Study on the Recharge Mechanism and Development of Groundwater in the Inland area of Tanzania

在坦桑尼亚中部的Makutapora盆地，年平均降雨量约为600毫米，而潜在蒸发量为2470毫米。因此，地下水补给高度依赖于降雨的数量和模式。为了解流域及周边地区地下水补给机制，选取小流域进行了密集水文观测。通过称重渗滤仪推导出实际蒸发量与土壤含水量的关系，通过入渗量测量计算出代表性站点的径流量比。这些结果结合起来模拟非饱和带的水分平衡，并计算出补给量为降雨量的15%。马库塔波拉盆地的地下水分为浅层地下水和深部承压地下水。后者又根据氯离子浓度分为1型和2型。深层承压地下水的停留时间一般在25年以上，可能几十年，而浅层地下水的停留时间短于20年。P_<CO2>、氚浓度和稳定同位素组成也表明1型组分为切内山地区组分，2型组分为靠近盆地底板的上平面组分。

In the Makutapora Basin in central Tanzania, mean annual rainfall is about 600 mm while potential evaporation is 2470 mm. Thus groundwater recharge is highly dependent on the amount and pattern of rainfall. To understand the mechanism of groundwater recharge in the basin and surrounding area, a small watershed was selected and intensive hydrological observations were carried out. The relationship between actual evaporation and soil water content was derived from weighing lysimeter and the runoff ratio of representative sites were calculated from the measurement of infiltration capacity. Those results are combined to simulate water balance in the unsaturated zone and recharge is calculated to be 15 % of rainfall.Groundwater in the Makutapora Basin is divided into shallow groundwater and deep confined groundwater. The latter is then classified into type-1 and type-2 according to chloride ion concentration. The residence time of deep confined groundwater is generally more than 25 years, probably a few tens years, whereas the residence time of shallow groundwater is shorter than 20 years. P_<CO2>, tritium concentration and stable isotope composition also show that type-1 is the component from Chenene Hill area and type-2 is the component from the upper plane near the basin floor.