Mill Creek Wetlands - A Demonstration of Regional Project Benefits, Public-Private Partnerships, and Water Quality Improvement in Southern California
Mill Creek Wetlands is a unique multi-jurisdictional project that creates, protects and restores the native ecosystems while enhancing recreational and educational uses. Located in Southern California, the project transformed a fallow, underutilized area within the Prado Basin (a major US Army Corps of Engineers flood control facility) into a natural water quality treatment system providing regional environmental and recreational benefits. The project’s unique regional approach was supported by the State Water Resources Control Board, the Department of Water Resources, and the California Natural Resources Agency through grant funding. It is also an integral part of the Santa Ana Watershed Project Authority’s Integrated Regional Water Management Plan.
The Project is a regional natural treatment facility designed to provide treatment of both wet weather and dry weather flows using natural wetland processes to address sediment, metals, bacteria, and nutrients. The Project has a wet weather treatment capacity of 147 acre-feet and is estimated to treat approximately 2,050 acre-feet of wet weather runoff per year on average, corresponding to over 11 percent of average annual wet weather runoff in the 77 square mile Cucamonga Creek Channel. The watershed includes portions of Ontario, Chino, Rancho Cucamonga, Upland, and San Bernardino and Riverside Counties. In contrast, a single-function water quality project of the same size in an upstream tributary would only be capable of capturing only 6% of the total wet-weather runoff from the watershed. The Project is also designed to dry weather flows and is estimated to treat 3,100 ac-ft per year of dry weather flow on average, about 10 percent of total dry weather flow volume from Cucamonga Creek Channel making the project is an effective means of leveraging water quality benefits for the region year-round.
Active and former agricultural uses, urban runoff, and urban stormwater from developed areas represent major contributors to the pollutants found in the watershed. In addition to creating water quality enhancement in Prado Basin, the Project protects the viability of native habitat and improves groundwater quality for downstream water users including the Orange County Groundwater Basin which is the primary source of drinking water consumed and used in Orange County. The project’s Native Habitat Plan creates several planting zones that benefit local wildlife, including endangered species, by utilizing plants that promote nesting, breeding and foraging.
Southern California, through its new MS4 permits, has a renewed focus on outcomes and receiving water quality; with TMDLs incorporated into MS4 permits, and limited financial resources, the need for innovative approaches to water quality project implementation (and funding) is critical. One area of opportunity is the development of public-private partnerships, and as significantly, the potential implications for water quality mitigation banking and alternative compliance methods. The Mill Creek Wetlands presents opportunities to demonstrate both regional project benefits, public-private partnerships, and mitigation banking currencies.