325
Similar equations can be derived from the myriad of prism/area relationships that
have been developed since that of O’Brien (1931). For example, from Jarrett (1976)
for twin jetties on the Pacific coast, the relationship is (in metric units):
v
A
E
E
max
.
.
= 0 509
0 081
(10.7)
Bruun (1978) presented a simple empirical relationship, based on the ratio of the
tidal prism to the rate of littoral drift transport to the entrance, which determined
whether an estuary may be prone to closure or may remain open. Low values of the
ratio denoted an unstable shoaling mode (in the terminology of O’Brien and Dean
1972). However, this method does not predict an unstable scouring mode or a stable
channel cross-sectional area. Further, the method does not apply to entrances where
the littoral drift transport to the inlet has been interrupted by jetties.
10.2.4.2 Analytical Formulations
Brown (1928) and Escoffier (1940) presented a generalized analytical approach for
a simple idealized estuary system, as shown in Fig. 10.4, relating the bay tide phasing and amplitude to that of the ocean tide through the hydraulic characteristics of
the entrance channel. The method is applicable to small and large tidal inlets on
shorelines where the rates of littoral drift transport are small. It favors estuaries with
relatively short and regular entrance channels connecting the bay to the ocean.
Through the construction of an Escoffier Diagram, the status of an inlet at any
point in time can be examined and, theoretically, the ultimate stable cross-sectional
area of the entrance channel can be predicted. The method is outlined as follows
(after O’Brien and Dean 1972).
Keulegan (1951, 1967) developed the relationships between the tidal phase lag,
the ratio of the bay-to-ocean tidal amplitudes (a B /a O ) and what is termed the
Fig. 10.4 Idealized estuary for Escoffier inlet analysis. The analysis assumes short regular
entrance channels without surf zone bars and shoals
10 Long Term Impacts of Jetties and Training Walls on Estuarine Hydraulics…
Similar equations can be derived from the myriad of prism/area relationships that
have been developed since that of O’Brien (1931). For example, from Jarrett (1976)
for twin jetties on the Pacific coast, the relationship is (in metric units):
v
A
E
E
max
.
.
= 0 509
0 081
(10.7)
Bruun (1978) presented a simple empirical relationship, based on the ratio of the
tidal prism to the rate of littoral drift transport to the entrance, which determined
whether an estuary may be prone to closure or may remain open. Low values of the
ratio denoted an unstable shoaling mode (in the terminology of O’Brien and Dean
1972). However, this method does not predict an unstable scouring mode or a stable
channel cross-sectional area. Further, the method does not apply to entrances where
the littoral drift transport to the inlet has been interrupted by jetties.
10.2.4.2 Analytical Formulations
Brown (1928) and Escoffier (1940) presented a generalized analytical approach for
a simple idealized estuary system, as shown in Fig. 10.4, relating the bay tide phasing and amplitude to that of the ocean tide through the hydraulic characteristics of
the entrance channel. The method is applicable to small and large tidal inlets on
shorelines where the rates of littoral drift transport are small. It favors estuaries with
relatively short and regular entrance channels connecting the bay to the ocean.
Through the construction of an Escoffier Diagram, the status of an inlet at any
point in time can be examined and, theoretically, the ultimate stable cross-sectional
area of the entrance channel can be predicted. The method is outlined as follows
(after O’Brien and Dean 1972).
Keulegan (1951, 1967) developed the relationships between the tidal phase lag,
the ratio of the bay-to-ocean tidal amplitudes (a B /a O ) and what is termed the
Fig. 10.4 Idealized estuary for Escoffier inlet analysis. The analysis assumes short regular
entrance channels without surf zone bars and shoals
10 Long Term Impacts of Jetties and Training Walls on Estuarine Hydraulics…