North Dakota State University
NDSU Extension Service
No. 185, September 2000
http://www.ext.nodak.edu/extnews/snouts
Irrigation Workshops
Irrigation and Ground Water Quality
Using GPS and GIS to Optimally Place Center Pivots
Kidder Aquifer System Marstonmoor Plain Aquifer
Sizing and Economics of Irrigation Pipelines
The North Dakota Water Users annual convention is scheduled for Dec. 6 and 7 at the Radisson Inn, Bismarck. An irrigation workshop for current irrigators will be held in conjunction with the convention on Tuesday, Dec. 6 and a workshop for new or potential irrigators will be held Dec. 7. As part of the convention, there will be an irrigation exposition where irrigation suppliers will demonstrate their products and services. On the afternoon of December 6, the North Dakota Irrigation Caucus will hold its annual meeting. If you have any suggestions for topics to cover at the workshop, please give me a call; send an email or a letter.
Water is a precious resource. Current agricultural practices use many chemicals to improve production and protect crops. However, these chemicals could pose a risk to our groundwater, particularly in areas that have coarse textured soils overlying shallow sand and gravel aquifers. To address these risks, in 1990 five Management Systems Evaluation Area (MSEA) projects were started. The MSEA sites were located in Iowa, Minnesota, Nebraska, Missouri and Ohio.
The Minnesota project was named the Northern Cornbelt Sand Plain MSEA and the primary research site was located in Princeton, Minn. The University of Minnesota provided project management of the research efforts. In addition to the main site in Minnesota, there were satellite research sites located in Oakes, N.D.; Aurora, S.D.; and near Arena, Wis.
The ultimate goal of the Northern Cornbelt Sand Plain MSEA was to identify and develop management tools (i.e. Best Management Practices) to protect water quality. The research portion of the project was completed in 1997 and the results have finally been compiled into useable information.
More information about MSEA can be found at http://www.ageng.ndsu.nodak.edu/msea/
A number of publications have been developed based on the research results from the five MSEA project sites. The publications are available and downloadable in pdf format at this web site:
http://idea.exnet.iastate.edu/idea/marketplace/mseancr/publications.asp
The publications deal with groundwater quality and atrazine, drainage, nitrogen management and many other topics. The Nebraska publication entitled "Managing Irrigation and Nitrogen to Protect Water Quality" is interactive and contains video clips on many subjects dealing with irrigation water management.
Tom Scherer, (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu
Placing a center pivot on a piece of land is not always an easy task. Over the years, one or more of the towers on many newly installed pivots have run into obstacles such as wells or telephone poles because of a small mistake in picking the location of the pivot point. Global Positioning Systems (GPS) used with Geographic Information System (GIS) computer programs provide a new and easy way to locate center pivots for irrigation, especially on odd shaped fields. Identifying the pivot point for a center pivot using GPS and GIS is a four-step process: 1) measuring the field boundary with a GPS unit, 2) transferring the field boundary information from the GPS unit to a computer, 3) using GIS software in the computer to locate the pivot point and 4) going back out to the field with the GPS to mark the location of the pivot point.
Mark the field using a differentially corrected GPS unit to get the necessary accuracy. A differentially corrected GPS unit can identify your location on the surface of the earth with an accuracy of plus or minus 3 feet. The GPS unit can be mounted on a vehicle then driven around the field boundary or you can walk around the edge of the field holding the GPS unit.
There are several GIS programs available to use with the GPS data. After transferring the field boundary data from the GPS unit to the computer, display the field boundary with a GIS software program.
With field boundary displayed on the screen, use the graphics drawing feature of the GIS program to draw the largest possible circle inside the field boundary. If the field boundary is a square, use the GIS program to locate the center of the circle, and note the location of the center of the point in latitude and longitude. That's about all there is too it for a square field, but where the GPS/GIS method really shines is on rectangular or other irregularly shaped fields.
