Mitigation of floodwaters inundation due to land subsidence in the coastal area of Semarang City

Semarang city is the capital of Central Java province, which is located on the cost. The Semarang coastal topography is flat, with slope percentage around 0-2%. Most area is almost the same as height as the sea level and in some places are lower. Environmetal problems faced by Semarang related to this topography area tidal inundation, land subsidence and flooding during rainy season. The research was conducted to model locations that area vulnerable to tide inundation. The data of spot height, countour line and the rate of subsidence were analyzed by using Geographic Information System (GIS). The results showed that the Semarang coastal had a high level of vulnerability to inundated area. Tidal flood inundation area was about 2,400 ha with depths varying from 1 to 66 cm. Mitigation of tide inundation impact must be adjusted to land use and social condition of the local community. The house on stilts or lightweight houses that are easy to dismantle pairs is one of the solutions that is suitable for fisherman residential areas. Whereas the trade and service areas must be carried out by raising of the building floor and making protective buildings from sea water.