Width parameter estimation through equivalent rectangle methodology

Ricardo Bonilla and Rafael Oreamuno


SWMM5 hydraulic modeling requires the estimation of different hydrological and hydraulic parameters allowing the determination of the basin's response upon a given precipitation event. Some physical parameters, such as area or perimeter, are measurable and can be accurately determined; however, other parameters present greater uncertainty when it comes to their estimation, such as the width parameter.  

When the drainage area is regular and uniform, “width” parameter estimation is relatively simple; however, when estimation of the hydrograph of a basin is required, for which the geomorphological characteristics define irregular patterns, the determination of the value of the “width” parameter presents great uncertainty and its representativeness becomes complicate to define. 

This publication attempts to estimate a representative value of the “width” parameter for an irregularly shaped basin by defining the equivalent rectangle of the drainage area, which takes into account the area, perimeter and compactness index of the basin. The compactness index can be used to classify the basin by its shape. The shape of the basin is an indicator of how the rainfall histograms are temporally distributed and how the water flows through the basin, i.e., it defines the response speed of the basin, as the width parameter does. 

The "width" parameter has a high sensibility in the SWMM5 modeling results; therefore, a good estimation of this parameter is of paramount importance to obtain representative results. For this reason, this publication seeks to find an optimal methodology to reduce modeling uncertainty and achieve more accurate simulations results of  a watershed's hydrological response. 

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