IMPACTS OF SHORELINE CHANGE ON THE NEARSHORE MARINE ENVIRONMENT AT GAZI BAY, KENYA; BETWEEN 1989 AND 2020

Abstract

Coastal zones are dynamic environments influenced by both human and natural processes. In the current study, the objectives were to estimate change in shoreline at Gazi bay between 1989 and 2020, to identify the spatial-temporal changes of the nearshore marine environment; particularly on mangrove forests and to establish hotspot areas of shoreline change. The study applied both longitudinal and ecological research design. Digital Shoreline Analysis System (DSAS 5.0), a software within ArcGIS Platform computed change statistics along the study area over the study period. Kalman filter model was used to project future shoreline positions. Supervised, and unsupervised classification methods were used in detecting vegetational change. The relationship between shoreline change and mangrove cover change was examined using the Pearson Correlation coefficient. The average End Point Rate (EPR) of shoreline change at Gazi bay was estimated at -1.38 m/y, with the northerner sections of the western creek showing an accretion rate of 2.38 m/y. At least 88.62 hectares of the mangroves had been affected by the sedimentation processes, representing 55% of mangroves in the study site. A hotspot area exhibiting a change of -4.99m/y was observed at the opening of the Mkurumudzi River, where sandspits and sandbars had formed. Other hotspots areas were at the site with introduced artificial rocks to serve as gabions, fish landing sites, and at the northern side of western creek that had enhanced sediment accretions killing mangroves. A negative correlation between shoreline change and mangrove cover loss was observed, though not statistically significant (r=-0.536, p=0.273, α=0.05). Assessing the dynamics and vulnerabilities of the coastal zones is very crucial in understanding sustainable coastal development and management. These findings provide valuable insights on shoreline changes that could contribute towards integrated coastal zone management strategies for the area.