Coastal protection techniques for storm damage : experimental and numerical study on rock seawall in swash zone to reduce wave overtopping and overwash of sand beach
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Swash
Seawall
Overwash
Coastal engineering
Storm Surge
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Yuan, S.; Li, L.; Amini, F., and Tang, H., 2014. Numerical study of turbulence and erosion of an HPTRM-strengthened levee under combined storm surge overflow and wave overtopping. Combinations of storm surge and extreme waves may cause overtopping of coastal protection of structures, resulting in structural damage and flooding behind these structures. The high turbulence of the overtopping flow is an important factor for soil erosion and may be responsible for the destruction of levees during combined overtopping. The goal of this study was to investigate the turbulence and erosion characteristics of one levee strengthening technique, high-performance turf reinforcement mat, under combined wave overtopping and storm surge overflow. A three-dimensional hydrodynamic and sediment transport model known as ECOMSED has been calibrated and verified with overflow discharge and full-scale overtopping experimental results. The study simulated 41 storm surge overflow and combined overtopping cases with different freeboards and significant wave heights. Overtopping hydrodynamic flow, turbulent shear stress, turbulent kinetic energy, and erosion rate at the toe of a landside slope under combined overtopping conditions were calculated. New equations for estimating turbulent shear stress, turbulent kinetic energy, and erosion rate at the toe of a landside slope were developed. The equivalency of erosion rate under storm surge overflow and combined wave and surge overtopping are provided. The range of the application of these equations is discussed.
Storm Surge
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The flow and the scour around a coastal structure due to tsunami flows are simulated by combination of the Large Eddy Simulation method of calculating turbulent free-surface flows and the bed-load sediment transport calculation method. The tsunami wave impinging on a structure is the case for which experimental data are available and the simulation results are compared with. Then the tsunami overtopping a seawall and the scour of its foundation, as seen at several sites during the East Japan Earthquake of 2011 is simulated. The wave impingement calculation is reproduced well and the scour simulation is reasonable compared with exsisting estimates. For more realistic simulation of long-period or equilibrium scour hole estimation, transport of the suspended sediment will be needed.
Seawall
Revetment
Large-Eddy Simulation
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In this paper, the effect of beach nourishment on wave overtopping in shallow foreshores is investigated with the non-hydrostatic wave-flow model SWASH. Firstly, the applicability of SWASH to model wave overtopping is tested by comparing results with a physical model setup with different storm wall heights on top of an impermeable sea dike. The numerical results show good agreement with the physical model. After validation, sensitivity analysis of the effect of beach nourishment on wave overtopping is conducted by changing bottom configurations with the SWASH model. From the sensitivity analysis, it becomes clear that wave overtopping discharge in shallow foreshores is characterized by the bores generated in surf zone due to wave breaking. To reduce wave overtopping discharge in shallow foreshore, it is important to reduce the horizontal momentum of the bores.
Swash
Surf zone
Wave height
Seawall
Wave model
Dike
Beach morphodynamics
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A laboratory experiment was conducted in a wave flume to compare sand beach profile evolution and wave overtopping of a sand berm for the three cases of (1) no structure, (2) a stone revetment protecting the steep sand berm, and (3) a stone sill reducing wave action on the berm. The revetment reduced onshore sand transport on the fronting beach but was effective in protecting the sand berm and reducing wave overtopping. The revetment crest was damaged during major wave overtopping. The sill reduced the beach profile change but was not very effective in reducing wave overtopping and berm erosion when the sill crest was submerged sufficiently. An existing numerical model (CSHORE) was upgraded for its application to the sill test where the emerged sill crest became submerged during the test. The upgraded model was compared with the measured wave transformation, wave overtopping, and overwash rates and beach profile evolution in the three tests consisting of 90 runs with each run lasting 400 s. The model was also used to predict the settlement of the revetment and sill for the case of no filter below the stone structure. The limited experiment and numerical modeling quantified the capability and limitations of the revetment and sill.
Revetment
Berm
Sill
Crest
Wave height
Overwash
Freeboard
Wave flume
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Four test series consisting of 14 tests and 140 runs (each run lasted 400 s) were conducted in a wave flume with a sand beach and a berm in order to compare the effectiveness of a dune and a rock (stone) seawall placed on the foreshore in reducing wave overtopping and sand overwash. The incident irregular waves were kept approximately the same for all the runs. The water level was increased to create dune erosion and crest lowering as well as stone displacement. The dune was effective in eliminating or reducing wave overtopping and overwash in comparison to the corresponding berm with no dune but the narrow dune was destroyed easily as the water level was increased. The stone seawall reduced wave overtopping and overwash even after it was damaged moderately. A stone seawall buried inside a dune was examined in the last test series. The buried seawall functioned like the dune initially and like the seawall after the sand on the seawall was eroded by overtopping waves. The buried seawall combines the aesthetics of the dune and the robustness of the stone seawall.
Seawall
Overwash
Berm
Tidewater
Coastal engineering
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Abstract : A two-dimensional physical model investigation was conducted at scales of 1:13 and 1:19 (model to prototype) to provide input for the design optimization of a seawall proposed for long-term storm protection at Virginia Beach. This was one of a number of tasks conducted in support of the detailed design of a beach erosion control and hurricane protection project at Virginia Beach. The 2-D tests were conducted to acquire data on the expected rate of overtopping for two design storm types (hurricane and northeaster) at selected still-water levels, determine a stable stone size for a proposed fronting riprap berm, and to determine the distribution of wave-induced pressures on the face of the seawall. As a result of the 2-D tests, a stable stone size was determined for the proposed fronting berm, and overtopping rates were measured. An improved seawall design was recommended and showed a significant reduction of overtopping rates over the initial seawall design. Wave-induced shock pressures were recorded on the face of the seawall; however, durations were small and probably insignificant. Measured surge pressure magnitudes were relatively consistent and durations were significant. No significant negative pressures were recorded.
Seawall
Berm
Riprap
Coastal engineering
Coastal erosion
Breakwater
Wave height
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Low rock structures have been constructed on some beaches to reduce storm-induced damage to backshore areas, but no method is available to design such structures. Four test series were conducted in a wave flume with a sand beach and a berm to compare the effectiveness of a narrow dune and a rock (stone) seawall placed on the foreshore in reducing wave overtopping and sand overwash. The incident irregular waves were kept approximately the same. The water level was raised to increase wave overtopping. The dune was effective in eliminating or reducing wave overtopping compared with the corresponding berm with no dune, but the narrow dune was destroyed easily as the water level was increased. The stone seawall reduced wave overtopping even after its deformation. A stone seawall buried inside a dune functioned like the dune initially and like the seawall after the sand on and inside the porous seawall was eroded by overtopping waves. An existing numerical model was extended to predict sand transport on and inside the porous structure in the swash zone.
Seawall
Berm
Swash
Overwash
Tidewater
Piezometer
Riprap
Flume
Silt
Coastal engineering
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Seawall
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