Andrews, E. D.. U.S. Geological Survey, eandrews@usgs.gov

 
SAND WAVES IN THE COLORADO RIVER BELOW GLEN CANYON DAM, AZ
 
Glen Canyon Dam traps 45 million tons of sand annually and significantly reduces the flux of sand through Grand Canyon National Park. The number and size of sand bars, which are an important recreational and ecological resource, have decreased significantly since the dam was completed. Sand supplied by tributaries is the primary source of material with which sand bars can be rebuilt. Twice daily sampling of sand transport during a period of 8 months revealed the passage of 8 sand waves. Each wave resulted from a flashflood in the Paria River, a major tributary located ~ 100 km upstream. A typical wave contained ~ 100,000 tons of sand and migrated downstream at ~ 0.04 m/s with a river discharge of 750 m3/s. The waves moved over a coarse cobble bed. As cobbles are progressively buried by a migrating wave, the form drag exerted on the flow is greatly reduced, and boundary shear stress and sand transport rate increase. Obseved sand transport rates near a wave crest were 5 to 20 times the background rate. A physically-based numerical model predicts the rate of flow and sand transport in excellent agreement with observed values.
 
Day: Tuesday, Feb. 2
Time: 09:45 - 10:00am
Location: Sweeney Center
 
Code: SS19TU0945S