New Zealand Journal of Marine and Freshwater Research abstracts
Transverse mixing and surface heat exchange in the Waikato River: a comparison of two models
J. CHRISTOPHER RUTHERFORD BRYAN L. WILLIAMS
Water Quality Centre
National Institute of Water and Atmospheric
Research Ltd P.O. Box 11-115 Hamilton, New Zealand
RAY A. HOARE
R. A. Hoarc & Associates
P.O. Box 4153
Hamilton East, New Zealand
Abstract
Two mathematical models of different complexity were used to study transverse dispersion and surface heat transfer in the lower Waikato River. A simple analytical streamtube model (HPLUME) gave adequate temperature predictions in a reach where the channel was fairly regular but performed poorly where there were extensive shallows. In the latter reach, a two-dimensional numerical model (SYSTEM21) gave good temperature and flow predictions once properly calibrated. Model calibration proved to be dif ficult in the Waikato River because the natural river temperature varied significantly along the channel. A search method was developed to estimate both the transverse dispersion and surface heat exchange coefficients from measured plume temperature profiles based on the observation that transverse variations in natural temperature were small. This method was used to calibrate S YSTEM21 in two separate reaches. Coefficient estimates were sensitive to measurement errors and slight departures in homogeneity of natural temperature and it would be desirable to corroborate the estimates of
Ez using
dye tests. In the upper reach, the average transverse dispersion coefficient was
Ez/hu* = 1 which is high but within the range of published values. A sharp bend and buoyant spreading contributed to the high
Ez value.
Ez increased with river flow because both h and «* increase with flow. In the lower reach,
Ez/h u* = 0.1 which is lower man expected but islands may have affected the model calibration. The surface heat exchange coefficient averaged
K = 84 -167 W m~
2 s-i o£-T
wjri
cn faUs within the range of published values. No significant relationship could be found between surface heat exchange coefficient and meteorological variables.
Keywords water temperature; excess temperature; thermal pollution; transverse dispersion; surface heat exchange; mathematical model
New Zealand Journal of Marine and Freshwater Research, 1992, Vol. 26:435-452 002e Royal Society of New Zealand 1992
Received 23 October 1991; accepted 28 August 1992
PDF file of entire paper: medium quality (1605K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
