112
B. Kjerfve et al.
jacent river basin to the north. An estimated 25m 3 s- 1 of this water becomes
runoff into Baia de Guanabara. Thus, the total mean runoff of freshwater
into Baia de Guanabara measures 125m 3 s- 1 •
8.6 Tidal Variability
Baia de Guanabara experiences mixed mainly semidiurnal tides with a
tidal form number of 0.33. Kjerfve et al. ( 1997) summarized harmonic tidal
amplitude and phase data for 15 stations within Baia de Guanabara, based
on water level measurements by the Departamento de Hidrografia e Navega<;:ao (DHN). The mean tidal range in Baia de Guanabara measures 0.7 m
and does not vary significantly spatially. The fortnightly spring tidal range
measures 1.1 m and the neap tidal range is 0.3 m. The semidiurnal M 2
and S 2 tidal amplitudes measure 0.32 and 0.18m, respectively, and are
dominant. However, the semidiurnal tidal range is strongly modulated by
the lunar declinational fortnightly cycle with diurnal tides exhibiting a
0.4-m tropic tidal range and a 0.1 -m equatorial tidal range. The tidal prism
ofBaia de Guanabara measures 2.3 x 10 8 m 3 • Tidal currents in the entrance
section are flood-dominant and reach 1.6 m s-1, whereas peak ebb-currents
measure 1.0 m s- 1 in the same cross section. Further into the bay, peak tidal
currents are on the order of0.5m s- 1 •
8.7 Salinity, Circulation and Flushing
The water circulation in Baia de Guanabara is composed of both gravitational circulation and residual tidal circulation. Based on surface and bottom salinity measurements by FEEMA at 13 stations from 1980 to 1993, the
mean salinity measures 29.5±4.8, and the mean water temperature
24.2±2.6 °C. The vertical salinity stratification is moderate to weak with a
vertical net salinity difference seldom exceeding 4. Based on these net
surface and bottom salinity measurements and simulated freshwater
discharge, Kjerfve et al. ( 1997) calculated a net surface outflow of 900m 3 s- 1
and a net bottom inflow of 775m 3 s- 1 • Thus, the water volume, which
participates in the two-layered gravitational circulation, is on average eight
times greater than the freshwater input. Baia de Guanabara, similar to
many coastal plain estuaries, also has a large residual tidal circulation.
Approximately half of the salt transported into the bay is due to the gravitational circulation and the remainder due to tidal dispersion. One
B. Kjerfve et al.
jacent river basin to the north. An estimated 25m 3 s- 1 of this water becomes
runoff into Baia de Guanabara. Thus, the total mean runoff of freshwater
into Baia de Guanabara measures 125m 3 s- 1 •
8.6 Tidal Variability
Baia de Guanabara experiences mixed mainly semidiurnal tides with a
tidal form number of 0.33. Kjerfve et al. ( 1997) summarized harmonic tidal
amplitude and phase data for 15 stations within Baia de Guanabara, based
on water level measurements by the Departamento de Hidrografia e Navega<;:ao (DHN). The mean tidal range in Baia de Guanabara measures 0.7 m
and does not vary significantly spatially. The fortnightly spring tidal range
measures 1.1 m and the neap tidal range is 0.3 m. The semidiurnal M 2
and S 2 tidal amplitudes measure 0.32 and 0.18m, respectively, and are
dominant. However, the semidiurnal tidal range is strongly modulated by
the lunar declinational fortnightly cycle with diurnal tides exhibiting a
0.4-m tropic tidal range and a 0.1 -m equatorial tidal range. The tidal prism
ofBaia de Guanabara measures 2.3 x 10 8 m 3 • Tidal currents in the entrance
section are flood-dominant and reach 1.6 m s-1, whereas peak ebb-currents
measure 1.0 m s- 1 in the same cross section. Further into the bay, peak tidal
currents are on the order of0.5m s- 1 •
8.7 Salinity, Circulation and Flushing
The water circulation in Baia de Guanabara is composed of both gravitational circulation and residual tidal circulation. Based on surface and bottom salinity measurements by FEEMA at 13 stations from 1980 to 1993, the
mean salinity measures 29.5±4.8, and the mean water temperature
24.2±2.6 °C. The vertical salinity stratification is moderate to weak with a
vertical net salinity difference seldom exceeding 4. Based on these net
surface and bottom salinity measurements and simulated freshwater
discharge, Kjerfve et al. ( 1997) calculated a net surface outflow of 900m 3 s- 1
and a net bottom inflow of 775m 3 s- 1 • Thus, the water volume, which
participates in the two-layered gravitational circulation, is on average eight
times greater than the freshwater input. Baia de Guanabara, similar to
many coastal plain estuaries, also has a large residual tidal circulation.
Approximately half of the salt transported into the bay is due to the gravitational circulation and the remainder due to tidal dispersion. One