New Zealand Journal of Marine and Freshwater Research abstracts
Predicting the effects of shade on water temperature
in small streams
J. CHRISTOPHER RUTHERFORD
SHANE BLACKETT
COLIN BLACKETT
LAUREL SAITO
ROBERT J. DAVIES-COLLEY
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 11 115
Hamilton, New Zealand
Abstract A computer model for stream water temperature was
developed, and tested in a small pasture stream near Hamilton, New Zealand. The
model quantifies shading by riparian vegetation, hillsides, and stream banks
using three coefficients: canopy angle, topography angle, and canopy shade
factor. Shade was measured directly and found to vary significantly along the
channel. Using the maximum measured shade, a close match was achieved between
observed and predicted daily maximum and minimum water and bed sediment
temperature. Model predictions of incoming and outgoing long-wave radiation
flux closely matched measurements, but there were unexplained discrepancies in
short-wave radiation flux. Model predictions indicate that moderate shade
levels (c. 70%) may be sufficient in temperate climates to restore
headwater pasture stream temperatures to 20oC, an estimate of the
thermal tolerance for sensitive invertebrates.
Keywords water temperature; computer model; shade; riparian
vegetation
New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31:
707-721
0028-8330/97/3105-0707 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (1283K); (scanned from paper original: notes about this process)
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