The average annual rainfall for the period October 1979 through September 1996 measured by Roy Farrington Jones on Olive Avenue in Ross was 49.33 inches. The lowest rainfall during that period was 28.29 inches in water year 1990 (October 1989 through September 1990) and the highest, 90.75 inches during water year 1983.
Average annual rainfall at the Marin Municipal Water District gage at Lake Lagunitas for the period 1875 to 1995 was 52.63 inches. Although this gage is not within the watershed, it is representative of rainfall in Kentfield, Ross, and San Anselmo. The lowest value during that period was 19.70 inches for water year 1924; the highest, 112.15 inches for water year 1890.
Between 1951 and 1993, the U.S. Geological Survey maintained a stream gage just upstream of the Lagunitas Road Bridge in Ross. Since 1993, the Marin County Department of Public Works has gathered data at the gage. Between 1951 and 1993, the lowest flows occurred July through September 1977 when the stream was dry. The highest flows occurred in early January 1982, when the peak flow within the channel was 6000 cubic feet per second.
For more information:
Discharge.pdf (44 KB)