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

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

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

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

Approach Estimate sediment production for the one tributary that has streamflow and suspended sediment transport data for 1972-78 Determine the sediment delivery ratio Consider applying this other tributaries in developing Green River sediment budget

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

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

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

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

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

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

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

Isoerodent Map of western US Red Creek

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)

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

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

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

Slope

Length-Slope factor 100 m contour interval

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

Land Cover Map and C - Factor Tables

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

Sediment Load, Red Creek near Dutch John, Utah

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

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

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)

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