Date of Award

Summer 2002

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Melching, Charles S.

Second Advisor

Novotny, Vladimir

Third Advisor

Crandall, Clifford J.

Abstract

Surface runoff due to rainfall in urban areas is very important in water quantity and quality studies. Many hydraulic and hydrologic models based on different routing theories have been developed to simulate the rainfall-runoff process in urban areas. Essentially, these routing models can be classified into two categories: conceptual models and physically based models. Conceptual models, also known as hydrologic models, are based on the hypothesized relation between outflow and water storage in the reservoir. The linear reservoir method and the non-linear reservoir method are two basic approaches in simulating this relation. The non-linear reservoir method is commonly used in hydrologic models. The Storm Water Management Model (SWMM) is a typical hydrologic model based on the nonlinear reservoir method. Physically based models, also known as hydraulic models, are based on the real physical rainfall-runoff process. The kinematic-wave theory is one of the most popular methods in hydraulic models. The Dynamic Watershed Simulation Model (DWSM) was chosen to test the accuracy of the kinematic-wave theory. Experimental data, provided by the late Professor Ben Chie Yen at the University of Illinois at Urbana-Champaign, were used to test the accuracy of these two routing methods. The experiments were done with the Watershed Experimental System (WES) nearly 30 years ago to simulate the rainfall-runoff process in urban areas. The numerical results simulated by the computer models were compared to the observed data, and the coefficients of model-fit efficiency were calculated as a criterion for the accuracy of the model. It was found that, for rainstorms with the duration greater than or equal to 120 seconds, the average value of the coefficient of model-fit efficiency by SWMM is 0.88, and that by DWSM is 0.928; for rainstorms with the duration shorter than or equal to 60 seconds, the average value by SWMM is 0.07, and that by DWSM is 0.8. It is concluded that, the non-linear reservoir routing method in SWMM may provide acceptable results for storms with durations longer than the watershed time of concentration, but for storms with durations less than or equal to the time of concentration, poor results may be obtained. More accurate results generally can be obtained using kinematic-wave routing. The kinematic-wave theory can simulate the actual physical process in surface flow generation, while the non-linear reservoir method does not consider the impact from the time lag needed for the flow depth to grow so that-runoff can commerce. Therefore, the former can achieve a better result than the latter in urban hydrology studies.

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