乍得湖盆地典型区域降雨入渗补给地下水试验

针对尼日利亚北部乍得湖盆地降雨入渗补给地下水的问题，选择典型区域开展土壤剖面取样工作，采用氯离子平衡法计算各剖面降雨入渗补给量，并结合野外调查、钻探等工作研究影响降雨入渗补给的主要因素。结果表明：4个取样点（Y₁、Y₂、Y₃、Y₄）土壤剖面年平均降雨入渗补给量分别为4.9、1.5、7.9、26.2 mm/a，平均值为10.1 mm/a，年平均降雨入渗补给率仅为0.72%、0.22%、1.17%、3.87%，平均值为1.49%；研究区降雨入渗补给量很少，降雨对地下水资源的补给有限，地下水的主要补给来源为Hadejia河；研究区蒸散发量大，植物根系发达、吸水能力强，地表入渗水分多在表层土壤中或泥质层与风积砂层交界面上消耗于蒸发蒸腾，最终散失到大气中。在人类活动严重改变Hadejia河水文情势的背景下，研究区这种独特的地下水补给特征导致地下水位快速下降，使得区内正面临较严重的地下水资源枯竭问题。

Rainfed Recharge Experiment in Typical Plain Area of Chad Lake Basin

Four moisture samples were obtained from the unsaturated zone profiles distributed in a typical plain area of Chad Lake basin to estimate the rainfed recharge based on the chloride(Cl) mass-balance method. The rainfed recharge results of the four sampling points(Y1, Y2, Y3, Y4) are 4.9, 1.5, 7.9, and 26.2 mm/a respectively;That is, the rainfed recharge rate are only 0.72%, 0.22%, 1.17%, and 3.87% correspondingly. Based on the survey work, combined with field investigation and drilling, the reason for the small amount of rainfed recharge is that the infiltration water from the surface is mostly consumed in evapotranspiration in the surface soil or the interface between the clay layer and the aeolian sand layer, and eventually lost to the atmosphere. Undoubtedly, the research area is facing a serious problem of water resources depletion under its single recharge source of Hadejia River, which has been interrupt by local people so greatly that the amount of infiltration to groundwater has been decreasing.