HYDROLOGICAL EFFECTS OF LAND-USE CHANGE IN A ZERO-ORDER CATCHMENT

Hydrologic modeling and relatively simple monitoring were used to estimate the hydrologic balance for two geographically close and, in the undisturbed state, hydrologically similar, zero-order basins: one undeveloped forest and the other suburban. Continuous precipitation and streamflow were measured in each basin; the model was used to estimate time series of evapotranspiration and ground-water recharge over a 40-yr period. The suburban catchment was denuded of forest cover, soil thickness was reduced, and 30% of the area was covered with impervious surfaces. The amount of annual precipitation that becomes runoff ranged from 12 to 30% in the forested catchment and 44 to 48% in the suburban catchment where runoff from pervious areas accounts for 40-60% of the annual total. The peak flow rate per unit area for an approximate 24-h, 50-yr rainfall was more than 10 times higher from the pervious area at the suburban site than at the forested site. These findings emphasize the need to consider surface flow from all sources in the catchment when considering mitigation measures.