Unsustainable groundwater extraction for domestic and agricultural purposes, particularly crop irrigation, is leading to dramatic reductions in the quantity and quality of groundwater in many developing countries, including Ethiopia. Assessing and predicting groundwater responses to hydraulic stress caused by overexploitation related to anthropogenic activities and climate change are crucial for informing water management decisions. The aim of this study is to develop a three-dimensional steady-state groundwater flow model for the Golina River Sub-Basin to understand the relationship between groundwater recharge and groundwater pumping and their impacts under steady-state conditions from the perspective of groundwater management. The model was created using MODFLOW 6 and discretized into 345 rows and 444 columns with a grid resolution of 100 m by 100 m. The subsurface was modeled as two layers: a clastic alluvial layer overlying a weathered and fractured bedrock. The surface-water divide of the Golina River Sub-Basin was treated as a no-flow boundary. The initial values of horizontal hydraulic conductivity ranged from 0.001 m/day for rhyolite to 27.26 m/day for alluvial deposits. The aquifer recharge rates from the WetSpass model ranged from 1.08 × 10⁻³ to 2.25 × 10⁻⁴ m/day, and the discharge rates from the springs, hand-dug wells, and boreholes were 2.79 × 10⁴ m³/day, known flux boundaries. Sensitivity analysis revealed that the model is very sensitive to hydraulic conductivity, moderately sensitive to aquifer recharge, and less sensitive to groundwater pumping. Calibration was performed to match observed and simulated hydraulic heads of selected wells and achieved a correlation coefficient of 0.998. The calibrated hydraulic conductivity ranged from 1.2 × 10⁻⁴ m/day for rhyolite to 20 m/day for gravel-dominated alluvial deposits. The groundwater flow direction is toward the southeast, and the water balance indicates a negligible difference between the total recharge (207,775.8297 m³/day, which is the water entering the aquifer system) and the total pumped volume (207,775.9373 m³/day, which is the water leaving the aquifer system). The scenario analysis showed that an increase in the pumping rate of 25%, 50%, and 75% would result in a decrease in the hydraulic head by 4.64 m, 10.18 m, and 17.38 m, respectively. A decrease in recharge of 25%, 50%, and 75% would instead result in hydraulic-head declines of 6 m, 15.29 m, and 46.97 m, respectively. Consequently, the findings of this study suggest that decision-makers should prioritize enhancing integrated groundwater management strategies to improve recharge rates within the aquifer system of the study area.

Groundwater is a natural freshwater resource and very important for multipurpose use in the Golina River basin. The determination of groundwater resource sustainability depends on the groundwater quality evaluation for specific uses. The objectives of this research work are: (1) to evaluate the groundwater quality and suitability for irrigation purposes and (2) to study the impact of irrigation activities on groundwater quality in the Golina River Basin. Alluvial deposits, basalts, granite, and rhyolite are the main stratigraphic units in the area. 34 groundwater and 3 river water samples were collected from the study area for water quality analysis purposes. Parameters of pH and EC were measured using WTW Multi 3430 and HCO3- was measured using Hach digital titrator in the field while parameters of Na+, K+, Ca2+, Mg2+, Cl-, SO42-, NO3-, PO4, and F-, were analyzed in the lab using Ion Chromatography (IC) in the Technical University of Darmstadt. Besides these, total dissolved solids (TDS), total hardness (TH), sodium absorption ratio (SAR), magnesium hazards (MH), Soluble Sodium Percentage (SSP)(Na%), Residual sodium carbonate (RSC), Permeability Index (PI) and Kelly´s index (KI) were calculated and interpreted. Based on the result of the analysis, the abundance of cations in groundwater in the study area is arranged as Ca > Na > Mg > K, and the anions are arranged as HCO3- > SO42- > Cl- > NO3- > PO43-. Similarly, the result also showed that the common water types in the area are Ca2+-Mg2+-HCO3- and Mg2+-Ca2+-HCO3-. TDS, TH, EC, SAR, MH, SSP, RSC, PI and KI have respective mean values of 530.45 mg/l, 279 mg/l CaCO3, 657 µS/cm, 1.24, 48%, 26%, 0.23 meq/l, 61% and 0.57. The suitability of the dominant water points in the Golina River Basin for irrigation is moderate in terms of TDS, hard to very hard water for irrigation in terms of hardness, medium salinity for irrigation in terms of salinity hazard and low sodium hazards, suitable for irrigation in terms of magnesium hazards, good and excellent water for irrigation in terms of soluble sodium percentage, safe for irrigation in terms of residual sodium carbonate, good for irrigation in terms of the permeable index, and suitable water for irrigation in terms of Kelly ratio. Few water samples in the Golina River Basin show slight contamination of nitrate from the irrigation activities which needs special attention.

