A survey of systems for recirculating runoff water from irrigation
in southern Idaho shows little evidence of formal system design.
Systems were constructed to handle approximately 20 percent of the
volume of irrigation water. Costs of the systems vary with the type
of installation. Sequence, reservoir, and cycling sump systems each
has certain advantages. Recirculating systems are not effective unless
the water is applied to a different area than that which is contributing
runoff. Recirculating irrigation systems can raise water application
efficiencies to 80 percent

Bondurant, J.A.

Willardson, L.S.

USDA - ARS - NWISRL

purchased by the Agrlcultaral Research Service,U.S. Department of Agriculture, for official use.RECIRCULATING FARM IRRIGATION SYSTEMSByJ. A. Bondurant l/ M. ASAEandL. S. Willardson a/ M. ASCE, M. ASAESYNOPSISA survey of systems for recirculating runoff water from irriga-lipn in southern Idaho shows little evidence of formal system design.9y teens were constructed to handle approximately 20 percent of thevolume of irrigation water. Costs of the systems vary with the typeof installation. Sequence, reservoir, and cycling sump systems eachhas certain advantages. Recirculating systems are not effective unlessthe water is applied to a different area than that which is contributingrunoff. Recirculating irrigation systems can raise water applicationefficiencies to 80 percent.Contribution from Soil and Water Conservation Research Divi-sion, Agricultural Research Service, U. S. Department of Agriculture.1j Research Agricultural Engineer, Snake River ConservationResearch Center, Northwest Branch, Soil and Water Conservation Re-search Division, Agricultural Research Service, U. S. Department ofAgriculture, Kimberly (Twin Falls), Idaho.2/ Research Agricultural Engineer, Southwest Branch, Soil andWater Conservation Research Division, Agricultural Research Service,!J. S. Department of Agriculture, Logan, Utah.243*L.244	IRRIGATION AND DRAINAGE CONFERENCEINTRODUCTIONConcepts of efficient irrigation are continually changing. Theyare modified by economics; the utilisation of labor, material*. bradcapital. The farmer, in order to gain a maximum economic returnfrom his farming operation, may use water as a substitute for laborwhen water is relatively abundant and inexpensive.Many irrigators consider an efficient irrigation one in which allthe water has been absorbed by the soil on the field. Current studies se-show that where cutback streams are not used, best irrigation efficiency.4•,will result when a specified amount of runoff occurs. Irrigation can be # taccomplished with no runoff and a minimum of deep percolation loss withwell designed border irrigation systems. In TreeeeletrOw systems andin poorly designed or operated border systems, irrigation with little orno runoff will result in large deep percolation losses.When deciding between the desirability of having either deep per-colation lams or runoff, several reasons become apparent as to the desir-ability of choosing runoff: (I) runoff water can usually be recovered;(2) it'tlone not contribute to groundwater, drainage, and salinizationproblems; and (3) it is not wasteful of fertiliser materials throughleaching. Runoff should be limited so that soil erosion does not occur.In addition, it appears that the present trend toward more mechanizationand automation of surface irrigation may introduce a need for controlledamounts of runoff.RECIRCULATING IRRIGATION	245Surface runoff suggests an obvious recoverable addition to thefarm irrigation water supply. As a result, in recent years there hasbeen an upsurge in interest in recirculating irrigation systems and pump-ing systems for recirculating runoff and waste water from irrigated fieldsare becoming an important part of economical irrigation. Little previouswork has been reported on the design of recirculating irrigation systems.The relationship of pump and sump size to the contributing area and pos-sible runoff has not been determined. The functional requirements -what, why, and how much each part of the system is expected to do