Providing Flood Protection and Restoration

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In past decades, water routinely flooded parts of Alameda County. With renewed attention to the status of flood control channels and levees, more accurate and extensive water flow data, new flood engineering technology, concerns about climate change, and the fact that our flood infrastructure has a life cycle and is currently over 50 years old, the District is working harder than ever to provide food protection for residents and property—and preserve this crucial system for future generations.

The regulatory standard, required by FEMA, is to provide flood protection against water flows that could occur during a 1% annual chance storm—an event that has a 1% chance of occurring in any given year year.

A storm that has a 1% chance of occurring in one year, has the same 1% chance of occurring the next year. Just like flipping a coin three times in a row can result in heads each time, the 1% annual chance storm can and does occur more frequently than the term “1% annual chance” suggests.

The District now provides flood protection along more than 80 miles of natural creeks in the San Lorenzo watershed. Creeks flow from the hills above Castro Valley and Hayward into the communities below. From there, water is conveyed in storm drains, channels and pipelines to San Lorenzo Creek, where it eventually flows into the Bay.

In this watershed, the District maintains:

• 80 miles of natural creeks

• 17 miles of open channel

• 44 miles of underground pipe

• 34 miles of fencing,

• Three pump stations (to pump water from below-sea level creeks into the Bay)

• Two dams (Don Castro, Cull Canyon)

• Two silt-recycling sites