Florida Drinking Water Operator "B" Practice Test

During which season does thermal stratification typically occur in a reservoir?

1. Winter

2. Summer

3. Spring

4. Fall

The correct answer is: Spring

Thermal stratification in a reservoir primarily occurs in the warmer months, particularly during summer. This is when the surface water heats up significantly due to increased sunlight, forming a warm upper layer known as the epilimnion. Below this layer lies the thermocline, where temperature rapidly decreases with depth, and further down is the colder, denser water in the hypolimnion. During spring, as temperatures rise, the warm water at the surface begins to mix with the cooler water below, which can lead to a turnover event. This turnover occurs in spring and fall when the temperature of the water becomes uniform throughout the lake, but the distinct thermal layering that characterizes stratification predominantly occurs during the summer months when the temperature differential is most pronounced. Thus, the correct understanding is that thermal stratification is a summer phenomenon, with the stratification breaking down in spring (and again in fall) as conditions change, leading to the mixing of water layers.