Environmental Engineering Reference
In-Depth Information
Fig. 4
Effect of phase lag between tidal and density currents through the harbor entrance
on the density-induced exchange flow. Source: [28]. Reproduced with permission
where:
V
d
=exchangevolumepertideduetodensitycurrents,
f
4
=coefficient
depending on
V
do
/
V
ha
with
V
ha
being the volume of the basin below MSL,
f
5
= coefficient depending on
V
do
/
ϕ
t
between
u
do
and
u
t
.
It is obvious that in a large harbor (low values of
V
do
/
V
t
and phase lag
V
ha
)theaveragewa-
ter density will hardly follow the density fluctuation of the water in front of
the harbor. In the case of a small harbor basin and
/
or strong density currents
(higher values of
V
do
/
V
ha
), however, the density of the water inside the har-
bor may follow the density fluctuations outside. This results in a reduction of
the characteristic density difference inducing the density currents. This effect
has been included in the coefficient
f
4
, which consequently reduces with in-
creasing
V
do
/
V
ha
. This effect has been estimated theoretically on the basis of
linear harmonic theory assuming a constant water level and neglecting tidal
flow (total water exchange
V
e
=
V
do
).
Under specific conditions of low tide, low flow, and low density differences
other exchange processes become more important in the exchange [34]:
