ASSESSING GEOMORPHOLOGICAL AND ECOLOGICAL RESPONSES IN RESTORED STEP-POOL SYSTEMS

River restoration has become increasingly common to address river ecosystems that have degraded due to a range of human impacts. Yet, restored river systems are rarely monitored, leading to incomplete understanding of how such systems function after restoration. This is particularly true of restored channels using step-pool sequences, a relatively new strategy to provide stable channels in high-gradient environments. This study assesses geomorphological and ecological responses in two urban restored step-pool systems in northern California. Baxter Creek and Cordornices Creek (in El Cerrito and Berkeley, respectively) were evaluated for channel changes following placement of step-pool sequences, and how these changes may be linked to ecological improvements. Surveys of longitudinal profiles and cross sections documented geomorphological characteristics in the study creeks. Analysis of benthic macroinvertebrates provided indication of ecological conditions. Samples were taken from 30-m sections of the restored reaches, as well as from upstream and downstream reaches, in addition to a nearby reference stream (Wildcat Creek). Results show how channel adjustment had occurred in Baxter Creek to yield a step-pool morphology that offers maximum stability in the system. In both cases, the creation of step-pool sequences increased micro-habitats in the restored reaches. Although such changes were expected to increase macroinvertebrate assemblages in the restored systems, only slight differences were found among micro-habitats. The muted response is likely attributed to the degraded conditions of the urban watersheds that resulted in a macroinvertebrate assemblage primarily dominated by a few tolerant taxa (e.g., Chironomidae, Coenagrionidae, Simuliidae, Tubellaria). Nevertheless, use of step-pool restoration techniques offers potential to enhance ecological conditions as well as geomorphic stability in less disturbed watersheds.