Boulder clusters could make a difference for urban fish

Flow
(Courtesy Bureau of Reclamation.)

If you fish and the above look like prime spots to cast your dry fly, you’ve got a good eye. The incredible part is that these images don’t come from a fast-flowing stream in Montana, but are lab representations of what could happen in the LA River to slow the water flow in certain areas, providing structure and habitat.

Currently, most of the river runs with an even flow, purposely created by engineers to move water out to the ocean. Flood control, not habitat, was the U.S. Army Corps original consideration after widespread destructive flooding in Los Angeles during the 1930s.

In all, the Bureau of Reclamation plans to test 12 designs alternatives that would “increase the size and roughness of a low-flow channel that would fit within the larger concrete flood control channel.” Features could include:
— a meandering low-flow channel with pools and riffles
— flow detectors
— a multi-threaded channel
— backwater areas
— boulder clusters (like the one pictured)
— mid-channel islands with alternating bank-attached bars

It’s all part of an innovative approach that may lead to a design within confined urban streams to create suitable depth and velocity conditions for native fish to thrive.

“The study only looks at hydraulics while recognizing that other biological factors, such as water temperature and cover are important,” said the Bureau of Reclamation Lead Investigator Nathan Holste by email.

Saying “hello” to native rainbows and “goodbye” to invasive carp is a stretch, but this is a welcome step in the right direction to return aquatic habit to our waters.

The Council for Watershed Health, in partnership with Holste, and several other project partners submitted a grant application to the Wildlife Conservation Board to fund a LA River Fish Passage Study, according to CWH Executive Director Eileen Alduenda, and are hopeful of receiving the additional funds to continue the study.

See you on the river, Jim Burns

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