Hydrodynamics Features and Coastal Vulnerability of Sayung Sub-District, Demak, Central Java, Indonesia

The Sayung sub-district is an abrasion area in Demak Regency that is mostly affected by sea level rise. The purpose of this research is to determine the features of hydrodynamics and coastal dynamics occurrence in the sub-district of Sayung. Collecting field data/information and modeling approach (tides, waves, currents, weather and coastline changes) have been done in Sayung, Demak. The wave height in the eastern coast is the highest. The significant wave height in 2004 was greater than March 2016 showing that in 2004 the wind energy transfers were larger than 2016. The refraction coefficient in 2016 for all directions was the greatest from the west at the depth of 8 m and the smallest one was identified in the south. The refraction coefficient in 2004 for any direction yielded the largest value in the southwest at the depth of 2 m and the smallest one was identified the south as well. During a cycle of tidal fluctuation, it occurs twice flood and ebb events. The maximum depth is 6.5 m located about 3.8 km from the coastline. The sediment thickness reached 564,886.39 m3. Coastline changes occurred in 2003 and started to gain sedimentation in 2015. Data and information produced can be useful as a basis for further developments to mitigate abrasion and to create policy-brief in managing coastline affected abrasion even though some improvement efforts have been made.