section 24 – irrigation system planning & design...
TRANSCRIPT
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Irrigation System Planning & Design ConsiderationsProper system planning and design is essential to Irrigation Water Management (IWM) and requires the thoughtful consideration of many elements. Selecting a system must include the following major items: Management, water, soil, and crops.
1. Management – The irrigator and planner need to collaborate in order to develop the best plan. The discussion of desired system type needs to include an understanding of management, operation, and maintenance requirements.
2. Water – The source, whether surface or ground, and the quantity, quality, availability, and flow rate, are needed to determine the type of system that is appropriate. Most sources of ground water require power, no matter which type of system is planned. With microirrigation, a ground water source might only need an inline screen to clean the water while a surface water source would require a sophisticated filtration system. Some sources, due to high salinity (EC), may not be suitable for sprinkler irrigation. A microirrigation system works best with a constant source while a surface system can operate on a longer interval between water applications. A surface system, in turn, requires a relatively high flow for most efficient application, while sprinkler or microirrigation systems can function well at a lower rate of application.
3. Soil – Many soil qualities are important when planning an irrigation system. Soil texture is a good indicator of water holding capacity (whc), permeability, and transmissivity. Whc is particularly important when considering a surface system, due to intervals between irrigations. Permeability plays a key role in surface system design, and to a lesser extent, sprinklers. Transmissivity, the ability of water to move through the soil, is important when considering a point source of irrigation, such as with drip emitters. The water needs to be able to move into and through the root zone.
4. Crops – Selection of crops to be grown can be limited due to water quality and quantity. High salinity (EC) can cause yield reduction and even crop failure, depending upon the crop planted.
Other important considerations should include growing season and location.
1. Growing season - The length of growing season is important for crop selection and also is important for justifying the expense for any system planned
2. Location - System structures and hardware must be able to withstand climate extremes of temperature, humidity, precipitation, or wind. Proximity to wildlife, cattle, and humans also suggest necessary precautions to consider.
Proper planning can help ensure that the best system will be installed. RDFISCHER March 08
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IISS –– 22 –– CChhoooossiinngg aann IIrrrriiggaattiioonn SSyysstteemm
This Chapter Includes:
Methods of applying water
Basin or Level Border Irrigation
Effect of land slope Requirements, Considerations, Advantages/Disadv tages
Su face Irrigation s
Furrow Irrigation
lood Irrigation
Corrugation Irrigation Graded Border Irrigation
an
r
Wild F
Method
Surface Irrigation Systems
Method
Adapted to Conservation Features Eff. %
Basins or Level Border
Close-growing crops on flat land with sandy soils.
Provides good control of water applied. Good for alkali control.
60-80
Graded Borders
Hay or grain on uniform slopes up to 3%; established pasture on uniform slopes up to 6%. Best adapted to light soils.
Provides uniform wetting and efficient water use. Utilizes large water streams safely and thus less time is required to cover area.
60-80
Corrugations
Close-growing crops on sloping land with soil slow to take water. Extreme care is needed in applying water to slopes of more than 2%.
Provides uniform wetting and prevents erosive water accumulation on land too rolling or steep for borders or basins. Makes use of small streams.
40-55
Furrows
Row crops, truck crops, orchards, vineyards and berries on gentle slopes with all but coarse-textured soils.
Provides no conservation features unless furrows laid on nearly level land on the contour and water applied with extreme care.
60-80
Controlled Flooding
Close-growing crops on rolling land; pasture sod established by corrugations or sprinkler.
Provides water control and fairly uniform wetting where land cannot be used for other methods.
65-80
Wild Flood
Water is allowed to flow over the land without the use of furrows, borders or other structures.
Provides little to no water control and non uniform wetting on sloping and rolling lands.
25-40
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Factors Affecting the Selection of Surface Irrigation Systems
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3
Sprinkler Irrigation Methods
Center Pivot
Hand Move Linear Move Center Pivot
4
Big Gun Traveling or Stationary Side Roll Solid Set
Sprinkler Irrigation Systems
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5555--6655
5
Factors Affecting the Selection of Sprinkler Irrigation Systems
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* Irrigation water shall be available on demand or if on rotation sufficient water storage is required! *
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Trickle Irrigation Methods
7
Surface Trickle
Subsurface Trickle
Micro Spray or Mist
Trickle Irrigation Systems
Method Adapted To Conservation Features Eff. %
Surface Trickle
Subsurface Trickle
85-95
Micro Spray or Mist
All terrains and most agricultural crops and soils
including steep or rocky ground that is unsuitable for
other forms of irrigation.
Permits storage of water in lower part of soil profile, good control over timing and water
application, less water required, chemicals and fertilizer are
efficiently applied, runoff and deep percolation are controlled, can be used on soils with low
infiltration rates and low water-holding capacity. Easily
automated. 85-90
Factors Affecting the Selection of Trickle Irrigation Systems
Adaptable to
Type of System
Max. Slope (%)
Max. Water Intake Rate Soils
(in./hr) Shape of
Field
Orchards and
Vineyards
Row Crops (row or bedded)
Sown, Drilled or
Sodded Crops
Labor Requirements
(hrs/ac)
Approx. Cost ($/ac)
Surface Trickle
No Limit Any Yes No No
Subsurface Trickle 5 1.5 No Yes Yes
Micro Spray or Mist
No Limit Any
Any Shape
Yes No No
0.06
8
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Improving Efficiencies of Existing Irrigation Systems
Irrigation System Ways to Improve Efficiencies Decrease the set time or irrigation frequency Land level fields or modify the slope Use gated pipe or cablegation Use surge irrigation Cutback inflow Use furrow diking
Surface
Reuse tailwater Check for leaks in the system Change out worn sprinkler heads or nozzles Use an irrigation timer Sprinkler Decrease set time or irrigation frequency Check for plugged filters Don’t over estimate water requirements Address plugging problems in emitters Trickle Avoid excessive backflushing
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SSuubbssuurrffaaccee DDrriipp IIrrrriiggaattiioonn aanndd IIWWMM
Subsurface Drip Irrigation (SDI) is one of several types of Microirrigation (Conservation Practice Standard 441). It is a planned irrigation system in which water is applied directly to the root zone of plants by means of applicators (E.g. orifices, emitters, and porous tubing) placed below the ground surface. It is operated under low pressure. It is one of the more advanced irrigation methods in use today. It is potentially more efficient than flood or sprinkler irrigation, due, in large part to reduced evaporation.
Basic requirements: An operational SDI system involves a pressurized water distribution system and includes a variety of components such as pumps, valves, filters, chemical injectors and a distribution system of solid pipes and flexible tape or tubes.
