In seawater, the water particles are moved in a circular orbital motion when a wave passes. The radius of the circle of motion for any given water molecule decreases exponentially with increasing depth. The wave base, which is the depth of influence of a water wave, is about half the wavelength.

Based on this passage, the depth of the wave base is approximately? Let's think fast. Stream of consciousness:
The relevant sentence in the passage is: The wave base, which is the depth of influence of a water wave, is about half the wavelength. So the final answer is half the wavelength.