San Diego basin‑plan biological objective prompts debate over science, flood‑control channels and implementation

The State Water Resources Control Board on May 6 hosted a workshop on the San Diego Regional Water Quality Control Board’s basin plan amendment to adopt a biological water‑quality objective based on the California Stream Condition Index (CSCI). Panelists and public commenters split largely along scientific‑and‑operational lines: scientists and environmental groups urged adoption and use of the CSCI threshold as the best available tool for measuring biological integrity, while flood‑control and county agencies warned that hard‑to‑restore, soft‑bottom flood channels require an implementation path that avoids unintended conflicts with flood‑control maintenance.

Scientists from the State Water Board’s monitoring programs and the Southern California Coastal Water Research Project described the CSCI as a robust index that compares observed benthic macroinvertebrate communities to minimally disturbed reference conditions, then uses a tenth‑percentile threshold (CSCI ≈ 0.79) to indicate probable departure from reference. The statewide peer‑reviewed index, experts said, is applicable in perennial and intermittent streams in southern California and can flag water‑quality issues including nutrients, toxicity and pesticides.

Opposing witnesses — county officials, flood control districts and public‑works staff — presented an analysis showing very few sampled soft‑bottom flood‑control channels in Region 9 currently meet the 0.79 threshold and argued that many of those channels are managed to Army Corps/FEMA flood‑control standards that require vegetation removal and mechanized maintenance. Those witnesses asked the board to clarify that channels managed for flood control would not be forced into an immediate compliance posture; they proposed either an explicit exemption for managed soft‑bottom flood channels or a case‑by‑case designation process with clear evidence criteria and a pathway to prioritize water‑quality remedies that do not compromise public safety.

Environmental groups and San Diego Coastkeeper said biological objectives are long overdue and that the CSCI is appropriately calibrated for southern California; they also noted that the basin plan amendment is limited to Region 9 and does not create a statewide automatic rule. Several public commenters noted that a causal assessment is required before enforcement and that citizen suits are unlikely to be driven directly by the new objective without additional diagnostic work. Board staff said they will take written comments on new evidence through May 19 and review the workshop record before the board considers formal approval.

Ending: The workshop clarified where scientific consensus exists and where regional operational complexities remain. Several board members asked staff to return with more precise program‑of‑implementation language that spells out how the objective will be used in permits and how the board will handle soft‑bottom channels that are actively managed for flood control; staff said it would continue refining the implementation language and accept written comments until the May 19 deadline.