havenot been investigated.Some general information is available on sump design and storagerequirements for given pumping rates. Little thought has apparentlybeen given to the potential quantity and rate of runoff from irrigatedfields under varying conditions of water supply, soils, crops, and topo-graphy, or how recirculated flows may be integrated in the supply system.Some individual return flow systems are described in the literature butthere is no indication that any engineering data are available for design.Typically, a sump is dug in an appropriate spot and a pump and returnline installed. It is not known whether the runoff is measured before-hand.SURVEY RESULTSA survey was conducted during the fall of 1964 and spring of 1965to obtain information about systems in the Eden-Hazelton-Murtaugh areaand the Oakley Valley area of southern Idaho. An attempt was made toobtain information about soils, topography, contributing area, sump246	 IRRIGATION AND DRAINAGE CONFERENCEarea, pump and controls, pipelines and costs. A total of 66 recirculatingirrigation systems pumping entirely from runoff were located in theseareas. The data obtained from the survey are summarized in Table 1.The area to which the recirculated water was applied varied from 40 to160 acres and averaged approximately 70 acres. The area contributingrunoff varied from 120 acres to 500 acres and averaged about 240 acres.This does not mean that all of the contributing area or the area usingrecirculated water was irrigated at one time.Few recirculating systems were being operated when the surveywas conducted and inflow and pumping rates were not available. Fewof the irrigators knew the rate at which they were pumping water. Ingeneral most systems appeared• to be pumping about 1.5 cfs. , with arange of 0.5 to 2.00 cfs. Most owners consulted did not think it econom-ically feasible to pump less than 1 cfs. There were no measuring devicesto be seen at any of the recirculating installations. The only measuringdevices in the area were those at the canal turnouts on farms obtainingwater from a canal system. All of the water supplies in the Oakley areawere from wells. The steeper topography in the Eden-Hazelton-Murtaugharea is reflected by the greater length of pipelines and results in increasedinstallation costs.In areas where the slope of the contributing area was greater than0.5 percent, silt problems were more in evidence than on systems hav-ing contributing areas with flatter slopes. In some systems it appearedthat the annual cost of silt disposal might be as much as annual powercosts for the pumping operation.•91Oq0ti)Oa0as0.10A01raqrw00C.04)a.004to000qCO000ti02'C..CdoA$401)•150•••1aRECIRCULATING IRRIGATION	 247kr,a,414q60COq0'4SO10•V0s.U4.)OfdCOCCro.-;E-1o0401q-.._0 0 00	 0	 m0	 1"--	 •.0	 •-k• •	 •	 •	 •	 •	 .0	 •cl•	 ,0	 ni	 0	 N	 ..0	 re/	 N1	 N	 co	 cr-rm	 43	 N-I	 a	 -	 r.,1 rq	 1-1	 Li,,--1V	 54 1.4► /AV.-q 0 o co.d0o._,P"o	 o	 rn	 0 0 ',:e	 N40 	 Li' 	 0	 c•- 	 f--	 e. 	 c;	 M 	 r..,	 ,•-,	 —iQ,nN	 N )r) N	 N-	 N el	 IN ^Ini	 N.	 C44- Or VI,(+'11 o 0 0"0gAVa..--,im•0	 xi	 co	 o	 -.0	 „q 	 co• •	 ..z.	 un	 0	 cr.	 0	 -1	 tn	 -d	 ,-,	 tn	 0	 c0N	 "	 0	 C- enG 0 M4_.	 ,..,-c12p --..„ v	 NIIR' is is17	 111)N 0'51k ',..li 0 0 rn0 0 0	 un	 c..	 a	 •tr	 a-1	 I--0'a) P...., 4)	 -;	 .-y ot 	 tn	 .4 	,i,	 ...	 •C:	 r.	 1l1 0:"041a. ..-.	 o	 4,	 rn	 CO	 I,	 .0"N	 Tr.-.	I--M+A-	 .69.	 4.s.•to	 •>	 td)0	 >0	 q'	 OA	 he	 -	 .	 C0 4.;	 4'	 coN	 4	 4	 .... 	....1)i	 , 2	 4	 •	 •iz	 •	 4-3	 0	 n.,	 440 ,3 4,71Jel	 eL;	 0	 C	 >g	 .1,	 V	 di	 ^..--r 	 Cd- 	 1-.	 -13	 -	 -	 S	 „„	 t	 47	 7;	 -v I	 u	 -	 .5	 v	 n!	 01	 0)	 k4-1.1" q 0	 >0	 0	 0,4).	 2	 „:3	 $.4	 .0	 00	 ...'rdb4 	...9•n-1	 k	 4	 k	.t	-	 sl). 	,-'	 '.	 .v.,	 9	 ,,	 a.  	 0x ft	 0	01—* 	 ..,	 0	 m a,	 u	 p,	 :0	 'O Vm0IA	 ....9	 g"	 ,_,0 	 k	 a..	 0	 k	 ti...	'1.v	 a 	 ;Ag	 L'	 a	 v	 0	 q s.4-'	P4	 t–	 .,-:	 eri	 in,	 q 	 >	 q 	 a	 a1Z	 11	p--,	 ::-1	 ,-,	 4	 rit,	 gk•(ij	 ctS	 a)	 g	 ',FL,	 a)	 S	 VI	 to'	 E	 E	 VF.	 00	 0	 01.	ry	E	 {00P4Pi	.,	 L)	 E-1	 1	 4	 -1	 C.)	 ..)	 1:1.	 