IRRIGATION canals and drainage
ditches often require periodic cleaning
to remove wind-blown or water-deposited
sediments. Ponds used to trap sediment
from irrigation runoff and food processing
wastewater also require periodic
cleaning if they are to remain effective.
The freshly removed sediment is usually
piled next to the canals or ponds for drying
and temporary storage.
Dredge materials often are stored near
the source until the piles become so large
they constitute a nuisance. Removal then is
necessary. Sediment piles frequently remain
in place for 10 years or more

Robbins, C.W.

Northwest Irrigation & Soils Research Laboratory Publications

Reclamation and Reuse of Irrigation Sediments

USDA - ARS - NWISRL

Settling ponds are used to remove soil fromsurface water used for sprinkler irrigationand to trap soil from runoff water andwashwater from fresh vegetableprocessing. To remain effective, theseponds must be cleaned periodically.Reclamationand reuseof irrigationsedimentsBy C. W. RobbinsIRRIGATION canals and drainageditches often require periodic cleaningto remove wind-blown or water-de-posited sediments. Ponds used to trap sedi-ment from irrigation runoff and food pro-cessing wastewater also require periodiccleaning if they are to remain effective.The freshly removed sediment is usuallypiled next to the canals or ponds for dryingand temporary storage.Dredge materials often are stored nearthe source until the piles become so largethey constitute a nuisance. Removal then isnecessary. Sediment piles frequently re-main in place for 10 years or more.A case historyTwo large irrigation tracts in southernIdaho are served by the North Side CanalCompany, which annually removes about325,000 tons of sediment from its canalsand drains, and the Twin Falls CanalCompany, which each year removes about86,000 tons of sediment from its canals andC. W. Robbins is a soil scientist with Agricul-tural Research Service, U.S. Department ofAgriculture, Route 1, Box 186, Kimberly, Idaho83341.drains (2). These quantities exclude thesediment removed by farmers from sedi-ment ponds within the irrigation tracts.The two irrigation companies supply ir-rigation water to 363,000 acres.The logical place to put the sediment isback onto the eroded fields or on areas thatneed fill. The materials usually are quitefertile with respect to phosphate and some-times other fertilizer materials (4). Most ofthe sediments are derived from topsoil (3).When sediment that has been stored nextto canals, ponds, or irrigated fields formany years is spread on cropland or usedFor landscaping, adverse effects from ac-cumulated salts are often observed in thefirst crops planted after the sediment appli-cation. Large volumes of sediment are nowbeing respread on farmland, necessitatingresearch on the two irrigation tracts to de-termine the salt concentration in the sedi-ments and the time required to leach thesalts from the sediments.Soil samples were taken from sedimentpiles of various ages (1 month to 10 years)and at different depths within the piles ad-jacent to canal banks and sediment pondson the two tracts. Samples were also takenfrom 12 canal-bank sediment pile cross sec-Reprinted from the Journal of Soil and Water ConservationJanuary•February 1987. Volume 42, Number 1Copyright 1987 Soil Conservation Society 01 Americations along a 500-foot reach of canal wheresediment had been stored for more than 10years. This last group of samples weretaken before, immediately after, one yearafter, and two years after the sediment pilewas pulled down and spread on adjoiningcropland. The sediment pile on the canalbank was leveled to increase the farm ablearea, improve weed control, and moder-nize the irrigation system. Saturation pasteextracts were made from each sample andthe electrical conductivity, a measure ofthe total soluble salts, of each was deter-mined.Some observationsIrrigation water for the two tracts,which comes from the Snake River, has anaverage annual electrical conductivity ofabout 0.45 millimhos per centimeter (0.45dS/ m or 300 ppm total dissolved solids).Soils irrigated from Twin Falls CanalCompany canals are predominantly siltloams, while the soils irrigated fromNorthside Canal Company canals are amix of silt loarns, fine sandy loams, andsandy lams (2).Both areas are easily eroded by water,Units or. moies/cm or c15/mOld Irrigation*WoosLinn than O.@20	 30 5010FEETr" - „CuIt Area-----Units ore mmhosiern or cr5/m•	 %OM &mews10	 20	 30FEETUnits ore ITO11110i/C IT Or dS/mFEETand the soils irrigated with NorthsideCanal Company water are also easily erod-ed by wind during the winter months. Thewind-blown material is deposited in canalsand drains and makes up a large portion ofthe materials that must be removed by thecanal company. These soils seldom containexcessive salt concentrations when reason-able irrigation management practices areused. The silt loam soils usually have anelectrical conductivity of less than 1.1millimhos per centimeter and the finesandy and sandy loams have electrical con-ductivities of 0.9 millimho per centimeteror less.The sediments removed from ponds orcanals and placed back onto fields immedi-ately, or those piled only long enough forthe excess water to drain from the sedimentand to dry sufficiently for easy removal,were usually no saltier than the water fromwhich they were removed. Samples frompiles stored for a few months had twice asmuch salt as the fresh samples, and theelectrical conductivities in one-year-oldpiles were about 2 millimhos per centime-ter. Three-year-old piles had values ex-ceeding 4 millimhos per centimeter, whilemost values in piles more than 10 years oldexceeded 10 millimhos