GENERAL CHARACTERISTICS OF SOLUTIONS TO THE OPEN-CHANNEL FLOW FEEDFORWARD CONTROL PROBLEM

Authors: Bautista, Eduardo; Strelkoff, Theodor; Clemmens, Albert

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2002
Publication Date: 6/1/2003
Citation: Bautista, E., Strelkoff, T., Clemmens, A.J. 2003. General characteristics of solutions to the open-channel flow feedforward control problem. Journal of Irrigation and Drainage Engineering. 129(2)129-137.

Interpretive Summary: A dimensionless formulation of the open-channel flow equations was used to study the feedforward control problem for single-pool canals. Feedforward inflow schedules were computed for specified downstream demands using a gate-stroking model. The analysis was conducted for various design and operational conditions. Differences in the shape of the computed inflow hydrographs are largely related to the volume change resulting from the transient, the time needed to supply this volume, and the time needed by the inflow perturbation to travel down the canal. The gate-stroking method will fail to produce a solution, or the solution will demand extreme and unrealistic inflow variations if the time needed to supply the canal volume change is much greater than the travel time of the upstream flow change. As an alternative, a simple feedforward-control flow schedule can be developed based on this volume change and a reasonable delay estimate. This volume compensating schedule can deliver the requested flow change an keep water levels reasonably close to the target under the range of conditions tested.

Technical Abstract: Development of improved control strategies for large irrigation delivery systems can improve service to farmers and on-farm water management. To this end, it is necessary to develop a better understanding of the relationship between the physical characteristics of canals and their control requirements. This study examines that relationship. Results show wthat two important factors affecting the effort necessary to control a canal when demands are known, are the relationship between the time needed to supply the canal with the required volume change for the new steady- state conditions, and the time necessary for the flow change to travel down the canal. Based on this knowledge, a simple but effective method has been developed for scheduling known demands in irrigation canals. This approach should be useful to operators of open-channel water delivery systems as well as to designers of such systems.