Indicator
Miles of Stream Habitat in Good Condition
2015 Evaluation
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2015 Evaluation
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Status
Considerably Worse Than Target
Trend
Insufficient Data to Determine Trend
Confidence
Low
Evaluation Map
streams map jpeg.jpg
Description

"Status” monitoring locations and streams in the Tahoe Basin rated as marginal, good, and excellent from 2009-2014 (TRPA 2015).

Rationale Details
Results from stream sampling spread out across the entire Basin (n=92) between 2009-2014, indicate that:
• 55 percent of streams are in excellent condition (considerably better than the target of 34 percent)
• 19 percent of streams are in good condition (considerably worse than the target of 48 percent)
• 26 percent of streams are in marginal good condition (considerably worse than the target of 17 percent)

The proportion of the streams in excellent condition well exceeds the target and is encouraging news for stream health in the Basin. The main concern is the proportion of streams in marginal condition. Being below the target for proportion of good streams is less worrisome as most of these streams instead are in the excellent category. The high number of marginal sites is being addressed through stream restoration and stormwater management, among other activities. Low water levels caused by drought are likely the largest contributor to poor biological health of at least four of the 24 marginal sites (4.3 percent of all streams included in the sample). Consequently, if sampling only occurred during normal or above normal water years, the proportion of marginal streams would likely be lower and closer to attainment.

In addition to BMI sampling, physical stream habitat data is collected. Physical habitat is a good indicator of the stream’s ability to provide habitat for fish, BMIs, and other aquatic life (Kaufmann et al. 1999). California’s Surface Water Ambient Monitoring Program used stream data compiled across California’s Sierra Nevada and North Coast regions to assess the linkages between habitat quality and biotic integrity of a stream. Out of all physical stream attributes, the following were deemed to have the closest link to biotic health: percent sand/fines of the substrate, level of human disturbance in the riparian area, intactness of woody riparian cover, and overall fish cover (large woody debris, undercut banks, overhanging vegetation, boulders, etc.) (Rehn 2015). Based on the data, break points were identified where, if below, the streams were very likely (greater than 90 percent) to have poor biological condition (Rehn 2015). Here is a summary of how Tahoe Basin streams sampled by TRPA measured against these attributes:
• Percent sand/fines of substrate: 63 percent of streams were above the break point
• Riparian disturbance: 72 percent of streams were above the break point
• Woody riparian cover: 81 percent of streams were above the break point
• Overall fish cover: 89 percent of streams were above the break point
Water temperature also plays a large role in stream health in the Tahoe Basin. Temperatures above 22 degrees Celsius are widely regarded in the literature as an acute stress threshold for salmonid species above which metabolism is impaired, fitness declines, and mortality increases (Purdy, Fesenmyer, and Henery 2014). In a 2012 study, continuous data loggers found water temperatures in the Upper Truckee River from Christmas Valley to Lake Tahoe were found to exceed 22 degrees Celsius for over 300 hours over the summer (Purdy, Fesenmyer, and Henery 2014). These high stream temperatures, in addition to high rates of stream bank erosion and high percent sand/fines of the streambed, likely play a large role in the low CSCI scores observed in the Upper Truckee River. Exposure to elevated temperatures below 22c can result in chronic stress in Salmonids. (Wenger et al. 2011; Isaak et al. 2012; Luce et al. 2014). Climate change is likely to both shift peak flows and increase stream temperatures in the Region, both of which influence the suitability of the Region’s streams for Salmonids(Jager, Van Winkle, and Holcomb 1999).

Insufficient data to determine trend. There are 48 trend sites and each site is sampled every other year (24 each year). For this analysis, there are three monitoring periods. Each monitoring period consists of two years of data collection (beginning in 2009/2010) since half of trend sites are sampled in one year and the other half the following year. The average score for trend sites decreased slightly since monitoring began, with an average CSCI score of 0.96 in 2009/2010 to an average score of 0.93 in 2013/2014 (Tahoe Regional Planning Agency 2015b). However, because only three monitoring periods exist it is determined to be insufficient data to determine trend. Additionally, no statistically significant trends in physical habitat were found during the monitoring period (Tahoe Regional Planning Agency 2015a).

