Trends in Iowa Water Run-off Rick Cruse, Matt Helmers, Greg Brenneman,

and John LaflenIowa 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 86Year

Sedi

men

t Yie

ld-t

on/a

cre

CV=135%

Average Annual

Treynor Surface Runoff -1964-87

0

5

10

15

Year

Surfa

ce ru

noff-

Inch

es

CV=85%

Average Annual

Treynor Iowa 1964-87

0

10

20

30

40

50

Year

Prec

ipita

tion-

Inch

es

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

Ann

ual 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