CHAPTER 2- The Maracaibo System: A Physical Profile
29
Harleman et al. 1967; Cadena 1968). The equation of mass conservation for the salt in
unidimensional analysis is
where Sand u are the mean salinity and velocity in the cross section of the channel,
A is the area of the cross section, and Dx the apparent coefficient of longitudinal diffusion; the velocity of the fluid is the addition of the velocity of the tide (u) and the
velocity of the freshwater (U). Introducing certain border conditions they obtained
where SL' So and Slws are the salinities in the lake, ocean and channel during low-water
slack (lws); Do and B are two characteristic parameters of the longitudinal salinity
distribution, the apparent diffusion coefficient in the ocean and the distance to a point
in the negative direction of x where the salinity is equal to the oceanic. Both parameters may be determined if the salinity of the low-water slack is known at least at two
points.
From these equations it is possible to determine the maximum and minimum intrusion. The salinity distribution parameter is related to a non-dimensional parameter (Estuary Number) which is a measure of the degree of mixing and depends on
the tidal prism, Froude Number, freshwater discharge and tidal period. The values for
these parameters were determined by Cadena (1968) from field measurements.
2.6.3
Salt Balance of the Lake
The relationship between rainfall and salinity in the lake has been studied by Redfield
and Doe (1964) by means of a simplified model of a lake of uniform salinity connected
to a constant salinity ocean through a rectangular channel. Beginning with an equation which relates the net rate F(t) at which salt is carried out of the lake through unit
area of any section of the channel by the combined effect of advection and diffusion,
they established the boundary conditions for distance and salinity, and obtained the
following equation for the change in the chlorinity of the lake, at a given moment,
during a finite period:
RL
_ (R)C O - Ce KWH
!l.C = -
RL
'
V . -
e KWH -1
where R is the outflow from the lake during a finite period; V is the volume of the lake;
L is the length of the channel; K is the coefficient of tidal diffusivity; Wand H are the
depth and width of the channel respectively; CJ is the salinity of the sea; C the mean
salinity of the lake during the period; is the mean value of C(t) during the period; and
C(t) is the salinity of the lake at time t.
29
Harleman et al. 1967; Cadena 1968). The equation of mass conservation for the salt in
unidimensional analysis is
where Sand u are the mean salinity and velocity in the cross section of the channel,
A is the area of the cross section, and Dx the apparent coefficient of longitudinal diffusion; the velocity of the fluid is the addition of the velocity of the tide (u) and the
velocity of the freshwater (U). Introducing certain border conditions they obtained
where SL' So and Slws are the salinities in the lake, ocean and channel during low-water
slack (lws); Do and B are two characteristic parameters of the longitudinal salinity
distribution, the apparent diffusion coefficient in the ocean and the distance to a point
in the negative direction of x where the salinity is equal to the oceanic. Both parameters may be determined if the salinity of the low-water slack is known at least at two
points.
From these equations it is possible to determine the maximum and minimum intrusion. The salinity distribution parameter is related to a non-dimensional parameter (Estuary Number) which is a measure of the degree of mixing and depends on
the tidal prism, Froude Number, freshwater discharge and tidal period. The values for
these parameters were determined by Cadena (1968) from field measurements.
2.6.3
Salt Balance of the Lake
The relationship between rainfall and salinity in the lake has been studied by Redfield
and Doe (1964) by means of a simplified model of a lake of uniform salinity connected
to a constant salinity ocean through a rectangular channel. Beginning with an equation which relates the net rate F(t) at which salt is carried out of the lake through unit
area of any section of the channel by the combined effect of advection and diffusion,
they established the boundary conditions for distance and salinity, and obtained the
following equation for the change in the chlorinity of the lake, at a given moment,
during a finite period:
RL
_ (R)C O - Ce KWH
!l.C = -
RL
'
V . -
e KWH -1
where R is the outflow from the lake during a finite period; V is the volume of the lake;
L is the length of the channel; K is the coefficient of tidal diffusivity; Wand H are the
depth and width of the channel respectively; CJ is the salinity of the sea; C the mean
salinity of the lake during the period; is the mean value of C(t) during the period; and
C(t) is the salinity of the lake at time t.