A recent study has found tree canopy and pond are in “good health” along two canals with reduced flows as a result of the Banner Cascade pipeline.

This monitoring study was part of the environmental mitigation measures NID needed in order to complete the pipeline project, which was constructed to ensure reliable water deliveries to Grass Valley and Nevada City. It also serves as the primary means for conveying raw water to the Loma Rica and Elizabeth George Treatment Plants.

The Banner Cascade Pipeline replaced both the Lower Cascade Canal and the Upper Grass Valley Canal, which had reached capacity and no longer met the needs of the area.

When the pipeline began operation in the fall of 2013, the flows of the Lower Cascade Canal and the Upper Grass Valley Canal were gradually reduced yet kept in limited service. For example, the flows in the Lower Cascade Canal were reduced from about 45- to 5 cubic feet per second. By keeping the canals in service, NID’s aim is to preserve the canals as a historical, cultural, scenic, and recreational amenity.

However, reducing the flows and water levels in these two canals have reduced the wetted perimeter in each canal potentially affecting riparian plants in the immediate area.

That’s where the monitoring study comes in. From 2013 through 2023, the goal has been to assess how the reduced flow affects canal area vegetation, canopy cover, and associated seep wetlands or ponds.

Results show “good health”

TREE HEALTH ASSESSMENT

Tree health score remains above 10 at all sites = “good health”

The 2013 (Year 0) to 2021 (Year 8) results indicate a slight increase in tree health at four Lower Cascade Canal sites and is in the “good health” category. The overall analysis concludes that after eight years of flow reduction, the tree health is fairly consistent with the baseline year surveys along both canals, as compared to the DS Canal reference site, which did not receive flow reduction.

Lower Cascade Canal sites, while sites along the Upper Grass Valley Canal and DS Canal (reference site) remained consistent with previous years’ results.

Contributing Factors

• Increases noted in new growth
• Overall decrease of insect infestation
• Disease and parasites limited

POND ASSESSMENT

Similarly, pond area and depth have varied slightly over the monitoring period, but the Year 8 and Baseline Year 0 pond characteristics were similar in the study sites and reference site.

NID will continue to monitor riparian and pond health until 2023, and will develop conclusions based on the full 10-year data set. Tree health data from the Lower Cascade Canal, Upper Grass Valley Canal, and DS Canal (Reference Site) has been compared for the following years: 2013, 2015, 2017, 2019, 2021

What is being monitored?

TREE HEALTH ASSESSMENT

• A total of six sites continue to be studied:
• 4 sites on the Lower Cascade Canal
• 1 site on the Upper Grass Valley Canal
• 1 site on the DS Canal (Reference Site)

Up to 20 trees were studied at each site. The following data was assessed:

• Growth monitoring
• Foliage cover and coloration
• Bark health
• New growth
• Evidence of disease, parasites, insect damage

Reach data was collected along approximately:

• 7 miles of the Lower Cascade Canal (273 readings)
• 0.5 mile of the Upper Grass Valley Canal (27 readings)
• 1 mile of the DS Canal [Reference Site] (85 readings)
• A total of 385 densiometer readings were taken.

POND STUDY

• Two sites along the Lower Cascade Canal and one along the DS Canal (Reference Site)
• Wildlife and habitat suitability assessments.
• The following data has been recorded:
• Delineation of inundated area / soil saturation
• Hydrology pattern
• Range of water depths
• Soil type
• Vegetation present
• Wildlife species observed
• California red-legged frog habitat assessment
• Site photographs

Discussion

• Some annual weather variability may influence results.
• To date, tree health remains relatively constant on both spatial and temporal scales.
• Sites have similar tree health trends to those of baseline conditions and remain in “good” health.
• Pond study results indicate little to no variability in ponded habitat
• Continued monitoring (final year)
• 2023 – Tree Health Assessment, Canopy Cover Assessment, and Pond Study
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Read more about the Banner Cascade Pipeline Project, click here

Read the Tree Health, Canopy Cover and Pond Monitoring Report, click here.