New Zealand Journal of Marine and Freshwater Research abstracts

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Water colour and clarity of New Zealand rivers under baseflow conditions

ROBERT J. DAVIES-COLLEY

Water Quality Centre
DSIR Marine and Freshwater
Department of Scientific and Industrial Research
P. O. Box 11115, Hamilton, New Zealand

MURRAY E. CLOSE

Ilam Research Centre
DSIR Geology and Geophysics
Department of" Scientific and Industrial Research
P. O. Box 29 181, Christchurch, New Zealand

Abstract Visual clarity and apparent colour (hue) of 96 New Zealand rivers was investigated under baseflow (< median flow) conditions. Visual clarity, measured as the horizontal sighting range of a black disk, ranged 40-fold from 0.25 to 10.75 m. Only 7% of the clarity observations were "low" (black disk range < 1.2 m), whereas 31% were "high" (> 4 m). Visual clarity was strongly related to nephelometric turbidity (r = -0.88) but was less strongly related to suspended solids concentration (r = -0.77), even though scattering and absorption of light by suspensoids accounted for most (87 % on average) of overall light beam attenuation. Hue, as described in the field while viewing black disk range, varied from the blues of optically pure water to orange in waters with high concentrations of organic material, particularly yellow substance. There was a weak tendency for clear river waters to be blue-green in hue whereast turbid waters were more typically yellow-coloured.

Keywords water colour; water clarity; appearance; suspended solids; turbidity; optical properties; New Zealand rivers

New Zealand Journal of Marine and Freshwater Research, 1990, Vol. 24: 357-365 Crown copyright 1990
Received 5 February 1990; accepted 5 June 1990

PDF file of entire paper: medium quality (1314K); (scanned from paper original: notes about this process)

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