The study was conducted ·during 20054/2005 season in the three Tihama (Northern, Middle and Southern) areas in addition to Abs area (Al-Jar and Haradh districts) to find out prevailing water quality classes and distribution. Results have shown a varying degree of Water Salinity from one area to another and sometimes within same area. Electrical Conductivity (EC) of water samples ranged between (0.61- 7.62 mmho/cm) with lowest value in Middle Tihama (AI-Kadan, Surdud Valley) and highest value in Northern Tihama (AI-Showagera). The PH of Water samples ranged between 7-8.1 indicating a normal range according to FAQ guidelines of irrigation water quality. Other ions' concentrations differed from sample to another. But, the Chloride and Sodium concentrations - being essential determinants of water use in irrigation - were found predominant in most samples especially those of high salinity water. Classification of water samples as regards quality and suitability for irrigation varied on bases procedures used in the study, i.e. American salinity laboratory classification and FAQ Guidelines. Results have also shown a consistent lowering of water level at an average rate of 1.5 - 3 m/year in Middle and Northern Tihama and 3.6 m/year in some Southern Tihama areas.
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