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The volume of water held in the chalk aquifer does vary from time to time, which means that during drier periods there may be insufficient water to feed into some of the tributaries known as ‘winterbournes’. One example is the River Swift between Upton and Hurstbourne Tarrant (Stage 1 and Walk 1).

The overriding influence of the chalk geology starts to reduce from about Houghton (Walks 11 and 12) onwards. There is a much greater prevalence of clay and gravel deposits in the lower part of the Test Valley where there are several quarries. As the Test progresses southwards it also broadens out into a more braided system or network of streams and channels that finally coalesce to form a single channel at the entrance to Southampton Water.

Water meadows

In the 18th century, water meadows were created along many stretches of the Test. This novel concept at the time was designed to extend the growing season to produce two crops of grass rather than just the one. A principal requirement was a supply of clear water at a constant temperature above freezing, and chalk streams were ideal candidates for the purpose. The intention was not to flood the ground but simply to keep it damp and at a temperature sufficient to minimise the effect of frosts during the winter and early spring. As a consequence, grass began to grow some weeks earlier than it would have done otherwise and therefore grew for longer; it was also of a higher quality as the ground absorbed the nutrients from the river.