What is a watershed?
The text book definition of a watershed is the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet. The Elkhorn Slough watershed stretches from the Pajaro Valley south to Castroville, and from the headwaters in San Benito County west to the Monterey Bay.
When it rains within the watershed, water "shed" from the land is carried downhill drop by drop into tributaries, streams, creeks and groundwaters eventually making its way into the Elkhorn Slough and with the outgoing tide to the Monterey Bay and Pacific Ocean. Water is the universal solvent meaning it can disolve more substances than any other liquid, but it also picks up and can carry with it the good and bad substances from all the lands it comes in contact with: the farms, grazing lands, residential areas and wild lands it traverses. So how we treat the land ultimately affects water quality for all the people, plants, and animals that depend on it at every level of the watershed- from the headwaters to the Ocean.
Elkhorn Slough and Surrounding Watersheds
Estuaries such as Elkhorn Slough are defined as coastal embayments consisting of deepwater subtidal habitats with adjacent intertidal wetlands. These estuarine habitats are usually semi-enclosed by land with open access to ocean waters that enter with the tides and are diluted by freshwater (Cowardin et al. 1979, Ferren et al. 1996).
Freshwater enters Elkhorn Slough from Carneros Creek and the Pajaro River (during fl ood events only) at the head of the estuary and the old Salinas River Channel draining the Tembladero watershed at the mouth of Elkhorn Slough. Intermittently during summer months, the water control structure between the Salinas River and Old Salinas River Channel is opened, and waters from the larger Salinas watershed may enter Elkhorn Slough. The Elkhorn Slough watershed is 30,292 acres. However, Elkhorn Slough is part of a larger interconnected network of estuarine habitats. Waters from the Moro Cojo watershed (13,349 acres) and Gabilan/Tembladero (Alisal) watershed (101,026 acres) also drain into Elkhorn Slough. These waters enter Elkhorn Slough through the Old Salinas River Channel at the Moss Landing South Harbor, where flooding tides push these waters at least three-quarters of the way up the estuary (Johnson et al. in press).
Further Reading / Sources:
Elkhorn Slough Tidal Wetland Project Team. 2007. Elkhorn Slough Tidal Wetland Strategic Plan. A report describing Elkhorn Slough’s estuarine habitats, main impacts, and broad conservation and restoration recommendations. 100 pp. (Download the whole plan or just parts here.)