ACCOUNTING FOR GEOMORPHIC AND HABITAT DIVERSITY FOR REHABILITATION OF URBAN LOWLAND STREAMS IN THE GREAT LAKES REGION, USA

In the Great Lakes region, the intersection of streams with a wide variety of glacial landforms results in a diverse range of potential geomorphic and habitat characteristics. From 2012-17, a study of the geomorphology, habitat, and benthic invertebrate assemblages of 27 lowland streams tributary to Lake Michigan in the Milwaukee, Wisconsin area was conducted. The lowland streams had slopes generally less than 1 percent and ranged from urban analog (near urban but ecologically highly valued) and minimally altered to concrete lined and recently rehabilitated. Reaches with slopes of less than 0.1 percent had narrow deep channels with fine-grained streambed substrates and plane bed or ripple-dune bedforms whereas reaches with slope of greater than 0.1 percent were relatively wide with coarse substrates and pool-riffle bedforms. In contrast, rehabilitated reaches, regardless of slope, were narrow and deep with the coarsest substrates, as they were designed to be stable under erosive urban-enhanced flood conditions and allow fish passage during low flows. Gravel-sized substrates were rare except in one urban analog reach downstream of a dam. Most reaches had maximum water depths of greater than the 0.7 m needed for fish cover from overhead predation and overwintering during ice cover. Large wood was missing from rehabilitated reaches. Minimally altered and rehabilitated reaches had ample natural vegetation along their corridors, but there were high percentages of invasive plant species in both. Results from this study will aid in the long-term ongoing assessment of the rehabilitation projects and inform future rehabilitation designs and monitoring plans.