USE OF THE BASINS MODEL TO ESTIMATE LOADING OF HEAVY METALS FROM THE BINATIONAL TIJUANA RIVER WATERSHED
Abstract:The Tijuana River Watershed (TRW) is a binational watershed on the westernmost portion of the U.S. - Mexico border. For decades, raw sewage from the city of Tijuana, Mexico, has flowed into the Tijuana River and across the international border into the Tijuana Estuary. This paper describes the use of the Hydrologic Simulation Program-Fortran (HSPF) model and the Nonpoint Source Model (NPSM) embedded in the Better Assessment Science Integrating Point and Nonpoint Sources system (BASINS) to predict the annual discharge volume and mass loading of the heavy metals, copper (Cu), lead (Pb), and zinc (Zn) from the binational TRW. The model was first calibrated for flow, using two ten year datasets (from 1980-1989) of actual flow measurements made by the U.S. Geological Survey for Campo Creek and the Rio Alamar. BASINS is then used in a predictive fashion to estimate both annual discharge volume and metal loading from the TRW to the downstream estuary for 1998-1999. Annual discharge volume of the Tijuana River predicted by the NPSM was only 11% above the volume actually measured from the gauge at the international border, suggesting the applicability of BASINS for modeling flow and discharge volume in a semi-arid watershed such as the TRW. The NPSM was then used to predict the annual loading of Cu, Pb, and Zn from the TRW for the period from November 1998 through October 1999. The modeled values were 2,354 kg for Cu, 2,164 kg for Pb, and 4,783 kg for Zn. These values are somewhat higher than the actual loading measurements (based on flow-weighted composite sampling for 1998-1999), but significantly lower than the values measured in 1986-88 (SCCWRP, 1992), suggesting that metal loading has decreased over the past decade despite increased development and industrialization of the watershed.
Document Type: Research Article
Publication date: January 1, 2000
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