where does the water come from?
Chalk streams are fed from groundwater held in the chalk that
makes up the Chiltern Hills, and this gives them some unusual
features. Chalk is an aquifer, which means that it is able to
soak up and hold water – a bit like a sponge. Water can
move through the chalk in cracks called fissures. The water
emerges at ground level in the form of springs that feed the
chalk streams. Since groundwater levels in the chalk vary according
to rainfall and season, chalk streams are naturally intermittent
in their flow.
why do chalk streams sometimes dry up?
During the winter, when rainfall is heavy and able to percolate
through the chalk, the aquifer will be well topped up. The head
of the stream moves up the valley as the water table rises.
In summer, little rainfall percolates into the chalk as it is
mostly taken up by plants and lost through evaporation. The
water table drops and the head of the stream moves down the
valley, leaving the top section of the stream dry. This section
is called a ‘winterbourne’ because it only flows
after the winter rains.
Winterbourne streams have their own special wildlife which is
adapted to cope with intermittent flows.
where does our water come from?
We take our water from the aquifer too. Every time we turn on
the tap, we take water which could be flowing in our chalk streams.
By using water wisely, we can reduce our impact on the streams
and help to maintain natural flows.
