By Walt Boyes, Editor in Chief
As we progress into the 21st century, water usage for domestic and industrial uses will increase, while new supplies are becoming less available. All you have to do is Google "Colorado River water rights" to get a good picture of how critical water and water use can be.
Many of the same drivers pushing industrial plants to implement plans for sustainable manufacturing are also pushing water utilities the same way. Moving water requires energy. Monitoring a far-flung water distribution system requires substantial manpower—manpower that is getting more expensive and hard to find. Energy is becoming more expensive, and water itself is becoming scarce and must be conserved.
All over the Southwest U.S. and California, water destined for potable service or for irrigation has traditionally been moved through a huge series of canals. Montezuma Valley Irrigation Company, Cortez, Colo., (www.mvic.us) uses such a system This irrigation district provides 1400 shareholders with water for their farms and crops. But MVIC realized that as much as 60% of the water that enters an open canal is wasted by evaporation, seepage and losses at the end of the canal.
So, MVIC decided on an ambitious project to conserve water, and save energy and manpower costs. "A decision was made to replace five miles of open-ditch irrigation canals with a poly pipe water distribution system," said Gerald Knudsen, PE, of AgriTech Consulting, the district's consulting engineer. "The projected savings were on the order of 1000 acre-feet of water per year."
Using high-density polyethylene (HDPE) pipe made it possible to lay the pipe down existing canals in most cases, because it is flexible and easy to work with. The main supply ranges from 12-in. to 36-in. in diameter and is pressurized to 30-50 psi. Each shareholder is served by a "turnout," also made of HDPE with a transition to the PVC pipe commonly used in farming for distribution and irrigation.
Each branch turnout is supplied with a flowmeter and two butterfly valves. The first valve is controlled remotely by MVIC and is used to set flow rates according to the number of shares of water allocated to that shareholder. The second butterfly valve is the throttle or shutoff valve for the owner.
In open-channel water distribution systems, such as MVIC's old one, flow measurement is made via Parshall flumes or wier boxes. Their accuracy ranges from a best of 5% of flow to a typical 20% of flow, and MVIC needed better if it was going to measure and control the entire water distribution system.
Traditionally, closed-pipe water distribution systems have used mechanical flowmeters. The first water turbine meter was produced in the 18th century, and its descendants are similar in design, with a mechanical register for totalizing water usage. They are very accurate and designed for water billing service. But, turbine and propeller meters are maintenance problems, and they are difficult to use as a flow transmitters.
MVIC decided to use transit-time flowmeters clamped to the outside of the HDPE pipe. Two transducers infer the velocity of the water by measuring the difference in the time it takes for an ultrasonic signal to move upstream and downstream through the fluid.
One of the reasons, Siscoe reported, is that the flowmeters can be solar- or battery-powered. The large turnouts are supplied with continuous power, either by line voltage or by solar power, which is highly advantageous in Colorado. Smaller turnouts are powered by the district's "ditch riders," who carry portable 12-VDC batteries with them. "While the flowmeter is under battery power," Siscoe explained, "the measured flow rate is used to manually adjust flow via the butterfly valve immediately downstream from the meter. Most turnouts require only one setting per season."
Another reason for using ultrasonic flowmeters was the drastically reduced maintenance requirement.
"The Dynasonics flowmeters are now our standard for both new and retrofit applications, particularly replacement of our impeller flowmeters," Siscoe said. "We especially like their non-intrusive aspect, which results in no maintenance, low cost, flexibility and ease of installation." The district now has to keep only one type of flowmeter in inventory.
"The MVIC's long term goal is to fully automate the system by installing wireless flowmeters and automatic control valves downstream of the meters," Knudsen said.
As a pilot, the district received a $75,000 Conservation Innovation Grant from the USDA's National Resources Conservation Service. Scope items for the CIG grant include a solar-powered gate to control water level in the feeder canal and a wireless flow control and measurement system.
"Using solar power saved $25,000 to install an electrical service line to this remote location," Knudsen said. "Based on this success, MVIC has ordered another solar powered flow control gate for another canal next winter."
A wireless SCADA system will be implemented at two turnouts. "This portion of the project will demonstrate flow control and measurement at a remote location where flow needs to be changed regularly throughout the season," Knudsen said. "Wireless automation at these two turnouts will demonstrate to the MVIC and its shareholders the benefit of remote flow measurement and control."
The transit-time flowmeters use strap-on transducers, which function as ultrasonic transmitters and receivers.
"All the turnouts on the closed pipe network have ultrasonic flowmeters with electronics capable of sending flow measurement data to the SCADA master control center at the MVIC office." Knudsen said.The project has been so successful that the U.S. Bureau of Reclamation (USBR) is providing $2.1 million in stimulus grants to MVIC for construction of a second, seven-mile project.
Knudsen reported that the final project costs were $2.9 million, with annual savings projected to be $2 million. These numbers would yield a payback in about 18 months.
Walt Boyes is editor in chief of Control.
