Clements is a longtime civil engineer specializing in water and how it drains and runs off properties, and has previously worked as a contract engineer for the Santa Clara Valley Water District, which proposed the project.
Flooding in 1950s
Clement explained that in the 1950s, Permanente Creek had a serious problem with overflowing its banks in Mountain View. The intended fix, built in 1959, was a cement diversion channel directing water from Permanente Creek's upper reaches to Stevens Creek most of the year. A portion of Permanente just north of the channel usually has water in it only during spring, when a diversion structure visible from Miramonte Avenue is opened.
The diversion channel begins near Miramonte and Portland avenues, running east along the city's southern border, and directly behind Blach Middle School in Los Altos. It apparently stopped the flooding of Permanente Creek in the 1950s, but then the diversion channel started overflowing behind the Blach school, most notably in 1983.
The 1983 flooding was linked to a design flaw in the channel, said water district engineer Afhsin Rouhani. The channel would become two underground pipes behind Blach school that would fill with sediment, backing up flows and causing homes nearby to be flooded. So water district officials changed the design in the mid-1980s, continuing the channel at full width behind Blach to keep the water flowing.
But the water district did one thing that drives Clements nuts. They put a constriction in the channel behind Blach, intended to replicate the flow of the original pipes without sediment blockage. The constriction is large enough to send 500 cubic feet of water rushing over the channel's banks in a 100-year flood, Clements says. Rouhani could not confirm that, but said 650 cubic feet per second would come out of the channel in a 100-year flood, reaching as far as downtown Mountain View.
"It's like imagining water spilling from a glass on a flat table, it would just keep going north," Rouhani said. "It doesn't get absorbed by the ground, it just keeps going up until it spreads out." He added that the water would be "2 to 3 feet deep" and then "6 inches to a foot deep once it hits downtown."
Rouhani said the amount of flooding caused by the constriction is roughly equal to the amount the water district planned to catch with a flood basin at the Cuesta Annex. The City Council approved the Annex project, but the water district board rejected it this year after public outcry about preserving the Annex, despite flood risks for El Camino Hospital and 300 nearby properties. Rouhani said that a flood basin at Rancho San Antonio will still be helpful to prevent flooding around Portland Avenue with the constriction removed.
Clements claims no flood basins are required if the district would just remove the constriction behind Blach school.
"They could remove the flood threat in one afternoon, it's incredible," Clement said of the constriction. He added that El Camino Hospital should be taken to task for offering to spend millions to help complete what the Annex basin was set to achieve. "Their ignorance or indifference should be challenged and exposed," Clements said of the hospital. "It's community money," he said.
Moving problems downstream
Legally, the constriction can't be removed because that would be moving a flood problem downstream to Stevens Creek, Rouhani said, although that's ostensibly what happened when the diversion channel was built. Rouhani confirmed that there's a portion of Stevens Creek, just north of El Camino Real, which now has less than half the capacity it would need in a 100-year flood. It would need to flow 8,300 cubic feet per second, but can carry only 3,800 cubic feet per second.
While Permanente Creek's alleged flood problems have been discussed over many years in dozens of meetings in Mountain View, little has been said of Stevens Creek's problems. Water district engineer Liang Xu said they water district did not have a flood map for Stevens Creek.
"They are working on the wrong watershed," Clements said of the Permanente Creek flood project, funded with $34 million from the Clean, Safe Creeks Natural Flood Protection Plan approved by voters in 2000. As much as $15 million from another fund has already been spent on its design. Despite the water district's obligation to fulfill the promise of the 2000 bond measure, the real fix is still needed on Stevens Creek, Clements said. "They have to do that anyways."
Brian Schmidt, Mountain View's representative on the water district board, couldn't say why a fix for Stevens Creek wasn't part of the
Safe, Clean Water and Natural Flood Protection measure which county voters approved in 2012 for flood projects throughout the county.
"I don't know if anyone has worked the numbers on how much it would cost to fix Stevens Creek," Schmidt said.
"In another 12 years we'll come back again," for another ballot measure, Schmidt said. "Depending on how it costs out, I could see it on the list."
Council member Jac Siegel, a retired aerospace engineer, called the Permanente flood protection project an example of "political engineering."
"I agree with Jerry, I really do," Siegel said.
"The problem is there (on Stevens Creek) — it's not really Permanente Creek," Siegel said. "If they just made a fix over on Stevens Creek, I think the problem will more or less go away."
Siegel remembers the diversion channel being advertised as the fix for Permanente Creek's flooding problem in the 1950s. He was the sole opponent on the council when the McKelvey Park flood basin was recently approved by the City Council as part of the project.
Rouhani said that even with adequate flow through the diversion channel and Stevens Creek, there is still a potential for flooding near McKelvey Park, caused by Hale Creek. Hale Creek dumps into Permanante Creek near the park, where an 18-foot deep basin is planned to catch excess flows from Hale Creek — 300 to 400 feet per second in a 100-year flood, he said.
Mayor John Inks also went on Clements' tour of the Permanente Creek, but said he wasn't convinced that a McKelvey Park flood basin isn't necessary.
"It came down to finally making a decision on McKelvey," Inks said. "Part of this is we're getting new (baseball) fields, much better lights, new trees and we're getting a neighborhood park," he said of the new $9 million park reconstruction to be paid for by the water district.
Siegel said that he believes the whole flood protection project is in jeopardy if the board of supervisors doesn't approve the Rancho San Antonio flood basin on Tuesday.
"If Rancho does not get approved by the county, the project is probably off," Siegel said.
Rouhani said the water district board would have to make the call.
"It's possible they might want to do a limited project," he said.
This story contains 1286 words.
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