Cimadur river basin is one of the most important catchment areas in Lebak District, Banten Province. For the past few years, the catchment has experienced floods during the rainy season. The big issue of flooding has been recorded recently in December 2019 which has caused damage and negative impacts to the local people and surrounding community. This study aims to analyze the possibility of flood peak discharges in the catchment area of the Cimadur river. The flood discharges are calculated for 2, 5, 10, 25, 50, and 100 years return period based on the daily rainfall data from the year 2011 to 2020. The rainfall and land use data are obtained from PT Saeba Consultant. In this study, the hydrological analyses are including 1) analyses of average annual rainfall using the Thiessen method; 2) analyses of rainfall distribution and estimation of design rainfall by considering three methods involving: Log-Normal, Log Pearson Type III, and Gumbel Type 1; and 3) analyses of flood discharges by adopting Nakayasu Synthetic Hydrograph Unit (SHU). The rainfall distribution analyses show that the Log Pearson Type III provided the best fit. Based on the flood peak discharges analyses, the results show that the flood discharges for the 5, 10, 25, and 50 years return period in the Cimadur river basin are 470.71 m3/s, 560.16 m3/s, 698 m3/s, and 820.4 m3/s, respectively.

Road damage often occurs in lowland areas, one of the reasons is unstable soil conditions. This study aims to determine the relationship between geotechnical characteristics of soil and road damage. Field observations were carried out in the Tanjung Api-Api lowland area to find out the type of road damage. Testing of soil physical and mechanical properties was carried out to determine the geotechnical characteristics of the soil at that location. Results from current study show that that generally the types of road damage lowland areas are cracking, grade depressions, potholes, and distortion. The soil properties test results obtained that the soil in the Tanjung Api-Api lowland area was classified by Unified Soil Classification System (USCS) as an inorganic silt (MH) and organic clay soil with moderate to high plasticity (OH). In general, soil of this type has a low bearing capacity so that it requires handling and selection of construction that is suitable with this type of soil. Based on the classification of American Association of State Highway and Transportation Officials (AASHTO), the soil in the Tanjung Api-Api area is A-7-5 and A-5, which are clay and silt land with moderate to poor criteria if used as subgrade so that this land usually require s special handling when used as subgrade because it has the potential to deformation.

South Sumatera is one of the provinces with a large number of lowlands in Indonesia consisting of tidal land and lowland swamps, one of which is located in Tanjung Api-Api. The conversion of lowlands into built-up areas will cause physical, socio-economic, environmental, and public health impacts. One of the impacts arising from the development of settlements and infrastructure in lowland areas is land subsidence and flooding. The purpose of this research is to create a model for mitigating land subsidence in lowland areas spatially. The spatial model is carried out by weighting with Analytical Hierarchy Processes (AHP) and then mapping mitigation efforts that will be carried out based on the potential for land subsidence. The results show that if the lowland area is developed into an industrial and residential area, it will have an impact on land subsidence with a moderate to high potential level. Based on the zoning of the potential for land subsidence, the best pre-disaster mitigation efforts to do are choosing the type of construction according to the type of soil, conserving groundwater, maintaining infiltration areas and green open spaces, and regional spatial planning.