What is happening at Lake Mathews, is the water level low, and should we be worried?
I have been hearing quite a bit of discussion about the water level at Lake Mathews and associated speculation on whether it is reflective of an impending water shortage. I will address those questions and give some background on Lake Mathews and how it is operated.
Lake Mathews is the end point of the Colorado River Aqueduct. It is owned and operated by the Metropolitan Water District of Southern California, commonly known as Metropolitan or MET. The Colorado River Aqueduct runs from Parker Dam 242 miles to Lake Mathews. The aqueduct and Lake Mathews were completed in 1939, and the first water flowed into Lake Mathews in early 1940. A reservoir expansion in 1960 raised the dams 31 feet and nearly doubled the storage capacity of Lake Mathews to its present 182,000 acre-feet. Both Western Municipal Water District and Eastern Municipal Water District are MET member agencies and can take Colorado River Water from Lake Mathews. Riverside Public Utilities could purchase Colorado River or State Water Project water from Western if it wished to. Currently RPU gets 100% of its water supply from local ground water basins. This is less expensive than importing water from hundreds of miles away. The City of Corona does purchase a significant amount of Colorado River Water for its customers. Western water purchases some Colorado River Water for irrigation customers, but does not use it as a drinking water supply.
MET has a very informative link on the Colorado River Aqueduct and Lake Mathews at mwdhto.com for anyone interested.
Lake Mathews is not intended to be a long-term storage reservoir like Lake Mead or Lake Powell. It is more of an operating reservoir intended to store enough water to avoid shortages during maintenance on the aqueduct or any of the associated pumping stations or tunnels. It also serves as backup supply in case of shortages of local water supplies, and now reductions in flow through the State Water Project which brings water from the Sacramento River Delta to Southern California.
As of September 16, Lake Mathews was at 56% of its capacity and 86% of normal level for this time of year. This is neither unusual nor alarming. MET has over 1.5 million acre-feet of water stored in Lake Mead putting Lake Mathews and those served by it in a good position for many years even in the face of proposed reductions in allocation of Colorado River Water.
A factor that did cause some recent drawdown of Lake Mathews is a test of a method to treat a recent invasive species; the golden mussel. Golden mussels clog pipes, pumps and other water infrastructure. They are found in the Sacramento River Delta and now the State Water project. MET is testing a control methodology on State Water Project Water, and has reduced its take of that water during the test. Lake Mathews was used to replace that water on a short-term basis. MET plans to begin refilling Lake Mathews in the near future when the test ends and to have it full again by the end of this year.
None of this is intended to suggest we do not have a long-term water supply issue in California. We do, and steps are being taken at both the local and state level to capture, transport and store more water in wet periods for use in dry periods. But none of this should affect Lake Mathews. It will continue to rise and fall depending on demand, and may occasionally be really low while maintenance of the dams and intake structures is performed, but it will not go dry.
