Comments about ‘Inspectors unsure why Santa Clara dam failed’

Housing development planners always need to project that eventually there will be a rain (usually after a drought) that will take out an old dam or create too much flow for streams to handle. Desirable as some places may LOOK for development, a cold hard look should be made at flood potential. You must always also assume that rodents will make holes.

Once on our farm (well out of any flood plain)a rat family moved in under a corral. My dad was in the hospital for an extended stay and the rats probably knew that. Within weeks they had an extended family of 100s, maybe 1000s. They had tunnels under the corral, under buildings and were an intimidating force. It took a monumental rat killing effort, and in the process there were collapsed tunnels to nab unsuspecting legs, to finally send the rats elsewhere. I am an animal lover and killing rats was hard, but it was us or them in a battle for survival.

Having a little experience with dam safety, it is my opinion that the old dam was built of earthfill, compacted with c.1919 machines and capability. The earthfill had rodent holes that allowed water to begin saturating into portions.

The saturation increased as the water depth increased behind the dam. At the top, where the dam is narrow, saturation overcame the holding capability of the earthfill. The earthfill gave way at the top first and rapidly eroded down, causing complete failure.

The primary causes: (1) Dam construction did not meet current compaction and design standards. (2) Rodent holes and other factors allowed saturation. (3) High rainfall and rapid water rising caused rapid saturation at the top, triggering the erosion.

Uh...earthen dam with limited reinforcement at the top...water crested over the top of the dam and ate it away...anyone who's played with flowing water and damming it up would understand the principles involved...