Erosion in the Palouse: A Summary United States Department ...pnwsteep.wsu.edu/resourcelinks/eip.pdf · extent of soil-protecting crops—pasture and hay—diminished, erosion accelerated.

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Erosion in the Palouse: A Summaryof the PalouseRiver Basin Study

United States Department of Agriculture

Soil Conservation ServiceForest ServiceEconomics, Statistics, and Cooperatives Service

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Erosion in the Palouse: A Summary ofthe PalouseRiver Basin Study

United States Department of Agriculture

Soil Conservation ServiceForest ServiceEconomics, Statistics, and Cooperatives Service

Complex topographyincreases erosion hazard ondry cropland of the basin.

WASHINGTON FEBRUARY 1979

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Introduction

In January 1976, three agencies of theU.S. Department of Agriculture initiateda study of the Palouse River Basin inWashington and Idaho. The massiveamount of data, observations, projections,and conclusions produced by the studyhave been consolidated and published asthe Palouse River Basin Study Report. Thispublication is a summary of that report.The study was undertaken at the requestof Washington State Department ofEcology (DOE). Making the study werethe Soil Conservation Service, ForestService, and Economics, Statistics, andCooperatives Service.

DOE requested the study to providefactual information and data it needed forwater quality planning to comply with theFederal Water Pollution Control ActAmendments of 1972. The amendmentscall for fishable, drinkable, swimmablewaters in our nation’s streams by 1985. Thishas provided new impetus for the planningand installation of conservation practices.

The primary use of the Palouse studydata is getting conservation on the landand improving the quality of water inthe basin:

• Local water quality committeesorganized under Section 208 of theClean Water Act of 1977 can use thestudy results as a basis for selectingbest management practices anddeveloping water quality plans.

• DOE can use the study in evaluatingthose plans and practices.

• Individual farmers can relate studyinformation to their own farmingconditions and cropping systems.

• Conservation districts and agenciesassisting farmers can use data andinformation from the study to guidetheir advice and assistance.

• The general public can achieve a betterunderstanding and perspective of thecomplex conditions and problems—andtherefore have a basis for supportingattempts to arrive at solutions.

Help in getting the conservationjob done can be obtained from severalagencies. Technical assistance is available

from local soil and water conservationdistricts, the Soil Conservation Service, andthe Extension Service. Financial assistancemay be received from AgriculturalStabilization and Conservation Service andthe Farmers Home Administration.

For a copy of the complete study reportor more information about it, contact theSoil Conservation Service, Room 360, U.S.Courthouse, Spokane, WA 99201.

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The LandCalled Palouse

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An early pioneer, writing about 1900, saidthis about the Palouse River:

I have followed its cool, winding currents totheir birthplace in the mountains...traveledthrough its shady forests and over its grassymeadows...and sought its shady banks inquest of trout. At that time, its waters werepure...the meadows and woods wereunmarred by civilization and it was a veryparadise for the sportsman. Since then,numerous herds have been driven to itsmeadows to graze. As far up as logs can befloated upon its surface, the hillsides havebeen made to contribute their wealth oftimber—fir, pine, cedar and tamarack—tofeed the mills on the river as far down asColfax. And the water has been pollutedfrom its source by the search for gold in theHoodoo mines.

Western portion

Annual precipitation: 12–15"Topography and soils: gently

rolling hills, mostly shallowloess soils over basalt

Primary use: rangelandCrops: winter wheat,

summerfallow

Central portion

Annual precipitation: 15–18"Topography and soils: steep

slopes and deep loess soilsPrimary use: croplandCrops: wheat, barley

Eastern portion

Annual precipitation: 18" +Topography and soils:

moderately steep loess hillsin Washington; steepmountain forests in Idaho

Primary use: croplandCrops: wheat, barley, field

peas, lentils

WA

SHIN

GTO

N

IDA

HO

Rangeland

Cropland

Forest landSNAKE RIVER

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The quest for gold continued only for arelatively short period. But the quest forever-increasing yields of golden wheat goeson—at the cost of millions of tons of fertilesoil each year.

The Palouse River heads in the ClearwaterMountains of north-central Idaho. Fromthere it winds through forested foothills,undulating cropland, and craggy scablands,plunging over Palouse Falls and into theSnake River.

Geological events that occurred millionsof years ago created the Palouse countrywith its many variations in topography:channeled scablands and gently rollingloess hills in the western part of the basin,very steep to rolling hills in the centralbasin, more gently rolling loess hills in theeast, and steep forested mountains in theupper watershed.

The basin drained by the Palouse Riverand its tributaries encompasses more than2 million acres in parts of five counties ineastern Washington and two counties innorthern Idaho.

The basin is noted for some of the highestgrain production in the world. It is also notedfor some of the worst erosion in the country.

