NCEES Principles and Practice of Surveying Practice Exam

What distinguishes a mixed semidiurnal tide from other tidal patterns?

1. It has one high tide and one low tide per day

2. It consists only of mild tidal changes

3. It features two successive high tides of different heights each day

4. It occurs weekly rather than daily

The correct answer is: It features two successive high tides of different heights each day

A mixed semidiurnal tide is characterized by the presence of two high tides and two low tides each lunar day, but importantly, the heights of the high tides are not equal. This distinguishing feature creates a pattern whereby one high tide can be significantly higher or lower than the other. This variability in the height of the high tides is what sets mixed semidiurnal tides apart from other tidal patterns, such as strictly semidiurnal tides, where both high tides are of approximately equal height. Understanding this concept is key to differentiating various tidal patterns. For example, in a simple semidiurnal tide, there is a consistent rhythm with uniform high and low tides. In contrast, mixed semidiurnal tides provide a more complex tidal cycle, reflecting variations due to factors such as the moon's position relative to the Earth and the sun, as well as local geographic factors. This complexity can lead to significant variations that are critical for navigational and environmental considerations.