Advantages: SDI has gained attention during recent years. SDI systems can apply water and nutrients directly to individual plants or trees, reducing the wetted surface area to a fraction of other types of irrigation systems.
• SDI is a low pressure, low volume irrigation system suitable for high return value crops such as vegetable and nut crops. • If managed properly, it can increase yields and decrease water, nutrient, pesticide, and labor requirements. • SDI applies water to the plant’s root zone reducing evaporation losses. • Weed growth is reduced. • It has a high distribution uniformity allowing for high application efficiency. • SDI can irrigate sloping or irregularly shaped land areas that cannot be flood irrigated. • There is no runoff which results in reduced soil erosion or wasted water. • Limited deep water drainage (with proper scheduling – management). • High Fertilizer efficiency: Fertilizer is applied directly to root area and can be applied at any time and any dosage without wetting plant
foliage. Any water soluble fertilizer may be injected through a SDI system. • Yields are typically increased. Soil moisture and fertility in root zone can be maintained at optimum levels. • Fewer tractor passes through field
Disadvantages: As with other irrigation methods, concerns arise and SDI is no exception. Some concerns include initial system cost, power cost, emitter uniformity, system hygiene, longevity, fertility, maintenance, germination, crop performance, and rotation into other crops.
• SDI requires a heavy initial investment. Presently, initial start up cost is between $1,200 and $1,500 per acre. As an example, amortizing a loan at 8% interest rate over a 10 year period amounts to 22% of the initial investment that must be recovered every year. This, along with other costs, has to be compared to the benefits.
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• As with anything, there is always apprehension about the decision to convert to a something different. A sizeable personal effort is required to understand the anticipated outcome as well as the operation and maintenance of a SDI system.
• SDI requires a higher skilled labor than most other irrigation systems. • The systems must be carefully designed to ensure proper emitter and row spacing for the crop grown. • Maintenance of the system must be performed in order to ensure the investment for the planned service life of the system. • Soil salinity issues must be addressed as well as the effects of excess calcium carbonate dissolved in the irrigation waters. • Filtration is critical. Emitter clogging will affect distribution uniformity. Algae growth and scale build up (CaCO3) must be controlled.
As with all systems that use filters, provisions must be made for utilizing the flush water. • Components can be easily damaged by vandals, rodents, or equipment operator error. • Few pesticides are available for injection. • Water must be available on a regular basis.
Micro Irrigation Methods for SDI and Other Systems Micro-irrigation can be the most water efficient of all systems. The irrigator has a high degree of control over the way water is applied. These systems must be designed, installed, operated, and maintained carefully. Systems are prone to clogging and need clean water. Water applications are so light and frequent but can be operated to ensure a full root zone. Soil moisture must be managed carefully throughout the season. Point source emitters: The numerous emitters available apply water in drops or trickles, spray or mist (micro-sprinklers), or small fountains (bubblers). Emitters are generally placed in or along polyethylene tubing and dissipate water pressure through the use of long paths, small orifices, or diaphragms. Some emitters are pressure compensating, designed to discharge at a nearly constant rate over a range of pressures. Most drip emitters are designed to be used above ground.
Line Source emitter systems (Also known as drip tape or tubing):
Line source emitters are basically flexible tubing with uniformly spaced emitter points. Some drip tape emits water through small laser drilled holes. Other drip tape designs (turbulent flow tape) include equally spaced tortuous path emitter devices within the tubing. Some drip tape is designed for above ground use, while other types may be buried.
Basin Bubblers: Basin bubblers apply water in a small basin or depression in the surrounding soil holds the water to allow infiltration. Basin bubbler systems are more applicable in orchards.
Spray or Mini-Sprinklers: Spray or mini-sprinkler systems emit droplets from small, low pressure heads. Some micro-sprinklers have spinners, while others contain no moving parts. These systems cover a wider area than most drip emitters, with a typical wetting diameter of two to seven feet. Mini-sprinklers are less prone to clogging than point source emitters. Typical systems in the southwest utilize groundwater, although surface water can be used.
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The following pictures show a typical SDI system. - Luna County
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Design Requirements for Subsurface Drip Irrigation - Irrigation System, Microirrigation (441): An irrigation system for distribution of water directly to the plant root zone by means of surface or subsurface applicators. This practice will be designed in accordance with all federal, state and local laws and ordinances. Micro irrigation Systems shall consist of acceptable pipe design and layout to distribute the water in a uniform manner for the intended life of the practice. Resource inventories, local conditions and the intended use will need to be assessed for the proposed Micro irrigation System design and location. A Micro irrigation System design will be developed with the client that meets the intended goals and objectives. All materials shall be of high quality. All appropriate job sheets, maps and reports must be developed with landowners input, review and concurrence (See Practice Standard, Specification and Job Sheet 441). The important components of a drip irrigation system include a water source, pump, backflow preventer, injector, filter, pressure regulator, valves, and a distribution system of pipes (main and submain lines) and tubes (laterals). Solenoid valves and a controller can be used to automate a system. The minimum system capacity shall be adequate to deliver the average daily water requirement during the peak use month in not more than 18 hours of operation. The system design capacity shall be adequate to meet the intended water demands during the peak use month for all plants planned to be irrigated in the design area. Design capacity shall include an allowance for reasonable water losses (evaporation, runoff, leaching requirements, and deep percolation). Determine the volume of water available and the maximum flow rate of that water. Currently most SDI system are being planned and designed by private contractors. The following information sheet is what the SW Area Engineer is requesting that the contractors provide upon review approval.
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Design Area (Plan Map) Submain/manifold Producers Name All Calculations & Input Structure locations, well locations (water supply location) per block Dimensions – elevations - slopes - scale pressure rating & pressure in pipe Block Layout type (diameter, type, etc) North Arrow length (from mainline to lateral total lengths of lateral) Water source and available Q layout (location) Location of Pressure relief & air relief valves show lateral location Location of all appurtenances Velocity & Q Crops Laterals Cu of crops All Calculations & Input How many blocks will be irrigated simultaneously # laterals / block how much time to irrigate each block or set spacing Maximum velocity 5 fps in pipeline type of drip tape - size, weight, etc Drip System (Design) emitter spacing All Calculations & Input Emitter flow rate @ __ psi according to manufacturer Filter System emission uniformity System Q distribution uniformity Capacity of filter & requirements of filter Total Q per lateral & block Chemigation-injection Flush lines All appurtenances required (well, filter, flushing, shutoff valves, air relief etc.) All Calculations & Input pressure @ filter inlet flows (Q) pressure @ filter outlet how many laterals attached to flush line pump pressure type (diameter, type, etc) All pipelines to be installed to NRCS standards (depths, velocity, psi, etc.) lengths Mainline layout All Calculations & Input Is mainline pressure same as pressure @ filter outlet velocity & Q type (diameter, type, etc) pressure rating & pressure in pipe Layout show submain locations- direction of outlet flow
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Maintenance of Micro Irrigation Systems Water quality is a factor in maintaining micro irrigation systems. A water quality test will measure silt or sand; algae; bacteria; dissolved solids such as iron, sulfur, salts, and calcium; and the pH of the water. For additional information on system maintenance, contact the equipment manufacturer. Maintenance tasks: Annually treat system with acid to neutralize calcium carbonates if the water is “hard”. Consult equipment manufacturer for type of acid and treatment interval.
