2.1 | Study Site
Degradation of the study site began in 1859 when gold was discovered in
California Gulch (USEPA, 1988). Acid-mine drainage and mine tailings
were released downstream into the Arkansas River over the next century,
degrading both aquatic and terrestrial resources. The California Gulch
Superfund Site was added to the national priorities list in 1983
(Stratus Consulting Inc., 2010a, 2010b). The Natural Resource Damage
Assessment (NRDA) under the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) led to a settlement of $20.5
million to be used for natural resource restoration as compensation to
the public (Stratus Consulting Inc., 2010a, 2010b). The U.S.
Environmental Protection Agency conducted in situ remediation of
fluvial tailings deposits located within the floodplain prior to
implementation of stream restoration. Although instream habitat
restoration was conducted for a larger 17.7-km reach, this study focused
on an 8-km project (Figure 1) that was designed and implemented by
Colorado Parks and Wildlife on lands with public fishing access. The
study reach is a fourth‐order stream in an unconfined alluvial valley
with cobble substrate, pool‐riffle morphology (Montgomery & Buffington,
1997), and a C3 Rosgen stream classification (Rosgen, 1994). Instream
construction activities began in July 2013 and were completed in August
2014, with some revegetation work occurring during the spring of 2015.
Detailed information on the restoration design was provided in Richer,
Gates, Kondratieff, & Herdrich (2019) and Richer et al. (2022).