Washoe County tries new flood protection measure
The North Valleys have long suffered from flooding problems, but wet weather over the last three years has made the situation particularly bad in Stead and Lemmon Valley.
In Lemmon Valley, residents living near Swan Lake have grown used to the flooding prevention measures in place there. They include things like diesel-fueled pumps and large barriers called HESCOs, with which some people may be unfamiliar.
“They're pretty clever,” said Dylan Menes, a senior Washoe County engineer. “They've saved a lot lives—because they were used in Afghanistan and Iraq. They're still being used as protection for the troops to stop bullets and car bombs and stuff like that. You take what's called ‘welded wire' or welded steel mesh that's in a series of squares that are linked together and then create a cube with that steel mesh. And then, within that, you place a heavy, geo-tech style of felt, and then you pour sand in there. The felt keeps the sand in, and it becomes a very massive and slightly flexible, adaptable barrier.”
HESCO barriers can be put up quickly and maintained over long periods of time. And early in September, Washoe County tried an experiment to see if the barriers could be made more effective.
“HESCOs work very well,” Menes said. “They're very resilient. They've done a good job for us, and we're very happy with them. But they can seep a little bit of water underneath—and sometimes through the seams of the big cubes. They're about four-foot-by-three-foot-by-three-foot cubes. And that's what we're seeing, a little bit of seepage—but they're performing well, and they're doing their job, for sure.”
To see if the seepage could be stopped, the county purchased 12,000 tons of bentonite clay and applied it to a section of the four miles of HESCO barriers around Swan Lake.
“We had two different gradations [of clay],” Menes said. “One was a finer gradation, and one was three-inch chips. And they came in different ways. One came in a giant sack called a ‘super sack.' The other came in small, 50-pound bags. The 50-pound bags, our crews just laid them out in the proper quantities on the top of the HESCO walls, and then we cut them open and poured them into the water and adjusted them as it settled into the water. The larger super sacks required some heavy equipment. We first put that into a dump truck. From the dump truck, we put into a front loader—a kind of equipment that has a long, wide front bucket—and then we very delicately but that over the HESCOs and dumped it in slowly in a controlled fashion.”
As of Sept. 9, Menes reported that the bentonite clay appeared to be working, at least to some degree.
“So this is a trial experiment,” he said. “And it's not the ideal way to apply it, but it's one of the ways we can at this point. And it's been six days now. We've had some rain storms in between, and it looks like it has worked somewhat. It hasn't quite knocked all of the water out, like our highest expectations would be. But we have noticed a decrease in water seepage. I mean, we haven't seen enough to make a decision whether to use it more yet.”
Menes also said the county may use bentonite in different ways in the future, including possibly incorporating it directly into new HESCO barriers along with the sand that usually fills them. One of the main reasons the county is keen to experiment with bentonite is that—if effective—it has the potential to reduce the costs of flood control at Swan Lake.
“Depending on the season, we've had upward of 40 pumps around the lake pumping that seepage water back into the lake,” Menes said. “Those pumps also serve another purpose, which is whenever it rains, we've created a barrier that prevents the storm water from going into the lake, which can create it's own set of problems with flooding. So the pumps also take that storm water and pump that into the lake, too. These pumps have to be maintained. We've got to keep diesel in them. We're constantly adjusting them and tweaking them. We have a vendor that helps us with that. And we spend a lot of money doing that—between $100,000 and upward of $250,000 a month in maintaining this pump system—to protect the residents of Lemmon Valley … to keep the lake in the lake.”
The bentonite cost the county $4,090. For now county engineers plan to keep an eye on the barriers—which are monitored daily—and see how the bentonite clay they've added to them performs as they continue work on other flood management projects.
“There's a lot of work going on regionally with our partners, the City of Reno and RTC,” Menes said. “And one of the things the county is working on with the engineering community is the Regional Hazard Mitigation Plan, which is countywide. But there's obviously a huge focus on the North Valleys now, where there hadn't been in the past. We're focusing most of our regional mitigation planning on Swan Lake. What that consists of is—we have a number of stakeholders from the engineering community and other agencies. We're sort of evaluating the nuts and bolts of a series of alternatives for hazard mitigation for Swan Lake.”
They're looking for long-term solutions to flooding hazards at the lake. While effective for the time being, the HESCO barriers and pumps aren't intended to be permanent fixtures of the lake.
“We don't want them to be there forever—definitely not,” Menes said.
But as to what long-term solutions might look like, he said, that's still unclear.
“We're just looking at them right now—we're not even into feasibility—but there's levees, pumping out of the hydro-basin,” Menes said.
For now, though, long-term solutions and the Regional Hazard Mitigation Plan that will contain them are still a ways off.