Since the completion of Glen Canyon Dam in 1963, the amount of sand supplied to Grand Canyon National Park has been reduced by more than 90 percent. The Paria River, a tributary to the Colorado River 15 miles downstream from the dam, is now the single most important supplier of sand to the Colorado River within the Park. This large reduction in sand supply has resulted in substantial decrease in the number and size of sandbars. Sandbars are important because they serve as campsites for river runner and hikers, provide important aquatic and riparian habitats, and are the source of sand that may help protect archaeological sites. The information collected by this project will be used to determine whether dam operations, including High-flow Experiments, cause increases or decreases in sandbars and associated campsites in Grand Canyon National Park.
The Sandbar Monitoring Data
Currently, topographic maps are made at a set of monitoring sites annually using conventional survey equipment. These surveys are used to calculate the size of each sandbar in terms of the area of exposed sand and the volume of sand contained in the bar. Both of these calculations are relative to an elevation of interest.
Recent Findings
Each of the five High-flow Experiments (HFEs) that has been released from Glen Canyon Dam between November 2012 and November 2018 resulted in deposition at more than 50 percent of 44 long-term sandbar monitoring sites in Marble Canyon and Grand Canyon. That deposition also resulted in small cumulative increases in sandbar volume at those same monitoring sites. Cumulative increases in sand volume between 2003 and 2018 are significant at two sandbar types—reattachment bars and upper pool bars. Hydrograph shape appears to affect sandbar topography for at least some sites. The lower downramp rate used in 2012 resulted in sandbar topography that was less steep compared to the downramp rate used in the 2008 HFE. However, because the adjusted hydrograph with lower downramp rate was tested in only one year and because topographic surveys were only available for three sites, it is uncertain whether this response would be consistent among many sites or repeatable in future HFEs.
In four out of the five years with HFEs, the sand mass balance for the July 1 to December 1 accounting period for all five account years has been significantly positive and in one year the sand mass balance was indeterminant. Thus, the objective HFEs to cause deposition on sandbars and increases in sandbar size without causing decreases in sand storage in Marble Canyon was achieved or exceeded each year.
Data and Resources
Sandbar monitoring data: www.gcmrc.gov/sandbar (https://www.usgs.gov/apps/sandbar/)
Sandbar monitoring photographs (including responses to High-flow Experiments): https://grandcanyon.usgs.gov/gisapps/sandbarphotoviewer/RemoteCameraTimeSeries.html
Below are other science projects associated with this project.
River Geomorphology and Geomorphic Change
Sediment Storage in Grand Canyon
River Campsites in Grand Canyon National Park
High-Flow Experiments on the Colorado River
- Overview
Since the completion of Glen Canyon Dam in 1963, the amount of sand supplied to Grand Canyon National Park has been reduced by more than 90 percent. The Paria River, a tributary to the Colorado River 15 miles downstream from the dam, is now the single most important supplier of sand to the Colorado River within the Park. This large reduction in sand supply has resulted in substantial decrease in the number and size of sandbars. Sandbars are important because they serve as campsites for river runner and hikers, provide important aquatic and riparian habitats, and are the source of sand that may help protect archaeological sites. The information collected by this project will be used to determine whether dam operations, including High-flow Experiments, cause increases or decreases in sandbars and associated campsites in Grand Canyon National Park.
The Sandbar Monitoring Data
Currently, topographic maps are made at a set of monitoring sites annually using conventional survey equipment. These surveys are used to calculate the size of each sandbar in terms of the area of exposed sand and the volume of sand contained in the bar. Both of these calculations are relative to an elevation of interest.
Sources/Usage: Public Domain.Surveying an exposed sandbar along the bank of the Colorado River in May 2014. (Credit: USGS. Public domain.) Recent Findings
Each of the five High-flow Experiments (HFEs) that has been released from Glen Canyon Dam between November 2012 and November 2018 resulted in deposition at more than 50 percent of 44 long-term sandbar monitoring sites in Marble Canyon and Grand Canyon. That deposition also resulted in small cumulative increases in sandbar volume at those same monitoring sites. Cumulative increases in sand volume between 2003 and 2018 are significant at two sandbar types—reattachment bars and upper pool bars. Hydrograph shape appears to affect sandbar topography for at least some sites. The lower downramp rate used in 2012 resulted in sandbar topography that was less steep compared to the downramp rate used in the 2008 HFE. However, because the adjusted hydrograph with lower downramp rate was tested in only one year and because topographic surveys were only available for three sites, it is uncertain whether this response would be consistent among many sites or repeatable in future HFEs.
In four out of the five years with HFEs, the sand mass balance for the July 1 to December 1 accounting period for all five account years has been significantly positive and in one year the sand mass balance was indeterminant. Thus, the objective HFEs to cause deposition on sandbars and increases in sandbar size without causing decreases in sand storage in Marble Canyon was achieved or exceeded each year.
Data and Resources
Sandbar monitoring data: www.gcmrc.gov/sandbar (https://www.usgs.gov/apps/sandbar/)
Sandbar monitoring photographs (including responses to High-flow Experiments): https://grandcanyon.usgs.gov/gisapps/sandbarphotoviewer/RemoteCameraTimeSeries.html
- Science
Below are other science projects associated with this project.
River Geomorphology and Geomorphic Change
River channels and their adjacent floodplains are ever evolving in form and composition in response to changing patterns of streamflow, the quantity and size of supplied sediment, and feedbacks with the riparian and aquatic ecosystems. Changes in channel form affect aquatic and riparian habitats, which are important for plants, animals, and insects. Erosion and deposition of river channels and...Sediment Storage in Grand Canyon
The sandbars exposed along the shoreline of the Colorado River represent only a small fraction of the sand deposits in Grand Canyon, most of which are on the bed of the river in eddies and the channel. Current management practice includes efforts to maintain and build sandbars by releasing high flows from Glen Canyon Dam that are timed to coincide with periods of fine-sediment supply from...River Campsites in Grand Canyon National Park
Sandbars have been used as campsites by river runners and hikers since the first expeditions to the region more than 100 years ago. Sandbar campsites continue to be an important part of the recreational experience for the more than 25,000 hikers and river runners that visit the Colorado River corridor each year. Because the Colorado River is dominated by bedrock cliffs and steep talus slopes...High-Flow Experiments on the Colorado River
Glen Canyon Dam has altered flow and fine sediment (sand, silt, and clay) dynamics of the Colorado River in Grand Canyon. Before the dam, the Colorado River experienced highly variable flows and carried a large amount of sediment through Grand Canyon, which maintained sandbars (highly valued camping areas in Grand Canyon) and provided sand that protected archeological and cultural sites from... - Data
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