Evaluating the performance of instream structures for a stream
restoration project in Colorado
Abstract
Metals pollution and channel disturbance associated with historical
mining, land use, and water development degraded aquatic and riparian
habitat along the upper Arkansas River near Leadville, Colorado. Stream
restoration was conducted for an 8 km reach to improve aquatic habitat
and increase trout populations. Instream structures were prescribed to
stabilize streambanks, create diverse stream morphology, and provide
overhead cover, refuge, spawning, and overwinter habitat for trout. At
least 90% of all structures were expected to be stable and functional
three years after implementation. The objectives of this study were to
investigate structure performance by (1) evaluating the integrity and
function of instream structures and (2) evaluating the change in
residual pool depths (RPD). Annual surveys utilized a rapid assessment
procedure to qualitatively rank integrity, erosion, and deposition at
each structure (n = 137). Rankings were investigated with ordinal
regression to determine if performance varied by structure type and
year. Longitudinal profile surveys were conducted annually and used to
estimate RPD for 86 pools. The change in RPD was investigated with
repeated measures ANOVA to determine if RPD varied between structure
types and changed over time. Results suggest that some structures were
more prone to failure, with higher rankings observed for boulder toe,
log vanes, log toe, and boulder vanes. Pool depths increased during
construction, decreased following the first runoff, and then remained
relatively stable in subsequent years. Understanding the performance of
instream structures from this case study will help inform the design,
evaluation, and expectations for future stream restoration projects.