Okanogan Highlands Alliance, US Fish and Wildlife Service, Trout Unlimited
Aug. 22, 2016
Long-term goal: Reestablish connectivity between stream and floodplain, with a healthy riparian plant community and beaver maintaining grade control onsite. Short-term goal: Improve ecological function and complexity within the Triple Creek project reach. Objectives: • Increase channel length • Raise streambed elevation • Increase sub-surface water elevation • Reestablish native riparian vegetation within the wetland complex • Reestablish favorable geomorphic and vegetative conditions for beaver
We installed two different BDA structure types at Triple Creek: Deflector dams and channel-spanning BDAs. Deflector dams are straight post-line structures that span approximately 80% of the channel, leaving an aperture at the end through which water can flow. The intent of the deflector dams is to deflect flows into the opposing bank to recruit sediment and to elongate the channel locally. Deflector dams are oriented diagonally to direct flow toward an eroding bank on the outside of a meander. Structure locations were chosen based on existing channel geometry, and to push water in specific directions to create the desired future planform for the stream. Channel-spanning BDAs, on the other hand, are post-lines installed in an arc that span 100% of the channel. These are generally built in tandem with deflector dams, to capture the sediment recruited from the banks just upstream. The channel-spanning BDAs impound water, which raises the water surface elevation and slows velocities to induce deposition. It can be ideal to locate channel-spanners near inset floodplains and where the channel is wide, since sediment will aggrade on these surfaces and the structure is more likely to be stable. We also installed 10 pieces of large wood upstream of all the BDAs with the objective of habitat enhancement, although significant aggradation also occurred upstream of one of the large wood installments.