Part I of a two-part report presents model and prototype research studies which have been conducted in the United States and Great Britain to evaluate how embankments for dams, levees, roadways, etc. perform when subjected to overtopping flows from probable maximum flood (PMF) or near-PMF events. With improvements in the collection of flood records and the development of estimated storm events a significant increase in predicted PMF has been realized in some areas of the United States and other countries. These studies provide the engineer with an understanding of the mechanics of overflow erosion through subjecting scale model and prototype embankments to overtopping flow events. The effectiveness of various protection systems in preventing overflow erosion is evaluated. These systems range from grass-lined embankments and spillways to more sophisticated protection using geotextiles, gabions, riprap, cellular concrete blocks and soil cement. Such research efforts provide for the development of cost-effective measures that allow embankments to pass these extreme flood events without breaching.