Indicator
Percent of Land Coverage Within Land Capability Class 4 (allow up to 20% impervious coverage)
2019 Evaluation
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Lands classified as land capability class 4 are considered non-sensitive in the Tahoe Region and can support development. The percent of land coverage within land capability class 4 indicator measures the percent of land coverage on class 4 lands in the Tahoe Region. The indicator allows up to 20 percent impervious coverage within land capability class 4. This non-sensitive land capability class includes scattered areas with moderately steep slopes that have moderate erosion hazards.

Status
Percent cover in each Bailey land capability class relative to the allowable coverage in class.
2019 Evaluation
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Status
Considerably Better Than Target
Trend
Little or No Change
Confidence
Moderate
Applicable Standard
SC6: Impervious cover shall comply with the "Land Capability Classification of the Lake Tahoe Basin, California-Nevada, A Guide for Planning", Bailey, 1974. Allowable percent of impervious cover in Land Capability subclass 4 - 20%.
Key Points
  • Impervious coverage within class 4 is estimated to be 1,322 acres, less than the threshold standard of 6,289 acres.
  • Approximately 16 percent of the land area in the Tahoe Region is class 4. 
  • Only 21 percent of the regional allowable coverage in class 4 has been utilized. 
Evaluation Map
Description

Land capability Class 4 lands and impervious surfaces within the Tahoe Region

About the Threshold
This indicator measures the percent of land coverage on different land capability classes as described by Bailey (Bailey, 1974) and updated with the most recent soil survey by the Natural Resources Conservation Service (NRCS) in 2007 (Loftis, 2007; USDA-NRCS, 2007). Impervious cover is a primary indicator of land disturbance. Excessive impervious surface within a watershed contributes to sediment and nutrient inputs to Lake Tahoe and its tributaries impairing water quality, altering surface hydrology and groundwater recharge regimes. The results are often negative impacts on soil health, fisheries, wildlife habitat, and vegetation growth. Impervious surfaces include hard coverage such as roads, buildings, driveways, and parking lots, and soft coverage with soil compaction as a result of use, but where no structure is in place.
Impervious cover is created through use or development on natural lands. 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 among the most important drivers of new land coverage in the basin.
Delivering and Measuring Success

No related projects or programs defined for this indicator.

Rationale Details
Impervious cover within each land capability class was determined by an analysis of LiDAR/multispectral data collected in 2019. Land capability Class 4 has fewer existing acres of impervious coverage than is allowed under Bailey, 1,322 acres of existing impervious surfaces with the threshold standard of 6,289 acres. This makes it "considerably better than target."
The trends for Impervious cover within each land capability class was determined to be "little or no change".
Confidence Details
Moderate. TRPA has used the best available science and technology over time to assess the Impervious Cover Threshold Standard, different imagery datasets (4-band IKONOS collected in 2002, LiDAR and 8-band multispectral collected in 2010 and 2019). However, because of variation in the methods used to assess impervious surface features and estimate impervious cover, the comparison across evaluations is unsuitable.
Moderate. There is “moderate” confidence in the current estimates of impervious cover from the LiDAR data and the resulting impervious surface layer.
Moderate. There is “moderate” overall confidence base on the accuracy assessment of the impervious surface data and the land capability class results.
Additional Figures and Resources

No documents available.