How far must erosion protection against wave action extend up the slope on the reservoir side of a dam?

The required extension of erosion protection against wave action up the slope on the reservoir side of a dam must be to the maximum water elevation. This is essential because wave action and associated erosion are most intense at this level during high water conditions, such as during storms or rapid inflow from runoff. By ensuring that erosion protection extends to the maximum water elevation, the integrity of the dam is maintained, and the risks of soil erosion and potential failure are minimized.

In contrast, extending protection only to the crest of the dam or the minimum water elevation would leave portions of the slope vulnerable during extreme conditions. Additionally, providing coverage to two-thirds the height of the dam may not adequately address the most severe erosive forces that can occur at full capacity. Therefore, the correct choice reflects the principle of proactive engineering to safeguard the structural and functional integrity of the dam under expected environmental pressures.