Análise dos aspectos hidrogeológicos aplicados a locação de poços em terrenos cristalinos no município de Quixeramobim, Ceará

Abstract

The paper presents the analysis of hydrogeological aspects that influence the flow of fourteen wells located in the municipality of Quixeramobim, state of Ceará. Low flow of wells in the county are reflections of regional caracterísitcas, such as lithology, low rainfall and small thickness of the mantle of change. Associated with this there is a large number of wells constructed whose leases did not take into account the favorable conditions for the occurrence of groundwater which reflects the low flows recorded in the database SIAGAS. We performed a quantitative analysis based on wells Database registered in SIAGAS, the interpretation of lineaments from SRTM image, thematic maps of lithology, lineaments and drainage density, hypsometry and field analysis. The results showed that most of the wells constructed in city has the yield lower 2.0 m³/h. The static level is variable. With 42.86% wells below 5.0 meters, 30.61% of wells depths of 5.0 to 10.0 meters and 26.53% above of 10,0 meters. The depth of the dynamic level is also variable, it has modal class for the interval from 20,0 the 28,0 meters. The specific capacity of most wells (69,57%) is less than 0,2m³/h/m. The nature of the wells is predominantly tubular (92%) and only 8% are amazons. The situation of the wells shows that the majority (33%) are equipped, 21%s closed, 19%s no data and 27%s are abandoned, dry or not installed. Only 14% wells are for domestic supply and 5% for public supply. The depth of the wells are mostly higher than 50,0m. The interpreted lineaments coincide with the field data (foliation and fractures rock) and assist in locating master joints that are often responsible for the high yield rates of wells in crystalline terrains. The use of GIS proved somewhat effective: data integration lithology versus yield have not worked ( wells with high and low yields are leased in the same lithotype); the integration of elevation data with yield data showed that the wells with low yield are located in areas with altitudes more recessed; the drainage density versus yield showed results most anticipated. High yield wells are positioned in areas with high drainage density and low yield wells, mostly, are positioned in an area of low to medium drainage density; the lineaments density versus yield showed that there are wells with low and high yield situated in areas of high lineaments density. With the investigation of the aspects hydrogeological was possible to make a new lease for the wells 01, 02, 04, 05, 07, 09, 11, 12 and 14. Could not to make new lease for the wells 03 and 08. The wells 06, 10 and 13, with yield above 5m³/h are positioned in areas that coexist surface drainage and fractures. The location of wells that municipality must take into account the coexistence of surface drainage with fractures, especially with E-W direction, or subparallel to them. Case such situation does not occur, the coexistence of drainage with relatively thick weathered mantle would be another alternative.