Noise

To minimize single event noise and ambient noise levels consistent with the needs of wildlife and values held by regional residents and visitors.

Watercraft Shoreline Test

Relevance - This indicator measures noise generated from motorized watercraft in the shorezone of Lake Tahoe. Residents and visitors are concerned about the declining serenity of their communities and their enjoyment of the outdoors due to excessive noise from sources such as motorized watercraft. Excessive recreational boat noise can also disturb sensitive wildlife. For this reason, TRPA adopted policies and ordinances to reduce noise levels and maintain serenity in Lake Tahoe’s shoreline area, while continuing to afford recreational opportunities.
Human and Environmental Drivers - Watercraft-generated single-event noise exceedances are driven by the type of watercraft engine and exhaust system and boater behavior (proximity to shore, operating speed, etc.). Shoreline topography, wave slap, and wind can also influence noise levels.

2015 Threshold Evaluation

Status

- Somewhat Worse Than Target
- Somewhat worse than target. TRPA’s maximum allowable noise level from any motorized watercraft in the shorezone is 75 dBA regardless of distance to shore. Measured noise levels in the shorezone from 2009 to 2013 (the last year of noise monitoring) put the Region in non-attainment with the zero-exceedance threshold standard, with watercraft responsible for:
• 47 recorded shorezone exceedances caused by watercraft in 2009 (0.12 exceedances/day, one exceedance every 8.2 days, n=386)
• 51 recorded shorezone exceedances caused by watercraft in 2010 (0.11 exceedances/day; one exceedance every 8.7 days, n=446)
• 91 recorded shorezone exceedances caused by watercraft in 2011 (0.21 exceedances/day; one exceedance every 4.7 days, n=428)
• 48 recorded shorezone exceedances caused by watercraft in 2012 (0.31 exceedances/day, one exceedance every 3.23 days, n=155)
• 12 recorded shorezone exceedances caused by watercraft in 2013 (0.097 exceedances/day; one exceedance every 10.3 days, n=123) (Bollard Acoustical Consultants 2014)

Data from boating surveys conducted in 2009, 2010, and 2011 indicate that 203,821; 188,047; and 193,540 boat trips occurred in those years, respectively. When placed in context of the total number of boat trips undertaken over the same time period, TRPA recorded noise exceedances from boats is 0.0002 percent to 0.0005 percent of the trips undertaken, or greater than 99.999 percent threshold standard compliance rate. Although the Region is not achieving the zero exceedance threshold standard, when viewed in context of the number of boat trips recorded over the same time period, it suggests that the Region is somewhat worse than target.

Trend

- Little or No Change
- Little to no change. A simple linear regression model showed there is little to no change in the exceedance rate from 2009 to 2013.

Confidence

- Low
- View Details Below

Methods not provided

Trend

Watercraft Shoreline Test.JPG
The average number of documented exceedances per day for motorized watercraft determined by the shoreline test (greater than 75 dBA) from 2009 to 2013. There was little to no change in the total number of exceedances per day and confidence in trend was determined to be low due to low sample size and annual variations in exceedance rates. Source: TRPA shorezone monitoring data.

Source: TRPA shorezone monitoring data.

The average number of documented exceedances per day for motorized watercraft determined by the shoreline test (greater than 75 dBA) from 2009 to 2013. There was little to no change in the total number of exceedances per day and confidence in trend was determined to be low due to low sample size and annual variations in exceedance rates. Source: TRPA shorezone monitoring data.

Connecting Actions to Outcomes

Actions

Intermediate Results

Outcomes

TRPA’s Watercraft Team enforces a 600-foot no-wake zone for the shorezone to reduce shoreline noise levels.
The existing program or action has not achieved total compliance (i.e., zero exceedances) with adopted threshold standards based on the status and trend evaluation of available data
Due to a non-significant trend, an interim target cannot be set.
Due to a non-significant trend, a target attainment date cannot be set.

Applicable Standard

- Pass-by test in shorezone shall not exceed 75 Lmax. Microphone 5 ft. above water, 2 ft., above curve of shore, dock or platform. Watercraft in Lake, no minimum distance.
- Pass-by test in shorezone shall not exceed 75 Lmax. Microphone 5 ft. above water, 2 ft., above curve of shore, dock or platform. Watercraft in Lake, no minimum distance.

Monitoring

TRPA regulalry monitors noise in the shorezone from motorized watercraft at up to ten locations around Lake Tahoe. Noise monitors are deployed for at least two weeks during peak boating season which occurs July 4th to Labor Day. Noise monitors automatically record all single noise events that exceed 75 decibles (dB), the noise limit for shorezone areas. Afterward, all noise events exceeding 75 dB are listened to by a noise technician to distinguish noise exceedancs from watercraft and non-watercraft. Noise monitors are regularly calibrated to industry standards to ensure accuracy. 

To download all of the shoreline noise data on this page please see Tahoe Open Data.

Locations

<p>Distribution of shoreline noise monitoring sites from 2009 to 2013.</p>

Confidence Details

- Moderate. There is a moderate degree of confidence in status because of noise monitoring protocol (SAE 1970), unit accuracy, data integrity, and spatial representativeness of monitoring sites. However, data has not been collected since 2013.
- Low. The confidence in trend for all single event noise exceedances due to watercraft was determined to be low with an analysis of only five data points showing little statistical significance (R2=0.0938, P=0.616).
- Low. Overall confidence takes the lower of the two confidence determinations.

Recommendations

No changes recommended

Re-engage shorezone noise monitoring once a new shorezone plan is implemented.

Recommendation from the current Shoreline Initiative planning process to modify the threshold standard or comprehensive update of noise threshold standards to respond to recommendations of 2011 Threshold Evaluation Report peer review regarding noise standards.

The conditions for this indicator could potentially improve with increased enforcement of the 600-foot no-wake zone regulation or re-enacting the prohibition on boats operating in the lake that have working, aftermarket exhaust bypass systems (invalidated by the 2010 shorezone litigation against TRPA).

Historic Evaluations

View Evaluation Legend