HR: 1330h
AN: B33E-25    [Abstracts]
TI: Advances in stream shade modelling. Accounting for canopy overhang and off-centre view
AU: Davies-Colley, R
EM: r.davies-colley@niwa.co.nz
AF: National Institute of Water and Atmospheric Research Limited, P.O. Box 11115, Hamilton, New Zealand
AU: * Meleason, M A
EM: m.meleason@niwa.co.nz
AF: National Institute of Water and Atmospheric Research Limited, P.O. Box 11115, Hamilton, New Zealand
AU: Rutherford, K
EM: k.rutherford@niwa.co.nz
AF: National Institute of Water and Atmospheric Research Limited, P.O. Box 11115, Hamilton, New Zealand
AB: Riparian shade controls the stream thermal regime and light for photosynthesis of stream plants. The quantity difn (diffuse non-interceptance), defined as the proportion of incident lighting received under a sky of uniform brightness, is useful for general specification of stream light exposure, having the virtue that it can be measured directly with common light sensors of appropriate spatial and spectral character. A simple model (implemented in EXCEL-VBA) (Davies-Colley & Rutherford Ecol. Engrg in press) successfully reproduces the broad empirical trend of decreasing difn at the channel centre with increasing ratio of canopy height to stream width. We have now refined this model to account for (a) foliage overhanging the channel (for trees of different canopy form), and (b) off-centre view of the shade (rather than just the channel centre view). We use two extreme geometries bounding real (meandering) streams: the `canyon' model simulates an infinite straight canal, whereas the `cylinder' model simulates a stream meandering so tightly that its geometry collapses into an isolated pool in the forest. The model has been validated using a physical `rooftop' model of the cylinder case, with which it is possible to measure shade with different geometries.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2005 Joint Assembly