What is Flow Enhancement?
Stream Flow Enhancement Projects change the amount, timing, and/or quality of water flowing down a stream, or a portion of a stream, to benefit fish and wildlife.
Why does it matter?
Here on the North Coast, our streams support diverse freshwater ecosystems including endangered and threatened species such as Coho Salmon (Oncorhynchus kisutch) and Steelhead trout (Oncorhynchus mykiss). However, in our Mediterranean climate, we have a timing problem; water is severely limited when farms, fish, and families all need it most – summer and fall. Juvenile salmon are extremely vulnerable during these summer months. When streamflow drops too low, pools become disconnected, water temperatures rise, and the amount of dissolved oxygen rapidly dwindles.
Streamflow enhancement projects look to increase the availability and quality of water in the summer and fall months by encouraging people to conserve water, coordinate diversions with neighbors, and store water for use during the dry season. Even small increases in streamflow (just 0.1 cubic feet per second!) between June – October can greatly improve the chances of survival for these keystone species.
A keystone species is an organism that helps define an ecosystem. The health of their population is intrinsically linked to the health of the entire ecosystem
Water Storage and Forbearance
Water storage tanks allow landowners to harvest rainwater or divert water during the rainy season in order to reduce or forego entirely pumping during the summer and fall. Reducing demand on surface and groundwater flows between the months of June – October leaves more water instream for juvenile salmon to survive the summer months.
Large Wood Augmentation
Many of our North Coast streams lack complexity, like riffles, pools, and runs, and are instead referred to as “bowling allies” – straight, flat reaches with little habitat value. Large woody debris in the stream channel helps creates habitat by sorting gravels for spawning, providing cover for juveniles, creating pool habitat, and adding stream complexity. These projects improve habitat for fish at multiple vulnerable life stages.
Historic land use and management has greatly altered the natural flow of water in our ecosystems, creating ‘flashier’ systems in which water moves much more quickly overland and through streams. This can create many issues including more significant flooding, erosion, and lower base flows during the dry season. Improving groundwater infiltration by slowing, spreading, and sinking runoff stores water in the soil profile and groundwater supply, allowing it to seep out more slowing, buffering high flows and augmenting summer flows.
Coordinated diversion is a voluntary cooperative agreement between neighbors to schedule dry-season pumping so they are not diverting at the same time. When multiple diverters are pumping simultaneously, stream flow drops dramatically for the duration of the pumping event. However, we see a rapid recovery of flow after the diversions stop. If we can schedule diversions so they overlap as little as possible, we leave more flow instream for wildlife.