In the syntheses of hydrograph characteristics of small urban watersheds, the distribution of water among the various phases of the runoff process is attempted by the concept of equivalent rural watershed. The urban parameters considered in the study are percentage impervious cover and characteristic impervious length factor. A mathematical model is developed for the equivalent rural watershed with precipitation as input. The hydrograph of outflow is obtained by chronologically deducting the losses due to interception, infiltration, and depression storages from precipitation and then routing through the watershed storage. This mathematical procedure is programmed on an analog computer and is tested with data from the Waller Creek watershed, at Austin, Texas. In the verification process, watershed coefficients representing interception, infiltration, and depression storage are established by trial and error such that the simulated and observed hydrographs are nearly identical with a high statistical correlation. Sensitivity studies indicate the relative influence of the watershed coefficients on the runoff process. The watershed coefficients determined by model verification for each year of study are related to corresponding urban parameters.
Dhruva Narayana, V. V.; Riley, J. Paul; and Israelsen, Eugene K., "Analog Computer Simulation of the Runoff Characteristics of an Urban Watershed" (1969). Reports. Paper 186.