CUMULATIVE IMPACTS OF SECTION-404 CLEAN-WATER-ACT PERMITTING ON THE RIPARIAN HABITAT OF THE SANTA-MARGARITA, CALIFORNIA WATERSHED

The Santa Margarita River is one of the few remaining free-flowing riv er systems on the Southern California coastal plain, and it provides o ne of the most expansive, unspoiled riparian habitats in Southern Cali fornia. Then is concern among resource managers that the cumulative im pacts associated with rapid development of the upper watershed will de grade the ecological integrity of the entire watershed. In response to this concern, we assessed the impacts of development projects in this watershed, which were subject to regulation under Section 404 of the Clean Water Act. Cumulative impacts were assessed by comparing the con ditions present at each project site prior to issuance of the Section 404 permit to conditions present after issuance of the permit. Changes between pre- and post-project site conditions were evaluated using a semantic categorization for the following six criteria: endangered spe cies habitat, structural diversity, spatial diversity, undeveloped ope n space, linear contiguity, and adjacent habitat. The impact assessmen t showed that although the Section 404 permit program has attenuated p roject impacts, it has failed at minimizing cumulative impacts. Projec ts permitted under Section 404 contributed to the disruption of moveme nt corridors linking the habitats of the upper and lower watershed and resulted in extensive floodplain encroachment, which may have hydrolo gic as well as ecological implications. More importantly, this assessm ent identified the types of activities and habitat functions that shou ld be addressed during revisions in permitting procedures and should b e emphasized in the watershed planning process. These conclusions will be incorporated into an ongoing Advanced Identification study sponsor ed by the U.S. Environmental Protection Agency and U.S. Army Corps of Engineers to develop a management plan for the Santa Margarita Watersh ed.