The tidal gates in the Palo Alto Flood Basin regulate water, allowing habitats for wildlife to flourish and protecting Palo Alto from flooding by the Matadero, Adobe and Barron creeks during heavy rains and high-tide events.
Tides over time have washed away sand and sediment from beneath the gate, causing a basketball-sized hole underneath, according to the district. Pooling water from tidal flows allowed dormant salt-marsh mosquito eggs to hatch in large numbers and caused a swell of mosquito bites on local residents.
If the seepage were to persist, it could threaten the tidal-gate's concrete foundation, district officials said.
Water-district contractors planned to pump an additional 54 cubic yards of fast-setting concrete into the hole during low tide between 8 a.m. and 2 p.m. Friday. If that doesn't fill the hole, work will continue next week, Grimes said.
A more permanent fix has not yet been developed, but it is planned. The gates, which were built in the late 1950s, are not weakened in any way, officials said.
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