Smestow Brook - Geology

Geology

The Smestow took its present shape as a result of the last Ice Age. Glacial action removed part of the low ridge, to the north of present-day Wolverhampton, which separates the River Trent and River Severn catchments, creating the Aldersley Gap. As a result, the Smestow was able to break through to the south, and was thus captured from the Trent by the Severn catchment.

In some areas, especially around Wolverhampton, the Smestow runs over beds of gravels, laid down in the last Ice Age. For a large part of its course, however, the Smestow flows over deep Bunter deposits of sandstone, also known as Triassic Sherwood sandstone - similar to the deposits underlying Sherwood Forest in Nottinghamshire and Cannock Chase in Staffordshire. These are highly permeable, allowing the land above to drain quickly and reducing the flow within river courses. As a result, the areas of South Staffordshire around the river, despite fairly high rainfall, had a natural vegetation of heath and open birch woodland. This was modified progressively after the Anglo-Saxon settlement, with a gradual clearance of farmland. With the emergence of modern, high input farming, from the 18th century onwards, the aquifer became increasingly vulnerable to nitrate pollution. The relative decline of heavy industry in the region makes this the main, and growing, pollution threat to water supplies in the Smestow valley.