Vulnerability map of Acaraú basin to irrigated water quality using GIS

Abstract

The water quality monitoring program is essential in Acaraú basin, Ceará, Brazil, due to large irrigation areas. To carry out the identification of irrigation fields with infiltration problems in the future due to the Acaraú River water sodicity this study was developed. 71 water samples were taken from 11 stations located along 315 km of the Acaraú River, from april/2002 to March/2003. Samples were analyzed for 13 parameters, namely pH, electrical conductivity (EC), Na+, Ca+2, Mg+2, K+, Cl-, HCO3-, PO4-2, NH+4, NO3-, SO4-2 and Sodium Adsorption Ratio (SAR). Surfer and ArcView softwares were used to compose the vulnerability map of Acaraú basin due to the sodicity risk that comes from the irrigation water. Results showed up that the Acaraú basin, in almost the total, presents increasing to high and moderate/high risks of infiltration problems because of sodicity of water used in irrigation and soil classes. Areas with the highest risks are those sited at left side of Acaraú River, where EC values were lower than 0.21 dS.m-1. Also, it was observed a reduction of sodicity risk when water from tributaries of right side was added to the Acaraú River. The vulnerability of Acaraú basin to sodicity is due to the lower values of EC in the water of Acaraú River.