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Home Land Landuse and Impervious Cover

Percent Hard Impervious Cover within Land Capability Classes

Status and Trend

Interpretation and Commentary


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Status: Considerably Better than Target
Trend: Insufficient data to determine trend.
Confidence: Low

  • Relevance - This indicator measures the percent of impervious cover on different land capability districts. Impervious cover is a primary indicator of land disturbance. Excessive impervious surface within a watershed can have far-reaching detrimental effects on water quality, surface hydrology, groundwater, soil health, fisheries, wildlife habitat suitability and vegetation growth. Impervious surfaces include hard coverage, which encompass man-made structures that act as complete barriers to prevent precipitation from infiltrating into the soil; common examples include roads, buildings, driveways, and parking lots; and compacted soil, which prevents most stormwater from infiltrating into the ground.
  • Adopted Standards  - Impervious cover shall comply with the Land-Capability Classification of the Lake Tahoe Basin, California-Nevada, A Guide For Planning, Bailey, 1974.
  • Indicator - Percent impervious cover within each land capability class.
  • Condition Status – When status scores were aggregated according to the methodology section, the overall average aggregated score was = 2.66, resulting in a determination of “considerably better than target.” Impervious cover within each capability class as determined by preliminary LiDAR/multispectral data modeling indicates existing hard impervious cover in Class 1b exceeds allowable land coverage by 657 acres, or 681 percent. All other land capability classes are estimated to have fewer existing acres of hard impervious cover than what is allowed. However, these numbers reflect the Regional aggregate, and there map be examples of smaller units of land that may be over-covered. Soft coverage has not been estimated for the Basin; the attainment status will likely need to be adjusted when soft coverage estimates and refined hard cover estimates are compiled and reported in December 2012.
  • Trend – The trend was determined to be “insufficient data to determine trend,” due to differences in data used, analysis methods, and because data presented here are preliminary. Although TRPA has used the best available science and technology over time to assess the Impervious Cover Threshold Standard, different imagery datasets (IKONOS collected in 2002, LiDAR collected in 2010), variation in the methods used to estimate impervious cover, along with an updated and improved soil survey, make comparison across evaluations inappropriate. The 2011 estimates of hard impervious cover are based on preliminary modeling from the 2010 imagery, in conjunction with the updated 2007 NRCS soil survey. In 2006, estimates of hard impervious cover were calculated using IKONOS imagery and the original 1972 soil survey.

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  • Confidence
    • Condition Status - There is “low” confidence in the current estimates of hard impervious cover because an accuracy assessment of the resulting impervious surface GIS layer has not yet been completed. In addition, evaluation techniques for soft coverage are currently being developed and, once completed, will help provide a more complete estimate of Basin-wide impervious cover.
    • Trend - Not applicable given trend determination.
    •  Overall Confidence - There is “low” overall confidence because of the low confidence in status and trend determinations.
  • Human and Environmental Drivers - Impervious cover is created through land use conversion from the natural to the built environment. This could be for commercial, residential, recreational, and other activities, and encompasses the spectrum of human uses that involve physical modification of the environment. The economy plays a large role in the housing market and the business environment, which are both historically among the most important drivers of new land coverage in the Basin. The recent economic downturn nationally and regionally may be partly responsible for the substantially lower new land coverage acres in 2006-2010.
  • Monitoring Approach – An objects-based image analysis (OBIA) system was developed to map land cover from the remotely sensed data. The first OBIA system established a baseline land cover map. The OBIA system algorithm was designed to produce accurate land cover data similar to what a human image analysis would generate, yet yield a clear economic advantage over manual interpretation. Particular attention was paid to insuring that the OBIA system was capable of leveraging data from both active and passive sensors to insure consistent and repeatable output over the entire study area. A second OBIA system will be developed and deployed to identify and quantify change using the original remotely sensed datasets, the base land cover map, and the newly acquired remotely sensed datasets (base map year + five years).
  • Monitoring Partners U.S. Geological Survey, Tahoe Regional Planning Agency, University of Vermont, Spatial Informatics Group, LLC., Watershed Sciences, LLC., and DigitalGlobe.




Distribution of Hard Impervious Cover

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Trend Charts

Chart data not available at this time.
Percentage of allowable land coverage within each capability class and estimated percentage of hard impervious cover in each capability class for the Lake Tahoe Basin. (Based on 2010 LiDAR and multispectral data with preliminary hard impervious surface modeling and updated 2007 NRCS soil survey.)

Additional Info



Additional Information

  3. Conceptual Model:
  4. Monitoring Plan:
Last Updated on Tuesday, 13 November 2012 11:15