How far below the top of the embankment must the top of the riser pipe be for a sediment trap?

The correct answer is that the top of the riser pipe must be at least 1.5 feet below the top of the embankment for a sediment trap. This requirement plays a crucial role in ensuring the effective functioning of sediment traps. By having the riser pipe positioned at this height, it allows for proper water flow and sediment settling.

The 1.5-foot depth is significant because it helps to maintain adequate storage capacity for sediment accumulation. If the riser pipe were too high above the embankment, it could prevent the trap from capturing the intended volume of sediment effectively, which could lead to overflow and a subsequent failure in controlling sediment runoff.

Setting the riser at this depth also ensures that the water can pond adequately in the trapping area, facilitating the sedimentation process before the water exits through the riser. Thus, maintaining the riser pipe at 1.5 feet below the top of the embankment not only aids in sediment management but also enhances the overall efficiency and longevity of the sediment trap.