Fast response to fast-forwarding nature: instream large wood habitat restorationAuthor(s): Cheryl A. Hayhurst; William R. Short
Source: Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 117-129
Publication Series: General Technical Report (GTR)
Station: Pacific Southwest Research Station
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How quickly and in what way does a channel bed respond when large wood elements are introduced in a way that imitates natural wood loading processes (un-anchored or anchored by burial)? Using a design streamflow threshold for determining the size of key large wood elements, what changes in channel bed and habitat complexity occur after streamflow events above and below the threshold? These are questions we are currently trying to answer with a large wood habitat enhancement project on the East Branch of Soquel Creek within Soquel Demonstration State Forest in Santa Cruz County, California. This project also aims to address a lack of instream habitat complexity that was identified in the National Marine Fisheries Service 2012 Central California Coast Coho Salmon Recovery Plan.
Large wood elements were placed in four project reaches (sites) along East Branch Soquel Creek in 2012 and 2013. These large wood elements consist of a combination of large key pieces (whole or nearly whole redwood trees with rootwads), log vanes with rootwad covers, and loosely racked wood structures. The large key elements were selected based on a size calculated to remain meta-stable through a 5-year return interval streamflow event and consist of single or multi-stem redwood trees with rootwads. The rootwad diameters range from 2.7 m to 3.81 m (9 ft to 12.5 ft) and the stems range from 0.8 m (30 inches) diameter at breast height (DBH; 1.37 m) to 1.3 m (51inches) DBH (largest stems on multi-stemmed structures). In all, 45 stems and 10 rootwads were introduced.
Monitoring observations have been conducted on four separate occasions at Site 1 (installed in 2012) and three times for the remaining three sites (2, 4, and 5) installed in 2013. Site 1 large wood elements experienced an event approximating the 7-year return interval the first winter after installation, which rotated the elements in place. Channel changes occurred the first winter after installation of sites 2, 4, and 5 in response to streamflow events below the design threshold. Thalweg profiles indicate increased complexity in the form of pool formation and localized aggradation and scour through the project reaches. On March 5 and 6, 2016, these structures experienced an approximately 10-year streamflow event which visibly affected the geometry and positioning of the structures along with generally increasing the number, and in some cases the size, of pools. The extent of thalweg changes and the position and orientation of large wood elements will be included as part of the physical monitoring of the four reaches that continues for 5 years after installation.
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CitationHayhurst, Cheryl A.; Short, William R. 2017. Fast response to fast-forwarding nature: instream large wood habitat restoration. In: Standiford, Richard B.; Valachovic, Yana, tech cords. Coast redwood science symposium—2016: Past successes and future direction. Proceedings of a workshop. Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 117-129.
Keywordschannel morphology, Coho salmon, geomorphology, large wood, salmonids, stream restoration, wildlife habitat
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