Impervious areas in urban areas can greatly influence rainfall runoff

Urban development and flooding

Urbanization can have a great effect on hydrologic processes, such as surface-runoff patterns. creek in Washington State. If you measured the area under both curves (the total volume of water that flowed by the measurement location for the time period shown on the X axis) in the chart, they might be the same. But in the urban stream, the water at the measurement site rose at a much higher rate and reached a much higher stage (height) than the rural stream did. The tall, steep curve of Mercer Creek showed that much higher streamflows occurred in the urban stream. The urban stream stage fell back towards baseflow much quicker, too, indicating that it wasn't receiving much seepage from groundwater. "Base floe" is the sustained flow of a stream in the absence of direct runoff. It includes natural and human-induced streamflows. Natural base flow is sustained largely by groundwater discharges.