New Tools to Assess Hydrologic Alteration in Texas

1. New Tools to Assess Hydrologic Alteration in Texas Presenter: Eric S. Hersh, University of Texas at Austin Center for Research in Water Resources TRRMS Annual Symposium May 18, 2006

2. Acknowledgements • Co-authors: • David Maidment, UT-Austin CRWR • Jordan Furnans, TWDB • Mark Wentzel, TWDB • Wendy Gordon, TCEQ • Thanks to: • Joe Trungale, Trungale Engineering and Science, formerly TPWD

3. environmental flow definition • Water left in or released into a river system, often for managing some aspect of its conditions • Endangered species protection • Healthy ecosystem • Sediment transport • Commercial fisheries yield • Freshwater inflows to bays and estuaries • Waste assimilation

4. flow- “the master variable” • Controlling factor in riverine physical, biological, and chemical processes • e.g.: water temperature, dissolved oxygen, available habitat, spawning cues, channel shape, substrate type, etc (Poff et al. 1997)

5. the natural flow regime Poff et al 1997 (Postel and Richter 2003)

6. the natural flow regime • Magnitude • Frequency • Duration • Timing • Rate of change of hydrologic events

7. characterizing streamflow Maidment et al 2005 • Subsistence flow • Water quality (temperature, DO, waste assimilation) • Restricted habitat and connectivity • Base flow • Dominant flow condition in many rivers • Determines available habitat • Maintains groundwater table

8. characterizing streamflow Maidment et al 2005 • Flow pulses • Within banks • Longitudinal connectivity • Nutrient and organic matter delivery • Sediment flushing • Flood flows • Overbank • Lateral connectivity • Restructure channel and floodplain • “Food bazaar”

9. quantifying environmental flows • 207 assessment tools (Tharme 2003) • 1950s-present • South Africa, Australia, United States • Hydrologic (Desktop) Models • Hydraulic Models • Habitat Models • Holistic Models

10. Senate Bill 2 • In 2001, the tri-agencies (TPWD, TWDB, and TCEQ) were directed to: • Establish and maintain an instream flow data collection and evaluation program • Develop methodologies to determine flow conditions in Texas rivers and streams necessary to support a sound ecological environment

11. (Austin 2005)

12. hydrologic alteration software USGS The Nature Conservancy

13. The Indicators of Hydrologic Alteration (IHA) • Richter et al., 1996 & 1997 • 33 Annual Statistics • Parametric (mean) or non-parametric (median) • One or two period analysis • Range of Variability Approach (RVA) to quantify hydrologic alteration • 34 Environmental Flow Components (EFCs) from NAS review (Mallard et al. 2005)

14. IHA • Input: 20+ yrs of daily flow data recommended • Output: scorecards spreadsheet, summary and alteration graphs

16. Hydrologic Assessment Tool (HAT) • National HAT: USGS Fort Collins Science Center and Colorado State Univ. • 171 indices from 13 papers (in Olden and Poff 2003), including the 33 IHA • Input: daily and peak (optional) flow data • Six stream classifications • from Poff 1996 • 420 U.S. rivers

17. HAT • New Jersey Hydrologic Index Tool (HIT) with NJ Department of Environmental Protection • Includes NJ Stream Classification Tool • Principal components analysis to identify 10 significant indices for each of 4 state-specific stream types • Missouri and Massachusetts under development • Texas possibly next year

19. IHA/HAT Comparison • Both are simple, user-friendly statistical tools to evaluate hydrologic characteristics • Both are based on daily flow data time series which typically encompasses flow alteration • Both have built-in temporal comparison tools; neither has spatial comparison tools • HAT features more statistical routines and flexibility, but ‘significant’ indices chosen from a national dataset likely not representative of Texas conditions • Ecological significance of specific indices in both is unclear in Texas

20. Texas Instream Flow Studies (Austin 2005)

21. TIFP priority basins n = 24 Trinity Brazos Sabine Guadalupe San Antonio

22. Spatial Patterns: Texas Streamflow

26. Spatial Patterns: Texas Streamflow • For streamflow periods of record at the 24 priority gages (average of 68 years): • Across the range of flow variability, streamflow follows a sinusoidal pattern with a spring peak (May-June) and a fall trough (August-September) • Signal is stronger to the east, muted to the west along the Texas coast

27. Spatial Patterns: Texas Hydrology P Q

28. P Q

29. P Q

30. P Q

31. Spatial Patterns: Texas Streamflow • For the period 1961-1990: • precipitation is bimodal, irrespective of geography, with spring (May-June) and fall (September-October) peaks • Signal is expressed in magnitude (more precipitation to the east) but not in timing

32. Spatial Patterns: Possible Causes • Evapotranspiration • More vegetation to the east • More available water to the east • Groundwater recharge • Water demand and reservoir operations timing

33. Future Work • Continue to investigate flow regime characteristics and patterns which may impact instream flow analyses in the six priority basins • Compare the relative merits of IHA and HAT for the Texas Instream Flow Program • Recommend enhancements to one of the tools to increase effectiveness in Texas studies • Work toward an integrated statewide stream classification system

34. Questions?

35. References • Austin, B. (2005) The Texas Instream Flow Program. Presentation at the Environmental Flows Conference, Texas State University, San Marcos, October 31. • Maidment, D., Montagna, P., Sansom, A., Ward, G., Winemiller, K. (2005). Scientific Principles for Definition of Environmental Flows. Statement for Environmental Flows Conference, Texas State University, San Marcos, October 31. • National Research Council Committee (2005). The Science of Instream Flows: A Review of the Texas Instream Flow Program. Committee on Review of Methods for Establishing Instream Flows for Texas Rivers, National Research Council. The National Academies Press, Washington, D.C. • Olden, J.D., and Poff, N.L. (2003). Redundancy and the choice of hydrologic indices for characterizing streamflow regimes. River Research and Applications, 19, 101-121. • Poff, N.L. (1996). A hydrogeography of unregulated streams in the United States and an examination of scale-dependence in some hydrological descriptors. Freshwater Biology, 36, 71-91. • Poff, N. L., Allan, J. D., Bain, M. B., Karr, J. R., Prestegaard, K.L., Richter, B. D., Sparks, R. E., and Stromberg, J. C. (1997). The natural flow regime. Bioscience, 47(11), 769-784. • Postel, S. and Richter, B. (2003). Rivers for Life: Managing Water for People and Nature. Island Press: Washington, D.C. • Richter, B. D., Baumgartner, J. V., Powell, J., and Braun, D. P.(1996). A method for assessing hydrologic alteration within ecosystems. Conservation Biology, 10(4), 1163-1174. • Richter, B. D., Baumgartner, J. V., Wigington, R., and Braun, D. P. (1997). How much water does a river need? Freshwater Biology, 37(1), 231-249. • Tharme, R. E. (2003). A global perspective on environmental flow assessment: Emerging trends in the development and application of environmental flow methodologies for rivers. River Research and Applications, 19(5-6), 397-441.