LAND LEVELLING ON IRRIGATED FARMSby

E. RappMember C.S.A.E.

P.F.R.A. Drainage Division, Vauxhall, Alberta

INTRODUCTION

Land Leveling Defined

Land levelling for irrigation is theprocess of modifying the surface reliefby grading and smoothing to aplanned grade and to certain specifications required to facilitate or improve the uniform application ofwater. It is the process of flatteningor modifying existing slopes or undulations rather than necessarily creating a level surface as the name mayimply. Normally land levelling requires earth moving over several hun-dreed feet and should not be con

fused with land planing, land smoothing or floating. These operations areusually accomplished with specialequipment to eliminate minor irregularities and do not change thegeneral topography of the land surface.

Need for Land Levelling

Most of the irrigation in WesternCanada is done on lands which are

not properly prepared for surface irrigation and as a result labor costshave been high and crops disappointing. The average irrigating time inmost areas is less than 5 acres per dayper man using a 3 cfs. stream. If theirrigator's wages are $15.00 per day,the labor costs of each irrigation arein excess of $3.00 per acre. On wellprepared land using the same streamit is possible for one man to irrigatemore than 20 acres a day which willgive a labor cost of less than $1.00 peracre. Depending on the original topography, levelling costs normally runfrom $10 to $100 per acre. Wheremoney is available, the increasedyields and reduced labor costs willsoon repay the original investment inland levelling and in many cases thisdevelopment is necessary to put irrigation on a paying basis.

Land Levelling Criteria

Land levelling is probably the mostintensive practice that is applied toagricultural lands and has little valueunless it is done right. Levelling jobscannot be easily changed once theyare completed and therefore the mostefficient type suitable to a particularfield should be selected and plannedfrom the start. This is less costly inthe long run than doing the work insuccessive stages and taking several

years to finish the job. Usually thestandard of farmers goes up fromyear to year and a job that is perfectlysatisfactory today may be consideredsub-standard tomorrow. Many fieldslevelled now will be relevelled severaltimes in years to come, each time toa higher standard. Therefore, it isdesirable to design as refined a jobas the soil will permit and the farmerwill accept and pay for.

Although the mechanics of landlevelling is essentially an engineeringoperation, the finished product represents a practical application of bothagronomic and engineering techniques and therefore requires a highdegree of co-ordination between thetwo technical fields. It is a highlyskilled operation, and experience andskill are of great value in doing agood job and doing it cheaply. Indesigning a land levelling job, theengineer must consider all factors,chief among which are: (1) depthand characteristics of the soil whichmay control the depth of cut. (2) landslopes, which influences grades, direction of irrigation, and method ofirrigation. (3) surface irregularities,which influence the division of a field

into smaller fields or benches. (4)water supply, which influences lengthor runs, grades, width of border stripsand sometimes method of irrigation.(5) crops grown which may determinethe method of irrigation. (6) economic considerations. (7) farmerpreferences. (8) equipment available.

Land Levelling Design Methods

There are four basic methods of

land levelling design and a greatmany variations of each in commonuse. These are: (1) the plane method,(2) the profile method, (3) the plan-inspection method, (4) the contour-adjustment method. Each has its advantages and disadvantages but whenused intelligently, all will providesatisfactory results. The merits of anindividual layout are often based onthe experience of the engineer or designer.

The profile method is commonlyused in Western Canada and is so

called because the designer works withprofiles on grid lines rather than withelevations on a map. It is especiallywell adapted to levelling design forrelatively flat lands or land with undulating topography. There are many

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variations of the profile method butessentially it consists of a trial anderror method of adjusting grades onplotted profiles until the irrigationcriteria are met and an earth work

balance is attained. Many workersfind it relatively easy to select gradeson a profile that will provide balanced cut and fill with a reasonablyshort haul and so this method iswidely used.

