Urbanization and adjustment of ephemeral stream channels

Comparatively few studies of stream channel adjustment following urbanization have been undertaken in dryland environments. In the new master planned community of Fountain Hills, a residential area near Phoenix, Arizona developed since the 1970s, surveys in 1987 and 2001 of ephemeral wash channels show that they are larger than comparable channels in humid areas, reflecting the effects of rare but substantial floods. Morphological adjustment is spatially varied and is influenced by wide road crossings that are responsible for fragmentation of the adjusting channels into segments. By 2001, these segments are characterized by scour immediately downstream of a crossing and a relatively high width-depth ratio farther downstream before the next road crossing. Such spatially distributed responses have caused management problems unique to arid environments, so that, although road drainage was originally allowed to flow into the washes at the crossings, the stormwater network has now been augmented to improve drainage and to inhibit scour at the crossings. In maintaining such washes, consideration of channel adjustments as a result of urbanization could form the basis for an approach comparable to restoration methods in more humid areas.