A GIS Application for the Study of Beach Morphodynamics

Abstract

This research is a continuation of work conducted at the University of Sunderland since 1990 on the impacts of the accumulation of millions of tonnes of colliery spoil on the beaches. Regular surveys of the beaches were undertaken from 1991 spanning a period of about 5 years during which all mining activity ceased on the Durham coast. During mining operations the accumulation of spoil on the beaches affected both the geomorphology and the geochemistry of the beaches. It may also have masked the impact that deep mining of multiple coal seams under the coasts had on the beaches. Once tipping ceased, it was expected that spoil would erode rapidly and that the pattern of erosion would show changes parallel to the shoreline. This was the case on some of the beaches but on others, notably the Dawdon blast beach, anomalies appeared showing localised patches of changes at orientations at variance with the expected pattern. Dawdon Blast beach has been extensively undermined and it is possible that some of these patterns may have been produced by structural changes in the bedrock caused by subsidence. To test this hypothesis, a Geographical Information System (GIS) was used to study changes of the beach surface over the years immediately superseding the cessation of mining, focusing on 3 study areas (Dawdon, Easington and Horden) which present different undermining conditions. It was found that the spatial pattern of significant elevation changes in the Dawdon beach is considerably different from that observed in Easington and Horden. The possible relationship to coastal colliery panels was further tested by obtaining the strain, subsidence and surface heights along the transect from the centre of the worked panels lying east and west of the beach area in Dawdon. The implications for coastal management on this coastline are that areas directly undermined may be suffering subsidence impacts causing increased levels of erosion of beach material. This is an important factor of local significance in assessing coast vulnerability and risk of cliff erosion since changes in bedrock caused by subsidence diminish the role of the beach as a protective influence on coastal defence. The role of the GIS in this research is not only to identify spatial patterns and relationships but also to combine, assess and weight the different factors affecting coastal vulnerability.