2.3 | Residual pool depth
Residual pool depth (RPD) was used to monitor the depth and longevity of
developed pools (Lisle, 1987). RPDs were derived for each pool included
in the as-built survey using the thalweg profile survey for each year.
Surveys were conducted between 2010 and 2013 to characterize preexisting
conditions. Instream construction occurred over two years, and as-built
surveys were conducted after each construction season in 2013 and 2014.
Effectiveness surveys then occurred annually from 2014 to 2018.
Topographic surveys were conducted using survey grade GPS tied into
pre-established control points. Survey data were used to create
Triangulated Irregular Networks (TIN) with ArcGIS. Breaklines for bank
tops, bank bottoms, and river thalweg were applied to TINs to improve
accuracy, after which thalweg profiles were extracted from the TINs to
support analysis of RPD. Thalweg profiles were then analyzed graphically
with RStudio (Posit team, 2022) to determine the minimum pool elevation
(MPZ) and riffle crest elevation (RCZ) for each pool and year. RPD was
calculated for each pool and year using Equation 1.
Equation 1:
\begin{equation}
RPD=RCZ-MPZ\nonumber \\
\end{equation}If a thalweg survey missed a pool, data for missed pools were excluded
from the analysis for that year. Developed pools were associated with a
structure type if present (Table 3). Some pools were associated with
more than one type of structure (e.g., log vane/log toe combination) or
no structure at all. The preexisting morphology (riffle or pool) was
also determined for each of the developed pools based on the
preconstruction longitudinal profile and aerial imagery.