Impacts of our water use

In Cambridge we get our water from an aquifer under the Gog Magog Hills. The water is pumped from boreholes. The same aquifer also feeds streams that flow the river Cam.

When there is low rainfall, our use of water lowers the water table reducing flow in the streams. This can seriously harm vegetation at the surface. To reduce the damage we can pump water directly into the stream. Compare the results of 'reset' followed by two or three 'no rain' periods with and without pumping.

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The diagram shows a vertical cross section through an aquifer, such as the chalk under the Gog Magog hills. Chalk has tiny spaces that can hold water, like a sponge. Water can also flow through the chalk but more slowly than at the surface. At the borehole, water is pumped out for our use. This lowers the level of water in the aquifer. The arrows on the borehole allow you to measure how deep is the water level.

The vegetation at the base of the tree is affected when the stream dries up. The trees are affected when the water level drops. After several periods of no rain the stream is dry (so tge vegetation is brown) and the water table has dropped enough to affect the first tree very badly. If you turn pumping into the stream, this protects the vegetation from drying up at first. However, the water table drops further affecting the trees worse than before. Also, the water in the stream dwindles (by evaporation and by soaking into the stream bed) so that vegetation can still be affected further downstream.

This is why the chalk streams that feed the River Cam suffered so badly in summar 2019. The chalk streams are a special habitat for wildlife and need protection. Read about the River Cam Manifesto here.

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Pumping into the stream