IDENTIFYING SOURCES OF BASEFLOW IN THE SANTA ANA RIVER, CALIFORNIA

摘要

The Santa Ana River is an important source of groundwater recharge for aquifers in Orange County, California. Under base-flow conditions, a substantial percentage of the Santa Ana River consists of treated wastewater. The objectives of this study were to characterize the interaction between the Santa Ana River and the shallow groundwater system, and to quantify the percentage of wastewater and other sources of flow in the Santa Ana River. To accomplish these objectives, stream discharge and dye-tracer concentrations were measured in the Santa Ana River and its tributaries. The study area was divided into an upper reach (8 mi) and lower reach (10 mi). Discharge measurements were made at 10 sites along the river, including a USGS gaging station (Santa Ana River at MWD Crossing), and on 5 tributaries. Water samples were collected every 5 to 15 minutes at seven sites to measure Rhodamine WT dye concentrations. The dye concentrations allow for a Lagrangian interpretation of the discharge data. By measuring the discharge associated with same mass of water, the percentage of wastewater can be quantified. The flow of the Santa Ana River at MWD Crossing, the end of the upper reach, was about 68 percent wastewater an at the Powerline site, the end of the lower reach, wastewater increased to approximately 77 percent of total flow.