In most water balance studies, basins are considered closed systems; however, interbasin groundwater flow (IGF), which is an unaccounted hydrological component in most studies, could occur at basin boundaries where there is a hydraulic gradient and appropriate permeability of the geologic formations. IGF is a complex hydrogeological process and hidden from direct observation, thus identifying and characterizing it is difficult. This study investigated IGF in the case of the contact between the Tana and Beles basins, located at the northwestern margin of the Ethiopian Highlands, using a multimethod approach: (1) morphotectonic analysis; (2) lithostratigraphy and geological structure analysis; (3) regional groundwater potentiometric-surface map; (4) presence of large-volume springs; (5) hydrochemistry and isotope tracing; and (6) water budget imbalances. Primary data (geological investigation, water point inventory, and water sampling), satellite images and gravity data, and other secondary data, were collected and analyzed. The results illustrate the extension of the fractured basaltic aquifer, high topographic contrast, and high lineament density along the boundary between the Tana and Beles basins. The connection of the hydro-stratigraphic units, fracture distribution and orientation, high hydraulic gradient, spatial distribution of high-flux springs, and water budget imbalance of Tana Basin revealed that there is IGF from Tana Basin to Beles Basin, despite poor indications from results for hydrochemistry and stable isotopes. These findings will have practical implications for groundwater and water balance studies of the two basins. The study demonstrates the importance of a multimethod approach to investigate IGF where a single approach is imprecise.

在大多数水平衡研究中，流域被认为是封闭系统；然而，流域间地下水流（IGF）在大多数研究中是一个未考虑的水文成分，可能发生在具有水力梯度和适当的地质构造渗透性的流域边界。IGF是一个复杂的水文地质过程，无法直接观测，识别和表征十分困难。本研究采用多种方法研究了位于埃塞俄比亚高地西北边缘的塔纳盆地和贝莱斯盆地接触处的IGF：（1）形态构造分析；(2)岩石地层学和地质构造分析；(3)区域地下水位-地表图；(4)存在大容量弹簧；(5) 水化学和同位素示踪；(6) 水预算失衡。收集并分析了原始数据（地质调查、水点清查和水样采集）、卫星图像和重力数据以及其他二手数据。结果表明，沿着塔纳盆地和贝莱斯盆地之间的边界，玄武岩裂隙含水层的延伸、高地形对比度和高线状密度。塔纳盆地的水文地层单元的联系、裂缝的分布和方向、高水力梯度、高通量泉水的空间分布以及水收支失衡表明，尽管结果表明从塔纳盆地到贝莱斯盆地存在IGF，用于水化学和稳定同位素。这些发现将对这两个流域的地下水和水平衡研究产生实际影响。该研究表明，在单一方法不精确的情况下，采用多种方法研究 IGF 的重要性。