Canal upgrading boosts efficient water use and promotes safety by moving water from an open concrete bed to HPDE 3-feet underground.
Since the 1870s, farmers in Washington County, UT, have relied on the Virgin River for supplying water to grow their crops. The St. George and Washington Fields canal got its start as a simple but well-graded earthen ditch that had to be cleaned between growing seasons of debris and sediment intrusion. Washouts during rainstorms were a problem, especially since the water source, the Virgin River, would increase its flow as much as ten-fold. About 30 years ago the canal got a concrete liner to help save water and reduce upkeep expenses. Still seepage, as well as debris and sediment deposits, remained two principal concerns.
A newer challenge has been the growth in population, the resulting skyrocketing of land price, and the need for more water. People in other states had begun moving in to take advantage of the mild winters, the congeniality of the earlier residents, and the proximity to Zion National Park, which doubles as the headwaters for the Virgin River. Subsequently, homes crept closer and closer to the open, unfenced nearly 8-mile-long canal.
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Photo: Washington County Water Conservancy District |
| Less than 10 inches of rain annually and little snowmelt makes irrigation a challenge in the Washington County community. |
This change from a remote rural area into a metro area increased the demand for secondary water—and increased the potential for a liability claim. Stockholders in the canal knew something had to be done, but with an estimated cost of $10 million, where was the money to come from when the only revenue was from water users?
Ron Thompson, general manager for the Washington County Water Conservancy District, explains, “The funds came from both a grant and a 30-year payback for the loan from the Utah State Board of Water Resources. We’re one of the biggest shareholders in the St. George and Washington Fields canal, and I’m secretary-treasurer on the board of directors. We oversaw the project, including timely payments and the providers, as well as overseeing installation of the pipeline.”
Thompson reports he’s been dealing with water issues throughout his adult life. “In some areas of the county, rainfall is just 7 inches a year.” Nor is there much snowmelt to boost early-season irrigation needs as the Virgin River makes its way to Lake Mead.
One element in the project included keeping board members current on canal progress and dispersal of funds. Says Melodie Sorensen, accountant with the Washington County Water Conservancy District, “All financial records were available any time a member of the board wanted to read them. They didn’t have to wait for a report given by Ron [Thompson] at the weekly board meetings.”
In the Beginning
Once the funding was secured, the water district contracted with Alpha Engineering in St. George to draw up the plans. Brent Gardner, president and founder, started Alpha Engineering 17 years ago. The company began as a one-person operation and has 25 people today. It supplies a broad coverage of civil engineering concerns in Washington, Iron, and Kane counties, providing design and construction management services for several governmental agencies including grading and drainage, water, wastewater, and roadway systems. “We have been involved in the development of several water resources and water conveyance systems,” Gardner says. In fact, the company has contracts with seven municipalities to handle its engineering needs.
Gardner points out the canal, which is one of the oldest and largest structures drawing water from the Virgin River, runs east of St. George, county seat for Washington County. “It has a fall of 1 foot every 1,000 feet, so it’s a very flat canal that serves areas in the city of Washington and the city of St. George. A design flow rate of 86 cubic feet per second called for a 63-inch high-density polyethylene [HDPE] pipe the first 20,000 feet and 54-inch pipe the final 13,000 feet. The reduction of the final stretch was possible because intermediate outlets had reduced the flow so a smaller pipe could handle the water.”
Besides the canal, there are approximately 30 16-inch outlets connected to lateral pipes, some stretching 0.5 to 1 mile. While the outlets were part of the overall $10 million project, other individuals or companies were responsible for constructing and maintaining those laterals.
Piping the canal has made it possible to eventually pressurize the system. This will be important for residents needing sufficient pressure to spray lawn and plants with this secondary water. Air/vacuum relief valves were placed every 2,500 feet to provide necessary air/vacuum relief. Better water utilization will make a significant impact on city parks and other public places needing water because many of those sites used to depend on culinary water. The switch to secondary water, whether residential or municipal, means there will be more potable water for further rural-residential development.
Silting and debris had been a long-term problem, which, even with the concrete-lined canal, continued to be a maintenance issue. The design solution was to install an automatic traveling trash screen to remove floating objects. The screen was placed on the inlet to the piping system to ensure that nothing—including fish—gets into the canal. “Another element was to remove the heavy sand at the diversion dam with the aid of a de-silting structure so that only fine silt ever enters the piped canal,” Gardner explains.
Eventually automatic filters could be used to further remove fine silts prior to use in secondary water systems for parks and golf courses. This strategy makes for cleaner secondary water, whether for farm fields, residential systems, city parks, golf courses, or other secondary water users.
