Assessment of Major Sources Controlling Groundwater Chemistry in Kombolcha Plain, Eastern Amhara Region, Ethiopia

The study area, Kombolcha town, forms an important industrial town situated in the Eastern Amhara region, Ethiopia. The geology of the area is mainly composed of basalts, rhyolitic ignimbrites, and Quaternary sediments. Hydrogeochemistry and the source of ions in the groundwater of the study area are poorly understood. Therefore, the current study aims to assess the factors and the different hydrochemical processes significantly controlling groundwater quality, source, and chemistry. For this purpose, a total of eighteen groundwater samples were collected using 250 ml sampling bottles at selected points in the dry season (May 2017) and wet season (November 2017). Gibbs diagram, correlation analysis, scatter plots of ionic molar ratio relations, saturation index values (estimated using PHREEQC Interactive 2.8) were used to decipher the hydrogeochemical process. Gibbs diagram shows that the rock-water interaction process is the predominant, Na+/Cl- and Ca2+/Mg2+ molar ratio value of all groundwater samples in both seasons reveals that the groundwater chemistry of the area is controlled by silicate minerals weathering. The strong correlation of Ca2+ with Mg2+ in the dry season, and Ca2+ with HCO3- and Na+ with HCO3- in the wet season could also be an indication of silicate weathering and ion exchange processes. The impact of anthropogenic practices on groundwater chemistry is also seen from the strong correlation of Ca2+ with Cl-, NO3-, PO43- and F-, NO2- with K+, Mg2+, and PO43- , PO43- with F- , and NO3- with Na+, Cl-, HCO3- . The negative values of chloro-alkaline indices in both seasons indicate base-exchange reaction where an indirect exchange of Ca2+ and Mg2+ of the water with Na+ and K+ of the host rock occurs. Saturation indices results for the wet season show that the groundwater is under-saturated with respect to calcite, aragonite, dolomite, gypsum, and anhydrite. In the dry season, however, some of the waters are oversaturated with respect to calcite and aragonite. To sum up, the groundwater quality of the study area is controlled by geological processes and anthropogenic effects

Quantitative Geomorphological Parameters Analysis for the Aynalem- Illala Streams, Tigray, Northern Ethiopia

Morphometric analysis is the measurement and mathematical analysis of the configuration of the surface, shape, and dimension of landforms. The objective of this study is to characterize the Aynalem and Illala streams using the morphometric parameter. The topographic map at a scale of 1:50,000 taken from the Ethiopian National Mapping Agency was used to characterize the linear and areal aspects. ASTER Digital Elevation Model with 10m resolution was used to characterize the relief aspect. The Arc GIS 10.4.1 was used during the morphometric analysis. The analysis result of the streams is summarized based on the linear, areal, and relief aspects. The area is characterized by a dendritic drainage pattern which is characteristics of massive hard rock terrain. The Aynalem and Illala streams are 4th and 5th order streams. Considering the number of streams in the Aynalem (75.81%) and Illala (74.66%) is composed of first-order streams that indicate a flashy flood and the mean bifurcation value of Aynalem (6.8) and Illala (4.7) shows that the Aynalem area is more structurally affected than Illala but both show less stream integration. The analysis of areal aspects such as elongation ratio, circularity ratio, and form factor has indicated that both streams are characterized as elongated streams, this implies that both streams are flowing in heterogeneous rock material, presences of structural effect, and slow runoff discharge.  The other areal aspect such as drainage density, stream frequency, infiltration number, and length of overland flow all show smaller values in both streams. This implies that the streams are characterized by a relatively permeable rock material with a higher infiltration capacity. The relief aspect of the Aynalem and Illala was also analyzed using basin relief, relief ratio, ruggedness number, hypsometric curves, and Hypsometric integral. The streams are characterized by a lower relief ratio and ruggedness number which implies a relatively flat slope and lower relief. The hypsometric curves and the Hypsometric Integral of the streams indicate that the Aynalem and Illala are at the maturity stage. This shows the area is characterized by higher erosion but less affected by recent structures. Based on the morphometric parameter analysis result it is possible to conclude that the stream development is dependent on the topography and geology of the study area and both streams show similar morphometric character

Numerical Groundwater Flow Modeling of Dijil River Catchment, Debre Markos Area, Ethiopia

Dijil River catchment is a sub-catchment of the Abay drainage basin and covers 138.28 km2. This paper presents numerical groundwater flow modeling at steady-state conditions, in a single-layer aquifer system under different stress or scenarios. A numerical groundwater flow models represent the simplification of complex natural systems, different parameters were assembled into a conceptual model to represent the complex natural system in a simplified form. The conceptual model was input into the numeric model to examine the system response. Based on geologic and hydrogeological information, confined subsurface flow condition was considered and simulated using MODFLOW 2000. The model calibration accounts matching of 24 observation points with the simulated head with a permissible residual head of ±10m. The sensitivity of the major parameters of the model was identified during the calibration process. According to the simulated water budget in the model, the simulated inflow is found to be 1.2791870E+05 m3/day which is nearly equal to the simulated outflow of 1.2791755E+05 m3/day with the difference being only 1.1484375E+00 m3/day. Water budget analysis reveals that outflow from river leakage accounts for 92.8 % of the total outflow and 14.1 % of the total inflow comes from the river leakage in the study area. Three scenarios of increased withdrawals and one scenario of altered recharge were used to study the system response. Accordingly, an increase in well withdrawal in scenario-I (existing wells pump simultaneously), scenario-II (existing drilled wells yield withdrawal increased by 30%), and scenario-III (additional eight wells having expected yield of 30 l/s drill and pump) resulted in an average decline of the steady-state water level by 1.06m, 1.68m, and 4.46m, respectively. They also caused the steady-state stream leakage to be reduced by about 2.93%, 4.58%, and 11.23%, and subsurface outflow by 9.41%, 14.67%, and 37.86%, respectively. A decrease in recharge by 25% and 50% results in a decrease of the head by 6.1m and 13.4m respectively, and a stream leakage decrease by 20.3%, and 40.3% respectively as compared to the simulated steady-state value. Therefore, adequate groundwater level monitoring wells should be placed in the catchment to control the total abstraction rates from the aquifer and fluctuations in groundwater levels