CHAPTER 9 . Geomorphological and Physical Characteristics of the Bahia Blanca Estuary
203
4.585.000
4.
C:' Sand wave field
o 1
2km
Depth contours (m )
5690 000
'--_"--_ _ _ .:.......:----l. .
o
5.685.000
Fig. 9.5. General bathymetry of the Principal Channel near its mouth where the largest sand wave
field is located. In the inserts examples of the echosounder records for the regular "saw sooth" type
(insert a) and the "solitary sand waves" (insert b) are shown
Both elements provided an endurance of the delta even though it is subject to strong
dynamic marine action. This can be observed because tidal discharge is being produced by a series of channels that were cut by them along the southern lobe of the
delta. These channels and the associated shoals are extremely movable whereas the
main body of the delta does conserve its position and general shape.
Mobility of the shoals corresponds to the way tidal currents hit the southern lobe
of the delta. In fact, tidal currents arrive to the southern lobe with large angles to it.
For example, the circulation on the Principal Channel has an angle of about 35
0
with
the channels cutting the lobe, whereas the flood currents have angles of the order of
20
0
with them. As a result of this situation sedimentation rates in some of the channels, specially El Toro Channel, can reach up to 1 m ye i (Perillo and Cuadrado 1991).
The complexity of this condition produce that sedimentation within the channels
are oblique to the general shape. Although one may expect that this dynamic situation
could reach some sort of equilibrium shape, the fact is that in the case of El Toro Channel the wrong orientation is maintained by dredging since it is the only entrance to the
Bahia Blanca harbour system. The harbour authorities dredge about 300000 m3 ye i
of sediment to allow adequate navigation conditions for 45 ft cargo vessels only in a
stretch of the channel less than 4 km in length and 800 m in width.
In several places along the Principal Channel and in the major channels flowing
into it, large and medium 3D dunes (sand waves) have been detected and described
(Aliotta and Perillo 1987; Aliotta 1988; Gomez and Perillo 1992; Ginsberg and Perillo
1997; Gomez et al. 1997). Because of the sediment distribution, these bedforms are
concentrated in specific places within these channels associated with large current
203
4.585.000
4.
C:' Sand wave field
o 1
2km
Depth contours (m )
5690 000
'--_"--_ _ _ .:.......:----l. .
o
5.685.000
Fig. 9.5. General bathymetry of the Principal Channel near its mouth where the largest sand wave
field is located. In the inserts examples of the echosounder records for the regular "saw sooth" type
(insert a) and the "solitary sand waves" (insert b) are shown
Both elements provided an endurance of the delta even though it is subject to strong
dynamic marine action. This can be observed because tidal discharge is being produced by a series of channels that were cut by them along the southern lobe of the
delta. These channels and the associated shoals are extremely movable whereas the
main body of the delta does conserve its position and general shape.
Mobility of the shoals corresponds to the way tidal currents hit the southern lobe
of the delta. In fact, tidal currents arrive to the southern lobe with large angles to it.
For example, the circulation on the Principal Channel has an angle of about 35
0
with
the channels cutting the lobe, whereas the flood currents have angles of the order of
20
0
with them. As a result of this situation sedimentation rates in some of the channels, specially El Toro Channel, can reach up to 1 m ye i (Perillo and Cuadrado 1991).
The complexity of this condition produce that sedimentation within the channels
are oblique to the general shape. Although one may expect that this dynamic situation
could reach some sort of equilibrium shape, the fact is that in the case of El Toro Channel the wrong orientation is maintained by dredging since it is the only entrance to the
Bahia Blanca harbour system. The harbour authorities dredge about 300000 m3 ye i
of sediment to allow adequate navigation conditions for 45 ft cargo vessels only in a
stretch of the channel less than 4 km in length and 800 m in width.
In several places along the Principal Channel and in the major channels flowing
into it, large and medium 3D dunes (sand waves) have been detected and described
(Aliotta and Perillo 1987; Aliotta 1988; Gomez and Perillo 1992; Ginsberg and Perillo
1997; Gomez et al. 1997). Because of the sediment distribution, these bedforms are
concentrated in specific places within these channels associated with large current