Res21 16010 final - Laserfiche WebLink

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8-13 Dam Failure jurisdiction has compiled a list of parcels that are in the inundation area and has posted at the offices of the county recorder, county assessor, and county planning agency a notice that identifies the location of the list. It is unknown if this list has been compiled for the planning area.  Dam failure inundation areas are often not considered special flood hazard areas under the National Flood Insurance Program, so flood insurance coverage in these areas is not common.  Dam infrastructure may require repair and improvement to withstand climate change impacts, such as changing in the timing and intensity of rain events.  Federally regulated dams have an adequate level of oversight and sophistication in the development of emergency action plans for public notification in the unlikely event of failure. However, the protocol for notification of downstream community members of imminent failure needs to be tied to local emergency response planning.  In the event of a dam failure that interrupted land line phone service, significant issues with communication could occur.  Inundation mapping in a digital format to support the risk assessment was available only for state- regulated high-hazard dams in the planning area. Such mapping was not available for federal dams.  Limited financial resources for dam maintenance during economic downturns result in decreased attention to dam structure operational integrity, because available funding is often directed to more urgent needs. This could increase potential for maintenance failures.  Mapping for federally regulated dams is already required and available; however, mapping for non- federally regulated dams that estimates inundation depths is needed to better assess risks associated with failure of these dams.  Although mapping is required for federally regulated dams, development downstream of dams and upgrades to older dams may have altered inundation areas; however, these inundation maps may not have been updated for significant periods of time. Encouraging property owners of dams to update EAPs and inundation maps will ensure availability of the most accurate data to assist emergency planners and local officials.  Most dam failure mapping required at federal levels requires determination of the probable maximum flood. While the probable maximum flood represents a worst-case scenario, it is generally the event with the lowest probability of occurrence. Mapping of dam failure scenarios for non-federal-regulated dams that are less extreme than the probable maximum flood, but have a higher probability of occurrence, can be valuable to emergency managers and community officials downstream of these facilities. This type of mapping can illustrate areas potentially impacted by more frequent events to support emergency response and preparedness actions.  The concept of residual risk associated with structural flood control projects should be considered in the design of capital projects and the application of land use regulations.  There may be dams located in the planning area that do not meet regulatory thresholds for jurisdiction under State of California or federal programs.  State and national dam lists are inconsistent regarding the number of dams in San Mateo County. These lists should be evaluated and corrected where needed. Currently, the National Inventory of Dams maintained by the U.S. Army Corps of Engineers lists 24 dams within the County, while DSOD has record of 21.