jam farm irrigation structures

5/28/2018 jam Farm Irrigation Structures

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FARM IRRIGATION STRUCTURES

A. R.Robinson

Handbook No. 2

ti. vcl\repared In ioopea oii "ith 'nined Statcs A., loInternational D)Celopmnn. (onlrac All) l)SAN-( (X)WsAll

reported opinions, oniclti+ons or raretonIr di hose Ilthedaior 'author I(cnlri (or)kiildnot tho .e l thi tizldlyaIgcII. or he

United States go%,rnmeIt. Mention o lo rt+erull poLdi 1t1IIIhilspublication issolel\ to pio idt: lwiiilii tlOiL It do lot ion;ttlL

endorseentrn h AlI) mer olher prodtIt, 1o rIl.ittIoCII L'

WATER MANAGEMENT SYNTHESIS PROJECT

University Services Center Agricultural & Irrigation E-ingineeringColorado State University Utah State University

Fort Collins, Colorado Logan, Utah

March 1983


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TABLE OF CONTENTSPage

TABLE O F CO NTENTS ........................................... L ISTIN(I OF fIGURES ........................................... H ILST IN(I 0)1. I'AP,LES ............................................ v FORLWORI) ... .. ............................................... vii

I. INTRODIA( I ( )N .. ............................................ I 1. C IIA NNt I.S ANt) '-IRtU TIJ RES .................................. 3

1. l)cli ,c ; ( hdnm.l mid I) i' ' .................................... 3 a. (Channcl[)e-ign ..................... 3 b. Iarth I)itchc., ... .................................... 7 c. I ned )i h . .. .. . . ... ..... .................. 12

l) (rm rctc I rning........................................... 12 2) :,.phalti ( o(tcreuc ............ . ................................ 15 3, N1si n r%, .. . ......................................... 15 4) \-pV lIt, l'lall k ihbcr Sheeting ........................... 15 5) ( h ij Se a t ............ ............................ 17 6) 1arth ci t i ld ............. ... ........................ . 17

2. Control S'rtrtucc, ......... ................. ........ 17 a. [)l,,i~l Stuc :tic.................................................. 19 h. )ro p . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 c. Chec . . ... ......... . ............................. .... 37 d. IIrrInr t,,()utlCt. .... ..... ........ ... ......................... 45

3. Water Mcasuring Structures ...................................... 62 a. Weirs .. . . . . . . . . . . . .. . . . . . . . . . . . . . ... . . . . . . . . . . . .. . . .. . . . . . 62 h. Flumes .... . ... . . ... . ... . . ... . .. . ... . .. . ... .. . ..... .... . .. .. 63 c. Orifice,. . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 68

4. ,Miscellaneous Stru tures,......................................... 68 a. Culverl,,, Biridges, Imines, Crossings, Siphons ................... 68 b. )rainage Structures .......................................... 69 ,c. Automated Structures ......................................... 71 d. Other Structure ......................................... 71

III. LOW tPKESSUIR[ PIPE SYSTEMS ................................. 73 I. Ppe )esign ... .. .. . . ... .. . . .. . . .. . .. . .. . .. ... ... ... .. .. .. . .. .. 73

a. Underground ................................................ 73 b.Surface ... .. ... .. . ... . .. . . .. . .. . . . .. .. .. ... . . .. .... . .. .. . . .. 73 c. Pipeline Capacity ................. ........................... 73

2. Structures ... . ... . .. . . . . . .. . . . .. .. .. . .. .. ... ... . .. . . .. .. .. . . . 77 a. inet Structures .............................................. 77 b. Pressure and Flow Control Stands .............................. 78 c. DischargeControl Structures................................... 83 d. Miscellaneous Structures ...................................... 84


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IV. CONSTRUCTION AND INSTALLATION .......................... 87 1.Ditch Construction ............................................. 872. Ditch Structures .................... 883. Pipe Systems................................................... 88

V. OPERATION AND MAINTENANCE ............................... 91 1. Opera tion .. . .. ... . .. .. .. ... . ... . ... .... . . .. .. . ... .... ... .. ... . 912. Maintenance ................................................ 91

VI. BIBLIOGRAPHY..............................................93 VII. DEFINITION OF TERMS........................................ 95

1. Channelsand Structures ....................................... 95 2. Hydraulics ........................... .......................... 96APPENDIX I - Concrete for Small JobsAPPENDIX 2- Standard Drawings ofSCS StructuresAPPENDIX 3 - ASAE Standard S261.5 Design and Installation of

Non-Reinforced Concrete Irrigation Pipe SystemsAPPENDIX 4- ASAE Standard S376 Design, Installation andPerformance of Underground Thermoplastic IrrigationPipelines


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LISTING OF FIGURES PageFigure

I Surface irrigation canal sy ,tcm ..... . .. .. . .. ..................... 3 2 Manning eLJuitin1 ',Olition for determining canal dcsign ................. 6 3 Animal pous,,ered V\-dcher ............... ........ ................ 10 4 Tra'tor pmc ,ercdV-ditch,r ......................................... I) 5 Sugce te. irte cd',etIor llechtijit al reconstruction ofearthen channels - I 6 Type, I ,mall c -anal Ic, ....... ................ ........... .. 13 7 Co icletc l icd atnal' .. .. . . . ............. . ... . .. .. ..... 14 8 l'rccaot concictu :hanm nel ,,cctik ,...... .. ... ... .. . ... . . ...... . 16 9 \ "i n w ri iti( I -,\ , t ill . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 18

1) l)ii,,n to h t . l'. lwt,.',tnt'.oditches .......... .......... 1.9 11 1)ii ioni ,)\i, lI t o ili l th"- . .... ...... 21 12 Seminoduil I,, r i,,ednidaii aid l lakita ......... 21 13 I)ivior-tu itmi, t .edit l} ttid Indil............... .............. 22 14 [renh type pro trtitoiil di'. ....................................... 22 15 ,%djU\tahie p ; ttt tl block di, i,,or .................................. 24 16 Tswo-vay concrete hl() kdi,. i,o ................... .......... ....... 25 17 Three-way divisor. .... . .. ................................ 25 18 Concrete trapezo'idal two-.as dikisol . ................................ 26 19 Portable gate,, tr- di,.i'or ,tftjctures ................. ................. 27 20 Di,,ision sntucmre, usine ,t ud d, piefabricated structures ............... 28 2 Drop struct t.-, ,,' tot tgrade control ................................ 29 22 Exat ples oI ,m all drop )trucmu ,, ....... ............................. 30 23 Drop stricture conibiicd ,Aith turnout ............................... 31 24 Concretc tr apeitmdd d,p lructire, ................................ .. 32 25 (oncrete "top-eck ......... ....... .............................. 33 26 Concrcte hlock droi and check ,,tructure ............................... 34 27 lDtop-ch,.xck ,t e treC ti,11e xIi ic:d Lwncrcte sections ................... 35 28 lDrop .,:ructure \%ith i-ra,el-i()ck ',tillingbasin ........................... 36 29 Tvpical pipe diop 'etructire ......................................... 37 30 Sloping rock drop stmucLtiL tc . ... .................................... 38 31 l)itch check iM ined ditch s'ith ,,iphon tubes ............................ 38 32 Small concrete ditch check ........................................... 39 33 Wooden ditch -heck, \kith different openings ............. ............. 40 34 Wood 'imt c \%all check with turnout .................................. 41 35 Concrete block check ,ith apron for erosion control .................... 42 36 Concretc blo.ck check ,(ructure .... ................................... 43 37 Portable can. as check vith dischar e sleeve ............................ 44 38 Flexible, portable ditch ch Ck ......................................... 45 39 Portable metal check .. . ........................................... 46 40 Two types of portable checks ....... ................................. 46 41 G ated pipeoutlet ................................................... 4 7 42 Commonly used turnouts for farm irrigation ditches ..................... 48 43 Concretepipe turnout ............................................... 49 44 Wooden turnout for basin and border irrigation ........................ 50 45 Two designs of wooden turnouts ..................................... 50 46 Turnout-check structure using extruded concrete sections ................. 51

ii'


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47 Neyrpicgates and modular turnouts..................................5248 Trapezoidal panel outlets ............................................ 54 4950

Concrete orifice pan l outlets........................................Brick masonry installation for panel outlets............................ 555651 Precast concrete slab installation for panel outlet........................ 5752 Head loss through circular concrete turnouts........................... 5853 Spiles used for furrow or corrugation irrigation ......................... 595455

Siphon tubes for furrow irrigation...................................L.arge siphon with priming pump for turnout ........................... 596056 licharge of siphon tubes ............................................ 6157 (.oncretelined ditch vith bank cuts for irrigating ....................... 6458 5960616364

Rectanguhir eir...... .... .....................................Ninety-degre V-notch 'cir ...........................................FParshall measuring flumne6 [1...........................................Cutthroat ea uring u e........ ..................................TIrapezoidal measuring flume.........................................Broad crested v,ir(fb-c-w) measuring flume ............................Flume for ,carryingirrigation water across adepression ..................

656566667676865

66Inverted ,ihon made from concrete pipe ..............................End details for siphon crossirg........................................ 697067 1Intstaid for indergroad pipeline .................................. 7768 piLal concrete pump stand ... ..................................... 7869 ombination gate and oerflo itaind.................................79

7071

Float valve stand.............. ..........................Typical alfalfa pmalhydrant........................................81 .. ....... 8072

73 Orchard valve hydrant.... ... .....................................Giated surface pipe and tubing attached to .ortable hydrants............... 8282 74 Open pot hydrant with orchard valve................................. 8275 Air vnt for underground pipelines ................................. 85

iv


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LISTING OF TABLESTable PageI Values ofManning roughness coefficient nfor earthen and lined canals.... 5 2 Suggested maximum flow velocities and side slopes for lined and unlined

channels ................................................. 8 3 Earth irrigation ditch sizes for different slopes, roughness and discharges... 9 4 Discharge capacity of spiles .......................................... 62 5 Head loss in concrete pipe withconcentricgasket joints .................. 75 6 Resistancecoefficient Afor fittingsand valves .......................... 76


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PREFACE Thepurpose ofthis handbook is topro

vide information on small structures usedin irrigated agriculture, primarily forselecting those structures needed to improve on-farm water management. Complete information on design, constructionand operation of the multitude of structures that are available is impossible toassemble in one publication. [his handbook is intended to emphasize the importance ofadequatecontrol anddistributionof irrigation water, enumerate some of the successful structures that are available, give a selected amount of design information, show a limited number of examples of design procedures, and givereferences where more information can beobtained. W ith the exception of lowpressure underground pipeline systems,only surface systems are discussed.Sprinkler and other methods of irrigationare not covered in this handbook.