A variation of the profile methodcommonly referred to as the Parkinson Method has been used quite extensively by the P.F.R.A. DrainageDivision on the Bow River Projectand by the Alberta Department ofAgriculture Extension Service. Thismethod was developed by Mr. E. J.Parkinson, a retired S.C.S. engineerat Great Falls, Montana. Some of theprocedures are essentially the sameas followed in laying out levellingwork while others are unique to thismethod.

PROCEDURE

Briefly, the method involves thefollowing steps:

(1) Staking the field and runninglevels.

A 100-foot grid survey is generallyaccepted as standard. Any existingphysical features between grid linessuch as ridges, swales, ditches, fencelines, etc., are tied in as "plus" shots.Elevations are taken to the nearest0.1 foot.

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(2) Plotting the grid map.This map, appropriately called the

"before levelling map", shows theground elevations before levelling. Itis at this point that the engineer muststudy the map thoroughly and use hisingenuity and experience to best advantage. Areas that require differentmethods or direction of irrigationmust be selected as sub-divisions and

each sub-division must be consideredseparately. Soils, topography, watersupply, field drainage, crops grown,method of irrigation to be used andthe farmer's preferences should influence any decisions made.

(3) Determining the best directionof irrigation. This is simply the resultant direction of the average slopesin the two grid directions. Borderdykes or border ditches should be laidout in this direction as this is the

most natural way for the water toflow.

(4) Establishing maximum andminimum grade line slope limits. Theamount of side slope and the numberof borders per hundred feet are thetwo primary factors in establishingslope limits of the grade lines. Thepurpose of establishing slope limitsis to be able to adapt the grade linesto the present ground surface asclosely as possible and by staying within these limits, the maximum sideslope per border will not be exceeded.A maximum side slope of 0.1 foot perborder width will give satisfactoryresults in irrigating. By varying theslope of the grade line above andbelow the average slope within limits,it is possible to follow the originalground surface very closely and thereby make large reductions in yardageremoved.

(5) Preparing after levelling map.This is done by laying grade lines onthe transverse (grid lines most nearlyparallel to the contour lines) anddownfield (grid lines most nearly perpendicular to the contour lines) profiles within the established limits. Thecut and fills are balanced. Cut shouldexceed fill by an amount equal tothe shrinkage factor which may varyfrom 20 to 60% depending on various factors such as soil type, moistureconditions, average depth of cut andthe degree of compaction. Shrinkagefactor is usually established by experience gained by observing results onspecific jobs.

Besides showing final elevations,the after levelling map should showlateral ditch layout, necessary struc-trues, number and direction of borders and the field drainage. In fact,everything should be planned that isto be done on a field before a singleyard of dirt is moved.

In designing a plan by the Parkinson method, a great deal of time isspent in plotting profiles. This stepcan be eliminated as the designer becomes more experienced. It requiresconsiderable proficiency because inselecting elevations to develop a plan,the designer must simultaneously consider transverse slope, downfieldslope, earthwork balance, and hauldistance. The average time requiredin developing a plan is generally 0.75to 1.0 man-hours per acre dependingon the roughness of the field, theshape and often size. A good planoften costs less than moving 10 yards

of dirt per acre so is almost alwaysjustified when land levelling is beingconsidered.

(6) Preparing a contractors map:Cuts and tills are shown on this mapin contrasting colors. When the mapis colored, the contractor can startat one end ol the field, cutting andfilling as he goes, thus taking advantage of the shortest haul.

These maps also show the computed quantities of earthworth. Yardagesare commonly calculated using thefour-point method. This method ismore accurate than the end area

method when 100-foot shots withoutplus shots were used and gives resultsreasonably close to those obtainedusing the prismoidal formula.

After the design is completed, estimates can be made of the earthwork

and its cost. At this tage, it is important to everyone concerned toknow exactly the plan of work andhow it is to be performed.

