DETERMINING PEAK DISCHARGE FACTOR USING SYNTHETIC UNIT HYDROGRAPH MODELLING (CASE STUDY: UPPER KOMERING SOUTH SUMATERA, INDONESIA)

Abstract

Synthetic unit hydrograph methods are popular and play an important role in many water resources
design especially in the analysis of flood discharge of ungagged watersheds. These methods are simple, requiring
only watershed characteristics such as area and river length and in some cases it may also include land use
characteristics. Therefore, these methods serve as useful tools to simulate runoff from ungagged watersheds and
watersheds undergoing land use change. To develop a synthetic unit hydrograph, several techniques are available.
Several most popular unit hydrographs methods such as Nakayasu, Snyder-Alexeyev, SCS, and GAMA-1 are
popular and commonly used in Indonesia for computing both peak discharge rate and the shape of flood
hydrograph. This paper presents a simple approach for determining a consistent dimensionless unit hydrograph
based on mass conservation principles. The results for peak discharge in several hydrographs methods are
Nakayasu 607.32 m3/sec, SCS 668.62 m3/sec, ITB-1 675.42 m3/sec, ITB-2 642.805 m3/sec in periode time return
2 years.