Quantifying surface water decreasing in Segara Anakan Lagoon

Abstract

Segara Anakan is the biggest mangrove-fringed lagoon on the south coast of Java Island. It is the estuary for three major rivers, Citanduy, Cibeureum, and Cikonde, Citanduy Watershed. The lagoon is subject to a significant sedimentation process. As a result, its surface water area is decreasing over time. It is separated from The Indian Ocean by Nusakambangan Island, a famous prison island in Indonesia. Lagoon's water shrinkage is threatening not only food security but also national security. Access to the island will be more easily. A rapid assessment was carried out to quantify surface water decreasing with a spatial analysis approach.  Historical cartographic maps and Landsat-5 images of Segara Anakan were digitized using ArcMap and delineated. The surface water area decreased from 65 km2 in 1942 to 8.5 km2 in 2017, and even the conservation project had been applied from 1989 to 2013. Universal Soil Loss Equation (USLE) was applied to quantify the sediment supply from the watershed. From 2005 to 2016, the watershed average sediment supply reaches 3 mm/year or equal to 22 million tons/year. The highest sediment supply rate occurred in 2010 at 5.14 mm/year or equal to 43 million tons/year. A combination of spatial and empirical analyses gives a better understanding of significant factors that influenced the lagoon's water decreasing process.