Predicting the effects of shade on water temperature in small streams

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...

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Bibliographic Details
Published in:New Zealand journal of marine and freshwater research 1997-12, Vol.31 (5), p.707-721
Main Authors: Rutherford, J. Christopher, Blackett, Shane, Blackett, Colin, Saito, Laurel, Davies-Colley, Robert J.
Format: Article
Language:English
Subjects:
computer model
Freshwater
riparian vegetation
shade
water temperature
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Summary: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°C, an estimate of the thermal tolerance for sensitive invertebrates.
ISSN:0028-8330
1175-8805
DOI:10.1080/00288330.1997.9516801