1. Estimating Annual Sediment Yield and a Sediment Delivery Ratio for Red Creek, Utah and Wyoming Paul Grams Department of Geography and Earth Resources Utah State University

2. Objective
Develop a method to estimate the sediment contribution of ungaged tributaries to the Green River downstream from Flaming Gorge Dam
These data will be incorporated in a sediment budget for the Green River

3. Background Operations of Flaming Gorge Dam affect downstream resources
Critical Habitat for Endangered Fish
Backwater habitat created by sand bars
Gravel bar spawning habitat
Function of Riparian Ecosystem
Cottonwood Trees
Ute Ladies Tresses Orchid

4. Controlled floods as a management tool to restore and maintain the downstream ecosystem
Recent floods have been mainly aggradational
System appears transport limited
Need to consider long-term effect of floods
Need to determine the relative importance of different sediment sources
Tributaries
Bed and banks in Brown’s Park

5. Approach
Estimate sediment production for the one tributary that has streamflow and suspended sediment transport data for
Determine the sediment delivery ratio
Consider applying this other tributaries in developing Green River sediment budget

6. Green River Basin
Red Creek
Great
Salt Lake WY
Flaming Gorge Dam UT CO

7. Red Creek 397 km2 (153 mi2) Average flow (6 yr record) Peak flood
7 ft3/s
Peak flood
600 ft3/s average
1440 ft3/s maximum
Debris Flows

8. Method Universal Soil Loss Equation -- USLE
Empirically derived equation
Based on > 10,000 plot-years of data
For agricultural plots -- NOT designed for watersheds
But it has been used for watershed-scale studies and there are few alternatives

9. Universal Soil Loss Equation A = RKLSCP
A = soil loss per unit area (t/ha)
R = Rainfall-Runoff erositivity (Mj*mm/ha*h*yr)
K = Soil erodibility (t*ha*h/ha*Mj*mm)
L = Slope length factor
S = Slope steepness factor
C = Crop (land cover) factor
P = Practice (erosion controls) factor

10. USLE based on Standard Soil Plot
72.6 ft (22.1 m) long uniform 9% slope in “continuous clean-tilled fallow”
the factors are meant to adjust for deviation from that condition

11. Some Assumptions Ignoring sediment deposition
Rainfall is represented uniformly over entire catchment
Hillslopes are represented as “uniform slope facets” in original model
Soil erodibility and land cover are adequately represented in the available soil and land cover GIS coverages

12. Rainfall-Runoff Erosivity -- R
Measure of the effect of raindrop impact (rainfall intensity) and total storm energy
Calculated on a storm-by-storm basis and averaged over many years of data
USDA has calculated these values for many stations in the US and published Isoerodent maps

13. Isoerodent Map of western US
Red Creek

14. Soil Erodibility -- K
“a lumped parameter that represents an integrated average annual value of the total soil and soil profile reaction to a large number of erosion and hydrologic processes”
Determined from long-term measurements at standard soil plots
Derived relationships between K factor and soil properties
Included in GIS soil coverages (STATSGO)

15. Soil Map Download and project
Extract K factor (used K including rock fragments)

16. Slope Factors -- LS
Used formulation of Moore and Burch (1986) for combined slope length and steepness factor
LS = (a/22.13)0.4 (s/0.0896)1.3
a = specific catchment area
s = slope
Physically derived from unit stream power theory

17. DEM Download DEM’s (10 quads) Import, merge, gapfill (twice)
SinMap to fill pits and calculate slope
TARDEM for contributing area and flow path lengths

18. Slope

19. Length-Slope factor
100 m contour interval

20. Land Cover - C factor
Ratio of soil loss under specified conditions to the corresponding loss from clean-tilled, continuous fallow
Table of values for undisturbed forest and range land

21. Land Cover Map and C - Factor Tables

22. Sediment Production Mean soil loss = 0.19 Mg per cell
(82,000 Mg total)

23. Sediment Load, Red Creek near Dutch John, Utah

24. Sediment Delivery Ratio
Apply this ratio to sediment yield for basin to estimate supply to Green River
82,000 * 0.91 = 74,600 t/yr
Is this a real sediment delivery ratio?
Transport is for suspended sediment
USLE is total sediment production
But it’s only the fine sediment that enters the Green River that we care about

25. Compare to Estimated Suspended Sediment Loads for Green River
About 30 mi downstream
186,000 t/yr pre-dam
60,000 t/yr post-dam
212,000 t/yr post-dam flood years
Estimated Red Creek Contribution
75,000 t/yr

26. Conclusions
Numbers are at least in the right range, but are they meaningfull?
Highly sensitive to rainfall factor
If increased from 10 to 15 (english units)
Total sediment yield increases proportionally (i.e. from 82,000 to 123,000 t/yr)

27. Future Work
Better representation of R factor (rainfall-runoff erosivity)
Perform similar analysis in other basins in region where sediment transport data are available to improve estimate of sediment delivery ratio
Field data