Testing of The Method of Gama I Synthetic Unit Hydrograph in The Analysis of The Tojo Watershed Design Flood

Abstract

Floods occur due to several factors including topographic conditions, high rainfall intensity, blockage of water flow, lack of water infiltration areas, deforestation, and so on. The Tojo watershed is included in the Parigi-Poso river area, with an area of 211,830 km2 and a river length of 25.52 km. In the Tojo watershed, it is necessary to study flooding, because the watershed always flows every year. This research aims to find out how much flood discharge was obtained from the analysis of the Tojo watershed design flood with the Gama I synthetic unit hydrograph method and to find out how much the Gama I synthetic unit hydrograph analysis compared to the design flood discharge based on river discharge data (AWLR). From the calculation results obtained a comparison between the design flood discharge value processed by rainfall data using the Gama I Synthetic Unit Hydrograph method to the design flood discharge value processed by the Tojo river discharge data using the log person III distribution method for a 2 year return period is 1957,45 %, for the 5-year return period is 1347,64 %, for the 10 year return period is 1224,65 %, for the 25 year return period is 1169,96 %, for the 50 year return period is 1165,67 % and for the 100 years is 1178,75 %.