Information on small canals and structures is given for flows of less tha; 0. 14cubic meters per second (5cubic feet persecond). Generally the flows will be in the0.03 to 0.06 m3/s (1-2 cfs) range. Structures that can be constructed from localmaterials and with local labor are emphasized. Precast structures and structures constructed from precast brickblock and sections are also presented.In addition to the extensive bibliographylisted for small canals and structures,there isa section presentingstandard definitions of terms used in the handbook.Appendices given include: 1)preparationof concrete for small jobs; 2) standard

designs of farm irrigation structures (including metr ic conversion factors); 3)standards for pipe irrigation systems; and4) standards for plastic pipe irrigationsystems.


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FARM IRRIGATION STRUCTURESA. R. Rkobin,,n

I. INTRODUCTIONSurface methods of irrigation are stillused on most of the 234 million hectares(1972 data) of irrigatcd,cultivated lands inthe world with tihe remaining lands beingirrigated by sprinkler and tricklc systems(3). It has been projccted that tile irrigatedarea will increase to about 273 million haby 1990. An estimated 86 million ha of'tileworld's irrigated lands have sv\,terns thatnow need improvement of both the mainand on-farm systems for di:ributing andapplying irrigation water. -Fhe United

States of America presently (1980) hasabout 21 million ha of irrigated,cultivatedlands, of which 70 percent is surface ir-rigation.The sprinkle and trickle methods of ir-rigation use pumps almost entirely.Pumps require a large energy input, andinitially, tile systems require a largecapital outlay. There is limited use ofgravity pressure sprinkle and tricklesystems. In the near future, the obvious

world shortage ofcheap fossil fuel energ,will probably mean a return to gravitypressure irrigation systems. The rapidlyexpanding world population will den'-Idan increasing food supply which will alsorequire an increase in production from ir-rigated agriculture, mostly From surfacergravity systems.Water application efficiencies for stirface irrigation systems a.otind the worldtypically have been quite low, 40-50 per-cent (11). Water conveyance efficienciescan be quite low also, possibly in the40-50 percent range, due to canal andditch seepage, leakage, and sp'llage.Overall irrigation efficiencies !hen mightrange as low as 28-35 percent indicatingthat 65-72 percent of the water is lost tothe individual farm use. Overall, the effi-ciencies can be materially increased withcanal and ditch mainter-ance and lining,use and improvement of control struc-tures, and improved on-farm watermanagement. Good farm irrigation watei

management includes all of these con-

cerns as well as reliable water delivery ainda regulated filo\% rate. Improvcd watcrcontrol structures, propcrlV used, canmaterially impro.c tihe use and control ofirrigation \water. li Ispossible for nsurface irrigation. ,,toil, to havc ,atcrap plication Cefticiencics of7)to 810)ercentand higher.The priuary purpose ot this handbookis to present in! rnalion oil siall irrieation channel, anld ,irlcturcs thai can be

used to inpro(\ C01- -LfiFi.a ICr inaIaCe-Iment. I.' presurc pipe ,,stems arC alsoconsidered. I lie applicati ( i1li infor-Illation w.ill result iII mtuch less, asIe of, irrigation watcr 'milthte icsultaiit inccasecin water tor existim crops ald tl irrigating -iddiiioialareas. lmpro\cnient ofwater management on individual farmswill result in higher crop yields also.There has bcen a lack of attention tothe design and (peration of the irrigationsystems at the farin level because governmeit custody usually ends v\ith the sccondary canal ,sstens, and farmers, either byorganizationotO individually, operate thebalance of the systems. [here also hasbeen tile asstlinptiOll that lari irrigationsirtic should be I)\% cost andtherefore, tialit v ha' been a sco1ndary

consideratiOt .It is imf1po-tant that the ,ystcns andstructires,be adapted for tlsC inI differentcoIntries v,ith consideration for

availability and existen,c of materials,skills, labor, financing and customs.Generally, the procedures and structuraldesigns in this handbook are describedsimply. The structures are usually easy tooperate, arc reliable and give good,positive control. Some will require moremaintenance than others. Structures andlinings that require specialized and expensive equipment for installation are notemphasized. Small, low cost structuresthat can be constructed entirely with localmaterials and labor are presented.


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3

II. CHANNELS AND STRUCTURES1. Delivery Channels and )itches

The channels discussed here are tertiaryand quaternary canals, i.e., the canalscommonly called farm and field laterals.They supply water to farm or field outletsand turnouts. The larger canals (tertiary)are called farm laterals (USA), tne.skA(Egypt) and minors (Pakistan and India),while the smaller ones (quaternary) arecalled field laterals and head-ditches(USA) and marwas (*gvpt ), (Tigur ).The channels may bC11nined carth or linied with concrete, masonry or asphalt,

a. ('hannel Ile.ign.In orcler to determine the channel sizerequired, the maximuim discharge,together with thedesired shapeof the sec-tion and an estimate of the channelroughness, must he known. The Manningequation isthe nmt cornmonly used rela-tiorslhip for determining channeldischarge and will be used in this hand-book.

.,\

Q = C AR2's' /n (1)where Q = discharge, (L/T).

A cross sectional area ofditch, (L2).R hydraulic radius--areadivided by the wettedperimeter,(L).

longitudinal slope,(L/L).

n =Manning roughnesscoefficient (L')(samevalue for both metric andEnglish units).

C 1.0when usingmetric units, 1.49 for Englishunits.

TertiaryQuternaryCanalFieldorm F

TertiaryFarmQuaternary

Field

Figure 1.Surface irrigationcanal system.


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The Manning roughness coefficient, n, given flow with a measured slope in afor canals varies from 0.010 for smooth given material or with a selected lining ofconcrete to over 0.10 for channels with a predetermined shape. In othersituationsweeds and brush. Table Ilists values of' n an estimate of the discharge is requiredfor earthen and lined channels that can be while knowing tic ditch size and slope,used for design. The value for n should be with an estimateof the roughness (Mannchosen only after a careful study of the ing n from Table I).Figure 2 gives a soltifield situation. tion for Equation I that can be used tomake estimates of the ditch shape andThe design problem isusually to deter- flow. The following are two examples usmine the width and depth required for a ing Figure 2.

Example 1Earth canal in clay loam after e.vathering, clean; n 0).022 (Table 1).Assume. Bottom width, B - 0.45 m(1.5 ft) Longitudinal slope, s = 0.001

Side slope, z 1.5(1.5 horizontal to I vertical)Discharge, Q 0.10 m's (3.5 cfs)Problem. Determine the depth of flow.Solution."Solve for the i',, in Figure 2.

'(Qn/ s)/f = i [(0.10)(0.022)/(0.032)l/(0.12) 0.57From Figure 2for z = 1.5, E,,, 0.57, then D/B 0.60.Since B = 0.45 m, thenD =0.27 m(0.89 ft).

Example 2Brick with vertical wall, mortar trowel finished surface, n - 0.013 ('[able I).Assume: Bottom vidth, 13 0.45 m(t.5 ft) Depth of'sction,0.45 m (1.5 ft)

Freeboard, 0.15 m(0.5 ft) Depth of f1obs, 1) 0.30 m ( .0 ft) Longitudinal slopc, s 0.001 Side slope, 1 0

Problem: Determine the discharge.Solution: From Figure 2, for )/B - 0.67 and z 0 then E,, = 0.28

"E,, (Qn.,sj; ' or Q,) L B31,n,,,s (0.28)(0.032)(0.12)/0.013Q - 0.083 m's (2.93 cfs)
http:///reader/full/0.10)(0.022)/(0.032)l/(0.12http:///reader/full/0.10)(0.022)/(0.032)l/(0.12


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5

Table 1. Values of Manning roughness coefficient, n, for earthen and lined channels (30).Roughness coefficient n

Type of' Channel and Description Ninimum Normal MaximumfA. Excavated earthen channelsa. Straight and un1iform1.(lean. rCceitlyCompleted 0.016 0.018 0.0202. (Ican, after veatherine 0.018 0.022 0.025it ctimi, 0.022 0.030. (Gra,.cl, tin ,in clean 0.0254. With short ,_s-, fey weeds 0.022 0.027 0.033and 0.030. With long Lt[I.t wecd, 0.040 0.0-45b. Winding and ,Iugish1.No vegetationr 0.023 0.025 0.0302. (irass, sonic weed, 0.025 0.030 0.0333. )ense weccds Or aquatic plants

in(feep chanelics 0.030 0.03 0.0404. Farth hottorn and rubble sides 0.028 0.030 0.035hottm ilad weedv banks. Ston 0 0.025 0.035 0.0406. Cobble hotil Iand clean sides 0.030 0.040 0.050c. Channels not maintaied, weedsand brush utlt.It1l)erse ,,ed,.highas flo, depth 0.050 0.080 0.1202. ('lean bottom, brush on sides 0.040 0.050 0.0803. Same, highest state of flow 0.045 0.070 0.1104. Detise brush, high Iage 0.080 0.100 0.14013. Lined or builtl-up channelsa. Cement1. Neat, ,mootli surface 0.010 0.011 0.0132. Mortar 0.011 0.013 0.015b. Concrete1. lrowel 1fi110h 0.011 0.013 0.0152. Float finish 0.013 0.015 0.0163. l:inisltCd, .ith gravel onbottom 0.015 0.017 0.0204. Urifinished 0.014 0.017 0.020c. Brick1.Glazed 0.011 0.013 0.0152. Incernei mortar 0.012 0.015 0.018

d. Masonry1. Cemented rubble 0.017 0.025 0.0302. Dry rubble 0.023 0.032 0.035


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0.2 0.4 0.6Ee

0.8=On/Is

1.0B84

2(English Unit)

4 6 8 10040

1.6 I

1.4-B

CI CC1.2 -

S0OC,,'2 0O-,14

1.0 - 00004 o020. 0 000 0,24"2028 0,228_ ' 001C 0C,320002 OC-50 80 006 C0 ,700 8 890.8 -- 00 6 0 2"'"'0010 0018900 20 O04

00 0890

Q_

0C C0,

250 "

e ,

0 00 '2 - .2001313770 02480 C-:I, 0

,

- -. 00 90100

20

8/ "

0 55 150 755 110000I626

-

0.6 0 50 0 908-9 60 6 3 50

0.40.1 0.2 0.4 0.6Em =

0.8 1.0Qn/f - B8/3

2(Metric Units)

4 6 8 10

Figure 2. Manning equation solution for determining canal design (30).


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Note that the amount of flow is inverse-ly proportional to the roughness, n; i.e.,an increase in roughness decreases thedischarge in direct proportion; withshape, slope and depth remaining thesame. If the discharge remains constantand the roughness increases (such as fromgrowing vegetation), then the depth offlow must increase.

