History of Marin County’s Water Supply
By Robert L. Harrison
Since California’s statehood in 1850 the supply of fresh water has been an ever growing concern for the state. In recent years issue has been especially severe in Marin County. Inadequate water storage has led to emergency projects to increase the local supply. The 1977 temporary pipeline across the Richmond-San Rafael Bridge installed to bring water from the East Bay into Marin remains as the prime example of a solution rushed to avoid a serious lack of water the County.
In early Marin water was obtained from either a local well or private companies that built small water systems primarily aimed at selling building lots. The Marin Water Company in San Rafael was the largest of these systems. In 1872 the company built Lake Lagunitas, Marin’s first reservoir. By today’s standards it was a small lake holding just over 100 million gallons. It served San Rafael for several years.
Reservoirs depend on rainfall and water runoff to keep them filled. In Marin County records of the amount of rainfall at Lake Lagunitas go back to 1880. Wet and dry periods can be easily identified by this data. Records from 1880 through 1900 show Marin enjoyed above average rainfall. The annual average rainfall for this period was over 70 inches or nearly six feet of rain per year. This compares to the 140 year annual average of 52 inches or a little over four feet of rainfall per year.
In spite of the especially wet 20 year period in the late 19th century ongoing concerns about drought often appeared in the press of the day. In the Olema column of the November 28, 1890 Sausalito News: “Complaints are heard that cattle are suffering from the long drought, although some ranches are producing fair quantities of butter.”
A letter to the News printed September 25, 1891 describes the water supply built by the Sausalito Land and Ferry Company:
“…residents have been totally unaware of the sparsity of our supply…water storage is not equal to twelve days of actual consumption…With our present meager sources, our scant resources for impounding, and our increase in consumers, a moderate rainfall, or a very warm summer will insure us a drought.”
From Jack Gibson’s book Mount Tamalpais and the Marin Municipal Water District [MMWD]: “As early as 1894, groups of citizens began to hold meetings at ‘Y’s Hall,’ in San Rafael, to express concern for the inadequate water system in Marin. Over the next 15 years those concerns grew louder…. In1911, the legislature passed laws that for the first time allowed for the creation of a publicly owned water system …. Immediately, volunteers in Marin began to circulate petitions to gather the necessary signatures for voter approval of a publicly owned system.”
In 1912 the voters of southeastern Marin approved creation of the MMWD (Today the entity is known as “Marin Water.”) The district incorporated on April 25th that year. Forming a municipal entity capable of supplying additional water was a fortuitous decision because Marin County was about to enter a period when rainfall totals were significantly less than average. The District’s first major reservoir, the Alpine Dam and Lake, was completed in 1919. This new facility provided water storage for about 1.1 billion gallons. In 1920 the District served a population of about 20,000 people meaning storage facilities held about 50 thousand gallons per consumer.
While the last two decades of the 19th century were wetter than average, the period from 1924 to 1934 yielded a meager 31 inches of average annual rainfall, the driest decade recorded in Marin County. Moreover, in 140 years of measuring rainfall, 1924–25 holds first place for the least amount recorded over a 12 month period — 19 inches. By 1930 the dry period of the late 1920s reduced the district’s storage supply to less than 40 thousand gallons per user. In response the Alpine Dam was raised in 1941. As of the completion of the raised dam the District’s total water supply grew to about 70 thousand gallons per resident of its service area.
The State of California Department of Water Resources (DWR) has identified four periods of severe statewide drought over the past 100 years. These periods were: 1929–34; 1976–77; 1987–92; and 2020–22. Marin also suffered below average rainfall at about the same times as identified by the State.
The MMWD continued to increase the capacity of its reservoirs during the period 1941 through 1982 by building Bon Tempe Lake, Kent Lake (including later raising Peters Dam), Nicasio Reservoir and Soulajule Reservoir. As a consequence, even with Marin’s strong growth at the time, in the 1980s the District had a supply of over 140 thousand gallons per user. The capacity of the district’s reservoirs has not been increased since 1982.
In the publication California’s Most Significant Droughts the DWR described the 1929–34 period as “…severe from a hydrologic perspective…on a par with similar events in the paleo-climate record.” Most of Marin’s major water supply projects were planned or built in the 1930s. Because of added supply and the county’s limited development, drought conditions did not seriously impact Marin.
Here’s the DWR summary description of the statewide drought of 1976–77: “Although only a two year event, its hydrology was severe…. The drought was notable for the impacts experienced by water agencies that were unprepared for such conditions…. Marin County was the large urbanized area most affected by the drought.” Annual rainfall in Marin averaged just over 22 inches during the two year dry period. The drought drained many of MMWD’s reservoirs leaving only small pools.
In 1977 a $10 million (about $50 million in 2022 dollars) temporary pipeline was laid on the bridge to the East Bay intended to tap into the State Water Project to answer the emergency. By 1982 the MMWD response to its obvious inadequate supply was to build the Soulajule Reservoir and to raise Peters Dam doubling the capacity of Kent Lake. The District also implemented a water conservation program and imported water from the Russian River following the 1977 crisis.
The six year 1987/92 drought was the first prolonged California dry period since the 1920s and 1930s. The drought caused MMWD to use water from the Soulajule Reservoir. The District limited use of this supply to drought periods only because of the expense of pumping water from the reservoir to the treatment plants. Water imported from the Russian River was an important added source to deal with the dry years.
During the first year of the current 2020–2022 drought Marin reported annual rainfall of less than 22 inches, the second driest year on record. A near average rainfall of 50 inches was recorded in 2021–2022. However, this annual total was primarily due to just two very severe storms amounting to nearly 60% of the total rain for the year. This pattern of unusually large storms separated by extended dry periods between storms is consistent with conditions frequently experienced in the era of climate change.
The capacity of current Marin Water reservoirs provide just two years of the water necessary to meet the District’s consumption demand. Including the imports from the Russian River the total local supply has been deemed by many as not adequate. To address this issue the district has initiated a 2022 study of alternatives to add to its supply. Under consideration are a wide range of possibilities: desalination; enlarged reservoir capacity; additional water import from Sonoma; import from the East Bay; use of treated waste water and increased conservation by consumers.
