Demich, Larry Ralph (2008-08). The Effects of Submerged Aquatic Vegetation on Flow in Irrigation Canals. Doctoral Dissertation. Thesis uri icon

abstract

  • Invasive aquatic species such as Hydrilla verticillata (hydrilla) have become a pervasive and nearly ineradicable part of the waterways of the American south. Hydrilla is an aggressive colonizer; grows rapidly and rapidly blocks flow areas, which greatly reduces the capacity of water supply canals. Hydrilla grows up through the water column and is present throughout flow zones that are typically assumed to be free flowing and without resistance, other than that transmitted via the mechanics of a Newtonian fluid. Hydrilla is highly flexible and its morphology in the flow field is dependent on many parameters, including flow, growth stage, cross-section geometry and substrate. Traditional methods of calculating canal flow capacities assume that resistance to flow originates at the boundary of the channel. These methods typically attempt to account for vegetation by increasing resistance coefficients, which are associated with the boundary of the canal. A combination of field studies and experimentation in three separate laboratory channels was used to characterize the behavior of hydrilla and its impacts on open-channel flow. This work developed relationships for energy losses of flow within the vegetation, as well as velocity gradients within the vegetation and through the vegetation water interface to the open water. The information developed in this investigation was used to develop a model of the cross-section of flow with vegetation growing in the center of the channel. The model is based on the Prandtlvon K?rm?n universal-velocity-distribution law; and uses modifications to the method of calculating the hydraulic radius, to account for the increased frictional elements and reduced flow areas in the canal cross-section. A simple function was developed to estimate the remaining flow capacity in a canal as a function of the remaining unblocked area. The Prandtl-von K?rm?n universal-velocity-distribution law, together with modifications to the method for calculating the hydraulic radius, can improve estimates of the flow in channels impacted by submerged aquatic vegetation. The effects of a broad range of parameters can thus be represented by a relatively simple function, which was developed in this project.
  • Invasive aquatic species such as Hydrilla verticillata (hydrilla) have become a pervasive and
    nearly ineradicable part of the waterways of the American south. Hydrilla is an aggressive
    colonizer; grows rapidly and rapidly blocks flow areas, which greatly reduces the capacity of
    water supply canals. Hydrilla grows up through the water column and is present throughout flow
    zones that are typically assumed to be free flowing and without resistance, other than that
    transmitted via the mechanics of a Newtonian fluid. Hydrilla is highly flexible and its
    morphology in the flow field is dependent on many parameters, including flow, growth stage,
    cross-section geometry and substrate.
    Traditional methods of calculating canal flow capacities assume that resistance to flow originates
    at the boundary of the channel. These methods typically attempt to account for vegetation by
    increasing resistance coefficients, which are associated with the boundary of the canal.
    A combination of field studies and experimentation in three separate laboratory channels was
    used to characterize the behavior of hydrilla and its impacts on open-channel flow. This work
    developed relationships for energy losses of flow within the vegetation, as well as velocity
    gradients within the vegetation and through the vegetation water interface to the open water.
    The information developed in this investigation was used to develop a model of the cross-section
    of flow with vegetation growing in the center of the channel. The model is based on the Prandtlvon
    K?rm?n universal-velocity-distribution law; and uses modifications to the method of
    calculating the hydraulic radius, to account for the increased frictional elements and reduced flow areas in the canal cross-section. A simple function was developed to estimate the
    remaining flow capacity in a canal as a function of the remaining unblocked area.
    The Prandtl-von K?rm?n universal-velocity-distribution law, together with modifications to the
    method for calculating the hydraulic radius, can improve estimates of the flow in channels
    impacted by submerged aquatic vegetation. The effects of a broad range of parameters can thus
    be represented by a relatively simple function, which was developed in this project.

ETD Chair

publication date

  • August 2008