The Bahia Blanca Estuary, Argentina
209
mean longitudinal current velocities in the Principal Channel and other
major channels are asymmetrical and largely caused by the extensive tidal
flats bordering the Principal Channel (Piccolo and Perillo 1990). The
peak ebb current is about twice the maximum flood current in the upper
reaches; however, flood usually has a longer duration. The residual circulation shows a significant difference in the direction of mass transport,
causing salt concentrations in the inner portion of the estuary often
exceeding those of the inner continental shelf.
14.3.3 Winds
Mid-latitude westerly winds and the influence of the Subtropical South
Atlantic High dominate the typical weather pattern of the region. The
resulting circulation induces strong NW and N winds with a mean velocity of 24 km h- 1 during 40% of the year and gusts of over 100 km h- 1 • Winds
generate waves, storm surges, and subtidal sea level variations in the
estuary. Wind waves (about 5-lOcm high and 1-3m long) occur in channels and on tidal flats when covered by water. The incoming tide, together
with N and NW winds, forms interaction waves, which are steep and up to
1.5 m high and 10-20 m long. However, the main effect of the predominant
NW and N winds is advancing the time of low water, delaying the time of
high water, and reducing predicted water levels. Large deviations between
predicted astronomical tides and actual tide levels occur at Ingeniero
White Port (-4.01 and 2.39m) and the Oceanographic Tower (-1.51 and
1.87 m; Perillo and Piccolo 1991). The maximum negative values coincide
with NW winds and maximum positive values with winds from the SW. At
the same stations, the low-frequency sea level response to wind indicates
that time scales of more than 10 days prevail while short-scale energy
peaks correspond to approximately 3-day periods (Piccolo and Perillo
1989).
14.3.4 Salinity and Temperature
Mean annual (13 °C}, summer (21.6 °C}, and winter (8.5 °C} surface water
temperatures in the Principal Channel are always slightly higher at the
head of the estuary (Piccolo et al. 1987; Fig. 14.3A), while mean surface salinity increases exponentially from the head to mid-reaches of the estuary
(Fig. 14.3B). Longitudinal temperature distributions vary between rainy
periods in spring/summer and low runoff in winter, when the vertical thermal structure of the estuary is homogeneous and longitudinal variations
209
mean longitudinal current velocities in the Principal Channel and other
major channels are asymmetrical and largely caused by the extensive tidal
flats bordering the Principal Channel (Piccolo and Perillo 1990). The
peak ebb current is about twice the maximum flood current in the upper
reaches; however, flood usually has a longer duration. The residual circulation shows a significant difference in the direction of mass transport,
causing salt concentrations in the inner portion of the estuary often
exceeding those of the inner continental shelf.
14.3.3 Winds
Mid-latitude westerly winds and the influence of the Subtropical South
Atlantic High dominate the typical weather pattern of the region. The
resulting circulation induces strong NW and N winds with a mean velocity of 24 km h- 1 during 40% of the year and gusts of over 100 km h- 1 • Winds
generate waves, storm surges, and subtidal sea level variations in the
estuary. Wind waves (about 5-lOcm high and 1-3m long) occur in channels and on tidal flats when covered by water. The incoming tide, together
with N and NW winds, forms interaction waves, which are steep and up to
1.5 m high and 10-20 m long. However, the main effect of the predominant
NW and N winds is advancing the time of low water, delaying the time of
high water, and reducing predicted water levels. Large deviations between
predicted astronomical tides and actual tide levels occur at Ingeniero
White Port (-4.01 and 2.39m) and the Oceanographic Tower (-1.51 and
1.87 m; Perillo and Piccolo 1991). The maximum negative values coincide
with NW winds and maximum positive values with winds from the SW. At
the same stations, the low-frequency sea level response to wind indicates
that time scales of more than 10 days prevail while short-scale energy
peaks correspond to approximately 3-day periods (Piccolo and Perillo
1989).
14.3.4 Salinity and Temperature
Mean annual (13 °C}, summer (21.6 °C}, and winter (8.5 °C} surface water
temperatures in the Principal Channel are always slightly higher at the
head of the estuary (Piccolo et al. 1987; Fig. 14.3A), while mean surface salinity increases exponentially from the head to mid-reaches of the estuary
(Fig. 14.3B). Longitudinal temperature distributions vary between rainy
periods in spring/summer and low runoff in winter, when the vertical thermal structure of the estuary is homogeneous and longitudinal variations