So that the ditch is riot overtopped,there should be a freeboard (distancefrom the maximum water surface to tiletop of the banks) of at least 15 cm (6 iri.)for the small canals. The banks tend 'olower with seasoning, aging of the canal,and use of the banks by traffic.b.Earth Ditches.Unlined earth ditches are the most corn-

mon means of conveying irrigation waterto the farm fields. Unlined ditches arepreferred by many farmers because theycan be built cheaply and easily, and main-tainedwith farm equipment. Also, unlin-ed ditches provide flexibility - itiseasy tochange the layout, increase capacity, oreven eliminate them after a rotation andrebuild them the next season. However,they have many disadvantages that makethem less desirable than lined ditches orunderground pipe.1.They occupy more land than linedditches.2. They usually lose more water due toseepage, leakage and spillage.3. Rodents can cause leakage.4. If weed growth is a problem, fre-quent cleaning isneeded.5. Earth ditches can erode andmeander, creating problems inmaintaining straight and properalignment.The slope for an earth ditch may be as

low as 0.00018. (Egyptian irrigationcanals generally have slopes ranging from0.00018 to 0.00020.) However, smallslopes result in slow flow velocities, largecross sections, and possible sedimentdeposition on the bed.

It is customary to use a gradient of0.001 in many areas. The slope of theditch should besuch that tle bed does noterode arid tile water flows at a selfcleaning velocitv; i.e., there is no deposition. A heavy clay soil will allow fairlyhigh velociilc:, without eroding, (Table2).At times it ikeces


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8 Table 2. Suggested maximum flow velocities and side slopes for linedand unlined channels (5).

Maximum FlowVelocities Side SlopesType of Surface m/sec ft/sec Range (z)*

Unlined Ditches, seasonedSand 0.3 -0.7 1.0 -2.3 3Sandy loam 0.5-0.7 1.6- 2.3 2-22Clay loam 0.6 - 0.9 2.0 - 3.0 1/2-2Clays 0.9 - 1.5 3.0- 5.0 1-2 **Gravel 0.9 - 1.5 3.0-5.0 1-1Rock 1.2- 1.8 4.0- 6.0 'A-ILined DitchesConcreteCast-in-place 1.5 - 2.5 5.0-8.2t 34-I

Precast 1.5 -2.0 5.0 -6.5 0-1 ttBrick 1.2- 1.8 4.0- 6.0 0-1 ttAsphaltConcrete 1.2 1.8 4.0 -6.0 1-1Exposed membrane 0.9 - 1.5 3.0 -5.0 1/2-2Buried membrane t 0.7- 1.0 1.6 - 3.3 2Plastic Buried membrane + 0.6 - 0.9 2.0 - 3.0 2

0 z is thehori/ontal unit to one (1)vertical unit.* Side ,lope,,of 1:1 for ,,mall canals in clay and clay loam are common.t Flows in this,scicity range may be supercrifical (see definitions)and difficult to con-Irol. They arc not recommended except forspecial uses.it Small preca,, and brick channels may have vertical walls (z - 0). I Nla.imu ,vloities ill depend the cover overt ,,, on the membrane.

Tractor drawn ditchers may he obtain-ed in many different designs and sizes,Figure 4. They may be adjusted manuallyor hydraulically. Generally the "no ;e"element isat an angle with the "wings'' sothat when tilted, a somewhat flat bottomis obtained. The wings are adjustable fordifferent widths. By combining tilt withwing spread, depth and topwidth can be

varied. In use, the first pass is not at fulldepth unless the earth is reasonably soft.On the second pass the tractor wheels ortracks will compact the earth moved outon the first pass. This will reduce seepageand stabilize the banks. Compaction ofthe banks and bed by manual or machinetamping or rolling is desirable.
http:///reader/full/5.0-8.2thttp:///reader/full/5.0-8.2t


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Table 3. Earthirrigation ditch sizes fordifferent slopes, roughness anddischarges (33).Flat bed before ditch is formed Finishedditch section

0.0005 s = 0.1301 s = 0.002 s =0.003n= 0.03 n 0.04 n = 003 n = 0.04 n= 0.03 n = 0.04 n = 0.03 n = 0.04

mB

ft mD

ft mF

ft InW

ft Inr

fi m2A

ft: InR

ft m.Q

It's nQ

ft. sQ

m's ft/sQ

m'/s ft'Q

m'. s ft' sQ

m'/s ft'isQ

mrs ft/sQ

m/s ft'/0.150.300.460.610.300.460.610.460.610.610.91

0.51.01.52.01.01.52.01.52.02.03.0

0.300.300.300.300.370.370.370.410.410.460.46

1.01.01.01.01.2121.21331.331.51.5

0.150.150.150.1511.210.21

1.210.240.240.300.30

0.50.50.50.50.70.70.0.80.81.01.0

0.300.460.610.760.380.46

1 0.610.530.610.460.61

1.001.502.(X)2.51)1.251.502(X)1.752.001.502.00

2.63.03.54.03.43.74.24.14.54.75.3

8.510.0!1.513.011.312.313.813.614.615.517.5

0.19o.230.280.33( I0,3"0420.430.49(.590.73

2.002.5(03X)3.50

i,.363.964.564.655.316.387.88

0.150.160.180.190.190.210.220.230.24(0.260.29

0.490.540.590.620.63O.680.30.74(.780.860.94

0.040.05O.70.081.080.10().120.120.140.18

1.4I.S2.32.52.73.44.14.24.96.4

0.030.040150.060.061.00.0S0.090.110.140.18

101.4172.12(02.51.13.23.84.86.3

0.050.070.09O.110.110.140.16

1.92.63.34.03.94.85.7

0.040.060.070.080.080.100.120.130.15

1.5202.53.02.93.64.34.55.3

0.080.10O130.160.16

2.73.74.75.65.5

0.060.080.100.120.120.140.17

2.12.83.54.24.15.16.1

0.100A30.16

3.44.55.7

0.070.100.120.150.140.18

2.53.44.35.25.06.2

A - cross sectionalareaR hydraulic radiusn - Manning's roughness coefficient0.03 - soil with gravel0.04 - soil with grasss - slopeQ - ditchflow capacity

-7. ATNN I Cut or Fill Bed Made to Elev.Design Water SurfaceTW Compacted FillISurface Wcter N- /

Ditch is FormedFlat Bed before Finished Ditch Section


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10

Figure 3. Animal powered V-ditcher

4 t i r

~Figure 4. Tractorpowered V-ditchers.


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Many old ditches become eroded anddeteriorated and it is better to remove theold ditches and form new ones. Figure 5gives a procedure for doing this that willresult in a new, more stable channel thatwill lose less water than the old one. Thecompaction and forming ofthe new chan-nel can be done manually or with amachine. Soil which hasahigh percentageof silt and clay will form the best channelfrom all standpoints.The importance of good constructionfor earth channels depends a great deal on expected ditch usage. Some ditches, suchas those run on a contour for grain and

rice, are used only one season and thenfilled in. Other ditches are relatively permanent and should be constructed withmore eflotrt and care. I)itches intendedfor lurro\% or border irrigation directlyfrom tile ditch need substantial banks;and the banks might be higher for usingspiles and siphon tubes than or openditch bank cuts. In this case the top of thebanks should be a minimum of 25 cm (10in.) above tlie surrounding field surtface.Banks must be high enough to allow tilewater level to be increased by checks ifneeded. If seepage isexcessive, compaction of lie banks or deposition of a clayblanket can be tried.

I) Remove the Old Banks and Pile the Organic, Vegetation Filled BankSoil away from the New Channel Site.

2) Build a Pad of Clean, Moist Soil on the New Channel Site and Compactthe Pad in 10-15 cm (4-6 in) Layers.

3) Pull the Ditch inStages, Compacting the Bank Soil between eachExcavation In 10-15 cm (4-6 in ) Layers

4) Continue Enlarging the Channel and Comlipacting the Moist SoilDeposited on the Banks in Layers.

5) Trim and Shape the New Compacted Banks to the DesignCross Section Figure 5. Suggested procedure for mechanical reconstruction of earthenchannels with atractor-drawn scraper, ditcher, and

compactor (30).


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12 c.Lined )itches.Often farm ditches are lined to reducewater loss and maintenance and to in-prove water control. lining can reducethe amount of seepage loss, control weedgrowth and prevent the ditch fromeroding. Lined ditches with sloping

sidewalls must have adequate supportfrom earthen banks that Thould be con-structed to an ele\,:tion of 10 to 15 cm(4-6 in.) above the topofthe lining.Thesebanks inlst be maintained to protect thelining from damage. I.inings also reducethe amount of land occupied hy thedit-ches and may provide some controlagainst damage hy rodents or burrowinganimals. iHowever, improved water con-trol isthe major benefit oflining. There isa reduction in watr storage and pondingand water moves through the system at afasterrate.

The most common types of lining forlarger canals are concrete and concretewiti masonry. Asphaltic liningsand corn-pacled soil materials are also being used.Limited use has been made of chemicalsealantsand plasticmembranes. [orsmallcanals and ditches, brick or rock masonrylinings are common in some areas. Theselection and construction of a lining isgoverned by: 1) the availability of thematerial, 2)equipment and labor requiredfor installation, 3)site of ditch, and 4)climatic and soil conditions. Chemoicalcomposition of the water may hea factor.Many times the initial cot governs thetype of ditch lining chosen. Iowever, t[leavailability and need for .water shouldalso be considered. FIluctuating watertables and intermittent streams of watercan damage linings. Tiledrains can be us-ed to lower the ,kater table below the hot-tom ofthe canal to prevent damage to thelining,

Livestock cat damage some liningsand, if necessary, special provisionsshould be made for livestock watering itsuitablelocations. Washing ofclothes andutensilsshould be anticipated and provid-ed for in some areas. Vegetation candamage some linings unless steps aretaken to control growth. Figure 6showssome types ofsmall channel linings,

1.Concrete Lining. Concrete liningshave many fine qualities. When properlyconstructed, and where site conditionsarefavorable, the liningswillgive longservicewith minimum repair and maintenancecost. They will withstand high watervelocities and are resistant to damagefrom animais, machines and man.Sulphate resistant cement should be usedwhen irrigation water or the soil containshigh concentrationsofsulphates. Instructions for preparation and mixing of theconcrete are given in Appendix 1.Concrete lining can be placed in manyI.handplaced by plastering on sides and bottom;2.using forms and pouring alternatepanels;3.pneumatically blown; or.precast concrete box part sec

tions; and5.slipform using heavy equipment(Figure 7a, b).The slipform method requiresverycarefulscheduling of operations and a largeamount of equipment, including atransitmixer for the concrete. For small canals,reinforcing steel isgenerallynot necessaryand theconcrete liningsare usually placedwithout it.In some areas, particularly India,Turkey and Egypt, precast sections areplacedmanually in thesmall farm ditches.Figure 8shows forms for casting small,rectangular sections. Precast concrete sections are usually manufactured at acentral place and hauled to the job site(22, 36). Precast sections may be madebox-shaped, semicircular, trapezoidalshaped or half-parabolic. The semicircular sections are usually made by pipe

companies, 1-2 m (3.3-6.6 ft) in length,46-61 cm (18-24 in.) in diameter. The sectionscan be placed above the ground surface, supported on cradle-type pedestalswhen needed to cross low areas. Parabolicsections20-30 cm (8-12 in.) wideare madein halves in Egypt, and when installedandmortared, can result in lined ditches witha range of top widths. This feature isdesirable since the same precast sectionscan be used for anarrow range of ditchsizes by varying the top width.