More than half the basin is highlyproductive cropland. Approximately 28percent is rangeland and 11 percent isforested. A major producer of winterwheat, peas, and lentils, the Palousesupplies more than 10 percent of thesoft, white winter wheat grown in theUnited States.

Annual precipitation ranges from lessthan 12 inches in the west to more than35 inches in the east. Most of it occurs inwinter and spring.

Rapid settlement of the Palouse did notbegin until the 1860’s. Although the deepsoils were capable of high yields, the marketfor grains was limited until railroads wereconstructed in the 1880’s. The railroadsbrought in newer, better equipment and thefarmers began working and planting thehillsides. From then on, soil erosion hasbeen a continuous and increasing problem.

The coming of the tractor broughtfurther changes. Steeper slopes could beworked. As tractors replaced horses, theextent of soil-protecting crops—pastureand hay—diminished, erosion accelerated.

During the 1930’s, the Soil ErosionExperiment Station, soil conservation

districts, the Soil Conservation Service,and Civilian Conservation Crops madeheadway in getting landowners to putconservation on the land. But World WarII fostered all-out production. And sincethen, economic fluctuations, allotments,and other factors have created otherobstacles to soil conservation.

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Erosion in the Palouse:How Bad Is It?

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Since 1939, total erosion on Palousecropland has averaged 360 tons peracre—more than 9 tons per acre per year.

Erosion rates on rangeland andforested areas average less than 1 tonper acre per year. On cropland, however,annual rates of 20 to 30 tons per acre arecommon and losses of 100 to 200 tonsfrequently occur on some steep slopes.

Erosion has consistently been highestin the intermediate 15-to-18 inchprecipitation zone, averaging 20 tonsper acre per year. The rates are usuallyless in the low-precipitation zone of thewestern basin (13 tons per acre per year)

and in the high-precipitation zone ofthe eastern basin (12 tons).

Gully erosion accounts for only aminor part of soil erosion in the basin.Stream channel erosion accounts for lessthan 1 percent of total erosion in thebasin, but it is serious in the mountainforests, where it accounts for 50 percentof the total.

The high erosion rates on croplandleave the land less productive. All theoriginal topsoil has been lost from 10percent of the cropland in the basin;one-fourth to three-fourths has beenlost from another 60 percent.

Frozen surface soilin early spring ishighly erosive.

Estimatedaverage annualsediment yield insource to streamsystem—PalouseRiver Basin

Source

Sedimentproduced byerosion—tons

17,471,0001,646,000

21,00019,138,000

Deliveryratio

30%11%90%

SedimentYield—tons

5,167,000184,00019,000

5,370,000

*Includes forest, rangeland, roads and other areas.

CroplandNoncropland*Stream channelsTotal

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Effects of erosionThe millions of tons of topsoil thaterode from cropland each yearrepresent not only the loss of anirreplaceable resource but also amajor source of silt and waterpollution. Silt smothers crops inbottomland areas, and it fills streamchannels, waterways, and drainageditches, increasing flood problems.

In late winter and spring,Palouse Falls is brown withsediment. From there thesuspended sediment is carrieddownstream, where it fills reservoirsof hydroelectric plants, destroysfish habitat, ruins recreation areas,and pollutes other waters, makingthem unfit for many uses.

Annual erosion on cropland inthe Palouse Basin is now estimatedto be more than 17 million tons.Unless farming systems change,the rates are expected to increase.The Palouse study shows, however,that the problems of erosion,sedimentation, and waterpollution can be greatly reduced.

Islands of silt depositedin the mouth of thePalouse River.

Pioneer relic andwheat coveredwith sediment.

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Cropland sedimentfills road ditch.

Sediment reducesSnake River Reservoircapacity.

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Fall chiselingpreservessurface residues.

What CanConservation Do?

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Some beneficial conservation practices

Farmers can’t change the weather, thekind of soil, or the slope of their land, butthey can change the way they farm theland. They can reduce acreages of summerfallow, till the soil less, retire steep areasfrom cultivation, change croppingsystems, divide long slopes with two ormore crops, and install terraces on long,gentle slopes.

Summer fallow, especially in the higherrainfall portions of the central and easternbasin, is a major contributor to soilerosion. When fields are summer fallowed,uncropped land is clean tilled duringthe summer to control weeds and storemoisture for growth of the next year’scrop. Erosion rates on summer-fallowfields average 25 to 30 percent higherthan those on nonfallow fields.

Excessive cultivation also increaseserosion. Minimum tillage for seedbedpreparation on annually cropped landor stubble mulching on summer-fallowfields can reduce erosion rates 35 percent.

More than 50 percent of the erosionin the basin comes from the steepest 25percent of its cropland. Retirement of thisland from cultivation would significantlyreduce erosion and sediment.

