Which characteristic is essential for a vegetated emergency spillway?

A vegetated emergency spillway is designed to safely handle overflow during high flow events and is intended to protect the integrity of the dam while facilitating natural drainage. The essential characteristic of being lined with erosion-resistant vegetation is critical because this type of vegetation helps stabilize the soil, preventing erosion that could occur during high water flows. By utilizing appropriate plant species that can withstand turbulent flow conditions, the spillway maintains its structural integrity and functionality over time.

Proper selection and establishment of vegetation also promote water absorption and filtration, enhancing the ecological benefits of the spillway while minimizing sediment runoff into downstream areas. This approach aligns with sustainable stormwater management practices that prioritize environmental health alongside structural integrity.

Other characteristics mentioned, such as the requirement for the spillway to be above the dam's height or developed with concrete materials, do not align with the purpose of a vegetated spillway, which relies on natural materials and vegetation to function effectively and sustainably.