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13

b) Poured Concrete- Trapezoidala) RectangularBrick Masonryon aPoured Concrete Pad

c)Sprayed or Hand PlacedCement d) Precast Concrete-Semicircular,Mortar, Soil Cement or Parabolic or RectangularAsphalt- Parabolic

N '?

$5~ $

e) Precast Concrete (SCS photo ) Figure6. Types of linings for small canals (30).


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14

4

(a) (b)

'VF

Figure 7. Concrete lined canals. Lining with slipform (a) and (b), and thealternatepanel method (c)(25).


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15

When the concrete lining ishand placcJand the ditch isnot over0.6 m(2It) deep,the side slopes can be as steep as ',.tancyhorizontal to I vertical. (are iust be ex-crciscd with the concrete mix w it docsnot ,lui rlll ilie sItep ,ide'. Whellsteeper slope, or %citicalsideslalre tis-ed, foriii, at(: Ic(s)rtoldhe con-crete inl place:_ uni it -et,. Nolnrinlorced,concrce lisiny< li ..tica sides cin belsed r)I-e(plh , !ip t 0.5 Il (I .6 It). lhebottom and sidcs ,stlh;ild hae t ;iickicsof at least I cil ( in) and expansioncontractioni 1ilt"Mreneded.

Thealternatepancl mthod call he usedIo to) iiii e iniall paratb)lic andtrapc/oidal diichlue, and ciual'. ( , 36). [-rthese sections, tide ti> are tl'sed andtie secltin, are i)tld altrnaticly%\itithe finisited scCtioin, used IhIi fltr llit ill-,iunt cenuiiis' oie,, (I iul e if). Itilt


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16 1.2 Dio.2-5 Long M.S. Rod Pin

Sliding Pin -'0.5 Dio. -

i...5Hinge M.S.Sheet10OX4X0.58 Gauge

Wooden ".. M.S. Sheet 12 Gouge ThickSide Board 0"--

OUTER FORM

15-29 0 USE THIS FORM TO- _250.6 Dia.255

MS. Handle -N N N NNl3 i

Cover ' ,. 5MS.10Gae N N "N ,/4-45 NN NCROSS SECTIONWooden 15-22 FORM ASSEMBLYFF F R A Inner BoardINNER FORM

13-25

MAKE THIS SECTION100

All Dimensions in cm

5-2

PRECAST CONCRETE CHANNEL SECTION

Figure 8. Precast concrvte channel sections. Wooden forms used for casting (22).


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17

5. Chemical Sealants. Chemical 1.availability of water requiring divisealants havebeen used toreduce seepage sion, equitable delivery, and minilosses from canals only to a limited ex- mizing leakage, spillage andtent. Some have been used successfully, seepage,but otlrshave failed after a short life. 2.topography ofthe areaandavailablehydraulic head for the system,6. EarthenMaterials.Oneofthe oldest 3.size of area served by each canal,methods for reducing seepage losses and lateral and turnout,improving ditches isto remove the porous 4. amount of time each canal is usedearth and replace ii with clay material, and number of times each turnout isWhen impervious earthen material is used,found near the ditch, it may be used to 5. number ofturnouts and the amountsolve the problem. Ifthe material isslight- ofregulation for each, ly moist, and if it isplaced in 10-15 cm 6.need for regulating flow depths in (4-6 in.) layers and rolled and/or com- the system requiring permanent pacted, theeffectiveness ofthe lining will and/or temporary checking, begreatly increased. However, some clays 7.importance of minimizing head loss are subject to excessive shrinking and in the system, cracking upon drying and should not be 8.need for flow measurement, and placed as lining material. 9.availability of materials and labor. Bentonite clay issometimes used to line Social and economic considerations areditches. This material swells greatly when very important for the improved systemwet and is best adapted to ditches thatare and include:not subject to frequent wetting and drying. It is usually mixed with the surface 1.availability of skills and cost oflayer of soil with a disk or spike-tooth labor for construction and irriharrow. It may also be placed as ablanket gation,on the ditch bottom and covered for pro- 2.cost of materials,tection with about . cm (2 in) of sodl or 3.marginal cost or value of water,gravel. 4. availability of capital to finance theimproved system,2. Control Structures 5. organization, or lack thereof, of thewater users,Small irrigation structures must be 6.level of experience and understanadapted for use in particular areas depending ofthe users,ding on the availability and cost of 7.cooperative nature of the users,materials and labor. The irrigation 8.pride in ownership, andmethods, customs in the area and the ir- 9.potential thef t p roblems of therigation water delivery schedule are fac- structures and materials for othertors also. Small, low cost structures that uses.can be bt'Alt and installed with local laborand materials are desired. Control struc- In someareas domestic uses (washing andtures must be easy to operate, relatively bathing) and animal access must be conleak proof and give good, positive considered also.trol. Both permanent and temporaryportable ,tructures are discussed. The layout ofa small canal system withdifferent structures isgiven in Figure 9.ItPhysical layout, operational features, is diff':ult to separate small irrigationand socioeconomic factors should be con- structures into distinct categories sincesidered when selecting small, irrigation division structures may also serve ascontrol struc..ures. The important deci- checks and/Gr turnouts. For this publicasion considerations of thephysical system tionthe primary function ofthe structuresofdivisors, drops, checksand turnouts in- hasbeen used to categorize the structures.elude:


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18

TURNOUT

NMF:ASUMRN(. S >I' _- f

-.. 401 '7..U i rd-"

44

F- f

G)1 ....E:1'-1"p, .,., E'9. A,. n. Fv. fLINS

' teiK ; ,."e, .

6.

I rIPE .'I_. f. I_ ROI

I'igure 9. A fat i irrig~ationi .ssteni.


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19

a. Divi'ionStructures. ed and the middle divisor ismovable foradjusting the flow between the middleDivisors (diversion structures) are used chan:c!,. The divisor shown in Figure 10to sepirateaflow into twoor more parts, doesint al avsaccluratelv divide the flow,These striciCiressiml)ly divide the flow, in due to) the larc pier aidthe lov,velocityaditch intw the dcsircd meICasurcd or pm()- fHim, [)i,,irs that .,cc accurate propoitioinal pa ts. ldJc lly, ,,tcr lc,l and porti)li, d c tile hk)v, at a cmliirol secflow iMthe tillr ti)n ,j tipCicriticai fhlo , dcfini1i-015,,ti ctitroll- i iee (sec,cd and ii iasUtlcJ. lieCJili i,is OfI tIle tion tuils) cm'ii 1ich asthass,l'tlinoclp liii. are 11t icctirie i ihc_ -ictur.C c 11.I,, can I): acUraly,,di,,idedprlopoltli is a , ilIC dC.iI di,linofl v,thout ,,uper,_ritic l t s iif:i1tlicre is adi-char-. h_,cu ,, I the Illo,ituation. lir -trailhi approach Ups rn ; 2) thereIhc ol'piiii_,.lai K'r lor- iiKid isno b,.ackvatercffc,_t inthe d ,lwnstreamlunabletlc pCili. in t)ehe iccd I(1 IleC\- Channels, and 3) tilt' sctutinls, have

, Iac w,a 11icuhn -,(3).bifitv. IIO\\C'C, t) i . C"ttl uniori r.1 lledi,,i-,orshowndilsl , tlhe tilt Cd;"ii) d vl+nIi in 11, cffcctic Vs ao Piuioic tllhoilhfltv, eoiiditoit " c and cid ticldistillctdlis-atantae ah'- t 1111ifiLt di. I, ha, olstidaid. I Itc1 Itt ,,iHal 1(1oo r la.ree hyt1rulic hitad los- Most small ir-tiscd 1t diid tlie til., hCtv c.ten lii- riwatioii nee>tdllItoco ,erve headcdcic,. Ftiume II ;,)1(nm lkii /uumr /iI and i ini i/C k)"',.mie di, isor in Fig'urc,O h-re teillilc . Mm.trC+.ll , tilc I]\- II is l'nt-talkv nW lctI cildllC d.

44., i

Figure 10. IDi~isor I(o distribtite (lie t IoNN beINeen tIvo ditches (4).


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20

....

Figuire 11. D~ivisioni box b'r FUoN% to t'our (titct- (.S(* Photo).

In some area,, the amount of' vate-r macle at the hliadoIthe terhiarv canal aniddelivered to a t mniav v.ary, hut al! euitultittle Cistrihutioni1 serves a,a si , fordeliveries ,..thinthe ,ystcil are to remain dellivery. This method c(ltlic, that theproportional It)lie Yro s ao ItlIIl catnalnIL tertiary be dsigit, lhil ittdelivered. Ih.1, rc tsrlcl%LtO , lex elcis '


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-------------

21

The semimodular turnout shown inFigure 12 delivers equitable amountsreasonablywell. The entrance isshaped so that an equitable share of the flow isex-tracted. Exit conditions are s>uch thatchanges in down.stream ,aLtcr ievel, donot significantlv chanL' the dischargeover a ralgec of dom ll,,:cmijl depths.HIowever, the dischar P, re:dti dMhcnthe r Ioii ,M\ce.dt iaid0p


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22

d

(a) Present Field Outlets

d

(b) Improved Outlets Figure 13. D)ivisor-turnouts used in Egypt and India.

Sharp EdgeapEdge WS.in Deiv r

Flow -

SE CTION

Flow _.A djustable "-

PLANFigure 14. French-type proportional divisor (6).


