CHAPTER 6 . The Argentina Estuaries: A Review
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est estuary after Rio de la Plata and Bahia Blanca, although its freshwater input is reduced. Other estuaries such as Deseado and San Julian have recently become fully
marine environments since no freshwater is being input there. Both San Antonio Bay
and Caleta Valdes only receive some freshwater from groundwater since no surficial
rivers flow into them.
The climate of Patagonia is semiarid to arid. It is characterized by strong westerly
winds throughout the year. Typical mean speeds are 30-35 km h- 1 (16-19 kts). The
predominant winds are from W, SW and NW, which also are the directions of the
strongest winds. The winds from the SW-NW quadrant have six times the frequency
of all the other directions combined.
Unfortunately there are few studies related to the geomorphology Patagonian estuaries. The more important ones are for the estuaries of the: Colorado, Negro and Chubut
Rivers (Fig. 6.1). There is a lack of studies about the dynamics of the estuaries of the
southern part of Argentina; therefore, different and disperse processes in different time
scales will be described here trying to update the present knowledge of them.
6.4.1
Colorado River Estuary
Colorado River sources (Fig. 6.1) are in the dry regions of the Central Andes mountains. The mean annual discharge is 148 m3 S-1, being the maximum and minimum
mean daily values 1053 m3 S-1 and 30 m3 S-1 (Evarsa 1995). Its maximum discharge occur in spring (October) because of the melting of the winter upper mountain snow,
ending in December or January. Nevertheless, this values are presently changing since
the end of 1996 because a dam was constructed some 340 km from the mouth that
has modified both water and sediment load discharge. In fact, the name of the river
came from its brownish color due to the high suspended sediment load.
As is explained in more detail in Perillo and Piccolo (this book), the Colorado River
Delta extended originally from Bahia Blanca to Anegada Bay, some 200 km of the coastline, although there is no information about its extension offshore. The present day
delta extends about 40 km along the coast and begins at 86 km from it. However, this
delta has suffered important modifications in the last 100 yr both in morphology and
channels of the delta (Fig. 6.9). According to Soldano (1947) in the delta there were
four main discharges of the river into the ocean. From North to South their names
were: Colorado Chico, Cauce Nuevo, Brazo Antiguo and Riacho Azul. Between the last
two river channels there were several tributaries of the Riacho Azul that formed a
micro delta. However, Weiler (1983) showed significant differences from the description of Soldano (1947).
The coast between Laberinto Point and Union Island shows a light convex curvature along the North-South direction. Extended beaches and a low geomorphology
are found in the river mouth. However, the region is characterized by a significant
erosional processes of the old delta, that still have not been evaluated. According to
Codignotto and Weiler (1980) model, the erosive process of the delta probably occurred
during the Flandrian ingression that has its maximum penetration 6900 yr ago and
a short regression spatial period 400 years ago. Colorado River mouth, as well as in
other river mouths in this part of the Argentina coast, shows a deflection towards the
North due to littoral drift.
117
est estuary after Rio de la Plata and Bahia Blanca, although its freshwater input is reduced. Other estuaries such as Deseado and San Julian have recently become fully
marine environments since no freshwater is being input there. Both San Antonio Bay
and Caleta Valdes only receive some freshwater from groundwater since no surficial
rivers flow into them.
The climate of Patagonia is semiarid to arid. It is characterized by strong westerly
winds throughout the year. Typical mean speeds are 30-35 km h- 1 (16-19 kts). The
predominant winds are from W, SW and NW, which also are the directions of the
strongest winds. The winds from the SW-NW quadrant have six times the frequency
of all the other directions combined.
Unfortunately there are few studies related to the geomorphology Patagonian estuaries. The more important ones are for the estuaries of the: Colorado, Negro and Chubut
Rivers (Fig. 6.1). There is a lack of studies about the dynamics of the estuaries of the
southern part of Argentina; therefore, different and disperse processes in different time
scales will be described here trying to update the present knowledge of them.
6.4.1
Colorado River Estuary
Colorado River sources (Fig. 6.1) are in the dry regions of the Central Andes mountains. The mean annual discharge is 148 m3 S-1, being the maximum and minimum
mean daily values 1053 m3 S-1 and 30 m3 S-1 (Evarsa 1995). Its maximum discharge occur in spring (October) because of the melting of the winter upper mountain snow,
ending in December or January. Nevertheless, this values are presently changing since
the end of 1996 because a dam was constructed some 340 km from the mouth that
has modified both water and sediment load discharge. In fact, the name of the river
came from its brownish color due to the high suspended sediment load.
As is explained in more detail in Perillo and Piccolo (this book), the Colorado River
Delta extended originally from Bahia Blanca to Anegada Bay, some 200 km of the coastline, although there is no information about its extension offshore. The present day
delta extends about 40 km along the coast and begins at 86 km from it. However, this
delta has suffered important modifications in the last 100 yr both in morphology and
channels of the delta (Fig. 6.9). According to Soldano (1947) in the delta there were
four main discharges of the river into the ocean. From North to South their names
were: Colorado Chico, Cauce Nuevo, Brazo Antiguo and Riacho Azul. Between the last
two river channels there were several tributaries of the Riacho Azul that formed a
micro delta. However, Weiler (1983) showed significant differences from the description of Soldano (1947).
The coast between Laberinto Point and Union Island shows a light convex curvature along the North-South direction. Extended beaches and a low geomorphology
are found in the river mouth. However, the region is characterized by a significant
erosional processes of the old delta, that still have not been evaluated. According to
Codignotto and Weiler (1980) model, the erosive process of the delta probably occurred
during the Flandrian ingression that has its maximum penetration 6900 yr ago and
a short regression spatial period 400 years ago. Colorado River mouth, as well as in
other river mouths in this part of the Argentina coast, shows a deflection towards the
North due to littoral drift.