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Sprinkle and Trickle Irrigation

by: Jerrell Nitzsche

Sprinkle and Trickle Irrigation BIE 5110

Marketplace > Utah State University > Biology > BIE 5110 > Sprinkle and Trickle Irrigation
Jerrell Nitzsche
Utah State University
GPA 3.51


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This 10 page Class Notes was uploaded by Jerrell Nitzsche on Wednesday October 28, 2015. The Class Notes belongs to BIE 5110 at Utah State University taught by Staff in Fall. Since its upload, it has received 13 views. For similar materials see /class/230409/bie-5110-utah-state-university in Biology at Utah State University.

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Date Created: 10/28/15
Lecture 14 Center Pivot Uniformity Evaluationl I Introduction The calculation ofan application uniformity term must take into account the irrigated area represented by each catch container It is more important to have better application uniformity further from the pivot point than nearer because the catch containers at larger distances represent larger irrigated areas lfthe catch containers are equally spaced in the radial direction the area represented by each is directly proportional to the radial distance Equation for Center Pivot CU The equation for CU proposed by Heermann and Hein is ASAEANSI S436 Zn rd Zin1diri i1 39 39 n i1ri n Zi1diri where CU is the coefficient of uniformity di is the depth from an individual container ri is the radial distance from the pivot point and n is the number of containers CU1OO 10 295 First calculate the summations Z m and 2 din Then perform the outer summation to determine the CU value That is don t recalculate the inner summation values for every iteration ofthe outer summation it isn t necessary It is usually considered that a center pivot CU should be greater than 85 296 lfthe radial distances ri are equal the sequence number of the can increasing with increasing radius can be used instead ofthe actual distance forthe purpose of calculating application uniformity Consider the following two gures Sprinkle amp Trickle Irrigation Lectures Page 169 Merkley amp Allen s ope catch containers catch contain level eld no wind CU 100 Merkley amp Allen Page 170 Sprinkle amp Trickle Irrigation Lectures Standard Uniformity Values ou cah atso catcutatethe stahdard cu or DU ttvou wetght each catch ce the tow tu rank the uhwetght surhrhthg radtt begthhthgwtth the radtustor the towest catch vatue uhttt the curhutattve vatue ts approwrhat v uat to tt otthetotat curhutattve radtus Thts rh or rhav hot be uat to tt otthetotat catch vatues because each catch represents a dtttereht ahhutar area ot the rtetd Ftrtatty dtvtde the sum ot the catches ttrhes the radh tor thts approwrhatetv tt area bv the curhutattve ra tus Thts gtves the average catch ot the tow tt Ht Ht u get htgh tor sorhe reaaort ahd vour ahswerwttt be wrong Don t catcutate the average ot the tow tt ttke thts because the towest tt ot the catches geherattv represents 4 sorheththg dtrrereht thah tt ot the trrtgated area Actuatty the eguattoh at the rtght ts att rtgm except tor the vatue hzt x whtch ts probabtv the wrong number ot ranked vatues to use th represehtthg the tow tt You can set up atabte ttkethts th a spreadsheet appttcattoh same depth vatues sothatthe radtusvatues wttt how be uhrahhed x att mtxed u To get the average wetghted depth tor the whote ptvot area dtvtde the totat Cumutattve dr bvthetotat Cumutattve r coturhh 5 dtvtded bv c rm 2 Ftrtd the row correspohdthg ctosest to tt ot the totat Cumutattve r vatue and take the same ratto as betor e to get the wetghted average ot the tow tt area 9 Look at the exampte data ahatvsts betow Page t7t Metktey StAHert 11055 22110 Merkley amp Allen Page 172 Sprinkle amp Trickle Irrigation Lectures Weighted Catch Values Notice that the depth values 3rd column are ranked from low to high Notice that the maximum value of cumulative r is 44220 amp maximum cumulative dr is 87784 Then the weighted average depth for the entire center pivot is equal to 8778444220 1985 whatever units One quarter of 44220 is equal to 11055 which corresponds most closely to the row in the table with depth 172 Forthe same row divide the two cumulative columns Col 5Col 2 to get 1604710760 1491 which is approximately the average of the low A Finally estimate the distribution uniformity for this data set as 1491 DU 2100 g 75 297 1985 Note that in this example the average of the low A was in fact based on approximately the first n4 ranked values Consider the weighed catchcan data plotted below 14000 12000 10000 8000 6000 4000 2000 Distance from Pivot Point As in any application uniformity evaluation there is no right answer The results are useful in a comparative sense with evaluations of other center pivots and other onfarm irrigation systems