Why do chalk streams sometimes 
dry up?
Unlike the Bengal tiger, chalk streams don’t deal well with the heat.
During summer, rainfall typically doesn’t reach 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, potentially leaving the top layer of a chalk stream dry. This layer is called a ‘winterbourne’ because it only flows after the winter rains.
During the winter when temperatures are cooler and there is less plant growth, more rainfall typically filters through to the chalk. This tops up the aquifer and the head of the stream moves up the valley as the water table rises.
Because of this natural water cycle, during the summer and autumn months, some reaches of chalk streams can dry up. Although the wildlife and plants that inhabit winterbournes are used to these conditions, they can be negatively impacted by lower flows. We are working hard to reduce the amount of water we take to leave it in the environment.
We’re not asking you to invite a family of otters to stay, instead if we can all waste less water, we can help support these rare and impressive eco systems.
What are water tables and 
aquifers?
A water table is the boundary between water-saturated ground and unsaturated ground. Below the water table, rocks like chalk are full of water. An area’s water table can fluctuate as water seeps down from the surface.
Pockets of water existing below the water table are called aquifers.