For example, look at the field boundary shown in Figure 1. This is an actual field, and locating a pivot on this piece of land using traditional methods would be difficult. But with the GIS program, place the largest circle possible that touches the boundaries on the north and south side (Circle #1). But we want to irrigate as much land as possible on this field. We can do this by adding a corner arm to the pivot. To do this, add a second circle (Circle #2) over the first using the same center point, but add on up to 350' to the circle to account for the maximum area that can be covered with a corner arm (200' extension tower with an 80' overhang and an end gun that covers another 70'). Convert the larger circular graphic to a shapefile, and edit the shapefile to fit within the field boundary. This can be accomplished in the GIS program in edit mode and moving the tick marks inside the field boundary or cutting off the parts of the circle that are outside the field boundary. Stop the editing and save the edits. Use the GIS program to calculate the acres of both the entire field and the pivot area. In this example, the field size was measured by the GPS to be 164 acres, and the maximum area to irrigate is 136 acres.
Figure 1. Using GPS and GIS to position irrigation pivots on irregularly shaped fields.
Use the GPS unit to locate the pivot point for the center pivot. With the latitude and longitude coordinates of the pivot point determined with the GIS program, use a differentially corrected GPS unit to drive back to the field, mark the point and you are ready to setup the pivot.
John Nowatzki, (701) 231-8213
NDSU Extension Water Quality Specialist
jnowatzk@ndsuext.nodak.edu
The Kidder aquifer system in Kidder County and the Marstonmoor Plain aquifer in northwest Stutsman County (Figure 1) consist of interbedded aquifer intervals of sand and gravel separated by aquitards of clay and silt. Surficial aquifer intervals are unconfined. Deeper aquifer intervals are usually leaky-confined and overlain by aquitards that transmit ground water in the form of leakage.
Figure 1. Location of the Kidder aquifer system, Marstonmoor Plain aquifer and approved points of diversion for the construction of irrigation wells.
Ground water pumped from the leaky-confined aquifer intervals is replenished by water held
in storage within the aquitards. Aquitard storage of ground water is maintained by
recharge and infiltration of ground water from the surficial aquifer intervals. Ground
water underlying Kidder and northwest Stutsman Counties is suitable for irrigation of clay
loam or coarser soils and all but salt sensitive crops.
Maximum combined annual water use for irrigation from the Kidder aquifer system and the Marstonmoor Plain aquifer was 13,219 acre-feet during 1998. The maximum total area of irrigated land was 22,013 acres during the 1999 irrigation season (Figure 2). The average annual application of water for irrigation over the past 25 years has been about 10 inches per acre.
Figure 2. Combined annual reported water use in acre-feet and acres of land irrigated:
Kidder aquifer system and the Marstonmoor Plain aquifer.
During the irrigation season, the pumping rate often exceeds aquitard leakage which
results in water-level drawdown within the leaky-confined aquifer intervals. Water levels
recover rapidly after each irrigation season. The amount of water-level drawdown and
recovery within the leaky-confined aquifer intervals decreases near land surface due to
increased storativity associated with the surficial unconfined aquifer intervals.
Seasonal water-level drawdown within the leaky-confined aquifer intervals and the resultant impact upon the pumping levels within irrigation wells is the most important consideration pertaining to future allocation of ground water from the Kidder aquifer system or the Marstonmoor Plain aquifer. The North Dakota State Water Commission monitors water levels at 270 observation wells and 8 surface-water staff gauge locations within Kidder and northwest Stutsman Counties. Based on the existing water-level data, there is no indication of long-term ground-water depletion within the Kidder aquifer system or the Marstonmoor Plain aquifer.
Scott Parkin, (701) 328-2754
Hydrologist, N.D. State Water Commission
When installing or retrofitting an irrigation system, an important decision is selecting the proper pipe diameter for the installation. From an engineering point of view, the proper pipe size is based on a tolerable amount of friction loss for a given flow rate. How do you determine what is tolerable? Generally, an average water velocity in the pipe of 5 feet per second is the maximum allowable for most installations; however, suction pipes for centrifugal pumps should have a velocity of 2 to 3 feet per second. This means the suction pipe on a centrifugal pump should have a larger diameter than the pipeline. Table 1 shows the maximum flow rate for various size pipelines when the water velocity is 5 feet per second.
Table 1. Maximum flow rate based on pipe diameter.
