Synthetic Unit Hydrograph Derivation Using Giuh And Giuh Based Nash Iuh Models forUngauged Catchments in Abbay
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Date
2011-06
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Addis Ababa University
Abstract
Geomorphologic instantaneous unit hydrograph (GIUH) can be used as a transfer function for
modeling the transformation of excess rainfall into surface runoff, in which excess rainfall is a
production function to the hydrologic system. These models can be used to predict the temporal
variation of the surface runoff at the outlet of ungauged catchment, which is useful in the
hydrologic engineering applications. In this study the two types of geomorphologic approaches
were studied, GIUH and GIUH based Nash IUH models, for unit hydrograph derivation from the
observed data.
The geomorphological characteristics of a catchment were related with the shape and scale
parameters of the Nash IUH to derive the complete shape of the GIUH based Nash IUH model;
and GIUH was developed from geomorphological characteristics of the catchments and
probability density function of travel time of rainfall excess to the catchment outlet. These two
models were developed in seven catchments in Abay basin (Fettam, Hoha, Neshi, Uke, Andassa,
Azuari and Jedebe) with range of areas 161 to 573km2.
In this study, velocity was set as a calibration parameter to calibrate the simulated unit
hydrograph with the observed unit hydrograph in both models. A regionalized streamflow
velocity equation was developed from the simulated data with R2 equal to 0.89 and 0.96 for
GIUH and GIUH based Nash IUH model respectively. Then, these equations were applied on
chemoga catchment, which was considered as ungauged catchment, to observe the reliability of
the models.
The performances of the calibrated models were evaluated using Nash-Sutcliffe efficiency
(NSE), Error (ERR), percentage error in peak discharge (PEP) and percentage error in time to
peak (PETP). From model evaluation results, GIUH model efficiency (EFF) varies from 81.95 to
97.9 percent while GIUH based Nash IUH model efficiency varies from 75.68 to 97.51 percent.
GIUH model is efficient in peak discharge estimation (R2=0.988) than GIUH based Nash IUH
model (R2=0.884). In general, the result of both GIUH and GIUH based Nash IUH models are
almost comparable and their results are acceptable but the GIUH model is superior.
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Moreover, a simple GIUH based regional triangular unit hydrograph equations were developed
and compared with the SCS triangular unit hydrograph. The R2 value in peak discharge
estimation using SCS method is 0.48 while using GIUH method is 0.95. This implies that the
derived GIUH based regional triangular unit hydrograph equation is quite different from SCS
triangular unit hydrograph and GIUH has better efficiency.
Finally, this paper concludes that, the regionalized GIUH based equation for peak discharge,
time to peak and base time of the triangular unit hydrograph can be used, within the errors
specified in this research paper, for any ungauged catchment found in neighbor of the study area
having similar character and varying in areas from 161 to 573km2. Further work may in the
future be required to explain any non linear relationship of rainfall runoff and homogeneity of
the catchments.
KEY WORDS: Geomorphologic Instantaneous Unit Hydrograph (GIUH), Nash IUH Model,
ILWIS (Integrated Land and Water Information System), Rainfall-Runoff modeling, Ungauged
Catchment.
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Keywords
Geomorphologic Instantaneous Unit Hydrograph (GIUH); Nash IUH Model, ILWIS (Integrated Land and Water Information System); Rainfall-Runoff modeling; Ungauged Catchment.