Distributing flow mismatches in supply-constrained irrigation canals through feedback control
Date
2010-03
Authors
Clemmens, Albert J., author
Strand, Robert J., author
U.S. Committee on Irrigation and Drainage, publisher
Journal Title
Journal ISSN
Volume Title
Abstract
The operation of main irrigation canals is complicated in situations where the operator does not have full control over the canal inflow, or where there are very long transmission distances from the point of supply, or both. Experienced operators are able to control the canal, but often supply errors are simply passed to downstream, thus creating problems further down the system. In previous work, the senior author showed that it is important to contain such errors and not let them pass downstream. With automatic upstream level control, all flow errors are passed to the downstream end of the canal. Distant downstream water level control requires full control of canal inflow. Without this, most errors will occur toward the upstream end of the canal. An alternative scheme is offered here where the canal check gates are controlled based on the relative water level error between adjacent pools. The scheme uses a simple linear model for canal pool response. The scheme is implemented as a multiple-input, multiple-output scheme and solved as a Linear Quadratic Regulator (LQR). Thus all gates respond to relative deviations from water-level set point. The scheme works to keep the relative deviations in all pools the same. If the canal has more inflow than outflow, the scheme will adjust gates so the water levels in all pools will rise together with the same deviation from set point. It thus distributes the error over the entire canal. When in equilibrium, operators will be able to judge the actual flow rate mismatch by the rate of change of these levels. The scheme acts like a combination of upstream level and distant downstream level control. It was tested on a simulation model of the Central Main Canal at the Central Arizona Irrigation and Drainage District, Eloy, AZ.
Description
Presented at Upgrading technology and infrastructure in a finance-challenged economy: a USCID water management conference held on March 23-26, 2010 in Sacramento, California.