Transient Simulation of Groundwater Levels within a Sandbar of the Colorado River, Marble Canyon, Arizona, 2004 By Thomas A. Sabol and Abraham E. Springer Open-File Report 2013–1277 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Sally Jewell, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2013 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod Suggested citation: Sabol, T.A., and Springer, A.E., 2013, Transient simulation of groundwater levels within a sandbar of the Colorado River, Marble Canyon, Arizona, 2004: U.S. Geological Survey Open-File Report 2013-1277, 22 p., http://dx.doi.org/10.3133/ofr20131277. ISSN 2331-1258 (online) Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. Cover: Eddy sandbar at river mile 30.7R after recession of the 2004 high-flow experiment, Colorado River, Marble Canyon, Arizona. Visible are piezometers in the bar face regions of the downstream part of the sandbar. ii Contents Abstract ....................................................................................................................................................................... 1 Introduction and Background ...................................................................................................................................... 1 Purpose and Scope ................................................................................................................................................. 4 Study Sites .............................................................................................................................................................. 4 Data Collection ............................................................................................................................................................ 5 Groundwater Model ..................................................................................................................................................... 7 Model Framework .................................................................................................................................................... 7 Hydraulic Conductivity ......................................................................................................................................... 9 Storage Coefficient ............................................................................................................................................ 11 Initial Head Values ............................................................................................................................................. 11 Boundary Conditions .......................................................................................................................................... 12 Model Calibration ................................................................................................................................................... 13 Calibration Criteria and Model Error ................................................................................................................... 13 Model Results ........................................................................................................................................................ 14 Conclusion ................................................................................................................................................................ 18 References Cited ...................................................................................................................................................... 19 Figures Figure 1. Map of the Colorado River in Glen, Marble and Grand Canyons, Arizona .............................................. 2 Figure 2. Continuous discharge record for the river mile 30.7 sandbar study site from November 20, 2004 through January 20, 2005. ..................................................................................................................... 5 Figure 3. Plan view image of the river mile 30.7R, Colorado River in Marble Canyon, Arizona ............................. 6 Figure 4. Matched oblique photographic views of the river mile 30.7R sandbar study site, Colorado River in Marble Canyon, Arizona ..................................................................................................................... 6 Figure 5. Idealized cross-section showing the eddy sandbar at river mile 30.7R, Colorado River in Marble Canyon, Arizona ......................................................................................................................... 9 Figure 6. Hydraulic conductivity (K) of model layers 1 and 2 within the three-dimensional groundwater model framework developed for this study, river mile 30.7R, Colorado River in Marble Canyon, Arizona. ..... 10 Figure 7. Plan view image of the river mile 30.7R eddy sandbar study site ......................................................... 12 Figure 8. Measured elevation of groundwater level in all piezometers at river mile 30.7R eddy sandbar site relative to river stage ............................................................................................................................ 14 Figure 9. Graph plot showing measured and modeled groundwater level in piezometers ................................... 16 Figure 10. Graph plot showing measured and modeled groundwater level in piezometer 10 ................................ 17 Tables Table 1. Locations and selected construction data for piezometers installed in the eddy sandbar at river mile 30.7R, Colorado River in Marble Canyon, Arizona. ........................................................................ 7 Table 2. Root mean squared error (RMSE) and mean absolute error (MAE) residual differences between the measured groundwater level in piezometers and the simulated model results at target locations ....... 15 Table 3. Root mean squared error (RMSE) and mean absolute error (MAE) for the measured groundwater level in piezometers and the simulated model results at piezometer 10 ............................................... 18 iii Conversion Factors Inch/Pound to SI Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) mile (mi) 1.609 kilometer (km) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) SI to Inch/Pound Multiply By To obtain Length centimeter (cm) 0.3937 inch (in.) meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) Area square meter (m2) 0.0002471 acre Flow rate cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s) Hydraulic conductivity meter per day (m/d) 3.281 foot per day (ft/d) Vertical coordinate information is referenced in meters to height above the GRS80 ellipse defined by NAD83(1982). Horizontal coordinate information is referenced to North American Datum of 1983, NAD83(1982). Elevation, as used in this report, regers to distance above the vertical datum. iv This page left intentionally blank v Transient Simulation of Groundwater Levels within a Sandbar of the Colorado River, Marble Canyon, Arizona, 2004 By Thomas A. Sabol1 and Abraham E. Springer2 Abstract Seepage erosion and mass failure of emergent sandy deposits along the Colorado River in Grand Canyon National Park, Arizona, are a function of the elevation of groundwater in the sandbar, fluctuations in river stage, the exfiltration of water from the bar face, and the slope of the bar face. In this study, a generalized three-dimensional numerical model was developed to predict the time-varying groundwater level, within the bar face region of a freshly deposited eddy sandbar, as a function of river stage. Model verification from two transient simulations demonstrates the ability of the model to predict groundwater levels within the onshore portion of the sandbar face across a range of conditions. Use of this generalized model is applicable across a range of typical eddy sandbar deposits in diverse settings. The ability to predict the groundwater level at the onshore end of the sandbar face is essential for both physical and numerical modeling efforts focusing on the erosion and mass failure of eddy sandbars downstream of Glen Canyon Dam along the Colorado River. Introduction and Background Emergent sandy deposits along the Colorado River in Grand Canyon National Park, Arizona, are a key fixture of the ecosystem downstream of Glen Canyon Dam (fig. 1; Rubin and others, 1998, 2002; Topping and others, 2006). Closure of the dam in 1963 reduced the supply of sand-sized sediment in the Colorado River at the upstream boundary of Grand Canyon National Park, located at the mouth of the Paria River, by about 94 percent from a mean annual sediment load of about 60 million metric tons to about 3 million metric tons (Topping and others, 2000a, 2006, 2010; Draut and others, 2005); the remaining 6 percent of the post-dam sand supply is contributed almost exclusively