per centimeter.The salt accumulations are the result ofcapillary water movement from adjoiningwaterways and irrigated soil. The piles,being higher than the adjoining water andirrigated soils, act as wicks and draw waterinto the piles. As the water evaporates or istranspired by weeds and grass growing onthe piles, the salts are left behind to accum-ulate in the sediments. Mineral weather-ing within the soil also releases some salt.The salt accumulation rate depends uponthe salt concentration in the irrigationwater, the pile's distance from nearbywater, soil texture, mineralogy, and rain-fall. The salts tend to be nearer the surfaceof each pile because the salts move with thewater.One reclamation test showed how dra-matically the quality of sediments can beimproved over a relatively short period oftime (see salinity profiles in box). A canalbank sediment pile more than 10 years oldwas leveled. The area was then plowedand irrigated with good quality water fortwo years. After the second season, the saltSalinity profile of s canal bank before It wasleveled and spread over adjoiningcropland (top). Salinity profile of the areaextended by leveling the canal bank andthen plowing the area (middle). Salinityprofile of the area after irrigating for onegrowing season (bottom).concentration had dropped below 1 mil-limbos per centimeter in most samples, in-dicating that the salty soil had been re-claimed. After two years' irrigation therewere a few small spots that still showed salteffects, but for the most part salt concen-trations were reduced to near normal.The rapid reclamation of the materialswas due in part to their being spread overnonsalty soil material with high infiltra-tion rates. This permited the salts to beleached readily from the root zone withgood quality water. For these soils, sodiumwas not a problem. In other cases wherethe water or soil may contain higher sodi-um levels, high sodium adsorption ratiosand high exchangeable sodium percentagesmay be a factor and must be considered inmanaging the redistributed materials.Management suggestionsWhen sediments stored in piles next towater bodies or irrigated fields for morethan a year are to be spread over croplandor used for landscaping, care should betaken to determine the salinity status of thesediment and the soil surface after the sedi-ment has been spread and mixed with theoriginal soil. Crops or plants should be se-lected that can be grown on the saltier con-ditions encountered during the first fewyears after spreading the sediment on theland. In the research mentioned here, bar-January-February 1987 25ley, sugar beets, or cotton would have beengood choices for the first year. Alfalfa orwheat could have been grown successfullythe second year, and most any crop couldhave been grown the third year, depend-ing, of course, on climate.Sufficient water must be applied to thesalty sediments to leach the excess saltsfrom the root zone. The amount neededwill depend upon the crops grown, the soiltexture, and the salt concentration in theirrigation water. If the sediment is spreadin the fall, while irrigation water is stillavailable, leaching the area once and go-ing into the winter season with a wet pro-file will also speed the reclamation process.This increases the effectiveness of winterprecipitation in leaching salts from theprofile.Once salts are leached out, more salt-sensitive crops can then be grown. Refer-ences showing the salt and sodium sensitiv-ity of many crops are available to deter-mine which crops can be grown success-fully at various salinity or sodium levels(1). Use of these references as guide-lines can help avoid crop failure on saltyareas.Salt buildup in sediments taken fromponds, canals, and drains can be avoidedIf the sediment is stockpiled for more thana few months (top), salts accumulate in thesoli and salinity problems develop when thesediments are spread back on productiveland. Sediment can be placed on erodedareas, used to improve field shape, or usedto fill low areas and combine small fieldsinto larger, more practical fanning unitsby placing the soil back onto the land assoon as it is dry enough to move. The sedi-ment can also be spread during the follow-ing fall and winter when more time isavailable to farmers or canal company per-sonnel and when crops are not growing onthe land. Thus, land is not tied up for sedi-ment storage, and the sediment piles arenot producing weed crops and weed seed.The sediment can also be a valuable addi-tion to eroded areas or low spots in fields.In many cases sediment spreading will in-crease the farm able area or improve theproduction potential on shallow or other-wise nonfarm able areas.REFERENCES CITED1. Bresler, E., B. L. McNeal, and D. L. Carter.1982. Saline and sodic soils, principles-dynamics-modeling. Springer-Verlag, NewYork, N.Y. p. 167-181.2. Brown, M. ., D. L. Carter, and J. A. Bon-durant. 19 4. Sediment In irrigation anddrainage water and sediment inputs and out-puts for two large tracts in southern Idaho. J.Environ. Quality 3: 347-351.3. Carter, D. L., R. D. Berg, and B. J. Sanders.1985. The effect of furrow irrigation erosionon crop productivity. Soil Sei. Soc. Am. J.49: 207-211.4. Carter, D. L., M. J. Brown, C. W. Robbins,and J. A. Bondurant. 1974. Phosphorusassociated with sediments in irrigation anddrainage water for two large tracts insouthern Idaho. J. Environ. Quality 3: 287-291.	 [128 Journal of Soil and Water Conservation

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Reclamation and Reuse of Irrigation Sediments

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Northwest Irrigation & Soils Research Laboratory Publications

USDA - ARS - NWISRL