Abstract

Meander incision was studied in a sixty-by-four foot flume in which bedrock was simulated by a kaolinite-sand mixture and overlying alluvium by a silt-sand mixture. The six independent variables controlled during the experiments were base level, bedrock structure, bedrock erodibility, flume (valley) slope, thickness of alluvium and stream discharge.

Incision was initiated by a drop in base level after an initial meander pattern had developed in the overlying alluvium. Once incised, only minor modification of the stream pattern occurred. Four distinct forms of incised channels developed under different general conditions: 1) a straight, incised channel developed in response to increasing valley slope or on a bedrock surface sloping in the direction of stream flow, 2) deformed, incised meanders developed on a bedrock surface sloping uniformly upstream, above structural axes and where stream gradients are decreased, 3) superposed meanders developed only on a horizontal bedrock surface overlain by a thin veneer of alluvium, and 4) armouring of the channel bottom and variations in bedrock erodibility caused oblique incision (ingrown meanders).

Experimental data duplicate incised meander patterns on the Green and Colorado Rivers in Canyonlands and the San Juan River where it crosses the Monument Upwarp. It is hypothesized that the experimental channels and those rivers have had similar histories. Data from this study provide information on the little known transition phase from alluvial to incised meanders.