Answer: hello :)
The student used wave height for the dependent variable and trench width for the independent variable. He followed the scientific method in his experiment:
Observation: Tsunamis can cause widespread damage.
Hypothesis or prediction: A trench can help limit tsunami destruction by reducing its energy.
Test: Measure the wave height. Build a model of a trench, and measure wave height again. Find the reduction in height as a percentage.
Analyze: The student discovered an 80% reduction in wave height after building the trench.
Communicate: The student presented his findings during a science fair.