Gestão interestadual compartilhada de água subterrânea na Chapada do Apodi entre os estados do Ceará e Rio Grande do Norte

Abstract

The present groundwater case study of Apodi aquifer system in Northeastern Brazil has been carried out over an area of 2538 km² in the frontier region between the states of Ceará (CE) and Rio Grande do Norte (RN). Apodi aquifer system is composed of an upper phreatic karstic groundwater reservoir known as Jandaira aquifer, used for irrigation and a lower confined reservoir named Açu aquifer, used for urban water supply. Increasing exploitation of Jandaira aquifer along with a rainfall shortage, has produced in 2004 excessive drawdown in groundwater levels and significant reduction in well yield. This unfavorable scenario, lead to difficulties in urban and rural water supply as well as in water supply for irrigation which is the main economic activity in the region of the Apodi plateau, particularly in Barauna county –RN. So, the Apodi Project has been conceived by Federal and State Water Authorities aimed towards a diagnostic of groundwater availability, quality, vulnerability and risk of contamination, as a basis for the proposal of a groundwater shared management model between the involved states. This task has been performed by PROJETEC-TECHNE ASSOCIATES, providing the basic scientific knowledge for the so called shared management. According to the results of the diagnostic the number of water wells in the region increased from 846 in 2002 to 1440 in 2009 and the global exploited flow rates increased from 3 m³/s to 7,71 m³/s. The mean annual rainfall in the 30 year period from 1979 to 2008 reaches 700 mm/year, but is extremely irregular ranging from 190 mm/year to approximately 2000 mm/year. In the same period the mean annual recharge is about 175 mm/year, being equally irregular and ranging from 5,6 mm/year to 594 mm/year. In terms of flow rates the available recharge in the study area is about 18,7 m³/s with 50% of probability, decreasing to as much as 2,95 m³/s with 90% of probability. The framework for a comprehensive management program to be developed by the present intrastate and Federal institutional structures is presented. The monitoring of groundwater quality including level and abstraction of water wells, enforcement of legal and institutional instruments besides control of water user attitudes are considerations to be taken into account. Both states CE and RN have the legal and institutional structure appropriate for implementing the management of water resources