Geomorphological and sedimentological characteristics

STEVAUX, JOSÉ C; ORFEO, OSCAR; PARSONS, DANIEL

The Paraná River Basin: managing water resources to sustain ecosystem services

Routledge

Lugar: Abingdon; Año: 2020; p. 42 - 60

?The upper reach of the Paraná River runs over a mixed rock alluvial bed, with a relatively narrow alluvial plain, two alluvial terraces and several breaks in channel slope in its longitudinal profile. Although the highest elevation in the basin is 1,200 m at the headwaters of the Grande River, it is generally recognized the Upper stretch of the Paraná River begins at the confluence of the Paranaíba and Grande rivers at an altitude of 290 m above sea level and extends for 600 km to the reservoir of the Itaipu Dam. ?At the Guaira gauge station in the Upper basin, the mean discharge is 10,800 m3 s-1, with extreme minimum and maximum values of 2,490 m3 s-1 (1944) and 39,870 m3 s-1 (1983), respectively. Because of the heavier rainfall in the eastern part of the basin, all the largest tributaries are situated on the eastern border, with mean discharges in these tributaries of between 860 and 3,000 m3 sec-1.?Owing to sediment deposition in the reservoirs of the numerous dams in the Upper Paraná, there are very low loads of suspended solids in the main channel. For instance, in the period before and after the construction of the Porto Primavera Dam, the mean concentrations of suspended sediments declined from 35 mg L-1 before construction to 10.85 mg L-1 at the completion of dam, and today the mean suspended sediment concentration is 0.3 mg L-1. ?The multichannel pattern of the Upper Paraná is characterized by more than two hundred islands of different morphology, size and age, plus hundreds of central and lateral sand bars. Some sections of the river present up to six multichannel stretches, although a main eastern channel is practically continuous and constitutes the primary navigation way.?Downstream of the basaltic plateau located at the Brazil-Argentina border, the Paraná River flows through the extensive Argentine plain. Andean tectonics have modified the regional slope and drainage to form the extensive Iberia wetland.?Downstream of the confluence with the Paraguay River, the Middle reach of the Paraná shows pronounced spatial and temporal differences in suspended sediment concentrations, related to the sediments transported from the Andean region by the Paraguay River. The suspended sediment concentration in the Paraná River downstream of the confluence with the Paraguay River shows extremes up to 616 mg L-1 on the eastern margin and up to 1,271 mg L-1 on the western margin.?The present multichannel pattern of the middle Paraná River is related to the abundance of the bedload discharge, which is greater than 25% of the total sediment discharge. Because of this and the regional slope, several kinds of sand bars and channels are located in the middle Paraná as a typical feature of this fluvial system.?In the Lower Paraná, the Delta region has a surface area of around 3,500 km2 and it is composed of islands with a central marsh or shallow lake, surrounding by meandering streams with sandy natural levees, where scroll meanders, point bars and oxbow lakes are also frequent.