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Dam Inundation and Property Risks

About Dams:

Dams represent a risk to public safety due to the massive impact of a possible disaster on populated areas and the environment. When a dam fails the energy of the water is capable of causing destructive flooding downstream, resulting in loss of life and serious property damage.

Unfortunately, dams have failed and can fail for one or a combination of reasons, such as:

  1. Overtopping caused by floods that exceed the capacity of the dam. - The El Nino weather pattern is to be noted.
  2. Structural failure of materials used in dam construction, inadequate maintenance and upkeep. - The average age of America’s dams is 51 years.
  3. Movement and/or failure of the foundation supporting the dam. - Earthquakes in California are common occurrences.
  4. Settlement and cracking of concrete or embankment dams. - Due to soil expansion, subsidence, seismic, or other factors.

 

Dam Failure Cases:

Potential flooding because of dam failure poses a threat anywhere in the world where water has been channeled, dammed, or harnessed.

In 2008, a magnitude 7.9 earthquake devastated China and prompted officials to evacuate 80,000 people below a natural dam formed by landslides which threatened to collapse. They feared the rubble-constructed dam would lose strength and a raging wall of water would charge down upon the villages below.

In 2011, Fujinuma Dam failed about 20 minutes after the Tōhoku earthquake. The reservoir was nearly full and the water overtopped the dam’s crest. Japanese authorities stated that the dam failure was caused by the earthquake. The flood washed away five houses while damaging others, disabling a bridge and blocked roads with debris. Eight people were missing and four bodies were discovered.

California’s Dam Safety Program:

In 1971, failure of the Lower San Fernando Dam during the Sylmar Earthquake generated increased focus on protecting the population and the country’s infrastructure, including ensuring the safety of dams. A dam safety program was established by Government Code §8589.5 in 1972.

As part of the program, the California legislature requires dam owners to provide the Office of Emergency Services with an inundation map showing the extent of damage to life and property that could occur, given a complete and sudden dam failure at full capacity, in a worst case scenario. The official dam failure inundation maps are used in California’s Natural Hazard Disclosure Statement (NHDS) as specified in Civil Code §1103 et seq. for real estate transactions. As a national disclosure leader, Property I.D. takes it a step further by disclosing the locally mapped dam inundation zones. Even though dam failure inundation can occur due to a seismic event, it has been placed as a separate item from the other seismic hazards of landslide and liquefaction on the NHDS.

Make an Informed Decision:

Buying a property is usually the largest investment most Americans make. Securing answers to seismic hazard concerns before the close of escrow is essential. The Property I.D. Report discloses if the subject property is located in an area of potential flooding due to dam failure based on local and state maps, and provides the name of the dam, along with all other required natural hazard information and more. The Property I.D. Report also discloses when the subject property is located within a 1/4 mile of a dam inundation zone which would provide security and empowers you to make an informed investment decision.

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