The impact of low flow on stream health is well documented (Mazzacano and Hoffman 2007), and recent drought conditions are likely impacting BMIs and overall stream health. Streams that rely more on snowmelt than groundwater and springs appear to be showing the greatest effects. Four trend and reference sites that went dry (Glen Alpine, Cascade, Ward, and General creeks) during the drought years of 2013 and 2014 saw their average CSCI score drop from 0.925 during the above average water years of 2010 and 2011 to an average score of 0.716 during the drought years of 2013 and 2014, a decrease of 23 percent (Tahoe Regional Planning Agency 2015b). Because human impacts around and upstream of these sites are minimal and are not likely to have occurred during the time period, this drop in biotic integrity is believed to be the result of natural factors. The change in these four sites accounted for 78 percent of decline in average site score. If these sites maintained their above average water year scores during times of drought the overall trend for all sites would be a decrease of 0.3 percent for this monitoring period, as opposed to the decrease of 1.42 percent that was observed. If the drought persists, it is likely the overall trend in stream health will continue to decline.
Confidence Details
There is high confidence in the status. A large number of sites (92) covering the basin are sampled following well established and published protocols for assessing stream biotic integrity.
There are only three monitoring periods represented, confidence in the trend is low.
Low
Outcomes
Programs and Actions Implemented to Improve Conditions
From 2011 to 2015, nearly 5 miles (26,314 feet) of stream have been restored or enhanced through the Environmental Improvement Program (TRPA 2016). Additionally, several large restoration projects are planned in the lower portion of the Upper Truckee River and elsewhere throughout the next five years. The lower portions of the Upper Truckee River are among the most highly degraded portions of Tahoe Basin streams (Purdy, Fesenmyer, and Henery 2014; Roll et al. 2013), and therefore represent great potential to improve their overall condition and potentially meet the stream habitat threshold standard. Additionally, nine of the 24 monitoring sites that ranked as marginal are located on stream reaches with recently completed or planned restoration projects (see map on right) (TRPA 2016). This suggests that if these restoration projects are successfully completed, the Basin can reach attainment of the stream habitat standard. Additionally, during the threshold reporting period of 2011-2015, eight fish passage improvement projects were implemented, providing access to an additional 7.66 miles of potential habitat (TRPA 2016). Additional fish passage improvement projects are planned beyond 2015.
TRPA and other agencies (e.g., Lahontan Regional Water Quality Control Board, California Department of Fish and Game, US Army Corps of Engineers) regulate projects and activities in the stream environment zones, including activities in the stream itself. Additionally, the Environmental Improvement Program has initiated large-scale BMP construction, reducing pollutant load in stormwater runoff and improving aquatic habitat (TRPA 2016)
Effectiveness of Programs and Actions
While Environmental Improvement Program investments have restored nearly five miles of stream habitat in the last five years, the positive effects of these projects on overall stream health have not yet shown up. Likely reasons:
1. The probabilistic nature of TRPA’s sampling design means only a small percentage of sampling points are within recently restored stream sections. As the monitoring program continues to select random sites in the future, sampling points will eventually fall in restored sections and capture improvements.
2. Many stream restoration projects have been completed only recently in the last few years. If a project was completed in 2014 or 2015, trend sites in these areas are likely to begin to show improvements in future evaluations.
3. The stream monitoring program assesses trend Basin-wide using 48 sites. The effects of individual restoration projects are often local and can be relatively small when aggregating scores for the whole Basin. Continued large-scale restoration projects and continuation of management practices across broad geographies that benefit stream health are likely required to dramatically improve aggregated regional scores.

Although the current status of stream habitat is below target, current policies and ordinances are appropriate due to their emphasis on protecting fish habitat and surrounding stream environment zones. Additionally, the Environmental Improvement Program’s work to reverse legacy impacts to streams and reduce stormwater pollution intro streams are appropriate and should begin to show effects on the Basin’s overall stream habitat over time.
Interim Target
Average stream habitat condition of trend sites is equal to, or better than 0.933 (the average trend site score 2013/2014).
Target Attainment Date
Because limited data exists and a statistically significant trend cannot be established, it is not possible to predict a target attainment date based on trend data. Instead, we can forecast with low confidence when the target will be reached based on projecting conservative implementation progress using already approved and planned stream restoration projects. Currently, the Basin has 19 more miles (9 percent) of marginal stream habitat than the target. Assuming streams in good or excellent condition stay the same or become healthier based on the protective rules and procedures in place for streams, SEZ’s, and minimizing stormwater flow to streams, we can assume streams in attainment status remain so and forecast an attainment date for other streams. During the last five years, nearly five miles of stream habitat were enhanced or restored (TRPA 2016). Large stream restoration projects are planned for the immediate future as well (TRPA 2016). If future stream restoration continues at a similar pace of approximately one mile per year, and restored streams with increased CSCI scores would move out of the marginal category, it is expected that 20 miles of marginal streams could be restored by 2035, bringing the marginal stream habitat indictor into attainment. However, if drought conditions persist or worsen, attainment may be pushed out further or may never be reached. Conversely, if wetter conditions and more sustained stream flows return, attainment may be reached sooner.
Recommendations
Analytic Approach
No changes recommended
Monitoring Approach
No changes recommended
Modification of the Threshold Standard or Indicator
Review or revision of this standard should attempt to clarify its intent. The current standard relates only to the physical habitat within streams, and is only an indirect measure of the health of fish populations in tributaries to Lake Tahoe. Factors such as connectivity between habitats types essential to support different life stages is important to population health, but not currently reflected within the standard. At a minimum, the standard should be revised so that streams moving from a lower category into a higher category would not move one category out of attainment. For example, the way the standard is currently written, if streams move out of the good category and into the excellent category, there would be less streams in the good category (and possibly move out of attainment) even though stream health is improving.
Attain or Maintain Threshold
Climate forecasts suggest a greater proportion of Region’s precipitation will fall as rain, which may increase winter runoff, but decrease spring and summer streamflow (U. S. Bureau of Reclamation 2015; Hayhoe et al. 2004). Higher air temperature will also likely mean more frequent and intense droughts(U. S. Bureau of Reclamation 2015). These shifts are likely to result in higher stream temperatures in the Region (Ficklin, Stewart, and Maurer 2013). As stream temperatures increase, riparian protection, shading, and marsh/meadow restoration may be increasingly important to maintaining high quality steam habitat. Prioritization of programs and projects to improve instream fish habitat should consider factors such as connectivity between habitats types essential to support different life stages is important to population health, in addition to the aggregate measures of habitat restored.
Additional Figures and Resources

No documents available.