Analysis of Design Flood Using Synthetic Unit Hydrograph Methods of Snyder and Soil Conservation Service in the Padang Watershed

Abstract

This research analyses the design flood discharge on the Padang River by using the Synthetic Unit Hydrograph (SUH) Snyder and SUH Soil Conservation Service (SCS) methods. The rainfall area calculation employs the Polygon Thiessen method while the rainfall intensity analysis implements the Mononobe method and the hourly rainfall distribution uses the Alternating Block Method (ABM). Based on the HSS Snyder method, the peak time lies in the 18^th hour with the peak discharge being estimated at 583,10; 668,04; 769,53; 841,59 and 911,11 m³/s for each return period of 5-, 10-, 25-, 50- and 100-year. This peak time is larger yet its peak discharge is smaller than the estimations based on the HSS SCS method. The peak discharge is predicted as much as 1037,80; 1187,31; 1365,95; 1492,80 and 1615,17 m³/s for the return period of 5, 10, 25, 50 dan 100 year with its peak time lies in the 10^th hour. Analysis of comparison between the predictions undertaken by the two different HSS methods suggests some practical considerations.