Regionalization of Mean Annual Flow for Ungauged Catchments (Case study: Abbay River Basin)
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Date
2019-10
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Addis Ababa University
Abstract
The future existence and development of potential water resources hinge mainly on the
past features of hydrological behaviors. Unfortunately, these features are not available
depending on the socio-economic and political stability of the country. Streamflow
measurement is one of the features of our country Ethiopia and other developed and
developing countries suffer to estimate. This study aims to identify the rainfall-runoff
relationships and develop an empirical equation that can be used to estimate the mean
annual flow for ungauged catchments in the Abbay river basin.
Based on the influence on runoff generation and easy availability climate variable (rainfall)
and physiographic variables (catchment area, land slope, and elevation) are selected as a
predictor of flow in the Abbay river basin. The selected 27 hydrometric stations split into
training (70%) and test (30%) datasets for the periods 1981 to 2013. Linear and non-linear
forms of the equation were tested to relate annual flow and annual rainfall at each
hydrometric station. A regression model used to relate the dependent variable mean annual
flow and independent variables climate and physiographic characteristics. Statistical tests
used for selecting the best trustworthy equation.
Analysis of the relationship between runoff and rainfall demonstrates fully dominance of
non-linear forms of equations and development of an empirical equation shows that the
catchment area, mean annual rainfall, and the average elevation is the trustworthy model
with both R
and Ns value of 0.96. Furthermore, the validation analysis strengthens this
equation statistically and graphically. The result reveals that relationships of rainfall and
runoff are non-linear and the size of the catchment, rainfall, and elevation of the catchment
highly governs the amount of flow expected at the outlet. On this root, it is recommended
that interested professionals on the estimation of flow at ungauged catchments carefully
delineate the area, estimate rainfall with enough rain gauge stations, and consider elevation
as the factor. Moreover, further studies need to incorporate additional catchment
characteristics to identify other influential factors in the formation of runoff.
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Keywords
Rainfall-Runoff relationships, Ungauged Catchments, Regionalization, Regression Analysis, Mean Annual Flow