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Leroy M. Young PA Fish and Boat Commission

UNDERSTANDING INSTREAM FLOW PROTECTION. Leroy M. Young PA Fish and Boat Commission. “Nature is not only more complex than we think but more complex than we can think” Egler 1973. To understand anything, its good to ask questions. Who needs instream flow? What is it? When is it needed?

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Leroy M. Young PA Fish and Boat Commission

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  1. UNDERSTANDING INSTREAM FLOW PROTECTION Leroy M. Young PA Fish and Boat Commission

  2. “Nature is not only more complex than we think but more complex than we can think” Egler 1973

  3. To understand anything, its good to ask questions • Who needs instream flow? • What is it? • When is it needed? • Where is it needed? • Why should it be protected? • How can the proper amount be determined?

  4. What is Instream Flow? A simple answer: Water flowing in a stream

  5. Who or what needs instream flow?

  6. When is Instream Flow Protection Needed?

  7. Natural stream flow is highly variable both within and between years

  8. The Natural Flow Regime (Poff et.al. 1997) - Natural variations in flow organize and define aquatic ecosystems

  9. The full range of flow variability is important and affects the following components of riverine ecosystems : 1. Hydrology 2. Geomorphology 3. Biology 4. Water Quality 5. Connectivity

  10. 1. Hydrology • Riparian zone maintenance • Valley form and floodplain maintenance

  11. 2. Geomorphology • Maintaining channel form: A dynamic equilibrium involving the transport of water and stream sediments (Streams are always changing in order to remain the same) • Floods are important!

  12. 3. Water Quality • Q7-10 and waste assimilation • Water temperature • Dissolved oxygen

  13. 4. Biology • Species composition • Life history cues • Physical habitat • Migration

  14. Intermediate-Disturbance Hypothesis (Ward & Stanford 1983) • “Moderate” disturbance explains the “biodiversity” of a stream

  15. 5. Connectivity • The flow, exchange, and pathways that move organisms, energy and matter through river systems • Has longitudinal, lateral, and vertical components (the Where? question)

  16. Connectivity n

  17. Why should Instream Flow be Protected?

  18. Some Reasons • It’s the right thing to do ecologically • It’s the right thing to do economically • It’s the right thing to do legally

  19. Pennsylvania ConstitutionArticle 1, Section 27 “The people have a right to clean air, pure water, and to the preservation of natural, scenic, historic, and aesthetic values of the environment. Pennsylvania’s natural resources are the common property of all the people including the generations yet to come”

  20. Surface Water Withdrawal Regulation in PA • PA Department of Environmental Protection • Susquehanna River Basin Commission • Delaware River Basin Commission • PA Fish and Boat Commission

  21. How can the proper amount of flow be determined?a.k.a “How much flow do the fish need???”

  22. Classes of methods • Standard setting • Incremental • Maintenance of flow variability

  23. Standard Setting methods • One flow selected as a minimum or optimum flow Examples: - Q7-10 method - Wetted Perimeter Method - Tennant Method

  24. Q7-10 Method • Drought flow which occurs for a period of seven consecutive days one time in 10 years • Design standard for wastewater treatment plant discharges • Normally exceeded about 99% of the time • Equals about 6% of the Average Daily Flow (ADF) in PA

  25. Wetted Perimeter Method • Relates amount of stream bottom which remains covered with water (wetted perimeter) to flow • Emphasizes riffle areas which are critical habitats for aquatic invertebrates

  26. Tennant Method • Developed by Donald Tennant of the U.S. Fish and Wildlife Service • Based on Tennant’s observations of rapid reductions in suitable habitat at flows below 20-60% ADF

  27. Incremental methods Instream Flow Incremental Methodology (IFIM) – Determines effects of incremental changes in stream flow on: • Depth • Velocity • Substrate • Cover

  28. Relates these conditions to their suitability for various fish species and life stages

  29. Historical Instream Flow Protection Criteria • Pennsylvania DEP, SRBC, DRBC - Q 7-10; ~ 6% ADF in PA • PFBC – Tennant method; 20-25% ADF

  30. The Pennsylvania/Maryland Instream Flow Study PA Dept. of Environmental Protection PA Fish and Boat Commission MD Department of Natural Resources Susquehanna River Basin Commission U.S. Army Corps of Engineers U.S. Geological Survey Chesapeake Bay Foundation

  31. OBJECTIVE To develop a procedure for determining instream flow requirements that does not initially require a stream specific impact analysis. The instream flow requirement for a specific stream must be derivable from hydrologic records.

  32. Study approach: • Wild trout waters with a drainage area < 100 mi2 • Regional application of IFIM • 67 streams; 97 stream segments

  33. Select Study Sites • Stratify by Physiographic Region • Stratify by stream length • Randomly select streams and sites • Sample size - 30 segments/Region

  34. Field Reconnaissance • Verify trout reproduction • Characterize mesohabitat • Select one representative pool, riffle, and run/site

  35. Collect Field Data • Depth, Velocity, Substrate, Cover • Three flows/site • Bracket range of median monthly Q’s

  36. Develop Hydraulic Models for Each Study Site • 254 transects calibrated • 97 sites

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