3.1 | Rapid assessment analysis
The percentage of structures meeting the performance criteria for
integrity and erosion was greater than the target objective of 90% from
2014 through 2018 (Figure 2). Both integrity and erosion dropped below
the target threshold in 2020. Deposition rankings met the performance
criteria (97%) for the first three years of monitoring (2014-2016), but
dropped below the 90% target in 2017. Based on the maximum integrity
ranking across all years, 74% of the structures met the performance
criteria by the end of the study period. Similarly, 80% and 72% of the
structures met the performance criteria for erosion and deposition,
respectively, based on the maximum rankings across all years. As project
construction was completed in 2014, the project met the goal that 90%
of all habitat improvement structures be stable and functional three
years after implementation, which corresponded to the 2017 survey.
However, structural integrity and function diminished over time as
rankings for integrity, erosion, and deposition all dropped below the
target threshold by 2020.
Boulder toe structures exhibited the poorest performance among structure
types, with 80% of those structures failing to meet the criteria for
integrity and erosion based on the maximum ranking across all years
(Figure 2). Log-vanes also failed to meet the performance target
(<10% of structures) for integrity (47%), erosion (30%),
and deposition (35%). Other structure types that failed to meet
performance criteria for integrity included boulder vanes (27%), log
toe (23%), and side-channel grade control (17%). In addition to
boulder toe and log-vanes, boulder vanes (36%), side-channel grade
control (25%), and log toe (18%) also failed to meet the performance
criteria for erosion. No boulder cluster, cobble toe, or main channel
grade-control structures were adversely affected by erosion. Boulder toe
and main channel grade control were the only structure types that met
the performance criteria for deposition. Deposition adversely affected
the performance of more than 30% of the log toe, log vane, and side
channel grade-control structures. Boulder clusters (25%), boulder vanes
(18%), and cobble toe (13%) structures also exhibited some issues with
deposition.
Results from the CLMM indicated that both year (p <
0.001) and structure type (p < 0.001) affected
integrity rankings for instream structures, with significance
differences occurring between all levels of response (p< 0.0001; Table 4). The odds of structures receiving higher
integrity rankings, noting that higher rankings are indicative of
diminished performance, increased in all subsequent years when they were
compared to 2014 (p < 0.011), which represented
as-built conditions following the completion of construction.
Conversely, integrity rankings were more likely to be higher in 2020
(p < 0.0001) when compared to all preceding years.
Higher integrity ranking were also observed in 2017 (p = 0.020)
and 2018 (p = 0.015) when compared to 2015. Boulder clusters were
more likely to receive lower integrity rankings than boulder-toe
(p = 0.041) and log-vane (p = 0.007) structures.
Cobble-toe structures were more likely to receive lower integrity
rankings when compared to boulder-toe (p = 0.048) and log-vane
(p = 0.084) structures. Log vanes received higher integrity
rankings compared to side channel grade control (p = 0.070) and
log-toe (p = 0.003) structures. Finally, boulder-toe structures
were more likely to receive higher ranking when compared to log toe
(p = 0.016).
Likelihood ratio tests indicated that both year (p <
0.0001) and structure type (p = 0.040) affected rankings for
erosion, with differences in response occurring between moderate and
severe rankings (p = 0.002; Table 4). Similar to the integrity
rankings, pairwise comparisons for year showed that erosion rankings
were more likely to be lower in 2014 compared to all subsequent years
(p < 0.056) and higher in 2020 compared to all
preceding years (p < 0.001). Differences between
structure types were less evident, as boulder toe was the only structure
type more likely to receive higher rankings when compared to log toe
(p = 0.027) and cobble toe (p = 0.085). Year also affected
deposition rankings (p < 0.0001), with differences
observed between all levels of response (p < 0.0001;
Table 4). Higher deposition rankings occurred in the years 2017, 2018,
and 2020 when compared to 2014 (p < 0.0001), 2015
(p < 0.001), and 2016 (p < 0.002).
Although the likelihood ratio test indicated that structure type had an
effect on deposition rankings (p = 0.092), pairwise comparisons
did not show any differences between structure types (p> 0.250). Complete results for the CLMMs and pairwise
comparisons between structure types and years were included in the
Supporting Information.