Causes and Trends in Shoreline Change in The Western Region of Ghana

ABSTRACT

Shoreline change is an issue of concern to most coastal managers because the coastal zone is home to over 60% of the world’s population. In Ghana, shoreline change has been associated with loss of economic lands and properties. Previous researches have shown that the Ghana coastline is eroding at variable rates; the Eastern and Central Zones are receding while the Western zone is thought of as stable. This opinion, however, contrasts field observations and interview with local coastal community members. This research therefore sought to determine the shoreline change trends in the study area through modelling the driving and resistive factors along the shores. The factors investigated are sea-level rise, wave impact, sediment supplied by rivers, resistance of coastal material and human impact. Multi-temporal spatial datasets, hydrodynamic datasets, geological map of the area and systematically sampled field measurements were used. Standard procedures were employed to compute values for the eight variables that were selected as proxies for the driving and resistive variables. Analysis was carried out in short-term (1974-2005) and long-term (1895-2005) change categories in shoreline trends. Average short term change rate of -4.18 ± 0.10 m/year and long term change rate of -7.25 ± 0.11 m/year were obtained for the entire study area.

The results revealed that the strength of hard shore outcrops, the shear strength of the soil, the sediment supplied by rivers and human impact contributed significantly to variations in the shoreline change trends along the study area. It was identified that shoreline change trends observed in the study area is mainly caused by physical processes of wave action, which is modified by the characteristic features along the shores, and aggravated by human impact. The shoreline change trends reflect the coastal material resistance at the various sections along the coastline; this is attributed largely to the formation history of the coast. It was, however, found out that the effect of sea level rise on the shoreline trends was minimal. The Western Section of the study area was found to be more vulnerable to erosive forces relative to the Eastern Section. It is recommended that a non-linear model be employed for confirmation of the findings.