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23

A simple typeof proportional divisor is are fastened to the surface, the area forshown in Figure 15 and has an adjLIstaJle 1oxN would be reduced by the widthof tihedivisor board. This divisor can be made two algle iron pieces. Stheet metal linerssermiportable (movable) roin vwood or for forimcd gare ,lots as )hownoil lIate2,metal and permanent froll HoncrCte or Appendi\ 2, ll hCben suc'C,fl also.masonry. Its usefulnesS is limited exceptas a means for temporarily dividing the Alotlier alterillti\toC I trucltlrc likeflow. The dcvice requires calibra.ition for [inure 18 ',wtuld be to(elimlinatC L'ate slotsdifferent settin, ofi the dli\Por board and entirely alld (1 ,C -labI gaile". Ihes 'different fio\'condiltion ... h er design Late ', %otld e placd iI trtpc/oidal orfor an adjustable di\ioi i,sio\% nillPlate rectalgular ,ction, and %kotildcomplcic-I,Appendix 2. o11truct 1m ashoitor parltiall 1hbin [inurC 19. Ibead"/lntanes are ease ofSeveral us 1)iC fthcwauv iiil III11oditches.r two (111d serillon\anl lie Thesmhill ivisnrsarc ,P(Ms n in 1[iLtures 16-IS. nesiLe LI in11citiaint Ctick 1 ad forThese .ltructre>u cit tCted iiI depth and po1iilit Man ibri rCm\cd-place to the inside dinnion, shown, 1 - for oher tL_,1.ing concrete, concrtce blocks, brick, orrock. The designs heen died to A rcent de' elopmnent of thea _e modlifprovide for an overflo\\ !ctlion ahose the [:A. () !dBaik (o)operatic Progate or )top log slots to a',ure that the gramell. is sllall irrination Strlictureswater ill not overflo\w Oltohe ditch fabricated Iron)l conct coiirpt ltsbanks, but that exceCsS Flow \ 1illpill into produced oll Cxtrus1in mai1ichics (9).the downstream ditch. They arc most Figure 20 Sho\,s a Jnil- consltctedoften used todivert the full incoming flow from the,'r/ib~rzUu'4r sections now beinginto one ditch or another. produced in InIdia. I o Sti/cs of

trap,.'oidal and rectangular sections areIn some are:as, structtlres Mith formed beiig produced h cxtrusion . Itollowgate slots and sliding gates are a source of blocks with uatecrooves are also beingproblems. The slotS become chipped and made.broken. Gates and s top logs become lostor stolen. When in use they Jam, leak and A conihination pump out let and divibecomeclogged with ,ediment and debris. sion structure isshovn in Plate 3,Appen-An alternative to the formed gate slots is dix 2. The wood (or metal) baftle isangle iron guides which are fastened to necessary to diffuse and still the flowthe inner face of the structtires in the same from the pipe.position as the slots . Since these guides


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, ~ DivisorBoard..... ."

.ingedoil

4" op0 1I -"" - .

(0.92m )_

Figure 15. Adjustable proportional divisor (see Plate 1, Appendix 2).


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25

(041m) J

(10cm)

4"Concrete Foundaton(F1cm)

Figure 16. Two-way concrete block divisor (12).

C'onc. Cap-4"' Concrete Foundation(l0cm)

I"X2"Slots 28&

Figure 17. Three-way divisor (12).


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26

/O6"'0... 1"X""SIO

(3X5rinY-'

((.

I55%

Figure 18. Concrete trapezoidal two-way divisor (14). (See Plate 2, Appendix 2).


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27

Top of Division Structure

ea Is / Flow

SlopingValIofDivisor or" 0Canal I \Flow(a) Trapezoidal

Gate Section\ Rubber zI Seals I '

Pipe or Rod Top of DivisorI oI I

L------------- ---------------Wall of Divisor Sectionor Canal (b) Rectangular Gate

Figure 19. Portablegates for divisor structures.

,.


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-00Top View

Isometric View

Section A-AFigure 20. Division structure using extruded, prefabricated sections (9).


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29

b. Drops (Grade Control Structures). left of the structure must be provided. Figure 24 shows a concrete drop and checkDrops are required to reduce channel structure under construction (a) andaftergrade whenever the natural grade would several years of operation (b). Rockresult in erosive flow velocities in unlined riprap can be used for a distanceearth channels. Drops are used to 1)con- downstream from the structure to prevent

trol the upstream water velociies to bank erosion. In someareas there may bereduce erosion, 2) drop the flow to a objections to water impounding in thelower level, 3)dissipate the excess energy, downstream apron because of mosquitoand 4) control downstream erosion, breeding. An opening in the lower sill isnon-Drops are particularly needed for newly often provided for drainage duringconstructed channels to reduce erosive flow periods. Plates4, 5,and 6, Appendixvelocities. After a period of time, the 2, give designs for trapezoidal drop strucbanks and bed may stabilize as the banks tures for drops ranging from 0.3-0.9 mbecome soddedwith grass, and dropsmay (1-3 ft).no longer be needed.For a steeply sloping chai

nel, erosion can be cotrolledby conveying water from on -.level to another in a stairstep . . ,.manner with drops (Figure21). Drops in series are .generally spaced so that thedifference in water surface -,rangeof"0.3-0.6 m (1.0-2.0 ft).levation at each drop is in the - -- - 4 -- O"r, ,The drop spacing may need to 7',...3t ...be modified if there a' - irrigation turnouts in the s-ries requiriLg a prescribed depth of " water between two drops.

Figure 22 shows selectedtypes of drop structures that , .can be constructed from con- 07crete, concrete block, brick orstone. T hese structures arc . -,quite effective but may be . .quite expensive to bui!d, particularly from formed con- .crete. Whcre water is to be diverted from one ditch to alower ditch or field, a drop ".>like that shown in Figure 23can be used. This structure is acombined turnout, check anddrop. The roughness blocks Figure 21. Drop structures used for grade control (4).(teeth) in the downstream section are used to accelerate the dissipationof energy and allow use of a shorter andshallower stillingbasin. Provision forerosion control in the earth channel to the


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30

V-~LAl o t j to.kSitI be I. ed ornorforb~dd o,


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31 The drop-check structure shown in developed ovcr along period ofyears byFigure 25 can be constructed ofconcrete, the USDA Soil Conservation Service areprecast concrete, or brick masonry. The shown in Appendix 2.Trapezoidal chutewall thickness isusually 7.5 to 10 cm (3-4 drops for ditch elevation changes ofin). For the small irrigation ditches, a 0.30-0.91 in (1.0-3.0ft)re given in Platesstructurewith an opening of60cm (2.0 ft) 4,5,6.Vertical, rectangular basin dropsshould generally be used. Optional side are given in Plates 7,8,9,10 forclevationwalls forthe stillingbasin are shown. The change. of0.15 to 0.61 m(0.5-2.0 ft). In

drop and check structure can be easily most cases, the smaller structures withconstructed with standard concrete block drops of0.30 in (I.0ft) or less do not re following the directions stated on Figure quire reinforcing steel for construction.26. The length of the stilling pool (L) Adequate cutoff walls arc provided atshould be at least twice the fall height (I/). either end of the structures to preventRockprotection isplaced at the end ofthe seepage and leakage which might causestilling pool to compensate for the the structures to be undermined. Theserelatively short pool. structures have many operational advantages, but disadvan.age intcluide high costConcrete dropstructures that havebeen and agreat aoun of labor to co mistrct.t

Figure 23. Drop structure combined with turnout.
http:///reader/full/0.30-0.91http:///reader/full/0.30-0.91


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32

44

No~te: Steel reinforcement must hesupported oil wire bridgesor small pieces of concrete so thatitsbove h1 wir/lC'. i.,roun.lFigure 24a. Forms fortrapezoidal drop structure ready for pouring concrete(SCS Photo).

'4, 1

4,a '

Figure 24b. Concrete trapezoidal drop structure(SCS Photo).


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33

Drive-thru irrigation drops made from can be used. For long life, the woodconcrete blocksand concrete are given in should be treated with a preservative.Plates 11 and 12 (Appendix 2). These Sheet meta! drop, can be made to thedrops are termed drive-through since one same basic dimeisions.set of wheels of tractor-powered ditchcleaning equipment can pass through the Drop-check structures made from thestructures. Since these structures are long cxtru(ded concretesections are shown inin length, wing walls are not necessary to Figure 27 (9). The opening in the reccontrol the seepage path. tangular check portion of the structure is30 cm (12 in) wide and the drop does no+In those areas where wood is available, usually exceed 30 cm (12 in).dropstructures like thatshown in Plate 13

J~

roo


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34

CheckBoard .Wooden Check Board, Metal Flange

Flow ConcreteBottom of Ditch -- BXBX16 Blocks

?../' [,i Crr,7rel3cm )Type of CheckfO/ptiona l MetalTie / / C Floor

Wooden Check H

/Metal Tie

8XBX16 0 eda

~ 4I Dig down as shown by survey2. Stock blocks to desired shape for correct.4location of wall and height of sill

3 Pour concrete In cares of blocks - eachH Lro e oapl

lotc 1 .0f2 t C.30mt 60rri4 Pourrand remnoiningFloor concrete for splash1.5"ft(.61m 3.0 ft 122n 5. Any steel (reinforcing ) in cores will12,0 f t (0.91m 4.0 ft 1.82 greatly strengthen the structure

Figure 26. Concrete block drop and check structure (21).


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-----

A

- I * ' i

Section A-A A12.0" \ End View

II II

-L-'Figr7 D c Isometric ViewFigure 27. Drop-check structureusing extruded concrete sections (9).


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36

In astudy made on the performance ofsmall drop-check structures (16) severalconclusions were made to aid futuredesigns.I. Commercial prefabricated struc-tures generally did not have ade-quate stilling basins.2. End sills and low tail water depthcaused excessie our de to wateridCasedi eXover thie end sills. [hecascadi r t il ee nd ilhScor grle Should be lined withrock or gravel.3. Wide basin.s performed better fordownstreamlscour pre,,ention.4. Trapezoidal basins operated s>tcessfullv only wi tl high tailwater.(Properly placed blocksio hrwould improve peration.)5. A nonaerated nappe (see definitionof terms) from the drop structureresulted in bcttei ,ilIn ,climch6. Headwall stRuCtur : % 1 ade t Ccutoff depth and "idiii siMiA gracl-lined basin or plain cp l"asef'fective andC 1l(!> (Ilic l051 e c e dCno l.

