Sediment Storage in the Colorado River Active
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 tributaries (High-flow Protocol Environmental Assessment). The success of this approach to build sandbars depends on the maintenance of a sufficient supply of sand within the channel. The purpose of the sediment-storage monitoring project is to track long-term trends in sand storage and thereby provide a robust measure of whether or not the supply of sand available for building sandbars is increasing, decreasing, or remaining stable over time-scales of years to decades.
Background & Importance
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 tributaries (High-flow Protocol Environmental Assessment). The success of this approach to build sandbars depends on the maintenance of a sufficient supply of sand within the channel. The purpose of the sediment-storage monitoring project is to track long-term trends in sand storage and thereby provide a robust measure of whether or not the supply of sand available for building sandbars is increasing, decreasing, or remaining stable over time-scales of years to decades.
General Methods
We measure changes in sediment storage by making repeat topographic maps of the river bed and banks. The maps are made by surveying exposed sediment deposits with conventional total station. These measurements involve the use of a survey instrument set on a known elevation (also called a benchmark) to measure the location and elevation of points on the ground selected by a rodman equipped with a reflective target. Most of the sediment is underwater and is measured with sonar. Multibeam sonar is the most efficient method to measure this sediment, because it is capable of mapping wide swaths of the riverbed. Singlebeam sonar measures depths directly below the instrument and is used to map areas too shallow for the multibeam equipment, but too deep for conventional survey. All of the sonar measurements are positioned by shore-based robotic total stations that track boat position in real time. GPS is not used for any of the measurements, because satellite signals are not sufficiently reliable in the deep canyon environment. Complementary measurements of changes in sediment storage are also made by measuring sediment concentration in the water.
Important Results
Initial results indicate that sand storage did not decline between 2002 and 2009. This period was one of average to above average tributary sand inputs and average to below average release of water from Glen Canyon Dam. These findings are based on a period that was favorable to sand accumulation. Periods when dam release volumes are greater and tributary sediment inputs are less frequent will likely result in less sand accumulation. Recent results also demonstrate that measurements of channel change made in short reaches (less than a few miles in length) can be used to track changes in deposits and transfers of sand among the storage locations within the short reaches. The results, however, cannot be extrapolated to long segments of the river (over 10 miles in length), because the size and distribution of sand storage locations is highly variable.
Additional Information
More infomation about sediment can be found at the Grand Canyon Monitoring and Reserch Center website: https://www.gcmrc.gov/research_areas/sediment_geomorphology/sed/Sed_Geo….
Sediment data is located at the Grand Canyon Monitoring and Reserch Center website: https://www.gcmrc.gov/dasa/default.aspx.
Below are publications associated with this project.
Linking morphodynamic response with sediment mass balance on the Colorado River in Marble Canyon: issues of scale, geomorphic setting, and sampling design
Sandbar response in Marble and Grand Canyons, Arizona, following the 2008 high-flow experiment on the Colorado River
Is there enough sand? Evaluating the fate of Grand Canyon sandbars
Influence of a dam on fine-sediment storage in a canyon river
Below are partners associated with this project.
- Overview
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 tributaries (High-flow Protocol Environmental Assessment). The success of this approach to build sandbars depends on the maintenance of a sufficient supply of sand within the channel. The purpose of the sediment-storage monitoring project is to track long-term trends in sand storage and thereby provide a robust measure of whether or not the supply of sand available for building sandbars is increasing, decreasing, or remaining stable over time-scales of years to decades.
Background & Importance
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 tributaries (High-flow Protocol Environmental Assessment). The success of this approach to build sandbars depends on the maintenance of a sufficient supply of sand within the channel. The purpose of the sediment-storage monitoring project is to track long-term trends in sand storage and thereby provide a robust measure of whether or not the supply of sand available for building sandbars is increasing, decreasing, or remaining stable over time-scales of years to decades.
