Determination of Flow Resistance Coefficients Due to Shrubs and Woody Vegetation
Abstract
The purpose of this Technical Note is to transmit results of an experimental investigation into the effect of vegetation (particularly ground cover plants, small trees, and shrubs) on flow resistance. An important consideration for determining the stage-discharge relationship in rivers and streams is the effect or influence of vegetation on the overall head loss along a channel and in the overbank. Plants in the floodplain and along the banks can increase or even decrease the effective flow resistance. The vegetation may be natural or it may have been planted to improve aesthetics or habitat, to prevent erosion, or for other reasons. Hydraulic losses and drag due to actual plants were measured at the Utah State University Water Research Laboratory utilizing a large wide flume and a smaller sectional flume. Research in the flume resulted in the collection of data from more than 220 experiments with 20 different plant species. Experiments were conducted with both homogeneous and mixed plant groupings. Single-stem and multiple-stem plants were included in the plant types evaluated. Plants with and without leaves were evaluated. Plant density, spacing, and size were varied in the experiments. Plants were evaluated over a range of velocities and depths. A methodology was developed from the laboratory data to predict head loss and resistance coefficients as a function of slope and depth. Input data can be collected from the field or estimated plant characteristics may be used in the methodology. The evaluation of vegetative impacts on proposed and existing channels to determine flow capacity and water-surface elevations requires proper hydraulic roughness values for shrubs and other aesthetically and environmentally desirable plants. Given the near complete lack of hydraulic roughness values for shrubs and similar vegetation, the accurate estimation of channel capacity and water-surface elevations has previously been difficult at best.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2000
- Accession Number
- ADA603072
Entities
People
- Ronald R. Copeland
Organizations
- Engineer Research and Development Center