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NEVADA CITY, Calif. September 1, 2017 – Three NID-owned dams are part of a priority re-evaluation list for spillways published today by the Department of Water Resources (DWR). Scotts Flat, Rollins and Jackson Meadows are all certified by DWR for operation and have no reservoir restrictions imposed.
The Downstream Hazard Status of all three is listed as extremely high, however “the downstream hazard classification is based on the size of the reservoir and the number of people who live downstream of a dam, not the actual condition of the dam or its critical structures.” [source: DSOD fact sheet]
NID’s Assistant General Manager Greg Jones stated the inclusion of the three dams was based on the construction of the spillways – very similar to the spillway on Oroville Dam. “We had some minor damage during the winter storms at the Scotts Flat spillway, but repairs have been completed.” According to Jones, NID worked in conjunction with DSOD and FERC to conduct safety inspections on all the spillways. The district is expected to expand their website with a dam section, kisting all of their infrastructure and detailed information about each dam. This was a request by Director Nancy Weber after the failure of PG&E’s South Yuba Canal early spring. Jones welcomed the inclusion of their dams in DSOD’s list, saying safety is paramount to the district.
Jackson Meadows in a rock dam, built in 1965, with a 52,500 acre-foot (AF) capacity.
Rollins is an earth and rock dam, built in 1965, with an 66,000 AF capacity.
Scotts Flat is an earthen dam, built in 1948, with a 49,000 AF capacity.
NID expects to release more information on the DSOD inspections and the state of the spillways later next week.
Today, the California Division of Safety of Dams (DSOD) released updated information on 1,249 dams under its jurisdiction, including downstream hazard classification, condition assessment, and reservoir restriction status for each dam.
DWR’s Department Division of Safety of Dams (DSOD) defines the hazards categories as follows: “The downstream hazard is based solely on potential downstream impacts to life and property should the dam fail when operating with a full reservoir. This hazard is not related to the condition of the dam or its appurtenant structures. The definitions for downstream hazard are borrowed from the Federal Guidelines for Inundation Mapping of Flood Risks Associated with Dam Incidents and Failures (FEMA P-946, July 2013). FEMA categorizes the downstream hazard potential into three categories in increasing severity: Low, Significant, and High. DSOD adds a fourth category of “Extremely High” to identify dams that may impact highly populated areas or critical infrastructure, or have short evacuation warning times.”
“In the wake of the Lake Oroville spillways incident, DSOD initially prioritized spillway re-evaluations for 93 dams with spillways similar to Lake Oroville’s. Owners of those 93 dams were notified this spring of requirements to submit a work plan to investigate the condition of their spillways. DSOD’s re-evaluations of those spillways are now underway,” a DWR news release states.