rick cruse, matt helmers, greg brenneman, and john laflen iowa water center, and iowa state...
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Trends in Iowa Water Run-off
Rick Cruse, Matt Helmers, Greg Brenneman, and John Laflen
Iowa Water Center, and Iowa State University Extension
Treynor Sediment Yield-1964-87
0
20
40
60
80
100
120
64 66 68 70 72 74 76 78 80 82 84 86
Year
Sed
imen
t Y
ield
-to
n/a
cre
CV=135%
Average Annual
Treynor Surface Runoff -1964-87
0
5
10
15
Year
Sur
face
runo
ff-In
ches
CV=85%
Average Annual
Treynor Iowa 1964-87
0
10
20
30
40
50
Year
Pre
cipi
tatio
n-In
ches
CV=20% Average Annual
>20”
16-20”
Runoff Occurs WhenRainfall Intensity exceeds rate (infiltration
rate) that water can enter the soil (sponge). Infiltration rate affected by
Physical characteristics of the soil-soil texture and soil structure
Soil moisture Cover on the soil and management of the soil Rainfall intensity
Tile Drainage Affects Infiltration Tile drainage can reduce soil water, improving
infiltration. Removes water from saturated ‘sponge’ Creates storage space for subsequent rainfall Reduces runoff for repetitive storms when soil
profile is full or nearly full
140 years of Iowa Land Use
0
5
10
15
20
25
30
35
1870 1890 1910 1930 1950 1970 1990 2010
Year
Acr
es-M
illio
ns
Corn
All Other
Small Grain
Soybeans
Iowa Land Area-35.76 Million Acres
Water Yield-Surface RunoffWatersheds 1 and 3, Treynor IA
0
4
8
12
16
64 65 66 67 68 69 70 71 Mean
Wat
er Y
ield
-Inc
h
Corn Grass
Trends in Precipitation
Cedar River Annual Flow Cedar Rapids
1880 1900 1920 1940 1960 1980 2000 20200
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
An
nu
al F
low
- C
FS
Cedar River Peak Flow Rates
Concluding CommentsLoss of continuous living cover, increased soil
disturbance, and limited use of conservation practices can increase runoffImpacts are greater for smaller events and dryer
soilsMuch smaller impacts for larger events or wet soils
Removal of water from soil profile (evapotransporation, tile drainage) reduces runoff
Extreme rainfall event frequencies have increased
High production and increased water infiltration (10% perennial cover) may coexist