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Potomac Instream Flow Methods Workshop

Introduction Agenda Participants List Panelists Presentations Breakout Group Reports Panel Recommendations Potomac Flow-by Studies


1. MDNR Introduction by Richard McLean (998 KB ppt file)

Habitat Assessment - 2002 Drought

2. Dr. Steve Schreiner of Versar presented a summary of the Habitat Assessment of the Potomac River from Little Falls to Seneca Pool, which Versar prepared for PPRP. The report provides background information describing the history of current low-flow requirements, a review of the studies conducted to support those requirements, and results of a habitat assessment conducted during record low flow conditions in 2002. The assessment included development of a habitat map, a field survey of habitat types, and measurements of hydraulic and water quality conditions, spanning the period July through October 2002 when flows were as low as 151 million gallons per day (MGD) at the gauge at Little Falls Dam.

Panelist Presentations

Each of the six expert panelists provided the workshop participants with their initial thoughts and considerations on the current state of the Potomac River and the flow-by requirements. The following recurrent themes emerged during the panelist presentations:

    1. The Potomac River is, for the most part, a healthy river system and this study is, therefore, a proactive effort.  The workgroup is to be commended, as typically this type of effort is reactive, after a severe problem has been manifested.
    2. The Potomac is largely unregulated.
    3. More biological information is needed.
    4. Goals/objectives of the study must be clear/precise.

The panelist presentations may be viewed or downloaded by clicking the link that follows each summary.

Presentation Summaries

    1. Evaluating Instream Flow Needs for Potomac River, Seneca Pool to Little Falls: Initial Thoughts
    Dr. Kondolf’s presentation began by listing the following key points:

    • The Potomac River is basically healthy.
    • Regulation of the river is minimal.
    • The real issue is the potential effects of drought, which is an event, not a chronic condition.
    • Biological responses to drought are key.
    • The Potomac is a highly irregular bedrock channel, whereas hydraulic models have been developed for and successfully applied only to alluvial river systems.
    These points were expanded upon, resulting in the following recommended approach:
    • Learn from the 1999 and 2002 droughts.
    • Develop clear objectives: biological, then hydrological.
    • Develop an understanding of the system’s biological responses to drought.
    • Acknowledge uncertainty.
    • Consider an Adaptive Management Framework, which embraces uncertainty.
    • Think clearly/critically about modeling approaches.

    • Presentation: web version
    • Presentation: 36 KB powerpoint file

    2. First Principles Based Attributes for Describing a Template to Develop the Reference River
    Dr. Nestler’s presentation made the following points:

    • Errors and uncertainties propagate and magnify as you go through a system.
    • Traditionally, people have tried to either use a natural system as a template, or engineer a hydrologic process to describe a system.
    • Goal should be to use the idea of “reference” and “template” to integrate the two approaches with ecological First Principles.
    • To be successful, it is important to relax the study’s connection to legal/institutional history and focus it instead on ecological First Principles.

    • Presentation: web version
    • Presentation: 1.5 MB powerpoint file

    3. Instream Flow Methods
    Dr. Orth presented his work on the Shenandoah River Basin as a possible model for use on the Potomac. The PHABSIM model was applied to the Shenandoah to study the effects of drought and increased water demand on that river system. Detailed information regarding the Shenandoah study is at: Based on his work on the Shenandoah, Dr. Orth suggested the following:

    4. Ecological objective•Mitigate effects of human induced alterations
    Dr. Parasiewicz described a method for mitigating the effects of human-induced alterations (ecological objective):

    5. Potomac Flow-by
    During his presentation, Dr. Poff observed that the Potomac is a largely unregulated river, which is highly unusual. He went on to provide an ecological context of the issue and an explanation of the following ecological principle: if a system is kept within a natural range of variation, the system will persist. Dr. Poff explained that the Potomac is a dynamic river system with significant natural flow variation and biological variation. The ability to detect response and recovery to a drought depends on biological data, which are currently limited. Also, a reduction in “habitat area” does not necessarily translate directly into linear biological response. It is necessary to consider aspects of the system that allow for resilience:

    • Species behavior (movement) and tolerance
    • Landscape scale (rufugia, connectivity).
    The presentation questioned the stated Management Objectives, asking if the goal is to provide a “high degree of protection” [risk assessment] or simply to “quantify habitat at low flows”.

    6. Prescribing Flows for the Potomac River Ecosystem: Six Recommendations
    Dr. Richter began by stating two basic principles:

    • River flows are inherently variable on daily, seasonal, and inter-annual time scales.
    • The life cycles and population dynamics of many aquatic, riparian, and estuarine organisms are tightly linked to natural river flow variability.
    Dr. Richter explained that it is important to identify the low flow conditions, as well as the high flow pulses that interrupt low flow conditions in the Potomac. These high pulses play important ecological roles (e.g., move food down the river, provide ability for organisms to move from place to place), depending on how large they are and how long they last. The flow regime (low flows, high flows and floods) is a “master variable” in river ecosystems and is related to the ecological integrity of the river through:
    • Physical habitat
    • Water quality
    • Connectivity
    • Energy supply
    • Species interactions
    Based on these discussion points, Dr. Richter provided the following recommendations:
    • Get straight about the goals.
    • Engage scientists from a variety of disciplines, using a toolbox of methods.
    • Be specific about the magnitude, duration, and timing of tolerable, extreme low flows.
    • Consider more than just low flows in the prescription.
    • Describe the desired inter-annual variability.
    • Expect to be wrong. Invest in learning and refine the prescription over time.

    • Presentation: web version
    • Presentation: 2.5 MB powerpoint file

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This page was updated on July 2, 2003.