Soil erosion and water storage

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<ul><li><p>Soil Erosion Impacts on Flooding: Lost water storage in Iowa uplands</p><p>Soil and Water Conservation Society</p><p>Annual Meeting, Madison, WI</p><p>2017</p><p>B. Sharmaa, B. Millerb, and R. Cruseca*Post-doctoral Research Associate, Oak Ridge National Laboratory</p><p>b Assistant Professor, Department of Agronomy, Iowa State Universityc Professor, Department of Agronomy, Iowa State University</p></li><li><p>Introduction Results ConclusionsMethodology</p><p>Erosion</p><p> Each year five billion tons of topsoil is lost in the U.S. It is transported </p><p>from hillslopes and deposited lower in fields, reservoirs, floodplains, </p><p>ditches, streams, shallow channels</p><p> In 200 years, the U.S. has lost 1/3 of its cropland topsoil, at a rate 10 </p><p>times faster than topsoil is formed</p><p>Corn belt states have </p><p>experienced some of the </p><p>highest erosion rates in the </p><p>country </p></li><li><p>Introduction Results ConclusionsMethodology</p><p>On-site</p><p> Loss of fertile top soil</p><p> Loss of nutrients</p><p> Impairing crop productivity</p><p>Off-site</p><p> Non-point source of pollution</p><p> Filling of reservoirs and dams</p><p> Degrading on water quality</p><p> Reducing ability to buffer against environmental impacts</p><p> Flooding</p><p> Loss of upland water storage</p><p>Impact of erosion</p></li><li><p>Introduction Results ConclusionsMethodology</p><p>Worlds largest sponge</p><p> Topmost layer of mineral soil approximately </p><p>50% pore space</p><p> It is the richest soil horizon and has the </p><p>most favorable effects on crop yield</p><p>[1]</p></li><li><p>Introduction Results ConclusionsMethodology</p><p>Goals</p><p> What is the potential flooding impact of current and past </p><p>soil erosion through its impact on reduced storage </p><p>capacity?</p><p>Decreases storage capacity and </p><p>increases runoff</p><p>Erosion reduces soil profile depth</p><p>Soil profile stores water</p><p>Lost waterholding capacity translates into </p><p>increased risk of flooding</p></li><li><p>Watersheds &amp; USGS Gauges</p><p>Introduction Results ConclusionsMethodology</p><p>Four watersheds were selected to </p><p> capture landscapes with different </p><p>hillslope and soil erosion potential.</p><p>Four gauges were selected to </p><p> determine days of water storage </p><p>lost relative to river flow volumes.</p><p>East Nishanbotna River near Atlantic</p><p>East Nishnabotna River at Riverton </p><p>Middle Cedar</p><p>Skunk Wapsipinicon</p></li><li><p>Scenarios and assumptions</p><p>Introduction Results ConclusionsMethodology</p><p>Scenarios Description</p><p>5T/A/yr Erosion rate: 5 tons/acre/year (Low)</p><p>DEP Erosion rate: From Daily Erosion Project (DEP) [9]</p><p>20T/A/yr Erosion rate: 20 tons/acre/year (High)</p><p>Scenarios represent range of erosion rates for Iowa landscape to understand the </p><p>impact of lost water storage capacity associated with soil erosion.