River Chess Association

Very little rain fell in this area during November, causing groundwater levels to fall and river flows to decline further. Just 45% of the long term average (LTA) rainfall fell in the North East Thames Area, making this the driest November since 1989. And more locally, the Colne-Chilterns-Chalk area that covers the Chess received only 11% of effective rainfall (that which contributes to refilling the aquifer which is the source of the Chess) which equates to just 4 mm.

With the upper reaches of the Chess having been completely dry for many months, an abnormally wet winter is needed to help the river to recover. Instead, however, the whole of the winter so far has been very dry with just 35% of the LTA rainfall recorded from the 1st October to the 30th November, with 9% of the LTA effective rainfall.

Unsurprisingly, the groundwater levels recorded at Ashley Green are defined as "notably low". The soil moisture deficit is the difference between the amount of water actually in the soil and the amount that the soil can hold; for the Colne-Chilterns-Chalk region this deficit was measured as 112 mm, compared to the LTA value of just 23 mm.

As the winter continues to be dry, there is less and less time for the aquifer to recharge before the spring, when the recharge period normally stops. This suggests that conditions could get even worse for the Chess in 2012. We believe that we are already seeing the damaging effects of low flows in the river. Our November riverfly monitoring, which is carried out at seven sites along the river, saw three failures (below acceptable levels of riverfly life) and two sites that cannot be sampled because they are dry. These results are contributing towards low flow investigations being carried out by the Environment Agency. To see the full Water Situation Report for November, visit the Environment Agency's web site.

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