Water Storage Update

I did not intend to give another water storage update so soon, but there have been a couple of important late season developments that are worth discussing today.
As the latest graph from the California Department of Water Resources shows, storage continues to climb in Lake Oroville — the largest of the State Water Project’s reservoirs, at nearly 4 million acre-feet of capacity. This is unique in the five years shown on the graph; by this time, levels are normally decreasing, since inflow from snow melt is usually small by the end of June. This is a direct result of the late, wet, cool Spring we have had this year. The fact that the level of Oroville is still rising is very good news.
Unfortunately, we don’t have a direct route from Oroville to the customers of the SWP. Water flows downhill from Oroville into the north end of the Delta, via the Sacramento River. The water supply for much of Central and Southern California comes from the south end of the Delta. From this low point — very near sea level — the water must be pumped. The pumps at the Clifton Court Forebay lift the water into the next major storage component of the SWP, San Luis Reservoir. San Luis is also a huge reservoir at about 2 MAF of capacity — split almost equally between the federal Central Valley Project and the SWP, so the State’s share is about 1 MAF.
The huge pumps at the south end of the Delta can fill San Luis in a couple of weeks, but they greatly impact natural flows within the Delta. So environmental rules are in place to try and protect the delicate ecosystem that is the Delta. And these rules often shut down the pumps completely, or restrict the rate at which water can be withdrawn. One of the important recent developments is that pumping restrictions have been relaxed until July 1. That’s not a lot of time, but the pumps that fill San Luis don’t need a lot of time — just a green light.
Storage south of the Delta is important to our water supply, because it is closer to the customers and it is beyond the reach of almost all the environmental restrictions. However, the sum of all the SWP storage capacity south of the Delta is only about one-half of the capacity of Oroville — and virtually all of it comes from Oroville, via the pumps and canals of the SWP.
Because of the good situation at Oroville and the pumping window we have until July 1, the DWR has increased this year’s allocation to 50% of requests. This is great news for municipal water users — way better than the 5% allocation of last year — but only marginally good news for the farmers. The planting season is over for most crops, so a little extra water this late in the season may not produce any real relief for the beleaguered agricultural industry.
It’s also important at this time to recognize this truth: one wet season does not end a drought. If we have another above average rainfall/snowfall next year, we will all be able to breathe a bit easier — unless the environmental restrictions come between us and our water supply.
Have a nice weekend!

Leave a Reply

Your email address will not be published. Required fields are marked *