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San Diego board’s proposed stream biological objective prompts implementation debate at State Water Board workshop
Summary
Regional board’s proposal to add a 0.79 CSCI biological objective to its basin plan drew support from environmental groups and concern from flood-control agencies about how the rule would apply to modified, soft-bottom flood channels and to emergency maintenance.
SACRAMENTO — A State Water Resources Control Board workshop on May 6 focused on a contested basin-plan amendment from the San Diego Regional Water Quality Control Board that would make the California Stream Condition Index (CSCI) a numeric biological objective (proposed threshold 0.79) for seasonal and perennial streams in Region 9.
Supporters, including San Diego Coastkeeper and other advocacy groups, urged the state board to approve the amendment as a long-overdue step toward measuring the biological integrity of streams directly rather than relying solely on chemical indicators. The CSCI measures benthic macroinvertebrate communities (aquatic insects, snails and other small organisms) and has been developed and peer-reviewed for California use.
Why it matters: Biological objectives are intended to put biological condition at the center of water-quality planning and prioritize actions when communities are failing to support healthy aquatic life. Environmental advocates called the objective a practical tool to focus limited resources and to assess whether programs such as TMDLs and stormwater controls actually improve aquatic life.
Flood-control concerns: Flood-control districts and county public-works officials warned that many modified, soft-bottom flood-control channels will not attain the 0.79 threshold because banks and bottoms are engineered to convey high flows and are actively maintained for public safety. Those managers urged either exempting actively managed flood-control channels from the objective or creating a case-by-case process that recognizes Army Corps/FEMA maintenance standards, emergency repairs and the need to hold channel capacity intact.
Science and implementation: Scientists on a State Water Board panel said CSCI is appropriate for perennial and intermittent streams in Southern California and that the chosen tenth-percentile threshold is consistent with peer-reviewed practice. They also noted the index integrates multiple stressors, but that channel engineering can mute correlations between water chemistry and biological condition. The San Diego board and state staff emphasized that adoption of an objective would not preclude routine or emergency flood maintenance and that the region plans implementation language and an assessment path (causal assessment/use attainability analysis) before enforcement would be considered.
Next steps: The state board is accepting written comments on new evidence submitted to the record (deadline May 19). Several regional and state staff said they will refine implementation/clarifying language to clarify how the objective will interact with Corps/FEMA flood-control standards and maintenance orders.
Ending: The workshop underscored the gap between a scientifically defensible biological benchmark and the pragmatic need to preserve flood-control capacity in urbanized watersheds; the state board said it will review written comments and the record before deciding whether to approve the basin-plan amendment.
