Development of a Direct Geomorphologic IUH Model for Daily Runoff Estimation in Ungauged Watersheds

Abstract

The aim of this paper is to propose a new geomorphologic method for deriving the complete shape of instantaneous unit hydrograph (IUH) in ungauged watersheds by calculating the mean travel time of excess rainfall in overland and channel segments. All required parameters for the calculations of travel time of sheet and channel flows for different hydrologic orders are determined based on geomorphologic data of a watershed. In the proposed model, IUH is obtained using the exponential probability density function (PDF) of mean travel time of possible flow paths in a watershed. In this method, the excess rainfall is determined using the National Resources Conservation Service) NRCS curve number (CN) method (SCS-CN). To investigate the performance of the proposed IUH model, it is applied for daily rainfall-runoff simulation in two separate watersheds with different climate conditions (i.e., cool-humid and semiarid) in Iran. Also, other geomorphologic IUH (GIUH) models are utilized as benchmark models for comparing their results with those obtained using the proposed model. The goodness-of-fit criteria show that the proposed GIUH model practically provides direct runoff ordinates in ungauged and partially geomorphologically homogeneous watersheds with an accuracy slightly better than one of the other GIUH (especially in terms of estimating peak flow) and much better than the other GIUH model. Additionally, the proposed model is beneficial to estimate the travel time of overland and channel flows in different orders of watershed, which can be worthwhile for flood management and designing flood warning systems in each segment of the watershed.