Abstract

The riparian communities of the Zou basin of West Africa rely heavily on drinking water supplied by fractured aquifer systems. This study aims to provide accurate fracture maps and derived products (fracture density, coincidence map and cross-points) using Landsat 8 (visible and infrared bands) and PALSAR DEM datasets with borehole data collected from the national integrated database. Digital image processing techniques through image enhancement and directional Sobel filters application were used to analyse Landsat 8 and PALSAR data. Results show that the main orientations of fractures are N10-N20, N90-N100 and N180 for the visible, N10-N20, N40-N50, N90, N140 and N180 for the infrared and for the PALSAR DEM, they are N10-N20, N90-N100 and N170-N180. The fracture length overall interval is 0.15 to 21.2 km and the cumulative length of each fracture map is adjusted to power law with characteristic of exponent respectively 0.86, 0.91 and 0.96. The chi square $({\mathrm{\chi }}^2)\mathrm{ }$ test of cumulative length versus class frequency reveals a significant relationship for the visible and PALSAR fracture maps. Although, the calculated ${\mathrm{\chi }}^2\mathrm{ }$ is greater than the theoretical chi square for the infrared, there is a strong and positive correlation for the three fracture maps (0.94, 0.99 and 0.98). More than 50% of the fracture cross-points (CP) occurs with the North-South (NS) orientations. The coincidence map analysis shows that the PALSAR fracture map has the highest ratio of 0.88, proving it should prioritize over the visible and infrared maps. High flow (Q $>$ 5 cubic m/h) boreholes located near the N10, N20 and N180 main orientations are more than 50% confirming their significant contribution to aquifers’ productivity. The spatial and statistical analyses of these fractured aquifers are critical to improve drinking water access and water resources planning for the basin communities.

摘要

西非邹盆地的河岸社区严重依赖破裂的含水层系统提供的饮用水。本研究旨在使用 Landsat 8（可见光和红外波段）和 PALSAR DEM 数据集以及从国家综合数据库收集的钻孔数据，提供准确的裂缝图和衍生产品（裂缝密度、重合图和交叉点）。通过图像增强和定向 Sobel 滤波器应用的数字图像处理技术被用于分析 Landsat 8 和 PALSAR 数据。结果表明，可见裂缝主要方向为N10-N20、N90-N100和N180，红外主要方向为N10-N20、N40-N50、N90、N140和N180，PALSAR DEM主要方向为N10-N20， N90-N100 和 N170-N180。裂缝长度总区间为0.15～21。2 km，将各裂缝图的累积长度调整为具有指数特征的幂律，分别为0.86、0.91和0.96。卡方$({\mathrm{\chi }}^2)\mathrm{ }$累积长度与类频率的测试揭示了可见和 PALSAR 断裂图的显着关系。虽然，计算${\mathrm{\chi }}^2\mathrm{ }$大于红外理论卡方，则三个裂缝图（0.94、0.99 和 0.98）存在强正相关。超过 50% 的裂缝交叉点 (CP) 发生在南北 (NS) 方向上。重合图分析表明，PALSAR 裂缝图的比率最高，为 0.88，证明其应优先于可见光和红外图。高流量（Q $>$ 位于 N10、N20 和 N180 主要方向附近的 5 立方米/小时）钻孔超过 50%，证实了它们对含水层生产力的重大贡献。这些破裂含水层的空间和统计分析对于改善流域社区的饮用水获取和水资源规划至关重要。