Study of Extreme Waves Propagating Over Reefs in Large Wave Flume

Waves propagating over reefs have been studied by many researchers. However due to limitation of small wave flume, most experiments focused on the normal waves. Extreme waves are the input parameters for structure design on reefs. Thus, experiments of extreme waves propagating over reefs were conducted in the large wave flume of the Tianjin Research Institute of Water Transport Engineering. Extreme wave hydrodynamic within surf zone will be focused on. Tests with different wave heights H_i, wave periods T and water levels on reefs h have been carried out. The model scale is set to be 1:15, then H_i from 4.5m to 12m, T from 9s to 17s, hr from 0 to 3m are generated in the test. Wave breaking points are observed by high speed camera. Wave breaking points move offshore as H_i and T increase and h decrease. Wave setups and wave-induced flows along the reef are measured at different locations. It can be found that wave setups increase with increasing H_i and T and decreasing water level h. Wave-induced flows increase with increasing H_i and h and decreasing T. As waves propagate towards landside, wave setups and wave-induced flows have a local extremum at the middle of surf zone. Compared with our test, Gourlay’s formulas overestimate wave setup while underestimate wave induced flow within extreme wave surf zone.