New Zealand Journal of Marine and Freshwater Research abstracts

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Natural water temperature variations in the lower Waikato River, New Zealand

J. CHRISTOPHER RUTHERFORD J. BURNS MACASKILL BRYAN L. WILLIAMS

Water Quality Centre
National Institute for Water and Atmospheric
Research Ltd
P.O. Box 11-115
Hamilton, New Zealand

Abstract Natural temperature in a 30 km reach of the Waikato River during autumn 1984 varied synchronously across the channel and for practical purposes can be assumed transversely uniform (within 0.03°C). Significant differences between sites were found in the amplitude and phase of diurnal temperature cycles which resulted in instantaneous temperature differences along the channel of up to 0.5°C. These were caused by a reduction in mean depth and a change in channel orientation along the study reach. The observed lag between peak radiation and maximum water temperature yielded preliminary estimates of the surface heat exchange coefficient K = 155-670 W nr² s¹ "'C-¹ but there is some doubt about the accuracy of these estimates. A heat budget model was used to predict longitudinal temperature changes. Model predictions were accurate only to within ± 0.2°C (RMS error) probably because meteorological data came from sites 40-50 km away from the study reach. Uncertainties in natural temperature of about 0.5°C will make it difficult to accurately estimate excess temperatures arising from waste heat inputs.

Keywords water temperature; excess temperature; surface heat exchange; transverse dispersion; temperature variation M91058 Received 30 August 1991; accepted 19 January 1993

The Royal Society of New Zealand 1993
Received 30 August 1991; accepted 19 January 1993

PDF file of entire paper: medium quality (1193K); (scanned from paper original: notes about this process)

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