Measurement of Irrigation Flows through Irrigation Turnouts

Accurate measurement of applied water volumes in surface irrigation fields is important towards improving irrigation efficiencies and management of the surface irrigation system. In flood irrigated fields, applied water may be supplied through spiles, or turnout pipes connecting the field directly to the supply canal. A simple measurement of head loss across the turnout pipe is all that is necessary to estimate onflow rates when the total head loss coefficient for the spile is known. The total head loss coefficient is primarily dependent on the entrance and exit head losses, and entrance head losses depend on the orientation of flow in the canal relative to the spile. For spile flows perpendicular to the axis of canal flow, the entrance head loss is greater than traditionally assumed. This paper reports results of field calibration of spiles having a supporting bracket for the cover plate, perpendicular flow and into which flow develops a sizable vortex that dissipates energy. A calibration curve relating head loss to spile discharge is developed from the field data.