Changes in California dam safety regulations

Posted in: Municipal, Water

O’Shaughnessy Dam in Yosemite National Park, California (photo courtesy of User ‘Inklein’ on Wikimedia Commons)

In a previous article posted in July 2017, we reported on the new dam safety regime in California brought about by the passage of Senate Bill 92. This piece of legislation was aimed at enhancing dam safety by requiring inundation maps and emergency action plans for jurisdictional dams, and by providing enforcement powers to the state’s Department of Water Resources.

Immediately after the passage of SB 92, DWR initiated the process of promulgating emergency regulations under the authority granted by the legislation. The new regulations prominently affect four areas of inundation mapping as prescribed in Title 23 of the California Code of Regulations: (a) hazard potential classification, (b) timing of updates, (c) technical study requirements and (d) map production requirements.

Hazard classification

The new hazard potential classification consists of four classes: low hazard, significant hazard, high hazard and extremely high hazard. While there is no inundation mapping requirement for low impact dams, the other three classes of dams are required to have inundation maps. DWR has requested dam owners to submit updated inundation maps on the following schedule, depending on dam classification:

  • ‘Extremely high hazard’ dams: Before January 1, 2018
  • ‘Significant hazard’ dams: Before January 1, 2019
  • ‘Significant hazard’ dams: Before January 1, 2021

If you are responsible for a California dam, you may check out DWR’s listing of dams showing the hazard classification for your dam here.

Timing of updates

Whereas California law did not previously specific when inundation maps should be updated, the new regulations mandate inundation map updates when any of the following conditions occur:

  • Significant change in the dam or critical appurtenant structure
  • Significant change in downstream development that involves people and property
  • Changes to hazard classification of the dam
  • No less frequently than every 10 years

Technical study requirements

Technical study requirements specified in the emergency regulations are substantially similar to requirements promulgated by California Office of Emergency Services and Federal Emergency Management Agency. Notable differences are: (1) the new regulations specifically require two-dimensional model, except under some conditions and (2) a storm-induced failure scenario is not required, but may be submitted in lieu of a sunny day failure scenario.

Map production requirements

Mapping requirements are substantially similar to those of FEMA’s P-946 document. Requirements specified include information to be contained in the maps, map layout, temporal contours, and depth grid.

It should be remembered that, under California law, emergency regulations are only valid for a period of 6 months. Therefore, the emergency regulations promulgated by DWR are valid until April 17, 2018. It is expected that DWR will commence the formal rule-making process in December 2017 to replace the emergency regulations with permanent regulations. We do not expect the permanent regulations to be significantly different than the emergency regulations.

Mead & Hunt will continue to support dam owners in California to operate their dams safely and maintain compliance with the post-Oroville laws. If you have any questions about the safety of your dam, please do not hesitate to contact me.

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