Integrating Surface Water Quality Improvements Into Coastal Restoration – An Urban Retrofit BMP Case Study
Big Canyon is a 1,300 acre coastal watershed in Newport Beach, California that drains to Upper Newport Bay, an important coastal ecological preserve. Big Canyon Creek, which drains the watershed, is a perennial urban stream that is impaired due to elevated levels of selenium, which has been shown to be toxic at high levels to wildlife. As a result, a total maximum daily load (TMDL) has been established for the creek to protect the stream’s biota and beneficial uses. Big Canyon Creek also suffers from anthropogenic alterations that have negatively impacted stream hydrology and water quality, as well as riparian vegetation and wildlife habitat. The Big Canyon Restoration and Water Quality Improvement Project (project), located less than a half-mile from the Creek’s discharge into Upper Newport Bay, is a multiple benefit project, integrating (a) water quality improvements of dry weather flows, (b) passive treatment of wet weather runoff with wetland creation, (c) flood plain reestablishment with streambed and streambank stabilization, (d) riparian restoration, and (e) enhanced public access. The project was initiated to reduce selenium concentrations in the creek to meet the targets of the TMDL while restoring the creek’s beneficial uses through water quality improvement and habitat restoration. Comprehensive groundwater and surface water investigations, which were conducted to understand the patterns of selenium loading in the creek, identified one reach where groundwater seeps greatly increased selenium levels in creek surface waters. In order to decrease selenium concentrations to meet TMDL requirements, these seeps were isolated and diverted to the sanitary sewer in order to reduce selenium concentrations in dry weather flows. The diverted flow is sent to the Orange County Water District groundwater replenishment system where it is purified and injected into groundwater aquifers to minimize seawater intrusion and replenish local groundwater supplies. During wet weather, stormwater runoff from a major arterial roadway is captured and treated through subterranean bioretention cells planted with native vegetation and specifically designed to remove a suite of pollutants common to urbanized watersheds (metals, nutrients, organics, and indicator bacteria). Treated water from these storm events then flows into newly created ephemeral wetlands that are hydrologically connected back to the creek. In addition, several elements were integrated into the project to further improve water quality by re-establishing the functionality of Big Canyon Creek. These elements include a re-connection of the creek to a newly restored floodplain, streambed restoration to enhance in-stream habitat, and stream re-alignment and bank stabilization with eco-friendly vegetated soil revetments to reduce erosion, prevent stream incision, and enhance recruitment of native vegetation. In addition, five acres of riparian habitat has been restored by removing invasive species, amending the degraded soil in the floodplain, and replanting with native vegetation. The restored area has been connected to a larger trail system to integrate the project with the Newport Bay Ecological Preserve and informational signage has been added to enhance public awareness of urban streams and promote environmental stewardship of the area. The project was funded through a collaborative effort involving grants from multiple agencies, matching funds from the City of Newport Beach, and a volunteer workforce from several local environmental groups.
Mr. Gruber is a Project Manager at Burns & McDonnell Engineering with more than 20 years of experience managing various water quality and natural resource assessment projects. He is experienced in NPDES permit compliance studies, TMDL implementation and regulatory support, biological assessments, and stormwater monitoring.
Dr. Robert Stein (PhD, PE) is the Assistant City Engineer at the City of Newport Beach with over 18 years of experience in the environmental field. He has led numerous investigations and projects related to stormwater issues, regulatory compliance, TMDL development and implementation, and watershed solutions to improve beneficial uses in freshwater and marine ecosystems.