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Fence-Out

The Fence-Out project was undertaken to allow a 1,000-ft-long stretch of the San Pablo Creek to become and remain heavily vegetated. The increased vegetation effectively hardens the zone to erosion during low flow and flash flood events. There were two reasons why this specific zone was particularly critical to stabilizing the creek bed.

Why Fence?
Why Fence?

One reason is that within this stretch, the streambed slope is steep, measured at a 6% grade. This is four to six times steeper than any other reach of the San Pablo after the stream leaves the mountain. With a steeper slope, the water has more erosive power.

The second reason is that this zone includes headcuts and log structures. The owner of this 4-acre parcel of land agreed that establishing a zone where livestock were permanently excluded would allow willows, sedges, grasses and other vegetation to return and thrive. The vegetation enables the streambed to endure seasonal flash floods with little to no erosion.
Vegetative Response
Vegetative Response
A standard barbed-wire fence was built in the winter and spring of 2003 and 2004. Making the fence elk-proof was considered but rejected. Damage by elk that pass through the area does not impact the vegetation enough to justify the much higher cost of an elk-proof fence.

The vegetative response due to the exclusion of cattle was tremendously successful. In only one full growing season, the response was significant enough to withstand a sudden, heavy water flow in the spring of 2005. Previously, this flow would have caused erosion. This time it actually improved the site by increasing a mat of dense vegetation. In particular, the sedges captured and held large amounts of sediment that help stabilize the area.

The Fence-Out project and the log structures complement each other well, each increasing the impact of the other.