Gallon for Gallon

Ensuring accurate water resource management

Think for a moment how you'd feel if you sold a gallon of bottled water and then discovered your customer got a third more than a gallon. Irrigation water suppliers in the arid West are apt to find themselves in this situation if farmers' open-channel irrigation systems are old and in disrepair.

An important measuring tool in many irrigation systems is a device called the flume, developed more than 60 years ago to measure water delivery to farmers' fields. The most popular flume used in Colorado and much of the West is the Parshall Flume, developed by Ralph Parshall, a Colorado State University (then Colorado A&M) engineer in the 1920s. Flumes are constructed of concrete or sheet metal. When properly installed and maintained, the Parshall flume provides water delivery accurate to plus or minus three percent.

The problem is that age takes its toll. Research by Steven Abt, civil engineering professor at Colorado State University, found that, after long periods of service, flumes can settle into the ground unevenly and cause inaccurate water measurements. It's a serious concern for farmers who rely on precise allocations of water for growing crops, and for ditch companies that have the task of delivering accurate amounts of it. "In this day and age of increasing demand for water resources, accurate water.measurement through the water conveyance system is vital," says Abt. "We've found flumes in Colorado that have settled enough to cause up to 30-percent measurement errors in water delivery."

Abt's research team examined 149 flumes on farms in seven different areas of northeast, southeast, south-central, and western portions of Colorado. They found a total of 392 defects at the 149 flume sites. Most are caused by settling, usually the result of years of exposure to the elements — wetting, freezing, thawing, and contact with machinery and equipment. In addition to settlement problems, some of the flumes were corroded or had bent metal components, holes in the floor or sidewalls, siltation and vegetation blockage, and instances where part of the water flow bypassed the flume. None of the flumes had all the gauges needed to perform all the required water flow measurements. Of the 149 flumes examined, only 39 were in good to excellent condition, and of those, most were newer — less than 10 years old.

Abt and his research team developed a computer program that allows farmers to evaluate their flumes and correct water flow measurements without expensive modifications or installations.

The program is called the Parshall Flume Discharge Correction Program and was developed by the Colorado Agricultural Experiment Station. Available to any producer who has access to an IBM-compatible personal computer, the program asks the water user to make five different field measurements regarding flume performance. The computer program then gives the user correction information for accurate water measurements. The best part is it's free. Research funds provide the computer disks and user instructions. Information and copies of the flume correction program are available from Steven Abt, Professor, Department of Civil Engineering, A227 Engineering Research Center, Colorado State University, Fort Collins, CO 80523; or call (970) 491-8203.

Abt has turned his attention to conducting similar research on another type of flume used in Colorado called the cut-throat flume, again looking for measuring inaccuracies and developing computer software programs to deal with them.

Abt says that although his research may appear to be a high-tech answer to a low-tech problem, the benefits of accurately delivering water to Colorado agriculture are important to everyone, especially as more people compete for this valuable resource.