Final answer:
To determine the Ordinary High Water Mark (OHWM), consider the still water mark as the equilibrium position and measure the amplitude, which is the crest height above this point.
Step-by-step explanation:
When trying to determine the Ordinary High Water Mark (OHWM), a concept which is often related to environmental and geological studies, the given context hints at the principles of physics, specifically wave motion and equilibrium. The information provided tells us that the harbour has a still water mark, which represents the equilibrium position of the water when it is undisturbed. This is a crucial concept as the still water mark acts as the baseline from which other measurements can be made.
Furthermore, we learn that the definition of amplitude in the context of wave motion is the height of a crest above this equilibrium position. From the information, we know that the crest—the highest point of a wave—is 2 meters above the still water mark. Therefore, in this particular case, the amplitude of the wave is 2 meters.
Knowing that the amplitude is a measure of the wave's strength or extent of displacement from the still water mark, a rider, in this case, can determine the Ordinary High Water Mark by recognizing that it typically corresponds to the point where the presence and action of water is so common and long-lasting in ordinary years as to leave a mark on the landscape, such as erosion patterns, changes in soil characteristics, or vegetation lines. Therefore, the OHWM can be quantitatively determined by measuring 2 meters above the recognized still water mark in this scenario, as this would correspond to the usual reach of the wave crests or the high water mark.