Metode hidrograf satuan sintetis adalah metoda yang populer digunakan dan memainkan peranan penting dalam banyak perencanaan di bidang sumber daya air khususnya dalam analisis debit banjir DAS yang tidak terukur. Metode ini sederhana, karena hanya membutuhkan data-data karakteristik DAS seperti luas DAS dan panjang sungai dan dalam beberapa kasus dapat juga mencakup karakteristik lahan digunakan. Oleh karena itu, metode ini merupakan alat berguna untuk mensimulasikan aliran dari DAS tidak terukur dan daerah aliran sungai mengalami perubahan penggunaan lahan. Untuk mengembangkan hidrograf satuan sintetis, beberapa metoda telah tersedia. Beberapa metoda hidrograf satuan sinteteis seperti cara Nakayasu, Snyder-Alexeyev, SCS, dan GAMA-1 sangat populer dan umum digunakan di Indonesia untuk menghitung debit puncak dan bentuk hidrograf banjir. Makalah ini menyajikan suatu pendekatan sederhana untuk menentukan hidrograf satuan tak-berdimensi yang konsisten berdasarkan prinsip konservasi massa. Hidrograf satuan dapat dibuat dengan menggunakan satu fungsi tunggal sederhana (HSS ITB-1) atau menggunakan dua fungsi sederhana (HSS ITB-2) yang dikombinasikan dengan faktor debit puncak yang dapat disesuaikan secara otomatis berdasarkan rasio antara luas DAS dan luas hidrograf satuan yang dihitung secara numerik menggunakan prosedur tabulasi sederhana.

Abstract. As a coastal city which lies in lowland area, Jakarta is prone to flooding. One major river which flow through Jakarta is Ciliwung River. There are alternatives to reduce flood risk, such as: river capacity improvement, existing natural reservoir and polder system improvement, upstream reservoir construction, city drainage improvement, flood channel construction and flood diversion. This paper presents capacity analysis of a proposed flood diversion of Ciliwung River to Cipinang River. Cipinang River has its downstream end at Eastern Flood Canal (Kanal Banjir Timur, KBT). This diversion is based on the available capacity of KBT. A 1-D numerical hydraulic model using HEC-RAS based on a proposed design is used to assess the performance of the diversion system in any combination of upstream and downstream boundary condition. Simulations were done for steady condition. The results show that capacity of the system can be achieved for certain condition at upstream and downstream boundary. The effects at the downstream reach of Ciliwung and Cipinang River due to the diversion are also obtained.

The dam break-induced propagation over a movable bed has given strong interest in numerical modeling. The shock wave, generally found in the wavefront, is a challenge in numerical modeling since this condition often leads to numerical instability. Additionally, the scouring beneath the wave requires coupling of hydraulic and sediment transport models. The objective of this research is to develop a one-dimensional model based on a finite element method to simulate an experimental case of a dam break-induced flow and the bed scouring beneath it. The two-step Taylor Galerkin scheme is used to solve the governing equations. In addition, Hansen numerical filter is used to handle shock wave and to increase the numerical stability of the developed model. The results show good agreement to the experimental data. Additionally, the applied numerical filter is able to reduce oscillation and improve the stability of the model.

Rainfall is one of the common triggering factors of the flood. Bandung City is located in the Upper Citarum river basin. Parts of the city, such as Bojong Sari, Bojong Soang, Cieunteung and Andir Sub district, are in natural floodplains. During the wet season, these areas are frequently flooded. This study analyzed the critical rainfall level that potentially caused flooding. The Hydrologic Engineering Centres Hydrologic Modelling System (HEC-HMS) rainfall-runoff model and the 1D HEC-RAS model were applied. A six storm pattern was simulated to determine the critical rainfall that generated the water depth that was equal to or greater than the critical water surface depth at specific points in the river. Hypothetical rainfall events are used to investigate the response of the river basin at critical cross-sections. It can be considered by different temporal distributions. The amount of rainfall is assumed to be distributed uniformly. The conclusion of this research is that the storm pattern (rainfall depth and rainfall duration) plays a crucial role in determining the critical rainfall at the flood location. The critical rainfall in a specific location is affected by the position at the river cross-section (in the upstream or the downstream area) and the bank full capacity of the river cross-sections.

In numerical modeling, dam break is one case that has its own challenges, because shock wave is found in the dam break modeling that usually provides a numerical instability. Usually, dam break problem is solved by Saint Venant equation using a finite difference method with artificial dissipation or Total Variation Diminishing (TVD) filter. But in this research, finite element method and the finite difference method are used. To verify the accuracy of the model, a comparison against the Stoker analytical method for dam break case was performed. Numerical modeling of dam break is required to find out the collapse area, thus it is used for determining mitigation that can be done in the area, related to dam safety. In numerical modeling, oscillation or numerical instability often occurs, for which special treatment is required to reduce or eliminate the oscillations. In this research, the treatment for that case is a Hansen filter for both methods. From the simulation result, it is found that Hansen filter is sensitive in reducing oscillation depending on the correction factor value and Δt that used. For dam break case, after filter applied, the value of Pearson Correlation Coefficient of Taylor Galerkin and Mac-Cormack methods are 0.999. The error rate for a Taylor Galerkin method are 0.118% at t = 3s and 0.123% at t = 10s. The error rate for Mac-Cormack method are 0.043% at t = 3s and 5.048% at t = 10s. From the comparison of the model, it can be concluded that Taylor Galerkin finite element method proved to be capable and more accurate in simulating dam break compared to Mac-Cormack finite difference method.