This report describes a number of studies which were concerned with the hydrologic impacts of urbanization. The principal studies have dealt with stream-channel enlargement due to urban development. The primary strength of the studies reported here is the very detailed treatment of urban land uses. Due to the use of large samples of streams, it was possible to consider the individual effects associated with a wide variety of land-use variables, and thus to establish the relative importance of factors such as the size of impervious surfaces, the provision of storm sewerage, the location of impervious area within a watershed, the relative amounts of building area and pavement area, etc. The studies thus have yielded predictive formulas which consider very specifically the type of urban development present in a watershed.