Evaluation of hydraulic roughness routines and properties in the presence of vegetation
Hydraulic roughness in the presence of vegetation is notoriously difficult to predict. However, reliable methods for predicting flow resistance in vegetated channels and floodplains are needed in order to address the needs of modern river engineering. To this end, the objectives of this research were: (1) to evaluate methods for determining hydraulic roughness within open channels in the presence of vegetation, and (2) to advance understanding of the influence of vegetation on the turbulence characteristics of the flow field. Three major activities were completed in order to address these objectives. First, a roughness calculator spreadsheet was developed based on a thorough review of available techniques for predicting hydraulic roughness in the presence of vegetation. The calculator includes the five most cited methods. Second, the roughness calculator and a Monte Carlo based MATLAB codes were used to investigate sensitivity and uncertainty within the techniques. Two of the techniques for predicting roughness were applied to a test case of the San Luis River in Oceanside, California. Third, a flume experiment was conducted to investigate turbulence characteristics in the presence of artificial vegetation elements. Study results revealed that of the various methods available for estimating hydraulic roughness in the presence of vegetation, two approaches showed the most promise with respect to data availability and ease of application: — Jarvela (2004) and Baptist et al. (2007). All of the hydraulic roughness estimating techniques showed a high degree of sensitivity to input parameters including descriptions of vegetation density and drag coefficients. Uncertainty in input parameters translated to uncertainties in predictions of hydraulic roughness and flow depth. Thus, future research should aim to improve species-specific estimates of common parameters and techniques for measuring field parameters. Turbulence metrics can provide much insight into the mechanisms in which energy is extracted from the bulk flow as a result of drag forces. This area of research shows promise with respect to developing general models for predicting hydraulic roughness.
Frictional resistance (Hydrodynamics)--Measurement, Channels (Hydraulic engineering), Riparian plants--Environmental aspects.
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