Nature has devised an extraordinary system that stores rainfall in our watershed for plants, animals, and people to use all year long. A watershed is a drainage area defined by mountains and ridgelines, where all the streams and rivers flow to a common outlet. They are also called drainage basins because the surrounding mountains and hills work like a bowl, directing the water down to the bottom of a valley. Some of the water in a watershed can be found above ground in lakes, reservoirs, marshes, streams, and rivers. Most of the water is stored beneath the ground in aquifers and water tables.
Napa county has 3 distinct watersheds, each named after the main body of water flowing through them: Putah Creek Watershed, Suisun Creek Watershed, and Napa River Watershed. The Putah Creek Watershed includes Lake Berryessa and the land east of Atlas Peak and Howell Mountain and west of the Blue Ridge and Vaca Mountains, all the way up to the Lake County border. The Suisun Creek Watershed is in the southeastern portion of the county and contains the headwaters of Suisun Creek, which eventually flows into Suisun Bay in Solano County. The largest of these watersheds and the focus of our virutal tour is the Napa River Watershed, defined to the north by Mount Saint Helena, to the west by the Mayacama Range, and to the east by Howell Mountain, Atlas Peak and Mount George. The Napa River Watershed is home to 95% of the county's population and has its headwaters (beginning point) in the southern slopes of Mount Saint Helena.
The seasonal flow of Kimball Canyon Creek in Robert Louis Stevenson State Park marks the start of the Napa River, although some consider Kimball Reservoir, just north of Calistoga to be the true headwaters, because it holds water year round. A large portion of the northernmost headwaters is protected by the Land Trust of Napa County and is closed to the public. However, you can get a glimpse of the headwaters at Pioneer Park in Calistoga, where water from Kimball Reservoir flows into town and begins its journey to the bay.
From its northernmost point, the Napa River flows for 55 miles south through Calistoga, St. Helena, Rutherford, Yountville, and Napa until it reaches the Napa-Sonoma marshes near American Canyon and eventually empties into San Pablo Bay. Tributaries flow from steep forested slopes and hilly chaparral (brushy scrubland) to join together and form the Napa River. Some tributaries never make it to the river and instead their flow moves below the surface to feed underground aquifers (rocks and soil saturated with water), while others are fueled by mineral springs that bubble up through volcanic rock formations formed millions of years ago. Several have been dammed to store water for nearby cities, reducing the amount of flow that eventually makes it to the valley floor and into the Napa River. Large reservoirs in the Napa River Watershed include Lake Hennessey, Milliken Reservoir, Rector Reservoir, and Bell Canyon Reservoir.
As the river reaches the city of Napa, it is influenced by the tides of San Pablo Bay. Water from the Pacific Ocean makes its way inland from the San Francisco Bay and up into its northernmost arm, San Pablo Bay. Salty sea water from the bay mixes with the freshwater of the Napa River in the Napa-Sonoma marshes of the southernmost part of the watershed, creating a estuarine habitat for a wide variety of fish, birds, mammals, and amphibians. Tidal influences can be observed on the Napa River as far north as the Trancas Street Bridge. The rise and fall of the tide is especially obvious in downtown Napa where tidal flats become exposed during low tides. The brackish (mixture of salt and fresh water) estuaries of American Canyon mark the joining of Napa River Watershed with the broader San Francisco Bay Watershed, the dominant watershed of the region.
The Napa River Watershed has undergone many transformations over the past 200 years. Its communities have emerged as leaders in watershed conservation and development. Extensive river restoration and flood control projects are helping to return the river to a more natural state; wetlands restoration projects are repairing the damage of agricultural and commercial use. Innovative land stewardship is helping to improve the water quality for fish, animals, and people.
Join us as we explore fascinating features of Napa River Watershed and learn about the efforts to restore and preserve the health of our river. We’ll visit beaver dams, count fish, plant trees, build owl boxes and learn how wastewater is being repurposed to bring life back into wetlands and estuaries. You will see how government and community agencies are working together to balance agricultural needs with those of people and animals to create harmony and beauty in our valley, and how the history of the Napa River Watershed shaped the river and valley as we see it today. Learn more about how you too can be a better steward of our watershed or even become a citizen scientist! Designed for students, families, and the general community, we hope you’ll learn something new about the watershed we live in.
Check us out! Books and resources available from the Napa County Library:
1). Rivers: Natures Wondrous Waterways by David L. Harrison
2). Where Do Rivers Go, Momma? by Catherine Weyerhaeuser
3). About Habitats: Rivers and Streams
by Cathryn Sill
4). Rivers and Lakes by Simon Holland
5). Napa Valley Historical Ecology Atlas by Robin Grossinger