The waters of the Boise River are rising, but to protect animals at the Zoo Boise from potential flooding, the city is building a "muscle wall," not an Ark. The wall will be a 2-foot-high, 2,000-foot-long water-filled bladder between the zoo and river. Construction of the barrier will close Julia Davis Drive from the bandshell to the tennis courts, but the Friendship Bridge between the park and Boise State University will remain open to pedestrian and bike traffic. Evacuating Zoo Boise would cost the city of Boise $500,000-$600,000, according to city officials, while the $130,000 barrier has been touted as the most cost-effective solution to potential flooding. Another consideration, zoo officials said, would be the potential distress caused to the more than 200 animals should they need to be relocated. A wall similar to the one used to protect the zoo was deployed to hold back floodwaters at a gravel pit near Eagle Island in May. Flows on Boise River measured 9,300-9,500 cubic feet per second Tuesday and Wednesday at the Glenwood Bridge. That's the highest flow rate in the past 35 years by more than 1,000 feet per second. Meanwhile, federal water managers have warned the city flows may increase in the coming week as warm weather persists and upstream reservoirs reach capacity. High water has been a consistent challenge this spring. Boise Mayor Dave Bieter and Garden City Mayor John Evans closed most sections of the greenbelt April 14, and those sections have remained off limits to the public ever since.

On Wednesday, the City of Boise will began taking precautionary measures to protect Zoo Boise in the event that hot weather this week and fast-filling reservoirs force federal water managers to release more water into the Boise River, according to a news release. City engineers and other agency partners with the Ada County-wide team working to manage flood response Tuesday began preparations to install a 2,000-foot-long, four- to two-foot-tall “muscle wall” flood barrier. “The structure is similar to the wall constructed to protect a gravel pit near Eagle Island last month,” said City spokesman Mike Journee. “Zoo Boise managers and emergency responders are taking the proactive step because of the difficult logistics, expense and potential stress to animals if relocating the Zoo’s more than 200 animals became necessary. Additionally, federal water managers are now saying that this week’s significantly warmer weather and quickly shrinking capacity in upstream reservoirs means that notice of river flow increases could come just 24 hours in advance. That would give zoo managers little time to plan an animal evacuation, if needed,” he added. “We are doing this out of an abundance of caution to ensure we are not faced with planning a full-scale evacuation of zoo animals on short notice,” said Doug Holloway, Director of Parks and Recreation for the City of Boise. “The investment to protect the animals and zoo property is a good one, given the circumstances.” The construction of the flood barrier will force the closure of Julia Davis Drive between the bandshell and tennis courts. Friendship Bridge, the pedestrian bridge between Boise State University and Julia Davis Park, will remain open to through-traffic for pedestrians and bike traffic. However, the Greenbelt through the park and the entire city remains closed due to the high water and safety concerns. “The conditions on the Boise River and the Greenbelt become more dangerous as time goes by and the water undermines the tree roots and the foundation of the Greenbelt,” said Boise Fire Chief Dennis Doan. “These conditions are potentially fatal to the public and first responders. We ask all residents to respect this closure to prevent any tragedies.” Evacuating the more than 200 animals at Zoo Boise would cost approximately $500,000 to $600,000, plus post-flood clean-up costs and revenue lost with the zoo’s closure, officials said. “Additionally, such a move would could be extremely stressful to many of the animals. The flood barrier is expected to cost approximately $130,000 and cause animals little or no concern. Of that cost, $118,500 will be covered by grant funds from Ada County Emergency Management. Installation is expected to take one or two days and the barrier will remain in place until the zoo is no longer threatened by high water,” Journee stated. Currently, the Boise River is flowing at approximately 9,300 cubic feet per second. While federal water managers have no immediate plans of increasing those flows, they have warned city and county officials that current weather conditions likely mean advanced warning of just 24 hours if and when increases are necessary -- much shorter than the three- to four-day window of previous weeks.

A long line of plastic barriers has appeared on the north riverbank as it snakes through the Logan River Golf Course. It’s a product called Muscle Wall and is expected to ease flooding worries as spring runoff have created flood watch conditions. Logan Parks and Recreation Director Russ Akina said the city purchased 600 wall segments about two weeks ago for just under $350,000. Akina said he feels confident that the Muscle Wall will prevent flooding along the golf course like Logan saw in 2011. The plastic, 6-foot-long wall segments — some 2 feet tall and some 4 feet tall — are hollow. Two people can easily lift a segment and drop the interlocking pivots into place, creating a continuous barrier. Then, they are filled with water and a tarp is draped over the top to prevent erosion underneath the Muscle Wall. Akina said city engineers have surveyed the Logan River and identified areas with low riverbanks, where water is dangerously close to overflowing. Based on reports from the National Weather Service in Salt Lake City, Akina said they are taking measures to prevent flooding. “We’re trying to stay ahead of the anticipated runoff to protect areas, whether that is residential property or city property, including the golf course,” Akina said. In 2011, large sections of the Logan River Golf Course were underwater. Roughly three weeks ago, Akina said, a section of the riverbank that failed in 2011 was six inches from flooding the bank. That encouraged Logan to look into options besides sandbags. He said approximately 300 sandbags would be needed for each segment of Muscle Wall, meaning somewhere in the tens of thousands would be needed along the river. “That’s a lot of sandbags, so as an alternative to that, we decided to go with this Muscle Wall in place of that,” Akina said. Muscle Walls are easier to install and can be reused year after year, while sandbags are heavy, labor-intensive and don’t last more than one season. “It’s much faster and more efficient for us to be able to move sections of wall, store them and then have them back ready to use when we have to do this again,” Akina said. Large sections of the wall were installed Saturday, and workers filled in other sections Monday. Akina said they are waiting for tarp anchors to be delivered, but as soon as they arrive the tarps will be set up and the Muscle Wall will stand ready. Along a residential section of the river, in the Sumac area, Public Works Director Mark Nielsen said city employees will place sandbags Monday night where houses back up to the Logan River. The river is running high and fast, but cooler temperatures are expected to bring some relief. “The river thus far has behaved very well,” Nielsen said. “It’s hot for a while, then it cools down, and that’s a great help to us to keep it where it should be.”