The structure describcd as a1111(Avullwithgravel-lii,(/ bu isi;%as erveffectiveas a drop. Only the %ertical wall of the

structure shown in igure 26 is used andcan he concrete or masonry. Precast concrete wkalls are quite comnmon andeconomicijal, buL are \cry heavv arid recltire hoists to place. [or ariasonrv wail,the ,hickrnrSo=tifcedloncet, 20 cur (12in.), unrcinre c-.doncre t ,20 cm (8 in.)and rinl'_t ,dcai nrte, M ce (4 in., Iopening or itli charnel ir n fastcned tothe edge, are u,ed %itfl stop logs to adjusteleation of the dro(p opening. [hCwidlhof he gravel-lined bain ,hIould be aboutt icthel ii catn all opcnniglcr de len 3l[lie enthe io e 1ehiot ac III l antotimes t dici c (ifp'all m aidnaiin llit all ihe b lalo\-,lal ditch capaciltCall ditch Iiiiiiall eh a


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37 A pipe drop structure is shown in It should be noted that many of theFigure 29. Capacities range from 65 /s dropscan also be used as water measuring(2.3 ft 3/s) for 25.4 cm (10 in.) diameter weirs. Drops like those shown in Figurespipe, to 154 1/s (5.5 ft3/s) for 38.1 cm (15 25 and 26 can be adapted for waterin.) pipe, both3.3 m (lIft)long operating measurement by carefully measuring thewith a 0.3 m (1 ft) water depth. The pipe width of the opening and the upstreamdiameter is sized specifically to maintain water depth. This function is discussed in

an upstream water level. The change in the sectiGa on measurement of flow.water surface elevation upstream todownstream of the pipe structure rangesfrom 0.30-0.91 m (1-3 ft) depending on c. Checks.thedesign. Concrete, asbestos cement andbaked clay pipe may be used as well as Irrigation ditch checks may be permacorrugated metal pipe. Riprap protection nentortemporary, portableorstationary.from erosion is usually needed on the They may check theentire flow orallow adownstream side. Disadvantages are that portion ofit to pass. The primarypurposethe pipe entrance is easily pluged with of a check is to increase the ditch storagedebris and the pipe alternately primc,: and and water surface elevation. Many times,breaks when the flow is less than the checks and drops are combined into one

PLAN ISOMETRIC VIEW OF CONCRETE SLABTop of Ditch Bank

D Corrugated MetalPipeDitchottom _ D,""_.,/

Watertight Level Line Ditch BottomWelded Joint

SECTIONAL ELEVATION ON CENTER LINE

Figure 29. Typical pipe drop structure (3, 21, 33).design flow, causing surging. One advci - structure so that a discussion of dropstage is that the structure can be used as a also applies to checks as indicated in theroad crossing, possibly using a somewhat foregoing section on drops.longer length ofpipe. Different designs ofpipedrops are given in Plates 14, 15, and16, Appendix 2. A variety ofchecks are used in both lined andunlinedditches. Thechecks are fit-

Chutes as drops can be cheaply con- tedwith checkboards, slide gates or otherstructed where rock is locally available, means for releasing a portion of the flowChutes as shown in Figure 30 are suitable while maintaining a desired water level. Itwhere falls (H)of 1.5 to 3m (5-10 ft) are is highly recommended that checks haveencountered. Fairly large rock, 15-20 cm an overflow provision so that the ditch(6-8 in) in diametercan be used, placed in will not be overtopped ifthe check is intwo layers. The rock layer extends above advertently left closed when turnouts arethe waterlineat theditch sides. The rough closed. This can be accomplished by prorock face ofthechuteassists in dissipating viding a weir overflow section on thethe energy of the falling water. A shallow check at an elevation lower than theditchstilling basin is desirable. bank.
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38

Flow._._,,, Not under 12"

Ditch Bed Line Stilling BasinH(optional)

I oM o r e "- Rock Drop=J 3XH

V Note:I. Gravel (If available) should bej used to fill between RocksDitch Cross Section 2. Rocks con be Grouted

Figure 30. Sloping rock drop structure (21).

, ,o-- -. * .) . .., 4., :. -

Att

Figure 31. Ditch check in lined ditch with siphon tubes.


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39 Several different types of ditch checks width is determined for the rectangularutilizing various methods to control the opening by the width of the ditch, bankflow are shown in Figure 31, 32, 33 and elevation, and maximum flow that the34. Figure 34 isa simlp check sructure structure will pass. However, the openingcombined with a turnool. Adequate ero- is usually 50-60 cm (20-24 in.) wide withsion protection for the bypassed f'low tilebottom within afew cen,],neters (5-10)must be provided downstream from a (2-4 in.) of the bottom of the ditch.check in the form of a basin, rock riprap, Checkboards in widths of 5-10 cm (2-4or a paved apron. Checks may be used for in.) are sometimes used to give incremenmeasuring irrigation flows using standard tal depths when required during an irrigaweir or orifice relationships (6, 35). It tion. Checks with rectangular or circularshould be kept in mind that when checked opening.,, are sized using the orifice equafor irrigating, the waler surface in the tion (6, 35) ith maxinum flow and aditch should typiclly he I10-I5 cm (4-6 small difference (5-10 cm) (2-4 in.) in thein.) above the field ground surface depth upstream and downstream from the(possibly more for piles and siphons). check. Inall cases the cutoff wall for theAlso a freeboard for the canal hank of 15 checks should project to a depth belowcm (6 in.) above tile water si",'ace raust be the ditch bottorn of 20Cmw(8in.) for claymaintained. This results in the top of soils and 30 cm (12 in.) for sandy soils.ditch banks being 25-30 cm (1M-I in.) The wall should extend into each bank

abovethe suLrron ndiriug g ro ndsurface. 20-30 cm (8-12 in.) at the elevation ofmaximum water level. With carefulSeveral simpl chwck.s that can be made backfilling and compaction, the checkfrom w ood, shect metal, concrete or should not "wash out."masonry are shown inFigure 33. The

Figure 32. Smallconcrete ditch check (21).


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40

Ditch Bank

- - - -. - - - L - - . -- . . . ..

(a) Top-opening Gate with Removable SectionCover

Ditch Bank- Opening

b) Center-opening Gate with Unit Slide Coverrl5tch Bank

(c) Bottom-opening Gate with Swinging Cover

Figure 33. Wooden ditch checks with different openings (19).


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41

GateBoardsRemoved

'' k Tu rno ut

Figure 34. Wood, single-wall check with turnout(19).


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42

Checksthat can be made from concrete Portable irrigationdamsare checks usblocksor bricktna.sonr set on a concrete ed to raise the water level in ditches forfoundation aregiven in Figures 35 and 36. direct irrigation. They can be made by theIn both cases, the bottom of the opening irrigators or purchased. Figure 37 showsashould be set at the level of the upstream canvas check with a sleeve for dischargingditch bottom. The depth and width of' part of the water. The sleeve can be tiedstructures will vary depend;.nc on the with a drawstring to control the flow to beditch but usually for small ditches they are bypassed. A pipe or long, strong stick isbuilt to the dimensions given in Figures 35 used acro',s the top. The canvas has alongand 36. The rubble or masonry spilay section upstream that is anchored in thebasin shown in Figure 35 should be set so soil and partlycovered to prevent leakage.that the bottom is5-7 cm (2-3 in.) below Plastic and rubber sheeting can be usedthe original ditch hottoni. The gravel lin- instead of the canvas cloth as shown ined plunge pool described in the section on Figure 38. The overflow section can bedrops can be used %,th acheck like Figure raised or lowered by turning and anchor36 it downstream erosion is a problem. ing the crossmember.The design of permanent, cast-in-placeconcrete checks isgiven in Plate 17, Appendix 2.

A>C36"

"-4"(10cm) Conc.F! " Foundation

Front View L..AI" m- Fr,',

F~u~b~eg 2' (cm x 5cm) Gap(Optono!) - 406em

" I- ." ....i' , .. on:_L _1 1rcrefe Cop

8"2 cn) .1 1 - 1 (9Cm) Conc' -'- -- ,,,, ojndot ont. ,(c r ,' r3(13rr A -ASection

Top View

Figure 35. Concrete block check with apron for erosion control (12).
http:///reader/full/depend;.nchttp:///reader/full/depend;.nc


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43

Ix2" ,' "

4 b

Figure 36. Concrete block check structure (14).


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44

?...6

/Foldand

Down Top 2"of'Double Stitch

Canvas 1/4x /4"Carstrip2

P Coole, L -----Jails Dounle

M ki "Reinfrcp

Soshcord forCloin

Op ; IJ trea,,m Face,and [Loubrle ' itch

SEAM DETAILSLEEVE

..

DETAIL

I)z,men,, for Crandos [-Jam1311es-6S0-me',.'O " c "2 7,-o

(j'-0 0X r 0 -'end

V "Gr m espaced equi64? r e tsdistant around

of Sleeve0

SLEEVE2-*

L.AYOU T

Fg, 3A.,, _. "./ /

Figure 37. Portable canvas check with discharge sleeve (21).


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45

177! .,, :,

Figure 38. Flexible, portable ditch check.Rigidandflexibleportable c'hck damts depending on availability. When the terare shown in Figures 39 and 40. The rigid tiary system has been designed to deliverdam in Figure 39 is made from metal and equal amounts of water, divisors used asdriven into the soil. Flow can then be turnouts are used as shown in Figures 12passed Jownstrearn through a gate. The and 13. These divisor-turnouts are comseries of dams in Figure 40a are flexible mon'y used in Pakistan, India and Egypt.and r-Ade from canvas. Siphon tubes areingr used to irrigate the area served bet- Turnouts and outlets are also used onween e... dam. Themetal dam in Figure the tertiary canals (farm laterals) for40bchecks the flow for discharge through water rel..'ase to the quaternary canalsthe upstream gateonto borders. When the (field ditches). They have gates or stopditch is in operation, this gate is held in logs for individual flow control (see Plateplace in the trapezoidal lined ditch by the 18, Appendix 2). These devices may alsowater pressure. serve as divisors as shown in Figures 17,18 and 20; drop structures, Figures 23, 24,d. Turnout, Outlets. 25, 26 and 27; and check structures,Figures 34, 35 and 36.When irri ation water is delivered fromthe distribut.ry or secondary canal to the Small control structures and devicestertiary canal, a gated turnout of some such as gated outlets are used to deliverdesign is used. Turnout structures are the water f rom the field ditches (quatersometimes similar to check structures but nary canals) to the farm fields. Devicesare placed into ditch banks to permit used for this purpose include siphonwater to be emoved from the ditch. A tubes, spiles (straight tubes), slots in linedrotation sv,,m of watcr delivery to the canals, andbank cuts in earth canals. Fortertiary :ana!s iscommon where thewater basin irrigation, regular outlet structuresis on fo:a prescribed number ofdays and like Plate 16, Appendix 2, are used tooff for a period. Variable amounts of deliver water to the field.flow are deliveredduring the "on" period
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46

/L4Ox4Omm (5x 15Ditch Bank

Water Level

Canal Bottom

'')7cm 120-180cm ,48'72 7cm

Angle Bar .O40x40 mmZ- 4E(1.5" )" \ D11 U!

Mt ll SECTION A-AMetallic Gotle-I

ELEVATION

Figure39. Portable metal check (21).

. *-

tN~

Figure 40. Two types of portablechecks (25).


