Effect of Water Hyacinth on Open-Channel Water Flow Behavior: Laboratory Scale

Abstract

Water hyacinth (Eichhornia crassipes) is one of the fastest growing plants. Due to its ability to adapt and reproduce, it causes various problems in waterways. The effect of water hyacinth was investigated on flow behavior in an open channel in a laboratory flume. Five different root depths of water hyacinth from natural streams were modeled using a plant floating plate. Four different water hyacinth densities were used. Controls without water hyacinth were also established. The vertical velocity profiles of the cases with and without water hyacinth were compared and the results showed that without water hyacinth, the velocity profile was similar to the theoretical logarithmic distribution in an open channel. In the cases with water hyacinth, the vertical velocity profiles were similar to the theoretical velocity distribution in a closed conduit, in which the velocity in the root zone was zero since water hyacinth floating on the water surface behaved like a solid wall. The experimental data showed that the plant caused flow resistance which tended to slow down the flow. Furthermore, the denser and longer root depth of water hyacinth caused greater flow resistance, as the flow-retarded region extended deeper, occupying about 65.0% of flow depth measured from the water surface. In addition, an empirical formula for flow in an open channel with consideration of water hyacinth effects was developed and a flow velocity empirical formula was obtained which was in good agreement with the observed data used in the verification process.