Reduce Fine Sediment Particle Load
This indicator measures the amount of fine sediment load reduction achieved in the Lake Tahoe Region. Sediment (particularly fine sediment) delivered to Lake Tahoe is known to directly affect the transparency of Lake Tahoe. Excessive amounts of fine sediment are the leading cause of impairment in streams and lakes of the United States. Landscape disturbances including, but not limited to, impervious road and parking lot surfaces, residential and commercial development, wildfire, and the degradation of stream environment zones, can contribute to sediment inputs to the lake and its tributaries. Fine sediment reductions are monitored by partners through the Lake Tahoe Total Maximum Daily Load (TMDL) program.
Status
Evaluation Map
Lake Clarity Tracker Projects
2023 Evaluation
- Status
- At or Somewhat Better Than Target
- Trend
- Moderate Improvement
- Confidence
- Moderate
Applicable Standard
WQ34: Reduce fine sediment particle (inorganic particle size < 16 micrometers in diameter) load to achieve long-term pelagic water quality standards (WQ1 and WQ2).
Key Points
- Between 2020-2023 TMDL implementors (CalTrans, CLST, Douglas, El Dorado, NDOT, Placer, Washoe) collectively prevented 2.3 million pounds of fine sediment particle from reaching lake, an average of 570,000 a year.
- The Winter of 2022 - 2023 was a historic year in terms of snowfall and low temperatures, which led to long and continuous periods of deep snow and cold temperatures that prevented full inspections necessary to award credits (2024 TMDL Performance Report).
- Urban land uses account for over 70 percent of total FSP loading to the lake (Lake Tahoe TMDL). The goal of the TMDL is nearly 100 feet by 2076, with an interim target of the achieve an interim target of 78 feet of clarity by 2031. Achieving the interim target requires reducing FSP by the load in 2026 by 34% from the TMDL baseline.
- The TRPA Code of Ordinances provides specific direction to ensure that activities and development in the Region are compatible with the Regional Plan and support the attainment and maintenance of the Region’s shared goals for restoration and environmental quality as expressed in the threshold standards.
- The Tahoe Science Advisory Council recommended that the discharge standards WQ19-WQ32 are not suitable for threshold standards, but should be retained in the TRPA Code (currently at Chapter 60) as management restrictions on discharge
About the Threshold
- Runoff from roads and other urban land uses is the single largest source of fine sediment particles (FSP) impacting Lake Tahoe’s clarity, accounting for more than 70% of the FSP load to the lake. TMDL research also found that urban stormwater also provides the greatest opportunity to control FSP pollution. Consequently, restoring Lake Tahoe’s clarity hinges on achieving FSP load reductions in urban stormwater.
- Landscape modification (e.g. impervious cover such as roads or residential and commercial development or logging) influences the volume of runoff, erosion rates, and the ability of the watershed to retain sediment and nutrients. The concentration of sediment and nutrients in stormwater runoff is influenced by the type, magnitude, and location of landscape modifications. Concentration is further mediated by the extent to which practices to mitigate potential impacts are in place. A variety of natural factors also influence the concentration of sediment and nutrients in stormwater concentrations including climate, weather, landscape topography, and vegetation. The Lake Tahoe TMDL estimated that urban upland areas contributed 348 metric tons of fine sediment particles to the lake annually, 72 percent of the annual total (Lahontan and NDEP, 2010a).
Delivering and Measuring Success
EIP Indicators
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Miles of Street Sweeping
Since 2009, EIP partners have swept more than 91,000 miles of roadway in the Tahoe Region collecting fine sediment particles before they reach Lake Tahoe.
Lake Clarity Indicators
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Fine Sediment Load Reduction
TMDL urban implementing partners have acheived greater than total fine sediment particle targets required by permits and agreements.
Monitoring Programs
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Regional Stormwater Monitoring
The Regional Stormwater Monitoring Program measures pollutants in urban runoff to evaluate the effectiveness of pollutant control measures and track and report monitoring findings.
Rationale Details
- At or Somewhat Better Than Target. WQ34) Reduce fine sediment particle (inorganic particle size < 16 micrometers in diameter) load to achieve long-term pelagic water quality standards (WQ1 and WQ2). The Lake Tahoe TMDL establishes a series of increasing pollutant load reduction targets necessary to restore the historic clarity of Lake Tahoe. During the four-year evaluation period, TMDL implementors exceeded load reduction targets by 8 percent, obtaining 11,319 credits relative to a target of 10,528. Implementors have exceeded annual load reduction targets in seven of the last eight years. In 2023, implementors fell just short, achieving 98 percent of the load reduction target.
- Moderate Improvement. Load reduction target attainment is verified through the Lake Clarity Crediting Program. Urban implementers document and report load reduction activities through the Lake Clarity Crediting Program which provides the standardized tools and protocols to consistently and transparently estimate, account, and report accomplishments. Lake Clarity Credit (credit) targets define load reduction milestones in California stormwater permits and Nevada interlocal agreements. Use the map and check boxes below to see the achievements relative to targets for each jurisdiction, state, and basinwide. To evaluate the effectiveness of management and track load changes over time, the crediting program modeling tools provide estimates on the average annual load that is verified through on-the-ground field condition assessment.
Confidence Details
- Moderate. The load reduction targets of the TMDL are designed to restore the long-term clarity of the lake. The TMDL crediting program is well-documented and science-based. Full details on implementation and crediting are available on the program dashboard: https://clarity.laketahoeinfo.org/Home/ProgramManagement
- Moderate. TMDL load reduction targets accelerate each year of implementation, building towards 34% fine sediment particle load reduction in 2026 from the 2004 baseline. The load reduction targets for the first 15 years of TMDL implementation accelerated from 10% in year 5 to 34% in year 15.
- Moderate.
Additional Figures and Resources
No photos available.
No documents available.