Time Step Issue in Unit Hydrograph for Improving Runoff Prediction in Small Catchments

Dyah Indriana Kusumastuti,Dwi Jokowinarno

doi:10.4236/jwarp.2012.48079

Abstract

Unit hydrograph is a very practical tool in runoff prediction which has been used since decades ago and to date it remains useful. Unit hydrograph method is applied in Way Kuala Garuntang, an ungauged catchment in Lampung Province, Indonesia. To derive an observed unit hydrograph it requires rainfall and water level data with fine time scale which are obtained from automatic gauges. Observed unit hydrograph has an advantage that it is possible to derive it for various time steps including those with time step less than an hour. In order to get a more accurate unit hydrograph, it is necessary to derive a unit hydrograph with small time step for a small catchment such as those used in this study. The study area includes Way Kuala Garuntang and its tributaries, i.e. Way Simpur, Way Awi with areas are 60.52 km2, 3.691 km2, and 9.846 km2 respectively. The results of this study highlight the importance of time step selection on unit hydrograph, which are shown to have a significant impact on the resulting unit hydrograph’s variables such as peak discharge and time to peak.

Highlights

The development of hydrology model in runoff prediction is very advance, in which there are several methods that can be used in runoff prediction in ungauged basin
There are several flood events recorded during wet season 2009-2010, and the events are presented in Tables 1 to 3 for flood events selected for Way Simpur catchment (Table 1), Way Awi catchment (Table 2), and Way Kuala Garuntang catchment (Table 3)
This study shows the impact of time steps on unit hydrographs with regard to time to peaks and peak discharges

Summary

Introduction

The development of hydrology model in runoff prediction is very advance, in which there are several methods that can be used in runoff prediction in ungauged basin. With the existence of PUB (Prediction in Ungauged Basin) [1,2], there are several supporting tools and methods which makes prediction possible in such catchments. The limitation of fine data such as data from radar, leave little choice to carry out prediction in some catchments. There was no runoff measurements recorded before. This increasingly grows into significant matter as floods occur more frequently in this region recently [3]. This study deals with instrumenting this ungauged catchment to gain important information and carry out necessary analysis, as well as predicting runoff using observed unit hydrograph (UH) method

Objectives

Methods

Results

Conclusion