JudyJB wrote:Why are they releasing water? Is it for agricultural use? Or because they don't want the lake to get too full?
Thanks for the question, Judy. It give me the opportunity to pontificate a bit, which I am never loath to do!!
Judy, I can't speak directly for DWR (California Department of Water Resources), and precisely why they have begun to do water releases at this time.
Short answer? Yes, you are correct - basically, because they don't want the lake to get too full. But this is not as simple an answer at it might seem.
Longer answer:
I know from long experience living downstream of Oroville dam, and of doing research, is that DWR (usually!) tends to look closely at weather predictions and to take the "long view" of possible upcoming weather events. I think they do this more carefully these days, after the failure of the Oroville Dam spillway in 2017, when around 200,000 people were evacuated because it was feared the emergency spillway might fail.
DWR is involved in a very tricky and complicated business (to spill or not to spill, that is the question!) when considering, and/or initiating water releases.
In looking at
http://www.weather.com (the United States National Weather Service website - my personal "go to" weather website) I can see that rain is predicted for the
city of Oroville every day over the next week, and possibly beyond.
I am not DWR, and just looking at the weather predictions for the
city of Oroville does not nearly give the entire picture and complexity of what is going on. (Oroville Dam is just east, and slightly north, of the city of Oroville).
The Oroville watershed (a watershed is the area of land that drains water into a lake) spans somewhere around 3,500 - 4,000 square
miles - so DWR is probably not generally concerned by the amount of rain falling in the valley so much (and falling in the city of Oroville, or over the lake itself) as it is of the rain falling/or might fall over the entire watershed.
The concern is the amount of rain falling over the lower and upper regions of the Sierra foothills, and beyond (again, a mountain watershed comprising of more than 3,500 square miles).
It generally rains a
LOT more over the mountains and foothills than it does in the valley (i.e., the city of Oroville) - although rainfall is, of course, variable. A good example might be that during a very heavy rainfall, a half inch or so of rain might fall in the
city of Oroville (which is a valley city), in the Sierra foothills over that same day 1 1/2 inches of rain might fall from the same storm.
Another complicating factor is if a lot of snow has fallen over, say, several weeks over the upper foothills of the watershed (which, as of this writing, it
has) - maybe accumulating many feet of snow - if a warm weather system then hits this snow as rain (because the storm is warm), it can melt these many feet of snow accumulation all at once - often within a few hours.
Of course, then sending all of that rushing water that once was snow on down towards the lake.
Also, within that watershed's 3,400 - 4,000 square mile "footprint" are many other, smaller dams. As these smaller dams also begin to fill to capacity, they too will need to do water releases - sending ever more water down into Oroville dam.
For DWR, it is a balancing act. And DWR does not have a crystal ball.
Release
too much water, and they look like fools for not conserving water if the rains should suddenly stop (which they can and do). Release
not enough water, when heavier, more intense rains than predicted arrive, over a longer period, disaster might strike (as it did in 2017). So they look like fools, and are in for public condemnation, for not releasing
enough water.
The "long answer" is actually quite a bit more complicated than what I write here, but I can feel everyone's eyes glazing over at the length of this post. So I will bring this post to a close.
Thanks for asking, Judy.
Anne
