OPTICAL CHARACTERISTICS OF NEW ZEALAND RIVERS IN RELATION TO FLOW1

Authors

  • David G. Smith,

    1. Respectively, Scientist, New York City Department of Environmental Protection, 465 Columbus Avenue, Valhalla, New York 10595; Scientist, National Institute of Water and Atmospheric Research Ltd., P.O. Box 11–115, Hamilton, New Zealand; and Students, Department of Water Quality Management and Aquatic Ecology; Wageningen Agricultural University, Wageningen, The Netherlands.
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  • Robert J. Davies-Colley,

    1. Respectively, Scientist, New York City Department of Environmental Protection, 465 Columbus Avenue, Valhalla, New York 10595; Scientist, National Institute of Water and Atmospheric Research Ltd., P.O. Box 11–115, Hamilton, New Zealand; and Students, Department of Water Quality Management and Aquatic Ecology; Wageningen Agricultural University, Wageningen, The Netherlands.
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  • Jeroen Knoef,

    1. Respectively, Scientist, New York City Department of Environmental Protection, 465 Columbus Avenue, Valhalla, New York 10595; Scientist, National Institute of Water and Atmospheric Research Ltd., P.O. Box 11–115, Hamilton, New Zealand; and Students, Department of Water Quality Management and Aquatic Ecology; Wageningen Agricultural University, Wageningen, The Netherlands.
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  • Gerritdina W. J. Slot

    1. Respectively, Scientist, New York City Department of Environmental Protection, 465 Columbus Avenue, Valhalla, New York 10595; Scientist, National Institute of Water and Atmospheric Research Ltd., P.O. Box 11–115, Hamilton, New Zealand; and Students, Department of Water Quality Management and Aquatic Ecology; Wageningen Agricultural University, Wageningen, The Netherlands.
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  • 1

    Paper No. 96073 of the Journal of the American Water Resources Association (formerly Water Resources Bulletin). Discussions are open until October 1, 1997.

Abstract

ABSTRACT: Six years (1989–1994) of data from New Zealand's National Rivers Water Quality Network were used to characterize the optical water quality regime of river waters as regards: visual clarity (black disc visibility), turbidity, and light-absorbing aquatic humic material (referred to as ‘yellow substance,’ measured as light absorption at 440 nm). Quantitative relationships between optical water quality variables and flow in rivers are well-described by power law expressions. Visual clarity usually decreases strongly with increasing flow in individual rivers. There is a strong, inverse relationship between turbidity and visibility, but, because of differences between sites, turbidity is not a good general predictor of visual clarity (the attribute of real interest) in rivers. Yellow substance tends to increase with increasing flow, probably because during rainstorms, soil water high in yellow-colored humic material, rather than rain water or ground water, dominates discharge. Therefore, rivers are typically clear and low in humic matter at low flow, and turbid and yellow-colored at high flow.

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