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Review of Brazos BBEST Base and Subsistence Flows

Review of Brazos BBEST Base and Subsistence Flows. Presentation to Brazos BBASC June 27, 2012 Tom Gooch, Brazos BBEST. Basic Approach of Brazos BBEST. Adopted Environmental Flow Regime Mimic Natural Flow Patterns Critical Flow Components: Magnitude Frequency Timing (seasonality)

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Review of Brazos BBEST Base and Subsistence Flows

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  1. Review of Brazos BBESTBase and Subsistence Flows Presentation to Brazos BBASC June 27, 2012 Tom Gooch, Brazos BBEST

  2. Basic Approach of Brazos BBEST • Adopted Environmental Flow Regime • Mimic Natural Flow Patterns • Critical Flow Components: • Magnitude • Frequency • Timing (seasonality) • Duration • Rate of Change in Flow

  3. Basic Approach of Brazos BBEST • Recommendations Protect Environmental Flow Regime by: • Subsistence Flows • Base Flows • High Flow Pulses • Recommended Environmental Flows Vary: • With Season • Hydrologic Condition (wet, average, dry) • Each Element HasEnvironmental Functions

  4. HEFR Flow Separation - Richmond Subsistence Base Flow High Flow Pulse Overbank

  5. Designation of Flow Regime • Used HEFR tool • Based on statistical analysis of separated flows • Flow recommendations example on following slide

  6. Environmental Flow Recommendation Brazos near Richmond

  7. Environmental Functions • Subsistence (Report page 4-7) • Minimum flow in drought • Maintain water quality • Provide minimal aquatic habitat for survival • 95th percentile low flow • Minimum of 1 cfs • Not to artificially sustain 1 cfs • Prevent increase of very low flows • Zero flows will occur naturally in some areas

  8. Environmental Functions • Base Flows (Report page 4-7) • Normal flows between storm events • Provide adequate habitat for aquatic communities • Maintain groundwater levels to support riparian vegetation • Lower Brazos – provide mix of shallow and deep habitats • Recommendations Vary with Season and Hydrologic Condition • Wet 75th percentile of seasonal base flows • Average 50th percentile (median) • Dry 25th percentile

  9. BBEST Implementation Recommendations – Base Flows • Define Hydrologic Condition Using Palmer Hydrol0gic Drought Index Data (Report pages 3-8 through 3-11) • Data published by National Climatic Data Center • Table 3.1 – Climatic zones to use for each gage • Table 3.2 – Boundaries for hydrologic condition by gage

  10. BBEST Implementation Recommendations – Base Flows • All Hydrologic Conditions • Flow below subsistence – no diversion • Dry Conditions • Flow below seasonal base flow and above subsistence flow – divert 50% of amount above subsistence • Average and wet hydrologic conditions • Flow below seasonal base flow – no diversion

  11. Questions?

  12. Double Mountain Fork Brazos River near Aspermont

  13. Climatic Zones to Determine Palmer Drought Index by Gage

  14. Palmer Drought Index for 25th and 75th Percentile by Gage

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