Regularly: • Irrigation system evaluation by a trained professional is highly recommended. • Check for leaks, rodent damage, and mechanical damage. • Inspect pressure regulating valves and pressure gauges for correct operation and pressure readings. Liquid filled pressure gauges are
recommended. • Flush lateral lines. Depending on water quality and filtration system, flushing should be done bi-weekly and after fertilizer or chemical
injection or chlorination. • Regularly check for and clean or replace clogged emitters. Drip emitters that are only partially clogged are difficult to identify without
catching the flow to determine the discharge rate. • Check emitters for correct flow. Take precise measurements at least twice each year by catching the flow from several emitters in a
calibrated cylinder (such as a rain gauge) during a carefully timed interval. • Backwash filters either manually or using automatic cycle, depending on system design and type of filter. • Replace cartridge filters. • If filter media (such as sand) cakes, replace media. For sand filters, periodically supplement with additional media. • Chlorinate system with 10 ppm if water has high organic load. • If clogging due to organic matter continues to be a problem, inject 50-100 ppm of chlorine and allow to sit for 24 hours. • If clogging due to precipitates (such as calcium carbonate) persists, inject system with acid to lower pH to about 5. Allow to sit for 24
hours. Contact equipment manufacturer before undertaking this task to determine the minimum pH allowable for system type.
At Season Shutdown: • Treat entire system with 40 ppm residual chlorine concentration for at least four hours, and completely flush the system. • Drain water from all pipelines. The system may have to be blown out lateral by lateral with an air compressor to accomplish this. Don’t
exceed 15 to 20 psi of air pressure, or you’ll blow off the emitters. Polyethylene pipes can withstand some freezing without breaking, so
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it isn’t critical that all water be removed. In cases where freezing may be a problem, add non-toxic antifreeze (type used in RV’s) to the piping system and distribute it throughout with compressed air.
Efficiency of Micro-Irrigation systems (SDI) Application efficiency, which is the percentage of applied water beneficially used by the crop can approach 100% for SDI. High efficiency is also realized with fertilizer application using SDI. Injected fertilizer (fertigation) is applied directly to root area and can be applied at any time and any dosage without wetting plant foliage. Properly designed systems are highly efficient in their use of water and energy. Below are a few suggestions for ensuring that the system is running efficiently: Make sure you know your exact field size. It’s common to overestimate field size, leading to overestimating water requirements. This concern is commonly taken care of by proper planning, design, and monitoring of the soil moisture. Avoid excessive back flushing that wastes water and energy and creates a water disposal problem. Measure back flushing amounts. Find and address causes of plugging. Investigate the source and fix the plugging problem. Check for plugged filter screens. Undo and clean any screens that are plugged.
Scheduling Irrigations – The Irrigation Requirement: To effectively schedule irrigations, you must know:
• The flow rate of each emitter • The crop (or plant) canopy area • An estimate of the plant’s daily water-use
(evapotranspiration or ET) The equation used to estimate the irrigation requirement (IR) per Plant is: IR = (0.623 x CA x Plant Factor x ETr) / IE Where:
IR = the irrigation requirement in gallons 0.623 = gallons of water required to fill 1 square foot 1 inch deep CA = plant canopy area in square feet Plant factor = 0.85 for tomatoes, chili, and sweet corn (may be higher for melons, squash, cucumbers, etc.) ETr = reference ET (refer to Irrigation water requirements by local/crop data) IE = irrigation efficiency (assume 90% for SDI)
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Calculating the Crop Canopy Area: Area of a circle = d2 x 0.785 (diameter x diameter x 0.785) Example: plant diameter = 18 inches or 1.5 ft. Area = 1.5 x 1.5 x 0.785 = 1.77 sq. ft.. EXAMPLE: Scenario Location – Albuquerque Date – May 25 (ETr = 0.41 inch)
Chile plant (plant factor = 0.85) Measured (circular) plant diameter = 1 foot Estimated irrigation efficiency (IE) = 90 % or 0.9 Calculations: CA = 1 x 1 x 0.785 = 0.785 IR = (0.623 x 0.785 x 0.85 x 0.41)/0.9 = 0.19 gallons (24 fluid ounces) per plant per day NOTE: There is no substitute for frequently checking the moisture in the soil profile.
Water Quality and SDI systems: The irrigation water to be used in a drip system should be evaluated carefully to assess any potential clogging problems. Materials suspended in the water, such as sand, silt, and algae, can block emitter flow passages or settle out in the drip lines. Other contaminants, such as calcium, bicarbonate, iron, manganese, and sulfide, can also precipitate to clog emitter flow passages. All water needs to be tested to determine levels of dissolved salts, pH, and turbidity (sediment levels). Growers need to be aware of high levels of pH (7.5) and high dissolved bicarbonate levels (=> 5.6 meq/liter). If water quality analysis indicates these levels, sulfuric acid and/or gypsum should be injected to acidify the water to lower the pH to prevent the emitters from clogging with precipitates. A pH of 6.5 is favorable for injecting fertilizers or other agricultural chemicals into the system.
References: NRCS Conservation Practice Standard: Irrigation System, Microirrigation (code 441) Water Management: The New Mexico Irrigator’s Pocket Guide Assessing Water Quality Before Installing a Chemical Injection System. Robert Flynn, Extension Agronomist, NMSU Circular 573, Drip Irrigation for Row Crops, Aug. 2001.
Maintenance of Microirrigation Systems. Larry Schwanki, Irrigation Specialist, UC-Davis, NMSU Circular 573, Seasonal or Minimum Tillage, Drip Irrigation for Row Crops, Aug. 2001.