P4248	 IRRIGATION AND DRAINAGE CONFERENCETwo types of pumps were used on the recirculating systems.One was a paddle wheel centrifugal pump and the other was a shortcoupled vertical turbine pump. Forty-six of the installations used thepaddle wheel centrifugal pump. The remaining 20 were short coupledvertical turbine centrifugals. The paddle wheel type generally haslower potential efficiency but has the advantage of being able to pumpsome trash. The vertical turbine type pump requires trash screeningand continuous bowl submergence while pumping, but is more efficientat higher heads.Many of the owners thought that enough water should be storedto irrigate a separate area using a 24 hour irrigation period. Accord-ingly, collection reservoir size ranged from 0.6 ac. -ft. to as high as8 ac. -ft. with the average volume being about 2.0 ac. -ft.Most installations appear to have been developed, not designed.This was evidenced at several installations by the spare pulleys foundlying around, indicating that the farmer changed the pump speed tomatch his particular runoff conditions.Pump stands in reservoirs were generally made by stacking twofour-foot lengths of 30- or 36-inch diameter concrete pipe on end. Aninlet hole was cut on the side of the bottom piece of pipe creating anunderwater intake that provided some escape from pumping trash. Fur-ther reduction of trash intake could probably be obtained by allowing alarger radius of inlet or by providing several radial pipe inlets to thepump stand creating several lower velocity intake points.•-RECIRCULATING IRRIGATION	249EXPECTED RUNOFFA recent study on farms in the Rupert, Idaho a/area showed anaverage farm runoff of 18.5 percent of the total water delivered to thefarm. Losses by deep percolation were computed to be of approxi-mately the same magnitude.Davis, from surveys made in California, reports that farmshaving an area size of 160 acres produced runoff of 10 to 20 percent ofthe water used for irrigation.A theoretical study was conducted by the authors to determine thevolumes of expected runoff from fields using typical irrigation stream ad-vance and infiltration data. Runoff, deep percolation and moisture storedin the root zone were computed for various combinations of length of runand desired depth of irrigation at the lower end of the field. Infiltrationwas represented by the expression:I = KtN (1) where I is the cumulative infiltration, t is time and K and Nare values characteristic of the soil. The stream advance was given bythe equation:t = A(1 — e Cx ) 	  (2)Tyler, C. L., G. L. Corey, and L. B. Swarner, "EvaluatingWater Use on a New Irrigation Project, " Idaho Agricultural ExperimentStation Research Bulletin No. 62, 1964.Davis, John R., "Design of Irrigation Tailwater Systems, "TRANSACTIONS of the ASAE, Vol. 7, No. 3, 1964. pp. 336-338.250	 IRRIGATION AND DRAINAGE CONFERENCEwhere t is time, A and C are constants for the particular condi-tions, x is the advance distance, and e is the natural logrithmbase.Results are presented for K, N, A and C values of 0.5,0.5, —2.0, and 0.002, respectively, and a 1320 foot length of run, Figure1. The values shown by the curves are computed at the total time requir-ed to apply the desired depth of irrigation water at the lower end of thefield. For any given time the runoff plus the absorbed water will equalthe water stored in the root zone. Presented in this manner, as a per-cent of the total applied water, the water stored in the root zone is theirrigation application efficiency.The curves in Figure 1 are easily used. For example, if a 12inch irrigation is to be applied, runoff will begin at approximately 5 per-cent of total time and will amount to about 50 percent of the applied water.The percent of total water absorbed by the soil will be approximatelyequal to that stored in the soil, 50 percent, since deep percolation willbe negligible. Similarly, if a 2 inch irrigation is to be applied, runoffwill begin at about 60 percent of the total time of irrigation and will beapproximately 10 percent of the applied water. Approximately 90 per-cent of the water applied will be absorbed by the soil, about 63 percentwould be stored in the root zone and about 27 percent lost to deep perco-lation.For this part icular set of conditions, maximum water applicationefficiency is obtained with a 3.5 inch depth of irrigation and a corres-ponding runoff of about 20 percent of the total applied water. If theRECIRCULATING IRRIGATION 	 251TrccU61 a)rLq 40cr 2Oa.0	 20	 40	 60	 80	 100ADVANCE IN PERCENT OF TOTAL TIMEFigure 1.	 