Flexible Porous Wave Barrier for Enhanced Wetlands Habitat Restoration

Abstract

A flexible porous wave barrier is proposed to increase the effectiveness of wetlands habitat restoration projects by protecting cordgrass seedlings from wave action during the critical initial stages of growth following planting. The barrier consists of a vertical porous membrane anchored to the sea bed and kept under tension by a small buoyant float. The structure is easily constructed, requires little maintenance, and may be deployed from a small boat without the need for specialized equipment or trained personnel. A numerical model is developed to assess the effectiveness of this structure as a barrier to wave action. The fluid motion is idealized as linearized, two-dimensional potential flow and the equation of motion of the structure is taken to be that of a one-dimensional beam of uniform mass per unit length subjected to a constant axial force. The boundary integral equation method is applied to the fluid domain, and the dynamic behavior of the structure is also described through an appropriate Green function. Numerical results are presented that illustrate the effects of the various wave and structural parameters on the wave reflection characteristics of the structure. Small-scale physical model tests have also been carried out in the University of Houston wavetank facility to validate the predictions of the numerical model. In general, good agreement was obtained between the theoretical and experimental reflection coefficients. It is found that for certain structural parameter combinations a porous tensioned membrane structure may provide a reasonably effective barrier in the short- to mid-wavelength range.