News

Smaller flood basin for Cuesta Annex?

Permanente Creek dam may be unnecessary, Water District says

A close look at the way water drains off the hills into Permanente Creek has revealed 300 acres that do not drain into the creek, reducing the need for proposed flood basins in Mountain View and a dam upstream that would destroy wildlife habitat.

The Water District examined the area after Los Altos school officials pulled the Blach School overflow basin from the project, said Santa Clara Valley Water District engineer Afshin Rouhani. That spurred a new look at building a dam upstream near Lehigh Quarry. Hydrologists found 300 acres nearby that were assumed to drain into the creek but actually drained into the quarry pit.

"When the school turned us down we had to go back to the dam alternative," Rouhani said. "That was the only feasible alternative at that point. When they looked at the upper watershed in detail, they assumed all of it flowed downstream, but some of it actually drains to the Lehigh Quarry pit. Once they removed that area it made a big difference."

Water flow projections down the creek in a major, 100-year flood, have been reduced by 10 percent, or as much 300 cubic feet per second, Rouhani said. A so-called 100-year flood is a flood that has a 1 percent chance of occurring every year.

The reduction in flow not only is enough to make the dam unnecessary to meet project goals, but could also reduce the size of a planned flood basin at the Cuesta Annex, which has been a controversial use of a much-loved piece of open space. The Annex basin was proposed to be 21 feet deep in some areas, and cover 7.5 acres.

Detailed revisions to the project will be released in a draft environmental impact report in two to three months, Rouhani said. Plans for the City Council-approved flood basin at McKelvey Park, which would lower the park 15 feet and create new baseball fields, are not expected to change. And the proposal is likely to retain a third flood basin on county land near Los Altos at Rancho San Antonio Park, Rouhani said.

Dam still an alternative

Without a flood basin at Blach School, residents of Mountain View who live south of Cuesta Park may still be subjected to increased flooding if a dam is not built upstream. The Permanente Creek diversion channel, which runs east to Stevens Creek through residential areas near the city's southern border, could overflow in a major flood, Rouhani said. The Blach School basin would have prevented that.

Whether to better protect those homes near the diversion channel is up to elected officials. The 2000 bond measure that is funding the project only specified flood protection for 1,600 Mountain View properties in flood zones north of El Camino Real, but could pay for added flood protection south of El Camino Real if an acceptable way of doing so is found. It is a hard sell to residents however, as there is no record or memory of major flooding from the creek since the area became developed.

Comments

Posted by Cuesta neighbor, a resident of Cuesta Park
on Aug 4, 2011 at 2:27 pm

The Cuesta basin in the original EIR was 4.5 acres, not 7.5 acres.


Posted by Ron, a resident of Waverly Park
on Aug 4, 2011 at 2:39 pm

I'm sorry, but this sort of smacks of "We over exaggerated our needs to get the things we wanted built. But now that one of them cannot be built, suddenly we find we need less than we thought so that it will still work." I also find it ridiculous that MV is putting so much effort into preventing a flood that they have no modern record of being an issue.


Posted by Steve , a resident of Sylvan Park
on Aug 4, 2011 at 2:59 pm

Another govenment spending plan based on flawed data? Hmmm. I see a pattern here...


Posted by Suggestion for Study, a resident of Cuesta Park
on Aug 4, 2011 at 3:00 pm

I've heard that another 1,000 homes in the area could be "saved" with improvements to Hale Creek. Those improvements are defined, but they didn't make the cut when the project plan called for basins at 4 locations. Perhaps with no investment now needed at Blach, the Hale Creek improvements could make their way into the plan.

It would surprise many residents that the current plan of improvements to Permanente Creek will not change their flood zone status...even some of those living very near Permanente. Their status would change with these known improvements to Hale Creek.

Maybe a local paper could do some investigation.


Posted by Bruce Karney, a resident of Old Mountain View
on Aug 4, 2011 at 3:15 pm

I've read that there was a very bad flood in Mountain View in the early 1950s in the area near Cuesta Park. Could the Voice dig up some of the details?

My understanding is that as a result of that flood a diversion canal was constructed flowwing east from Miramonte to Stevens Creek near MVHS.


Posted by @Bruce, a resident of Cuernavaca
on Aug 4, 2011 at 5:13 pm

The diversion canal you mention is the diversion channel in the last two paragraphs of the article. There has been no major flooding since the channel was built. That doesn't mean it can't happen but it's at least less likely than it once was.


Posted by NeHi, a resident of Cuesta Park
on Aug 4, 2011 at 5:33 pm

"300 Acres that do not drain into [Permanente] Creek"; that's less than 1/2 sq. mi. And that would eliminate a dam and make a flood basin smaller?? What else would "reduce the need for a dam" mean??

Bruce, my house is in the area where there was a flood in 1955 or 1956 [I chased high-water marks from those floods thru N. Cal., brutal]. I drove El Camino from P.A. north in the 1958 flood which was pretty bad, couldn't always see the median line. I see no evidence of damage from any flood.

Conclusion: I don't think there is nearly enuf info for a conclusion.


Posted by Waldo, a resident of Waverly Park
on Aug 5, 2011 at 1:22 pm

I was here in the 1950s, and there was lots of rain and flooding, along with logging in the mountains and new construction throughout the area. If it happened to that extent today, Hwy 237 would be underwater near Alviso, and parts of MV could be underwater as well, in which case flood basins at Cuesta and McKelvey would be invaluable.


Posted by Steve, a resident of Sylvan Park
on Aug 5, 2011 at 4:18 pm

Let's say you own one of the 1600 houses 'at risk'. Why should everyone else get billed to save your b*tt?


Posted by Rick, a resident of Rex Manor
on Aug 5, 2011 at 7:21 pm

How many minutes would it take to fill these little basins in the great flood. Not many I suspect. If the basins are below the drain system, how would they be drained after a normal winter day of rain. One of them is a ball park. Needs to be kept dry. Stagnant water can't stay in these basins.


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