Ecology, Environment and Conservation Paper

HYDROLOGICAL CHARACTERISTICS ANALYSIS OF OGAN WATERSHED, SOUTH SUMATRA, INDONESIA

Utari Hikmah Pratiwi, Eddy Ibrahim, Edward Saleh and Ngudiantoro

Abstract

Ogan Sub-watershed in South Sumatra is one of the relatively large Musi river sub-watersheds which area crosses several cities with management complexity. The Ogan watershed experiences flooding during rainy season annually, especially in the downstream of Ogan Ilir District and one of the reasons of flooding in Palembang City. The information about hydrological characteristics was needed for water resources management. Therefore, it is necessary to analyze the hydrological characteristics of the Ogan watershed based on the morphometric conditions, geomorphology, and climatology. Data used was digital elevation model for analyzing the distribution and characteristic of sub-watersheds based on morphometric conditions, sentinel satellite imagery maps for land use analysis, and maximum daily rainfall data. Rainfall data used for analyzing climatology of sub-watersheds (hourly rainfall) using the Alternating Block Method (ABM) of the Intensity Duration Frequency (IDF) curve with time intervals of 10 minutes for 360 minutes in return periods of 2, 5, 10, 25, 50, and 100 years. Peak discharge was analysed by developing hydrological model of synthetic unit hydrograph SCS using HEC-HMS 4.3 software. Flood discharge hydrograph analysis measured with Soil Conservation Service (SCS) by inputting characteristic of sub-watersheds based on the morphometric condition, geomorphology, and climatology. The result of analysis showed that the total area of the Ogan Watershed is 841,721 ha, which is classified as a large watershed with a length of 343.19 km. Ogan watershed divided into 12 sub-watersheds, namely Ogan Tengah, Rambang, Kuang Besar, Sakatiga, Ual, Gelas, Kisam, Kurup, Ogan Ulu, Ogan Ilir, Kelekar, and Tebangka. Ogan sub-watersheds were dominated by rubber plantations, oil palm plantations, and dry land forests. The highest depth of the rain occurred at 180 minutes and the lowest depth at 360 minutes and 10 minutes. Result of hydrological model using HEC-HMS 4.3 software presented a peak discharge hydrograph with a return period of 2 years from 12 sub-watersheds revealed that Ogan Ulu sub-watershed had the highest discharge of 180.9 m3s-1 and the lowest was Kisam sub-watershed at 24.7 m3 s-1. The results of the overall peak discharge analysis of the Ogan watershed with a return period of 2 years is equal to 516.4 m3 s-1.