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 2017 B. Sharma a , B. Miller b , and R. Cruse c a* Post-doctoral Research Associate, Oak Ridge National Laboratory b Assistant Professor, Department of Agronomy, Iowa State University c Professor, Department of Agronomy, Iowa State University

Transcript of Soil erosion and water storage

Page 1: Soil erosion and water storage

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

Soil and Water Conservation Society

Annual Meeting, Madison, WI

2017

B. Sharmaa, B. Millerb, and R. Crusec

a*Post-doctoral Research Associate, Oak Ridge National Laboratoryb Assistant Professor, Department of Agronomy, Iowa State University

c Professor, Department of Agronomy, Iowa State University

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Introduction Results ConclusionsMethodology

Erosion

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

country

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Introduction Results ConclusionsMethodology

On-site

Loss of fertile top soil

Loss of nutrients

Impairing crop productivity

Off-site

Non-point source of pollution

Filling of reservoirs and dams

Degrading on water quality

Reducing ability to buffer against environmental impacts

Flooding

Loss of upland water storage

Impact of erosion

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Introduction Results ConclusionsMethodology

World’s 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

[1]

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Introduction Results ConclusionsMethodology

Goals

What is the potential flooding impact of current and past

soil erosion through its impact on reduced storage

capacity?

Decreases storage capacity and

increases runoff

Erosion reduces soil profile depth

Soil profile stores water

Lost waterholding capacity translates into

increased risk of flooding

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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

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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.

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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

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Introduction Results ConclusionsMethodology

𝑊𝐻𝐶𝑤𝑝 𝑚3 =

𝑖=1

𝐼

𝐷𝑒𝑝𝑡ℎ𝑖 × 𝐴𝑟𝑒𝑎𝑖 × 𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦 ∀ 𝑤

𝑊𝐻𝐶𝑠 = 𝑊𝐻𝐶𝑤𝑝 − (𝐸𝑅𝑠 × 𝐴𝑟𝑒𝑎𝑤𝑠 × 𝑆𝐷𝑅𝑤 × 𝑛𝑌 × 𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦)

Parameter Description

𝑊 Set of watersheds indexed by w

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

𝑆 Set of scenarios (5T, 12T, 20T)

𝑊𝐻𝐶𝑤𝑝 Water holding capacity of watershed w for pre-settlement scenario

𝐷𝑒𝑝𝑡ℎ𝑖 Depth of A-Horizon for hillslope classification i

𝐴𝑟𝑒𝑎𝑖 Area of hillslope classification i

𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦 0.5

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

𝐸𝑅𝑠 Erosion rate for a scenario s

𝐴𝑟𝑒𝑎𝑤𝑠 Area of watershed w

𝑆𝐷𝑅𝑤 Sediment delivery ratio of watershed w

𝑛𝑌 Number of years (10 years)

Loss in water holding capacity

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Introduction Results ConclusionsMethodology

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

Watersheds

Scenarios

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

watersheds

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)

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Introduction Results ConclusionsMethodology

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

Watersheds

5T DEP 20T

Days

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

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Introduction Results ConclusionsMethodology

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

discharge during a flood event

Watersheds

5T DEP 20T

Days

East Nishnabotna_Riverton

East Nishnabotna_Atlantic .02 (26 minutes)

Middle Cedar .02 (31 minutes)

Wapsipinicon

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

(m3/sec.)

USGS 06809900 Nishnabotna River at

Riverton

1105

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

Randloph

1326 6/15/1998

1https://pubs.usgs.gov/wri/2000/4025/report.pdf

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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

occur

• Soil conservation practices can play important roll in

reducing down stream flood losses by lowing flood

flows

• We have only placed a decimal point on erosion

impacts on flooding potential; more complex analysis is

warranted

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Thank you

Bhavna Sharma: [email protected]

Bradley Miller: [email protected]

Richard Cruse: [email protected]