Sieben Creek Confluence Restoration

CRBC improved more than 10 acres of riparian corridor, 16 acres of floodplain habitat, and 2,100 linear feet of channel by increasing the frequency and duration of hydrologic connection to the side channel and floodplain, along with instream habitat improvements from large wood installations and riparian vegetation management and planting. Salmonids, primarily juvenile coho migrating down the Clackamas River will benefit from the improved access, increased duration of stream flow and improved habitat complexity through large wood placement in the side channel and invigorated riparian areas. The Lower Columbia Salmon recovery plan identified the lack of access to side channels, low habitat complexity from a dearth of large wood and degraded riparian forests as factors limiting the recovery of our iconic salmon in the Clackamas River, all issues addressed by the project. Channel structure placement was incorrectly omitted in proposed project reporting.
Because the projects scheduled end date is after the PCSRF FFY 2019 award closes, no funds allocated for this project are reported as match to PCSRF funds.

Clackamas River basin focal fish species (i.e. spring and fall Chinook, coho and winter steelhead, Pacific lamprey) are negatively impacted by loss of habitat, impaired water quality and lack of access to historic spawning areas. A limiting factors analysis identified a lack of mainstem rearing habitat as a primary limiting factor for the survival of anadromous salmonids in the Clackamas River. This project will restore habitat elements believed to be most limiting to salmon and steelhead as identified in local and regional assessments.

Off-channel habitats including side channels, wetlands, ponds and alcoves have been found to provide critical habitats for both juvenile salmonids and a variety of wildlife species. The presence of side channels, especially a series of side channels in various stages of succession, increases the diversity of aquatic habitat available within a stream corridor. Also, during flood events, side channels frequently offer aquatic species refuge from adverse mainstem conditions while attenuating flood flows. Juvenile coho are known to actively and preferentially migrate from mainstem rearing locations to Off-channel habitats (that would be off mainstem channels) in both fall and spring for protection from winter freshet activity and where they experience high survival rates. They are also recognized for their value as summer and winter rearing habitat for coho salmon and cutthroat trout. Such projects also have significant benefits for a suite of wildlife species that either use or indirectly benefit from such habitats (e.g., amphibians as refuge and reproductive habitat, birds as foraging habitat). This project aims to restore geomorphic processes that would be sustainable under the current Clackamas River morphology.

The improved hydrologic connection is important because of the diversity of fish species and life cycles in the mainstem lower Clackamas River; and improved hydrologic connection should improve on the overall survival rate as opposed to fish rearing in the mainstem Clackamas River. More frequent hydrologic connection into and out of the side channel helps to ensure access in and egress out for fish during the year. As conditions deteriorate in the mainstem river through summer, juvenile fish will seek refuge in off-channel areas due to presence of cooler water in the side channel. The side channel will provide cooler water to an existing alcove at the outlet. Water in the side channel is expected to be cooler due to cooler inflows from Sieben Creek and hyporheic upwelling from the mainstem and maintained by shade canopy.

The project benefits are intended to increase the inundation frequency and duration of flows from the mainstem entering the upstream inlet that is currently blocked by a large sediment plug. These side channels are not common in the lower river, a result of channel simplification over the last half-century. The project will increase the amount of available side-channel habitat in a reach currently lacking adequate thermal and flow refuge. The installation of large and small wood will improve habitat and geomorphic conditions. and notably utilized by salmon and steelhead throughout the year. The lower alcove currently supports fish holding in the summer months. This reach of the mainstem is very important for spawning Chinook salmon, and being close the urban fringe, these types of habitats are less available further downstream. This project will include hydrologic re-connection of nearly 2,100 feet of side channel habitat, the addition of large wood structures for habitat, and improvement of riparian conditions. The project will benefit all native fish species that currently and historically utilized this reach of the lower river. The design focus is on improving juvenile rearing conditions for spring Chinook Salmon, coho salmon, and winter steelhead but will benefit a multiple other species.