How Deep is the River? Sand, Floods, and the shape of the Colorado River in Grand Canyon
Matt Kaplinski, Dan Buscombe, Joe Hazel Geology Program, School of Earth Sciences and Environmental Sustainability, Northern Arizona University
Paul Grams, Keith Kohl Grand Canyon Monitoring and Research Center USGS 6.17 meters 20.28 feet 0
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-6 Depth (meters) Depth
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Outline
• Flow – Floods – Sandbars
• Sediment Budgets
• Channel Mapping - why, how, and when
• Geomorphic characteristics of the Channel
• Bed Sediment classification
• Bedload transport studies
• Sub-bottom profiling
Floods build sandbars
(in lots of places) 9 Floods build sandbars
Pre-2008 HFE – RM 6 Post-2008 HFE – RM 6
(not everywhere)
10 High Flow Experimental Release (HFE’s or Floods) Protocol began in 2012 (EA, finding of no significant impact)
• There will be flood! Releases above power plant capacity when there is enough sediment – positive sand mass balance.
• Fall and Spring opportunities
• Hydrograph developed to NOT export all sand in reach – primarily upper Marble Canyon (0-30 mile). From: Glen Canyon Dam Long-Term Experimental and Management Plan October 2016 Final Environmental Impact Statement Change in sand mass determined from measurements at gaging stations – “flux-based sand budget” change in sand mass or sediment mass balance = what came in (upstream gages) – what went out (downstream gage)
• Instruments at gages measure sand flux every 15 minutes • Error for change accumulates with each measurement (through time)
Monitoring Sand Mass and Storage change by Mapping the Channel
“Morphologic-based sand budget”
Sand Storage Monitoring Goals
• Track long-term trends in sand storage
• Provide a direct measure of changes in sand storage in the channel and in eddies over the time scale of long-term management actions, such as the HFE protocol.
• Track the location of changes in sand storage between the channel and eddies and between high- and low-elevation deposits. How we map the channel
Multibeam Accuracy
Mez -0.013 MAE 0.024 StdDev 0.018 68% conf. 0.030 95% conf. 0.061 2009 to 2012 Comparison of Flux-based and Morphologic-based Sand Budgets
• Agreement between flux- based sand budget and morphologic sand budget flux-based sand budget o Flux budget: -550,000 ± morphologic-based sand budget 300,000 Mg (-320,000 ± 70,000 m3) Sand Budget for Lower Marble Canyon 2009-2012 o Morphologic budget: - 520,000 ± 430,000 Mg (- 300,000 ± 250,000 m3) o All of the erosion occurred in February - August 2011
Discharge, 2009-2012 Where Was Sand Eroded?
Most Net Changes in Sand Storage Occurred in Channel
• Only ~2% of net sand storage change in sandbars above 8,000 ft3/s stage • 77% of net change in channel adjacent to eddy (scour holes below rapids) • 17% of net change in other main channel locations • 5% of net change in eddies below 8,000 ft3/s stage
Eddies: Small Net Change, But Large Gross Change
• Erosion and deposition approximately cancel in eddies (+ bars): 3 o 290,000 m of erosion 3 o 270,000 m of deposition • Much less deposition in channel • During the 7 month period of sediment evacuation, sand was redistributed among the eddies (moved in and out) without a large net loss • Suggests eddies have some “buffering” capacity during sediment evacuation Cumulative downstream change in net sediment storage in lower Marble Canyon by depositional setting. Geomorphic structure of the river Large scale (10’s of kilometer) shape is controlled by the river level geology
Smaller scale (1’s of kilometer) shape is controlled by tributary debris flows
Exploring Sand Dune Scaling Relations
Many ‘scaling’ relationships have been proposed to link flow and dune dimensions, because of the possibility of • … estimating dune dimensions from flow variables (depth, velocity) which are easier to measure/model • … estimating paleo-flow variables from dunes preserved in the rock record
481 bedform fields analyzed over 140 km
178 fields from 50 km of channel mapped in upper Marble Canyon (UMC) in 2013, 171 fields from 50 km of channel mapped lower Marble Canyon (LMC) in 2012, and 132 fields from 42 km of channel mapped eastern Grand Canyon (EGC) in 2014. Large variation in dune H for given dune length, Large variation in dune H for given dune length, but but within previously observed ranges within previously observed ranges Larger H and L dunes in unconstrained shallow reaches
Dune in spatially constrained fields such as in scour hole exit slopes have smaller lengths. Conclusions
1) Colorado river sand dunes have about the same ~1 order magnitude variability in H and L for a given depth as observed in other large sand-bedded rivers.
