Instream Flows and the Public Trust

63 Pages Posted: 15 Jan 2009 Last revised: 17 Mar 2009

Date Written: January 13, 2009


Empirical evidence suggests that diversion of instream flows for human use, coupled with the potential impacts of changing climatic conditions, is threatening the sustainability of aquatic life. Nonetheless, several states merely prevent stream flows from being reduced below the "7Q10 flow," or the average flow during the driest consecutive seven-day period that has a likelihood of recurring only once every ten years. Overwhelming scientific consensus suggests that 7Q10 merely preserves water quality standards by calculating the concentration of pollutants in point source discharges, without considering water quantity and numerous other core principles of instream management.

The protection of instream flows preserves water management options for future generations, and a varied size structure and level of species diversity is reflective of a healthy watershed. This Article examines whether states have an affirmative common law duty to these future generations beyond the strictures of their water codes to ensure the sustainability of watercourses to support freshwater and marine life in the face of growing stresses on these resources.

Since Hawaii became the first regulated riparian state to recognize explicitly that the public trust doctrine operates independently of the state's legislatively pronounced water code in a 2000 state Supreme Court decision, several commentators have suggested that Hawaii's approach could assist mainland states facing an urgent need to move proactively, rather than wait to react to imminent water conflicts and crises. However, there is little evidence that the decision has played any appreciable role in addressing water quantity issues in the many regulated riparian jurisdictions in the eastern United States.

This Article suggests that the Hawaii high court's decision can function as the foundation for a conceptual framework where the public trust doctrine serves as an independent operative in instream flow protection in select regulated riparian states. To demonstrate the implementation of the proposed framework, the Article applies the approach to the current state of instream flow protection in Mississippi.

Keywords: instream flows, public trust doctrine

Suggested Citation

Mulvaney, Timothy M., Instream Flows and the Public Trust (January 13, 2009). Tulane Environmental Law Journal, Forthcoming. Available at SSRN:

Timothy M. Mulvaney (Contact Author)

Texas A&M University School of Law ( email )

1515 Commerce St.
Fort Worth, TX 76102
United States

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