Irrigation Water Disposition CurvesDepthAbsorbof IrrIgotl.nz3mildlatit	 s•/AIllibtStored/141prDee . 	 • ercolot .	 AINn252	 IRRIGATION AND DRAINAGE CONFERENCErunoff from the field is recirculated and reapplied at the same efficiencyas the original irrigation, the application efficiency can be increased ap-proximately 15 percent. For typical sit uations application efficienciesof 60 to 70 percent are attainable when runoff is approximately 20 per-cent. Recirculating the lunoff will raise the application efficiency over80 percent.	 Maximum application efficiencies with recirculation of run-off are obtained with about 30 percent runoff from the original stream.This applies to systems having average infiltration rates and neitherfast or slow advance rates, i. e., advance time/total time ratios between1 and 9.SYSTEM MANAGEMENTRecirculating systems can generally be classified into three types:(1) sequence systems, (2) reservoir systems, and (3) cycling sumpsystems. Depending on the individual situation, one or more types ofsystem may be applicable.Sequence systems are the simplest. They may consist only of ameans of collecting runoff at the end of a field and applying it to an ad-jacent field. Under ideal conditions this may not even require a pump.Several sequence systems were found in the previously mentioned sur-vey. These systems generally had only a small sump, a pump, and ashort length of pipe. The runoff water collected from one field was pump-ed across the road and applied to the next field, which was at a slightlylower elevation. With proper planning and some land leveling, it maybe possible to install sequence systems which do not require a pump.These should have enough elevation difference between fields to allowrunoff water to be applied to the lower field without having to be pumped.RECIRCULATING IRRIGATION	 253Reservoir systems were the most common found in the survey.For this method, a reservoir sufficiently large to hold all the runoffwhich may occur in a 24 hour or longer period is required. The re-covered water may then be pumped as a fully independent supply to someother part of the farm or may be combined with the original water supply.Cycling-sump systems are usually designed using criteria simi-lar to those for pump outlet drainage systems. They have a small sumpand a float system which controls the pump operation. Shahroody andDavis give specific recommendations for the hydraulic design ofsumps for vertical turbine pumps. Sump size, pumping rates andcycling frequency were discussed by Davis in an earlier article.Management of the recirculated water in the irrigation systemis a problem that has not received sufficient attention. Unless someconsideration is given to this problem, the desired increase in efficiencymay not be obtained. Care of small streams may be an inefficient useof labor. The water may be largely wasted if it is not carefully applied.Combining recirculated water with a primary flow from the farm supplymay result in better efficiencies of labor and water use. Where therunoff water is recirculated into an irrigation system the area beingirrigated will have to be increased.Shahroody, Ali M. and John R. Davis, "Efficiency of PumpingFrom Small Circular Sump, " JOURNAL OF THE IRRIGATION ANDDRAINAGE DIVISION, ASCE, Vol. 90, No. IR 1, Proc. Paper 3817,March 1964, pp. 1-8.254	 IRRIGATION AND DRAINAGE CONFERENCEIn the sequence use system water is applied to a small portion	 n•nof an adjacent field. If a storage reservoir is included in the recirculat-ing system, fewer problems will be encountered as the pumping ratefrom the reservoir will be constant and the flow can be treated as