Quantifying surface water decreasing in Segara Anakan Lagoon

Abstract

Segara Anakan is the largest mangrove-fringed lagoon on the south coast of Java Island. It is a productive coastal system that provides environmental services for the community in the vicinity of the lagoon, such as fisheries production and tourism. Right now, the lagoon is facing surface water shrinking due to the intensive sedimentation process. The fishing ground area becomes limited; thus, the fisherman should sail further to the sea zone to catch fish. To quantify the lagoon’s surface water decreasing rate, we applied a spatial analysis method. Historical cartographic maps and satellite images of Segara Anakan were digitised using ArcMap. We used a reclassification tool to classify land and water for the satellite image before digitising it. The result showed that the lagoon’s surface water area decreased from 65 km2 in 1942 to 8.5 km2 in 2017. Since the lagoon received freshwater supply from Citanduy River, we applied Universal Soil Loss Equation (USLE) to calculate sediment supply from the watershed. The result showed that from 2005 to 2016, the average sediment supply reached 3 mm/year or equal to 22 million tons/year. The highest sediment supply rate occurred in 2010 at 5.14 mm/year or similar to 43 million tons/year. Linking between integrated coastal zone management with watershed management should be implemented to reduce the rate of sedimentation.