Bourne again... one bourne every minute etc.

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I live in a village which has a chalk stream: the River Nar flowing through it. It is not a long river, eventually making its way towards King's Lynn where it meets the Great Ouse. 

In other parts of the country, there are more ephemeral watercourses, which may only flow during prolongd periods of wet weather. The name these water courses go by is 'bourne', especially when they are called 'winterbournes'. The possible routes these take can be identifed from geology: where chalk meets clay and springs may appear (often along spring-lines) and also possibly by contour patterns such as the one shown here: where there is a valley obviously created by flowing water, but no stream running down it.

These are often called dry valleys, and were formed when previous conditions meant that the ground was frozen, and water ran over the surface as it couldn't infiltrate into the soil, eroding a valley shape as it went. In other cases, these may be the course followed by occasional streams when the water table reaches the surface, or during infiltration excess overland flow. 

The recent heavy rainfall has meant that some chalk streams have come back to life again, which is greate for the riparian (river) ecosystem in those locations, although there is an accompanying flood risk for some residents.


Here's an example of a winterbourne:


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