Caracterização hidrodinâmica-sedimentológica do estuário e delta do rio São Francisco

Abstract

São Francisco river, the largest genuinely national river has a drainage area and extension respectivelly of 640,000 km2 (until the mouth) and 2,700 km crossing the states of Minas Gerais, Bahia, Goiás, Pernambuco, Sergipe and Alagoas, besides Distrito Federal, flowing into the Atlantic Ocean at the coast, of Alagoas and of Sergipe. Its waters are used for hydroelectric plants mainly.The present study has the objective of evaluating the consequences originated with the construction of the dams series for hydroelectric plants in the whole fluvial system of low San Francisco, mainly inthe area of the estuary and delta, between the states of Alagoas and Sergipe. The study was made for the year of 2000, through the acquisition of precipitation and discharge date, water sampling and sediments, current, discharge water, depth profile and beach profile measurements, in three compartments of the different systems: fluvial, estuarine and coastal. Empirical formulas of transport estimat of were used to evaluate the total discharge of sediments and of material in suspension. The rainfall presented different regime sand precipitation period samong the high and médium course with lo west area, presenting the largest values in the regions of the high est and médium San Francisco. The water discharge regime of San Francisco river presented a minimum in the period of small precipitation in the high and medium course and maximum water discharge for high rainfall total. The vertical profile of speed presented larger values at the surface, decreasing to the bottom. In the estuary the speeds, varied positively and negatively, in agreement with the direction of the flow. The periodsof tide flooding and ebbing were of 6h and 37min, and 5h and 37 min, respectively. The total discharge of sediment transported into the coastal área was of1,57x106ty-1thatcorrespondsto2,45t km2 of specific discharge. The sediments grain size, varied from fine on the banks and large inside of the channels. The inclination of Sergipe coast makes waves to travel northeastward, causing southward.The preferential sediment deposition was in front na datthes out hof themouth of the river . Flooding control, due to dams structures blocking sediment transport, caused problems such as silting of the river channel and coastal erosion.