The Spring snow melt discharge record-- Merced River at Happy Isles, Yosemite National Park-- is a valuable, pristine baseline for identifying downstream spring flows to San Francisco Bay. Decadal averages filter out the large year-to-year fluctuations. The Hetch Hetchy Reservoir, on Merced's twin sister Tuolumne River, is used to put the discharge decrease into perspective.

Before and after Hetch Hetchy Reservoir, 1923
Photos courtesy of San Francisco Water Department
Click here for a closer look at these photos

The volume of water in the photo is one Hetch Hetchy unit.
1 Hetch Hetchy unit:
= 360,000 acre-feet
= 120,000 acres of irrigated farm land per year
=  59,000,000 toilet flushes
= 190,000,000 glasses of water

	In this column, follow the decline in discharge and rise in San Francisco Bay salinity.

Simulated decadal rise in South Bay salinity
1932-1981