TR-144 : Intercomparison of urban watershed models

Abstract

The term drainage applies to the process of removing excess water. to prevent public inconvenience and to provide protection against loss to property and life. In an urbanised area runoff is contributed by (i ) excess surface water after a rainfall from roofs, streets etc. and (ii ) wastewater from household, commercial establishments and industries. Past practice was to convey the entire runoff through a single system known as combined sewer system. The present practice is to construct a system to discharge rainfall excess only and a separate system to transport wastewater. In this report various urban drainage models currently used in various parts have been discussed and a comparison has been made regarding the suitability of each model. Rational method, Illinois Urban Drainage Area Simulator Model,TVA continuous daily stream flow model, Soil Conservation Services (T R-55) model, United .State Geological. Survey Model, the Wallingford Model consisting of Wallingford Rational Method, Wallingford Hydrograph Method, Wallingford Optimising Method, Road Research Laboratory Method and Storm Water management Model have been described in detail. the choice of which method/model is most appropriate among the several models available are hardly straight forward. the second factor which may prevent a user from making a clear choice between different method is a lack of Information on their relative performance. the results obtained by various users showed that several of the methods were capable of simulating observed event to an accuracy approaching that of the recorded data. It was found that Storm Water Management Model gives best performance but at the expense of large computer storage and time requirements.