FLOOD ANALYSIS OF CIKAPUNDUNG WATERSHED (UPSTREAM – DOWNSTREAM) USING HEC-RAS METHOD AND ESTIMATING ECONOMIC LOSSES IN THE AFFECTED AREA

• Main Author: Loy Pandia, Stenfri
• Format: Theses
• Language: Indonesia
• Subjects: Teknik saniter dan perkotaan; teknik perlindungan lingkungan
• Online Access: https://digilib.itb.ac.id/gdl/view/64651
• Institution: Institut Teknologi Bandung

The Cikapundung Watershed (DAS) is one part of the Citarum sub-watershed, which functions as a raw water provider for the needs of residents in the city of Bandung. The exploitation of space and high water resources can trigger flooding. Floods can be minimized by paying attention to flood risk mitigation measures. This study tested four types of methods in analyzing the frequency of rainfall, namely Normal Distribution, Log Normal, Log Pearson Type III, and Gumbel. Design rainfall is calculated with 2, 5, 10, 25, 50, and 100 years return periods. Furthermore, to analyze the design discharge, this study used the Nakayasu Synthesis Unit Hydrograph method. The hydraulics analysis was carried out using the HEC-RAS method with different return periods to calculate the flood depth. From the results of testing four types of frequency analysis methods, it was found that the Log Pearson Distribution Type III is the only method that meets the requirements for using this type of distribution. Based on the Chi-Square test, the Log Pearson Type III distribution has a calculated X2 value of 1 smaller than the critical X2 value of 5,991. Meanwhile, the Smirnov – Kolmogorov test results also have the same value, namely the P-value calculated at 0.15, which is smaller than the critical P-value, 0.41. Based on the calculation results, it is stated that the runoff coefficient value of the Cikapundung watershed in 2020 is 0.4. There has been no significant change in land use in the Cikapundung watershed in the past ten years, namely from 2011 to 2020. Based on all the results of the design flood discharge calculations using the Nakayasu HSS Method, it can be seen that the increase in the return period will be directly proportional to the discharge value. Based on the verification results of several flood events in the Cikapundung watershed area, most of them were in the model obtained from this study. The total estimated loss for the 2 year return period is Rp491,889,939,469.45, the 5 year return period is Rp738,067,972,741.58, the 10 year return period is Rp858,613,213,635.49, the 25 year return period is Rp1,124,679,289,990.78, the 50 year return period is Rp1,288,798,279,295.97 and the return period is Rp1,288,798,279,295.97 100 years amounting to Rp1,441,551,710,834.97