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Home Water Streams and Wetlands

Restoration Acres of Naturally Functioning Stream Environment Zones

Status and Trend

Interpretation and Commentary

Status: Considerably Worse Than Target
Trend: Moderate Improvement
Confidence: High (acres restored)

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  • Relevance - This indicator measures the progress made toward the restoration and enhancement of stream environment zones in areas within and adjacent to urban areas, and areas considered more natural or rural. A major importance of SEZs is their ability to provide natural treatment, storage, and conveyance of surface runoff. Encroachment on these areas reduces their potential to filter sediment and nutrients, and also reduces the amount of surface runoff they can effectively treat. Natural SEZs also provide open space, flood flow capacity, riparian vegetation, and fish and wildlife habitat, and buffer urban uses in developed areas. SEZ protection and restoration help achieve all other environmental Threshold Standards, including water quality, wildlife, fisheries, vegetation preservation, recreation, and scenic resources. Even seemingly unrelated Threshold Standards such as air quality and noise are affected by SEZs. For instance, aspen stands in SEZs next to roadways have been shown to help physically block air particulates from spreading to adjacent areas. Such vegetation also help moderate roadway noise.
  • Adopted Standards  - Preserve existing naturally functioning SEZ lands in their natural hydrologic condition, restore all disturbed SEZ lands in undeveloped, un-subdivided lands, and restore 25 percent of the SEZ lands that have been identified as disturbed, developed, or subdivided, to attain a five percent total increase in the area of naturally functioning SEZ lands.
  • Indicator - Acres of restored SEZs in urban and rural areas.

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  • StatusPreserve existing naturally functioning SEZ lands in their natural hydrologic condition: This element of the Threshold Standard is a management directive, which cannot be quantified other than to note that TRPA, since the adoption of the 1987 Regional Plan, prohibits the creation of any new coverage in SEZ unless it can be fully mitigated. No indicator has been developed to verify the preservation of naturally functioning SEZs; indeed, preservation has never been defined. However, preservation is commonly interpreted to mean that no new development should occur in naturally functioning SEZs. When interpreted in this way, it could be concluded that the Region is achieving this element of the adopted Threshold Standard. In addition, land acquisition of SEZs by TRPA partner agencies also aids in achieving this element of the Threshold Standard. Basin-wide policies and programs are in place that recognize the myriad critical functions of SEZs, but it is unclear to what extent naturally functioning SEZs are being “preserved” considering that past SEZ mapping efforts were limited to urban and urban influence areas (i.e., did not map SEZ in more remote locations within the Region).

    Restore all disturbed SEZ lands in undeveloped, un-subdivided lands: This component of the Threshold Standard in numerical however has not been consistently quantified across Threshold Evaluations. No current estimates for the acres of disturbed SEZs in this category are available. “Undeveloped, un-subdivided” has been interpreted in past Threshold Evaluations to be those lands outside the urban boundary. Many SEZ restoration projects in these areas have occurred, are ongoing, or are being planned, but a comprehensive database for tracking them has not been developed. Acres of restored SEZs for this category for the period 2005-2011 was 83.5 acres. The majority of SEZ projects in “undeveloped, un-subdivided” areas are vegetation enhancement projects, and totaled 695 acres. Because this element of the Threshold Standard is not the focus of the Threshold Standard, no status determination was made.

    Restore 25 percent of the SEZ lands that have been identified as disturbed, developed or subdivided, to attain a five percent total increase in the area of naturally functioning SEZ lands: There are approximately 21,944 acres of SEZ in the Lake Tahoe Region, which is about 11 percent of the Basin area (TRPA 2001). A total of 4,400 acres of these SEZs are estimated to be “disturbed, developed, or subdivided.” The Threshold Standard calls for 25 percent of this 4,400 acres, or 1,100 acres, to be restored. Total SEZ restoration acreage from 1980 to 2011, for projects completed in, or adjacent to “disturbed, developed or subdivided” areas (i.e. urban boundary or urban areas), is 546 acres. This is about 50 percent of the target achieved; thus, the Threshold Standard status is designated “considerably worse than target.” An additional 554 acres is needed to achieve the 1,100 acre Threshold Standard. Restored SEZ acres are from stream channel restoration projects only, recognizing that an addition 801 acres of vegetation enhancement and restoration has been completed outside of the “urban area” (see Table below).

    Vegetation enhancement projects may improve SEZ biologic and hydrologic functions, but have not been considered SEZ restoration in the past. These projects have been completed in SEZs throughout the Basin, and total 23 acres in or adjacent to urban areas, and 695 acres outside the urban areas.

    The following table provides a summary of SEZ restoration acres and vegetation enhancement acres from 1980-2011. SEZs restored within or adjacent to “disturbed, developed or subdivided” areas (i.e. urban areas) contribute to the 25 percent SEZ restoration goal. Source: 2001 and 2006 Threshold Evaluations and EIP database.

      Within or Adjacent to Disturbed, Developed or Subdivided Areas Within Undeveloped, Un-subdivided Areas Total
    Acres of SEZ Restored 546 83.5 629.3
    Acres of Vegetation Enhancement in SEZ 23 695 718
    Total Acres 569 778.5 1,347.3
  • Trend The average restoration rate in or adjacent to urban areas for the period of record 1980-2011 is 17.6 acres per year resulting in a trend determination of “moderate improvement” (1.6 percent SEZ area restored/year).


  • Status – There is “high” confidence in the current status determination for SEZ restoration acreage because the project information was provided directly from EIP partner agencies and previous Threshold Evaluation reports that documented completed projects. However, the effectiveness of these projects for achieving the restoration objective of restoring “natural hydrologic function” is “unknown” because effectiveness monitoring efforts have not been sufficiently implemented.
  • Trends – Even though a statistical analysis was not used to test if trends were significant, there is “high” confidence in the cumulative accounting of acres restored because partner agencies regularly track and report project information.
  • Overall Confidence - Overall, there is “high” confidence in the status and trend information related to acres of SEZ restored. However, there is low confidence in our understanding of the effectiveness of SEZ restoration efforts.
  • Human and Environmental Drivers - SEZs have been disturbed in the Lake Tahoe Basin since the 1800s through logging, grazing, stream and river channelization, damming, fire suppression, and other activities, with environmental consequences that are still evident today. These legacy issues, along with continuing development pressure, have required comprehensive SEZ restoration Basin-wide. These legacy issues have also required regulations and policies that prevent development and limit disturbance in SEZs, and support public acquisition of these sensitive parcels. Restoration efforts by Basin partners are occurring, with the rate driven by available funding, primarily from the federal and state governments.
  • Monitoring Approach – SEZ restoration projects are tracked by the agencies that implement them. SEZ restoration effectiveness monitoring sometimes occurs on a project-by-project basis. However, because data are often collected for different purposes, analysis of Regional SEZ restoration effectiveness is limited.
  • Monitoring Partners – California Tahoe Conservancy, U.S. Forest Service, Nevada State Lands, El Dorado County, Placer County, City of South Lake Tahoe and all EIP partners.




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Locations of SEZ restoration projects completed in the Lake Tahoe Basin, 2005 to 2011.

Trend Charts

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Cumulative total acres of SEZ restored within or adjacent to the urban boundary during three different periods in the Lake Tahoe Region. The target is to restore 1,100 acres. Source: 2001 and 2006 TRPA Threshold Evaluations and EIP database.

Additional Info


Additional Information

Last Updated on Tuesday, 13 November 2012 06:56