Important Data Resources
This section of the web site is devoted to facts. We have assembled as much useful data as we have been able to find and posted it here. Occasionally when the data speaks for itself we will provide those conclusions as well. For opinions check our Political Action section.
We have assembled data in the following areas:Water level and rainfallWater level and rainfall
Westside Basin hydrogeology
Fauna & flora
History and land use
Emissions pathways, climate change, and impacts on California (pdf file)Water quality
This analysis, which has been widely reported in the media, was conducted by a team of 19 researchers, and appears in the Proceedings of the National Academy of Sciences. It's projections for the amount of water available in California over the course of the next century, with and/or without prompt action to curtail emission of greenhouse gases, is most alarming. Its implications for relying on "surplus system water" as a sustainable solution for maintaining Lake Merced are clear. We have also provided a summary of the implications of this analysis, prepared by Michale Hanemann, Director, California Climate Change Center, University of California, Berkeley.Lake level and rainfall data, monthly from May 1996
This page presents data in both chart and table formats. For data that you can more easily analyze choose one of the Excel files listed below. (The South Lake gauge has been out of service for nearly a year now. While repairs are being made, we have been unable to secure a current record of lake level from the Public Utilities Commission.)Change in lake level with rainfall data from September 1999
Since 1999 the lake has experienced a renewed downward trend in spite of near normal rainfall. We have tracked this on a separate chart that illustrates the decline of lake level that can be expected without continued addition of Hetch-Hetchy water.
N.B. Beginning in Summer 2003 the Public Utilities Commission has undertaken a program adding water to the lake. We have not continued to post lake levels, but leave this chart in place to indicate recent experience, about a 1-foot decline in lake level annually, without such additions.
Lake level vs. 10-year average rainfall from 1962
We have observed a good relationship between lake level and the prior 10-year average rainfall. This page plots that relationship for the past 40 years, pointing out the failure of the lake to respond to increased rainfall after the drought of the mid-nineties.
Lake level and rainfall, monthly data from 1996 (Excel)
Monthly lake level and rainfall data from 1979 (Excel)
Annual lake level and rainfall data from 1951 (Excel)
Monthly readings of rainfall taken at SFO from 1950 (Excel)
Quarterly readings of key quality parameters from February 1997 (Excel)
Dave Dingman, chemist with the Water Department in Milbrae, has taken quarterly water quality readings at Lake Merced for more than five years. These are presented here in both tabular and graphic format.
We have written to Jim Salerno, Environment Manager for the San Francisco Public Utilities Commission. Jim's department collects and publishes the water quality data usually reported bi-monthly by the PUC. We have noted several trends in this data that seem to have statitical significance, and have asked Jim to comment on their practical significance if any. We will publish that report here when it is available.For the past several months (as of February 2005) there have been unprecedently high readings of E-coliform bacteria, at first in North Lake and more recently in South Lake as well. (See reports in Political Action.)
Fortunately, very high readings of E-coli bacteria reported in North Lake for December 2004 proved to be the result of a scaling error that magnified the actual count tenfold. However, this error brought new focus on the need to develop a practical yet effective monitoring program to protect the health and safety of the lake's many users.We are working with the Public Utilities Commission Water Quality Bureau to develop a more effective program for water quality monitoring and pubic notice. Useful references can be found in these documents:
Westside Basin hydrogeologyModel Monitoring Program for Municipal Separate Storm Sewer Systems in Southern California, A report from the Stormwater Monitoring Coalition’s Model Monitoring Technical Committee, August 2004
The California Department of Health Services (Draft) Guidance for Freshwater Beaches.
Plankton and Ammonia readings seasonally indexed
Lake Merced Hydrology and Water Quality, by Vivian Matuk and Nick Salcedo, Graduate Students in Geography, San Francisco State UniversityTechnical Memorandum TM-18, published as a part of the San Francisco Groundwater Master Plan (1967) describes a model of the Westside Basin developed by the consulting firm CH2M Hill using the MicroFem simulation tool.Fauna and floraTable A provides a detailed description of both monitoring and production wells in the Westside Basin. (Excel file) The accompanying text describes the data collection procedures.Geology and Hydrogeology of Lake Merced, San Francisco, California, by Yu Shimuzu, Graduate Student, Geography, San Francisco State University
Table B describes land use, including per cent irrigated, and per cent impervious surface. (Excel file) Again, the accompanying text describes the data collection procedures.
The Climatology of Lake Merced, San Francisco, California, by Graeme Somerville. Graduate Student, Geography, San Francisco State UniversityField Surveys: Technical Memorandum (Draft), EDAW, February 5, 2003 (pdf file, 6.5MB)
Complete listing of birds both nesting and visitors at Lake MercedAnnual bird surveys: 1999 2001
Invertebrate Fauna at Lake Merced, by Nelia White, Graduate Student, Geography, San Francisco State University
Birds of Lake Merced, by Doug Johnson, Graduate Student, Geography
San Francisco State UniversityFish Species of Lake Merced, by Ian Singer, Graduate Student, Geography, San Francisco State University
Mammals, Reptiles and Amphibians of Lake Merced, by Elizabeth J. Proctor, Graduate Student, Geography, San Francisco State UniversityThe Flora at Lake Merced, by Juan Ochoa, Christopher Campbell, and Paul Pribor, Graduate Students, Geography, San Francisco State UniversityHistory and land useThe History of Human Use at Lake Merced, by Sara Marcellino and Brandon Jebens, Graduate Students, Dept of Geography, San Francisco State UniversityWeb statisticsWe continue to be pleased with the interest in Lake Merced. Check the number of visitors to this site each month.