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The Oroville Dam has fallen apart, which has caused the evacuation of 200,000 on the Feather River in Northern California in and around the town or Oroville. The dam is the highest in the United States and built of one of the most primitive technologies used to create dam structures.

Oroville Dam is 770 feet high. Construction was started in 1962 and ended in 1968. The design is called “earthfill,” which allows builders to make use of local materials for building.

According to Construction Engineer, earthfill damns have “non-overflow sections with separate spillways.” The spillway is part of the Oroville Dam that has failed.

“Once you have damage to a structure like that it’s catastrophic,” acting Water Resources director Bill Croyle told Reuters.

A construction engineer describes earthfill dam hallmarks:

The foundation requirements are not as rigorous as other dams
Local available soil is the main construction material
High skill not required
No special plants are required. Most earth-moving machines can be used

In its manual on earthfill dams, the Army Corps of Engineers wrote:

An understanding of the causes of failure is a critical element in the design and construction process for new dams and for the evaluation of existing dams. The primary cause of failure of embankment dams in the United States is overtopping as a result of inadequate spillway capacity.

Apparently, the most badly damaged part of the Oroville Dam is its spillway. Stati0n KRCA reported:

As tensions remain high around Butte County and the surrounding areas, water levels at Lake Oroville continue to drop Monday morning, stopping water from spilling over the potentially hazardous auxiliary spillway.