If made of earth, how high should dykes be at a minimum?

The minimum height for dykes made of earth should be at least 3 feet. This height is significant for several reasons related to flood management and erosion control.

Firstly, a dyke's primary function is to prevent water from overflowing onto land that is ordinarily dry. If the dyke is too low, it may not effectively hold back water during periods of heavy rainfall or flooding. A 3-foot minimum height is generally considered adequate to provide a sufficient barrier against typical flood levels, assuming the surrounding landscape and water body dynamics support this.

Additionally, a dyke of this height allows for some freeboard – the distance between the water surface and the top of the dyke – which is important to accommodate wave action, localized flooding, and potential settlement of the dyke material over time. Having a height of at least 3 feet helps ensure that these factors are considered, enhancing the dyke's effectiveness in protecting the area it serves.

The other height options could provide more protection but might not be necessary under normal circumstances, which aligns with standards and practices in flood management. Hence, 3 feet is a balanced and practical height requirement for earthen dykes.