However a plot of the catches can give indications of localized problems along the center pivot radius Sprinkle amp Trickle Irrigation Lectures Page 173 Merkley amp Allen IV The Field Work It may take a long time for the full catch in containers near the pivot point and because these represent relatively small areas compared to the total irrigated area it is usually acceptable to ignore the inside 10 or 20 of the radius The pivot quickly passes the outer cans but takes longer to completely pass the inner cans so you can collect the data from the outer cans sooner The pivot should not be moving so fast that the application depth is less than about 15 mm Catch containers can be placed beyond the physical length of the lateral pipe but ifthey are so far out that the catches are very low these can be omitted from the uniformity calculations Catch containers should be spaced in the radial direction no further than about 30 of the average wetted diameter of the sprinklers There is often an access road leading to the pivot point for inspection manual operation maintenance and other reasons fthe crop is dense and fairly ta eg wheat or maize it will be difficult to perform the evaluation unless the cans are placed on the access road OthenNise you can wait until the crop is harvested or do the test when the crop is still small Some people recommend two radial rows of catch cans or even two parallel rows to help smooth out the effects ofthe non continuous movement of towers they start and stop frequently to keep the pivot lateral in alignment Some have used troughs instead of catch cans to help ameliorate this problem Note that if the eld is sloping or undulating the results from one radial row of catch cans may be quite different from those of a row on another part of the irrigated circle See Merriam and Keller 1978 Merkley amp Allen Page 174 Sprinkle amp Trickle Irrigation Lectures Linear Move S stems I Introduction 0 Mechanically a linear move system is essentially the same as a center pivot lateral but it moves sideways along a rectangular eld perpendicular to the alignment of the lateral pipe 0 The variation of ow rate in a linear move lateral is directly proportional to distance along the lateral pipe whereas with center pivots it is proportional to a function of the square of the distance from the pivot point 0 A center or end tower sets the forward speed of the machine and the other towers just move to keep in line with the guide tower this is like the far end tower on a center pivot 0 Usually each tower is independently guided by cables and microswitches as for a center pivot this keeps the lateral pipe in a straight line aligned with itself 0 Alignment with the field is usually not mechanically enforced but it is monitored through switches in contact with a straight cable along the center ofthe eld or along one end of the eld 0 The center tower has two quot ngersquot one on each side ofthe cable usually slightly offset in the direction oftravel they aren t side by side The ngers should be in constant contact with the cable if one is lifted too far a switch will be tripped shutting the system down because the whole lateral is probably getting out ofalignment with the eld 0 lfthe cable is broken for any reason this should also shut the system down because the ngers will lose physical contact 0 lfthe lateral gets out of alignment with the eld and shuts off it will be necessary to back up one side and or move the other side forward until it is in the correct position 0 This can involve electrical jumps between contacts in the control box but some manufacturers and some installers put manual switches in just for this purpose Some linear moves are tted with spray nozzles on drop tubes or booms lfthey are spaced closely along the lateral it may be necessary to put booms out beyond the wheels at tower locations either in back of the lateral or on both sides ofthe lateral Water Supply 0 Water is usually supplied to the lateral via 1 a concretelined trapezoidalsectioned ditch or 2 a exible hose often 150 m in length or 3 automatic hydrant coupling devices with buried mainline Sprinkle amp Trickle Irrigation Lectures Page 175 Merkley amp Allen Hosefed systems require periodic manual reconnection to hydrants on a mainline it is kind of like a periodmove system and you have to ask yourself whether the linear move machine is worth the cost in this case V th the automatic hydrant coupling machines see Fig 153 there are two arms with pipes and an elbow joint that bends as the linear move travels down the eld The two arms alternate in connecting to hydrants so as not to disrupt the irrigation nor the fonNard movement of the machine These are mechanically complex The advantage of hosefed and automatic coupling linear moves is that you don t need to have a small uniform slope in the