Systematic Postproject Appraisals to Maximize Lessons Learned from River Restoration Projects: Case Study of Compound Channel Restoration Projects in Northern California

摘要

We conducted systematic postproject appraisals (PPAs) of seven compound channel restoration projects, supplementing available data with new field data and analyses to produce comparable datasets for all seven projects. We describe how systematic PPAs can be developed and illustrate a systematic PPA for compound channel projects organized around performance with respect to geomor-phic, habitat, and conveyance objectives. We found that preexisting monitoring programs for a group of similar restoration projects can be supplemented with relatively low-effort data collection and analyses to produce lessons on a "class" of restoration projects. Using this approach to assess a set of seven compound channel projects, we found that two fully achieved geomorphic objectives, three appear likely to achieve geomorphic objectives with additional time and/or minor interventions, and two did not achieve geomorphic objectives. Further, four projectsrnachieved habitat objectives and three projects appeared likely to achieve objectives if given more time to develop and/or a minor intervention to mitigate limitations on critical ecological processes. Finally, four of the projects satisfied conveyance objectives, and the remaining three appeared likely to satisfy objectives with minor interventions to maintain design roughness and geometry conditions. Based on observations from our new systematic PPA approach applied to compound channels in Mediterranean climates, we suggest application of systematic PPAs for other classes of river restoration projects to evaluate scale and geomorphic setting issues in project design, to refine postproject monitoring guidelines, and to predict vegetation recruitment, growth, and succession patterns to avoid potential vegetation problems.