3.1. 2020 Field Study
Our results demonstrate the wash habitat feature is more physically
diverse than any other river segment along the lower SRR with wash and
boundary habitat reaches containing 17% more unique geomorphic units
(e.g., pools, riffles, backwaters) on average than reference reaches,
with 70% of primary wash habitat comprised of diverse habitat. We found
that boundary habitat was the most complex, containing a combined
greater diversity of geomorphic units and substrate composition when
compared to sampled reference and valley plug reaches (Figure 2). Our
reference sites contained >800 m2 of
riffle habitat and only a very small area (<7
m2) of large woody debris (Figure 2A). Reaches within
the valley plug itself were composed of only a small area of pool
habitat (16 m2). In contrast, the boundaries of the
valley plug contained >123 m2 of pool
habitat, 149 m2 of riffle habitat, >34
m2 of large woody debris and a very small section (4
m2) of backwater habitat. On average, boundary habitat
contained >1,100% more pool habitat than the other
reaches. Based on the results of pebble counts, we found that boundary
sites contained a mixture of silt and sand substrate, with 64% of
substrate comprised of silt. In comparison, reference sites were more
complex than anticipated, containing >54% silt substrate,
>33% sand, >4% gravel and 7% boulder.
Valley plug reaches were comprised entirely of silt (Figure 2B).