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 into the river Cam. This demonstration shows how the trees and vegetation around the chalk streams are affected when we pump out water during periods of drought.
Run the simulation and watch the water level drop. Turn the rainfall down and abstraction up - see the trees and vegetation go brown.
When there is not enough rainfall to replace the water taken for our use, the water level in the aquifer drops. When the aquifer level is very low the flow in the streams reduce to a trickle. To reduce the damage to wildlife and vegetation we can pump water directly into the stream. However, the water gradually soaks into the stream bed.
Switch on the pump into the stream and try again. Pumping protects vegetation close to the pump site.
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 the depth of 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 the 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 as well as 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 summer 2019. The chalk streams are a special habitat for wildlife and need protection. For further information: