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State program ramps up sampling to test CSCI performance in intermittent streams
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Summary
SWAMP reported statewide efforts to identify and monitor intermittent reference sites to evaluate whether the California Stream Condition Index (CSCI) performs reliably across flow regimes; teams will add data loggers, recon sites, and prioritize regions lacking coverage.
Chad Laughlin (San Diego Regional Water Board) and Nathan Mack (California Department of Fish and Wildlife, Aquatic Biosassessment Lab) presented a statewide effort to evaluate the California Stream Condition Index (CSCI) in intermittent streams and to expand reference‑site coverage.
Their two‑pronged approach first re‑examines flow status at existing CSCI reference sites to determine whether reference sites used in the index development are intermittent or perennial. Second, teams are identifying and sampling new intermittent reference sites, prioritizing ecoregions with large gaps (North Coast, Modoc, Lahontan, Western Sierra, Central Coast and Interior chaparral areas). Recon efforts have created thousands of candidate points from road/NHD intersections and a rudimentary reference screen using NLCD code 21 (open space/developed), road density and active mine presence.
Nathan Mack described field screening methods used during recon: crews will deploy Onset Tidbit loggers to record presence/absence of water and temperature for two years, and use photos and PHAB habitat notes to confirm reach‑scale human influence and hydrologic state. Teams reported 58 stations with benthic macroinvertebrate (BMI) data so far (not counting Bay Area sites), and 30 new stations from 2025 fall recon planned for 2026 sampling. SWAMP staff and partner biologists can field up to ~30 sites per week during recon.
The presenters noted regional differences: Southern California has dense intermittent‑site coverage and shows good CSCI performance there; other regions remain data‑poor and will need targeted effort. They emphasized that the CSCI was developed without explicit flow‑type stratification and that establishing intermittent reference sites will inform whether a single statewide threshold (0.79) is appropriate or whether region‑ or flow‑type‑specific thresholds are needed.
Audience questions covered sampling windows for short‑flow sites, groundwater‑dependent ecosystem mapping as a data source, and practical constraints such as logging and drilling for water table monitoring. Presenters said sites flowing <3 months may not develop benthic communities suitable for the CSCI model and might be non‑applicable, and that they will prioritize resampling 2025 sites with low CSCI scores and possible later index‑period timing in 2026.
