The Coyote Creek, California Streamflow Augmentation Pilot Project: Recycled Wastewater and Creek Water Quality Issues

Abstract

The City of San Jose plans to augment flows in Coyote Creek annually between May and November, depending on stream flow conditions. The project design sets a maximum release volume of 30,280 cubic meters per day, which should double the average dry weather flow in Coyote Creek at the release site. At a tidally influenced reach of the creek, the recycled water should increase the average dry weather flow by 50 percent. The goals of this project were to supplement current efforts by the City of San Jose in determining the impact of the addition of recycled water on water quality in Coyote Creek, San Jose. Our focus was on assessing the potential effects of augmentation using recycled water on the loading of nutrients and resulting changes in algae biomass, pH, dissolved oxygen, alkalinity, and unionized ammonia concentrations in the creek. Coyote Creek is located in Santa Clara County, California. It flows through urban and industrial areas into the South San Francisco Bay. Beneficial uses of the creek include industrial process supply, water contact recreation, ocean commercial and sport fishing, warm fresh water habitat, preservation areas of special biological significance, wildlife habitat, marine habitat, and fish migration. Coyote Creek currently provides poor cold water habitat and suitable warm water habitat to a variety of aquatic species. Following implementation of stream augmentation activities, Coyote Creek may provide improved cold water habitat. Additions of recycled water are expected to act beneficially in several ways; these include the flushing of fine particulate solids, an increase in flow within the Creek and potentially, the enhancement of habitat to anadromous fish. Deleterious impacts as a result of increased flows may include increased loading of dissolved inorganics ( e.g. , nutrients and metals such as zinc), and increased incidences of algae blooms. The latter could result in low concentrations of dissolved oxygen, elevated pH and increased concentrations of unionized ammonia.