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AAcceeqquuiiaa CCoommmmuunniittyy DDiittcchh DDeessiiggnn IIrrrriiggaattiioonn SSyysstteemm
Achieving Irrigation Water Management on Acequia Systems
Overview: Acequias in New Mexico are usually historical community ditches that carry snow runoff, spring flows, or river water to distant fields. Most acequias irrigation systems convey irrigation water through earthen ditches, concrete lined ditches, pipes, or aqueducts. Some are of modern fabrication and others are decades or centuries old.
The acequia organization is administered by a governing board (i.e. ditch riders, majordomo or ditch commissioners), who regulate the water right holders and release water on a rotational or demand basis.
Water Rights: In New Mexico the right to use water from a stream belongs to the first user of the water, whether the user owns the land next to the water or not. Senior water right holders are typically Native Americans, acequias, and other agricultural water users. Junior water right holders are typically municipalities, industrial, residential, and recreational water users. Water is given to senior water right holders first due to a “grandfather clause” which gives preference to those who used water before the passing of new laws.
Basic Requirements: • Source of Irrigation Water: Acequia or Canal, Well • Usual Flow Available: Measured in CFS or AC Ft. • Is Irrigation Water Available on Demand or Rotation? • Conductivity of Irrigation Water: • SAR (Sodium Absorption Ratio): • Obtain Soil Inventory
Suggested Irrigation Practices for Most Acequias:
Surface Irrigation Sprinkler Irrigation
Drip, Micro Irrigation
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Community Ditch Assistance from NRCS
1. The Community Ditch group requests assistance from the NRCS Field Office (FO). • The group must be an organized Community Ditch as defined by state statutes. The CD must have its by-laws current and on file with
Interstate Stream Commission (ISC). • The group submits an Assistance Request Form to the District Conservationist (DC) with appropriate signatures from the 3
commissioners. 2. Once the FO receives the request form, they can request assistance from the Acequia Engineer or start the project themselves.
• The planning form (NM-E-251) needs to be completed and signed by AC, DC, AE, and the group. • The DC submits the planning forms to the NRCS Acequia Liaison (AL). The AL will send a copy of the forms to ISC and request an
approval to start the design. The AL will assign a tracking number and request a drawing and file number from the State Office (SO). The AL informs the designer that the design can be started.
3. The design is completed and sent to the NRCS State Conservation Engineer (SCE) for approval. The SCE forwards the design to ISC for acceptance.
• After the SCE receives the accepted design from the ISC, it is sent to the NRCS FO for distribution to the group. • The group is responsible for bid advertising and obtaining funding. NRCS can assist with the site showing, pre-construction meeting,
and construction inspection (upon groups request) pending available personnel.
IS-5: Achieving Irrigation Water Management (IWM) with Pivot Sprinkler System
Basic Requirements:•Water Source•Pumping Plant•Power Source
•Mainline•Laterals
•Sprinklers•Chemigation Valves
•Pressure Gauge•Water Meters
LEPA SystemLow Energy Precision Spray
LESA SystemLow Elevation Spray
MESA SystemMid Elevation Spray
Page 2 Title Purpose
Page 1 Achieving Irrigation Water Management (IWM) withPivot Sprinkler Systems
To describe the basic requirements of pivot sprinkler systems
Page 2 Table of Contents Table of Contents
Page 3 Pictures of basic sprinkler system hardware To demonstrate the components that are required for a sprinkler system
Page 4 Pictures of basic LEPA system characteristics To demonstrate agronomic characteristics of a lepa system
Page 5 Characteristics of Pivot sprinkler systems Criteria: Design Capacity, Design App. Rate, Distribution Patterns, Nozzle Spacing, Heights, Slopes.
Page 6 System Planning and Design Planning, Design and System Performance Requirements
Page 7 Crop and Soil Characteristics Needed for planning & design and used for IWM documentation of irrigation efficiencies achieved
Page 8 Detailed Evaluation for Center Pivot Lateral Worksheet Catch Can Data Worksheet
Page 9 System Evaluation and Potential Water Savings Evaluates system performance
Page 10 Pictures of a basic sideroll irrigation system To demonstrate basic characteristics of a sideroll system
NOTE: The above information and documentation is intended to serve as a simple-to-use GUIDE by producers, Natural Resource Conservation Service (NRCS) planners and others involved in Irrigation Water Management. For further assistance on the use of this GUIDE, contact your local NRCS.
Chemigation Valve
Pressure Gauge (Start)
Pressure Gauge (End)
Flow meter
Furrow Diking Soft Middles
CriteriaCenter Pivot or
Linear MoveLEPA LESA LPIC & MESA
Design CapacityEither: Capacity to meet the peak water demands of all irrigated crops in the design area,
Or: Capacity adequate to meet requirements of selected irrigations during critical crop growth periods when planning less than full irrigation
Design Application
RateRunoff, translocation and unplanned deep perculation shall be minimized
Distribution Patterns
CU ≥ 85% or DU ≥76%, Nozzles ≤ 7 ft.
high shall have a CU ≥ 90%
CU ≥ 94% CU ≥ 94%
CU ≥ 90% for nozzles ≤ 7 ft. high,
CU ≥ 85% for MESA for nozzles greater than 7 ft.
high
Nozzle Spacing
Spray Nozzles shall be ≤ 25% of wetted
diameter, and Impact Nozzles shall be ≤ 50%
wetted diameter
Not to exceed twice the row spacing of the crop or 80 inches
Not to exceed every other row when
operated in canopy for 50% or more of the growing season
Heights Varies 8 - 18 inches 12 – 24 inches 5 – 10 feet
Slope Not to exceed 20%Not to exceed 1% on more than 50%
of the field
Not to exceed 3% on more than 50%
of the field
Not to exceed 3% on more than 50% of the field for fine textured soils, and
not to exceed 5% on more than 50% of the field for coarse
textured soils
CHARACTERISTICS OF PIVOT SYSTEMS
SYSTEM PLANNING & DESIGNPLANNINGCalculate the required system capacityDetermine water availabilityEstimate your irrigated areaPhysical considerations- H20 quality, Soil variationsDESIGNPivot- labor savings, operating costsSYSTEM PERFORMANCESystem checksSystem CapacitySystem UniformitySystem Average Application RateSystem Field Application Efficiency
PLANNING DESIGN SYSTEM PERFORMANCECalculate the required system capacity
Q= 453 Adf T
Pivot LaborOperating CostSprinkler Package
System Checks The supplier should provide this service1. System Capacity2. Distribution Uniformity3. Energy Consumption
Determine water availability
This is done through well testing System Capacity Q= 453 Ad A=Irrigated area (acres)f T d=Gross depth of water applied (in.)
f= Irrigation period (#days in #day interval)
T=hrs./day (operating system)
Estimate your irrigated area
A= Q f T453 d
System Uniformity
Catch Can
Physical considerations
H20 quality, Soil variations System Average Application Rate
Ratio of nozzle flow rate to its wetted area
Where AAR exceeds the infiltration rate runoff results
System Field Application Efficiency
App. Eff. = Irr. Water available to crop x 100Volume of water supplied
NOTE:.
