Abera Debele, Berehanu Behailu, Ayenew Tenalem
Department of Natural Resources Management, College of Agriculture and Environmental Sciences, Arsi University, P.O. Box:193, Asella, Ethiopia.
Department of Earth Sciences, Addis Ababa University, P.O. Box: 1176, Addis Ababa, Ethiopia.
Heliyon. 2024 Nov 29;10(23):e40831. doi: 10.1016/j.heliyon.2024.e40831. eCollection 2024 Dec 15.
The Abijata-Langano-Ziway Lakes Basin (ALZLB) is situated in the Central part of the Main Ethiopian Rift. The availability and dynamics of groundwater in the Abijata-Langano-Ziway Lakes Basin (ALZLB) are primarily controlled by its geological and hydrogeological characteristics, shaped by volcanic-tectonic and sedimentary processes. The basin faces significant challenges, including drastic change in land use pattern, rapid population growth sustained by subsistence farming, over-extraction of water resources, and vulnerability to climate change and fragile ecosystems. These issues emphasize the urgent need for effective water resource management. To understand this complex system, a numerical groundwater flow model was employed to characterize the groundwater flow system within the ALZLB and examine its interaction with surface water bodies. The MODFLOW model translates the conceptual understanding of the basin's hydrogeology into a mathematical representation, allowing for numerical analysis. The model incorporates input parameters such as hydraulic conductivity and boundary conditions representing groundwater inflow and outflow. Steady-state numerical calculation was used to characterize the qualitative hydrogeological conceptual model into numerical representation and thereby describe the groundwater system. The calibrated model exhibited excellent agreement between simulated and observed groundwater levels. Statistical measures indicated a strong correlation (R = 0.98) and high efficiency (NSE = 0.97) in replicating the observed data. Additionally, the Mean Error (ME) of -8.3 m suggests minimal bias in the simulations. Further analysis of the histogram residuals revealed that a significant portion of the simulated values (65 % and 82 %) fell within ±20 m and ±30 m of the observed groundwater levels, respectively. This revealed the model's accuracy in capturing the groundwater system's behavior. The model identified groundwater recharge and constant head boundaries as the primary sources of groundwater inflow, contributing 445 million cubic meters per year (MCM/year) and 90 MCM/year, respectively. Conversely, constant head boundaries represented the most significant outflow pathway, with a simulated discharge of 519 MCM/year. The calibrated balance between inflow and outflow (discrepancy of -0.75 %) confirms that the model effectively simulates steady-state groundwater flow conditions. The calibrated model demonstrates the model's capability to accurately represent the basin's groundwater system.
阿比贾塔-朗加诺-齐瓦湖流域（ALZLB）位于埃塞俄比亚主裂谷的中部。阿比贾塔-朗加诺-齐瓦湖流域（ALZLB）地下水的可利用性和动态变化主要受其地质和水文地质特征控制，这些特征由火山构造和沉积过程塑造而成。该流域面临着重大挑战，包括土地利用模式的急剧变化、以自给农业维持的人口快速增长、水资源过度开采以及易受气候变化影响和生态系统脆弱。这些问题凸显了有效水资源管理的迫切需求。为了解这个复杂的系统，采用了一个数值地下水流模型来描述ALZLB内的地下水流系统，并研究其与地表水体的相互作用。MODFLOW模型将对流域水文地质的概念理解转化为数学表示，以便进行数值分析。该模型纳入了诸如水力传导率和代表地下水流入和流出的边界条件等输入参数。使用稳态数值计算将定性的水文地质概念模型转化为数值表示，并由此描述地下水系统。校准后的模型在模拟地下水位和观测地下水位之间表现出极好的一致性。统计指标表明，在复制观测数据方面具有很强的相关性（R = 0.98）和高效率（NSE = 0.97）。此外，-8.3米的平均误差（ME）表明模拟中的偏差最小。对直方图残差的进一步分析表明，分别有很大一部分模拟值（65%和82%）落在观测地下水位的±20米和±30米范围内。这揭示了该模型在捕捉地下水系统行为方面的准确性。该模型确定地下水补给和定水头边界是地下水流入的主要来源，分别贡献每年4.45亿立方米（MCM/年）和90 MCM/年。相反，定水头边界是最主要的流出路径，模拟排放量为每年519 MCM。流入和流出之间校准后的平衡（差异为-0.75%）证实该模型有效地模拟了稳态地下水流条件。校准后的模型展示了该模型准确表示流域地下水系统的能力。
