Seasonal and Spatial Water Quality of Awash River for Irrigation at Dubti/Tendaho, North Eastern Ethiopia

Abstract

Salt affected soils are common in the irrigated arid and semi arid regions where irrigation with poor quality water is a common practice. In all irrigation farms, particularly at Dubti/Tendaho state farm, clear information on Awash River water quality for irrigation is lacking. Therefore, this study was conducted at Dubti/Tendaho state farm to investigate seasonal and spatial variations of irrigation water quality in Awash River. Water samples were collected from four sampling sites (dam to field) in monthly interval from September 2013 to August 2014. Relevant data were collected and interpreted as per the irrigation water quality guidelines. The result showed that pH, electrical conductivity (EC), sodium adsorption ratio (SAR) and adjusted sodium adsorption ratio (adj.SAR) were beyond the permissible limit in Autumn and Summer. The residual sodium carbonate (RSC) and bicarbonate (HCO₃^-) were unsuitable in all seasons except in Spring. Sodium percentage (Na %) was permissible in Winter and Spring whereas doubtful in Autumn and unsuitable in Summer seasons. Sodium toxicity was severe in Summer and Autumn (>9 meq l^-1 SAR) while slight to moderate in Winter and Spring (3 - 9 meq l^-1 SAR) seasons. However, chloride (Cl^-) hazard was safe (< 4 meq l^-1) in all seasons except Summer which showed slight to moderate. Spatially, an increasing trend on  Cl^-, pH and Na% from the dam to the end of field drain water(FDW) whereas a decreasing trend on EC, Na, Mg, Ca, K, HCO₃^-, total dissolved solids (TDS), SAR, and RSC were observed. The results revealed that irrigation water quality was highly saline and toxic in Summer and Autumn whereas slight to safe in Winter and Spring seasons. Hence, it is possible to infer that the planting date of crops should be adjusted in Winter and Spring seasons when the quality of irrigation water becomes safe.

Keywords: Awash River, irrigation water quality, Electrical conductivity, pH, residual sodium carbonate, sodium adsorption ratio , toxicity, water quality parameters

DOI: 10.7176/JRDM/85-02

Publication date:May 31^st 2022