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.