Abstract

A substantial part of the natural runoff from the south slope of the Uinta Mountains is now diverted within the Uinta Basin or is transferred to the Great Basin via tunnels. The natural runoff of the Duchesne River once supplied approximately 1.1 × 10⁹ m³ to the Green River, as estimated for the period 1912-1924 at the gaging station near Randlett. Today, mean annual runoff at the same site is much less; between 1925 and 2000, mean annual runoff was 52% less. The 1.5-year and 2-year recurrence floods near Randlett have been reduced by 61 and 53%, respectively, for the same periods. The degree of alteration of tributary flow where Duchesne River tributaries exit the Uinta Mountains is variable and depends on the size and purpose of the associated dams and diversions.

Reduction in total and flood flows have caused channel narrowing in much of the main-stem Duchesne River, as measured at Myton and in the 30 km between Randlett and Ouray, where the bed is sandy gravel or sand. Analysis of discharge measurement notes and other geomorphic measurements of tributaries where they exit the Uinta Mountains demonstrate that the magnitude of channel change of these coarse-bedded streams is less than downstream. The difference in the style of channel change indicates that proximity to water development projects is not the sole determinant of downstream channel change.