New Zealand Journal of Marine and Freshwater Research abstracts

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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 20^oC, 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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