The Colorado River Estuary and Upper Gulf of California, Baja, Mexico
333
loss from the water between October and January, the mean annual net
surface heat flux is into the sea (69 W m- 2 near the coast and 83 W m- 2 offshore). These conditions require an export of heat and salt out of the northern Gulf to achieve a balance, thus the mean annual thermohaline circulation must have an inflowing component at depth (Lavin and Organista
1988). Since inflowing deep water has higher inorganic nutrient concentrations than outflowing surface water, the thermohaline circulation in the
northern Gulf is a natural fertilization mechanism.
22.3 Environmental Settings
The Colorado River forms a 2- to 8-km-wide and 50-km-long estuarine
basin, which opens at the mouth into a 16-km-wide delta. Numerous submarine channels and shoals extend for about 50km in a northwest-southeast direction. The semidiurnal tide regime has a range of 6.95 m at San
Felipe, which is even larger at the entrance of the delta (Gutierrez and Gonzalez 1989). Extensive low lands on the western and eastern shores and the
low and flat Montague and Pelicano islands are periodically flooded by
tides (Fig. 22.1). Tides produce current velocities of 1.5 m s- 1 over the shallow platform adjacent to the delta and up to 3m s- 1 inside the estuarine
basin (Meckel1975; Cupul1994). The evolution of the Colorado River delta
has been controlled by the interaction between constructive and destructive processes, like sediment supply (about 160 x 10 6 tons year- 1 ) from the
Colorado River and one of the largest tidal regimes in the world, respectively (Carriquiry and Sanchez 1999). Human intervention, in particular
the construction of the Hoover and Glen Canyon Dams in the Colorado
River basin, has almost eliminated the discharge of sediments into the
delta (Meckel 1975) that has become subjected to destructive processes,
such as strong tidal currents and wind-induced waves. The delta is passing
through an erosional phase and exports sediments to the northern Gulf of
California at rates similar to those of unaltered river flow prior to 1935
(van Andel and Shor 1964; Carriquiry et al. 1992; Cupul1994).
The construction of the dams and the diversion of freshwater for irrigation, industrial and municipal uses also had a profound effect on the
amount and timing of freshwater into the Upper Gulf of California. Before
the filling of Lake Mead (1935) , freshwater discharge had a seasonal modulation with a peak in June (Fig. 22.2). In the absence of freshwater flow from
the Colorado River, surface salinity generally increases northwestward,
from about 36 outside the estuary to about 38.5 at the northern end of
Montague Island in winter, and from 38 to about 40 in summer, thus
333
loss from the water between October and January, the mean annual net
surface heat flux is into the sea (69 W m- 2 near the coast and 83 W m- 2 offshore). These conditions require an export of heat and salt out of the northern Gulf to achieve a balance, thus the mean annual thermohaline circulation must have an inflowing component at depth (Lavin and Organista
1988). Since inflowing deep water has higher inorganic nutrient concentrations than outflowing surface water, the thermohaline circulation in the
northern Gulf is a natural fertilization mechanism.
22.3 Environmental Settings
The Colorado River forms a 2- to 8-km-wide and 50-km-long estuarine
basin, which opens at the mouth into a 16-km-wide delta. Numerous submarine channels and shoals extend for about 50km in a northwest-southeast direction. The semidiurnal tide regime has a range of 6.95 m at San
Felipe, which is even larger at the entrance of the delta (Gutierrez and Gonzalez 1989). Extensive low lands on the western and eastern shores and the
low and flat Montague and Pelicano islands are periodically flooded by
tides (Fig. 22.1). Tides produce current velocities of 1.5 m s- 1 over the shallow platform adjacent to the delta and up to 3m s- 1 inside the estuarine
basin (Meckel1975; Cupul1994). The evolution of the Colorado River delta
has been controlled by the interaction between constructive and destructive processes, like sediment supply (about 160 x 10 6 tons year- 1 ) from the
Colorado River and one of the largest tidal regimes in the world, respectively (Carriquiry and Sanchez 1999). Human intervention, in particular
the construction of the Hoover and Glen Canyon Dams in the Colorado
River basin, has almost eliminated the discharge of sediments into the
delta (Meckel 1975) that has become subjected to destructive processes,
such as strong tidal currents and wind-induced waves. The delta is passing
through an erosional phase and exports sediments to the northern Gulf of
California at rates similar to those of unaltered river flow prior to 1935
(van Andel and Shor 1964; Carriquiry et al. 1992; Cupul1994).
The construction of the dams and the diversion of freshwater for irrigation, industrial and municipal uses also had a profound effect on the
amount and timing of freshwater into the Upper Gulf of California. Before
the filling of Lake Mead (1935) , freshwater discharge had a seasonal modulation with a peak in June (Fig. 22.2). In the absence of freshwater flow from
the Colorado River, surface salinity generally increases northwestward,
from about 36 outside the estuary to about 38.5 at the northern end of
Montague Island in winter, and from 38 to about 40 in summer, thus