What minimum vertical clearance between the normal water level and the top of the dam is recommended?

What minimum vertical clearance between the normal water level and the top of the dam is recommended?

• A. 1 foot
• B. 2 feet
• C. 3 feet
• D. 4 feet

Answer: (C)

The concept being tested is freeboard—the vertical distance between the normal water surface and the top of the dam. This space acts as a safety cushion to absorb wave action, wind setup, and fluctuations in water level, helping prevent overtopping and giving room for debris and maintenance access. Three feet is a common minimum because it provides a practical safety margin without excessive cost. It reduces the risk of the dam being overtopped during storms or higher-than-normal water levels. A smaller clearance, like one or two feet, would leave little room for waves or surges and raises the chance of overtopping. A larger clearance, such as four feet, offers more protection but isn’t typically required as the minimum and would add unnecessary expense for most sites.

The concept being tested is freeboard—the vertical distance between the normal water surface and the top of the dam. This space acts as a safety cushion to absorb wave action, wind setup, and fluctuations in water level, helping prevent overtopping and giving room for debris and maintenance access.

Three feet is a common minimum because it provides a practical safety margin without excessive cost. It reduces the risk of the dam being overtopped during storms or higher-than-normal water levels. A smaller clearance, like one or two feet, would leave little room for waves or surges and raises the chance of overtopping. A larger clearance, such as four feet, offers more protection but isn’t typically required as the minimum and would add unnecessary expense for most sites.