Suitability of groundwater and surface water for drinking and irrigation purpose in Zio River Basin (Togo)

Abstract

Zio River basin plays a particular importance as a potential water resource for irrigation, drinking and for other various purposes relating to socioeconomic activities. These socioeconomic activities considerably change water quality and quantity in this basin. An investigation was carried out by collecting 52 groundwater samples and 168 surface water samples during four sampling campaigns to assess the water quality with respect to drinking and irrigation uses. In situ parameters such as pH, Electrical Conductivity (EC), Temperature, dissolved oxygen (O₂) and Total Dissolved Sells (TDS) were measured using a multiparameter portable apparatus (model HANNA). Major cations and anions, nutrients and suspended materials (MES) were determined in the laboratory using AFNOR methods. Water quality for irrigation purpose were determined by sodium absorption ratio, soluble sodium percentage (SSP), magnesium adsorption ratio (MAR), Kelly’s ratio (KR), permeability index (PI), residual sodium bicarbonate (RSC) to investigate an eventual ionic toxicity of water on soil and plants. In this study, HCO₃^- is preponderant in surface water samples and groundwater is dominated by Na⁺ and Cl^-. More than 50% of groundwater could present an unfavorable effect on crop yield, on soil and on human health, particularly during the low water flow. Comparing irrigation indices values obtained from target study to conventional limits we note that about 95% of surface water samples are suitable for irrigation. Principal component analysis performed on irrigation parameters of 220 water samples show that in the study area we can use mainly, SAR, EC, PI and MAR to evaluate all qualitative aspects of water for irrigation use.

Keyswords: Agriculture, quality, irrigation parameter, Zio River, Togo