Area (ac) 120Depth of water applied (in) 2Irrigation period (days/interval) 3Operating time (hrs/day) 24
Flow rate (gpm) 1510
Flow rate (gpm) 1000Depth of water applied (in) 2Irrigation period (days/interval) 2Operating time (hrs/day) 24
Area (ac) 53
Critical soil to manage: 0.75
Crop Name Rooting DepthMoisture
Replacement Depth (ft)
Water Holding
Capacity (in)
Mgt Allowed Depletion (MAD) (%)
Net Water to Replace
(in)
Time Needed to Infiltrate
(hrs)Alfalfa, hay, northern; Albuquerque Deep 4.0 5.0 50% 2.5 2.0
Crop: 41.5 ac in/ac
Month Est. Frequency (days between irr.) In/Mo Month In/Mo
Jan 0.0 Jul 9.7Feb 0.0 Aug 7.8Mar 0.0 Sep 5.3Apr >1 Mo. 1.4 Oct 2.2May 12 6.1 Nov 0.0Jun 8 9.0 Dec 0.0
Soil Interpretations for Irrigaiton
Crop Consumptive Use (CU) Information (inches/month needed)
Soil (Series, Texture, and Map Unit) Select the soil to manage for:Intake Family (in/hr):Zia SL; 91
Est. Frequency (days between irr.)
81014
Alfalfa, hay, northern; Albuquerque
Total Irrigation Needed:
>1 Mo.
Catch Can Spacing ft
Can No. Factor No.
Catch (cc)
Catch x Factor
Catch (in.)
Can No. Factor No.
Catch (cc)
Catch x Factor
Catch (in.)
1 0 0.00 44 44 35 1540 0.182 0 0.00 0 0.003 0 0.00 0 0.004 4 60 240 0.30 0 0.005 0 0.00 36 36 55 1980 0.286 0 0.00 28 28 55 1540 0.287 0 0.00 0 0.008 8 70 560 0.35 0 0.009 0 0.0010 0 0.0011 0 0.0012 12 75 900 0.3813 0 0.0014 0 0.0015 0 0.0016 16 70 1120 0.35 108 506017 0 0.0018 0 0.0019 0 0.00 520 20 80 1600 0.40 1 1521 0 0.00 2 2522 0 0.00 3 3523 0 0.00 4 2524 24 60 1440 0.30 5 2025 0 0.00 35
Max application rate data for
Detailed Evaluation Center Pivot Lateral Worksheet
Low 1/4 Summation
Catch Timemin
alfalfa 16" 26 50% 14.9 24 80
pivot point pivot pointend tower wetted edge
1205 1345 50 10.8 850
278 27.3 130.5 0.39
58.94 0.29 46.85 0.23 79.49 87.08
0.752 59.760219 0.21 2.10 64 24.9
Potential Application Efficiency
%
Potential annual gross
applied (in)
Total Water Conserved
(ac-ft)
80 18.6 68.6
Annual Net application
(in)
Hours operated per
day
Revolutions per season
Distance from/to End tower speed System Flow Rate
Crop Stage of growth
Hours per revolution
Speed setting
Distance (ft)
Time (min) Flow rate (gpm)
Method of measuring flow
flow meter
System EvalutationCircumference of end
tower (ft)
7571
End tower speed (ft/hr)
Hours per revolution
Area irrigated
(ac)
Gross app. per irrigation
(in)
Re Eq
Potential Water Savings
Existing System Data
Catch Can EvalutationWeighted system
ave. application
(cc)
Average Application
(in)
Weighted low 1/4 ave. application
(in)
DU
Low 1/4 Average
Application (in)
Pivot revolutions
required
Annual Gross
application (in)
CU
Application (in)
Max ave. app. Rate (in/day)
SYSTEM EVALUATION AND POTENTIAL WATER SAVINGS
Sideroll Irrigation
(IS-6) Achieving Irrigation Water Management (IWM) With Irrigation Water Conveyance – Pipeline
IS-6
Basic requirements: Benefits:
Irrigation pipelines come in a variety of diameters (4” to Increases efficiency of water delivery from well
24” are the most common) and a variety of materials to point of irrigation.
(Poly Vinyl Chloride, Steel, Non-reinforced concrete, and Maintenance is minimal compared to an earthen
Aluminum). ditch or concrete lined ditch.
Irrigation pipelines are used with sprinklers, drip systems, Will work on any field, regardless of shape.
and flood applications on a variety of crops.
Photo From Ft. Sumner FO
24” PVC Pipe
Page 2 Table Of Contents
Page # Title Purpose
1 Achieving Irrigation Water Management (IWM) with Irrigation Pipelines
To describe the basic requirements and benefits obtainedwith irrigation pipelines
2 Table of Contents Table of Contents
3 Friction Loss Table Example of friction loss table to assist in sizing irrigation pipeline
4 Pump Discharge Assembly To show valves on a typical pump discharge assembly
5 Typical Pump Discharge Assembly To show typical set up of valves for a pressurized irrigation pipeline at the well assembly
6 Pump Dogleg Assembly To show typical pump dogleg assembly
7 Typical Gravity Discharge Assembly To show typical gravity discharge assembly
8 Pipe Markings To provide explanation of typical pipe markings
9 Tee & Elbows To show tees and elbows in an irrigation pipeline system
10 Thrust Blocks To show typical types of thrust blocks
12 Documentation of Depth of Cover Photo verification of depth
11 Minimum Depth of Cover To show minimum depth of cover for different sizes
IS-6
Page 3 Friction Loss In Plastic Pipe (Ft / 100 Ft)(example)
Diameter In Inches
8 8 10 10 12 12 15 15 18 18
FlowGPM
FlowCFS
VelFt/sec
Hf VelFt/sec
Hf VelFt/sec
Hf VelFt/sec
Hf VelFt/sec
Hf
450 1.00 2.865 0.330 1.833 0.101 1.273 0.038
600 1.33 3.820 0.588 2.445 0.179 1.698 0.068
900 2.00 5.730 1.322 3.667 0.402 2.546 0.152
1500 3.33 9.549 3.672 6.112 1.118 4.244 0.423 2.716 0.129 1.886 0.049
2000 4.44 8.149 1.987 5.659 0.752 3.622 0.229 2.515 0.087
2500 5.56 7.074 1.175 4.527 0.358 3.144 0.135
3000 6.76 5.432 0.515 3.773 0.195
4000 8.89 7.243 0.916 5.030 0.346
To properly size the pipeline diameter, choose a velocity less than 5.0 Ft/sec and a friction loss (Hf) equal to, or less than, 1.0 Ft/100 Ft. Friction loss will vary based on pipe material, pipe diameter, change in elevation, and flow rate.
