ORCID
https://orcid.org/0000-0001-7873-4897
Abstract
The main objective of this study was to determine the hydrogeochemical processes controlling the groundwater chemistry on the Island and assess its suitability for human consumption and irrigation. The methodology used in the study include hydrogeological assessment of the study area and laboratory analysis for general physico-chemical parameters of groundwater. Other parameters such as Soluble sodium percentage (SSP) or % Na+, Sodium Adsorption Ratio (SAR), Magnesium adsorption ratio (MAR), Residual sodium carbonate (RSC), hydrochemical facies classification, and Water Quality Index (WQI) were calculated using empirical formulae. The effects of salinization of groundwater were classified using the chloride-Bicarbonate (Cl/HCO3) and the Na+/Cl- ratios. The major geological units of the study area are sandstone, clays, alluvium, beach sands and laterite soils of Cretaceous to Quaternary age. A total of 21 groundwater samples were collected and analyzed for physical parameters and major ions. Analysis results for pH shows a mean value of 7.47 while the mean value for TDS is 1618.47mg/L. Groundwater classification based on the piper trilinear diagram shows that the dominant hydrochemical facies are Ca-Cl (42%), Ca-Mg-Cl (33%) and Ca-HCO3 (23%). The cation exchange processes indicates that Ca2+ replaced the Na+ and this is an indication of freshening geochemical processes in the aquifer matrix. The findings also show that mean value for total hardness (TH) is 92.44 mg/L, soluble sodium percentage (SSP) or Na% is 15.29%, Sodium adsorption ratio (SAR) is 1.08, Electrical conductivity (EC) is 2447.1 μS/cm, Residual sodium carbonate (RSC) is -11.29 meq/L, and Magnesium adsorption ratio (MAR) is 56.89%. Water quality index (WQI) results show that the groundwater is of very poor quality since the WQI value is 298.8 which is in the range of (200 - 300), this range is designated as very poor water quality for human consumption.
Recommended Citation
Melchioly, S. (2024). General Hydrogeochemical Characterization of Groundwater in Coastal Aquifers of Kilwa Kisiwani Oceanic Island, South East Tanzania. Tanzania Journal of Engineering and Technology, 43(1), 14-34. https://doi.org/https://doi.org/10.52339/tjet.v43i1.927
Publisher Name
University of Dar es Salaam
Included in
Civil Engineering Commons, Dynamics and Dynamical Systems Commons, Numerical Analysis and Computation Commons, Risk Analysis Commons