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.

Banjir merupakan bencana yang sering terjadi di ibukota DKI Jakarta dengan kejadian terbesar pada tahun 2007. Penentuan langkah yang tepat dalam menyelesaikan masalah banjir dapat dibantu dengan pemetaan resiko banjir. Daerah studi kasus dalam penelitian ini adalah Kelurahan Bukit Duri, Kecamatan Tebet, Jakarta yang terletak di hulu pintu air Manggarai. Penelitian difokuskan pada estimasi bahaya banjir, kerentanan, kapasitas, dan resiko di daerah studi. Peta genangan banjir dikembangkan dengan model matematis aliran 1-D tak tunak DUFLOW dengan hidrograf banjir tahun 2007. Limpasan hidrograf banjir akan membebani daerah retensi dan menyebabkan variasi genangan. Indeks bahaya banjir dianalisis berdasarkan peta genangan dengan diverifikasi data lapangan. Analisis indeks kerentanan menggunakan parameter jaringan pipa dan kabel, jenis bangunan, sebaran populasi, dan potensi bahaya kolateral. Analisis indeks kapasitas memakai parameter kondisi pompa, tanggul, dan intervensi (peningkatan kewaspadaan banjir). Peta resiko dievaluasi menggunakan GIS dalam skenario optimis dan pesimis dengan persamaan: resiko = bahaya x kerentanan / kapasitas. Intervensi pada skenario optimis menunjukkan penurunan resiko signifikan di beberapa daerah, sedangkan pada skenario pesimis tidak berbeda dibandingkan kondisi eksisting. Peta resiko kondisi eksisting dianalisis serupa dengan keadaan aktual, dimana daerah studi merupakan daerah beresiko banjir tinggi karena perumahan penduduk yang padat dan kapasitas penanggulangan banjir yang tidak memadai.

Understanding and forecasting tsunami wave run-up is very important in mitigating tsunami hazards. The bed stress under wave motion governs viscous wave damping and sediment transport processes, which change coastal morphology. One of the most common methods used for simulation is the shallow water equation (SWE) model, often used with a Manning-style approach for modeling bottom friction. Boundary-layer approaches provide better information regarding bed stress, particularly since they are also valid for nonsteady flows. In this study, a simulation of wave run-up is carried out by simultaneous coupling of the SWE model with the k-ω model. The k-ω model is used near the flow boundary at the bottom, only for assessing the boundary layer shear stress. Free stream velocity and calculations of the free surface evolution are obtained from the SWE model. Both this method, and the conventional method, are applied to the canonical problem of a solitary wave propagating over a constant depth and then up a sloping beach (Synolakis, 1987). The new method is found to increase the computational accuracy and physical realism compared to the conventional Manning method. Comparison of bed shear stresses shows that the new method is able to accommodate the effect of deceleration, which leads to sign changes and a phase shift between the free stream velocity and the bed stress. Furthermore, it is found that during the run-up and run-down process, bed stress in the direction of leaving the shoreline is more dominant.

The Great East Japan Earthquake of March 11, 2011 generated a massive tsunami wave that severely damaged coastal areas of Japan. Furthermore, the wave propagated into rivers, causing damage upstream far from shore. Videos recorded during this tsunami event were collected and analyzed to estimate the celerity of tsunami propagation in river and on the land. The result shows good comparison with estimation based on theoretical approaches that use water level measurement data. It was found that the tsunami celerity in river is approximately 25–30 km/h, and moved upstream with gradual deceleration. However, wave celerity on land was decreased significantly due to debris and dominant ground friction. The propagation trend in river mainstream and floodplain behaves differently in the location where the mainstream is not parallel to the embankment. Tsunami discharge and velocity in a river induced by tsunami wave were estimated based on continuity equation using the measured water level variation along the Sunaoshi River. The maximum estimated discharge is approximately 152 m3/s with the maximum velocity of 1.4 m/s.

No abstract

This study investigates the morphology changes near the Nanakita river mouth in Japan. The morphology of the river mouth was greatly influenced during The Great East Japan Tsunami of 2011. The gradual morphological changes at the river mouth was investigated using two sets of data, o which, one was the continuous water level measurement data in the river entrance and in the sea, and the other being the intermittent aerial-photographs. The statistical parameters, viz., the correlation coefficient and the linear gradient between the two water level data were analyzed, which formed as the basic for understanding the behavior of the river mouth, like river mouth closure or opening detected by the analysis of the water level variation. The proposed method is found efficient and effective in the evaluation of the morphological changes near a river mouth.

No abstract

Abstract. The flood in Jakarta has become a national concern in Indonesia. It is a haunting disaster, with a high probability to happen when heavy rainfalls in Jakarta and/or its upstream area. Based on data that was provided by Public Work Agency of DKI Jakarta, there are 78 vulnerable points of inundation in which, most of them are located in Ciliwung river basin, commonly in the meandering segments. One of the worst flooding occurs in Pancoran, at Kebonjati to Kalibata segment in particular. The river discharge in this segment is much higher as compared to the carrying capacity. In addition, this area has a high density of population and thus, difficult to increase the *river capacity* by enlarging the river dimension. In this research, a closed diversion canal is proposed as a solution. The effectiveness of the solution is evaluated using a numerical model, HEC-RAS 4.1. The diversion canal is designed as two culverts, with 2.0 m in diameter. Nevertheless, hydraulic jump may occur at the outlet of the canal due to the relatively steep slope. Therefore, the canal outlet should be designed accordingly. A Hydraulic structure such as a stilling basin can be employed to reduce the energy. The results show that the diversion canal has a good performance in decreasing water level and flood discharge in the study area. The canal has the capacity of 17,72 m3/sec and succesfully decreases the water level by 4.71 -5.66 m from flood level for 2 -100 years returned period.