Note: Cubic Feet Per Second (CFS) x 450 = Gallons Per Minute (GPM)
IS-6
Page 4Pump Discharge Assembly
IS-6
Air Vent & VacuumRelief Valve
Pressure Relief Valve
Chemigation Valve
Injection HosePhotos From Alamogordo FO
Page 5 Typical Pump Discharge Assembly
IS-6
VRV = Vacuum Relief ValvePRV = Pressure Relief ValveA-VRV = Air and Vacuum Relief
Valve
Typical Pump Dogleg AssemblyPage 6
IS-6
ChemigationValve
Flow Meter
Air Vent & Vacuum Relief Valve
Pressure ReliefValve
PressureGauge
Photo From Alamogordo FO
Page 7 Typical Gravity Discharge Assembly
IS-6
Plastic Irrigation Pipe MarkingsExample
Page 8
IS-6
Manufacturer’sName
Pipe Diameter
Pressure Rating
Pipe Description -i.e. Plastic IrrigationPipe (PIP)
NRCS PracticeDescription
MaterialDesignation
Photo From Clayton FO
Irrigation PipelineTee and Elbow
Page 9
IS-6
Coupler
Tee
Elbow
Photo From Alamogordo FO
Page 10 Typical Types Of Thrust Blocks
IS-6
MINIMUM DEPTH OF COVERPage 11
Pipe shall be installed at sufficient depth below the ground surface to provide protection from hazards imposed by traffic crossings, farming operations, freezing temperatures, or soil cracking. The minimum depth of cover for pipe susceptible to any of these hazards shall be:
Pipe Diameter (in.) Depth of Cover (in.)
½ through 2 ½ 18
3 through 5 24
6 or more 30
In areas where the pipe will not be susceptible to freezing and vehicular or cultivation hazards, and the soils do not crack appreciably when dry, the minimum depth of cover may be reduced to:
Pipe Diameter (in.) Depth of Cover (in.)
½ through 1 ½ 6
2 through 3 12
4 through 6 18
6 or more 24
IS-6
Documentation of Depth of CoverPage 12
IS-6
Photo from Estancia FO
1
IISS -- 77 –– CCoonnccrreettee––LLiinneedd DDiittcchh IIrrrriiggaattiioonn SSyysstteemm
Achieving Irrigation Water Management (IWM) with Concrete Lined Ditches
Why replace earthen ditches with Concrete Lined Ditches? The ditch in this picture is subject to friction losses, erosion, seepage and irrigation water is difficult to quantify. Efficiency will be greatly improved by concrete lining. Irrigation water management will be achievable.
• Current (2007) average cost of a concrete lined ditch is approximately $26/linear foot (cost can vary greatly according to construction methods)
• This structure requires enough water (gallons per minute or cfs) in order to work effectively
• Used primarily for irrigation water delivery on surface flood irrigation systems
• Fields should be graded border systems and/or level basins
• Works well with all cropping systems
2
IWM works with Surface Irrigation
• Concrete Lined Ditches are capable of delivering high flows to a field, enabling a high irrigation efficiency.
2 Types of Concrete Lined Ditches
Slip-Form Ditch
Hand Placed Ditch
3
Slip-Form Ditch
Can be used with High Flow Turnouts or pull gates
4
Slip form ditch under construction
W e hen finished, this lined ditch will allow for thefficient conveyance of water.
5
This hand-placed ditch acts as weir flow, which minimizes irrigation-induced erosion and distributes water evenly
6
7
8
An apron reduces the An apron reduces the undercutting and erosionundercutting and erosion
This ditch is undercut and This ditch is undercut and soil erosion is uncontrolledsoil erosion is uncontrolled
Division Boxes are Division Boxes are used with both types used with both types
of CLDof CLD
Constructing a division box.
9
ReplogleReplogle flumes are used to measure flumes are used to measure irrigation water irrigation water –– note rule at rightnote rule at right
10
ReplogleReplogle flumes are also known flumes are also known as broad crested weirsas broad crested weirs
Benefits of Lining a DitchConserves water (e.g. reduces friction loss and
seepage loss from earthen ditches)Minimizes irrigation-induced erosion and
invasive weed growthWorks well with a gravity system; No pumping
is required.Maintenance is minimal compared to a dirt ditch
and works well in conjunction with irrigation pipeline; less labor intensive
Will work on any field, regardless of shape and can be tailored to site-specific conditions
Increased irrigation uniformity means increased yields and uniform crop quality
11
Considerations• Cost of construction
Varies according to thickness of lining, 2500 psi concrete required by NRCS standards and specifications
• Water availabilityMust be designed to carry adequate flow for crop
• Field sizeSize of ditch depends on width and length of area to be irrigated
Setting a check gate
12
Considerations • Weather conditions and temperatureMust be installed in dry conditions and when temperatures are between 50 and 90 degrees for a period of not less than 7 days
• Crop requirementsConsumptive use Consumptive use (CU) varies with (CU) varies with different crops different crops and according to and according to climate conditionsclimate conditions
Irrigation water is flowing evenlyto the left
13
Operation & Operation & MaintenanceMaintenance
•• Practice life of a CLD is approximately 25 Practice life of a CLD is approximately 25 yearsyears
•• Need to address sediment and debris removalNeed to address sediment and debris removal•• Exclusion of livestock helps to protect ditchExclusion of livestock helps to protect ditch•• Embankment integrity must be maintainedEmbankment integrity must be maintained•• Ongoing repair necessary Ongoing repair necessary -- replace cracked replace cracked
or broken canal sectionsor broken canal sections
14
IS-8 Irrigation Water Management (IWM) with Hiflow Irrigation Turnouts and Laser Land Leveling
BASIC REQUIREMENTS1. FIELDS MUST BE LASER LEVELED – High precision leveling eliminates “pockets” of standing water that reduce efficiency
due to deep percolation. Slopes can be as flat as 0.0001 ft/ft. 2. HIGH FLOW RATE and SMOOTH FILEDS - This is important in order to get water across the field as quickly as possible –
Directly related to time of opportunity. 3. DESIGN GUIDELINES – The width at the outlet should be about 1 foot wide for each 1 cfs of capacity. The floor should be about
8 inches below the level of the field. The outside blocks on the last row should be joined to the side of the “wall” to prevent water from concentrating at the outside of the structure. The outlet should have a 1 inch high x 4 inches wide lip.
