Abstract
Restoring riparian shade helps maintain healthy stream ecosystems and
computer models are helpful in guiding restoration. The effects of
meandering and orientation on shade to direct and diffuse lighting was
investigated using a simplified model of riparian vegetation. Previous
studies have shown that straight streams oriented east-west (EW)
experience higher lighting than those oriented north-south (NS).
Meandering decreased reach-averaged direct lighting in EW valley streams
but increased lighting in NS valley streams. When meander amplitude
equalled 50% of meander wavelength, lighting of streams in EW and
NS-aligned valleys was similar. Meandering and valley orientation had
little effect on diffuse lighting. In EW valleys lighting was highest at
stream bends and a strategy to reduce lighting quickly would be to
prioritise planting of tall vegetation on bends. In NS valleys lighting
was lowest at bends, suggesting the opposite planting strategy. Shade
exceeding 70%, a criterion for preventing nuisance aquatic plant
growths and stressfully high water temperatures, occurs in ‘typical’
meandering streams on cloudless, mid-summer days at mid-latitudes once
H/ W exceeds about 2. The model over-simplifies riparian
vegetation and the effects of canopy shape and overhang merit further
investigation.