direction oftravel because water is supplied from a pressurized mainline instead of an open channel On ditchfed systems there can be a structure at the end ofthe eld that a switch on the linear move contacts shutting down the pump and reversing the direction of movement so that it automatically returns to the starting end ofthe eld The advantages and disadvantages of the ditchfeed system are m 0 Low pressure energy requirement 0 Totally automated system c More frequent irrigations than hosefed since no one needs to be available to move the hose Cons 0 Trash and seeds and sediment pass through screen and may plug nozzles o The pump must be on move with the lateral causing extra weight 0 Should have uniform slope along the lateral route Pros and Cons Compared to a Center Pivot Pros Easy irrigation of a rectangular field important if land is expensive but not important if land is cheap and water is scarce Application rate is uniform over length of lateral rather than twice the average value at the end ofthe center pivot o No end gun is required Cons o The lateral does not end up right back at the starting point immediately after having traversed the irrigated area you either have to deadhead back or irrigate in both directions 0 May be more expensive than a pivot due to extra controls pump on ditch feed or more friction loss in the exible feed hose the hose is fairly expensive Merkley amp Allen Page 176 Sprinkle amp Trickle Irrigation Lectures II System Costs Relative costs for linear move systems are 50000 for a 1280ft hosefed machine perhaps 160 acres 55000 for a winchtow hose fed 1280ft machine perhaps 160 acres 55000 for a center pivot 1280 ft m a corner system about 150 acres 140000 for a 12mile 2560ft linear with automated hydrant coupling system no ditch or hose required The mainline is down the middle a 1A mile lateral on each side Perhaps 320 acres or more irrigated Ill System Design 0 A main strategy in linear move design isto minimize the cost per unit area This is done by maximizing the area covered per lateral length of field Generally the lateral length is limited to 400 to 800 m Therefore the major dif culties and objectives in linear design are to Maximize the irrigated area per lateral this minimizes area In other words how large a eld can be irrigated by one machine 2 Prevent runoff by matching ARX with lsoil SSti this tends to limit the eld length because if AR is small it won t be possible to nish in f39 days where 88 is the allowable surface storage in mm or inches and ti is the time of irrigation 3 Determine whether spray nozzles can be used without causing runoff 4 Minimize labor for moving hoses and supervising m lt 1 K j as long as pOSSIble The allowable surface storage 88 is the maximum amount of ponding without incurring surface runoff 0 SS is a function of the general topography and the microtopography and of the amount of foliar interception water can pond on the crop leaves too Sprinkle amp Trickle Irrigation Lectures Page 177 Merkley amp Allen 0 SS is usually less than about 5 mm unless small basins are created along furrows for example 0 ARX limits the field length because it corresponds to some minimum time to nish an irrigation for a given gross application depth whereby a maximum interval f is calculated in the preliminary design steps Lateral Inlet Head 0 This is the same as for periodicmove systems 0 The pressure balance equation for linear move systems is similar to set systems both are linear with uniform discharge from each outlet minor hf hose 298 P 3 1 HI a hf Hr AHe hf y 4 2 0 Or if using ow control nozzles with a minimum pressure required at the end assuming the minimum pressure occurs at the end P H eTnd hf Hr AHe hf minor hf hose 299 where Hr is the height of the lateral or spray boom above the ground and hfminor are the hydrant coupler and tower connection losses 0 The parameter hfhose is the loss in the exible hose connection on a hose fed system 0 Note that hfhose may be a major loss since the hose diameter is usually less than 5 or 6quot Q 1852 hf khFLEJ Dquotquot87 300 where kh 1050 for hf and L in ft Q in gpm and D in inches Kh 121 1010 for hf and L in m Q in lps and D in mm F is the multiple outlet friction factor for a linear move F m 036 o For hosefed systems the maximum hose length for dragging the hose is 220 ft Therefore there could be about 400 ft between hydrants o For hosefed systems with a cablewinch system for assisting in dragging the hose towers only have a moderate amount oftractive power the maximum hose length is 330 feet 640 feet between hose hydrants 0 Flexible hoses normally come in 5inch 18ft and 6inch 25ft diameters o The HazenVWliams C value for the hose can usually be taken as 150 Merkley amp Allen Page 178 Sprinkle amp Trickle Irrigation Lectures


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