Limits and conditions for the exploitation of alluvial aquifers in the Brazilian semi-arid region

ABSTRACT Easily exploitable aquifers are formed along river beds in the Brazilian semi-arid region and present characteristics that enable the construction of underground dams. The estimate of the potential effective exploitation of these aquifers must take into account the pumping limits of the wells, the upstream groundwater inflows and the flows to downstream reaches and through the underground dam, whose reduction influences the downstream supply. The current research presents a real case study about an aquifer reach, with underground dam and wells, which was analyzed through computational model. We simulated the groundwater flow patterns according to different exploitation scenarios and found that there should be water extraction limitations to assure the required downstream flows. The limitations can be minimized through appropriate well locations and exploitation regimes, as well as through the implementation of underground dams. The definition of these measures becomes possible through the sound use of computational simulation, but their effective implementation will depend on negotiations among users at the basin scale, so that appropriate water permits can be issued.

摘要：巴西半干旱地区的河床沿线发育有易开发含水层（aquifer），此类含水层具备修建地下坝（underground dam）的水文特性。对这类含水层潜在有效开采量的评估，需兼顾水井抽水限额、上游地下水流入量、流向下游河段的流量以及通过地下坝的流量，而地下坝流量的削减会直接影响下游供水。本研究针对一处配备地下坝与水井的含水层河段开展实际案例研究，并通过数值计算模型（computational model）对其展开分析。研究针对不同开采情景（exploitation scenarios）模拟了地下水流场形态，结果表明需设定取水限值以保障下游所需流量。通过合理布设水井位置、优化开采制度以及修建地下坝，可最大程度弱化取水限值的约束。借助科学的数值模拟手段可确定上述管控措施，但措施的有效落地需依赖流域尺度下各用水主体间的协商，以此核发合理的取水许可（water permits）。