1 | INTRODUCTION
Instream structures have been
employed to restore streams and improve fish habitat for more than
century, yet the design of many structures has changed very little over
that time (Thompson, 2005). Stream restoration and habitat enhancement
projects have utilized a variety of structures designed to reduce
erosion and improve aquatic habitat (Miller & Kochel, 2010). These
structures can generally be classified as dams, deflectors, or bank
protection/cover, and are typically constructed from boulders, logs, and
sediment (Thompson, 2005). Projects have used structures to address a
variety of objectives, including bank erosion, riparian vegetation,
grade control, recreational boating, flow diversions, fish habitat,
reintroduction of large wood, infrastructure protection, flooding,
sediment transport, energy dissipation, and other stream functions
(Rosgen, 2011; Wohl, Lane, & Wilcox, 2015). Some structures are
designed to enhance aquatic habitat by providing velocity refuge,
overhead cover, improved over-winter habitat, more profitable feeding
positions, and increased habitat complexity (Roni, Hanson, & Beechie,
2008; Richer, Gates, Kondratieff, & Herdrich, 2019). Although stream
restoration has grown into a multibillion dollar business (Cockerill &
Anderson, 2014), the effectiveness of treatments is rarely evaluated for
most projects (Bash & Ryan, 2002; Roni, Aberg, & Weber, 2018).
Understanding the effectiveness of stream restoration structures will
inform the design, evaluation, and expectations for future projects.
This case study evaluates a stream restoration project in the headwaters
of the Arkansas River near Leadville, Colorado. The project was intended
to rehabilitate and enhance aquatic habitat for a 17.7-km reach of the
Arkansas River and Lake Fork to restore natural resources equivalent to
those injured by the release of hazardous substances from the California
Gulch Superfund Site (Stratus Consulting Inc., 2010a). The primary goal
of restoration was to improve instream aquatic habitat and increase
Brown Trout Salmo trutta populations. Restoration treatments were
designed to stabilize streambanks, reduce the risk of erosion at fluvial
tailings deposits, create diverse stream morphology including deep-water
pools for overwinter habitat, provide overhead cover for trout, increase
spawning habitat, and provide refuge for juvenile trout. Monitoring
targets included instream structures, fish populations (Richer et al.,
2022), riparian vegetation (Cubley et al., 2022), benthic
macroinvertebrates (Clements, Vieira, & Church, 2010; Wolff, Duggan, &
Clements, 2019), and habitat quality (Richer, Gates, Kondratieff, &
Herdrich, 2019). The goal for instream structures was that at least 90%
of all habitat improvement structures be stable and functional three
years after implementation (Stratus Consulting Inc., 2010b). The
objectives of this study were to evaluate structure performance by
evaluating (1) the integrity and function of instream structures and (2)
the change in pool depths following completion of instream construction.
2
| METHODS