Browsing by Author "Mjemah, Ibrahim Chikira"

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Estimation of groundwater recharge in Makutupora basin located in a semi-arid region in central Tanzania using soil moisture balance (SMB) and chloride mass balance (CMB) techniques.
(Geological Society of India, 2022-02) Kisikia, Clarance Paul; Ayenewa, Tenalem; Mjemah, Ibrahim Chikira
The objective of this study is to assess the groundwater recharge in the Makutupora basin, Central Tanzania using the soil moisture balance (SMB) and chloride mass balance (CMB) methods. The SMB method considered the estimation of both evapotranspiration in CROPWAT 8.0 software and surface runoff by the curve number (CN) method. The CN of the basin was determined based on hydrological soil group (HSG), antecedent moisture condition (AMC) and land use type using Arc GIS 10.2. Distributed land- use maps, slope and soil texture maps, daily climatological data (e.g., precipitation, temperature, wind speed, etc.), chloride concentration in rainfall and groundwater are the basic data used in this study. Input data were prepared in the form of digital maps using GIS and remote sensing tools and finally excel models were created to compute recharge using a set of given conditions. The results indicate that the average chloride concentration measured in the groundwater samples of the study area is 282.88 mg/L; much higher than the average concentration in rainwater samples which is 3.47mg/L while the average potential evapotranspiration is 2280 mm/year with an average rainfall of 680mm/year. Runoff computed using the CN method is ranging from 7.6-246mm/year or 0.68-22%. The final recharge from SMB is ranging from 0.025-117.86mm/year or 0.006-10% of annual rainfall equivalent to an average annual volume of 41.58Mm 3 while recharge from CMB ranges from 2.57-44.6mm/year or 0.38-6.56% of annual rainfall equivalent to an average annual volume of 23.85Mm 3 . The results show that CMB underestimated the recharge compared to the SMB method. The reason for this is thought to be caused by the high chloride concentration analysed in groundwater compared to rainfall samples which may be caused by increased chloride concentration as water passes through the rock formations (unsaturated zone) to the saturated zone. Further lack of atmospheric chloride deposition data may be another contributing factor.
The origin of high sulfate concentrations and hydrochemistry of the Upper Miocene–Pliocene–Quaternary aquifer complex of Jifarah Plain, NW Libya
(Springer-Verlag Berlin Heidelberg, 2016-10) Alfarrah, Nawal; Berhane, Gebremedhin; Mjemah, Ibrahim Chikira; Van Camp, Marc; Walraevens, Kristine
he high uncontrolled groundwater extraction in Jifarah Plain, NW Libya, causes a modification of natural flow systems, inducing seawater intrusion and causing groundwater quality deterioration. The principal aim of this study is to identify the hydrogeochemical processes in this coastal aquifer in order to verify the main sources of sulfate concentration increase that occurs in the system. In order to achieve this aim, water samples were collected from 134 sampling wells in the study area and analyzed for the major cations and anions; physical and chemical parameters were measured, such as water level, electrical conductivity, pH and temperature. The analytical results obtained in the hydro- chemical study were interpreted using Piper diagram, ion correlations with Na ? /Cl - , SO 42- , Cl - and TDS, in con- junction with calculation of the ionic deviations of the con- servative freshwater/seawater mixture and saturation indices using the PHREEQC 2.16 software. The large SO 42- anomaly observed in groundwater near the coast was explained by the presence of seawater intrusion and upconing of deep saline water in these areas. This conclusion is based on high chloride concentrations, the inverse cation exchange reactions and the lower piezometric level compared to sea level. Inland, in Sabratah, the high SO 42- values are related to gypsum dissolution from the Upper Miocene Formation in the lower part of the upper aquifer. These locally high SO 42- concentrations in the south of the study area show overall increase in the upstream direction, which also suggests the dissolution of evaporites from the mountain aquifers in the south. High SO 42- concentration is also related to the effect of the scattered sebkha deposits in some areas along the coast.