Sonoma Valley Historical Hydrology Mapping Project Phase I FINAL REPORT Task 2.4b Arthur Dawson, Baseline Consulting Alex Young, Sonoma Ecology Center Rebecca Lawton Consulting Funded by the Sonoma County Water Agency November 2016 Prepared by: Baseline Consulting, 13750 Arnold Drive, P.O. Box 207, Glen Ellen, CA 95442 Sonoma Ecology Center, P.O. Box 1486, Eldridge, CA 95431 Rebecca Lawton Consulting, P.O. Box 654, Vineburg, CA 95687 BASELINE CONSULTING, SONOMA ECOLOGY CENTER, REBECCA LAWTON CONSULTING 2 CONTENTS OVERVIEW 3 METHODS 5 RESULTS 17 DISCUSSION 22 Comparison of Modern & Historical Conditions 24 RECOMMENDATIONS 27 BIBLIOGRAPHY 30 FIGURES 1. Project Area, Sonoma Valley Watershed, Sonoma County, California 4 2. Definition of Terms and Assumptions 6 3. Wetland Designations Used in this Study 10 4. Certainty Level Standards 14 5. Data Limitations and Temporal Context 15 6. Dates of Sources Used in this Study in Relation to Long-Term Rainfall 16 7. Estimated Pre-Settlement Freshwater Channels and Wetlands 18 8. Estimated Pre-Settlement Freshwater Channels and Wetlands (LIDAR Basemap) 19 9. Estimated Pre-Settlement Freshwater Channels and Wetlands (USGS quads) 20 10. Certainty Levels for Presence of Features Mapped from Historical Sources 21 11. Average annual hydrographs for the historical watershed for Napa River 25 APPENDIXES A. Selected Historical Maps A1. Detail from O’Farrell’s 1848 Rancho Petaluma Map A-2 A2. Confluence of Agua Caliente and Sonoma Creeks in 1860 A-3 A3. Confluence of Agua Caliente and Sonoma Creeks in 1980 A-4 A4. Alternate Channels Occupied by Pythian, an Unnamed Creek, and Sonoma Creek A-5 B. Fieldwork Notes and Selected Photos B1. Field Survey Locations B-6 D. Phase II Mapping Sample D1. Sample High-Resolution Map C-1 SONOMA VALLEY HISTORICAL HYDROLOGY MAPPING PROJECT, TASK 2.4.b: FINAL REPORT BASELINE CONSULTING, SONOMA ECOLOGY CENTER, REBECCA LAWTON CONSULTING 3 OVERVIEW Rationale. Prior to extensive human modification, the Sonoma Valley watershed (Figure 1) enjoyed an abundance of surface and ground water, extensive wetlands, and high water quality. Previous studies (Lawton 2006; Micheli 2006; San Francisco Estuary Institute 2012; see also “Comparison of Modern & Historical Conditions,” pg. 24) have demonstrated that changes over the last two centuries have caused increased runoff, flooding, and sedimentation; decreased surface and groundwater; degraded habitat for salmonids and other species; and a loss of wetlands. In coming years, climate change is expected to aggravate these conditions with projected increases in both flooding and drought. Understanding how the watershed functioned before significant human modification is essential to planning projects that will reduce flooding, increase groundwater recharge, improve water quality and restore habitat. Project Goal. To complete a medium-resolution (1:72,000) historical hydrology map documenting historical freshwater channels and wetlands recorded for the Sonoma Valley watershed at the time of European-style settlement in the mid-19th century. Approach. An initial literature review was followed by a review and assessment of previous efforts in Sonoma Valley, particularly the Sediment Source Analysis (Lawton 2006) and the uncompleted Critical Coastal Areas (CCA) project begun in 2007. Geomorphologist Laurel Collins of Watershed Sciences and botanist and wetland expert Phillip Northen also provided additional guidance and feedback at various stages of the project. Drawing from, refining, and expanding on these earlier studies, the current project compiled, analyzed, integrated, and mapped data from a wide variety of sources into a computerized Geographic Information System (GIS). Sources included historical maps, documents, and photos; soil and heritage oak surveys; and oral histories from local elders. Historical channels and wetlands were mapped. The majority of sources that were consulted included data up to the 19th century, while a few also included information from the early 20th century (see Appendix A for examples). After verifying the historical presence of a feature, more recent sources were used to refine its attributes. In particular, Sonoma County’s LIDAR data was invaluable for identifying and mapping historical channel alignments to a high degree of precision. The Sonoma County Soil Survey (1972) was used to support the identification of seasonal wetlands from early aerial photos. Once the draft map was completed, field surveys were undertaken to “ground-truth” sites where historical conditions were in question and to test preliminary conclusions. In some cases, field evidence supported the mapping of features that appeared ambiguous in the historical record. In other cases, where field evidence was lacking, SONOMA