This paper deals with the results of a pilot study conducted to estimate the shallow groundwater resource potential and irrigation capacity at the household level in Tahtay Koraro Woreda, northwestern zone of Tigray, Ethiopia. The potential evapotranspiration and actual evapotranspiration of the study area are estimated to be 1484 mm/year and 814 mm/year respectively. The runoff is approximately calculated to be 280 mm/year and the annual groundwater recharge is estimated to be 29 mm/year. The total annual groundwater abstraction for human, livestock, and irrigation is estimated to be 25 mm/year. It should be noted that the groundwater recharge rate is expected to remain constant while the total annual groundwater discharge is expected to increase from year to year. This relation when projected over a long period may result in a negative groundwater budget which can result in depletion of groundwater (lowering of groundwater levels), reduced baseflow to streams, and deterioration of water quality. The computed values for hydraulic conductivity of the aquifers range from 1.63 m/day to 7.27 m/day with an average value of 4.9 m/day and transmissivity from 48.9 m²/day to 218.1 m²/day with an average value of 147.14 m²/day. The aquifers in the highly weathered basalt and highly weathered siltstone – sandstone intercalation have transmissivity values ranging from 99 m²/day to 218.1 m²/day with an average value of 157 m²/day and are grouped into the moderate potentiality aquifers category. The aquifers in the slightly weathered and fractured metavolcanics grouped under low potentiality based on the lower transmissivity values (<50 m²/day). The study area has low to moderate groundwater potentiality, hence, large-scale groundwater pumping is not possible. Therefore, the current activity of using hand dug wells for household-level irrigation is the best way of using groundwater for irrigation and other uses as well. Increasing the depth of the existing hand dug wells that are constructed in highly weathered basalt and highly weathered siltstone – sandstone intercalation can also enhance the yield of the hand dug wells. It is recommended to use water-saving irrigation technologies rather than increasing the number of wells. This will also help in increasing the irrigation area. Groundwater recharge enhancement structures such as trenches, percolation ponds, and check dams be constructed in scientifically selected localities to further enhance the groundwater potential.

Identification of recharge sources in the Mekelle area is controversial, as some studies indicate that precipitation is the only source of recharge, while others indicate the existence of inter-catchment/inter-basin groundwater transfers with the possibility of intermediate-to-regional flow system recharge sources. The objectives of this study were, therefore, to identify the sources of recharge, quantify the groundwater recharge and develop a local meteoric waterline (LMWL) for the Mekelle area using the stable isotopic compositions (δ¹⁸O and δ²H) of rainwater. To that end, 13 precipitation, 34 groundwater, and two surface water samples were analyzed for δ¹⁸O and δ²H signatures. Accordingly, the local meteoric water line (LMWL: δ²H = 6.78 δ¹⁸O + 9.83) was developed from ten monthly accumulated precipitation samples and three rainfall event samples. Moreover, the spatial variations in the isotopic compositions of the groundwater with respect to the LMWL showed the existence of three zones/groups with different groundwater flow conditions, namely, shallow, intermediate, and deep flow systems. Two groundwater recharge sources were also identified from the dual-isotope slope of the groundwater isotope lines with respect to the LMWL. Furthermore, the groundwater recharge was estimated to be 49 mm/year using the chloride mass balance (CMB) method.