On how the Colorado River affected the hydrography of the upper Gulf of California

The hydrography of the shallow (< 30 m) Upper Gulf of California was mapped during a rare Colorado River fresh water discharge, which occurred during March and April, 1993. This provided (a) an opportunity to observe what may have been the hydrographic conditions before the damming of the river, and (b) a data base that can be used to calibrate numerical models with a view to simulating those conditions for ecological applications. In opposition to the now normal inverse estuarine situation, salinity and density decreased toward the head. Dilution was detectable in a coastal band flowing to the right-hand side of the river discharge, up to some 70 km from the river mouth. Tidal mixing maintained vertical homogeneity during spring tides, but stratification was established during neap tides, in an estuarine salt-wedge structure. (C) 1999 Elsevier Science Ltd. All rights reserved.