Proposed Model For Evaluating Urban Hydrologic Change

Abstract

Evaluation of the effects of land‐use change in a natural catchment and what can be done to mitigate these effects requires accurate quantitative representation of the mechanisms by which precipitation contributes to run off in the natural and changed states. It is necessary to predict the locations of flow production zones, how these zones change with time, and where flow from each zone enters the channel system. A model is presented that simulates flux rates and spatial distributions of evapotranspiration, Horton and saturated overland flow, subsurface storm flow, and dry‐weather base flow. The model is operated continuously in time and has parameters that are readily measured or estimated, allowing land use changes (forest cover removal, regrading, litter zone removal) to be explicitly represented. The model is applied to a 39‐ha (97‐acre) ungauged catchment in King County, Washington, and an approximate calibration is achieved by comparing the location of simulated runoff production zones against field‐mapped locations. The model is used to explore the relative temporal and spatial effects of land use change on storm hydrographs, flow duration, and long‐term mass balance. The utility of a model structure that permits comparison of directly observable field states with comparable model predicted states is demonstrated.