Abstract.A dam break induced-flood propagation modeling is needed to reduce the losses of any potential dam failure. On the 25 July 2013, there was a dam break generated flood due to the failure of Way Ela Natural Dam that severely damaged houses and various public facilities. This study simulated the flooding induced by the failure of Way Ela Natural Dam. A two-dimensional (2D) numerical model, HEC-RAS v.5, is used to simulate the overland flow. The dam failure itself is simulated using HECHMSv.4. The results of this study, the flood inundation, flood depth, and flood arrival time are verified by using available secondary data. These informations are very important to propose mitigation plans with respect to possible dam break in the future.

No abstract

Abstract. Depth averaged equations are commonly used for modelling hydraulics problems. Nevertheless, the model may not be able to accurately assess the flow in the case of different flow regimes, such as hydraulic jump. The model requires appropriate numerical method or other numerical treatments in order to simulate the case accurately. A finite volume scheme with shock capturing may provide a good result, but it is time consuming as compared to the commonly used finite difference schemes. In this study, 1D St. Venant equation is solved using Artificial Viscosity Lax-Wendroff and Mac-Cormack with TVD filter schemes to simulate an experiment case of weir overflow. The case is chosen to test each scheme ability in simulating flow under different flow regimes. The simulation results are benchmarked to the observed experimental data from previous study. Additionally, to observe the scheme efficiency, the simulation time between the models are compared. Therefore, the most accurate and efficient scheme can be determined.

Way Ela dam is a dam to be built in the Negeri Lima village. In the negeri lima village there was also a dam that formed naturally by landslide due to high rainfall on 13 July 2012. A year after it was formed, on 25 July 2013 flooding occurred due to an extreme rainfall that caused the failure of the natural dam. The event of the failure on 2012 generated flood that severely damaged houses and various public facilities to negeri lima village down toward to the coast. As a result of this event, a small-scale reservoir is formed. The Government plans to utilize the established reservoir to build the new Way Ela Dam. This study was conducted to analyze floods with scenarios in the event of a failure in the new Way Ela Dam. The overland flow is simulate with two dimensional numerical model HEC-RAS v.5. Determining strategies for mitigation needs to be assessed comprehensively, by simulating disaster scenarios on the dam, analyzing the impacts and then planning recommendations for disaster risk. The results are expected to be a reference for mitigation plans for the new Way Ela Dam.

This research is an extension from a previous study titled modelling the diversion channel at Kalibata-Kebonjati meandering segment in Ciliwung watershed. Based on http://pusatkrisis.kemkes.go.id data, there are five sub districts that were flooded because of the rainfall in 5 February 2018 i.e : Pasar Minggu, Pancoran, Cilandak, Jagakarsa and Tebet. Their flood levels were achieved 300 cm, and the worst disaster happened in Pancoran, at Kebonjati to Kalibata segment in particular. Thus, this segment needs to manage accurately with appropriate structures. Formerly, the last study using 1D HEC-RAS, but the model has several lackness related to the rates of meandering velocities and discharges at the river edges, whereas, these numbers have significant effects for river scouring. Since several studies which applied 2D and 1D/2D coupling hydraulics modelling have been providing satisfactory results on complex river, this research was redeveloped and compared the meandering segment by using 2D HEC-RAS and Coupling 1D/2D HEC-RAS. Using rainfall data from three stations (Bendung Gadog, FT UI and Gunung Mas), the models indicated better results comparing with 1D model beside relations between velocity and discharge, respectively. Further, a diversion channel and stilling basin will be held in order to manage the flooding and scouring issues.

Kulon Progo Airport is an airport development project located in the coastal area near Yogyakarta, Indonesia, which is expected to complete in 2019. With the increase in population, huge land acquisition will be difficult, so the development of coastal areas for the airport became inevitable. Kulon Progo is located in the disaster-prone zone area of the earthquake and tsunami, the airport design must consider the risk management and mitigation from tsunami and earthquake disaster. Although the airport is already calculated the danger of earthquake and tsunami, the development of the coastal area also needs to consider the danger of the natural coastal process itself such as sedimentation and erosion. Shoreline changes due to the new infrastructure in the coastal area can disrupt the equilibrium of coastal process especially the longshore sediment transport. A satellite image shows that Kulon Progo shoreline retreats over 60 meters due to the heavy sediment longshore transport in the past 10 years. Breakwaters in Tanjung Adikarto fishing port also made a great contribution in huge sedimentation behind the infrastructure up to 90 meters. This research will conduct an analysis trough satellite and numerical model to observe the shoreline changes along Kulon Progo Coast. A numerical model shows a high erosion rate along the coast. High sedimentation also observed at the river mouth of Bogowonto and Serang Rivers.

There are two types of floods in Jakarta: upstream flooding and local flooding. In general, floods in DKI Jakarta are caused by local floods. The main cause of this flood is the occurrence of high rainfall, poor drainage system, and land subsidence. This study will analyse the local flood that occurred in Gunung Sahari, Central Jakarta. Judging from the existing conditions, sedimentation occurs in the drainage channels. This sedimentation causes a reduction in the existing channel capacity. Based on a hydrological and channel capacity analysis, the existing drainage channels are designed based on annual rainfall i.e. return period 1-2 years, which is 133.10 mm/day. Flood modelling is done for existing conditions. Based on the results of modelling, floods that occur in locations between 50 cm - 100 cm. Due to dense housing conditions, widening and normalizing the channel is difficult. Therefore, flood reduction will be assisted by pumps. The pump will be installed in the downstream of the main drain, which is connected to Mati River. This pump is designed with a capacity of 0.5 m3 / sec. Based on the results of modelling, with a largest pump capacity of 0.5 m3/sec, flooding is only reduced by 5 cm - 7 cm. Due to the lack of effectiveness of the pump, retention ponds will be designed to reduce surface runoff. Retention ponds are designed with an area of 1 ha and a depth of 1.5 m. Modelling is done in the presence of a retention pond. With the addition of retention ponds, annual flooding for the 2-year return period on Gunung Sahari could be reduced. Therefore, the discharge that will be received by the drainage channel will be smaller than the capacity of the channel itself and the flood will be completely reduced.

No abstract