A reach-averaged model of diurnal discharge wave propagation down the Colorado River through the Grand Canyon

As part of the Glen Canyon Environmental Studies, we have developed a discharge model that routes daily discharge waves released from Glen Canyon Dam to Diamond Creek, 386 km downstream. Owing to the length of the diurnal discharge wave and the sparseness of the available topographic data, the latter were averaged over the entire length of the system. Terms too small to be significant in the momentum equation were identified by scaling arguments based on data from past dam releases and on channel hydraulic geometry. Channel friction results primarily from form drag on large topographic elements and from variations in cross-sectional area and flow depth, rather than bed roughness, producing a stage-dependent friction that is not well represented by a constant value of standard channel roughness parameters, such as Manning's n. Channel friction as a function of stage was determined from field data available at high discharge (792 m(3)/s) and intermediate discharge (425 m(3)/s) and by using simple kinematic wave theory together with wave speed measurements to determine channel friction at low discharge (about 142 m(3)/s). Model predictions of wave speed and shape agree well with data from five streamflow gaging stations and 42 stage gaging stations located along this segment of the Colorado River.