General Methods
We measure changes in sediment storage by making repeat topographic maps of the river bed and banks. The maps are made by surveying exposed sediment deposits with conventional total station. These measurements involve the use of a survey instrument set on a known elevation (also called a benchmark) to measure the location and elevation of points on the ground selected by a rodman equipped with a reflective target. Most of the sediment is underwater and is measured with sonar. Multibeam sonar is the most efficient method to measure this sediment, because it is capable of mapping wide swaths of the riverbed. Singlebeam sonar measures depths directly below the instrument and is used to map areas too shallow for the multibeam equipment, but too deep for conventional survey. All of the sonar measurements are positioned by shore-based robotic total stations that track boat position in real time. GPS is not used for any of the measurements, because satellite signals are not sufficiently reliable in the deep canyon environment. Complementary measurements of changes in sediment storage are also made by measuring sediment concentration in the water.
Important Results
Initial results indicate that sand storage did not decline between 2002 and 2009. This period was one of average to above average tributary sand inputs and average to below average release of water from Glen Canyon Dam. These findings are based on a period that was favorable to sand accumulation. Periods when dam release volumes are greater and tributary sediment inputs are less frequent will likely result in less sand accumulation. Recent results also demonstrate that measurements of channel change made in short reaches (less than a few miles in length) can be used to track changes in deposits and transfers of sand among the storage locations within the short reaches. The results, however, cannot be extrapolated to long segments of the river (over 10 miles in length), because the size and distribution of sand storage locations is highly variable.
Additional Information
More infomation about sediment can be found at the Grand Canyon Monitoring and Reserch Center website: https://www.gcmrc.gov/research_areas/sediment_geomorphology/sed/Sed_Geo….
Sediment data is located at the Grand Canyon Monitoring and Reserch Center website: https://www.gcmrc.gov/dasa/default.aspx.
- Publications
Below are publications associated with this project.
Linking morphodynamic response with sediment mass balance on the Colorado River in Marble Canyon: issues of scale, geomorphic setting, and sampling design
Measurements of morphologic change are often used to infer sediment mass balance. Such measurements may, however, result in gross errors when morphologic changes over short reaches are extrapolated to predict changes in sediment mass balance for long river segments. This issue is investigated by examination of morphologic change and sediment influx and efflux for a 100 km segment of the Colorado RAuthorsPaul E. Grams, David J. Topping, John C. Schmidt, Joseph E. Hazel, Matt KaplinskiSandbar response in Marble and Grand Canyons, Arizona, following the 2008 high-flow experiment on the Colorado River
A 60-hour release of water at 1,203 cubic meters per second (m3/s) from Glen Canyon Dam in March 2008 provided an opportunity to analyze channel-margin response at discharge levels above the normal, diurnally fluctuating releases for hydropower plant operations. We compare measurements at sandbars and associated campsites along the mainstem Colorado River, downstream from Glen Canyon Dam, at 57 loAuthorsJoseph E. Hazel, Paul E. Grams, John C. Schmidt, Matt KaplinskiIs there enough sand? Evaluating the fate of Grand Canyon sandbars
Large dams have the potential to dramatically alter the flow regime, geomorphology, and aquatic ecosystem of downstream river reaches. Development of flow release regimes in order to meet multiple objectives is a challenge facing dam operators, resource managers, and scientists. Herein, we review previous work and present new analyses related to the effects of Glen Canyon Dam on the downstream reaAuthorsS.A. Wright, J. C. Schmidt, Theodore S. Melis, D.J. Topping, D. M. RubinInfluence of a dam on fine-sediment storage in a canyon river
Glen Canyon Dam has caused a fundamental change in the distribution of fine sediment storage in the 99-km reach of the Colorado River in Marble Canyon, Grand Canyon National Park, Arizona. The two major storage sites for fine sediment (i.e., sand and finer material) in this canyon river are lateral recirculation eddies and the main-channel bed. We use a combination of methods, including direct meaAuthorsJ.E. Hazel, D.J. Topping, J. C. Schmidt, M. Kaplinski - Partners
Below are partners associated with this project.