Gardner reports the system is designed to handle stormwater concerns. The Virgin River typically is 1 foot deep and 30 feet wide. During storms the flow can boost the river’s size to 10 feet deep and 100 feet wide, bringing down a much heavier load of debris and silt. “The river is pretty clean during dry periods, but it turns brown when there’s a storm. The river comes from several tributaries, with a portion of the headwaters originating in Zion National Park.” Still, erosion is an ongoing challenge.
Besides providing cleaner water, burying the pipe makes it possible to use the canal easement for a maintenance road or trail. Best of all, the buried pipe removed safety concerns.
When Alpha got the contract in July 2004, it had to have the design completed that November. “We also had to prepare a list of materials for the canal company, and they took it from there. The first phase of the three-year project ran from December 1, 2004, until March 1 2005, and saw a mile of pipe installed. Basically, the contractor, Interstate Rock Products in nearby Hurricane, Utah, removed and pulverized the concrete, which they mixed with backfill material. Their trenching was deep enough to allow 3 feet of cover over the HDPE pipe.”
Another challenge was to find HDPE with the massive diameter called for. JM Eagle of Livingston, NJ, the largest manufacturer of HDPE and PVC piping in the world, supplied the solution. With 14 plants in the US alone, the nearest one, located about 200 miles south in Kingman, AZ, took on the challenge to manufacture the first 63-inch pipe in the nation.
As the project continued, Alpha reps attended weekly meetings with the conservancy district and canal officials. Gardner’s people also were onsite to help with any unexpected situations. “We had up to five people involved with the project during the design and construction periods. Because of the long growing season, time was a limitation. We also had several other ongoing projects we were working on at the same time and had to be efficient to get this project done in a timely manner. We are in a relatively small community so we need people with all kinds of skills, people who can do everything connected with civil engineering.”
Coordinating the Project
With timeliness and avoiding cost overruns two essential elements, a key player in a project is the program coordinator. In this case, Doug Wilson, special project coordinator for the Washington County Water Conservancy District, was given that responsibility. He says, “The district covers the whole county and we are one of the largest shareholders in the canal company. Before I got the assignment to coordinate the construction, the project was pretty well thought out. My main responsibility during the construction phases was to keep everybody on the go.”
Coordination with all parties involved in the project was essential because there wasn’t much time each year to spend replacing the old open canal. “We have a long growing season with acres of corn, alfalfa, and other such crops relying on the canal for their water supply.” He adds that because of the high mineral content, there are no commercial orchards on the acreage served by the canal.
A plus for the canal is the mild winters. Snow is rare, happening perhaps once a winter. Ice is not a problem with the open canal. Now that it’s 3 feet underground, it’s well insulated. This further helps ensure better longevity for the buried canal, making the investment even more sensible.
“The canal runs west, then south and west again. High land values are prompting farmers to sell their acreage for residential construction. The canal used to supply water strictly for agriculture, but now it’s used as secondary water in residential lots. It’s also used for recreational use where turf is important. For example, some golf courses rely on the canal for water.”
Like Gardner, Wilson sees the project as a means for making better use of water than possible when exposed to evaporation—and seepage. Some estimates report that as much as 10% of the water in the concrete canal was lost to seepage. Eventually, seepage led to washouts. “By piping the canal, those problems are behind us. It has cut down on the maintenance workload because the canal doesn’t have to be cleaned every year like it used to.”
Another natural challenge of seepage and open ditches was that those at the end of the canal got less water than those at the head. Water delivery is timed, rather than measured. So the more flow water users get for the time allowed, the more they can utilize it.
Wilson, who has been dealing with water issues for 10 years, comments the full length of the canal goes through the Moenkopi formation of rock and clay, interlaced with gypsum. This combination of soil caused settlement in parts of the canal, which led to cracks, which led to washouts in some places. The company first used liners in the troubled areas. But even the liners proved merely to be a temporary fix.
He adds that the low grade of the canal slowed water flow, causing sediment to drop and settle on the bottom of the canal. Naturally, this decreased the capacity of the canal. “We’ve had no silt dropout since we put in the silt and sediment control devices to make for cleaner water before it entered the pipe.”
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Photo: Washington County Water Conservancy District |
| The canal supplies water for agriculture and secondary water in residential lots. |
Wilson emphasizes that keeping the project on time and within budget took a lot of work in planning, design, and coordination of the elements that make up a complicated project.
One complication involved the roads the canal crossed under. “Fortunately there were just five of those, with only one paved road in the entire length. When the contractor came to those, his people trenched under the roads from both sides and pulled the HPDE pipe through. This avoided any problems with traffic.”
He says, “The public reaction has been positive for the city because there’s more water available for city recreation use. The concrete canal had a 25-foot right of way on each side. By placing the canal underground, that level ground is becoming more and more popular for recreational use.”