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Nominal pipe diameter (inches) 2 3 4 6 8 10 12 16
Flow rate (gallons 50 110 200 440 780 1225 1760 3140
per minute)
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The velocity and the roughness of the pipe determine the amount of head loss due to friction in a pipeline. Head loss or pressure loss due to pipe friction translates directly to energy loss. The more head loss, the more you pay for pumping energy. Smooth pipe has less friction than rough pipe. Plastic pipe, such as PVC and polyethylene, is the smoothest followed by aluminum, steel and concrete, in that order. Table 2 shows the friction head loss of aluminum and PVC pipe for several pipe diameters. The head loss is given in feet per 100 feet of pipeline. For example, if you are pumping 750 gallons per minute through an 8-inch diameter PVC pipeline that is 1000 feet long, the friction loss would be 8 feet of head loss (0.8 x 10). To convert this the pounds per square inch (psi) of head loss, divide by 2.31, which calculates to 3.5 psi of head loss.
Table 2. Head loss due to pipeline friction in feet of head per 100 feet of pipe
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- - - - - - - - - - - Pipe Diameter - - - - - - - - - - - -
4" 6" 8" 10" 12"
----------- ----------- ----------- ----------- -----------
Flow Rate (gpm) Alum PVC Alum PVC Alum PVC Alum PVC Alum PVC
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100 0.9 0.6
150 1.8 1.2 0.2 0.2
200 3.0 2.1 0.4 0.3 0.1 0.1
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250 4.8 3.2 0.6 0.4 0.1 0.1 0.1
300 6.2 4.3 0.8 0.6 0.2 0.1 0.1
400 10.6 7.2 1.5 1.0 0.3 0.2 0.1 0.1
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500 2.5 1.6 0.6 0.4 0.2 0.1 0.1 0.1
750 5.0 3.4 1.3 0.8 0.4 0.3 0.1 0.1
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1000 8.6 5.7 2.1 1.4 0.7 0.5 0.3 0.2
1250 3.2 2.1 1.1 0.7 0.4 0.3
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1500 4.5 3.0 1.5 1.0 0.6 0.4
1750 2.0 1.3 0.9 0.6
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2000 2.6 1.7 1.1 0.7
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Note: Flow rates below the horizontal line for each pipe size exceeds the recommended 5-feet per second velocity.
For electric pumping systems, the annual operating cost of a pipeline can be estimated
with the following equation:
Q x H x T x C
$ = ---------------
5308 x E
Where:
$ - Annual operating cost to overcome pipe friction Q - Flow rate in gallons per minute H - Head loss in pipeline in feet (use Table 2) T - Total pumping time per year in hours C - Energy cost per kilowatt-hour ($/kWh), including demand and/or annual charges E - pumping plant efficiency (decimal)
As an example of how to use this formula, lets say you pump 1000 gallons per minute through a 1500 foot pipeline to a center pivot for about 800 hours per year. You want to compare the annual operating cost of PVC and aluminum pipe for 8, 10 and 12-inch diameter pipeline. The average regular power costs in North Dakota are about 9 cents per kWh, which includes demand and/or annual charges. The average off-peak power costs are about 5 cents per kWh. Assume the pumping plant efficiency is 75%. The results are shown in Table 3. As you can see, it costs less to pump through PVC than aluminum. It also appears that the larger the pipeline, the more economical the pipeline, but remember, these are estimates of the annual operating cost. The capital cost of the pipe and installation will have a major impact on the total cost.
Table 3. Comparison of annual pumping costs for 1000 gpm through a 1500-foot pipeline.
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PVC Aluminum
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Regular Power ($0.09/kwh)
8 inch $379.80 $569.71
10 inch $135.64 $189.90
12 inch $ 54.26 $ 81.39
Off-Peak Power($0.05/kwh)
8 inch $211.01 $316.51
10 inch $ 75.36 $105.50
12 inch $ 30.14 $ 45.22
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Tom Scherer, (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu
Water Spouts -- No. 185, September 2000
NDSU Extension Service, North Dakota State University of Agriculture and Applied
Science, and U.S. Department of Agriculture cooperating. Sharon D. Anderson, Director,
Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June
30, 1914. We offer our programs and facilities to all persons regardless of race, color,
national origin, religion, sex, disability, age, Vietnam era veterans status, or sexual
orientation; and are an equal opportunity employer.
This publication will be made available in alternative formats for people
withdisabilities upon request, 701/231-7881.
North Dakota State University
NDSU Extension Service