Co-evolving Physical and Biological Organization in Step-pool Channels: Experiments from a Restoration Reach on Wildcat Creek, California

Thursday, 18 December 2014: 8:45 AM
Anne Chin1, Alison P. O'Dowd2, Patina K Mendez3, Katrina Z Velasco3, Roger D Leventhal4, Rune Storesund5 and Laura R. Laurencio1, (1)University of Colorado Denver, Geography and Envinronmental Sciences, Denver, CO, United States, (2)Humboldt State University, Environmental Science and Management, Arcata, CA, United States, (3)University of California Berkeley, Berkeley, CA, United States, (4)FarWest Restoration Engineering, Alameda, CA, United States, (5)Storesund Consulting, Kensington, CA, United States
Step-pools are important features in fluvial systems. Through energy dissipation, step-pools provide stability in high-energy environments that otherwise may erode and degrade. Although research has focused on geomorphological aspects of step-pool channels, the ecological significance of step-pool streams is increasingly recognized. Step-pool streams often contain higher density and diversity of benthic macroinvertebrates and are critical habitats for organisms such as salmonids and tailed frogs. Step-pools are therefore increasingly used to restore eroding channels and improve ecological conditions. This paper addresses a restoration reach of Wildcat Creek in Berkeley, California that featured an installation of step-pools in 2012. The design framework recognized step-pool formation as a self-organizing process that produces a rhythmic morphology. After placing step particles at locations where step-pools are expected to form according to hydraulic theory, the self-organizing approach allowed fluvial processes to refine the rocks into adjusted sequences over time. In addition, a 30-meter "experimental" reach was created to explore the co-evolution of geomorphological and ecological characteristics. After constructing a plane bed channel, boulders and cobbles piled at the upstream end allowed natural flows to mobilize and sort them into step-pool sequences. Ground surveys and LiDAR recorded the development of step-pool sequences over several seasons. Concurrent sampling of benthic macroinvertebrates documented the formation of biological communities in conjunction with habitat. Biological sampling in an upstream reference reach provided a comparison with the restored reach over time. Results to date show an emergent step-pool channel with steps that segment the plane bed into initial step and pool habitats. Biological communities are beginning to form, showing more distinction among habitat types during some seasons, although they do not yet approach reference values at this stage of development. Research over longer timeframes is needed to reveal how biological and physical characteristics may co-organize toward an equilibrium landscape. Such integrated understanding will assist development of innovative restoration designs.