Development of LowFlow Statistics

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Development of Low-Flow Statistics From a
Statewide Network A cooperative program with the
Kentucky Division of Water
Gary Martin, Hydrologist
U.S. Geological Survey Department of the Interior
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OVERVIEW

• Uses
• Definition
• Data collection
• Estimating equations

Low-Flow Network and Statistics
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USES OF LOW-FLOW STATISTICS

• Water-resources modeling, planning and management
• Waste load allocation to receiving streams for
  protection of aquatic and human life
• Assessment of surface-water availability to
  supply users

Low-Flow Network and Statistics
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DEFINITIONS

• N-day, T-year low flows 7Q10, 30Q20
• Lowest mean flow for N consecutive days having
  a 1/T probability of not being exceeded in any
  given year
• Harmonic-mean flow
• Flow-duration percentiles

Low-Flow Network and Statistics
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Low-Flow Network and Statistics
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Low-Flow Network and Statistics
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HYDROGRAPH OF DAILY MEAN DISCHARGE
7-day low 10 cfs
Low-Flow Network and Statistics
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FLOW-DURATION CURVES
Low-Flow Network and Statistics
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LOW-FLOW CHARACTERISTICS

• Climate precipitation patterns in time and
  space, temperature regimen
• Lithology and structure of rock formations

Low-Flow Network and Statistics
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GROUND-WATER CONTRIBUTION
Low-Flow Network and Statistics
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Low-Flow Network and Statistics
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LOW-FLOW FREQUENCY ANALYSIS
LOW-FLOW FREQUENCY ANALYSIS

• Long-term continuous-record stations with 10 or
  more years of data (climate year AprilMarch)
  annual N-day low flows
• Check for trends, serial correlation
• Log-Pearson Type III distribution (nonzero)
• Log QT X KS f (M, SD, SKEW)
• Adjust graphically, if necessary
• Adjust for zero flows using conditional
  probability

• Long-term continuous-record stations with 10 or
  more years of data (climate year AprilMarch)
  annual N-day low flows
• Check for trends, serial correlation
• Log-Pearson Type III distribution (nonzero)
• Log QT X KS f (M, SD, SKEW)
• Adjust graphically, if necessary
• Adjust for zero flows using conditional
  probability

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ANNUAL 7-DAY LOW-FLOW TIME SERIES
ANNUAL
ANN
Low-Flow Network and Statistics
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EXAMPLE GRAPHICAL FREQUENCY CURVE
Low-Flow Network and Statistics
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FREQUENCY CURVES
Low-Flow Network and Statistics
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FREQUENCY CURVES
Low-Flow Network and Statistics
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DATA COLLECTION NETWORK
Low-Flow Index Stations
59 Index Stations 13 new, 46 previous
Low-Flow Network and Statistics
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DATA COLLECTION NETWORK
Low-Flow, Partial-Record Stations
Low Flow Index Stations
310 LFPR Stations 98 new, 212 previous
Low-Flow Network and Statistics
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DATA COLLECTION NETWORK
INDEX AND LFPR STATIONS
379 Total Low-Flow Stations
Low-Flow Network and Statistics
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RELATING CONCURRENT BASE FLOWS AT INDEX AND LFPR
STATIONS
Low-Flow Network and Statistics
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DEVELOPMENT OF REGIONAL ESTIMATING EQUATIONS
Regressions Qt aAdBeCf 10 basin
physical and climatic characteristics tried in
regression analyses A and V in final estimating
equations
Low-Flow Network and Statistics
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STREAMFLOW-VARIABILITY INDEX
Low-Flow Network and Statistics
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STATION VALUES OF STREAMFLOW-VARIABILITY INDEX
Low-Flow Network and Statistics
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KARST DISTRIBUTION
Low-Flow Network and Statistics
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Low-Flow Network and Statistics
Low-Flow Network and Statistics
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MAPPED STREAMFLOW-VARIABILITY INDEX REGIONS
Low-Flow Network and Statistics
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OBSERVED AND PREDICTED 7Q10
Low-Flow Network and Statistics
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EQUATION ACCURACY

• Time-sampling errors--record length
• Spatial-sampling errors--gage density
• Model error

Low-Flow Network and Statistics
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SAMPLE SPACE CHARACTERISTICS
Low-Flow Network and Statistics
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ESTIMATING EQUATION ACCURACY
MEAN ANNUAL FLOW 14 PEAK FLOW Q100
20-62 LOW FLOW 7Q10
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Low-Flow Network and Statistics
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Development of Low-Flow Statistics From a
Statewide Network A cooperative program with the
Kentucky Division of Water
Gary Martin, Hydrologist
U.S. Geological Survey Department of the Interior
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Low-Flow Network and Statistics
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Low-Flow Network and Statistics
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Low-Flow Network and Statistics
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Low-Flow Network and Statistics
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test

• test

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