Time in Urban Hydrology

Abstract

An analysis of lag time (defined as time between centroids of effective precipitation and runoff) from nine small urban watersheds shows that lag time variability is small and that lag time is not correlated with storm intensity. Effective precipitation can be routed through storage by the Muskingum method to accurately reproduce an observed runoff hydrograph. Effective precipitation is separated from total precipitation by the phi-index. Precipitation loss on a watershed is closely represented by a linear relationship between total storm precipitation and total storm runoff. On impervious watersheds, precipitation loss seems to be related to watershed slope. Instrumentation requirements for adequate data collection on urban watersheds include synchronization of precipitation and runoff records, use of at least two rain-gages, and accurate runoff measurement at high and low flows. Watershed selection is important for successful data collection.