Research Areas > Wetlands > Historical Ecology > Coastal Watershed Historical Ecology

Project Group: Coastal Watershed Historical Ecology

SCCWRP Research

The overall goal of the watershed historical ecology program is to provide new understanding about a given historical baseline condition of streams and wetlands across southern California’s coastal watersheds based on information from the mid- to late-19th century through the early 20th century. This project will compile sentinel data sets on historic condition, and use these data to evaluate how the distribution of wetlands have changed over time in response to key changes in land use or stream management. The changes to be examined include distribution of wetland and riparian habitat in the watershed during the period from 1850-1910, structure and composition of riparian habitat changes over historical times, changes in riparian structure of the floodplain in wet vs. dry years, and spatial distribution of wetland and riparian vegetation community types and wildlife species.

Unlike contemporary habitat analysis, historical analysis relies on interpretation of multiple data sets that were not collected to meet the objectives of our analysis. Therefore, conclusions must be developed from multiple data sources that collectively provide a “weight of evidence” that supports inferences about historical condition. The process consisted of the following general steps:

1) Compile primary data sources on historical condition, including: maps, soil and geologic surveys, and aerial photography. Sources were considered ‘primary’ if they were collected using a structured procedure that allowed for general quality control at the time they were produced.

2) Use primary data sources to refine study area and to prioritize locations and time periods for additional analysis.

3) Compile secondary data sources that expand on or clarify primary sources. Secondary sources include personal and written accounts, ground-level photographs, and floral and faunal records.

4) Digitize and georeference acceptable data sources.

5) Overlay all suitable data sources to create an initial set of historical wetland polygons.

6) Classify inferred historical wetland polygons using a system that is compatible with the contemporary National Wetlands Inventory (NWI) mapping system. This allows comparison of historical and current wetland extent and distribution.

7) Assign confidence levels to the wetland polygons based on estimated accuracy and concordance of available data sources.

The first watershed that underwent study was the San Gabriel River Watershed. The next investigations looked at the lower Ventura River and lower Santa Clara River watersheds. A fourth planned investigation will focus on the Ballona Creek watershed.

• San Gabriel River Historical Ecology