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47

'unul or ditch guaes attached to p ipe thegate stem, theamoint of flow isdeter(Figure 41) arethe most common type of mined haed on prcvious calibrations. tUrnout. 1he .arema he aittachd to a concrete or itimt ',,hca(kall or Jirectl '1(a/I)i/' ulcs arcCoit olYV for'e.Ldto a steel, concrtc or platic pipc , ich tulrnout colltrl inI held outlets on lined protrudes thloulmif the dit:h Kink (se diths ( icure, 42a tnd 43). le gate."arc1Plate 19, 1 ,at, 1mio llijitte.1 i 1 t ila1-shapedppcrili\ 2). ttialll,,the[ l,1roI the ,ide,bittl placed o i tcip"ireti 'tbe concrete i itm l\ lined dithch and )tl dt llli t icld pipe ; thcew lltiltI lapcioidal lin11s. l )I (ie or alon ,cawe of o)perlit n ditch .'letilirie. (late", to pilpe, h lll(tllt111d attclcd caIl l [here alrr ltil . ()tcII ll\ d.'iried eithIr +e:rticIllv or 11 tl anulc, aildCtl he ditch gates iII tl'. I lleplate% uso,,%tlledth mo,,t ,._cases,;hlit II cine itcte',.i:n rock. he stlUl olrtitlld li teltl I \ elm,.'licit .'anti riprap \kill be neteed Lit tile pipe dischare he contollel'cd ,1 ant ljlat end t er,,i,. itdimensionitli rod om t)l atichand . as l Ii I in,14 . and l II a t I I I,,43. heel 1 aIIIre II- IiIi i

()te type (f /:/:: has been used as ()ii//'z bo,>'" are l ii init1res, 42/i.a tliiut al l aiti ticd ,iill tihe 44 and 45. lic.,e turliu tare eC rterllyl.,.S.,\. 5. fhlie di, tititcld t I tlie pipe limde.Ilrrnllt od but be,t l Iatllltel hehas ar ll) ,, tlar c,v ttlkiii t ipu d I te tue. lhie\ ;ti.' iportale ;itd Itiav c

-pipe L hio\I,, i ,lI, .resct\ tieirri;attir '1.eeded. IIlie 1otll. il. ithPot .. d,ceo , imt sltd he ,bat[reir,,,, lie fiCld 1utl,1tcevteestor I idie dter-itenc tile fWrarlt cIlwtid il tie CLtllil atlld -ipto 15 iii h flw- i t tiiit'Cer,,io0 .(c ll-trat ltio (t pipe c.tec. \Vitl Il'hct are tile rhow"s pritiularl\ adapted 1ordilfeCrricn' illi(1 d[tlie the larte flo\,snccd-d,itt borderatd basinv,)eads",ial areof galc op'ntitlu rittited h\ tie ri,,e itt irriationt.

Figure 4i.(ated pipe outlet.


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48

A (colnf'ie/lockuA lurtu ditch con- for 5, 10, 15 and 3()I , flo\ forama\structed from extruded block. for an itim flmo of 6() , (2.1 cf\).For corrcclunlined ditch I.sloAn IIin t-mr 46 (9). operalion, the parnlt canial should[he turnoul is combined with a check operate 'Aithinaprcribed depth with onstructure and 1tiltc, block Mith formed lv sniall fluctualioln. 10 ntIlltillI lie neargate grooves set on a 5cin (2 in.) thick collatl opcrat in.depth up-lirlal flotllcolrete slah. [rosion protection is need- the modulc, c.tllslill tipsI ortC,11led dowlsrcam hi011 do c . u-edrmhe' [turnout[. lus-,trane ,ie(eaoe inI111Cpar cllan a as -,lh1(M i1 inL t'ur47. I lie. 1'IPir//'Ct'C /?t0uc/It's 21),used ad ai ti,, s temCI (0i, taeC,, 0f ,,% are:I 1as intakes for seCCOndart aLd tertir\ atom.tic. Clati\ el \Cas otion.ttCaalsla, Iswk',ell as iarll trntllrOlsarc Jio\i 2) prc,ct di,,char'. miromwIts, and 3) llotlin Figure is a cas, to A i1h.7. Thc modulc metering tamllp \ii. di",ad an',tac',device with nmo ahl ,lidos ,tich can he arc: I)relai cil\e\pesi' e, 2) ,iiiijccl toopened singlyoriin mnltiplesto obtain tie clOtgeintig 'Ailhdcbris, attd .3)ctiiilCs andesired f'lowv. Typically, the sInaII alllost ct.an depthi ( \ iAi icl indistributor (mOdulC) has compartments tuFn requires depti cI iIl.

~IMM* "&' ." ' ..

*' .~ " :.~ ,.-- }:*'t "u" ''

iv"'

Figure 42. CommonIN usedI turnouts for farm irrigation ditches (SCS Photo) (25).


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49

3Rivets I"% I"Strop Iron

Bottom - 1"I -~ -2" H oI es *

3 D.C.3",C. WL1

GATEI 3 I4- 4 ~-9 Iron 114

. .- - Welded to Me!;h ,-.--- ---7 D Flow L

b .GUIDE DETAIL

SECTION1AL ELEVATI)r Wr I I i f i! 2 Z

Gale Gride as [-irectpd

L. . Additionol osDrill -Ho l r L - Needed-Not Port of END ELEVATION8 Structure Described PLAN H4K)

4"#10 (2Wires across TopH------IDE ELEVATION Mesh " .C,Min,\ -2"4"o0.C.Mox.

VIEW NORMAL TOHEADWALL

H, W Capraciti Rang

in Cm.. in . n cm cm ,n CfsC. ,n cIT s6 15.2 22 56 17 43 14 6 1 28 7 - 10 20-288 203 25 64 17 43

I0 25.- 2 -4 2 1 53 122 56 15 38 1.6-24 45- 5812 3051 33 84 2 1 53 125 64 15 38 24- 3 1 58 - 88

Figure43.Conc H',' (34).ipelurrlou


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--

50 t"x4"%2'- 2"

Ix% 4x I-I0,Ground Level

I" 3" Gole1Handle

2"X4"X3L6z/ _ Vx6


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__

51

H~ Flow-II[II I I i' - 0

Top View

12. CC(3 Jcm)

II

I 7I IIIiiLL___JJ

Section A-AFigure 46. Turnout-check struc!ure using extruded concrete sections (9).


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52

Constant Level Gate RubberSeal . -- "

. ....... Turnout

ConstantvlGate Module

ContaLevel

,\ ' , C n t aX': GateLel

Module

Figure 47. Neyrpic gates and modulrturnouts (6,21).


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53

Trapezoidalpanel outlets as used in be moist when placed and compacted inSpain and Pakistan (31) are shown in layers. A hand tamper should be used.Figure 48. They are precast fromconcrete For some installations a cutoff wall as and easily inserted in the ditch by the shown in Figure 50 may be needed, butfarmer. Forms are used for constructing forcohesive soils, the wall is probablynotthe panel and lid so that the two fit needed. However, since water leakagetogether closely for a minimum of around structures is a major problem,leakage. Outletsofvariable heights can be care should be exercised to prevent leaksconstructed. The outlets do not have an and possible loss of the structure.adjustment for variable openings andmustbe operated either fullyopen or fully Spiles are used to release irrigationclosed. This feature is not desirable for water from the head ditch into the fieldmany systems. for furrow or corrugation irrigation.Spiles are usually short pieces ofpipe in-Circularconcrete turnouts have been serted through the ditch bank. Normally,recently developed and are widely used in the spiles are installed each se aso nPakistan (Figures 49, 50and 51) (31). The although they can be left in place foroutlet gates are operated fully open or longerperiods. Figure 53 gives the generalclosed, which is particularly adapted to plan for using spiles and Table 4 gives thethe system. Irrigation water is rotated to discharge for sizes ranging from 1.0 cmeach farmer on Pakistan watercourses on (0.5 in.) to 10 cm (4.0 in.) in diameter.a weekly basis. Consequently, outletsfrom tertiary toquaternary ditches areus- Siphon tubes are widely used for fured frequently. The water is seldom divid- row and flood irrigation from l ined anded, so gatesdo notneed to regulate flows- unlined head ditches, as shown in Figure-only todirect it. Fieldsizes aresmall, and 54. Aluminum and plastic tubes are quitethus the conveyance system is extensive, common and are set manually over therequiring numerous outlets along the ter - ditch bank with each irrigation. Verytiarychannels. The turnouts are generally large siphons can be used for turnouts asused in pairs--one to check the flow in the shown in Figure 55. The flow is started usditchand theother todivert the flow. The ing a hand pump. The large siphons arecircular concrete turnouts also serve as useful for irrigating large, level borders.drops when opened in series along a ter- The discharge for individual siphon tubestiary canal, is given in Figure 56 and Table 4. Head isthe difference in elevation of the waterBecause cement, sand and bricks are level in the ditch and the discharge fromreadily available and local craftsmen are the pipe if flowing free, or the water leveltalented in constructing masonry struc- in the ditch and water level in the furrowtures, the outlet structures are particularly or field if the end is submerged.adapted to fit local needs. The circularpanel is precast using steel molds con- For conventional siphon tubes, asstructed locally. The lid is,cast in thepanel shown in Figure 54, there is need to resetand then ground smooth by turning the orreprime after an interruption offlow inlid in its panel to assure a light, relatively the supply canal. Siphon tubes areleakproof fit. Most of the supporting available that hold their "prime" afterstructures are brick masonry and are con- flow interruption, so that flow continuesstructed in place as shown in Figure 50. after the supply canal is refilled.Another turnout design using precast con- However, these tubes are quite expensivecrete sections is shown in Figure 51. The compared to the conventional ones.head !osses for a range of discharges andsizes of circular panel turnouts are given Be sureto set the di ,argeend ofspilesin Figure 52 (31). and siphon tubes as low as possible tominimize erosion. If there is erosion,To install, the soil placed around the cloth, sacking, plastic sheeting orstructures needs to be carefully com- vegetative material should be place underpacted to prevent washouts. Soils should the discharge.


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54

K- PANELM = 6m m = VARIABLEHEIGHTS , LID--

dM 2.5cm=43cm

65cm

41 cm--.-5m

19 cm

-70cm -

'----- ------FRONT VIEW

/, */5 cm 4.4cmCROSS SECTION

Figure48. Trapezoidal panel outlet (31).


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55

Grooves for Handles ReinforcingMdSeal 1-7Ba

Concave to Reduce WeightCross Section

PanelI/Enlarged Cross Section of the

Sealing Surface

Figure 49.Concrete orifice panel otlet (31).


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56

t '"-Optional

,'-.,, Cutoff

Isometric View

T0cm IBrickFlo0cm6cr

38cm

50cm-- 2 Brick

Panel ,,,

Floor

96cm-Top View

98cmSide View

Figure 50. Brick masonry installation for panel outlet (31).


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57

Isometric View0;i& //

I-91cm (35 8'' /Panel Shape for

---- Adjoining Structures

E /C-)/ 0/E/S rf)rf)0 L / ro - "](5. 6m(6" I

GroovesGrooves " 1 5.Pone,//66cm(26.0")

ii 31cm 56cm 2. 46 cm"(12 2")|' (220") 11."M- "-'-LO

5.7"

Side Sections (2) Bottom Section

Figure 51. Precast concrete slab installation for panel outlet. (31).


