Unit Hydrograph Modeling using Geomorphological Instantaneous Unit Hydrograph (GIUH) Method

Abstract

Flood forecasting at Wonogiri Reservoir is restricted on the availability of hydrologic data due to limited monitoring gauges. This issue triggers study of unit hydrograph modeling using Geomorphological Instantaneous Unit Hydrograph (GIUH) which is based on Geographic Information System (GIS). Analysis of physical watershed parameters was conducted on Digital Elevation Model (DEM) data using software Watershed Modeling System (WMS) 10.1 and ArcGIS. Nash model and S-curve method were used to process triangular GIUH into hourly Instantaneous Unit Hydrograph (IUH) and Unit Hydrograph (UH) and then was compared with the observed UH of Collins method. A sensitivity analysis was conducted on parameter of RL and Nash-model k. Evaluation of accuracy of the simulated GIUH runoff hydrograph was also conducted. The GIUH model generated UH with smaller peak discharge Qp, also slower and longer of tp and tb values than the observed UH. Accuracy test of the simulated GIUH runoff hydrograph using Nash-Sutcliffe Efficiency (NSE) shows that Keduang watershed gives a satisfying result, while Wiroko watershed gives less satisfactory result. The inaccuracies occur due to limited flood events used to derive the observed UH and stream tributaries that were not properly modeled based on Strahler method.

The Influence of Two Different Time of Concentration Equations on the GIUH-based Flood Hydrograph Estimates of Keduang and Temon Sub-Watersheds, Indonesia

“…Through the WMS Software application to analyze the DEM data from ASTER, the areas of the Keduang and Temon Sub-watersheds were found to be 362.56 and 46.29 km 2 , respectively. A previous study [3] showed that the Keduang and Temon Sub-watershed areas were 360.73 and 68.08 km 2 , respectively. These differences arose presumably due to the difference of control points used in both Keduang and Temon Rivers.…”

“…The relative mean error (RME) differences between values obtained from the model or simulation and the actual or observed values according to the following equations [3]:…”

“…The root mean square error (RMSE) is one of the commonly used error index statistics to measure the differences between values obtained from the model or simulation and the actual observed values [3,25]. The RMSE is calculated using the following equation:…”

“…There were several works related to GIUH model developments, and among of them were those carried out by Azizian [1], Chen et al [2] and Sulistyowati et al [3]. Azizian [1] recommended both Kirpich and Ventura time of concentration equations whereas Chen et al [2] and Sulistyowati et al [3] only utilized the Kirpich time of concentration equation.…”

“…There are many formulas for Tc that utilize the first approach including Kirpich and Ventura. The Kirpich time of concentration is more widely used than that of Ventura due to basin size considerations [1,[3][4][5] because of the Kirpich equation is more suitable for relatively small catchment areas (0.004-0.453 km 2 ). The Ventura time of concentration was developed for rural basins in Italy; however, it is considered suitable for application in tropical climates and relatively large catchment areas.…”