2.4.4. Mapping Tier 1 and Tier 2 Geomorphic Units
Wheaton et al. (2015) defines the primary tier 1 geomorphic units that
comprise the riverscape or valley bottom as the river’s floodplain and
channel(s). In our study, we used the presence of upland plant species
as an indicator of floodplain activity vs. inactivity. Within these
classifications, we defined active floodplain as a polygon shapefile in
Esri ArcGIS. Similarly, we mapped primary and secondary channels as a
polygon feature class.
We defined tier 2 geomorphic units as the depositional or erosional
instream features that contribute to diversified habitat and were
visible at 1:450 zoom (e.g., confluences, diffluences, riffles and woody
debris structures; Palmer et al., 2009; Horan, Kershner, Hawkins, &
Crowl, 2000). We classified large wood structures as those found both
in- and out-of-channel that fell within a zone of inundation, and
riffles as clear changes in flow visible on the channel surface. We
identified confluences and diffluences as channel breaks and joins
stemming from the active channel or former active channel. We mapped
these within the riverscape through visual estimation via digital
imagery. When possible, we confirmed the presence and form of tier 2
geomorphic units through on-the-ground field surveys.