3.2 | Residual pool depth analysis
Results from the repeated measures ANOVA for riffles indicated that
structure type did not affect the change in RPD, nor did the interaction
between structure type and years post construction (Table 6). However,
the number of years post construction did have a significant effect on
RPD (p < 0.0001). Pairwise comparisons indicated that
the change in RPD within preexisting riffles was greatest in year 0,
which represented the as-built condition, compared to all subsequent
years (p < 0.0001; Figure 4). RPD then decreased in
year 1 following the first runoff cycle (p < 0.0001),
with all subsequent years (2-4) exhibiting less change in RPD (p< 0.001). The change in RPD indicated that pools that were
developed within preexisting riffles were likely over excavated in year
0, filled in to some degree in year 1, and then remained relatively
stable in years 2-4 (Figure 4). The estimated marginal means for each
year indicated that the net change in RPD was 0.26 m across the study
period for pools that were developed within preexisting riffles,
suggesting that the treatments effectively increased RPD in these
locations. Detailed results from the RPD analysis, including pairwise
comparisons for any significant effects, were included in the Supporting
Information.
Analysis of RPD at preexisting pool locations indicated that there was a
significant interaction between structure type and years after
construction (p = 0.003; Table 6). Structure types that performed
differently in year 0 included log toe (p = 0.034), log vane/log
toe combination (p = 0.071), and no structure (p = 0.011),
all of which exhibited a greater change in RPD when compared to log
vanes. The boulder vane/boulder toe combination treatment also performed
differently in year 1 when compared to other structure types (Figure 4),
exhibiting a greater change in RPD when compared to boulder clusters
(p = 0.002), boulder vanes (p = 0.017), log toe (p= 0.094), log vanes (p = 0.007), and no structure (p =
0.002). The log vane/log toe combination also demonstrated a greater
change in RPD at preexisting pool locations when compared to no
structure in the first year after construction (p = 0.048). No
differences in RPD were observed between structure types for preexisting
pool locations in years 2, 3, or 4. The change in RPD was generally
smaller at preexisting pools when compared to riffles (Figure 4), with a
net change in RPD of 0.13 m across the study period.