LAKEPORT, Calif. – The city of Lakeport has completed a state-required dam breach inundation study and emergency action plan, which the Lakeport City Council approved at a June meeting.
In the wake of the February 2017 Oroville Dam incident, which involved the failure of its main and emergency spillways, the state is now requiring jurisdictions to identify dams, identify hazards and have an emergency action plan in the case of a failure.
At the council's June 18 meeting, Andrew Britton, the city’s compliance officer, and Melissa Larsen, a project manager and senior hydrologist with WEST Consultants Inc. presented the study and plan for the Lakeport Dam to the council.
At that meeting, the city also solicited public comment on the plan.
The discussion on the Lakeport Dam begins at the 52:29 mark in the video above. The staff report starts on page 219 of the agenda packet published below.
The written report by Britton and Utilities Superintendent Paul Harris said the state has classified the Lakeport Dam as a “high hazard facility,” which he said is “based solely downstream hazard considerations, not the actual condition of the dam or its critical appurtenant structures. Dams in the high hazard category have the potential to cause loss of life and impacts to downstream property should they fail or undergo an uncontrolled release from the dam.
Britton explained to the council that the Lakeport Dam is an important component of the city’s wastewater treatment plan.
The earthen embankment dam initially was built in 1980 and raise and expanded from 1990 to 1991. It’s 51 feet high and has a crest length of 890 feet. The report said the dam retains treated effluent stored in a reservoir that has a maximum capacity of approximately 650-acre feet, or nearly 212 million gallons.
The city’s treated wastewater is stored in the reservoir before the effluent can be applied on pasture land via a sprinkler irrigation system.
Britton told the council that the state responded to the Oroville Dam failure by passing Senate Bill 92 in June 2017. That bill added sections to state water code requiring dam breach studies and inundation maps that are required to be publicly accessible, as well as emergency action plans. The plan and maps are to be updated every 10 years.
Larsen said they completed maps for each type of failure, showing how long it would take for the water to reach certain areas. The maps start on page 258 of the agenda packet.
An arrival time map for an east breach on the dam anticipates it could reach Highway 29 in about 10 to 15 minutes and Clear Lake in between 30 to 50 minutes. For a north breach, inundation would be slower, with water expected to reach the highway in about 20 minutes and Clear Lake in about 45 to 60 minutes.
Britton said the plan is now complete, and once approved by the California Office of Emergency Services, the city will be in compliance with the new state requirements.
The plan calls for city personnel to immediately determine the emergency level once a failure event is observed or reported.
Three emergency levels are:
• Emergency Level 1: Unusual event, slowly developing;
• Emergency Level 2: Potential dam failure situation, rapidly developing;
• Emergency Level 3: Dam failure appears imminent or is in progress.
Each of those emergency levels then has a number of potential actions that are laid out in the plan, including plugging leak flows, lowering the water level, completing an immediate engineering exploration, contacting law enforcement, closing inlets, opening gates, placing sandbag and riprap, and more.
Councilman Kenny Parlet asked why Lakeport’s dam is classified as a dam and not a pond.
Larsen said he wasn’t alone in asking that, noting many cities and counties have the exact same questions and concerns. She explained that it just means there is the potential for the loss of one life if an uncontrolled release of water occurs.
Parlet complained that millions of dollars for such plans are now being spent and the city forced to fulfill another state mandate because of the earthen dams.
Britton noted that until WEST Consulting did the hydraulic modeling, taking into account the topography, it really wasn't clear how a potential dam release by a north breach would impact nearby homes on Linda Lane.
Larsen said the maps are a conservative estimate of how a water release would behave.
Councilman George Spurr asked how the city would stop it if a dam release occurred. Britton said very little can be done to stop it, but they can react to it, which is why there are specific steps and procedures set forward in the plan.
Spurr asked if the city would need to evacuate people in such a circumstance. Britton said yes.
Britton said dam inspections are done on a daily basis, and there is a lot of monitoring to make sure the dam remains stable and fully functional.
Larsen said it is unlikely that one day the Lakeport Dam would simply fail, as it’s walked and checked regularly.
“On a big earthquake you don't know it's going to happen,” said Spurr. He asked if there isn’t something they could do to keep it from getting into the lake.
Public Works Director Doug Grider said the water coming out of the dam is cleaner than what comes from the creek. He said he can back that up with testing done on the water when the city had an overflow of effluent several years ago, but it still cost the city $2 million.
The water in the dam is not raw sewage but treated water with chlorine injected. He added that it’s not a hazard to cause huge public health crisis.
Spurr, remembering a release of treated wastewater the city had several years ago, asked if the city would once again be fined millions of dollars if it happened. Grider said yes.
Britton said the water is treated to a quality where cattle eat the grass from the pastureland where the water is applied.
The council opened up the discussion for public comment that could be incorporated into the final plan but none was offered.
Parlet moved to approve the plan and maps, which the council approved 4-0.
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061819 Lakeport City Council agenda packet by LakeCoNews on Scribd