ABSTRACT
Glen Canyon Dam has dramatically affected the sediment resources by eliminating the upstream source of sediment and changing the flow regime. The historical major source of sediment to the Grand Canyon is now deposited in Lake Powell and the tributary sources of the Paria River and the Little Colorado River now supply the Grand Canyon with a majority of the sediment input. The new flow regime created by Glen Canyon Dam has eliminated the historical periods during the year when sediment accumulated during low flows and when sediment was redistributed to high-elevation sand bars during the high flows. The obvious change in the hydrograph due to the dam has been the elimination of the annual high flow events but just as critical is the fact that the new flow regime is substantially more erosive due to the reduction in the duration of low flows that allow for sediment accumulation. This more erosive flow regime has substantially degraded the sand bar resources of the Grand Canyon that provide campsites for river runners and habitat for a diverse collection of native plants and animals that are now largely threatened. Efforts, including the 1996 and 2004 controlled floods, have been made to more effectively manage the sediment resources to benefit the vast amount of constituencies concerned with the Grand Canyon’s future. While these efforts have provided many lessons for researchers, they have not reversed the trend of sand bar degradation. More research associated with the use of controlled high flow events needs to be done to better utilize the available sediment supply from tributaries to rebuild sand bars. However, since the loss of sediment supply to this system is so profound, the idea of sediment augmentation also needs be explored.