Wind effects on runup and overtopping of coastal structures

The effects of strong onshore winds on the maximum elevation to which a wave will run up on a coastal revetment, or the rate at which water flows past the crest of the revetment if the crest is not high enough to prevent overtopping, were studied in a series of physical model tests in a wind/wave flume. Runup elevations and overtopping rates were determined for both smooth and rough slope surfaces with slopes of 1:1.5, 1:3, and 1:5, using a range of structure freeboards, incident wave conditions, and wind speeds. The study demonstrated that elevation of maximum runup or overtopping rate increased significantly under the influence of wind speeds of 12 m/s and 16 m/s for similar wave conditions at the revetment toe. All measurements of runup elevations or structure freeboards were adjusted for wind-induced setup in the wave flume.; Sources of energy input to the wave runup were examined. Tangential sheer stresses on the runup bore were calculated and found to be negligible. Normal stresses affecting wave growth shoreward of the wave gage used to measure incident wave conditions were calculated and found to have only a small effect on runup elevations. Increases in surface current velocity due to wind-induced wave breaking appeared to be the major cause of the observed increases in runup elevations under the influence of strong onshore winds. Increases in surface current velocities were evidenced by higher velocities of the runup bore under the influence of wind.; No known scaling laws exist to apply model test results of wind effects on a gravity wave system directly to the prototype. Methods are discussed for separately calculating wind effects in the flume that do not scale to the prototype directly with the waves.; Correction factors for applying smooth-slope runup equations to rough surfaces are examined. It is shown that correction factors should not be constant values but should vary with incident wave conditions and structure slope. Recommendations are made for improved roughness correction factors.