Trend analysis of groundwater levels in the monitoring boreholes within basalt formations in Dak Lak province

Groundwater from the basalt formations is the main source for the irrigation domestic use in Dak Lak province. Groundwater levels are important information for sustainable management water resouces in the region. The evolution of Groundwater level in the basalt aquifer in Dak Lak province is analyzed and evaluated by using the statistical test method. The results of the Mann-Kendall test indicated that the annual groundwater level had downward trend at 6/8 monitoring holes. The reduction was approximately from 0.03 m/year to 0.1 m/year at boreholes LK71T, LK29T, and CB1-II with high reliability in statistics (p-value < 10%). The downward trend also appeared at 6/8 observed boreholes in the rainy season (0.05÷0.2 m/year) and dry seasons (0.03÷0.15 m/year). Groundwater level changed, in this work, was interpreted and linked to precipitation data. Comparison with annual rainfall monitoring data during the period 2010÷2016 at three stations in the study area, the Pearson correlation coefficient showed that the changed in rainfall amount overtime govern the groundwater level in the study area. Specifically, the results have identified a close correlation between the groundwater level at the boreholes LK29T, C4a, LK71T, and LK75T with average rainfall in the dry season in the study area. The strong correlation continued to be maintained at 3/8 monitoring holes (C4a, LK29T, and LK75T) in rainy season. Mann-Kendall statistical method and Pearson correlation can be applied to analyze long-term Groundwater level changes for sustainable management and exploitation of groundwater resources.