Abstract
The hypothesis that alterations in bottom friction might reduce shoaling wave amplitude before the wave arrives at the beach was tested. Alterations of the near-shore seafloor to absorb wave energy have not been previously examined. An above ground swimming pool was used to house a 2 X 1 X 1 meter wooden impoundment tower that opened into a 4-meter experimental pool. Waves were generated by using a pneumatic system to raise a vertical floodgate. They passed over an 8% slope that could hold 10-centimeters deep substrate. A laser was used to measure wave amplitude every 10 milliseconds. Ten individual waves were observed for 20 seconds each, with the 2,000 water levels per wave transferred into Excel for analysis. Rock, pebbles and sand as well as near shore trench and three different semi-permeable “erosion” barriers were tested in all combinations. Each method of coastal modification, substrate alteration, near-shore trench, and erosion barrier were individually shown to reduce wave amplitude. The use of all three in combination was additive and reduced wave amplitude by 29%. Almost all reductions in amplitude were highly statistically significant. The evidence provided here suggests that near-shore coastal modification might serve as an additional approach to tsunami mitigation.