California State University, Fresno, California 93740-0018
May 1989
Modeling Sprinkler Coverage with the SPACE Program
By Joe C. Oliphant

Computer modeling is a way to see the results of an irrigation design before you actually install the system. The Center for Irrigation Technology has developed a computer program for use by irrigation designers to aid in the sprinkler and spacing selection process.

The computer can "model" a sprinkler and spacing design by using data from a single leg test or from a full grid catchment pattern of a single sprinkler.

With CIT's new SPACE program, irrigation designers now have the ability to analyze the uniformity of a sprinkler design by evaluating different spacing designs with the aid of a computer. Rectangular and triangular spacings of up to 120 feet between the sprinkler heads can be evaluated with the touch of a few keys. Different sprinkler models from various manufacturers and sprinkler nozzle and pressure combinations can be compared to determine the most efficient design with the coverage you want at the least cost.

The SPACE program is menu driven. You select from different options listed on the screen. The program is designed to be simple to operate and comes with complete documentation. An on-line help file is available by touching a single key that will display instructions on the screen whenever a response is required. There are many editing features for data entry that help eliminate frustration when entering large amounts of data (for a full grid pattern there may be as many as 3600 catchments).

Creating a matrix from a single leg profile

The computer fills the grid by measuring the distance from the sprinkler head to each catchment and ooking up in the profile the application rate at that distance.

C = Square root(A2 + B2)

The SPACE program calculates Christiansen's Coefficient of Uniformity (CU), Distribution Uniformity (DU), mean application rate, minimum and maximum application rates, and a Scheduling Coefficient which is normally based on 1% of the covered area. Five reports can be generated as follows: A listing of the calculated values for the overlap pattern, A Denso-gram (See "A New Way To View Sprinkler Patterns", Irrigation Notes, August 1988, CATI pub. #880802) of the calculated values, A Histogram of the calculated values, a Profile of the data from a single leg test, and a "Sliding Window" report which is a summary of
calculated Scheduling Coefficients for different sized "Critical areas", (1%, 2%, 5%, and 10% of the total pattern area, and individual catchment values in the pattern). These reports can be displayed on the screen or a hard copy can be generated. A listing and a denso-gram of the actual values from a full grid catchment pattern can also be produced. The program can evaluate data from previously tested sprinklers that are stored on disk files. The Center makes available to interested users a disk containing all of the current sprinkler tests on file. The program can also be used to evaluate new data from tests performed in the field or from your own single leg tests. There is also a section of the program for copying and deleting data files and records in the files.

This test consists of setting up the sprinkler on a test bench with a single row of catchments that are normally spaced in one or two foot increments away from the sprinkler. The test is run at a specified pressure with the sprinkler set at a specified height above the catchments. The test is run for a time long enough to collect an average of about one half inch of water in the catchments. The computer uses the data obtained from this test to create a matrix that would simulate a field test where catchments were placed in a grid pattern that covered the entire area between the sprinkler heads. The matrix size is based on the catchment spacing of the test and the distance of the sprinkler spacings in the sprinkler system design. The computer creates a matrix of catchments and fills the matrix by measuring the distance of each catchment from the sprinkler head and then looking up in the test profile the application rate at that distance. The computer performs the same process for each sprinkler head in the design, as well as outlying sprinklers that would contribute to the pattern, and adds the amount to each catchment that is covered within each sprinkler's radius of throw. This process assumes a no wind environment and that each individual sprinkler pattern is uniform in all directions.

This test is performed by setting up a pattern of catchments in a grid and placing the sprinkler in the pattern so that the full spread of the sprinkler is covered by the catchment pattern. The test conditions are similar to a single leg profile test. The catchments are then read and recorded on a data sheet and later entered into the computer. The computer creates a matrix that contains a number of catchments between the sprinklers that is based on the catchment spacing of the test and the design distance between the sprinklers. For instance if you tested a sprinkler that had catchments at two foot increments and you wanted to see what the design would look like in a spacing of 30 feet by 40 feet in a rectangular pattern, the computer would create a matrix that was 15 catchments by 20 catchments (30 feet between the sprinklers divided by 2 foot catchment spacings = 15 catchments ). The test data is sectioned into quadrants as shown in the example to the right. The computer fills the grid by using the section of the throw pattern that corresponded to each placement of sprinklers in the system design. For instance, in a rectangular pattern it would use the lower right hand quadrant of the throw pattern to fill the catchments covered by the sprinkler head in the upper left hand corner of the matrix. The computer will perform the same process for each sprinkler in the design as well as outlying sprinklers that would contribute to the pattern.

Sprinkler Location

Creating a matrix from a full grid catchment pattern

The above pattern shows the actual values of catchment data in a full grid pattern for a single sprinkler. The catchments are on one foot spacings. The pattern below is the calculated values for a 15 by 15 rectangular spacing. The value for the sprinkler head is calculated by averaging the four closest catchments to the sprinkler head

The SPACE program is designed to be used with an IBM® PC or compatible with 640K of memory and a graphics adapter. A math co-processor is strongly recommended. The reports generated by the program require a dot matrix printer with graphics capabilities.

The program is available on a 5 1/4" or 3 1/2" floppy disk. The package comes with an initialization program that will set up the program and files to run on systems with a fixed disk, dual floppy disks, or a single floppy disk drive

The package also comes with a menu file for use with a LOGITECH™ three button mouse, and instructions for using the mouse with the program.

One of the most useful aspects of the program is it's ability to generate denso-grams, as shown to the right. The denso-gram clearly shows the difference between a good coverage pattern (above right) and a poor one (below right). The denso-gram represents graphically, the wet and dry areas in the pattern with the darker portions showing the wettest areas and the lighter portions showing drier areas.

You can obtain an order form for the program and program documentation by contacting the Center for Irrigation Technology, California State University, Fresno, CA 93740-0018, (209) 278-2066