Quantifying the Environmental Performance of a Stream Habitat Improvement Project

Abstract

River restoration projects are being installed worldwide to rehabilitate degraded river habitat. Many of these projects focus on stream habitat improvement (SHI), and an estimated 60%of the 37,000 projects listed in the National River Restoration Science Synthesis Program focus on SHI for salmon and trout species. These projects frequently lack a sufficient monitoring program or account for the environmental costs associated with SHI. The present study used life cycle assessment (LCA) techniques and topographic effectiveness monitoring to quantify environmental costs on the basis of geomorphic change. This methodology was a novel approach to assessing the cost-benefit relationship of SHI. To test this methodology, two phases of the Lower Scotts Creek Floodplain and Habitat Enhancement Project (LSCR) were used as a case study. The LSCR was a SHI project installed along the northern coast of Santa Cruz County, California, USA. A limited scope LCA was used to quantify the life cycle impacts of raw material production, materials transportation, and on-site construction. Once these baseline results were produced, a topographic monitoring program was used to quantify the topographic diversity index (TDI) in pre-and post-project conditions. The TDI percent change was used to scale the baseline LCA results, which quantified the environmental impacts based on geomorphic change. Phase II outperformed phase I. Phase I had greater cumulative environmental impacts and experienced a 7.7 % TDI increase from pre-to post-project conditions. Phase II had 43% less cumulative environmental impacts and experienced a 7.9% TDI increase from pre-to post-project conditions. The impacts in phase I were greater because of the amount of material excavated to create off-channel features, which were a key feature of the LSCR. A scenario analysis also was conducted within the LCA component of this study. The scenario analysis suggests that life cycle impacts could be reduced by 30%-65% by using the accelerated recruitment method in place of importing materials to build large wood complexes. The results of this study suggest that managers may improve the environmental performance of SHI projects by: (1) using the accelerated recruitment method to introduce larger key pieces to the channel, reducing the need to import materials; (2) using nursery grown plants as opposed to excavating plants for revegetation; (3) minimizing fuel combustion in heavy equipment and haul trucks by ensuring clear access to the channel and streambank, using small engine equipment to clear access corridors during site preparation, running more fuel-efficient machinery or bio-fuel powered machinery, and by attempting to minimize haul distances by sourcing materials locally; and (4) utilizing a "franken-log" design (a ballasted LWC configuration with a rootwad fastened to the downstream end of a log) in LWCs which led to favorable TDI change. This study concluded that LCA could be a valuable tool for monitoring SHI and river restoration projects and that further research ...