Assessment of shoreline changes in the western side of Zanzibar channel using satellite remote sensing

Abstract

The present study uses a satellite remote sensing approach for assessing coastal sediment dynamics in the western side of the Zanzibar channel, Tanzania. Four Landsat images (1986, 1998, 1999 and 2000) were used for the study. Investigation of the four images revealed that the Ruvu delta north of the river mouth has been growing rapidly, especially between 1986 and 1998, with an annual northward linear growth rate of about 133 m year⁻¹ and an annual areal growth rate of about 1 km² every 3 years. The study identified a palaeo-shoreline feature that is parallel to the present shoreline and located about 1.9 km inland from the present shoreline. An important sediment contributor to river Ruvu is derived from the Uluguru Mountains, a tropical mountainous area located about 200 km from the coastline of the Tanzania mainland. The working hypothesis is that either the observed growth of the delta occurred at a gradual rate between 1986 and 1998 or it was mainly an episodic event related to the extreme rainfall events such as the 1997/98 El Niño–Southern Oscillation (ENSO) event, which was associated with extreme rainfall and widespread landslides.

Acknowledgments

The authors gratefully acknowledge the financial support from Sida/SAREC. We wish to thank Dr Eve Arnold (Stockholm University) who critically reviewed the manuscript and suggested many constructive comments. We are also very gratefully to Dr Otto Hermelin (Stockholm University) for his assistance with the map files. Drs Ntahondi Nyandwi and Alfred Muzuka (IMS, Zanzibar) are acknowledged for their good company during the field trip to Ruvu delta.