We could see a couple of inches of rain from the storm systems this week with gusting winds that could lead to downed trees and power outages. The so-called Pineapple Express storm will deliver somewhat warmer precipitation which will raise the snow level in the Sierra.
With all of that water entering our reservoirs and channels, the Folsom Dam Auxiliary spillway is in service to ease some of the pressure. I had a chance to fly over the dam and spillway this week which is a fascinating new piece of infrastructure having just been completed in 2017. The spillway consists of an 1100 foot long approach channel and a 3027 foot long spillway chute with six submerged gates. The auxiliary allows water to be released earlier and more safely from Folsom Lake during a high water event...which is what we're facing this week.
The spillway is not only useful but could be life saving. The structure adds significant protection from flooding and can clear high levels of water more quickly than releases from the dam since the spillway sits 50 feet lower than the water level. It also allows water managers to match the downstream levee capacity instantaneously giving them more control over flows and impacts downriver.