Since 1894, the flow in the Yakima River has exceeded flood level 47 times. Since 1970 the area was declared a federal disaster area due to flooding 8 times in 27 years. The largest flood of record occurred in December 1933, despite completion of the Yakima Project reservoir system by the U.S. Bureau of Reclamation.
In 1938 designs for a federal levee system on the Yakima River were completed, but this project was not constructed until after World War II, completed in 1948, and repaired and extended the next year after the 1948 flood. These works were constructed to protect the urban areas of Yakima and Terrace Heights. A series of large floods during the 1970s prompted further studies by the Corps, and the levees earlier constructed under Corps authority were raised twice in the 1970s and the 1990s. There were three major flood events in the 1990s culminating in the 1996 flood. During this flood several areas along the Corps levees protecting the urban area received successful emergency reinforcement during the flood.
Most of the same floods occurred on the Naches River. In the 1970s, SR 12 was constructed adjacent to the river, to an elevation to withstand the 200 year flood. The area of SR 12 upstream of the 16th Avenue exit has experienced repeated flood damage since the 1980s and failure of this roadway during a major flood event would inundate a significant portion of Yakima.
