The effects of aquatic macrophytes on channel roughness and flow parameters

Watson, David (1986) The effects of aquatic macrophytes on channel roughness and flow parameters. University of Southampton, Doctoral Thesis.

Abstract

Knowledge of the effects of aquatic plants on water flow in stream and river channels is extremely limited despite the need for values of roughness coefficients in relation to river maintenance and channelization. Although the river engineer can select values of roughness from sets of tables derived by experience, such values are not always confirmed by the values measured for specific sites affected by aquatic plants. Previous research on open channel roughness and flow-parameter interaction has concentrated upon non-vegetated channels. The limited published research on the effects of in-channel plant growth has mainly been restricted to grass-lined farm drainage channels in the U.S.A. and to flume studies of artificial vegetation elements. There has been a minimal consideration of large aquatic plants (aquatic macrophytes) within this context. The methods used for, and costs of maintenance for vegetated channels have been assessed by a questionnaire sent to English water authorities. This revealed a total cost, for maintenance of channels affected by aquatic plants, greater than 2.25 million per annum. The impact of aquatic macrophytes on factors of open channel flow is examined, firstly by monitoring and experimentation on the River Ebble, Wiltshire, and secondly from experiments in the Freshwater Biological Association, River Laboratory flume (using actual plants). Implications of the results are analysed with reference to effects of aquatic marcophyte growth on relationships established between discharge and stage, width, depth, velocity, water surface slope, and Manning's n roughness coefficient. Two methods

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