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This article in JEQ

  1. Vol. 3 No. 4, p. 356-361
     
    Received: Nov 5, 1973


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doi:10.2134/jeq1974.00472425000300040012x

Ground-Water Quality Related to Irrigation with Imported Surface or Local Ground Water1

  1. H. I. Nightingale and
  2. W. C. Bianchi2

Abstract

Abstract

Ground-water quality in an arid irrigated area that imports high quality surface water was compared with an adjacent up-gradient area that uses local pumped ground water. A large irrigation canal separates the two areas which are up-gradient from the pumping depression of the Fresno-Clovis, California metropolitan area, which is dependent on ground water. Intensive sampling (154 wells) was done in the fall of 1972 after it was shown by previous sampling that the ground-water electrical conductivity (EC), NO3, and Cl content had not significantly changed since 1967. Diagrammatic distribution maps for ground-water quality showed great variability. The Wilcoxon-Mann-Whitney nonparametric statistical tests showed the significance probabilities for EC, NO3, and Cl differences above and below the canal were 0.093, 0.114, and < 0.00006, respectively. The significance of these differences are determined by the reader or decision-maker by his chosen error probability, the error risk he is willing to take in rejecting the null hypothesis of no difference when it is true. Areas of higher ground-water NO3 and Cl were generally related to soil drainage-recharge and agricultural use. The use of local ground water without supplemental surface supplies above the canal has led to ground-water EC, NO3, and Cl concentrations to be 9.5, 18.6, and 91.8% higher, respectively, than below the canal which uses mostly high quality surface water.

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