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Universidade de Brasília (UNB) 2016

Avaliação de viabilidade de aplicação de técnicas de recarga artificial em aquíferos salinizados, fraturados, Petrolina - PE

Silva, Priscila Sousa

Titre : Avaliação de viabilidade de aplicação de técnicas de recarga artificial em aquíferos salinizados, fraturados, Petrolina - PE

Auteur : Silva, Priscila Sousa

Université de soutenance : Universidade de Brasília (UNB)

Grade : Mestrado em Geociências Aplicadas 2016

The Petrolina County, State of Pernambuco, Brazil has several peculiarities that make it particular in the hydrogeological point of view. The water resources scarcity issue is related to quantitative (depending on the weather, the soil and the nature of aquifers) and qualitative (due to the high salinity of groundwater). The climate of the region is classified as semiarid, with scarce rains irregular on time and spatially and with high temperatures. The geology is represented by granites, gneisses and metassediments, of the São Francisco Craton and of the Riacho do Pontal Mobile Belt, with ages since Paleoarchean to Neoproterozoic, in addition to recent sediments of alluvial, lateritic and paleo dunes deposits. The coverage soil and regolith show small thickness and alluvial sediments can accumulate up to 10 meters. In this way, the regional aquifers occur in low connected fractures resulting in a limited circulation of groundwater. The aquifers recharge is reduced due to the climate and the high evaporation rate. The salinity of groundwater is high due to joint action of factors such as : climate, soil, plan relief, restrict recharge (low water availability), low connectivity of fractures, and restricted circulation of water in the aquifer and high water-rock time contact. In order to improve the quality of the groundwater of the region, decreasing its salinity, a pilot artificial recharge system was proposed. With the salinity decreasing it is possible to increase the groundwater usage potential. In a synthetic form, the pilot systems consist of a set of gutters and pipes of rainwater collecting on roofs, a recharge trench filled with gravel and a tubular well for pumping and monitoring groundwater quality. Three artificial recharge systems were built in the Petrolina area to verification of hydraulic feasibility and applicability. The tests were conducted by the induction of artificial recharge by injecting water in the recharge trenches by tanker trucks. The monitoring was conducted with analyses of stable isotopes, δD (‰) and δ18O (‰), and in situ measures of electrical conductivity, pH and reduction-oxidation potential. The tests showed that the systems show hydraulic feasibility, and that its success depends on the adequate location and construction of the pilot systems. By the other hand, the applicability and effectiveness of the pilot system exhibit greater complexity due to the necessity of large amounts of water in artificial recharge to result on groundwater more widely usage. As the rains in the region are restricted, it is estimated the need of a long period of time to recharge systems get results. In addition to the pilot systems test, hydrochemical analysis of groundwater samples, 87Sr/86Sr ratio analyses of rock and water, isotopic analysis (δD (‰) and δ18O (‰)) of samples along the irrigation channel, isotopic characterization of aquifers and groundwater dating were carried out. The joint assessment of the data allowed reaching contributions to the knowledge about the natural recharge, water-rock interaction and salinization of groundwater from the semiarid Northeast region of Brazil.

Mots Clés : Isótopos Estáveis (δ18O e δD), Recarga Artificial, Semiárido Nordestino, Salinização, Aquífero Fraturado Stable Isotopes (δ18O and δD), Artificial Recharge (MAR - Managed Aquifer Recharge), Brazilian Semiarid Northeast Region, Salinization, Fractured Aquife


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