BENEFITS 1. SAVES WATER – Conventional surface systems use 6-9 inches of water per irrigation. Some Hiflow systems have the ability to
apply less than 2 inches per irrigation. 2. REDUCES IRRIGATION TIME – Conventional surface systems routinely cover an acre an hour. Hiflow systems have increased
that to over 9 acres an hour. 3. PROTECTS GROUND WATER QUALITY – Reduced leaching due to improved distribution of water. 4. MISCELLANEOUS – Works in any field shape. Especially suited to large (20 acres or more) fields and “permanent” applications
such as orchards and long-term pastures and hay fields. COST
1. COST – Current costs vary from a few hundred dollars for smaller structures (10 feet wide outlet) to $1,500 for large structures (20 feet wide outlet). Ability to directly use canal gates often eliminates the need for ditches. RDFischer March 08
IS-9Canal and Ditch Turnouts Capacity in CFS
Pipe Diameter in InchesHEAD - FT 8" 10" 12" 15" 18" 21" 24"
1.0 1.3 1.8 The flow rate for this shaded area is indeterminate.1.5 1.8 2.7 3.6 5.02.0 2.2 3.3 4.5 6.6 8.8 11.02.5 2.5 3.8 5.3 7.9 10.8 13.9 17.03.0 2.8 4.3 6.0 9.0 12.5 16.3 20.33.5 3.1 4.7 6.6 10.0 14.0 18.4 23.14.0 3.3 5.1 7.2 10.9 15.3 20.3 25.7
NOTES:1. HEAD - Distance from the invert (bottom) of the entrance of the pipe to the water surface in the canal or ditch2. The pipe is assumed to be 10 feet long, level, and have an "n" value of 0.0173. The centerline of the outlet of the pipe is assumed to be at the level of the field.4. The yellow zone of the chart represents a velocity of 7 fps or greater. This is important for considerations to reduce erosion.Example: A 12" diameter turnout with 3.0 feet of head will flow about 6.0 cfs. The velocity of the water is in the yellow zone and erosion protection measures should be considered.
Reference: USDA-NRCS Hydraulic Formula - Culverts RDFISCHER March08
IS-10
Water Measuring Methods
Irrigation Best Management Practices depend upon conservation of water and the key to conservation is accurate water measurement. (NEH 9, Chapter 1)
Water is measured in a variety of ways. Measuring equipment commonly used include, weirs, flumes, submerged orifices, current meters, acoustic meters, and various other open channel and closed conduit devices. Generally water measurement is reported in different units, mainly depending upon type of irrigation and local custom. In the United States, it is commonly reported, in gallons per minute (gpm), millions of gallons per day (mgd), cubic feet per second (cfs), acre inches (ac-in), and acre feet (af).
Flow Meter (Propeller) mounted on steel pipe. (Mike Standefer, Portales, NM)
QT=DA Q – Flow rate in cubic feet per second T – Time in hours D – Depth in inches A – Area in acres E.G. – 10 cubic feet per second flowing for 12 hours will cover 40 acres to a depth of 3 inches.
Without measurement, there can be no management.
IS-10
IS-10
March 08
IS-11 Energy Use in Irrigation Water Management
One of the primary reasons to utilize irrigation water management (IWM) is the proper use of water; i.e. - conservation. The primary use of energy in irrigation is for pumping water. By logical extension, IWM is critical in the conservation of energy.
Energy sources for irrigation are primarily derived directly from fossil fuels, such as natural gas and diesel, and from electricity, which is generated from a variety of sources. Some water sources provide sufficient energy for irrigation due to the elevation difference between the source and the field. When discussing alternative energy sources for irrigation, a primary focus is on solar energy producing electricity from photovoltaic cells. The current initial cost of these systems, which is about $10,000 per kilowatt (equals about $7,500 per horsepower), preclude their use for production irrigated agriculture. The greatest return on investment for energy could easily be the proper operation and maintenance of the irrigation system.
Power = (Flow rate x Pressure)/Efficiency Energy Use Example #1 – A farmer has a well-maintained electrically powered pumping plant that has an overall efficiency of 60%. Electricity cost $0.10 per kilowatt hour. The required total pressure is 100 psi and 30 inches of water are applied during the season on a 100 acre field. IWM determines that 25 inches could be applied and still provide for the crop needs (A savings of 5 inches). How much money for energy can be saved by applying IWM?
Result: (5 inches x 100 acres x (3,630 cf / ac-in) x (62.4 # / cf) x (100 psi) x (2.31 ft / psi) x (1 HP/ 33,000 ft # / min) x (0.746
kwh / HP-hr) x (1hr / 60 min) x ($0.10 / kwh))/(Eff = 0.60)) = $1,642.84 saved by reducing the water applied from 30 inches
to 25 inches.
Energy Use Example #1A – How much more money could be saved in the above example, if the overall pumping plant efficiency could be increased from 60% to 70%? Result: ($1,642.84) x ((70/60) - 1) = an additional $273.80 saved by increasing pumping plant efficiency from 60% to 70%.
Movement takes energy RDFISCHER
IS-12 Economics and Irrigation Water Management
ECONOMICS: The study and method that deals with the production, distribution, and consumption of commodities. In other words, a farmer needs to be concerned about what is being produced and what is being used to produce it. ______________________________________________________________________________________________________ Decisions by a producer ultimately come down to one basic question: “Is, what I’m about to do, worth it?” Worth can certainly be measured in terms of money, but worth can also be measured in terms of time, effort, quality of life, and quality of the environment. The worth of a change can be determined by answering the following three questions: 1. Why do this at all? This begs an answer to the question – Can the present method sustain itself indefinitely? If the present method can sustain itself, then change is optional. If the present method cannot sustain itself, then there is no option but to change. 2. Why do it now? Compelling reasons to change at this time can be manifold, such as:
a. A change can produce higher profit, b. A change can reduce effort, or c. If I don’t change, I’m out of business.