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120 2Flow Rate,

30 (cfs)

4 5

10-D=20 cm

(79in) 25(98) 30 (11.8) 35(138)

40 (15.7)

-4.0

3.5

E

600

/ 45(1773.0

25

_

0n

0 50 2.0 04 - '- I1.5

2 / 22.760 23.6 in.)

1.0

0.5

00 20 40 60Flow

80 100Rate, Q ( ps)

120 140 10160

Figure 52. Head loss through circular concrete turnouts of various diameters,1), flowing full, assuming a submerged orifice coefficient of 0.8(31).


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59Water Surface, Checked Water Surface, Unchecked

Ground Level

Water SurfaceWaterSurface, Top of Spiles CheckCheck Checked

C~ek"[3aom ofSlope 09001Wo ierSJrface, Unchecked 1 lIioror e t-,.',.r, ottornof First Spile and Unche!cked W'Nter Surface

HEAD DITCHFigure 53. Spiles used for fuirro, ,,rcorrugation irrigation (34).

7-. .j-- -,;

, ,4Figure 54. Siphon tubes for furrow irrigation.


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60

, 0 ilium."'.4.

I ;: 4 '" - .- z. I . *: -,, ' -, 3. , '.w#

........... i ,;:. .... - - ,

V.

- A bJ

it1-iurt- 55 lare 'Niphon%1ith priming pump for turflOut (SCS Photo).

-7


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6

isiphon Tubee/ h Tb Field DitchField [ /

Note:For Siphons Constructed of Metal,WaterSurface in Head Plywood or PlasticField or Furrow Discharge(Eps)

10 0.1 02 I 0.4 0.6 08, 1.0 2 4 6 8 108 ,i / K; , 2

"" - : bE"~ ./-' ..-- o. o/ .Q,,. (70 . ... I...... . ..I.. t- --" c--: .. -- . //./ .....

0.81.0 2 4 6 80 20 40 6080I00 200Discharge (gpm)

Figure 56. Discharge of siphon tubes (34).


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62 Table 4. Flow through small spiles and siphons (5).Diameter PresSure head (ceniimeters) of Spite ..... or Siphon 2.5 5 7.5 10 12.5 15 17.5 20

cm. I.iter,, per seconld

1 0.03 0.05 0.06 0.07 0.07 .O8 0.09 0.092 0.13 0.19 0.23 0.26 0.3(0 0.32 0.35 0.733 0.30 0.42 0.51 0.59 0.66 0.73 0.79 0.844 0.53 0.75 0.91 1.06 1.18 1.29 1.40 1.495 0.83 1.17 1.43 1.65 1.85 2.02 2.18 2.336 1.19 1.68 2.06 2.38 2.66 2.91 3.14 3.367 1.62 2.29 2.80 3.24 3.62 3.96 4.28 4.588 2.11 2.99 3.66 4.23 4.72 5.18 5.59 5.989 2.67 3.78 4.63 5.35 5.98 6.55 71.07 7.5610 3.30 4.67 5.72 6.60 7.38 8.)9 8.73 9.34Bank or ditch cutl, (notches) are the each held, o\er tile entire season. Watersimplest method for irrigating f'rom a incasirements can he made at the fieldhead ditch. FigLure 57 isaconcrete ditch and farm level by ,evcral means (4,6,7,with notches and small gates spaced fre- 21, 25, 27, 35). .\ sunniary of' thequently along he ditch. The least characteristics and ltintations of severaldesirablemethod isCUtS made in the earth methods isgi,,en by Hi/ (6).canal bank with ashovel. This method isprobably the least costly but result,, in a. W$eirs.variable flow rates and the channel bankcuts erode. Also, the refilled Cuts fre- (ne method of Measurement is to usequently leak or wash out. an existing drop, check or turnout structure as arectangular wir.Structures likeTo avoid num,.'rous cuts in the canal Figures 24, 25, 26, 32, 34, 35 and 36 canbank in farrow irigation, use small, tern- be adapted for mCasurenent by det, .,inporary .,'etditches.These are small ditches ing the \, idth of the opening aidmrounrunning parallel to the quaternary canals. ting astaff gage upstream to otain the The water isdiverted from the quaternary depth of flo, over the base of the opencanal into the set ditch by one bank cut, fig. Ior an accurate measurement, the or preferably, by some type of turnout. do,lnstrcatn water surface must he below Thewater isthendistributed bycuts in the the base of'the opening arid the nappe of set ditches to 6-12 furrows, depending on the jet must be aerated underneath. The conditions. This method is better than rectangularvseir equation Is having acut in the quaternary canals for each furrow, although siphon tubes are Q (I'I (2)the most desirable method. where Q discharge - In's (cfs)3. Water Measuring Structures C coefficient - 1.83 (metric)3.33 (English)width of opening, i (ft)On-farm water measurement has L =generally been ignored in many areas of andthe world, but isvery important forgood andirrigation water rnanagement arid use. h head over the weir, m(ft).Just as it is important for the farmer toknow ,iow, nLuch seed he plants, how Actually, Lquation 2is for asharp edgemuch fertilizer he applies, and how Much weir with adeep pool upstream, but usingcrop he harvests, lie should know how it as suggested will not result in asignifimuch water was applied to each crop, canterror in measurement provided thatIfand L are de'.ermined with care.


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63

Thestandardrectangularweiriseasy toconstruct and simple to use. It can be made from concrete, masonry, steel orwood but should haveametal blade (4,6,35), Figure 58. In the U.S.A., small rec-tangular weirs are usually made in stan-dard widths of 30.5, 45.7, 61.0 cm (1, 1.5and 2 ft) for which rating tables areavailable. A prescribed distance must be maintained between the tip of the weirblade and thebottom oftheditch and bet-ween the sides of the opening and theditch banks. Only the upstream measureofwater depth over the weir crest (Figure58) and aratingtable are needed to obtainthe discharge. One major drawback isthelarge head loss equirement to obtain anaccurate measurement. The downstreamdepth must be at some point below theweir blade elevation for correct measure-ment.

The 90-egree [,'-notch weir(Figure 59)has some advantages in irrigation watermeasurement (35). The water depth overthe bottom of the Visdetermined as withthe rectangular weir and the installationrequirements are similar.The V-notch hasthe advantage of being able to accuratelymeasure a large range of flows, particularlylow flows. However, thehead re-quirement is even greater than the rec-tangular weir, which can be a distinctdisadvantage.b.Hlumes.

Thereare several measuring flumes thatshould be considered when measuring ir-rigation flows less than 142 I/s (5cfs). TheParshall meusuring fh;me has receivedwideacceptance and isu.,ed in many areas(Figure 60) (6,21, 35). The 15.2 and 22.9cm (6and 9 in.) flumes have the desiredflow range and rating tables have beenprepared for them. The ParshaI! flume, as with other flumes, can be used while

submerged, i.e., when the depth of flowdownstream relative to that upstream isgreater than approximately 70 percent.This means that the lossof hydraulic headcan be considerably less than when usingweirs. This is a distinct advantagc. Requiremcnts, rating tables and cures fordischarge with ,arious degrees ofsubmergence are a,ailablc (35). [he Parshall flume can be constru, ted as apermanent installation %I.h concrete, masonry,metal and w.ood, or as aportable deviceusing metal, \,ood or fiberglass.

The Cutthru meauring./uuc' isanacceptable flume for irrigation uses. Itcan be constructed from the abovematerials and can he permanent or portable (27). The construction is muchsimpler than the lParshall flume sincethere isa flat bottom throughout and theparallel-walled throat section iseliminated (Figure 61). The 11unic willoperate under free- tlo\ or s'-ubmergedconditions, and thereare tablesandchartsavailable for determining the flow. The 4in. hy 3 ft and 8 in. by 3 ft flumes (27)cover the desired range of discharges forsmall gravity irrigation systeis.

The trapezoidul ./lume is used tomeasure flow in small systems (26). Thisflume, which has sloping sidewalls, wasinitallydesigned to bean integral part ofaconcrete-lined irrigation ditch(Figure 62).Flume F-I (26) has the desired flow rangeup to 5cls (14- l/s). It has aflat bottomthroughout arid 1:1 sloping sidewalls.Theflume can be constructed with concrete,masonry, metal, wood and fiberglass.Theadvantages are: 1) the shape fits the common ditch shape, 2) there isless head loss,and 3)it accommodates a large range offlows. The disadvantages are: I) itismoredifficult to construct, and 2) the cost isgreater than other flumes.


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-- - . -. 4... . . . -.* . . .,-.

>-. "..-..- 4.

-V 4- I

Iigure 57. oncrete lined ditch with bank cuts for irrigating


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65

oint to MeasureDepth (h)

4h min.

t.,,

VA-

Figure 58. Rectangular weir used asacombination measuring device and drop: "n structure (35).:..7\ . . '.. : ,

/Point to Measure4".,.'.'- / Depth (h)

.m h' .

scurety (35). r ot- we r

Fiur. 4ieydgreVnther(3)


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66

Figure 60. Parshall measuring flumes. (35).

Figure 61. Cutthroat measuring flume (27).


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67

Figure 62. Trapezoidal measuring flume (26).

Optional Staff - -4Gage -"Stilling Well - - for Recorder~~

-"-_- Concrete Lined~-'~- 4 CanalSurvey Point for Establishing

- Gage Zero ReferenceFigue6 a-w- .m s e g

Figure 63. Broad crested weir (b-c-w) measuring flume (7).


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68 A recent development has been the adapted for measirement by determiningbroad crested weir flume (b-c-w) (7), theareaoftheopening andthe flow depthwhich is particularly adapted for place- on theupstream and downstream sides ofmerit in an ex'sting lined ditch. Details of the opening. Figure 52 can be used tothe flume are shown in Figure 63. The determine the flow rate for the circularconstruction is simply a concrete block panel turnout (Figures 50 and 51).with an approach ramp placed with defined incremental heights; the correct height Forsmall flows, spiles andsiphon tubes

being determined from a design discharge (Figures 53 and 54) can be used for flowand corresponding normal depth of flow. measurement usingTable4 andFigure 56.Thc design discharge is usually the max- An accurate measurement of the pipe inimum sustained flow in the channel, side diameter and the hydraulic head isDepth of flow through the b-c-w flume is necessary.determined at a definitive point upstream

1

Figure 64. Flume for carr)ig irrigation water across a depression (SCS Photo).using astaffgage or water stage recorder. 4. Miscellaneous StructuresThe advantages are: 1)simple cois'_ruction, 2) 'idequate accuracy of measure- a. Cuherts, Bridges, umes, Cross..me t, and 3) low head loss at design ings, Sip howls . discharge. The disadvantages may be: 1)high head losses at flows less than design Open irrigation ditcles must havedischarge, 2)canal blockage, and 3)sedi- crossing structures so that people andment depositio

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