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Central Columbia Plateau - Yakima River Basin NAWQA Study -- Publications

USGS Fact Sheet FS-069-98
July 1998

Soil Erosion in the Palouse River Basin: Indications of Improvement

by James C. Ebbert, USGS, and R. Dennis Roe, USDA

Findings

Figure 1. Land use in the Palouse River Basin is predominantly dryland agriculture. Sediment data discussed in this fact sheet were collected at Palouse River at Hooper.

History of the erosion problem

Since the Palouse River Basin was first farmed in the late 1800s, soil erosion resulting from runoff water has been an ongoing problem. The erosion problem became particularly acute in the early 1900s when steep lands once used for hay and pasture were converted to grain production. It is estimated that 40 percent of the rich Palouse soils have been lost to erosion (Pimentel and others, 1995).

A U.S. Department of Agriculture (USDA) study reported that from 1939 through 1977, the average annual rate of soil erosion in the Palouse River Basin was 9.2 tons per acre (tons/acre) of available cropland, or about 14 tons/acre of cultivated cropland (USDA, 1978). The study concluded that without erosion control practices, the average annual rate of erosion would increase to 14 tons/acre as more cropland was put into production.

Photo (29,716 bytes)

Photo © by Phil Schofield. Used with permission.
Strip-cropping is a widely used erosion control practice in the Palouse River Basin.

Innovative farmers and other agriculture professionals have been developing ways to reduce soil erosion in the Palouse River Basin since the 1930s. The first soil conservation district in Washington State was organized by a group of farmers at Palouse in 1940. In 1972, Public Law 92-500 mandated a water-quality management plan for dryland agriculture. The final plan, adopted by the Washington State Department of Ecology in 1979, recommended best management practices to control soil erosion and reduce runoff of nutrients and agricultural chemicals from cropland.

Effects of erosion control practices

Many farmers voluntarily implemented erosion control practices that were appropriate for the slopes, soil types, and climatic conditions of their fields. These practices have reduced erosion by about 1.7 million tons annually according to model results (see table); this represents about a 10 percent reduction in the annual rate of erosion when compared with erosion controls applied to the 1.2 million acres of cropland in the Palouse River Basin (USDA, 1978).

Erosion control practices in the Palouse River Basin

Erosion control
practice
Acres under erosion
control1
Predicted average annual
reduction in erosion2
1979
1994
Tons per
acre
Total tons 3
No-till seeding
600 
56,000 
9
500,000 
Crop Reserve
Program
6,400 
60,600 
5
270,000 
Stripcropping
divided slopes
0 
239,000 
1
240,000 
Terraces
680 
4,500 
2
7,600 
Grass water-
ways
482 
41,550 
51
1,500 
Planting trees
and shrubs
0 
3,670 
10
37,000 
Conservation
tillage
0 
81,000 
8
650,000 
Totals3 
7,680 
445,000 
1,700,000 
1 U.S. Department of Agriculture progress records for 1979 and 1994.
2 Prediction based on Universal Soil Loss Equation (Wischmeier and Smith, 1978). For grass waterways, based on gross erosion prediction method (Renard and others, 1997).
3 Numbers have been rounded.
4 Linear feet.
5 Tons per linear foot.

Monitoring erosion by sampling suspended sediment

Erosion rates represent the amount of soil displaced from slopes, not the amount transported to streams. However, because some of the eroded soil is transported to streams, a relation would be expected between basin-wide erosion rates and loads of suspended sediment carried by streams. Ten years of data on annual yields (loads per unit area) of suspended sediment from the Palouse River (USGS, 1962-1971) were plotted against annual estimates of field erosion (Kaiser, 1967) for winter wheat and barley cropland in the Palouse River Basin. The correlation between the data sets (fig. 2) indicates that long-term sediment sampling can help substantiate estimates of erosion rates.
 
GRAPH:Soil erosion estimates
Figure 2.Soil erosion estimates correlate with yields of suspended sediment from the Palouse River, 1962-71

Until 1981, soil erosion rates were estimated annually; currently they are estimated every five years (USDA, 1988). When estimates are not available, sediment data can be used to infer trends in erosion. For example, comparing historical with recent year-to-year variations in annual average concentrations* of suspended sediment in the Palouse River reveals that the average concentration for the years 1993-96 is one-half the average for the years 1962-71 (fig. 3). These data are in general agreement with model results that indicate reduced erosion from fields during recent years (see table). However, the difference in annual averages of suspended sediment is explained partially by a skewed average for 1962-71 that resulted from a large storm in February 1963 (fig. 4). Frozen ground and other conditions that preceded this storm caused extremely high erosion rates (Boucher 1970), and these conditions did not occur in 1993-96.