2) Constricted dunes are growth-limited. Dunes in spatially limited fields are slightly smaller for a given flow depth, and shorter for a given height, than in other systems.Constrictions on dune fields imposed by larger morphologies (sand & cobble bars, bedrock) and debris fans.
3) Steep slopes promote steep dunes. Short fields of steep (large H, small L) dunes form in scour holes and on the flanks of submerged bars. All dunes: steep dunes are found in short dune 4) Variation among unconstructed dunes may be fields where local driven by grain size or flow recirculation. In relatively slope is high. large dune fields, smaller height dunes are in areas of recirculating flow and relatively fine sand. Bed Sediment Classification
Observations of sand dune migration on the Colorado River in Grand Canyon using high- resolution multibeam bathymetry
Matt Kaplinski1, Daniel Buscombe2, Thomas Ashley3, Robert Tusso2, Paul E. Grams2, Brandon McElroy3, Erich Mueller2, Daniel Hamill2 1 School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011 [email protected] 2 Grand Canyon Monitoring and Research Center, U.S. Geological Survey, Flagstaff, AZ 86001 3 University of Wyoming, Laramie, WY. Funded by Glen Canyon Dam Adaptive Management Program, USGS Grand Canyon Monitoring and Research Center Background • Develop a better understanding of bedload sediment transport
• Suspended load is currently measured acoustically at 15 minute intervals at gaging stations spaced throughout the canyon
• Bedload is calculated as a constant 5% of suspended load based on one set of measurements of bedform migration made at one discharge (595 m3/s) using rotating side-scan sonar (Rubin, 2001)
Rubin, 2001 • Sediment budgets are constructed from the time-integrated total load to estimate changes in stored sediment mass DATA COLLECTION
Bathymetry - Multibeam Sonar (Reson 7125, IxSea hydrins IMU &Heading, Trimble SPS930)
Current Velocity - ADCP (RDI workhorse)
Bed Grain Size - Underwater Camera (Buscombe et al., 2013; www.digitalgrainsize.org)
Suspended Sediment – Acoustics samples @ 15 minute intervals, calibrated with D96 & P61 point samples from cableway DATA COLLECTION 14500 22,000 14000 21,000 13500 13000 20,000 12500 19,000 12000 11500 18,000 Discharge (ft3/s) Discharge 11000 17,000 10500 10000 16,000 2/28 3/1 3/2 3/3 3/4 3/5 7/11 7/12 Time
Multibeam ADCP Suspended Grain-Size Surveys Surveys Sediment Surveys Samples
Multibeam Tracklines 30 and 50 cm in height, 5 m in length, and migrating downstream at about 1 m per hour 75 and 130 cm in height and 10-15 m in length, and were migrating downstream at rates of 5 to 2 m per hour.
Sediment Flux (Million Tons (Million Flux Sediment
Bedload calculated from migration of bedforms Bedload calculated using 5% bedload coefficient 0.3 800
0.2
400
0.1 P er Year)er Water Discharge (m^3/s) Water
0 0 3/1/2015 3/2/2015 3/3/2015 3/4/2015 7/11/2015 7/12/2015 20
• Bedform geometry statistics (particularly 15 height and velocity) calculated for groups of downstream transects 10 • Flux calculated using the Simons and Richardson (1965) bedform bedload 5 Universally Applied Bedload Equation Coefficient BedloadPercent of Sand Suspended 300 400 500 600 Water Discharge (m^3/s) Sub-bottom Profiling Chirp (Compressed High Intensity Radiated Pulse) system Cobbles/ S A Boulders an d
A CHIRP system uses a swept Interpreted frequency of acoustic energy pulses to Sand Bottom produce a subsurface image similar to seismic reflection. B Widely available in newer “fish finders” and does not impact fish!
Questions?