Aspectos da hidrografia brasileira

Resumo

In this work, the author first. proceeds to a number of general considerations giving an idea of the size of the Brazilian hydrographic network and indicating the principal river basins that make up the system of watercourses throughout the country. In so doing she adopts the officially accepted criterion for her division into hydrographic basins, but also mentions those previously recommended by various authors. This introduction is followed by discussion of a series of topics forming the essential part of the survey and related to features of the relief, morphology, structure, geology and edaphic factors, conditions and problems of inland navigation, hydraulic potential, relevance of hydrography to settlement etc.

            The influence of the relief, morphology and structure can be readily traced in the marked aspects of Brazilian hydrography. In this connection, the author analyses the types of drainage, the divides and communications between basins, the rivers of the uplands and those of the plains, as well as other characteristics linked to land forms, such as: the narrow sections of the profiles (canyons), the phenomena of captures, the problem of the river mouths, etc.   The geological and edaphic factors have a striking· repercussion on the water supply to springs and the ensuing type of water table. As to climate. the influence on the rate of flow of the rivers ls enormous, particularly where rainfall ls concerned. Basing her deductions on climatic differences, the author considers four groups of streams with. divergent fluviometric regimes corresponding to the following areas: the Amazon and Middle-Northern regions; the really tropical areas; the Northeast; and the South of Brazil.

            The conditions and problems of river navigation are examined in the light of a knowledge of the main characteristics of the relief, morphology, structure, soils, climate, etc., and a study of the economic and technical possibilities of developing the resources pertaining to rivers in the various regions of Brazil.

            The role played by the rivers in directing the flow of settlement, economic distribution and occupation in the different regions of the country has been considerable. In a number of cases, the spread of population up a valley can be shown to> have been strongly influenced by the course of a river centering the economy of a vast area. Perhaps the Paraíba and the São Francisco are the best examples of this.

            In the course of the article, the author does not neglect the lake basins, but points out that, in comparison with the extensive river network, they are relatively unimportant. Among them, the lagoons behind barrier bars built up by marine or fluvial sedimentation deserve particular attention, the most outstanding along the seaboard being strung out from Alagoas to Rio Grande do Sul, where the largest of all are situated, namely the Lagoa dos Patos and the Lagoa Mirim, the latter traversed for half its length by the frontier with Uruguay. In the Amazon region, a distinction is made between the floodplain lagoons or swales and those on higher ground not subject to flooding (lagos de várzea and de terra firme).