(7) Marking stakes and final inspection. The contractors map is usedto mark stakes before the contractormoves onto the field. Generally onthe original grid survey, stake linesare established only every 400 feet andintermediate stations are located quiteaccurately by eye. The remainder ofthe stakes are set now and markedaccording to the contractors map.Hargus markers are now generallyused. The cost of these markers isnominal at 3 cents each if bought inquantity. They are convenient to useand in some cases, reduce yardagecost. Zero points are left unmarkedor are marked by cross stakes.

In checking completion of levellingin a field, a tolerance of 0.1 loot is allowed, litis tolerance can be eliminated by the use of the land planelater on.

Final checking is very important.Much loss of time and misunderstanding can be avoided by a close relationship between the operator andengineer. Any errors involving cutsand fills may require considerabletime and money to correct if notdetected at once. The frequency ofchecking depends on the job beingdone, the experience of the equipment operator and the engineer incharge. A final check should alwaysbe made before the contractor leaves

the field. The cost of engineeringwork should be a limiting factor. Thebest job should be done and it willbe found that the technical excellenceof the job will be remembered longafter the cost has been forgotten.

OPERATIONS

Equipment

Most levelling is accomplished withtractor - drawn loading - type scraperequipment. Tractors used are bothcrawler or rubber-tired wheel typeand vary in size from small farm tractors to large heavy construction units.If properly matched, they are efficientoutfits because they can cut to grade,spread dirt evenly and haul economically up to 500 feet and even to 800feet it soil conditions are unfavorable. Rubber-tired tractors can beused to advantage where hauls areextra long. Small wheeled scrapersdrawn with farm tractors move dirtjust as cheaply as large equipment buttake more time to finish the job.Elevating scrapers of the 5, 8 and 11yard size pulled by large farm tractorsare becoming increasingly popular inWestern Canada. A desirable featureis the ability to get a heaping loadeach time under varying depths andsoil textures. Also, cutting and spreading can be done evenly. Costs ofearth moving is often less than forthe carrier-type scrapers.

Finishing

Normally it is impractical to accomplish a high finish with scraperequipment, and where possible theuse of large land planes or floats arerecommended to remove minor irregularities. Although a field may belevelled perfectly, sometimes after tillage and irrigation the fill areas willsettle and the cut areas "fluff up".It may be advisable to delay planinguntil after the initial settlement hastaken place and corrections made,especially if perennial crops are tobe grown.

Cost

Most of the work in Western Canada is done on an hourly basis atcommercial rates but some experienced dirt movers are contractingland levelling on a yardage basis.An average cost of 20c per yard isusually assumed in estimating costof earthwork. The following tabulation is a summary of some costs available from P.F.R.A., Bow River Project and the Alberta Department ofAgriculture Extension Service.

Acres Av. Yds. Av. Cost Av. Cost

Agency Levelled Per Acre Per Acre Per Yard

P.F.R.A. 1952 125 182 $44.70 24.6c

P.F.R.A. 1953 90 222 46.90 21.2c

P.F.R.A. 1955 942 245 49.60 19.5c

P.F.R.A. 1956 656 212 40.25 19.0c

P.F.R.A. 1959 403 309 64.80 21.0c

Alta. 1958 400 228 35.70 15.6c

Alta. 1959 511 214 33.20 15.6c

Alta. 1958* 531 231 42.85 18.5c

Alta. 1959* 550 260 41.60 16.0c

* Government machines.

These costs do not distinguish between soil types and conditions, thedegree of finish, amount of topsoilsaved, type and cost of equipment orthe experience of the equipment operators, all of which greatly influencethe cost. On one job alone, with allother conditions being practicallyequal, inexperienced operators morethan doubled the cost of earthmoving.Costs on various fields ranged from12.8c per yard to 34.4c per yard. Thelack of experienced operators seemsto be the main drawback in reducingthe cost of land levelling.

