Hydrochemistry and quality appraisal of groundwater in Birr River Catchment, Central Blue Nile River Basin, using multivariate techniques and water quality indices

Abstract

Due to the continuous population growth and the expansion of industry and agriculture in Ethiopia, groundwater demand has been increasing to supplement the erratic surface water. Therefore, the availability of sufficient and clean groundwater should be appraised and tracked regularly to secure its multi-purposes. This work aims to assess the appropriateness of groundwater for drinking, and irrigation uses and identifies the key factors controlling groundwater quality in the Birr River Catchment (BRC), Blue Nile River Basin, Ethiopia. For this purpose, a total of 79 groundwater samples were assessed for physicochemical parameters. Major ion analysis, multivariate techniques (MCA, HCA, and PCA), and multi-hydrochemical indices were applied in the analysis of groundwater quality data. Hydrochemical analysis indicated that the principal cation and anion were Ca²⁺ and HCO₃^-, respectively. The spatial analysis of the major ions revealed a positive trend for Mg²⁺, Na⁺, K⁺, HCO₃^-, Cl^-, and SO₄^2- along the groundwater flow path from the upland to the Birr river valley. Conversely, Ca²⁺ shows a deleterious tendency along the groundwater flow direction. The aquifer has three principal hydrochemical facies: Ca-HCO₃, Ca/Mg-HCO₃, and Na-HCO₃. The water quality analysis indicates that with the exception of TDS, Ca²⁺, Mg²⁺, and HCO₃^- in a few locations, most of the parameters analyzed are within the WHO allowable limits and are thus considered suitable for drinking water. The combined use of Gibbs and ionic ratio plots confirmed that silicate weathering was invariably prevailing in the region. The Chloro-Alkali Indices (CAIs) have indicated that cation exchange occurs in more than 85% of groundwater samples. However, there were indications of the influence of reverse ion exchange in the rest of the data. The MCA, PCA, and HCA disclosed that geo-genic sources accompanied by human activities mainly control the groundwater quality of the catchment. However, water quality assessment indices show that groundwater in the highest proportion of the catchment is suitable for human consumption and agricultural use.

Keywords: Birr River Catchment; Groundwater quality; Hydrochemical processes; Hydrochemistry; Multivariate analysis.