An Integrated GIS Method – The Influence of Human Activities on Shoreline Change in Western Indian Small Island States: A Two Centuries Analysis of Urban West Unguja - Zanzibar Shoreline

Purpose: Urban areas have a high impact on shoreline changes that are more influenced by human activities rather than natural factors, together with hard structural mitigation and management, which are more practiced compared to other areas. This paper describes shoreline changes of small islands specifically; the shoreline of Urban West of Unguja Island in Zanzibar United Republic of Tanzania. This island has been changed for 174 years in different stages due to human activities including; reclamation of Darajani creek, port expansion at Malindi, Mtoni beach nourishment, sewer and stormwater channeling at Kilimani, construction of walls, groins, jetties, etc.   Methodology: The study uses an integrated method to analyze and detect changes using a sketch plan survey map of 1846 and 1892, a topographic map of 1907 and 1987, an aerial photo of 2004, Landsat images, and google images of 2019 and 2020. These maps were carefully georeferenced with latitude and longitudes, digitized using ArcGIS and demarcated along the study area supported with ground truth observation to analyze the coastal shoreline changes. Findings: The results show that the area experiences more accretion rather than retreat, integrated analysis and projections of the overall accretion and retreat for 174 years is 1,527,693.85 m2 (1.53 km2) and -936,135.48 m2 ( -0.94 km) receptively. The average accretion of land from 1846 to 2020 is 8,779.85m2/yr. (0.0088 km2/yr.) and retreat is -5,380.09m2/yr. (-0.0054 km2/yr.). A major accretion was observed and detected during the early 1900s to late 1987 which were major land transformation while other minor development activities were between 2010 to 2020. Sea walls, groins, beach nourishment, mangroves, barrier islands, and islets are major management practices of the shoreline which show a positive impact. Recommendations: The study finds it more appropriate to use multi datasets as an integrated method to analyze long-term coastal shoreline changes especially when there is limited data.