The Big Canyon Restoration and Water Quality Improvement Project – Integrating Water Quality Improvements into Coastal Restoration
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), 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. Phase I of the Project (completed in 2017) focused on a comprehensive groundwater and surface water investigations, which were conducted to understand the patterns of selenium loading in the creek. The assessment identified one reach where groundwater seeps greatly increased selenium levels in creek surface waters. In order to decrease selenium concentrations to meet TMDL requirements, flows from these seeps were isolated and diverted to the sanitary sewer in order to reduce selenium concentrations in the creek during dry weather. During wet weather, stormwater runoff from a major arterial roadway was 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. These pollutant reduction best management practices (BMPs) were coupled with streambed stabilization, invasive species removal, and five acres of riparian habitat restoration. Phase II of the Project is located between the downstream end of Phase I and the Newport Bay Ecological Preserve. This reach of Big Canyon Creek has been documented as suitable for habitat restoration and enhancement because of stream channel incision; loss of floodplain connectivity; unstable stream banks; water quality impairments due to high levels of metals, toxics, nutrients, sediment, and bacteria; and native riparian habitat now dominated by non-native invasive plants. Phase II of the Project is currently being designed to (1) restore historic riparian habitat by removing non-native vegetation and replanting native species, (2) restore and create a mosaic of native and sustainable habitats, 3) stabilize the creek and floodplain with erosion control measures, and (4) integrate the Project with informational signage and a larger trail system connected to the Newport Bay Ecological Preserve. In Phase II, we will also conduct a feasibility study to assess options for restoring freshwater ponds at the base of the watershed that have become a sink for selenium and a suite of stormwater pollutants. This presentation will discuss the elements of the Project outlined above as an integrated approach to watershed assessments that couple water quality improvement BMPs with riparian restoration techniques.