PEMODELAN MIKE21 DALAM KEJADIAN BANJIR ROB MENJELANG GERHANA BULAN DI PESISIR SEMARANG
Coastal Semarang is vulnerable area affected by the flood disaster. Almost every month the area is inundated by tides. The most publicly remembered tidal flood event is the time leading up to the lunar eclipse on January 31, 2018. Early warning tidal flood information needs to be made with a high degree of accuracy and in a form that people can easily understand for mitigation purposes. Tidal type on Semarang Coastal needs to be identified to know the trend of tidal flood events. The Mike 21 Hydrodynamics Model is used to process tidal observation data throughout 2017 into tidal forecast information throughout January 2018. The accuracy value of Mike 21's tidal forecast is measured by Root Mean Square Error (RMSE), as compared with the accuracy of tidal forecasts from Pushidrosal (Hydrography and Oceanography Center, Indonesian Navy) and BIG (Geospatial Information Agency). The best tidal forecast results are then processed in the ArcGIS application, taking the highest tidal forecast values on the day of the event as input data for the creation a map of tidal flood inundation area. The peak of tidal flood incident tends to occur at 06.00 WIB and 17.00 WIB, which based on the identification in Coastal Semarang includes double daily tidal type. Mike 21's tidal forecasts have the best RMSE values. The RMSE for Mike 21, Pushidrosal and BIG forecasts are 10 cm, 30 cm and 22 cm, respectively. The both of Mike21 model and observation result highest tidal value are at 20.00 WIB. The Mike21 model's highest tidal value of 122 cm resulted in a map of the tidal flood inundation area of 1753.35 ha, while the observation result’s highest tidal value of 133 cm resulted in 185.31 ha wider.
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