quarta-feira, 8 de julho de 2009

Conservar nascente em pequenas bacias hidrográficas

Nascentes são manifestações superficiais de água armazenada em reservatórios subterrâneos, conhecidos como aquíferos ou lençóis, e que dão origem a pequenos cursos d’água. Estes pequenos constituem os córregos que se ajuntam para formar riachos e ribeirões e que voltam a se juntar para formar os rios. É assim que surge tanto um pequeno ribeirão, quanto os rios Amazonas e São Francisco, e tantos outros.

Mas nem todas as manifestações superficiais dos lençóis subterrâneos chegam a formar cursos d’água, pois podem ficar simplesmente formando poças e constituindo as conhecidas fontes. Já os lençóis são abastecidos pela parte da água das chuvas que penetra no solo e desce pelo perfil do mesmo até encontrar uma camada impermeável (rochosa, por exemplo). Com a impossibilidade de continuar descendo, ela se acumula, preenchendo os poros, encharcando ou saturando o solo logo acima da referida camada impermeável. Esse volume de solo saturado constitui o lençol ou aquífero.

A conservação de nascentes é, portanto, uma tecnologia que precisa estar baseada em fundamentos hidrológicos. Sobre tais fundamentos, que variam com a variação dos ecossistemas, é que são estabelecidas as tecnologias de manejo. Toda a parte do ciclo hidrológico envolvida na conservação de nascentes ocorre numa área da superfície que se enquadra na definição de bacia hidrográfica. Pode ser pequena, uma simples grota, e aí está o segredo de tudo, pois a hidrologia de pequenas bacias tem peculiaridades que a difere daquela usada nos estudos de grandes rios, para construção de hidrelétricas, por exemplo.

Artigo do Professor Osvaldo Ferreira Valente. Engenheiro florestal, especialista em hidrologia e manejo de pequenas bacias hidrográficas e professor titular da Universidade Federal de Viçosa (UFV) / ovalente@tdnet.com.br. Do jornal O ECO http://www.oeco.com.br/

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