Creek restoration: Building a better home for fish while taking care of Lake Tahoe
October 1, 2010
TAHOE CITY, Calif. and#8212; When Craig Oehrl, restoration hydrologist with the U.S. Forest Service, saw a large adult rainbow trout seeking shelter under a habitat he helped install at the lower reach of Blackwood Creek earlier this summer, he was thrilled.
and#8220;That’s it,and#8221; he said during a tour of the Lower Blackwood Creek Restoration Project site. and#8220;That’s why I love this job.and#8221;
The forest service is currently restoring the lower reach of Blackwood Creek on the West Shore to its natural state by creating more sinuosity, or curves, in the steam’s course, while removing concrete culverts and other impediments to fish passage.
This year, the forest service is concentrating restoration on the lower reach of the creek; next year, it will tackle the upper reach, Oehrl said.
The purpose of the project and#8212; which began its design phase in 2001 and#8212; is two-fold: creating fish habitat suitable for reproduction, and reducing the sediment load that siphons into Lake Tahoe, Oehrl said.
Slowing the river by installing more curves will reduce erosion and stream channelization, which in turn, will reduce sediment loading into the lake, Oehrl said, and allow the creek system to retain more water in natural pools throughout the year, meaning fish can utilize such areas to spawn.
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and#8220;Blackwood Creek is very dynamic,and#8221; he said. and#8220;What we are really trying to do is install the framework that will allow the system to heal itself.and#8221;
Another by-product of the restoration project is allowing cottonwood and aspen trees the opportunity to reclaim their natural territory along the banks of the stream, where conifers took advantage of the stable environment to shoulder out deciduous trees, Oehrl said.
Cottonwoods and aspens prefer a dynamic, wet environment, said Oehrl.
In the 1960s, a private gravel company occupied the restoration site. The company collected rocks, built concrete bridges with narrow culverts and redirected the creek’s channels to suit its purposes.
The forest service purchased the property in the late and#8216;60s, installing grade control measures in the 1970s.
It wasn’t until 2001, that a full restoration plan was put in place.
Oehrl said the forest service was not privy to the precise course of the creek prior to the gravel company’s occupation; however, the restoration project attempts to restore the natural function of the creek as opposed to a historically accurate replication of the creek.
Next year at the upper reach of Blackwood Creek, the forest service will raise the level of the river bottom until it is approximately level with the banks, which will restore the natural flood plain. If successful, it will complete the entire restoration project.
Currently, the upper reach has two distinct channels, north and south, with the north channel functioning as the primary egress for spring runoff due to its deep and straight path through the topography.
Once the floor of that channel is raised, the water will spread out through a natural flood plain while utilizing both channels.
The flood plain will capture much of the sediment, which will in turn supply local vegetation rather then compromise Lake Tahoe, said Oehrl.