3. Why do it this way? There are generally many ways to accomplish a particular task. How do we know if the best option is being used? Specifically, the inputs and the results of those inputs need to be evaluated. ______________________________________________________________________________________________________ EXAMPLE: A farmer has a conventional center pivot system (60 psi) covering 125 acres, with water supplied from a 500 GPM well with a drawdown to 400 feet below the surface. Electricity cost $0.12 per KWH. Well water quality is 1000 ppm TDS (WQ-6). Of the 18 inches of annual precipitation, 1/2 is effective and evenly spaced from May through August. Potential(1) crop consumptive use (CU) averages 0.25 “/day in May, 0.30 “/day in June, 0.35 “/day in July, and 0.30 “/day in August (IWM-19 and Irrigation Guide) (Assume production is directly related to the actual CU and is worth $25 per acre inch of CU.). The farmer is considering converting to a LEPA system which will cost $10,000. Make the necessary assumptions and evaluate options.
IS-12 Items Common to All Systems:
Well Capacity = 500 GPM (26.52 Ac-Inches / Day) Effective Rainfall during season = 9 inches (0.073 “/day) Well Drawdown = 400 Feet Crop Potential CU for season = 36.9 inches divided as follows: Pumping Plant Efficiency, Overall = 60% = 0.25”/Day in May, Electricity cost = $0.12 / KwH = 0.30”/Day in June, Well Water Salinity = 1,000 ppm = 0.35”/Day in July, and Crop Value = $25 per inch of effective rain and irrigation water = 0.30”/Day in August
SYSTEM COMPARISONSITEM Existing LEPA ALTERNATIVE LEPAArea System Pressure Irrigation Application Efficiency Water to apply per day (2), inches - May (0.25) - June (0.30) - July (0.35) -August (0.30) Pump Operation Time, Hours (4)
- May (744) - June (720) - July (744) -August (744) Water Pumped During Season, Ac-Ft EXPENSES Pump Electricity Cost – - May (744) - June (720) - July (744) -August (744) Annual Pumping Cost Capital Cost for the new LEPA system ( $10,000, 7%, & 10 year life - CRF =0.1424)
125 Acres 60 PSI 65 % 0.272 0.349 0.426 0.349 954* 1,191* 1,494* 1,224* 271.82 $9.10/hr $6,770* $6,552* $6,770* $6,770* $26,862 -0-
125 Acres 30 PSI 90% 0.197 0.252 0.308 0.252 691 860* 1,080* 884* 266.96 $7.93/hr $5,480 $5,710* $5,900* $5,900* $22,990 $1,424
100 Acres(3)
30 PSI 90% 0.197 0.252 0.308 0.252 553 688 864* 707 247.89 $7.93/hr $4,385 $5,456 $5,900 $5,607 $21,348 $1,424
IS-12 Crop Establishment(5)
Fertilizer(6) Per-Acre Annual Cost PRODUCTION AND INCOME (7)
Irrigation Water Applied / Acre Effective Irrigation and Rain, aka CU. Based on $25 / Inch of CU (8)
Yield loss due to salinity Net income / acre Net Annual Income for Farm
$12,500 $21,293 $485.25 26.10 inches 25.97 inches $649.25 / acre 20% = ($129.85) / acre $34.15 $4,268.75
$12,500 $15,833 $421.98 25.63 inches 32.07 inches $801.75 / acre 10% = ($80.18) / acre $299.59 $37,448.75
$10,000 $12,667 $454.39 29.75 inches 35.78 inches $894.50 / acre 0% $440.11 $44, 011.00
NOTES for this example: (1) Actual Consumptive Use is less than potential Consumptive Use because of growing conditions such as water limitations and salinity. This principle is readily apparent in high frequency, low salinity environments, such as with some drip irrigation systems. (2) To determine the amount of “water to apply per day”, subtract the effective rainfall from the potential CU and divide by the application efficiency – E.g. Existing system for May: (0.25” – 0.073”) / 0.65 = 0.272” equals the amount of water that has to be applied per day in order to meet the potential CU. (3) To determine the area for the Alternative LEPA system, the daily well capacity is divided by the average water to apply per day for the growing system as follows: (26.52 Ac-Inches / Day) / ((0.197 + 0.252 + 0.308 + 0.252) / 4 ) = 105 Acres. (4) The asterisk (*) indicates that there are not enough hours in a month to meet the water requirement and thus the pumping cost is capped at the number of hours in a month. (5) Crop establishment includes all cultivation practices, to include planting and seed cost, needed to establish a crop.
IS-12 (6) Fertilizer – Assume the crop needs 150 units of N per acre and it is applied through the system. Also assume that the amount of nutrients that is used by the crop is dependant upon the efficiency of the irrigation system. Assume that more N will be applied to compensate for the irrigation application efficiency and that N is from Urea at $700 per ton – or $0.76 per unit of N. (7) Production is assumed to be based upon the amount of water applied minus corrections for salinity. Production in some crops is more affected by salt than others. (8) Production is very responsive to water quantity, up to the potential CU. This is very evident in Alfalfa. DISCLAIMER: The above example is simplified for purposes of instruction. Some of the assumptions that would be verified for actual conditions are as follows:
A. Pump and motor efficiency, flow rate, pressure, and power consumption would be determined and matched to the irrigation system, B. Crop CU would be determined for the crop and location, and C. All expenses and projected income would be verified for the specific time and location. NOTES on Capitol Recovery Factor (CRF): This factor can be very useful to help determine the cost of an investment or purchase versus expected income. The following is an abbreviated table, a short explanation of CRF, and a simple example:
Capitol Recovery Factors
Lifespan Interest Rate - % Years 4 5 6 7 8 10 1 1.0400 1.0500 1.0600 1.0700 1.0800 1.1000
2 0.5302 0.5378 0.5454 0.5531 0.5608 0.5762
The CRF x Present Debt = the uniform end-of-year payment necessary to repay the debt in a given number of years at a given interest rate.
5 0.2246 0.2310 0.2374 0.2439 0.2505 0.2638 10 0.1233 0.1295 0.1359 0.1424 0.1490 0.1628 15 0.0899 0.0963 0.1030 0.1098 0.1168 0.1315 20 0.0736 0.0802 0.0872 0.0944 0.1019 0.1175 25 0.0640 0.0710 0.0782 0.0858 0.0937 0.1102 50 0.0466 0.0548 0.0634 0.0725 0.0817 0.1009
100 0.0408 0.0504 0.0602 0.0701 0.0800 0.10001
Example: A farmer buys an irrigation system for $20,000. It is financed for 10 years at 7% interest rate (Hint: From the chart, the CRF = 0.1424). Question: What is the Annual Payment? Answer: Annual Payment = 0.1424 x $20,000 = $2,848 / year
RDFISCHER – APRIL 2008