The water district now proposes an option for an 11-foot-deep, 4-acre flood basin at the Cuesta Annex, replacing the 22-foot-deep, 4.5-acre basin that was previously proposed. Several large trees would be kept that would have been removed in the previous plan, angering proponents of keeping the untouched piece of open space as-is.
Annex basin or not, flood basins at McKelvey Park and Rancho San Antonio remain in the water district's plans.
The Annex basin would cost $7 million more than the catchment pipe option, water district engineer Afshin Rouhani said. The pipe could run under Cuesta Drive or another street running east-west north of Permanente Creek's diversion channel to Steven's Creek.
As the Voice reported Aug. 5, a new look at Permanente Creek's hydrology found that 100-year flooding of Permanente Creek will not be as bad as previously thought.
Dam alternative dropped
When the Blach School flood basin was removed from the plan by Los Altos school officials in January, the district was spurred to take a look at an area near the Lehigh Quarry where a dam could be built on Permanente Creek instead. That's when a 300-acre area previously thought to drain into the creek was found actually drain into Lehigh's several-hundred-foot-deep quarry pit, reducing projected creek flows in a flood by 10 percent.
In addition to making the Annex basin unnecessary to met the project's goal of providing flood protection north of El Camino Real, the change in hydrology has also caused the water district to drop the option of building a dam at the quarry, which would have disturbed wildlife habitat, including that of the rare red-legged frog.
"The changed hydrology makes the dam less effective," Rouhani said. "There's less that the dam would capture in the upper watershed."
A date for the City Council meeting on Permanente Creek flood protection is not set in stone, but is expected to occur in early October.
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