Download - 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
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
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
Introduction Results ConclusionsMethodology
Worldβs 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]
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
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 β10 m raster
Field-scale Land-use & Management
~430,000 IA fields
Introduction Results ConclusionsMethodology
ππ»πΆπ€π π3 =
π=1
πΌ
π·πππ‘βπ Γ π΄ππππ Γ πππππ ππ‘π¦ β π€
ππ»πΆπ = ππ»πΆπ€π β (πΈπ π Γ π΄ππππ€π Γ ππ·π π€ Γ ππ Γ πππππ ππ‘π¦)
Parameter Description
π Set of watersheds indexed by w
πΌ Set of hillslope position classification indexed by i (1 = Summit, 2 = Shoulder, 3 = Backslope, 4= Footslope, 5 = Toeslope)
π Set of scenarios (5T, 12T, 20T)
ππ»πΆπ€π Water holding capacity of watershed w for pre-settlement scenario
π·πππ‘βπ Depth of A-Horizon for hillslope classification i
π΄ππππ Area of hillslope classification i
πππππ ππ‘π¦ 0.5
ππ»πΆπ Water holding capacity for scenario s compared to pre-settlement scenario
πΈπ π Erosion rate for a scenario s
π΄ππππ€π Area of watershed w
ππ·π π€ Sediment delivery ratio of watershed w
ππ 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
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)
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
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
Introduction Results ConclusionsMethodology
β’ Soil erosion seems to have substantially decreased
upland water storage quantities
β’ Lost storage capacities associated with soil loss
suggests substantially greater flooding is also likely to
occur
β’ Soil conservation practices can play important roll in
reducing down stream flood losses by lowing flood
flows
β’ We have only placed a decimal point on erosion
impacts on flooding potential; more complex analysis is
warranted
Thank you
Bhavna Sharma: [email protected]
Bradley Miller: [email protected]
Richard Cruse: [email protected]