Project Title: Tijuana Estuary Hydrologic Evaluation

SCERP Project Number: W97-5

Principal Investigator: Kathryn Thorbjarnarson

Task Manager's affiliation: San Diego St. University

Goal: This is an integrated surface- and ground-water monitoring study of the Tijuana Estuary to further understand the impacts of watershed changes on freshwater inflow regimes, the salinity structure and, in turn, on the ecological functioning of the Tijuana Estuary. The information gathered will allow resource managers to make science-based decisions which balance the human needs to utilize resources with the need to protect and enhance the valuable natural resources within the Tijuana Estuary.

The Tijuana Estuary contains some of the most valued salt marsh habitat remaining in Southern California. It is both a National Estuarine Research Reserve (NERR) and a National Wildlife Refuge for endangered species. Located in southern San Diego County, the estuary receives waters from a 1,700-sq.-mile watershed, three-quarters of which is located within Mexico. The natural balance of fresh and salt water flows into the Tijuana Estuary has been dramatically altered by the damming of approximately 80% of the runoff from Mexico, U.S. water importation and release, wastewater discharges, groundwater extraction, and extensive urbanization (i.e., increased runoff and wastewater discharge). These watershed changes have the potential to increase the frequency, extent, and duration of brackish water conditions within the estuary, and would have substantial impacts on estuarine biota, including endangered species.

This study, which includes monitoring both surface- and groundwater levels and salinities over a one-year time period, will be the first integrated hydrologic study of Tijuana Estuary. Ground- and surface-water monitoring points will be established at strategic locations throughout the estuary and its margins. The integrated study of the ground- and surface-water salinities and fluxes into the Tijuana Estuary is critical to balancing the protection of the estuary's valuable habitat with the increasing need to utilize water resources within the basin. The information gathered will be valuable to potential dischargers (the International Boundary Water Commission and US EPA are building a wastewater treatment plant that may discharge excess water to Tijuana River), regulators (the Regional Water Quality Control Board), and estuary resource managers (the City and County of San Diego, the California Coastal Commission, the California Dept. of Parks and Recreation, US Fish and Wildlife Refuge, and the National Oceanic and Atmospheric Administration). The public will also benefit from having an interactive, animated simulation model of Tijuana Estuary at the Visitor Center, where users can specify river or tidal flows and see changes in a color display indicating the corresponding impact on estuarine salinity.

Project is ongoing.

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Last updated 5/6/99