Timely Construction
After the canal company got the materials list from Alpha, it put the construction portion out for bid. Interstate Rock Products, which has a branch southeast of St. George in Hurricane, proved to be the low bidder. “We prepared the ground and put 5,000 feet of 63-inch pipe the first winter, 30,000 the second winter, and 13,000 feet of 54-inch pipe in the third season,” says Craig Stratton, secretary-treasurer for the corporation.
Advance material ordering helped Interstate meet the timeline demands. “We couldn’t shut off the canal until the first of December and had to have the flow back in place the first of March. With 15 to 25 employees on the site we were able to get a lot done even with such a short work window.”
One element that helped was ordering the 63-inch from local supplier Isco Industries in West Jordan, UT, a month prior to use. Stratton adds, “The pipe came in 50-foot lengths. We fused 10 to 15 pipes together above ground and then placed the completed sections in the trench. We used a portable crusher to deal with the concrete, and saved it to mix with the soil brought in to use for overburden.”
He says this move made it possible to fill 20% of the overburden needs. Sourcing soil for fill ranged from 3 miles to 10 miles. The portable crusher moved along the canal as workers dumped crushed concrete in the hopper. This reduced the time needed to get fill material onsite, which reduced the cost of installation.
“We had to dig 3 feet below the old canal, which was 6.5 feet below grade. The old canal was 8 feet wide at the bottom and 20 feet wide at the top. After we put the pipe in place and fused to the newly installed segments, we did a vision inspection of each seam before covering the pipe.”
But what about dealing with the road crossings? After noting his company also had 21 utilities to deal with, Stratton comments that by working with an excavator on each side of a bridge, crews were able to remove the concrete and dig a trench at the right depth. After that, it was a matter of pulling fused segments of the pipe underneath each bridge so there was 50 feet of exposed pipe on each side of a bridge. This strategy made it easier to fuse those segments to the approaching line.
“We’ve been using HDPE for seven to eight years, but never any this large. Up to that time, the biggest HDPE we had installed was 30 inches. We rented a machine large enough to fuse the segments. There are a limiter number of machines that can handle pipe with such large diameters. Plus, with such a machine costing about $400,000, it made sense to rent instead of buying. We have our own smaller machine, which can handle 24-inch tubes.”
Stratton, who has been dealing with construction for 25 years, emphasizes his company used all the construction windows each year to ensure timely completion. “We have a crew that does the outlets; another crew builds boxes for concrete gate valves. It was a straightforward construction project. The only problem we had was during the second year when some material for the outlets didn’t arrive on time.” But material supply wasn’t a problem during the third phase because some of the products were onsite a week before the end of the second phase. Again, timely delivery kept the project on the go and offered a timely disposal of funds, which is another money saver.
Stratton comments that weekly meetings with the Water Conservation District year-round helped to make the project easier to complete. He emphasizes advance orders of outlets and flow valves avoided a repetition of the problem during the final phase.
Keeping Neighbors Happy
A common chore for all elements of the St. George and Washington Fields canal project was keeping the neighbors happy, especially during construction. Stratton comments, “We met with property owners to explain our schedule for working near their homes or farms, and exactly what we were going to be doing. Since safety issues were being addressed, most people were happy to see the canal go into the pipeline. Basically, our contract called for installing the pipe with different outlets for secondary rural residential use. Both Washington City and St. George have future outlets planned so as the cities grow they can plan to pipe water into those areas.”
With 150 to 300 employees in this branch of Interstate Rock Products, the company has placed all kinds of other pipe, but the 63-inch and 54-inch HPDE was the largest it’d ever dealt with. “We really enjoyed this project because it had good working conditions and good coordination with the engineering company, owners, and residents. People along the route were satisfied because we kept moving along the canal. Neighbors don’t like construction sites to last a long time. We also kept out of people’s front yards.”
Crag Stratton notes Interstate has been in business since the late 1950s and has always tried to maintain a working relationship with all involved in a given project. “We work hard to get the job done. It’s a win-win situation.”
Meanwhile, Back to the WSD
Looking back on the St. George and Washington Fields canal project, Ron Thompson comments, “This project was particularly remarkable because it required a lot of people working together. Thanks to everyone involved, the project went smoothly, and has saved a lot of water. That savings can be used to help both cities improve their parks’ turf and there will be more secondary water available as the population continues to increase. At the same time water availability to farmers using the canal will be more consistent.”
What about the small reservoir serving the canal? Thompson responds, “A regular reservoir is on the agenda at the head of the canal. It will hold 25,000 to 30,000 acre-feet, and has the capacity to ensure even more water during dry times. Naturally, the reservoir will make room for other distribution systems without compromising water delivery through the St. George and Washington Fields canal.”
Ron Thompson, along with everyone else involved in piping the canal, is pleased that the project saves about 4,400 acre-feet. Again, this savings means greater use of cleaner secondary water. And a substantial share of that savings means greater utilization of culinary water.