Indicator
Clarity - Vertical Extinction Coefficient (VEC)
2015 Evaluation
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2015 Evaluation
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Status
At or Somewhat Better Than Target
Trend
Little or No Change
Confidence
Moderate
Evaluation Map
Clarity VEC Map.JPG
Description

Locations of long-term monitoring sites for VEC and other water quality constituents. The Index Station is located along the west shore.

Rationale Details
At or somewhat better than target. The annual average in 2014 was a Vertical Extinction Coefficient of 0.075, which means the standard is in attainment. However, 12 of 27 VEC measures in 2014 were above the state standard of 0.08.
Little or no change. Since around year 2000, VEC measurements have been better than predicted by the long-term trend of linear decline observed since 1969. Statistical analysis supports the observation that the decline in VEC has slowed since 2000, and the overall trend is now better represented by a curve (see figure above), rather than a straight line. The line of best fit to describe the long-term trend was determined statistically using a polynomial regression.
Confidence Details
Moderate. The annual average in 2014 was a Vertical Extinction Coefficient of 0.075, which means the standard is current in attainment. However, 12 of 27 VEC measures in 2014 were above the state standard of 0.08 per meter.
High. According to the standard methodology of this report, the trend is statistically significant R² = 0.7672, P < 0.01.
Moderate. Overall confidence takes the lower of the two confidence determinations.
Outcomes
Programs and Actions Implemented to Improve Conditions
The TMDL Management System Handbook guides the actions of agencies in the Region to reduce inputs of nutrients and sediments into Lake Tahoe (Lahontan and NDEP, 2014). Stream environment zone (SEZ) restoration and enhancement, urban growth control limits, best management practices (BMPs) to reduce nutrient and sediment discharge from disturbed soils, retrofit regulations for private and commercial property BMPs, reducing private automobile use through improvements to public transit and alternative transportation modes (with the goal of reducing air pollution and the subsequent deposition of nitrogen, and fine sediment), and ongoing allocation of water quality mitigation funds to support erosion control and stormwater pollution control projects. Projects completed by EIP partners since between 2009 and 2015 have:

• Restored or enhanced 27,150 linear feet of stream channel
• Retrofitted 120.55 miles of road and decommissioned an additional 7.4 miles
• Restored or enhanced 120 acres of disturbed forested uplands
• Inspected 108.72 miles of unpaved non-urban roads and maintained 98.2 miles
• Issued 18,076 BMP certificates to commercial, multifamily and single family residential

Public outreach and educational campaigns (such as the “Take Care” campaign) highlight for residents and visitors what they can do maintain a healthy environment. Between 2012 and 2015 the South Tahoe Environmental Education Coalition delivered 36 educational programs and reached nearly 30,000 individuals.
Effectiveness of Programs and Actions
Each year the actions of the TMDL implementation partners are summarized and evaluated in the TMDL Performance Report (Larsen and Kuchnicki, 2015a).
Interim Target
No target set as the standard is in attainment.
Target Attainment Date
Standard is in attainment.
Recommendations
Analytic Approach
Consideration should be given to how attainment is assessed. Potential options include; 1) annual average, 2) multi-year average, and 3) with respect to individual measurements.
Monitoring Approach
No changes recommended
Modification of the Threshold Standard or Indicator
The VEC standard is a state standard. See recommended changes for modification of the analytic approach.
Attain or Maintain Threshold
No changes recommended. Continue TMDL implementation.
Additional Figures and Resources

No photos available.

No documents available.