aseparate full irrigation supply. It is the equivalent of having an addi-tional irrigation stream.The most difficult management problem exists when cycling-sumpsystems are used. Analysis of the problem of integrating recirculatedrunoff into the original supply shows that the cycling-sump is not a feas-ible idea. All that is accomplished if the water is added to the areaalready being irrigated is storage of the runoff water on the surface ofland. This only prevents it from ending up in the borrow pit at the ex-pense of pumping costs. The runoff water from any recirculating systemmust be applied to another or additional area in order to actually makeuse of it.HYDROLOGYThe hydrology of the collection area should not be ignored. Ifthe surface water from the entire farm is channeled by waste ditch intothe holding reservoir for recirculation, there is a possibility of damagedue to runoff from rainfall or melting snow. During irrigation, runoffis usually received from only the area being irrigated and the reservoirand pumping system are designed for this condition. If rainfall occurs,a small amount of runoff from the larger farm area may be enough toovertop the reservoir. Therefore, overflow or spillway capacity mayRECIRCULATING IRRIGATION	 255have to be built into the system if this is a possibility. Such damage oc-curred during the 1964-65 winter in some of the Idaho installations survey-ed. Rains falling on a snow cover produced a large amount of runoff at atime when the systems were not attended. As a result several reservoirshad major washed-out sections.SI LTAT IONBasic soil conservation practices should not be ignored in theinstallation of recirculation system; . Irrigation systems should be de-signed so that a minimum of silt is produced from the contributing fields.In general the systems surveyed in Idaho did not conform to this recom-mendation. Some of the reservoirs accumulated so much silt that theyhad to be cleaned annually. The cost of silt removal in some systemswas estimated to be approximately as much as the pumping costs for re-circulation of water.While not practiced in all of the systems surveyed, the silt removedfrom the reservoir can be redistributed on the contributing field. Thistopsoil can be used to reduce the slope of the field or to fill in depres-sions, swales, etc. which contribute to uneven distribution of irrigationwater.CONCLUSIONSAnalysis of the status of design of recirculating irrigation systemsshows that very little work has been done to determine design criteria orfunctional requirements of such systems. It has been shown that thewater application efficiency of typical surface irrigation systems can ber256	 IRRIGATION AND DRAINAGE CONFERENCEimproved by about 15 percent if the runoff water is recirculated and usedat the same efficiency on additional land.Estimates of the volume of runoff expected for various field con-ditions have been obtained from general field observations. Reservoirsize is usually flexible but pumping rates will depend on the method ofuse of the recirculated water. Sequence and reservoir recirculatingsystems will give a continuous flow which can be used independently orcombined with another water supply. If the recirculated water is com-bined with the original supply the irrigated area must be expanded to ob-tain any benefit. The cycling-sump system can be used effectively onlywhere the water can be applied to an area which is separated from thearea producing the runoff being recirculated.A survey of existing recirculating systems in southern Idahoshowed a definite lack of design criteria and engineering design data.These systems also show lack of basic soil conservation and hydrologicdesign considerations. Two-thirds of these installations had pumpingplant installations which could be improved by better equipment andbetter plant design.

Recirculating Farm Irrigation Systems

Northwest Irrigation & Soils Research Laboratory Publications

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Recirculating Farm Irrigation Systems

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