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Farfield model shows small, localized salinity changes near proposed desalination outfall; scientists urge independent review
Summary
Spheros Environmental told the Corpus Christi City Council its hydrodynamic model predicts small, mostly short‑lived increases in bottom salinity near the proposed Inner Harbor outfall (typically 0.5–1.0 ppt; conservative upper bound ~2 ppt). Farfield advisory scientists said the model needs independent peer review and dissolved‑oxygen analysis before policy action.
Spheros Environmental presented a two‑year hydrodynamic modeling study to the Corpus Christi City Council on June 2 that simulated the effect of a proposed 30‑million‑gallon‑per‑day desalination discharge in the Inner Harbor. Nick Wkelman, chief operating officer for Corpus Christi Water, introduced the team and the five‑member farfield advisory committee that reviewed the work.
Lead modeler Praep Mintan described a three‑dimensional model with roughly 12,300 horizontal cells and up to 10 vertical layers, validated against high‑frequency 2023–2024 observations (water level, salinity and temperature from NOAA, USGS and TWDB stations). Modelers reported close matches to measured tides and salinities at multiple locations, and said the model is “worthy” of assessing farfield impacts.
Under the study’s base‑case runs — which compared model simulations with and without the proposed discharge — Spheros reported that increases in bottom salinity and stratification occurred chiefly inside the inner harbor and adjacent channel. The team said typical modeled changes were about 0.5–1.0 parts per thousand (ppt) in salinity at the bottom near the discharge and that an upper‑bound, conservative estimate reached about 2 ppt locally. At the surface and in shallow bayfront areas, the difference was negligible; tidal flushing frequently reset anomalies in the model runs. Ship‑traffic mixing, when included, tended to reduce predicted stratification, making the initial (no‑ship) runs conservative, the presenters said.
Several farfield advisory committee members praised the technical work but emphasized limits in scope. David Lobe and Jason Hail acknowledged the model’s calibration, while others raised concerns about key omitted factors: Brad Bartles said longer model runs and additional bulk‑mixing sensitivity tests were needed; committee scientists led by Dr. Sharon Herzka and Dr. Michael Wedz said dissolved oxygen was not modeled and that the study has not yet produced convincing evidence the discharge would avoid detrimental ecological effects. Deanna King and other committee members requested longer ship‑traffic records, vertical profiling in more locations, and a full, independent peer review of both model inputs and the final report.
Spheros respondents said some of those items were outside the firm’s original scope but that the model files and final deliverables would be provided to the city and available for independent review once the report is finalized at the end of June.
Why it matters: the study addresses whether a desalination discharge would create sustained stratification that could worsen bottom‑water oxygen conditions. The modelers reported only small, mostly transient changes in stratification outside the immediate discharge area, but several independent scientists on the advisory committee said additional biological and dissolved‑oxygen analyses are needed to translate modeled salinity changes into ecological risk estimates.
What’s next: Spheros will deliver the final report and model inputs at the end of June. Multiple committee members requested at least a two‑month independent review window after the city releases those files. City staff said the model outputs will be peer‑reviewable and that monitoring and permit conditions would require ongoing water‑quality checks if the project proceeds.
