Soil erosion and water storage

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  • Soil Erosion Impacts on Flooding: Lost water storage in Iowa uplands

    Soil and Water Conservation Society

    Annual Meeting, Madison, WI


    B. Sharmaa, B. Millerb, and R. Cruseca*Post-doctoral Research Associate, Oak Ridge National Laboratory

    b Assistant Professor, Department of Agronomy, Iowa State Universityc Professor, Department of Agronomy, Iowa State University

  • Introduction Results ConclusionsMethodology


    Each year five billion tons of topsoil is lost in the U.S. It is transported

    from hillslopes and deposited lower in fields, reservoirs, floodplains,

    ditches, streams, shallow channels

    In 200 years, the U.S. has lost 1/3 of its cropland topsoil, at a rate 10

    times faster than topsoil is formed

    Corn belt states have

    experienced some of the

    highest erosion rates in the


  • Introduction Results ConclusionsMethodology


    Loss of fertile top soil

    Loss of nutrients

    Impairing crop productivity


    Non-point source of pollution

    Filling of reservoirs and dams

    Degrading on water quality

    Reducing ability to buffer against environmental impacts


    Loss of upland water storage

    Impact of erosion

  • Introduction Results ConclusionsMethodology

    Worlds largest sponge

    Topmost layer of mineral soil approximately

    50% pore space

    It is the richest soil horizon and has the

    most favorable effects on crop yield


  • Introduction Results ConclusionsMethodology


    What is the potential flooding impact of current and past

    soil erosion through its impact on reduced storage


    Decreases storage capacity and

    increases runoff

    Erosion reduces soil profile depth

    Soil profile stores water

    Lost waterholding capacity translates into

    increased risk of flooding

  • Watersheds & USGS Gauges

    Introduction Results ConclusionsMethodology

    Four watersheds were selected to

    capture landscapes with different

    hillslope and soil erosion potential.

    Four gauges were selected to

    determine days of water storage

    lost relative to river flow volumes.

    East Nishanbotna River near Atlantic

    East Nishnabotna River at Riverton

    Middle Cedar

    Skunk Wapsipinicon

  • Scenarios and assumptions

    Introduction Results ConclusionsMethodology

    Scenarios Description

    5T/A/yr Erosion rate: 5 tons/acre/year (Low)

    DEP Erosion rate: From Daily Erosion Project (DEP) [9]

    20T/A/yr Erosion rate: 20 tons/acre/year (High)

    Scenarios represent range of erosion rates for Iowa landscape to understand the

    impact of lost water storage capacity associated with soil erosion.

  • NEXRAD Precip

    1 km2 X 2 minute

    LiDAR Elevation2 m resolution

    gSSURGO Soils 10 m raster

    Field-scale Land-use & Management

    ~430,000 IA fields

  • Introduction Results ConclusionsMethodology

    3 =


    = ( )

    Parameter Description

    Set of watersheds indexed by w

    Set of hillslope position classification indexed by i (1 = Summit, 2 = Shoulder, 3 = Backslope, 4= Footslope, 5 = Toeslope)

    Set of scenarios (5T, 12T, 20T)

    Water holding capacity of watershed w for pre-settlement scenario

    Depth of A-Horizon for hillslope classification i

    Area of hillslope classification i


    Water holding capacity for scenario s compared to pre-settlement scenario

    Erosion rate for a scenario s

    Area of watershed w

    Sediment delivery ratio of watershed w

    Number of years (10 years)

    Loss in water holding capacity

  • Introduction Results ConclusionsMethodology

    Table 1: Loss in A-horizon water holding capacity after 10 years



    5T (0.85 mm/year) DEP 20T (3.39 mm/year)

    Cubic meters

    East Nishnabotna_Riverton 1,930,402 4,451,507 7,721,608

    East Nishnabotna_Atlantic 863,457 2,851,137 3,453,830

    Middle Cedar 5,690,222 3,783,997 22,760,887

    Skunk Wapsipinicon 1,381,204 860,490 5,524,814

    Erosion rates (tons/acre/year) and depth lost (mm/year) for DEP scenario for


    East Nishnabotna_Riverton 11.5 (1.95 mm/year)

    East Nishnabotna_Atlantic 16.51 (2.80 mm/year)

    Middle Cedar 3.33 (0.56 mm/year)

    Skunk Wapsipinicon 3.12 (0.53 mm/year)

    Scenarios Description

    5T Erosion rate: 5 tons/acre/year (Low)

    DEP Erosion rate: From Daily Erosion Project (DEP) [9]

    20T Erosion rate: 20 tons/acre/year (High)

  • Introduction Results ConclusionsMethodology

    Table 2: Equivalent days of flow for water holding capacity lost after 10 years


    5T DEP 20T


    East Nishnabotna_Riverton 0.9 2.0 3.4

    East Nishnabotna_Atlantic 0.8 2.8 3.4

    Middle Cedar 0.4 0.2 1.5

    Wapsipinicon 0.4 0.2 1.5

    A-horizon lost water holding capacity (m3)

    Mean daily discharge (m3/day)

    Days water storage

  • Introduction Results ConclusionsMethodology

    Table 5: Equivalent days of flow for water holding capacity lost after 10 years at peak

    discharge during a flood event


    5T DEP 20T


    East Nishnabotna_Riverton

    East Nishnabotna_Atlantic .02 (26 minutes)

    Middle Cedar .02 (31 minutes)


    Table 4. Peak discharge for flood events at stream flow gaging stations in different river basins in Iowa

    Streamflow-gaging station Drainage area

    (Square miles)

    Date Peak discharge


    USGS 06809900 Nishnabotna River at



    USGS 06809210 East Nishanbotna River

    near Atlantic 1436 6/15/1998 1,844

    USGS 05464500 Middle Cedar 6510 6/13/2008 2,011

    USGS 05421740 Skunk Wapsipinicon

    River near Amamosa

    1576 6/10/2008

    USGS 06808500 Nishnabotna River at


    1326 6/15/1998


  • Introduction Results ConclusionsMethodology

    Soil erosion seems to have substantially decreased

    upland water storage quantities

    Lost storage capacities associated with soil loss

    suggests substantially greater flooding is also likely to


    Soil conservation practices can play important roll in

    reducing down stream flood losses by lowing flood


    We have only placed a decimal point on erosion

    impacts on flooding potential; more complex analysis is


  • Thank you

    Bhavna Sharma:

    Bradley Miller:

    Richard Cruse: