Natural Mimicry: Man-made Structures Mimic Natural Processes In Lagunitas Creek

By David Wentworth:

During our visit to Lagunitas creek, we were shown many different structures that had been created around and in the creek to better improve the health of its inhabitants. These man-made structures were created from a combination of natural materials (mainly wood) held together by rebar. The main objective of these structures was to help benefit the Coho Salmon during their breeding season and during juvenile growth. We got to take a look at two different structures. We looked at a man-made dam built to imitate a beaver dam and some water breaks built to slow water and create pools for the salmon to lay their eggs.

The dam was built to hold back large amounts of water and allow the water to flood over the banks of the creek and create flood plains during the rainy season. It was constructed with upward standing logs dug into the ground in a line across the creek with more logs laid down length-wise, wedged in between the vertical logs. Even though we were visiting while the creek was at its lowest, it was considerably deeper where the water was being held back by the dam. The surrounding area near the dam had been leveled out into a very gradual slope so the water could flood over the banks and create a wide floodplain for the salmon to swim up into during the winter rainy season.

We also viewed many water breaks which had been placed to slow down the water during the rainy season when the current is at its strongest. The breaks are fallen trees and logs placed on the sides of the creek so that the logs cut into the sides of the creek. The logs were secured with rebar and then partially buried to hold them in place. As the water slows, pools of slow moving water form behind the logs giving the salmon a place to lay their eggs and providing habitat for the young salmonoids to mature.

These structures we saw, while no perfect substitute for their natural counterparts, still managed to mimic the natural functions of a creek suitable for salmon to spawn and mature in. The Lagunitas Creek is already seeing improvements in Coho salmon populations with more and more visiting every year.