GIUHGeomorphological Instantaneous Unit Hydrograph
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The GIUH was first proposed by Rodriguez-Iturbe and his colleagues (1979) and restated by Gupta et al (1980) whom defined it as "the probability density function of a drop's travel time in a basin".
Rodriguez-Iturbe and Valdez (1979) defined in a very simple expressions for the time to peak ([]) and the peak flow discharge ([]) of the GIUH:
The response function of the GIUH is characterised as a "impulse response function".
Therefore, in order to implement the GIUH, data needed include:
Several rainfall data sources were used for correction as a proper rainfall distribution is needed for the GIUH approach.
Model parameters of the GIUH include the Horton's ratios, hill slope and stream flow velocity.
Having obtained the effective rainfall and the Horton ratios and estimated hillslope and stream velocity ([V.sub.o], [V.sub.s]) to derive the GIUH (figure 4), the surface runoff is calculated based on equation (3) using an Excel spreadsheet in a discrete time domain (see Chow et al., 1988, p.211) taking into account the catchment area.
For the GIUH approach, the initial abstraction was assumed correctly, therefore the CN value was kept constant as 85.
Therefore, it can be confirmed the GIUH model approach can be successfully implemented to data scarce catchments as was the case here, the ungauged Can Le catchment.
The GIUH is an event-based model, it does not take into account the changes in soil moisture, etc (e.g.
The GIUH only takes into account the surface runoff of the catchment and routes it through the channel network.