Abstract: In recent years, several serious incidents occurred at embankment dams which highlight the importance of evaluating and understanding spillway exit flow conditions at dams. In all cases, the peak spillway flows during these incidents were significantly less than the design flood flows; and although the spillways performed satisfactorily, the outflows from the spillways led to significant erosion and near breaching of the dam embankments or adverse impacts to the outlet works. In most cases, had the spillway design flows occurred, they would have likely resulted in complete breaching and catastrophic failure of the dams.
This paper presents the lessons learned from several case studies and discusses several failure mechanisms related to exit flows from spillways. Inspection techniques and modeling tools that are available to engineers to evaluate downstream spillway flow conditions and their potential to adversely impact embankment dams will also be discussed.

Key words: spillway, failure, erosion

摘要： 近年来，多座土石坝发生了严重的事故，凸显了理解和评估大坝溢洪道出流工况的重要意义。在这些案例中，溢洪道的峰值出流量均明显小于设计洪水流量。虽然溢洪道性态令人满意，但溢洪道出流会对土石坝造成严重侵蚀，导致其接近溃坝，或对泄水建筑物造成不利影响。大部分情况下，若达到溢洪道设计流量，则土石坝很可能会完全溃决，发生灾难性的失事。
笔者介绍了几个典型案例，讨论了与溢洪道出流相关的几种失事机制。另外，就工程师可利用的、用于评估下游溢洪道出流工况及其对土石坝潜在不利影响的检查技术和建模模拟工具，笔者也进行了讨论。

关键词: 溢洪道, 失事, 冲蚀