Rainfall-Runoff Modelling of Koshi River Basin Using HECHMS
This paper presents the results of frequency analysis of rainfall and Rainfall-Runoff modelling of Koshi River basin. The simulation was carried out by model software HEC-HMS. The Gumbel’s method was used for the frequency analysis of 1 day, 2 day and 3-day maximum rainfall data of forty-nine stations. The mean value of PMP for 1 day,2 day and 3 day rainfall were 324 mm, 415 mm and 554 mm respectively. The calibration of model was mainly based on the observed discharge data at Chatara station (outlet of whole basin). The Nash-Sutcliffe efficiency was 83% for calibration and 77% for validation. The volume bias is +1.1% for calibration and +20% for validation. Four types of modelling results in terms of parameters namely deficit and Constant loss parameters, Clark runoff transform parameters, Monthly base flow (m3/s) parameters and Muskingum routing parameters were estimated. The minimum base flow in all sub-basins except Arun lower were resulted in the month of March whereas maximum base flow was estimated in the month of August in all sub-basins. The highest contribution of base flow was resulted in Arun up sub-basin ranging from 107 m3/s even in the month of February to 530 m3/s in the month of August. On the other hand, among sub-basins, the lowest contribution of base flow was resulted in Likhu sub-basin ranging from 11 m3/s in the month of March to 70 m3/ s in the month of August.