possible that this can be good news for the “mending the Misbourne” agenda by forcing the originally preferred scope of the “improvements” in favour of the failed compromise scheme, and  providing a natural river adjacent to the Way.
 
The Greyhound at Chalfont St Peter has been having a terrible time but should be open again Monday 18th.  Let’s plan for a “not-a-meeting” there on Wednesday 27th March from 7.15 pm.  We can talk then about resuming river care and particularly removing some of the accumulated larger debris with a view to helping the valley drain as quickly as possible.
 
Well done and thank you if you’ve made it to the end of this long spiel.  As always, there is more info on our website and up to the minute comms on the WhatsApp – just drop me a line if you would like to join the Group.