Low Flow of Cascade Reservoir in Sekampung Watershed

Abstract

Purpose: This research intends to analyze the low flow in the cascade reservoir in Sekampung watershed Theoretical reference: The low flow analysis uses the HEC-HMS model with the input parameters are GPM satellite rainfall that is calibrated by the ground station data in the Sekampung watershed, variation of land use, and soil type. Method: The methodology consist of by using the HEC-HMS model. Then, this model is calibrated with the flow discharge in Batutegi reservoir. Result and Conclusion: The model result produces the linear average discharge with the comparation ratio of sub-watershed area in each outlet is as follow: 11.0% (W1), 10.4% (W2), 39.9% (B1), 9.2% (W3), and 30.5% (B2). Half monthly average discharge is in the range of 2.6-40.8 m3/s (W1), 2.6-35.8 m3/s (W2), 11.9-151.4 m3/s (B1), 2.6-34.8 m3/s (W3), and 8.8-116.2 m3/s (B2). Percentile of dependable discharge that is used is >66.6% for dry year, 66.6%-33.3% for normal year, and <33.3% for wet year with the value between 6.6-25.4 m3/s (W1), 5.7-23.2 m3/s (W2), 24.2-97.3 m3/s (B1), 5.4-22.4 m3/s (W3), and 18.0-74.8 m3/s (B2). Implication of research: The calibration of discharge as the modelling result to the observed discharge produces the RMSE value is 0.462, the NSE value is 0.787, the PBIAS is 0.04% with the result interpretation is very good. The validation produces the RMSE value is 0.632, the NSE value is 0.601, and the PBIAS value is 0.01% with the result interpretation is very good. Originality/ value: The model that is used for analyzing flood in the study location is the HEC-HMS software by carrying out the watershed division into smaller sub-watershed.