Stemple Creek Watershed
The Stemple Creek watershed begins just west of Petaluma and empties into the Pacific Ocean through the Estero de San Antonio, draining 50 square miles. The watershed is characterized by grassy, rolling hills that are used extensively for agriculture. The drainage is cut almost exactly in half by the Sonoma-Marin county line. The watershed changes sharply from Highway 1 west. Slopes increase in steepness, and coastal scrub and dense stands of native perennial grasses take over the hills. The Estero de San Antonio, a small coastal lagoon, is part of the Gulf of the Farallones National Marine Sanctuary and is also included in the Central California Coast Biosphere Reserve (UNESCO Man and Biosphere Program). A sandbar often closes the mouth of the Estero in the summer or early fall. It remains closed until winter rains with heavy runoff break open the sandbar.
From the beginning of European settlement to the mid 1900s, the watershed has been farmed with small livestock herds and large areas of land cultivated for barley, wheat, vegetables, and potatoes. Poultry and egg production was an important part of the local economy from the 1930s through World War II.
Changes to Watershed Processes
A geomorphic and hydrodynamic analysis of the Estero de San Antonio prepared for the 1994 Enhancement Plan (Williams, et al 1993 1) found that 80% of the lagoon’s volume has been lost through historic sedimentation. This reduction in tidal prism has led to an increase in the frequency and duration of lagoon closures from the sandbar that forms at the mouth. Evidence from the 1992/93 winter rains indicated that natural scouring of the lagoon bed could occur over time if sediment delivery to the Estero is reduced.
The land draining into Stemple Creek is largely grassland. Willows have been re-established along parts of the mainstem and tributary streams; coastal oak woodland can still be found along some of the higher tributaries. Eucalyptus, planted in rows for windbreaks and fuel, is now one of the most common trees.
Stemple Creek was once a marginal Coho salmon and steelhead trout stream. A small dam for livestock built on the Button Ranch in the early 1960s closed off the last available spawning areas. Residents tell of dense flocks of waterfowl, but, as in most areas along the Pacific Flyway, their numbers have dropped. Farm ponds, especially those with shallow edges, now provide some of the best remaining habitat for waterfowl, northwestern pond turtles, and other aquatic species.
California Department of Fish and Game has identified the Estero de San Antonio and Estero Americano as among the most significant habitat areas in the State. It is a remarkable mosaic of intermingling habitat types—densely wooded riparian ravines, saltgrass areas, mudflats, eelgrass beds, and small freshwater ponds. The area between the two Esteros contains extensive areas of native coastal terrace prairie.
Fish and Wildlife
Special-status species in the watershed include California freshwater shrimp, northwestern pond turtle, tidewater goby, Myrtle’s silverspot butterfly, and California red-legged frog.
River otters have been observed in the Marin County portion of Stemple Creek east of Highway 1. Eelgrass beds in the Estero de San Antonio provide nursery habitat for Dungeness crabs. The Estero is used by over 40 species of waterfowl and is an important winter feeding area for migrating birds. Golden eagles are known to nest in the upper watershed.
Human Habitation, Land Use, and Resource Conservation
Land Use Imperviousness
Land use in the watershed is almost exclusively agricultural; 90% of the watershed is used for livestock grazing, mostly beef and sheep ranches in the Marin County portion, as well as some dairies. Sonoma County Agricultural Preservation and Open Space District and Marin Agricultural Land Trust are both active in the watershed, protecting agricultural land use through conservation easements.
Although the Estero itself is part of the Gulf of the Farallones National Marine Sanctuary, the land surrounding it is all privately owned. Since access across land is by permission only, recreational use is limited. There are no cities or towns in the watershed.
Resource conservation efforts in the watershed are extensive. In 1990, Stemple Creek was listed on the federal Environmental Protection Agency’s 303(d) list as an impaired waterbody due to excessive nutrients and sediment. In 1994, the Marin and Southern Sonoma County Resource Conservation Districts (Marin RCD and Southern Sonoma County RCD, respectively) completed an Enhancement Plan for the Stemple Creek/Estero de San Antonio watershed (Prunuske Chatham, Inc. 1994 2). Implementation of the enhancement plan has been a decentralized effort. Although the two RCDs have led the way with grant-sponsored projects, local landowners have also implemented many measures on their own and with support from NRCS. The Shrimp Club, a nationally-recognized project of Brookside School in San Anselmo, began its stream restoration work in Stemple Creek. The Shrimp Club and its successor, STRAW (Students and Teachers Restoring a Watershed, a project of the Bay Institute) have replanted native riparian vegetation for erosion control and habitat enhancement along 8 miles of mainstem Stemple Creek and its tributaries and their efforts in the watershed are ongoing.
In 1997, the North Coast Regional Water Quality Control Board adopted a Total Maximum Daily Load (TMDL) and Attainment Strategy for nutrients and sediment in the watershed (Salisbury 1997 3). The TMDL has been adopted into the Basin Plan for the North Coast. The Marin RCD has received Prop 50 funding for a project called “Conserving Our Watersheds: TMDL Implementation in Tomales Bay and Stemple Creek Watershed.” Through this program, the RCD supports ranchers in adopting voluntary conservation practices.
The 1994 Enhancement Plan states that over 80% of the accelerated erosion in the watershed comes from the lower watershed with large gully systems as the primary source. Gully stabilization projects have been implemented by local landowners with support from the RCDs and NRCS.
The two RCDs and NRCS have also collaborated to bring funding through the Watershed Protection and Flood Protection Act (Public Law 83-566) into the watershed to improve water quality.
Finally, the Stemple Creek watershed has been designated one of 24 special emphasis watersheds as part of the NRCS’ Conservation Effectiveness Assessment Program (CEAP). This Program is a joint effort of the NRCS, UC Cooperative Extension, the Agricultural Research Service, and the Departments of Land, Air, and Water Resources and Plant Sciences at UC Davis. The purposes of the project are to test models for predicting the water quality impacts of conservation practices, and to evaluate the effectiveness of dairy waste management systems, riparian restoration, and soil and water conservation practices for improving water quality in the Stemple Creek watershed.
For more information about Stemple Creek, please contact:
Southern Sonoma County Resource Conservation District at 707.794.1242 x5 or at http://www.sscrcd.org/.
Marin Resource Conservation District at 415.663.1170 or at http://www.marinrcd.org/
1 Geomorphic and Hydrodynamic Analysis for the Estero de San Antonio Enhancement Plan. In Stemple Creek/Estero de San Antonio Watershed Enhancement Plan.
2 Stemple Creek/Estero de San Antonio Watershed Enhancement Plan
3 Total Maximum Daily Load and Attainment Strategy for the Stemple Creek Watershed