Monday, February 20, 2017

The latest on Oroville.

Lake Oroville reached an important goal Monday: The reservoir measured 50 feet below capacity as of 6 a.m. PT.    The lake is at 849.4, and water goes over the emergency spillway at 901 feet.

State water officials have said the 850-foot mark is important so crews can have more flexibility on releasing water during coming storms.  It also allows managers to lower outflows from the dam, so they can start working on the diversion pool.

There are three ways to get water out of the lake.  The damaged main spillway, which seems to be holding up right now, the emergency spillway, which has shown itself to be prone to nearly immediate failure, and through the powerhouse at the base of the dam.  However, huge amounts of debris are now in the river just below the powerhouse.  They consist of rubble from the lower end of the main spillway, enormous amounts of dirt and mud from the washout when the main spillway ruptured, and from the uncontrolled flow over the emergency spillway and down the bare mountainside.

This is all damming up the river, which backs water up to the powerhouse, and potentially into it.  The powerhouse can blow through about 15 thousand cubic feet per second of lakewater, but it must go through the turbines, and the electricity thus generated must go into the state's power grid.   At this time, no more water can be drained this way both because the water from the dammed up river is right there, and no more can safely be sent downriver, and also because the power lines from the powerhouse have been taken down due to the potential damage from the flow over the emergency spillway.  Thus, for both reasons, no water can be released.  

In the immediate future, the managers will be working to remedy this situation below the powerhouse.  They will need that 15k capacity desperately when the spring runoff hits in a few weeks or a month.

For now, the situation is stable.  Although it is raining hard now, much of this rain is turning to snow in the mountains, where is will stay for now.  

As has always been the case, the main dam is in no danger. 

Nevertheless, the situation will be interesting to watch from here.



  1. Ignorant question time. If the dam is 770 feet tall, how is the lake at 850 feet, with the emergency spillway kicking in at 901 feet? I assume that's the depth from the lowest point in the lake? Did they dig an additional 150 feet out of the bottom?

    1. Steve, I think all lake levels are given as elevation above sea level. However, the dam itself, without any water, would stand 770 feet tall (NOT above sea level) from the base to the top.

    2. I thought about that, but I was thinking that area would have been more than around 150 feet above sea level. Makes sense, though.