Influence of inner channel changes in the morphodynamics at the outer Bahía Blanca Estuary, Argentina.

GOMEZ, EDUARDO A; PERILLO, GERARDO M. E.

Bayreuth

Congreso; 16th Latin American Conference on Geosciences,; 1998

Latin American Conference on Geosciences

The Bahia Blanca Estuary has great economicalimportance for Argentina, since one of the mostimportant harbour complexes of the country isplaced here. The major channels that form theBahia Blanca Estuary are partly closed by highlymodified tidal deltas. There is a system ofshoreface-connected sand banks in its outer areathat, combined with the tidal deltas, results in acomplex bottom topography that is constantlyevolving.The first outward 10 km of the access channelto the harbour complex in the outer area, exhibitnatural depths greater that 13 m below the DatumLevel, therefore it was not necessary to dredge ituntil present. By means of bathymetric and sidescan sonar surveys, and sedimentological andmorphological studies, it was determined that thosenatural depths were the consequence of a localacceleration of tidal currents due to the westwardpresence of Largo Bank, which concentrate tidalcurrents during ebb. Largo Bank is composed byfine sand, and each of its sides are dominated byopposite tidal currents sense. Such tidal currentsdominance have caused a constant eastwardmigration of the bank towards the access channel.However until present, the sediments transportedby flood currents from one side through the bankcrest and then to the access channel, were washedaway by the strong currents occurring during ebb.Therefore, Largo Bank had constantly increased itsvolume and the steepness of its east side whichfaced the access channel. Twelve years ago theincrement in bank volume started to obstruct theflow of ebb currents and then a new channelthrough the extreme northern part of the bank crestbecame to develop.An internal channel (Bermejo Channel) whichtuns between two major islands, have abruptlychanged the configuration of it~ mouth around 15years ago making to its ebb currents, once flowingsouthward, to change eastward. Those ebbcurrents have changed the equilibrium´ of thenorthern part of Largo Bank counterbalancing the