Scaling the effects of riparian vegetation on cross-sectional characteristics of ephemeral mountain streams-a case study of Nahal Oren, Mt. Carmel, Israel

Four 50 m segments were chosen in the middle part of Nahal Oren, each being characterized by a different vegetative structure. In each segment six cross-sections were preformed 10 m apart as well as a longitudinal profile. Additionally, at three of the cross-section sites vegetation transects were conducted at mid-bank up stream of the cross-sections. Average width/depth ratios at the different sites varied from 5.5 to 9.5 and were not correlated with channel slope. Regression analysis indicated that tree coverage is positively correlated with higher width/depth ratios, at a distance of 1 m above the cross-section. The average shrub coverage at 5 m was negatively correlated with width/depth ratios. We suggest that shrubs and trees may have a similar function in stabilizing banks via the root system, but the above-ground structure of these vegetative types has different effects. Possibly the dense foliage of the shrubs reduces water velocities, thus further increasing bank stability.