GroMoPo Metadata for Nasia catchment (White Volta Basin) model

A transient finite difference groundwater flow model has been calibrated for the Nasia sub-catchment of the White Volta Basin. This model has been validated through a stochastic parameter randomization process and used to evaluate the impacts of groundwater abstraction scenarios on resource sustainability in the basin. A total of 1500 equally likely model realizations of the same terrain based on 1500 equally likely combinations of the data of the key aquifer input parameters were calibrated and used for the scenario analysis. This was done to evaluate model non-uniqueness arising from uncertainties in the key aquifer parameters especially hydraulic conductivity and recharge by comparing the realizations and statistically determining the degree to which they differ from each other. Parameter standard deviations, computed from the calibrated data of the key parameters of hydraulic conductivity and recharge, were used as a yardstick for evaluating model non-uniqueness. All model realizations suggest horizontal hydraulic conductivity estimates in the range of 0.03-78.4 m/day, although over 70 % of the area has values in the range of 0.03-14 m/day. Low standard deviations of the horizontal hydraulic conductivity estimates from the 1500 solutions suggest that this range adequately reflects the properties of the material in the terrain. Lateral groundwater inflows and outflows appear to constitute significant components of the groundwater budgets in the terrain, although estimated direct vertical recharge from precipitation amounts to about 7 % of annual precipitation. High potential for groundwater development has been suggested in the simulations, corroborating earlier estimates of groundwater recharge. Simulation of groundwater abstraction scenarios suggests that the domain can sustain abstraction rates of up to 200 % of the current estimated abstraction rates of 12,960 m(3)/day under the current recharge rates. Decreasing groundwater recharge by 10 % over a 20-year period will not significantly alter the results of this abstraction scenario. However, increasing abstraction rates by 300 % over the period with decreasing recharge by 10 % will lead to drastic drawdowns in the hydraulic head over the entire terrain by up to 6 m and could cause reversals of flow in most parts of the terrain.

本研究针对白沃尔特河流域纳西亚子流域，完成了瞬态有限差分地下水流动模型（transient finite difference groundwater flow model）的率定工作。该模型通过随机参数化过程完成验证，并被用于评估流域内地下水开采情景对水资源可持续性的影响。基于1500组关键含水层输入参数数据的等概率组合，针对同一研究区共生成1500个等概率模型实现方案，并将其用于情景分析。此举旨在通过对比各模型实现方案，以统计学方法确定其相互差异程度，进而评估由关键含水层参数（尤其是渗透系数（hydraulic conductivity）与补给量（recharge））的不确定性所引发的模型非唯一性问题。研究以渗透系数与补给量关键参数的率定数据计算得到的参数标准差，作为评估模型非唯一性的衡量标准。所有模型实现方案均显示，水平渗透系数（horizontal hydraulic conductivity）的估算值介于0.03~78.4 m/d之间，尽管研究区内超过70%的区域其取值范围为0.03~14 m/d。基于1500组模拟结果得到的水平渗透系数估算值的标准差较低，表明该取值范围可充分反映研究区岩土体的水文地质属性。尽管估算得到的降水直接垂直补给量约占年降水量的7%，但侧向地下水补给与排泄量构成了研究区地下水均衡的重要组成部分。模拟结果显示研究区具备较高的地下水开发潜力，这一结论佐证了此前对地下水补给量的估算结果。地下水开采情景模拟结果表明，在当前补给条件下，研究区可承受的开采速率最高可达当前估算开采速率（12960 m³/d）的200%。若在20年周期内将地下水补给量减少10%，则不会对该开采情景的模拟结果产生显著影响。但倘若在同一周期内将开采速率提升300%，同时补给量减少10%，则会导致整个研究区的水头（hydraulic head）最大降深达6m，并可能引发研究区大部分区域的水流反向。