Geospatial Analysis of Predicted Tidal Flood Inundation (2024–2059) on Coastal Land Use in the Semarang-Demak Toll-Seawall Integration Plan, Central Java, Indonesia

Abstract

The low topography of the Semarang-Demak coastal area makes it prone to tidal flooding, primarily caused by land subsidence. This study aims to model the existing tidal flood inundation area in 2024 and make predictions for 2054 and 2059, focusing on land use in coastal regions based on geospatial modeling before and after the construction of the Semarang-Demak toll road and sea wall integration. The data used include tidal levels, sea level rise, land subsidence, and land elevation, obtained from BMKG, CMEMS, SAR Sentinel 1-A, and Sentinel 2-A imagery. The least square method was used to analyze tidal components, while sea level rise was assessed using a linear approach. InSAR and DInSAR methods were used to process topographic and land subsidence data. The analysis results indicate that the coastal area of Semarang-Demak has a mixed semi-diurnal tidal type, with a Formzahl number of 0.68. The annual sea level rise is 4.7 mm/year, while the average land subsidence rates in Gayamsari, Genuk, and Sayung Districts are 14.16 cm/year, 15.5 cm/year, and 17.8 cm/year, respectively. In 2024, the tidal flood inundation area is 523.67 hectares. After the integrated toll road and sea wall construction in 2054, the inundation area is reduced to 19 hectares but increased to 5023.41 hectares in 2059 due to overtopping. The toll road-sea wall integration project is considered highly effective, successfully reducing tidal flooding by 96.37%.