Although the California Department of Water Resources is claiming Oroville Dam is safer because the water level has fallen by 52 feet, that feat was largely accomplished by over-filing 9 upstream reservoirs that are all expected to flood as another Pineapple Express storm-train brings 48 hours of heavy rain through Wednesday.
The last winter storm caused an evacuation of about 200,000 people downstream from Lake Oroville due to the threat of a catastrophic failure of the dam.
Although most Americans have been told that the fissure in the side of the dam has been stabilized by opening up the spillway to drain the lake, and helicopters have dropped huge bags of rocks in a crack, the water flow into Oroville Lake has been restricted by overfilling the upstream reservoirs.
The nine State Water Project and PG&E earthen reservoirs on the Upper Feather River Watershed that feed directly into Lake Oroville were already at maximum capacity prior to the new storms. This next storm is expected to bring 1-3 inches of rain in the valleys. But the Central Sierras are expecting 10 inches of snow and rain over the next 7 days.
With all the higher elevation reservoirs brimming, Supervisor Kevin Goss from mountainous Plumas County told the Sacramento Bee, “I’m watching, and I’m worried.” Flooding from the last set of storms shut down escape in all directions in his Indian Valley district.
The towns of Greenville and Taylorsville were isolated, and sewer systems for the sparsely populated county suffered extensive damage as many roads washed out. The flooding from the new storm is expected to be much more serious.
In addition,tRelatively warm temperatures of up to 49 degrees in nearby Tahoe caused snowmelt this week. With the “Snow Water Equivalents” for this time of year in the Central Sierras at 183 percent and the Southern Sierras at 205 percent; the National Oceanic and Atmospheric Administration warned that the mountains could see significant runoff.
The total capacity of the upstream dams is about 400,000 acre feet, or about one tenth the capacity of Lake Oroville. Last week, the upstream reservoirs were allowed to fill in an effort to take pressure of Oroville Dam. But with the dams full, virtually 100 percent of the rain and runoff from the coming storms will flow into Oroville Lake.
Despite the upstream restricting of water flow, Lake Oroville added over 1 million acre feet of water in three days during the last storm. Engineers from the California Department of Water Resources hope that a combination of releasing 800,000 acre feet of water from the lake will be enough to prevent another Oroville Dam flood.