Saving Topsoil

Reference has often been made tosome of the harmful effects of disturbing the top soil. For this reason,heavy land levelling has often metwith much opposition and criticism.Several methods of saving top soilhave been devised. One method isstock-piling the topsoil but since thisinvolves moving earth twice, the costis prohibitive on a large scale.

The common method of saving top-soil is known as the "trench" or"strip" method. It consists of cutting-trenches or strips below the desiredgrade throughout a cut area and laterborrowing topsoil from adjacent untouched strips to bring the area tograde. There is some mixing of top-soil and subsoil but it does avoidcomplete removal of all top soil fromany portion of the field. The extracost involved varies according to thesoil profile and the amount of levelling. One cost study showed that 9%of the total area required topsoilsaving. This represented a cost of$8.15 per acre or 12.6% of the totalcost of levelling. The problem ofbringing these cut areas back intoproduction has been a major concern,especially where shallow soils are encountered. On deeper and lightersoils, there has been no depression ofyields. The problem is primarily one

of introducing sufficient amounts oforganic matter into the soil and astimulation of biological activities.The best way to do this is by planting green manure crops or by makinglarge applications of manure to theunproductive areas. This should befollowed by applications of commercial fertilizer. Many farmers who havefollowed one or more fertility improvement practices have reported80 to 100% production within 3 to4 years.

Another problem experienced byfarmers after a levelling job is poorwater penetration on cut areas. Chiselling or subsoiling immediately afterlevelling will correct the situation allowing air to enter the soil and alsomix the disturbed soil in fills. Frostaction and water will aid in improving infiltration.

BENEFITS

The benefits from a well-planned,well-constructed and well-operatedland levelling job are many. In Western Canada, we are often guilty ofaccepting these apparent benefitswithout having definite informationor figures to prove it. There is needfor research and economic surveysto evaluate the resultant benefit ofland levelling and good land preparation.

The immediate benefit of landlevelling is the saving of irrigatingtime and labour. Almost all farmersreport that they can irrigate 2 to 3times as much land as previouslyusing the same head of water. Thisvaries from 5 to 20 acres a day depending on the water applied, moisture conditions at the time of irrigation, the crop, soil type and the slopeof the land. Also an irrigator canapply water much easier and it isoften possible to handle extra headsof water on other fields.

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Improved water management hasresulted in some yield responses afterlevelling. In a survey on the BowRiver Project, half the farmers reported average yields and some farmers who had done heavy levelling reported 25 to 40% increases in yieldsafter levelling. This can possibly beattributed to the fact that the highspots suffered from drouth and lowspots drowned out. After levelling, auniform application was possible.There are so many factors such asfertility of the soil before levelling,physical soil conditions such as tilthand moisture as well as the farmer's

management that it is impossible todetermine the after effects of levellingon production.

There are other inherent benefitsof land levelling besides saving timeand labour and increased productionsuch as better field drainage, improved surface conditions, bettershaped fields, better control of waterand longer runs. These are only a few.

From a farmer's point of view, theoperation of land levelling is highlyprofitable. Because of the improvedcondition the land has an increasedsales value that quite often excels thecost of the work. Aside from the moretangible benefits, the general appearance of the farm is enhanced if agood levelling job is followed up withother improvements in the irrigationlayout.

The importance of land levelingand good land preparation can besummed up by saying that is the firstessential to good irrigation farming.Without it, money spent on fertilizer,good seed and farm machinery ispartly wasted. It is difficult to believethat the majority of farmers are notaware of this. The fact remains thathundreds of irrigated farms lackproper land preparation.

REFERENCES

(1) Engineering Handbook, Regi5, U.S. Dept. of Agriculture.

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(2) S. C. S. National EngineeringHandbook, Section 15, Irrigation. Chapter 12, land levelling.

The author gratefully acknowledgespermission to use information andfigures given by the Alberta Department of Agriculture, Extension Service and P.F.R.A., Bow River Project,Vauxhall, Alta.