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Wilderness and Roadless & Critical Wildlife Habitat Area

Status and Trend

Interpretation and Commentary

Wilderness and Roadless

Status: At or Somewhat Better Than Target
Trend: Moderate Improvement
Confidence: Low

Critical Wildlife Habitat

Status: Considerably Worse Than Target
Trend: Insufficient Data to Determine
Confidence: Low

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  • Relevance - This indicator measures 24-hour noise levels in the Wilderness and Roadless and Critical Wildlife land use categories in the Lake Tahoe Basin. Noise by definition is “unwanted sound” and is therefore a subjective reaction to acoustical energy or sound levels. In recent years, visitors to and residents of the Lake Tahoe Basin have expressed concerns about the decline in serenity of their community and their enjoyment of the outdoors due to excessive noise from sources such as on-highway vehicles, off-highway vehicles, over-snow vehicles, watercraft and aircraft(TRPA 2007c). Excessive noise levels, specifically in wilderness and critical wildlife habitat areas, can be especially disruptive in environmentally sensitive natural areas. Agencies in the Basin have adopted specific restrictions and Threshold Standards to protect sensitive wildlife habitat, and have identified this unique fauna on a Special Interest Species list. In addition to existing federal, state, and local noise control regulations toaddress impacts of noise on both wildlife and people, the Tahoe Regional Planning Agency adopted Community Noise Equivalent Levels (CNEL) for all land use categories in the Basin.
  • Adopted Standards  - For the Wilderness/Roadless and Critical Wildlife Habitat land use category, noise levels shall not exceed a CNEL of 45 dBA.
  • Indicator - Number of exceedances of the Wilderness/Roadless and Critical Wildlife Habitat land use category CNEL (A-weighted Decibel (dBA)). The A-weighted decibel measurement is used in evaluating the effects of environmental and industrial noise effects on human health.
  • StatusWilderness and Roadless The Wilderness and Roadless land use category was previously reported in “non-attainment” in 1991 (46 dBA) (Engineering Dynamics 1991). In 2011, an annual mean CNEL value of 38.5 dBA was measured, ranging from 38 to 39 dBA (TRPA 2011d). A status of “somewhat better than target” was determined because it was 13% better than the adopted standard.
  • Status Critical Wildlife Areas In 2011, an annual mean CNEL value of 54 dBA (range 46 to 58 dBA) for critical wildlife areas was measured (TRPA 2011d). A status of “considerably worse than target” was determined because the indicator was 29% worse than the adopted Threshold Standard.
  • TrendWilderness and Roadless This land use category has only been measured once in 1991 when it was determined that CNEL was 46 dBA. Change in CNEL for the wilderness and roadless areas land use category between 1991 and 2011 was -0.35 dBA/year or -0.8% indicating a trend determination of “moderate improvement.”
  • Trend Critical Wildlife Areas No CNEL data has been collected or reported prior to 2011 for the Critical Wildlife Habitat land use category. Consequently, it was not possible to characterize change in CNEL for this land use category; the trend was determined to be “unknown” because there was “insufficient data to determine trend.”

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  • Confidence
    • Status - Even though 1) noise monitoring equipment was calibrated according to manufacturers’ specifications, 2) sampled land use units and locations within each land use category were randomly selected to improve inferences about the population of these land uses, and 3) additional sampling effort was deployed in 2011, a documented and peer-reviewed protocol for CNEL monitoring does not exist. Consequently, the confidence in the status was determined to be “moderate,” and the spatial and temporal characterization of CNEL across these land use types.
    • Trend -  The confidence in the trend for both land use categories was determined to be “low” due to insufficient available data and inconsistent monitoring of this indicator.
    •  Overall Confidence - The overall confidence for the Wilderness and Roadless and Critical Wildlife Habitat land use categories was determined to be “low” because there is “medium” confidence in status and “low” confidence in trend.
  • Human and Environmental Drivers - Noise sources that affect Critical Wildlife Habitat and Wilderness and Roadless areas in the Basin are primarily generated from automobiles, motorized watercraft, aircraft and other recreational activity(TRPA 2011c).Natural events such as thunderstorms, wave slap, and wind can influence noise levels as environmental drivers(TRPA 2011c).
  • Monitoring Approach – There is currently no established peer-reviewed monitoring plan or protocol for monitoring and evaluating the CNEL indicator. Historical monitoring consisted of gathering a single 24-hour sample per measured plan area. Threshold Standard attainment status was based on a single sample representing a land use type. In contrast to historic monitoring efforts, a more comprehensive CNEL monitoring effort was implemented in 2011. The 2011 monitoring approach was based on recommendations provided by a noise expert (Brown-Buntin Associates, Inc.). This approach included randomized land use unit sampling within land use categories, and a replicated and intensified sampling effort that spanned multiple 24-hour periods to capture the variation in CNEL.
  • Monitoring Partners – Monitoring was conducted by TRPA with land access granted by the U.S. Forest Service and California State Parks.


  • Monitoring Plan
  • Conceptual Model


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A map of Wilderness and Roadless and Critical Wildlife Habitat land use category areas in the Basin, relative to monitoring locations.

Trend Charts

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High and low single day CNEL values (bar endpoints), with annual mean CNEL in land use categories having a Threshold Standard of CNEL 45 dBA from 1991 to 2011. Source: TRPA noise monitoring data, Engineering Dynamics, Inc.

Additional Info


Additional Information

Last Updated on Wednesday, 19 September 2012 14:11