CHAPTER 6 . The Argentina Estuaries: A Review
119
Mean tidal amplitude is 1.8 m and it penetrates into the river 60 km inland, approximately. Due to the construction of the dam (Casa de Piedra), the discharge has suffered a great reduction to its historical minimum. Therefore, an important sea water
ingression into its channel is anticipated, exceeding what it was observed in 1984
(20 km from the coast). However, there is no physical data from the estuarine sector.
Nevertheless, Cuadrado et al. (1998) analysed temperature, salinity, suspended sediment and tidal current data obtained from the inner shelf offshore the Colorado River
Estuary. They detected for the first time the influence of the Colorado River plume
into the inner shelf. The distribution of the suspended sediment concentration in the
surficial water showed two well defined plumes with values higher than 50 mg I-I. One
of them was at the North of the Colorado River exceeding 100 mg I-I with a NNE direction. The other plume was located southwards, with concentrations of 80 mg I-I.
Unfortunately, to the authors knowledge little is known about the biology, tides, etc.
of this estuary.
6.4.2
Negro River Estuary
Both the Colorado and Negro Rivers constitute the northern border of Patagonia. From
economical and hydrological reasons, the Negro River valley is the most important of
the region. The Limay and Neuquen Rivers are its main tributaries joining at about
550 km from the mouth and it does not receive any other tributary along the way. The
mean annual river discharge is 858 m3 S-I, being its maximum and minimum mean
daily 3405 m 3 S-1 and 75 m 3 s-" respectively (Evarsa 1995). In the estuary mouth current velocity was estimated in 3.83 m3 S-1 for a discharge of 550 m3 S-1 (INCYTH 1975).
According to satellite data, the plume of the Negro River discharges towards the South.
Even though some geological surveys have been done in the lands around the estuary only one has deal directly with the geomorphologic characteristics and sediment transport processes occurring at the mouth of the estuary (del Rio et al. 1991).
At the mouth the estuary has a width of 1 km and flow along a valley of 12 km approximately; however, the river width varies between 500 and 800 m.lts depth vary between
5 and 10 m (Soldano 1947). Two banks are found in its mouth (Miguel at the SW and
La Hoya at the NE, Fig. 6.10). They form an open ebb delta although they have different characteristics without the frontal shield.
The ebb delta presents a principal channel, which is dominated by ebb currents,
and marginal ones which are dominated by flood currents. Both banks are formed by
swash bars and shelves of fine sands with a high range of selection. Del Rio et al. (1991)
mention the presence of megaripples produced by the variations of the tidal currents
during the ebbing tide. The authors also indicated that the ebb delta has an asymmetric form due to the littoral drift that characterize the area, which is from South to North
(Aliotta 1983). The Miguel bank had grew about 2500 m towards the East. On the other
hand, La Hoya bank has a clear tendency of migration towards the coast.
Mean spring and neap tides at the mouth are 3.35 m and 2.44 m, respectively, and
tidal influence are observed up to 66 km from the mouth (Soldano 1947). Naturally,
ebb currents are more important in magnitude than flood ones. They reach values of
2.5 m S-1 (del Rio et al. 1991). The slack water of high water is 30 min and at low water
is 17 min. Strong winds from the S, SW and W advance the ebb tides and delay the
119
Mean tidal amplitude is 1.8 m and it penetrates into the river 60 km inland, approximately. Due to the construction of the dam (Casa de Piedra), the discharge has suffered a great reduction to its historical minimum. Therefore, an important sea water
ingression into its channel is anticipated, exceeding what it was observed in 1984
(20 km from the coast). However, there is no physical data from the estuarine sector.
Nevertheless, Cuadrado et al. (1998) analysed temperature, salinity, suspended sediment and tidal current data obtained from the inner shelf offshore the Colorado River
Estuary. They detected for the first time the influence of the Colorado River plume
into the inner shelf. The distribution of the suspended sediment concentration in the
surficial water showed two well defined plumes with values higher than 50 mg I-I. One
of them was at the North of the Colorado River exceeding 100 mg I-I with a NNE direction. The other plume was located southwards, with concentrations of 80 mg I-I.
Unfortunately, to the authors knowledge little is known about the biology, tides, etc.
of this estuary.
6.4.2
Negro River Estuary
Both the Colorado and Negro Rivers constitute the northern border of Patagonia. From
economical and hydrological reasons, the Negro River valley is the most important of
the region. The Limay and Neuquen Rivers are its main tributaries joining at about
550 km from the mouth and it does not receive any other tributary along the way. The
mean annual river discharge is 858 m3 S-I, being its maximum and minimum mean
daily 3405 m 3 S-1 and 75 m 3 s-" respectively (Evarsa 1995). In the estuary mouth current velocity was estimated in 3.83 m3 S-1 for a discharge of 550 m3 S-1 (INCYTH 1975).
According to satellite data, the plume of the Negro River discharges towards the South.
Even though some geological surveys have been done in the lands around the estuary only one has deal directly with the geomorphologic characteristics and sediment transport processes occurring at the mouth of the estuary (del Rio et al. 1991).
At the mouth the estuary has a width of 1 km and flow along a valley of 12 km approximately; however, the river width varies between 500 and 800 m.lts depth vary between
5 and 10 m (Soldano 1947). Two banks are found in its mouth (Miguel at the SW and
La Hoya at the NE, Fig. 6.10). They form an open ebb delta although they have different characteristics without the frontal shield.
The ebb delta presents a principal channel, which is dominated by ebb currents,
and marginal ones which are dominated by flood currents. Both banks are formed by
swash bars and shelves of fine sands with a high range of selection. Del Rio et al. (1991)
mention the presence of megaripples produced by the variations of the tidal currents
during the ebbing tide. The authors also indicated that the ebb delta has an asymmetric form due to the littoral drift that characterize the area, which is from South to North
(Aliotta 1983). The Miguel bank had grew about 2500 m towards the East. On the other
hand, La Hoya bank has a clear tendency of migration towards the coast.
Mean spring and neap tides at the mouth are 3.35 m and 2.44 m, respectively, and
tidal influence are observed up to 66 km from the mouth (Soldano 1947). Naturally,
ebb currents are more important in magnitude than flood ones. They reach values of
2.5 m S-1 (del Rio et al. 1991). The slack water of high water is 30 min and at low water
is 17 min. Strong winds from the S, SW and W advance the ebb tides and delay the