Groundwater levels

Central Region

*The long term average (LTA) has been calculated statistically, using the long term data record for this hydrograph. The respective drought zones are used as operational triggers, and have been derived using the LTA.

August rainfall was above average in Central region, at 154% of the LTA. Groundwater levels have continued to decline at a slightly steeper rate than the LTA trend, and have now dipped below the LTA curve for the time of year. Soil moisture deficit (SMD) has decreased although remains slightly above average. This combined with warm temperatures and continued plant growth means that groundwater levels are likely to continue to decline until the next recharge season begins later this year.

Predictions indicate that groundwater levels are likely to remain above drought zone 1 for the remainder of 2020 if we receive average rainfall or above. If we receive less than LTA rainfall, levels could drop into drought zone 1 in the Autumn. The amount of rainfall and its distribution through the Autumn will influence when the recharge period begins, which is when groundwater levels turn and start to increase again.

The Chalk-derived baseflow of streams across the Chilterns has remained within the normal range (as classified by the Environment Agency) due to the average Chalk groundwater levels. In catchments where the rivers are also strongly supported by shallow aquifers (Cam, Rib, Mimram, Beane), flows have remained lower, however above average rainfall over the last month has prompted some recovery. The Cam and Ely Ouse river catchment is experiencing below average flows, as reflected in the Environment Agency’s water situation status of prolonged dry weather.