Evaluation of groundwater level fluctuation and groundwater Recharge using spring discharge and groundwater level hydrographs in Mekelle area, Tigray, Northern Ethiopia

The surface water and groundwater in the Mekelle area have experienced seasonal and annual variations due to fluctuations in pumping and recharge. Over the last two decades, the groundwater level across the study area has been significantly declining. A study was conducted to investigate groundwater level fluctuations and estimate groundwater recharge using spring discharge and groundwater level hydrographs. Eleven monthly spring discharge measurements were taken using tracer, current-meter, and volumetric methods. Additionally, four diver data loggers-based and one dipper-based groundwater level measurements, along with five pumping rate data from five deep wells, were collected. The spring discharge and groundwater level hydrographs were analyzed to determine the average spring discharge, the average seasonal groundwater level fluctuation, and the correlations between the hydrographs of spring discharge variations and depth to groundwater level in the study area. The results showed that the total annual average discharge of the investigated springs is 5.02 mm³/year. The average wet and dry season groundwater level fluctuations for the entire study area are 3.43 and 2.4 meters, respectively. Furthermore, the four-year hydrograph analyses in DW-20 indicated that the average groundwater level declining rate is 2.25 meters per year. The recharge estimated using the Water Table Fluctuation (WTF) method is 36 mm/year, which is 6.4% of the annual precipitation. The hydrograph correlation of spring discharge variations, depth to groundwater level, and pumping rates indicated that the springs and deep wells are tapping the same regional aquifer, suggesting the possibility of inter-catchment groundwater flow.