Experimental investigation on set-up of irregular waves over fringing reef flat

Wave-induced set-up brings severe impacts on the safety of the land area behind the reef through increase of the mean water level on the fringing reef flat. Flume experiments were carried out under irregular wave conditions to study the wave-induced set-up on reef flat. The experimental tests were carried out with 3 reef flat depths,4 significant wave heights and 4 spectral peak periods. It was found that:① Stable hydrodynamic conditions on reef flat can be achieved only when the sampling time lasts for more than 200 peak periods;② Irregular wave trains have more complex breaking process than that of regular wave trains,in that the larger waves in the same wave train break on the fore-reef slope in plunging manner,while smaller waves break on the reef flat in spilling manner or do not break;③ The maximum set-up on reef flat was found to increase with the increase of the peak period,and decrease with the increase of the water depth on the reef flat,and be proportional to the significant wave heights. The formula,proposed by Gourlay for estimating set-up on reef flat under regular wave conditions,was extended to irregular wave conditions. It was found that the maximum set-up can be well predicted by replacing the regular wave height and period in the formula with the significant wave heights and peak periods for irregular waves,respectively.