Hydraulic Resistance due to Aquatic Vegetation in Small Streams: Field Study

This technical note examines vegetation effects on hydraulic resistance in small streams and suggests simple quantitative relationships for predicting and quantifying these effects using the plant characteristics with the greatest explanatory power. In particular, we examine the effects of aquatic plant biomass, stature, and architecture on hydraulic performance of five New Zealand streams representing a wide range of channel dimensions, flows, aquatic plant species, and assemblages. Comparisons among the vegetation parameters indicated that ratios of the site-averaged canopy height to the mean flow depth and of the site-averaged plant length to the mean flow depth were the best roughness descriptors. Effects of individual plant species and their characteristic patch patterns were not significant. The data from all sites collapsed around single lines, suggesting that general physical parameters of vegetation should be the primary determinants of hydraulic resistance in streams studied, not species-specific parameters, as often assumed.