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