Fields planted to small grain crops,such as wheat or barley, erode the least.Increasing the acreage planted to thesecrops can reduce erosion significantly.

Divided-slope farming and fieldstripcropping can reduce erosion rates 15to 28 percent. Terraces can reduce erosionrates an average of 8 to 13 percent. Onsome long slopes, terraces can reduceerosion rates by as much as 50 percent.

Annual croppingreduces soil moistureas well as erosionhazard.

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Level terraces keepwater where it falls.

Stripcropping dividesa slope to reducerunoff and erosion.

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Using appropriatecombinations of practices

The Palouse study evaluated the effectsof applying combinations of theseconservation practices with differentcropping systems. It concluded thaterosion rates on nearly level and gentlysloping lands can be reduced to lessthan 5 tons per acre if the right combi-nations are used.

Erosion on steeper slopes can also bereduced significantly, but on the steepestslopes it will remain high if cultivation iscontinued. Erosion on steep land can bestbe controlled by retiring it from cultivationand establishing a permanent plant cover.

There is no single “best conservationpractice” for all farms. Combinations ofvarious practices that meet the needs ofthe land are the most successful. ThePalouse study can guide (individual andgroup) efforts to select the proper combi-nations.

Applying various levels of conserva-tion treatment to the land will affect theeconomy of the basin. But erosion rates

can be reduced by 40 percent in the lowand high precipitation zones and 60percent in the intermediate precipitationzone—without decreasing farm income.

The erosion rate can be reduced 80percent through maximum levels ofconservation practices and retirementof 35,000 acres of steep, erodible land.Achieving this level of reduction wouldcost more than $29 million in reducedproductivity and increased operatingcosts.

As erosion rates are reduced throughconservation, less sediment will bedelivered to stream systems. Croppinginstead of summer fallowing increasesfuel and fertilizer use but reduces erosion.Reducing erosion improves water qualitygreatly by reducing sedimentation.Retiring very steep, erodible land fromcultivation can increase wildlife habitatvalues 4 to 18 percent and decrease fueland fertilizer use.

Percent of erosion on cropland bypercent of slope*

*Source:Idaho, Oregon, and Washington Agricultural Experiment Stations andAgricultural Research Service, USDA. Economics of cropping systemsand soil conservation in the Palouse. Bulletin No. 2. August 1961.

South andwest slopes

North andeast slopes

Class II Class III Class IV Class VI

DepositionTopsoilSubsoil

Range ofslope

Averageslope

CroplandareaPercent oferosion

12–30%

16%

71%

46%

0–12%

8%

7%

2%

0–30%

12%

15%

25%

30–45%

36%

7%

27%

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To reduceerosion...

reducesummer fallow...

and increase use ofconservation practices...

Pres

ent

con

dit

ion

Alt

ern

ativ

e 1

Alt

ern

ativ

e 2

from:14 tons per acre

from:305,000 acres

from:546,000 acresminimum tillage

to:8 tons per acre

to:246,000 acres

to:1,221,000 acresminimum tillage

to:4 tons per acre

to:114,000 acres

to:1,221,000 acresminimumtillage andstripcroppingwith terraces on517,000 ofthose acres

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The Palouse River Basin Study confirmswhat has long been suspected: Soilerosion threatens the future of farmingin the basin and the quality of waterflowing out of the basin. But it can becontrolled and reduced.

• The basin’s cropland will continueto lose at least 17 million tons ofsoil each year—14 tons per acre—unless effective conservationmeasures are practiced.

• Five million tons of sediment areproduced in the basin each yearby runoff— polluting water,silting in reservoirs, damagingfish habitat.

• Over 90 percent of the soil lossresults from sheet and rill erosion.Over 50 percent occurs on thesteepest 25 percent of the basin’scropland.

• Summer fallow, which leaves thesoil bare, is a major contributor toerosion.

• Conservation practices can reduceerosion rates: minimum tillage, 35percent; field stripcropping, 15 to28 percent; terraces, 8 to 13percent.

• Retiring steep, highly erodibleland to grass or other protectivecover would greatly reduceerosion and would benefitwildlife.

• Proper combinations of variouspractices could reduce erosionrates 40 to 60 percent withoutadversely affecting farm income.Erosion rates can be reduced up to80 percent, but would result infarm income reduction.

✩ GPO 697-385

Summary of Findings

The chart (left)summarizes theconservationtreatment neededto reduce averageannual erosion inthe Palouse from14 ton/acre to 8and 4 ton/acre. Italso shows how thealternatives wouldaffect productioncosts and net farmincome. For adetailed discussionsee the PalouseRiver Basin StudyReport.

Productioncost and returnin millions of dollars

Cost Return

61

97

69

82

106

83

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