How much lower must the center of a check dam be than its outer edges?

The correct answer indicates that the center of a check dam must be 4 inches lower than its outer edges. This design is crucial for effective water management in the context of sedimentation and erosion control. The primary function of a check dam is to slow down the flow of water, allowing sediments carried by the water to settle out rather than being washed further downstream.

When the center of the check dam is lower, it creates a small pool or a depression that water can flow into, which helps to reduce velocity. This helps to capture sediments effectively and prevents the erosion of the stream bank and surrounding areas. If the dam were too flat or the center were not sufficiently lower than the edges, it would not effectively slow the water down, leading to increased sediment transport and potential erosion.

This specification of 4 inches is a best practice guideline commonly adopted in erosion control measures and reflects engineering principles aimed at maximizing the efficiency of check dams.