Chesham Sewage Treatment Works released sewage into the Chess for nearly 11 hours following Friday's heavy rain.
The River Chess water vole population has declined by 46% since 2013. We need to act now to prevent their local extinction.
Last year saw an expansion of our work, getting more people - especially children, involved in the river and we helped to initiate a study into low flows on the upper Chess.
Upon first glance, it seems peculiar that the Chesham stretch of the River Chess is dry in Winter; our cooler, wetter season.
The Mystery of Abstraction & Flooding in the Chesham Vale
Feb 19, 2014
The upper River Chess has three main water sources. They are springs at Missenden Road, Bury Brook (Pednor) and Vale Brook (Chesham Vale). The flow from these three sources is fed by springs from the chalk aquifer. The chalk aquifer is recharged by rain, mainly during the autumn and winter. The aquifer is emptied as water is abstracted for drinking water from boreholes and through the natural spring flows. During spring and summer, rainfall rates decline and what rain does fall is mainly lost to vegetation and evaporation. There is little or no recharge during the summer and as this happens, flows in the river decline.
By the end of November 2013 all three sources of the Upper Chess were almost dry.
Left: Combined flows from the Missenden Rd and Bury Brook sources, 22nd November 2013. Right: Lord's Mill Weir, Chesham, so dry a cat can sun itself with no fear of getting wet, 26th November 2013.
As a result of exceptional recent heavy rain, we now see the springs flowing at significant rates. However, there is one exception; the Vale Brook refuses to flow spring water. As can be seen from the picture below, taken on the 7th February 2014, the Vale Brook only flows dirty runoff. This is a mystery to us.
The Vale Brook "flowing" at Townsend Road next to Topps Tiles, 7th February 2014.
Conversely, the Bury Brook and Missenden Road sources are flowing at considerable rates. These two sources merge at the 1879 Lawn Tennis & Squash Club and pass the Queen's Head pub as one flow. Note how different this looks from the picture taken at the same location on the 22nd November 2013 and how different it looks from the Vale Brook.
Combined flows from the Missenden Road and Bury Brook sources, 7th February 2014.
The Vale Brook joins the Chess in Duck Alley behind the Water Meadow Surgery. We can see from the picture below the water entering the Chess from the Vale Brook is highly polluted.
The Vale Brook enters the Chess in Duck Alley delivering highly polluted water, 7th February 2014.
So why is the Vale Brook effectively dry when all around springs are flowing so strongly? We suspect this is due to the fact that the Chesham Vale, the location of the Vale Brook, is also home to two of the biggest aquifer abstraction sites. One at Hawridge is operated by Thames Water and the other at Alma Road is operated by Affinity Water. The Hawridge Pumping Station supplies drinking water to customers in Thame and the Alma Road Pumping Station supplies drinking water to Chesham. These two sites are responsible for 50% of all water abstracted from the chalk aquifer in the Chess catchment.
In February 2001, Chesham was flooded by groundwater from the Chesham Vale (Vale Brook) continuously for more than 4 months. Leading up to and during this period there was exceptional rain, similar to that we are currently experiencing. The Vale Road in Chesham did flood on the 7th February 2014, but this was from runoff, not groundwater. The groundwater levels in the Chesham Vale today are still low, especially when compared to the rest of the Chess catchment.
Left: Bury Brook source in the Pednor Vale, full and flowing towards Chesham, 7th February 2014 and Right: Water flowing at Lord's Mill - this is where the cat was sitting in November 2013, taken 8th February 2014
During the groundwater floods of 2001, the equipment yard at George Browns in Vale Road was flooded for 6 months. To avoid this happening again, a groundwater drainage system was installed. We inspected the groundwater drainage manhole in George Brown's yard on the 7th February 2014. It was the driest place in the Chess Valley, despite the heavy rain and the fact that it is 3m deep.
Groundwater drainage at Brown's Yard, Vale Road - dry as a biscuit tin, 7th February 2014.
We suspect that a contributing factor to the groundwater flooding of 2001 might have something to do with the rates of abstraction at the Hawridge Pumping Station at the time. We have heard verbal statements from neighbours in the Chesham Vale saying that in December 2000 and Jan-Feb 2001, Thames Water were carrying out major engineering works at Hawridge, which might have meant the abstraction pumps were shut down.
All the rain we have had recently may result in groundwater flooding in the Chesham Vale. If that is the case, we should be preparing for it. This would have major ramifications for the state of the Vale Brook and the Vale Brook Culvert.
We are in discussion with the Environment Agency, Thames Water and Affinity Water to see if we can resolve this mystery and return spring water flows to the Vale Brook.