Sea Level Change and Its Impact To The Coastal Area of Semarang City, Central Java

Abstract

Sea level changing along the time with Mean Sea Level (MSL) shows increasing trend. Semarang City that facing subsidence also impacted by the change of sea level in term of sea level rise and tides. The recorded and reconstructed data (from CSIRO) shows that global sea level rose to 6.83 cm by Dec-2009. Regional sea level change data from University of Colorado also shows the increasing trend of sea level. Three months (Dec-2011 to Feb-2012) realistic tides model that has been generated using FVCOM shows the highest level of the sea surface was 0.473 m while measured sea level in coastal water area of Semarang City by 2010 was 94.669 cm. Measured sea level has to be corrected because the area where it measured experiencing land subsidence. Correction result shows isostatic mean sea level in 2010 was 52.070 cm. Subsidence rate in the location where sea level has measured (Tanjung Mas) can be estimate with the deviation between mean sea level data from tide gauge that experiencing subsidence and isostatic sea level. The result of estimation shows subsidence rate in Tanjung Mas is 7.1 cm/year. The impact of sea level change until 2011 has been formed 1,043.527 Ha of submergence area. Projection in the future shows that in next ten years submergence area will reach ± 3,627 Ha while in next 15 years submergence area will reach ± 4,364 Ha and in next 20 years submergence area will reach ± 4,641 Ha. When spring tides occur, the impact of sea level change will getting worst because area with altitude up to 0.47 from submergence area will be inundated by seawater.