Detrimental effects of river channelization.

The East and West Prairie Rivers in Alberta, Canada, drain the Swan Hills uplands and debouche upon a Lacustrine plain that once constituted part of the bed of Lesser Slave Lake . The streams naturally aggrade in their downstream reaches, and thus are prone to frequent flooding. Development of the flood plains has increased the sediment load and aggravated the flood problem in the cultivated plain. Extensive reaches of both rivers were channelized and straightened between 1953 and 1971 in an attempt to provide flood relief. The morphologic consequences of the channelization became manifest in a relatively short time. The improved ability of the channels to handle floods is being destroyed in the lower channelized reaches by aggradation. In the upper reaches, as much as 15 feet of degradation was observed between 1964 and 1974. Incipient meandering s apparent in the lower reaches, and in the naturally meandering reaches above the channelized portion a combination of degradation and channel migration has destroyed some farmland. Channel straightening is an engineering technique that has been used frequently, in recent years, with varying degrees of success. In this paper, an in-depth analysis of one specific case is presented as an evaluation of the technique. Furthermore, existing theories are applied in an attempt to see if the detrmental effects could have been predicted with some quantitative accuracy before Lhe straightening had been undertaken. The question of possible alternatives to channel straightening is also addressed. (A)