This is because evapotranspiration was reduced, storage of water in the soil was reduced, and so rainfall quickly became floodwater. Hydrology may be the first or most fundamental change in response to an altered landscape. However, it is far from the only change. With less surface vegetation and more runoff, sediments are eroded, entering streams and degrading habitat. Floods are larger than in the past.
Banks widen during floods, causing bridges to collapse and fish habitat to degrade further.
With less water stored in ground water, streams tend to dry up during dry periods. The diversity of insects and fishes declines, until only the most tolerant species remain. While much of the landscape is agricultural, some regions are highly agricultural, others have more heterogeneous land use. Our studies show that habitat quality and fish diversity decrease as the percentage of agricultural land cover increases. It is widely believed that protecting the stream margins will do much to protect stream health.