River Bank Erosion and the Influence of Frost: A Statistical Examination

Abstract

River bank retreat around two meander bends in South Wales was monitored over a two-year period with dense grid-networks of erosion pins. Results show that strong seasonality in river bank erosion occurs, with almost all retreat taking place in the winter months of December, January and February. Catchment instrumentation and field observations allowed this seasonal pattern to be interpreted with respect to a range of geomorphological, hydrological and meteorological processes or indices. Frost action emerges as the strongest control of average and maximum bank erosion at the upstream sites. Intense cryergic disturbance of the bank surface often takes place in winter and prepares a layer of material for ready removal during subsequent stage rises. Minimal fluvial erosion occurs on unprepared banks. Detailed regression analyses provide the first statistical demonstration in a bank erosion study of the dominance of frost-related variables over other factors. Moreover, multiple regression equations developed for the first half of the study period successfully predicted bank erosion rates in the second half, and vice-versa. Although fluvial or hydrological factors seem to control the area of bank eroded, the indication here that the amount or intensity of erosion is largely determined by previous cryergic activity suggests that these processes may warrant closer scrutiny in future investigations.