Conceptual Hydrologic Models for Urbanizing Basins

After a preliminary analysis of several conceptual models, the single linear reservoir and the Nash Model were selected for further study. Analysis of about two hundred storms from watersheds with different degrees of development indicated that the parameters of the aforementioned two models varied not only with the urbanization factor (related to the ratio of the built-up area in a watershed to the total watershed area) but also with other physiographic and meteorological factors. Regression relationships between the parameters of the models and the more significant meteorological and physiographic factors including the urbanization factor were developed. These regression relationships were used to simulate the instantaneous unit hydrographs on a watershed for various urbanization factors. Changes in runoff from a watershed with increasing urbanization factors were then simulated for a variety of rainfall characteristics.