Experimental study of wave dynamics in coastal wet

Authors: Melanie K Truong Kerri A Whilden Scott A Socolofsky Jennifer L Irish

Publish Date: 2014/10/01

Volume: 15, Issue: 4, Pages: 851-880

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Abstract

This paper presents laboratory experiments of wavedriven hydrodynamics in a threedimensional laboratory model of constructed coastal wetlands The simulated wetland plants were placed on the tops of conicallyshaped mounds such that the laboratory model was dynamically similar to marsh mounds constructed in Dalehite Cove in Galveston Bay Texas Three marsh mounds were placed in the threedimensional wave basin of the Haynes Coastal Engineering Laboratory at Texas AM University with the center of the central wetland mound located in the center of the tank along a plane of symmetry in the alongshore direction The experiments included two water depths corresponding to emergent and submerged vegetation and four wave conditions typical of winddriven waves and ocean swell The wave conditions were designed so that the waves would break on the offshore slope of the wetland mounds sending a strong swash current through the vegetated patches Three different spacings between the wetland mounds were tested To understand the effects of vegetation all experiments were repeated with and without simulated plants Measurements were made throughout the nearshore region surrounding the wetland mounds using a dense array of acoustic Doppler velocimeters and capacitance wave gauges These data were analyzed to quantify the significant wave height phase average wave field and phase lags wave energy dissipation over the vegetated patches mean surface water levels and the nearbottom current field The significant wave height and energy dissipation results demonstrated that the bathymetry is the dominant mechanism for wave attenuation for this design The presence of plants primarily increases the rate of wave attenuation through the vegetation and causes a blockage effect on flow through the vegetation The nearshore circulation is most evident in the water level and velocity data In the narrowest mound spacing flow is obstructed in the channel between mounds by the mound slope and forced over the wetlands The close mound spacing also retains water in the nearshore resulting in a large setup and lower flows through the channel As the spacing increases flow is less obstructed in the channel This allows for more refraction of waves off the mounds and deflection of flow around the plant patches yielding higher recirculating flow through the channel between mounds An optimal balance of unobstructed flow in the channel wave dissipation over the mounds and modest setup in the nearshore results when the edgetoedge plant spacing is equal to the mound base diameterPublication supported in part by an Institutional Grant NA14OAR4170102 to the Texas Sea Grant College Program from the National Sea Grant Office National Oceanic and Atmospheric Administration US Department of Commerce In addition the authors would like to thank Mr John Reed and Dr PoH Yeh for their technical guidance and the sharing of their experience in the Haynes Coastal Engineering Laboratory Special thanks are also given to Mr David Dailey and Ms Kristie Drawe student workers in the research group and also Mr Paul Ramsey Mr Christopher Ryan and Mr Eric Sonne student workers at the Haynes Laboratory for their help and input during the laboratory experiments All experimental data used in preparation of this paper are available from authors KAW or SAS

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