Assessing Geomorphic and Habitat Metrics for Functional Lift from Urban Stream Restoration in the East Tennessee Ridge and Valley Province

Urban watersheds experience a variety of ecosystem stressors including hydromodification and impaired water quality. Impacts of hydromodification include rapid geomorphic adjustment to the channel and degraded habitat which potentially can harm benthic macroinvertebrate and fish communities. Stream restoration is occasionally implemented to mitigate damage to habitats that support these communities, but often the ecological component is ignored, or design criteria is improperly implemented. Because geomorphic attributes often define habitat structure, they are a necessary component to stream condition and restoration design. However due to watershed-scale stressors impacting urban streams, ecological recovery from geomorphic-habitat restoration practices remains mixed, and the potential for functional lift not well quantified. The following research explores the degree to which functional lift is possible in restored urban streams by comparing three classifications of streams: urban impaired (UI), urban restored (UR), and ecoregion reference (ERR) sites. Because compensatory mitigation is required by the U.S. Clean Water Act for aquatic resource loss and functional lift to be quantified, this research also assess the utility of the Tennessee Stream Quantification Tool (TNSQT) from urban stream restoration by using the tool to estimate existing condition scores (ECS) among UI, UR, and ERR sites. The study assessed multiple geomorphic, channel stability, riparian corridor, and mesohabitat characteristics using many field-based metrics measurements (e.g., channel longitudinal profile, pool-riffle-bar structure, etc.); utilized existing assessment indicator tools including the Rapid Geomorphic Assessment (RGA), a modified EMAP procedure, and the Rapid Bioassessment Protocol (RBP); and applied the TNSQT. All data were assessed to quantify the departure of impaired and restored streams from the reference streams. The RGA and RBP index scores were significantly different among the three stream condition types. The RGA and RBP index scores were governed by individual metrics related to bank stability/erosion, channel incision, riparian vegetation, and sediment deposition and embeddedness. The scoring provided by the current version of the TNSQT failed to reflect any improvement between stream condition types. The findings of this portion of the study indicate that a combination of the RGA and RBP may conditionally be a better indicator of functional lift from urban stream restorations than the TNSQT.