Bar Chart:Average annual concentrations of suspended sediment
Figure 3.Comparing the historical record (1962-71) to recent years (1993-96) shows a decrease in the average annual concentration of suspended sediment in the Palouse River at Hooper.

Chart:Sediment Load and Water Discharge
Figure 4.At the Palouse River at Hooper, highest average concentrations of suspended sediment were observed during 1962-71 storms.

Highest concentrations of suspended sediment during storm
runoff occurred from 1962 to 1971

Comparing sediment transport during periods of storm runoff is another way to infer trends in erosion rates. Most suspended sediment is transported during periods of storm runoff. Boucher (1970) found that from July 1961 through June 1965, 81 percent of the sediment transport from the Palouse River Basin occurred during storm runoff. Average concentrations of suspended sediment tend to be higher during storms producing large discharges, but the highest concentrations per unit discharge were observed during 1962-71 (fig. 4) when predicted erosion rates were higher.

Importance of long-term monitoring

Since the passage of the Food Security Act in 1985, farmers have been required to apply conservation measures in order to receive USDA program benefits. As attention is focused on the effects of farming on natural resources, farmers will be asked to apply measures to satisfy natural resource standards as well.
Long-term monitoring of discharge and suspended sediment, such as the USGS does at the Palouse River at Hooper, can help document trends resulting from the application of erosion control and other management practices.

*These annual average concentrations were computed by dividing annual sediment loads by annual water discharge at the Palouse River at Hooper.

Photo (52,457 bytes)
U.S. Department of Agriculture photo
No-till seeding is another effective method of erosion control.

References

Boucher, P.R., 1970, Sediment transport by streams in the Palouse River basin, Washington and Idaho: U.S. Geological Survey Water Supply Paper 1899-C, 37 p.

Kaiser, V.G., 1967, Soil erosion and wheat yields in Whitman County, Washington: Northwest Science, v. 41, no. 2, p. 86-91.

Pimentel, David, Harvey, C., Resosudarmo, P., Sinclair, K., Kurz, D., McNair, M., Crist, S., Shpritz, L., Fitton, L., Saffouri, R., and Blair, R., 1995, Environmental and economic costs of soil erosion and conservation benefits: Science, v. 267, p. 1117-1123.

Renard, K.G., Foster, G.R., Weesies, G.A., McCool, D.K., and Yoder, D.C., 1997, Predicting soil erosion by water: a guide to conservation planning with the revised universal soil loss equation (RUSLE): U.S. Department of Agriculture, 384 p.

U.S. Department of Agriculture, Economics, Statistics, and Cooperatives Service, Forest Service, and Soil Conservation Service, 1978, Palouse co-operative river basin study: U.S. Department of Agriculture, 182 p.

U.S. Department of Agriculture Soil Conservation Service, 1988, Washington's soil and water--conditions and trends 1982-1987: Spokane, Wash., U.S. Department of Agriculture, 12 p.

U.S. Geological Survey, 1962-1971, Water resources data for Washington: Tacoma, Washington, annual tabulation for years indicated.

Wischmeier, W.H., and Smith, D.D., 1978, Predicting rainfall erosion losses--A guide to conservation planning: U.S. Department of Agriculture Handbook No. 357, 58 p.

Acknowledgments: Data collection; production of daily sediment records: Brett Smith; Editorial review: Martha Erwin

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This fact sheet and data collected in the 1990s is part of the National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey, which is designed to describe current water-quality conditions for a large part of the Nation's ground and surface water, to describe how water quality is changing over time, and to improve our understanding of the natural and human factors that affect our water quality.

Suggested citation:

Ebbert, James C., and Roe, R. Dennis, 1998, Soil erosion in the Palouse River Basin: Indications of improvement: U.S. Geological Survey Fact Sheet FS-069-98, on line at URL http://wa.water.usgs.gov/ccpt/pubs/fs.069-98.html, accessed [date of access].

For a paper copy of this report, sendEmail to nawqa_ccpt_wa@usgs.gov

Central Columbia Plateau - Yakima River Basin NAWQA Study
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