Stream map of San Juan Creek watershed with three major tributaries in dark blue, smaller streams in light blue, and cities and towns in orange. Trampas Canyon Creek is the short waterway flowing north into San Juan Creek, near the lower edge of the map.
A study was prepared in 1999 by the City of San Juan Capistrano, and it was found that a failure of the earthen Trampas Canyon Dam would do more damage to the lower course of San Juan Creek than for a 100 year flood. A failure would cause a floodwave over 0.5 miles (0.80 km) wide to rush down the lower 4.7 miles (7.6 km) of San Juan Creek to Doheny State Beach, flooding parts of San Juan Capistrano and Dana Point. A 100-year flood would cause a slightly smaller inundation.[4]
