The spectral evolution of swell propagating across a wide, shallow continental shelf is investigated with extensive data from the North Carolina shelf, on the East coast of the United States. A spectral energy balance equation is proposed for the evolution of swell that includes refraction and shoaling, bottom friction over a movable bed, and Bragg scattering of waves by wavelength-scale bottom topography. This equation is solved numerically using a hybrid Eulerian-Lagrangian model (Ardhuin et al., 2001). Hindcasts of swell events during recent field experiments show large variations in wave heights that can be attributed to refraction and bottom friction, and are consistent with a variable bottom roughness. Wave height attenuation up to 73 % (93 % of the wave energy) was observed in moderately energetic conditions. Bragg scattering of waves by wavelength-scale bottom features significantly increases (up to a factor two) the directional spread of waves.
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