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Table 2. Modeled sand budgets for 8.23 million acre -foot annual release volume
<br />Rank
<br />Scenario
<br />Annual sand
<br />budget (Tmt)
<br />Sign (includes
<br />uncertain)
<br />Rank
<br />Scenario
<br />Annual sand
<br />budget (Tmt)
<br />Sign (includes
<br />uncertainty)
<br />Marble Canyon
<br />Grand Canyon
<br />I
<br />SYR
<br />+1,032
<br />Positive
<br />1
<br />SYR
<br />+248
<br />Positive
<br />2
<br />SDF
<br />+945
<br />Positive
<br />2
<br />SDF
<br />+208
<br />Positive
<br />3
<br />EMV
<br />+919
<br />Positive
<br />3
<br />EMV
<br />+200
<br />Positive
<br />4
<br />MLFF
<br />+796
<br />Positive
<br />4
<br />MLFF
<br />+156
<br />Positive
<br />5
<br />IDR
<br />+699
<br />Positive
<br />5
<br />IDR
<br />+123
<br />Positive
<br />6
<br />SAS
<br />+677
<br />Positive
<br />6
<br />SAS
<br />+65
<br />Positive
<br />The first observation from the tables is that the SYR scenario is consistently ranked 1 in terms of the annual sand
<br />budgets and is the only operation that results in a positive Marble Canyon sand budget for 11.0 MAF (table 1, fig. 9A). This
<br />ranking is an expected result and is consistent with the choice by Wright and others (2008) to evaluate this scenario as the
<br />optimal flow regime for building and maintaining sandbars below Glen Canyon Dam. The nonlinear relationship between
<br />sand transport and water discharge (with exponent greater than one) dictates that a steady flow will transport less sand than
<br />an equivalent - volume fluctuating flow, and thus a steady year round flow yields the least sand export. For the 11.0 MAF
<br />simulations, the MLFF and IDR operations consistently ranked 5 and 6, owing to the fact that the other four scenarios all
<br />constrain the MLFF fluctuations to some degree (either monthly variations or daily fluctuations are constrained). MLFF
<br />ranks higher than IDR because IDR relaxes the MLFF constraints and allows for increased fluctuations and increased down
<br />ramp rates (which allow for longer peaks within each day). The SDF operational scenario ranks 4 for both reaches. The SAS
<br />and EMV operations rank 2 and 3 and the order is swapped for the two reaches; however, these operations produce quite
<br />similar results for this annual release volume.
<br />The results and rankings for the 8.23 MAF annual volume are substantially different from the 11.0 MAF results, the
<br />only similarity being that SYR is ranked I (tables 1, 2). For this annual volume, the SAS operation ranks 6 for both reaches,
<br />whereas for 11.0 MAF, this operation ranked 2 or 3, depending on the reach. This difference results from the 18,000 cfs
<br />maximum release imposed by SAS. For all other scenarios, the 11.0 MAF annual volume results in higher peak flows that
<br />substantially increase sand transport and export rates. MLFF and IDR rank above SAS at positions 4 and 5, again with MLFF
<br />resulting in more sand in both reaches than IDR. Finally, SDF and EMV yield similar results for 8.23 MAF, with SDF
<br />ranked 2 and EMV ranked 3 for both reaches.
<br />Finally, it is noted that these simulations should not be considered absolute predictions of the sand budgets below Glen
<br />Canyon Dam for WY 2011. It is unknown what the actual annual release volume and tributary inputs will be. Also, the initial
<br />conditions with respect to sand in the reaches are unknown. Rather, these simulations provide realistic estimates of the sand
<br />budgets for the hypothetical initial and boundary conditions simulated, as well as comparisons of the various operational
<br />scenarios, in a relative sense, that may be used by decision makers within the GCDAMP.
<br />References Cited
<br />Bureau of Reclamation, 2001, Strategic plan, Glen Canyon Dam Adaptive Management Program: Glen Canyon Dam
<br />Adaptive Management Work Group, 53 p., accessed on December 31, 2009, at
<br />http: /Avww. usbr.gov/uc/rm/amp/pdfs/sp f nalpdf.
<br />Grams, P.E., Schmidt, J.C., and Topping, D.J., 2007, The rate and pattern of bed incision and bank adjustment on the
<br />Colorado River in Glen Canyon downstream from Glen Canyon Dam, 1956 -2000: Geological Society of America, v. 119,
<br />no. 5 -6, doi: 10.1130/1325969.1, p. 556 -575, accessed on February 12, 2010, at
<br />http. //gsabulletin. gsapubs. org /content /119/5- 6/556. abstract.
<br />Hazel, J.E., Jr., Topping, D.J., Schmidt, J.C., and Kaplinski, M., 2006, Influence of a dam on fine - sediment storage in a
<br />canyon river: Journal of Geophysical Research, v. 111, no. F010252004JF000193, doi: 10.1029/2004JF000193, p. 1 -16,
<br />accessed on December 28, 2009, at hitp :/Avww.agu.org/ journals /jfljIO601 //2004JF000193.pdf.
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