The Geological Survey Memoir for Canterbury and Folkestone “The Memoir” (Smart et al., 1966) includes an explanation for the right-angled bend at the eastern end of the shallow valley referred to in “An Odd Couple of Valleys” (Photo 1). The Memoir proposes that the original stream was diverted by stream capture.
It suggests that this valley contained a headwater of what is referred to as the “Little Stour” (The Nailbourne) flowing eastwards parallel to the escarpment before turning north along the Elham Valley. At the same time, to the south of the escarpment, a headwater of the East Stour was extending its valley northwards by a process called spring sapping. Eventually, the northward progression of the spring intercepted, or “captured”, the headwater of the Nailbourne, diverting it southwards into the East Stour catchment, and cutting off the water supply to the upper reaches of the Nailbourne.
“The Memoir” also refers to a second stream capture affecting this same head water of the ’Little Stour’ (The Nailbourne). They propose that this capture has occurred in the deeper valley which is on the same alignment and immediately upstream of the valley referred to above. It is described in “An Odd Couple of Valleys” (Photos 2 – 4) where it is referred to as a coombe. The Memoir suggests that the right-angle bend is the elbow of capture. However, it is difficult to accept that that valley was caused formed by stream erosion. Its shape is typical of an Ice Age chalk coombe, and they are formed by the effects of melting permafrost.
Andrew Coleman
23/05/2024
Reference:
Smart, J. G. O., Bisson, G., & Worssam, B. C. (1966). Geology of the Country around Canterbury and Folkestone. Her Majesty’s Stationery Office.
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