Where must vegetated emergency spillways be constructed?

Where must vegetated emergency spillways be constructed?

• A. Within the underdrain area
• B. In embankment fill
• C. On top of the embankment
• D. In existing ground or cut

Answer: (D)

Vegetated emergency spillways are placed in existing ground or a designed cut because this location provides a stable, erosion-resistant channel that can be vegetated to slow flow and trap sediment. Placing the spillway in embankment fill or on top of the embankment risks instability: flow through fill can cause internal erosion and piping, and overtopping the crest can scour and undermine the dam. Interfering with the underdrain area would jeopardize drainage performance and the integrity of the seepage system. Excavating into natural ground or a cut creates a defined, stable path that aligns with the dam’s structure and allows vegetation to establish, enhancing erosion control and long-term stability.

Vegetated emergency spillways are placed in existing ground or a designed cut because this location provides a stable, erosion-resistant channel that can be vegetated to slow flow and trap sediment. Placing the spillway in embankment fill or on top of the embankment risks instability: flow through fill can cause internal erosion and piping, and overtopping the crest can scour and undermine the dam. Interfering with the underdrain area would jeopardize drainage performance and the integrity of the seepage system. Excavating into natural ground or a cut creates a defined, stable path that aligns with the dam’s structure and allows vegetation to establish, enhancing erosion control and long-term stability.