Knowledge of Sedimentation in Urban Environments

The population explosion, coupled with technological progress of the last century, has created megalopolis. Urbanization-suburbanization of America has changed the hydrology of affected areas, but little is known as yet other than qualitatively of the changes. Sediment data are widely collected in the United States, but mostly in large streams to measure runoff from nonurban areas for studies of reservoir silting. Measurements of sedimentation are scarce, and analytical studies are almost nonexistent for urban areas. Urbanization increases the proportion of impervious areas, which changes the surface water hydrology by increasing peak discharges appreciably without necessarily affecting larger flood runoff volumes. This change of stream regimen should increase sediment yield and have a marked geomorphological effect, if channels are not lined. Of more significance are drastic effects of urbanization on sediment yield which occur during construction when loads may increase. Studies have been semi-quantitative, particularly with respect to the relation of effects to causative factors. More intensive studies are needed for quantitative predictions of the effects of urbanization on sediment yield.