The introduction of California’s Water Conservation Act of 2009, known as SBx7-7, requires irrigation districts to increase water measurement accuracy, improve reporting, and introduce volumetric water pricing.
Turlock Irrigation District (TID) had over 1,200 manual slide gate supply points, each serving an average of six properties on a rotational basis. The approximate volume of water delivered was determined by inferring flow rate from the gate’s opening height and multiplying this by order duration. Accuracy was dependent on maintaining constant water levels – both upstream in the supply channel and downstream on each of the farms served by the supply point. Even when channel water levels and gate opening remained constant, varying farm topography and operating practices meant there was considerable downstream water level variation across farms. The same supply point could return dramatically different flow rates depending on the property being supplied. Flow measurement was not accurate enough to meet the requirements of SBx7-7 and would have led to inaccurate billing.
This prompted TID to look for accurate metering solutions, beginning with a pilot study to test Rubicon’s FlumeMeters™, SlipMeters™ and meters from two other companies for accuracy, ease of installation, maintenance requirements and overall cost.
“Installing 121 SlipMeters covering 30,000 hectares will provide a better level of service to our customers and reduce fluctuations system wide which will ultimately save water.”
While accuracy was found to be similar across all meters tested, TID chose Rubicon as the primary meter provider because of lower installation and maintenance costs. In most cases, the in-pipe meters tested could only be installed on the farmer’s property, making installation and troubleshooting difficult and expensive. They also commonly experienced blockages from weeds and rubbish, which required maintenance crews to travel to the site to resolve the problem.
FlumeMeters and SlipMeters feature Sonaray™ ultrasonic flow measurement, which is accurate to ±2.5% without the requirement for extensive upstream or downstream flow conditioning. This uniquely enables them to be installed in-channel, directly upstream of control gates and outlet pipes. In addition to flow measurement, SlipMeters have an integrated control gate.
TID installed SlipMeters at 121 sites serving 120 hectares or more and FlumeMeters at supply points serving between 12 and 119 hectares. The FlumeMeters are mounted to slide-in frames fixed to the channel wall, directly upstream of existing manual supply point gates – making installation quick and easy and keeping civil costs low.
TID now has a meter fleet that comfortably exceeds the SBx7-7 accuracy requirement of ±5%, and customers can be confident that they are being fairly charged under the new volumetric pricing structure. Remote management using TID’s third-party SCADA system means that the required reporting data is automatically recorded and readily at hand. With flow to half of the district’s irrigated land being managed by SlipMeters, service has also improved. The SlipMeter´s integrated control gate adjusts throughout a delivery to maintain a constant flow rate, even with varying upstream and downstream water levels.
SlipMeter gates constantly adjust to deliver the requested flow rate, even with fluctuating downstream and upstream water levels