</p></li><li><p>NEXRAD Precip</p><p>1 km2 X 2 minute</p><p>LiDAR Elevation2 m resolution</p><p>gSSURGO Soils 10 m raster</p><p>Field-scale Land-use &amp; Management</p><p>~430,000 IA fields</p></li><li><p>Introduction Results ConclusionsMethodology</p><p> 3 = </p><p>=1</p><p> = ( )</p><p>Parameter Description</p><p> Set of watersheds indexed by w</p><p> Set of hillslope position classification indexed by i (1 = Summit, 2 = Shoulder, 3 = Backslope, 4= Footslope, 5 = Toeslope)</p><p> Set of scenarios (5T, 12T, 20T)</p><p> Water holding capacity of watershed w for pre-settlement scenario</p><p> Depth of A-Horizon for hillslope classification i</p><p> Area of hillslope classification i</p><p> 0.5 </p><p> Water holding capacity for scenario s compared to pre-settlement scenario</p><p> Erosion rate for a scenario s </p><p> Area of watershed w</p><p> Sediment delivery ratio of watershed w</p><p> Number of years (10 years)</p><p>Loss in water holding capacity</p></li><li><p>Introduction Results ConclusionsMethodology</p><p>Table 1: Loss in A-horizon water holding capacity after 10 years</p><p>Watersheds</p><p>Scenarios</p><p>5T (0.85 mm/year) DEP 20T (3.39 mm/year)</p><p>Cubic meters</p><p>East Nishnabotna_Riverton 1,930,402 4,451,507 7,721,608</p><p>East Nishnabotna_Atlantic 863,457 2,851,137 3,453,830</p><p>Middle Cedar 5,690,222 3,783,997 22,760,887</p><p>Skunk Wapsipinicon 1,381,204 860,490 5,524,814</p><p>Erosion rates (tons/acre/year) and depth lost (mm/year) for DEP scenario for </p><p>watersheds</p><p>East Nishnabotna_Riverton 11.5 (1.95 mm/year)</p><p>East Nishnabotna_Atlantic 16.51 (2.80 mm/year)</p><p>Middle Cedar 3.33 (0.56 mm/year)</p><p>Skunk Wapsipinicon 3.12 (0.53 mm/year)</p><p>Scenarios Description</p><p>5T Erosion rate: 5 tons/acre/year (Low)</p><p>DEP Erosion rate: From Daily Erosion Project (DEP) [9]</p><p>20T Erosion rate: 20 tons/acre/year (High)</p></li><li><p>Introduction Results ConclusionsMethodology</p><p>Table 2: Equivalent days of flow for water holding capacity lost after 10 years</p><p>Watersheds</p><p>5T DEP 20T</p><p>Days</p><p>East Nishnabotna_Riverton 0.9 2.0 3.4</p><p>East Nishnabotna_Atlantic 0.8 2.8 3.4</p><p>Middle Cedar 0.4 0.2 1.5</p><p>Wapsipinicon 0.4 0.2 1.5</p><p>A-horizon lost water holding capacity (m3)</p><p>Mean daily discharge (m3/day)</p><p>Days water storage</p></li><li><p>Introduction Results ConclusionsMethodology</p><p>Table 5: Equivalent days of flow for water holding capacity lost after 10 years at peak </p><p>discharge during a flood event </p><p>Watersheds</p><p>5T DEP 20T</p><p>Days</p><p>East Nishnabotna_Riverton</p><p>East Nishnabotna_Atlantic .02 (26 minutes)</p><p>Middle Cedar .02 (31 minutes)</p><p>Wapsipinicon </p><p>Table 4. Peak discharge for flood events at stream flow gaging stations in different river basins in Iowa </p><p>Streamflow-gaging station Drainage area</p><p>(Square miles)</p><p>Date Peak discharge</p><p>(m3/sec.)</p><p>USGS 06809900 Nishnabotna River at </p><p>Riverton</p><p>1105</p><p>USGS 06809210 East Nishanbotna River </p><p>near Atlantic 1436 6/15/1998 1,844</p><p>USGS 05464500 Middle Cedar 6510 6/13/2008 2,011</p><p>USGS 05421740 Skunk Wapsipinicon </p><p>River near Amamosa</p><p>1576 6/10/2008</p><p>USGS 06808500 Nishnabotna River at </p><p>Randloph</p><p>1326 6/15/1998</p><p>1</p></li><li><p>Introduction Results ConclusionsMethodology</p><p> Soil erosion seems to have substantially decreased </p><p>upland water storage quantities</p><p> Lost storage capacities associated with soil loss </p><p>suggests substantially greater flooding is also likely to </p><p>occur</p><p> Soil conservation practices can play important roll in </p><p>reducing down stream flood losses by lowing flood </p><p>flows</p><p> We have only placed a decimal point on erosion </p><p>impacts on flooding potential; more complex analysis is </p><p>warranted</p></li><li><p>Thank you</p><p>Bhavna Sharma:</p><p>Bradley Miller:</p><p>Richard Cruse:</p></li></ul>


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