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United States Department of Agriculture

Agricultural Research Service

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 CPED

CPED: Center Pivot Evaluation and Design

New versions of CPED FULL and CPEDLite were released on Dec 16, 2004.  They correct several problems that have been found in the previous versions.  For information on how to download and install these programs: Contact Kris Stahl at  kris.stahl@ars.usda.gov

Authors:  Dale F. Heermann, Kristine M. Stahl
USDA-ARS-NPA-WMU, Ft. Collins, CO

Platform:  WIN2000  WINXP

Brief Description:

CPED models water distribution under a Center Pivot or a Linear Move sprinkler system. Water distribution is modeled using the sprinkler inventory, the pump characteristics, and terrain changes in the field. The output from CPED can be used to replace can tests when calculating system uniformity. It assumes no wind conditions.

Model Inputs:

Pump - A second order regression equation describing the pump curve is used. Alternately, a constant head with an estimated discharge, or a constant discharge can be used to describe the pump.

System Inventory - Most of this information is provided by the manufacturer. It should include the length, inside diameter, and Darcy Weisbach resistance coefficient for each pipe; the tower locations; and the sprinkler inventory for the system. The individual information on each sprinkler should include: the model name, the distance from the pivot, pattern shape, range and spreader diameter, pressure regulators, start and stop part circle angles, and right and left offset distances.

Terrain - The relative elevations of the pivot pad and each of the towers on the system is needed. All values must be positive, so the pivot elevation must be set high enough to accommodate this.

Sprinkler Coefficients - For each sprinkler model used on the system , two regression equations are needed. The first predicts the discharge coefficient based on nozzle diameter and pressure. The second also uses nozzle diameter and pressure to predict pattern radius. The Water Management unit maintains a database of the most commonly used sprinklers and distributes it with the program.

Run Time Parameters -Total Dynamic lift, Hours per Revolution, Booster Pump Increase, and the starting distance, stopping distance and the distance increment for the depths simulation; also whether a particular sprinkler or all sprinklers are being simulated.

Model Output:

The model gives a summary of the sprinkler inventory. It is expanded to include hydraulic characteristics such as pivot pressure and system discharge based on both the pump curve and the depths, and the line pressure, nozzle pressure, discharge and pattern radius of each sprinkler. Results include the effective irrigated area, the mean depth, the uniformity coefficient, and the individual depths at the specified distances.

System Requirements:

Windows 2000 with a pentium processor 32 megs of memory and 5-10 megs of free disk space.

Documentation and Availability:

A users manual is provided with the program. Both the manual and the program can be downloaded from the FTP site. Contact Kris Stahl for permission to download.

References:  Available upon request.