Browsing by Subject "Erosion Control"

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    Selection of vegetation and flexible vegetal drag coefficients for erosion control in lacustrine wave environments
    (2014-06) Chapman, John
    The restoration of plant communities in littoral zones often fails. Because littoral habitats around the world often are subject to changing water regimes and potentially changing future climates, a better understanding of species competitive interactions under such conditions is needed for restoration plant selection. To represent shoreline plant communities, we grew eight freshwater species used in shoreline restoration projects in Minnesota and Wisconsin, USA, in outdoor basins and manipulated water levels to determine the effect on above ground biomass. Biomass production of some species in the competing environment was related to the proximity to water or inundation depth and frequency. Sparganium eurycarpum and Bolboschoenus fluviatilis dominated the total biomass in all water manipulations. These findings allow for better design of plant community composition and better vegetative erosion control under a variety of water conditions. This thesis also investigates the ability of plants to reduce waves and flow, through a comparison of parameters that characterize vegetation flexibility effects on flow resistance and drag. Drag forces measured in a flume for simple cylindrical obstructions of the same shape and size but with different flexibility under several flow conditions. A novel formulation is developed where the drag coefficient is evaluated as a function of the relative velocity and the elastic modulus of the obstruction. Current methods for estimating energy dissipation require plant specific parameters that are difficult to estimate for the large variety of plant morphologies used in shoreline protection, requiring testing on each species of interest. The method developed herein directly measures hydrodynamic forces on individual plant shoots using a torque sensor mounted beneath the bed of a flume. The data collected also suggests that more flexible objects result in less drag force on each element and suggests that frequency response is related to the frequencies existing in the driving wave and the natural frequency of the obstruction element, although harmonic synchronization appears to occur in some cases, doubling the expected drag force magnitude. A case study is also included as an example of how the findings presented here can be applied to a shoreline erosion control evaluation. The case study is an inland lake in northern Minnesota currently having erosion soil losses. Data from this research is used to develop a vegetation scenario that is predicted to limit the erosion.