Brawley, California Wetlands: Design Considerations for Water Quality Improvement

The purpose of the Brawley Constructed Wetlands Demonstration Project is to study how wetlands can improve the quality of agricultural drain water, New River stream flows and, ultimately, inflows to the Salton Sea. To achieve this end, two demonstration wetlands are proposed for construction in Imperial County near Brawley, California: the 7-acre Brawley Site and the 68-acre Imperial Site. These sites will serve to demonstrate the effectiveness of using constructed wetlands through a 3-year monitoring program to treat constituents of concern in the water column, sediment, and biota. Healthy freshwater habitats are at a premium in the Imperial Valley. Creation of additional wetland habitats has long been desired. The goal of these constructed wetlands is to provide wetland habitat while removing sediment, nutrients and contaminants such as DDE and selenium that currently are degrading the New and Alamo Rivers and the Salton Sea. In addition to nutrients, the biota of the Salton Sea is stressed by the slowly increasing salinity now at 44 parts per thousand (ppt), considerably higher than the 33 ppt of ocean water. Physical and biochemical processes within the wetlands are expected to reduce nutrient loads, pesticide/herbicide toxicity, and selenium concentrations, while increasing dissolved oxygen in the water returned to the New River, thus improving water quality for wildlife habitat and contributing toward the achievement of Regional Water Quality Control Board standards. There is evidence that wetlands can reduce the concentration of available selenium by rendering it insoluble. The slightly elevated levels of selenium in the New River and Imperial Valley drains may be reduced, further improving waterfowl habitat. Concern over the decline of the Salton Sea, the need to improve the quality of agricultural effluent, and the history and perception of pollutant flows from Mexico have led to the formation of the Citizens Congressional Task Force on the New River, which is responsible for the development of the Brawley Constructed Wetlands Demonstration Project.