The evolution of the rivers of East Devon and South Somerset, UK

Abstract

With the exception of the River Tone, which appears to have been separated at an early stage from its neighbours to the south by a major fault, the rivers of south Somerset and east Devon were initiated on a southward dipping Tertiary planation surface. The evolutionary histories of the present-day catchments of the rivers Exe and Otter are complex and inter-related. Those of the adjacent Axe and Teign appear to be less complex and may have evolved relatively independently from the Exe-Otter system. The differences in the histories of the catchments are most clearly demonstrated by their terrace systems. The Exe-Otter catchment has 10 or more terrace levels at heights of up to 140 m above the modern floodplain. In contrast, the Axe, Teign and Tone catchments contain only one or two terrace levels all of which are less than 20 m above the present-day valley floor. The explanation suggested here for the difference involves a sequence of river captures that changed the forerunner of the present-day Otter from a major river capable of producing a 3-km wide gravelly braidplain into a minor stream