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Microirrigation design

United States Department of Agriculture. NRCS. Natural Resources Conservation Service. Microirrigation design. Oregon NRCS Engineering Meeting January 11-14, 2005. Over view Water requirement –System Flow rate Pressure requirement Component design. Wind breaks/trees. Orchards.

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Microirrigation design

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  1. United States Department of Agriculture NRCS Natural Resources Conservation Service Microirrigation design Oregon NRCS Engineering MeetingJanuary 11-14, 2005

  2. Over view • Water requirement –System Flow rate • Pressure requirement • Component design

  3. Wind breaks/trees

  4. Orchards

  5. Vine crops

  6. Nursery crops

  7. High Dollar crops

  8. Low Dollar crops

  9. Water Quality • Water quality factors can be divided into three major categories: • physical clogging caused mostly by suspended solids, • chemical clogging resulting from pH of the water, dissolved solids, sodium, calcium, magnesium and total iron and • biological clogging resulting from algae and bacterial populations.

  10. System Flow rate

  11. NRCS Standards Depth of application. • Net depth of application shall be sufficient to replace the water used by the plant during the plant peak use period. • Applications shall include adequate water for leaching to maintain a steady state salt balance.

  12. Depth of application . Fn = 1.604 QNTE AF Where: Fn = net application depth, in/day/design area Q = discharge rate, gal/hr/emitter N = number of orifices or emitters T= hours of operation per day, 22 hours maximum E = field application efficiency, expressed as a decimal, not greater than 0.90 for design purposes. A = ft2 of field area served by N (number of emitters) F = the design area as a percentage of the field area, expressed as a decimal 1.604 = units conversion constant

  13. System capacity. • shall be adequate to meet the intended water demands during the peak use period • shall include an allowance for reasonable water losses (evaporation, runoff, and deep percolation) during application periods. • shall have the capacity to apply a specified amount of water to the design area within the net operation period.

  14. System capacity Continued • should have a minimum design capacity sufficient to deliver the peak daily irrigation water requirements in 90% of the time available, but not to exceed 22 hours of operation per day. • Field application efficiency (E) for design purposes shall not exceed 90 percent.

  15. Number and spacing of emitters. • shall be adequate to provide water distribution to the plant root zone and percent plant wetted area (Pw).

  16. Wetted Area

  17. Percent Wetted Area • For widely spaced crops such as vines, bushes, and trees, a reasonable design objective is to wet at least one-third and up to one-half of the horizontal cross-sectional area of the root system. • smaller Pw is favored for economic reasons. • rows spaced less than 6 ft. (1.83 m) apart, the Pw may approach 100 %.

  18. Wetted area single row

  19. Wetted area single plant

  20. Components of a Drip system

  21. Subunit Design • Plant and emitter spacing • Average emitter flow rate and allowable pressure head variations • Desired number of operating stations • Overall length of plant rows in field or subset • Number of plant rows in field or subset • Field topography

  22. Emitter types • Long path emitters, • Short orifice emitters, • Vortex emitters, • Pressure compensating emitters, • Porous pipe or tube emitters.

  23. Emitter manufacturing variability The manufacturer’s coefficient of variation (CV) shall be less than 0.07 for point source emitters and less than 0.20 for line source emitters.

  24. Emitters • Flow is characterized by the following equation q=kPx • K and x obtained from manufacture

  25. Lateral Design • Types of laterals • Heavy wall drip line • Thin wall drip line • Drip tape • Polypipe with punch emitters • Polypipe with sprays

  26. Design Considerations • Select emitter/flow rate • Determine required operating pressure • Calculate friction loss • Quick estimate use multiple outlet factor • Manufacture’s software • Built spreadsheet • Decide whether to use single or paired laterals • Make adjustments • Check with flushing conditions

  27. Slope and topography

  28. Hydraulics F= multiple outlet factor L= length of lateral (ft) Q= lateral flow rate (gpm) Se= emitter spacing (ft) Fe= equivalent length of emitter connection loss qa= average emitter flow rate

  29. Emission Uniformity • Emission Uniformity Rating 90 - 100% Excellent 80 - 90% Good 70 - 80% Fair Less than 70% Poor

  30. Lateral Flow flat slope

  31. Lateral Flow 2% downhill slope

  32. Lateral flow 2% uphill slope

  33. Lateral flow varied slope

  34. Eurodrip program print out

  35. Lateral flow Plot

  36. System flushing. • Appropriate fittings shall be installed above ground at the ends of all mains, submains, and laterals to facilitate flushing. A minimum flow velocity of 1 ft/sec is considered adequate for flushing.

  37. Manifold Design Needed information • Flow rate • Inlet location • Pipe sizes • Inlet pressure • Flow variation • Emissions uniformity

  38. Below ground

  39. Above ground

  40. Allowable pressure variations. Manifold and lateral lines. • shall be designed to provide discharge to any applicator in an irrigation subunit operated simultaneously such that they will not exceed a total variation of 20 percent of the design discharge rate.

  41. Allowable Pressure Variations Greatest Emitter Discharge - Smallest Emitter Discharge x 100 Average Emitter Discharge • This is reported in Percent and must be less than or equal to 20%

  42. Flushing • Method • Manual • Manifold • Size • friction loss through manifold and valves • Frequency

  43. Flush Manifold

  44. Main line design • Size • system flow rate • pressure loss

  45. Filters • shall be provided at the system inlet. Under clean conditions, filters shall be designed for a head loss of 5 psi or less. • shall be sized to prevent the passage of solids in sizes or quantities that might obstruct the emitter openings. • shall be designed to remove solids equal to or larger than one-fourth the emitter opening diameter, or the emitter manufacturer's recommendations, whichever is more stringent

  46. shall provide sufficient filtering capacity so that backwash time does not exceed 10% of the system operation time. Within this 10% time period, the pressure loss across the filter shall remain within the manufacturer's specification and not cause unacceptable EU. • Filter/strainer systems designed for continuous flushing shall not have backwash rates exceeding 1.0% of the system flow rate or exceeding the manufacturer's specified operational head loss across the filter.

  47. Filter Design • Select Type • May need two • Pre-filter and primary filter • Size • Flow rate • Must account for pressure through filter • Must account for pressure required to back flush

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