USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

A collaborative definition, classification refinement, and mapping of the stream environment zones in the Lake Tahoe Basin

Principal Investigators:
David Saah, Spatial Informatics Group, LLC
Jason Moghaddas, Spatial Informatics Group, LLC
Ken Roby, Spatial Informatics Group, LLC
Shane Romsos, Spatial Informatics Group, LLC
Jarlath O'Neil-Dunne, Spatial Informatics Group, LLC
Josh Collins, San Francisco Estuary Institute
William Loftis, Spatial Informatics Group, LLC

Proposal [pdf]

Final Report [pdf]

Project Files [zip]

Please contact Shane Romsos with questions regarding the final report.

Project Summary

The Stream Environment Zone (SEZ) is a land designation unique to the Lake Tahoe Basin that includes lands surrounding and including streams, lakes and wetlands – areas that owe their physical and biological characteristics to the presence of surface water and/or shallow groundwater. In addition to providing water quality protection, SEZ conservation policies and management strategies conserve and protect aquatic and associated upland and riparian habitats, provide recreational opportunities and enhance scenic quality and associated real estate values. This project responded to Lake Tahoe Basin stakeholders’ identified needs to review and potentially update the current SEZ policy to ensure implementing ordinances and program elements are consistent with best available science and data, and support desired SEZ conditions, functions, processes and values.

For this project, our project team and individuals representing technical expertise from multiple Tahoe Basin agencies, a non-profit environmental group and other topic area experts were organized into task workgroups. One workgroup was tasked with the review and providing recommendations for potential changes to: 1) SEZ definitions, 2) SEZ field delineation criteria and indicators, 3) desired SEZ conditions, functions, processes and values, and 4) SEZ classification approaches. A second workgroup was charged with mapping aquatic resources (e.g., streams, wetlands, lakes, seeps, and springs) and SEZs in the Tahoe Basin using current data and mapping procedures. This report summarizes the findings and recommendations of these workgroups.

No changes to TRPA SEZ definitions are recommended, however several recommended changes to SEZ field delineation indicators are proposed for consideration by implementing agencies. Recommended changes would provide indicators that are technically sound and can be consistently applied across SEZ specialists. Proposed changes maintain the fundamental purpose and elements of the current SEZ delineation criteria in that the approach would still be based on soil, geomorphic, hydrologic and vegetation characteristics and the existing core concept of primary and secondary SEZ indicators would also be retained. The primary recommended changes are related to vegetation and soil saturation indicators and are based on advances to the understanding of riparian and wetland systems that have been incorporated into industry standards since the adoption of existing Lake Tahoe Basin SEZ policy. Minor refinements to aquatic habitat and floodplain indicators are also recommended to improve clarity in their application.

Existing direction for the use of vegetation to identify SEZ boundaries is based on a description of Tahoe Basin vegetation communities published in 1971. Field work related to SEZ delineation has since demonstrated that that several of the plant species listed within different identified riparian vegetation communities are rarely, if ever found in the Tahoe Basin. To make consistent with current industry wetland vegetation identification standards, the Field Delineation Workgroup recommends using "wetland species indicator status" instead.

Existing soils indicators include and rely heavily on soil maps units. This approach has proved problematic, because soil map units include some areas that would be improperly defined as SEZ and also miss areas that should be defined as SEZ. Consequently, the Field Delineation Workgroup recommends eliminating soil map units as a means of identifying SEZ, and instead using soil characteristics observed in the field. The specific recommended indicators include presence of hydric soils, presence of groundwater and evidence of saturated soils.

Another Field Delineation Workgroup finding recommends three intensities of SEZ survey and delineation depending on the type of project being proposed. The most spatially extensive (and least field intensive) survey and delineation level includes mapping of SEZs for broad scale planning and tracking. An intermediate level of intensity would be applied for delineating SEZ boundaries in the field when extensive and non-permanent activities, such as fuels reduction projects, are proposed in or near SEZs. In such cases, physical and ecological SEZ indicators would be used but would be applied conservatively to yield SEZs boundaries typically wider than those delineated by the most intensive delineation survey. The most intensive SEZ field delineation techniques would be applied on the ground when a precise determination of SEZ boundaries is needed, for example in cases where a permanent development project is proposed.

Three map and map-related products were produced for this project: 1) a Basin-wide aquatic resource map (showing more accurate and precise locations, boundaries and alignments of stream tributaries, wetlands, springs, seeps, ponds and lakes), 2) a SEZ classification scheme based on the review of previously established riparian and wetland classification system and informed by the project’s field and mapping workgroups, and 3) a Basin-wide SEZ map showing the approximate boundaries of different SEZ types (following the classification scheme agreed to by workgroup participants).