Mapeamento e quantificação da água subterrânea nas terras húmidas de Macaneta

Abstract

Wetlands occupy approximately 892,166 hectares in Mozambique and provide a series of ecosystem services, such as the development of agriculture, which is conditioned by the availability of water and nutrients. Most of the time wetland water comes from rivers when they pass from plains and/or from groundwater upwelling. The retention of nutrients is facilitated by the low flow speeds and vegetation typical of wetlands, and the progressive variation in agroecological characteristics combined with the variation in river flow and dune discharge and the overexploitation of water resources due to population growth have contributed to salinization of areas intended for agricultural development in the Macaneta wetlands on the lower Incomati River. There are already some studies that evaluate how the flow affects the salinization of the lower Incomati river, however, studies on groundwater upwelling are limited. The present study was carried out in Marracuene District, Maputo Province, Mozambique, with the aim of estimating groundwater flow to support studies on the contribution of upwelling to freshwater availability in the Macaneta wetlands. For the quantification of groundwater, numerical modeling methodology was applied, and in situ infiltration tests were carried out for the unsaturated zone and slugtest for the saturated zone to determine the hydraulic conductivity. The data obtained were treated by applying the Hvorslev and Bouwer and Rice equations to determine the hydraulic conductivity. The quantification of water was done through Darcy's law and finally, a groundwater flow map was prepared. The hydraulic conductivities determined by the methods of Hvorslev, and Bouwer and Rice are in the order of 10−6 and 10−5respectively. The estimated groundwater discharge flow is 3,378 𝑚3/ℎ when using the hydraulic conductivity obtained by the Hvorslev method and 3,669 𝑚3/ℎ when using the hydraulic conductivity obtained by the Bouwer and Rice method, and the slope of the land as well as the lithological composition of the area influence the discharge flow of the dune.