Spatial and temporal variations in soft-cliff erosion along the Holderness coast, East Riding of Yorkshire, UK

Abstract

The Holderness coast is composed largely of ‘soft’ Quaternary sediments, mainly glacial till, which form cliffs up to 38 m high. Cliff erosion rates have shown a complex pattern of spatial and temporal variation over the past 160 years which reflects interaction of natural processes and human interventions, notably building of coastal defences at Bridlington, Hornsea, Withernsea, Mappleton, and Easington. A former single coastal cell, extending between Flamborough Head and the Spurn Peninsula, is breaking down into a series of separate sub-cells defined by sections of defended coast. Between these ‘hard points’ the shoreline is developing as a series of shallow bays which are deepest immediately to the south (downdrift) of the defences. Superimposed on this pattern are smaller-scale variations which reflect the effects of dynamic beach features on wave energy exposure at the cliff toe. Cliff recession rates can exceed 4 m a−1 when beach troughs lie in front of the cliff toe but may fall close to zero as a sand wave passes. Erosion rates on the undefended coast showed an increase in the period 1989–2013 compared with earlier epochs and further increases can be anticipated due to sea level rise over the course of the next century. The effects of climate change on storminess remain uncertain but any increase would further enhance the erosional trend. The implications are future increased rates of cliff top recession and increased risk to infrastructure close to the coast in the medium to longer term. Increased erosion rates will increase the rate of sediment supply to the nearshore system, but it is unclear how much of the fine sediment released will be transported into the Humber estuary to maintain tidal flats and saltmarshes, and how much of the sand and gravel will travel along the beach system to sustain the Spurn Peninsula.