Impact of Canal Design Limitations on Water Delivery Operations and Automation

Irrigation canals are often designed for water transmission. The design engineer simply ensures that the canal will pass the maximum design discharge. However, irrigation canals frequently operated far below design capacity. Because demands, and therefore the distribution of flow at bifurcations (branch points), can vary from day to day, or even from hour to hour, to meet user demands, the hydraulic grade line of the canal can vary significantly over the range of flows encountered. This complicates the operator's job of distributing flow to users. Common problems include; insufficient head at low flows for turnouts in the upper end of pools, gates that transition from free to submerged flow over the range of conditions, culverts that greatly change the pool volume over the range of discharges due to backwater effects, canal gates that are oversized for safety which limits small discharge changes, variable backwater conditions that compromise flow measurement devices (both in pipes and channels), incompatible hardware for automated control of check gates, etc. Examples from canal systems in Central Arizona are given with options for improving operations. This quote from an irrigation district engineer says it best "Design engineers should be forced to operate the canal systems that they design."