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Natural Flood Protection

A history of flooding
Long before the Santa Clara Valley was developed, local streams naturally flooded with great regularity. Floods cleared streams of debris, and silt flowed from the streambeds to adjacent land, replenishing the nutrients in the soil. Far from a disaster, flooding benefited the environment.

Today, flooding in Santa Clara county is far from innocuous. Communities can suffer millions of dollars in property damages and vital roadways can become impassable. The vast majority of homes and commercial buildings were built on lands that had flooded for eons. In the 1950s, the water district began addressing flood problems in earnest.

Early flood protection efforts
In the early days, flood protection meant straightening creeks and lining them with concrete. While these channels are great for moving water quickly, they are not much to look at. We now have new flood protection methods that are not only more scenic, they foster natural habitats, and often include trails and interpretive benches.

A more natural approach
The water district balances the need to provide flood protection with the need to protect streams and natural resources. Various factors are considered in determining the best methods to improve a creek's capacity for flood water while minimizing impacts to the ecosystem. A few examples of these methods are:

  • Crib-walls 
  • Overflow channels 
  • Bypass channels

Gabion WallThe water district employs numerous flood protection technologies that help keep creeks as natural and beautiful as possible. Water district goals have kept pace with changing community values. New multipurpose flood protection projects protect property while preserving habitat, improving water quality and providing creekside trails.

Crib wallCrib walls 
One technique to strengthen creek banks is to use crib walls--dead trees arranged in a Lincoln-log fashion. After the logs are buried, natural vegetation can flourish. Over time, the logs will decompose, and the root structures of newly planted trees and shrubs will eventually provide protection from erosion.

The photo at right, taken during construction of a crib wall, shows how high waters had eroded the banks. The second picture below shows how another bank, along Bodfish Creek near Gilroy, looked one year after installation, with native plants already beginning to establish themselves.

A crib wall, one year after installation

Overflow channels
Another technique to increase a creek's capacity for flood waters is to build an overflow channel parallel to a creek.  This channel is only used when water flows are at their highest.  This way, the natural creek bed can be left alone, preserving wildlife habitat.

Bypass channels
The Guadalupe River runs right through downtown San Jose and has caused millions of dollars in flood damages. To increase protection from flooding, a system of bypass channels has been constructed. But you will never see them. They are under ground. When the river rises, water will begin flowing through massive culverts that run under downtown streets. These culverts divert the excess water around the developed areas of downtown, preventing flooding of downtown San Jose.

Last resort
Unfortunately, housing developments built very close to creeks over the years limit the options for restoring these creeks. Often, there is just no space left to create a natural creekbed. In those areas, concrete channels with steep sides are often the only way to protect homes and businesses from floods.

(Right: Matadero Creek in Palo Alto )