VALLEY HISTORICAL HYDROLOGY MAPPING PROJECT, TASK 2.4.b: FINAL REPORT BASELINE CONSULTING, SONOMA ECOLOGY CENTER, REBECCA LAWTON CONSULTING 4 features or attributes were removed from the draft map. A rubric for assigning “certainty levels” was refined from versions used in other studies (Dawson 2010, 2013; Grossinger 2001, 2012). This rubric was based on the strength of evidence for each mapped feature’s historical presence, dimensions, and location. Certainty levels of high, medium, and low were assigned under each of these categories to all mapped features. The final maps (pages 18 - 21) are based on dozens of historical sources, informed by similar studies in Sonoma County and elsewhere in the Bay Area, years of fieldwork and local observations, and the expertise of many scientists, residents, and local elders. More than 300 channel segments and wetland features were mapped. The resulting maps are key tools in understanding how the Sonoma Valley watershed functioned before significant human modification. Next Steps. Phase I of this project, which is covered in this report, provides a medium- resolution hydrological picture of the Sonoma Valley watershed in the mid-19th century. Phase II, the second and final part of this effort, will use the information developed in Phase I to identify sites that show promise for restoring hydrological function. SONOMA VALLEY These sites will be mapped at a high WATERSHED level of detail (1:18,000 or better) to support modeling, change analysis, and multi-benefit project planning designed to reduce flooding, increase groundwater retention and recharge, improve water quality, and restore habitat. This report is intended to assist the Sonoma County Water Agency, the North Coast Water Quality Control Board, Valley of the Moon Water District, the City of Sonoma, the Sonoma Ecology Center, the Sonoma Resource Conservation District, private landowners, and other stakeholders concerned with improving the ecological health of Sonoma Valley. FIGURE 1. Project Area. Sonoma Valley Watershed, Sonoma County, California SONOMA VALLEY HISTORICAL HYDROLOGY MAPPING PROJECT, TASK 2.4.b: FINAL REPORT BASELINE CONSULTING, SONOMA ECOLOGY CENTER, REBECCA LAWTON CONSULTING 5 METHODS The Sonoma Valley Historical Hydrology Mapping Project was carried out by Arthur Dawson of Baseline Consulting, Alex Young of the Sonoma Ecology Center, and Rebecca Lawton of Rebecca Lawton Consulting. The following sequence of methods and steps was used in developing the estimated pre-settlement freshwater channels and wetlands map of the Sonoma Valley watershed. Initial Planning and Review. Project staff held an initial meeting to refine our approach and address the following questions. What is our working definition of a “mappable channel?” How can the recently acquired LIDAR data be incorporated into this effort? Do certainty level standards need to be adjusted, refined, and/or clarified? How should distributary systems be evaluated and mapped? What is our working definition of a “mappable wetland feature”? What criteria should be used for delineating various habitat types? Is our approach compatible with that used for mapping historical aquatic resources in the EcoAtlas? What should be included in the literature review? What are our definitions and assumptions (Figure 2)? The literature review (see Bibliography) preceded a review of previous efforts to map and understand historical conditions in Sonoma Valley, particularly the 2010 draft map from the CCA project. All features from the CCA map were reviewed. After identifying needed changes, it was decided that the most efficient way to proceed was to draw and attribute all features for the current project from scratch. Technical Guidance. Before commencing the initial mapping, the project team conferred with experts Laurel Collins, geomorphologist with Watershed Sciences; and Phillip Northen, wetland delineation expert and professor emeritus at Sonoma State University. Robin Grossinger of the San Francisco Estuary Institute (SFEI) was contacted but was unable to provide direct feedback on this project. Project staff are familiar with SFEI’s approach, having worked with them on the CCA mapping effort and reviewed their work in other Bay Area watersheds (see Bibliography). Source Compilation and Georectification. With one exception, all mapping sources (see Bibliography) for this project had already been compiled and were ready to bring into GIS for mapping. The exception was a map of the upper watershed recently discovered in the private collection of Kenwood resident George MacLeod (Rowe 1871). This map was an SONOMA VALLEY HISTORICAL HYDROLOGY MAPPING PROJECT, TASK 2.4.b: FINAL REPORT BASELINE CONSULTING, SONOMA ECOLOGY CENTER, REBECCA LAWTON CONSULTING 6 Figure