Coastal Inundation and Land Subsidence in North Coast of West Java: A New Hazard?

The North Coasts of West Java are increasingly affected by human activities. The area has been utilized as settlement areas, industrial estates, and associated infrastructures including roads, school, hospital, market, etc. Consequently, this massive landuse and uncontrolled natural resources extraction have contributed to environmental degradation such as coastal erosion, accretion, pollution, inundation, and land subsidence. To date, we have so far very few field measurement data of land subsidence to support its importance. However, satellite image and on-ground observations used to determine spatio-temporal changes in the shoreline and area of inundation indicated the existence of land subsidence. Groundtruth data on selected areas also indicated the indicators of land subsidence such as damages of infrastructures including houses, roads, and sea dikes. The most noticeable shoreline changes in the North Coast of West Java are situated in Muara Gembong Bekasi and Legon Kulon Subang constituting maximum rates of shoreline retreat up to 200 and 150 m/year respectively for the last two decades (from 2000 to 2020). Whilst, the total areas of inundation in Muara Gembong and Legon Kulon based on recent satellite studies are 10.2 km2 and 7.4 km2 respectively. Coastal inundation might be linked to the combination of long-term behavior of oceanographic variables such as wave and sea level, in coincidence with hydrological changes due to river works (i.e. dam constructions and channellings) and an increase of settlement areas, fish ponds, groundwater extraction, etc. A set of preliminary engineering measures, in conjunction with sediment managing schemes, is proposed for the sustainable development of the coastal zone.

Sea-level prediction for early warning information of coastal inundation in Belawan coastal area using Delft3D model

Coastal inundation has a great impact on the environment, such as damage to infrastructure and pollution of land and water. One of the efforts to prevent coastal inundation is to predict the water level. Delft3D is a hydrodynamic model that's able to simulate the water level. Coastal inundation research using the Delft3D model is still rarely done in Indonesia, especially on the east coast of Sumatra. This research is conducted in Belawan coastal area by simulating the water level that caused the coastal inundation using the Delft3D model. The best bathymetry for the prediction of water level and the magnitude of the wind effect was obtained from the simulation. The final step is to predict the water level in Belawan coastal area. The result of this research shows that the Delft3D model can simulate the water level which causes the coastal inundation in the Belawan coastal area. The correlation of the Delft3D model is 0.9, and the RMSE of GEBCO bathymetry is 0.39 meters and the RMSE of NOAA bathymetry is 0.46 meters. The GEBCO bathymetry is better than NOAA bathymetry in describing the water level in the Belawan coastal area. The wind effect on the water level simulations is not significant because the coefficient of determination is 0.47%. Besides, the Delft3D model with GEBCO bathymetry input can predict the water level which causes the coastal inundation with correlation reaches 0.92 and RMSE is 0.39 meters.

Prediksi spasio temporal rob berbasis model LISFLOOD FP di Pesisir Jakarta.

Abstrak Jakarta khususnya daerah pesisir sangat rentan dengan adanya permasalahan lingkungan berupa rob. Pemetaan daerah yang berpotensi terdampak rob sangat diperlukan guna menyusun upaya mitigasi. Pada penelitian ini dilakukan prediksi tinggi muka laut dengan model Delft3D dan digunakan untuk memprediksi daerah tergenang rob menggunakan model LISFLOOD FP pada tanggal 18 – 20 November 2019 di pesisir Jakarta. Hasil penelitian menunjukkan bahwa prediksi tinggi muka laut memiliki akurasi yang baik, dengan koefisien korelasi pada tingkat kuat sebesar 0,93 dan nilai RMSE sebesar 0,13 meter. Sementara itu, prediksi rob model LISFLOOD FP menunjukkan luas maksimum yang terjadi 2 hingga 3 jam setelah fase puncak tinggi muka laut dan menggenangi 8 kecamatan di Jakarta Utara dan Jakarta Barat. Abstract Jakarta region especially the coastal areas are very vulnerable to environmental problems such as coastal inundation. Mapping of areas potentially affected by coastal inundation is needed to arrange mitigation efforts. In this study, sea level prediction was estimated using the Delft3D model and used to predict coastal inundation areas using the LISFLOOD FP model on 18-20 November 2019 on the coast of Jakarta. The results showed that the sea-level prediction model has good accuracy, with a correlation coefficient at a strong level of 0.92 and an RMSE error value of 0.13 meters. Meanwhile, coastal inundation prediction from the LISFLOOD FP model inundated 8 sub-districts in North Jakarta and West Jakarta and showed the maximum area in 2 to 3 hours after the peak phase of sea level.

Nonlinear Model of Coastal Flooding by a Highly Turbulent Tsunami

When a tsunami wave comes from ocean and propagates through the shelf, it is very important to predict several dangerous factors: (a) maximum flooding of the coast, (b) tsunami wave height on the coast, (c) velocity of the tsunami front propagation through the coast, and (d) time of tsunami arriving at a given point in the coast and around it. In this study we study the separate case where the angle of inclination α of the seacoast is equal to zero. A linear solution of this problem is unsatisfactory since it gives an infinite rate of the coastal inundation that means the coast is flooded instantly and without a frontal boundary. In this study, we propose a principally new exact analytical solution of this problem based on nonlinear theory for the reliable recognizing these essential tsunami characteristics. The obtained formulas indicate that the tsunami wave can be stopped (or very strongly eliminated) in the shelf zone until approaching the shoreline. For this aim, it is necessary to artificially raising several dozens of bottom protrusions to the level of the calm water.

Coastal Inundation Model in the Coastal Area of Palopo City, South Sulawesi Province

The impact of sea-level rise is perceived by many archipelagic countries such as Indonesia. The higher the sea level rises every year, the larger the disaster threat in the coastal area. The current condition of most coastal areas indicates various pressures caused by city development, including the coastal area of Palopo City in South Sulawesi Province. The sea-level rise is suspected to be the cause of coastal inundation in Palopo City which, so far has not been identified. Therefore, this study aims to draw a coastal vulnerability map of sub-districts in Palopo caused by coastal inundation using GIS technology. Analysis of the areas affected by coastal inundation is carried out by processing spatial data. The sub-districts areas affected by coastal inundation are only those located in the coastal zones. The affected area in Bara, Wara Selatan, Wara Utara, Wara Timur, and Telluwana sub-districts are 160.64 ha, 21.41 ha, 73.55 ha, 87.56 ha, and 56.65 ha, respectively. In Bara Sub-district, the areas affected by coastal inundation are residential and mangrove conservation areas. The affected areas in Telluwana Sub-district are residential, production forest, coastal conservation, and mangrove conservation areas. The affected areas in Wara Selatan, Wara Timur, and Wara Utara Sub-districts are all residential areas. By using sea-level rise data of 27 years with its highest tide model, the coastal inundation in 2040 which is predicted to occur in Palopo City can be modeled properly.