DAS Cimadur merupakan salah satu DAS yang berada di wilayah Kabupaten Lebak, Provinsi Banten. DAS Cimadur mengalami masalah banjir sejak beberapa tahun yang lalu terutama disekitar sungai Cimadur. Salah satu permasalahan banjir terbesar terjadi pada tahun 2019 yang mengakibatkan terendamnya sebagian daerah perkampungan, pendangkalan dasar sungai, dan rusaknya infrastruktur keairan. Dalam rangka penanganan masalah banjir di sungai Cimadur tersebut, maka diperlukan adanya kajian terlebih dahulu mengenai karakteristik aliran sungai. Oleh karena itu, kajian ini bertujuan untuk mengetahui karakteristik aliran sungai di bagian hilir sungai Cimadur, dengan cara menghitung debit banjir di DAS sungai Cimadur untuk kala ulang 5, 10, 25, dan 50 tahun dan mesimulasikan karakteristik aliran di sungai Cimadur dengan menggunakan program HEC-RAS 4.1. Berdasarkan perhitungan debit, debit banjir untuk kala ulang 5, 10, 25, dan 50 tahun adalah 281,8140 m3/dtk, 352,8301 m3/dtk, 459,6876 m3/dtk, 553,1754 m3/dtk. Berdasarkan simulasi HEC-RAS, aliran sungai pada profil sungai yang lurus memiliki kecepatan aliran lebih besar dibagian tengah section melintangnya dibandingkan dengan bagian kanan dan kiri dari section melintang sungai tersebut. Namun, kecepatan yang hampir sama besar pada bagian tengah dan kanan section melintang sungai diperlihatkan pada profil sungai yang membelok kearah kiri.

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.

Based on the governing equations of steady incompressible fluid, renormalization group (RNG) turbulence model and SIMPLEC algorithm are used to calculate the steady flow field of regulating tank in the pumping station with six different geometries operating under same condition. The impacts of the layout schemes of guide walls for the flow field of the regulating tank are analyzed. The numerical results are verified by physical model experiment and good agreement is found. The results show that: 1) serious flow separation of side wall will occur in the regulating tank when the interval of diversion wall is 10 L; 2) the flow velocity in the regulating tank will be too low when the diversion wall spacing is 16 L; 3) the improvement of the flow pattern of the regulating tank is not obvious; and the project cost is increased when the excavation depth of the regulating tank is increased by 1 m; 4) the bottom velocity reached the non-silting velocity and the head loss of the regulating tank reducing nearly 1.2 m by using arrangement form of wide 21 L and narrow 10L of the guide walls, which provides a certain guarantee for the safe operation of the pumping station. The regulation tank layout scheme proposed in the paper can be applied to engineering practice.