Water Resources Division Annual Report - Fiscal Year 2017-18 WaterResourcesAR-FY17_18 | Page 21

Forward Thinking (continued)
RESOURCE MANAGEMENT AT LAKE MERCED
Lake Merced is made up of four interconnected lakes and provides a vital link for wildlife, particularly for
migrating birds. The Lake also provides a regional recreational venue offering fishing, boating, bicycling,
and wildlife viewing. In an emergency, Lake Merced water can also be used for firefighting or sanitation
purposes if no other sources of water are available. SFPUC has identified a goal of restoring water levels
in the Lake to serve beneficial uses and provide a reliable emergency non- potable water supply. The
SFPUC and the City of Daly City are working together to improve the Vista Grande stormwater system,
which drains the northwestern portion of Daly City and an unincorporated portion of San Mateo County –
areas originally within the watershed of Lake Merced. Project goals include improving stormwater drainage,
minimizing flooding risk and providing a sustainable water source for Lake Merced management. The
project environmental review was completed in 2018.
The SFPUC is currently implementing a Demonstration Aeration Mixing Project to determine if water quality
can be improved in the southern portion of Lake Merced’s South Lake. The project installed 1,500 feet of PVC
tubing, connected to three air compressors located at the Lake Merced Pump Station. Compressed air is
pumped through these pipes connected to diffusers located along the bottom of the lake. The compressed
air released at the bottom of the lake assists in mixing various lake layers, potentially minimizing periods
of very low dissolved oxygen concentrations that fall below the warm water quality objective of 5 mg/l.
This could result in higher dissolved oxygen levels within the lower layers of the lake and general lake water
quality improvement. The system was installed and activated in July 2017. The SFPUC is currently compiling
and evaluating the resulting data to determine whether there is sufficient improvement in dissolved oxygen
concentrations to justify implementation of a larger scale aeration mixing project.
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