9385 - Laserfiche WebLink

Home Browse Search

In addition to mainstem dams, small off-channel flow depletion projects can have cumulative impacts which may be superimposed on the mainstem response to upstream reservoirs. Butler (1988a) indicated that both large water projects and cumulative impacts of smaller projects in the upper basins have the potential to alter the sediment supply to downstream river reaches through streamflow regulation. A number of reports discuss the potential impacts related to water resource development in the Little Snake River, Yampa River and Green River basins. Andrews (1978) projected an increase in sediment yield due to a potential increase in coal surface mining but confined his analysis to the Yampa River basin. He analyzed suspended sediment measurements collected at the Maybell and Lily Gages as well as the sediment records for 16 other gages in the Yampa River basin. Andrews concluded that the impact of increased sediment load will depend on where in the basin it enters the river channel. In 1980, Andrews published an important paper on effective and bankfull discharge in the Yampa River basin which used his 1978 data base (Andrews 1978). This study addressed the concept of effective discharge and it's significance to the river channels in the Yampa River basin. The premise of the paper, as introduced by Wolman and Miller (1960), was that channel morphology characteristics, particularly meander length and channel width, were formed by relatively frequent flows and not by rare catastrophic events. Recurrence intervals for the effective discharges ranged from 1.18 to 3.26 years for 15 selected gaging stations. Based on a Little Snake River cross section surveyed near Dixon, WY, Andrews (1980) determined that the effective and bankfull discharges were in close agreement and concluded that the stream channels were adjusted to the 31