Effect of Urbanization on Storm Water Peak Flows

Urbanization of a natural watershed modifies the original shape and proportions of the hydrograph that may be considered representative of the natural watershed. The unique runoff coefficient of the rational formula is, in fact, the product of three factors, each on having some correlation with the degree of urbanization given to the watershed. The influence of urbanization is mainly expressed by the degree of imperviousness and the degree of artificial canalization given to the watershed. The presented general rational formula is related to other rainfall-runoff relationships derived by Snyder and by Horner-Flynt. Results from the formula are compared with these obtainable by the Chicago Method. The concepts presented must be considered as one way of demonstrating the relationship between rainfall and runoff in areas which are urbanized or not, rather than a completely developed and tested method of calculating storm water peak flows.