US Geological Survey Charleston, WV

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US Geological SurveyCharleston, WV

• Water quantity assessments and trends in low flow
• October 29, 2004

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Definition

• Climatic year

April 1 through March 31
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Definition

• Hydrologic-based frequency (7Q10)

• Compute the n-day of a set of time series values
  (only one per year)
• Fit the n-day data to a log-Pearson Type-3
  probability curve
• Compute the flow for a particular probability

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Definition

• Biologic-based frequency (4B3)

• Calculate the allowed number of excursions for a
  set of time series values (years of
  record/n-year)
• Calculate the running average of n-day
• Trial and error solution to determine the number
  of excursions for a particular flow to calculate
  the design flow (more than one excursion can
  occur in one year)

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Definition

• Harmonic daily-mean flow (harmonic mean)

• Calculate the reciprocal for a set of time series
  values (daily mean streamflows)
• Calculate the mean of the reciprocals
• Calculate the reciprocal of the mean 2)

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Selected Annual Flow Statisticsfor the
Greenbrier River at Alderson (station number
03183500) for the entire period of record
PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE

• 1B3..46.8 cfs
• 1Q10..47.8 cfs
• 4B3..49.5 cfs
• 7Q10..52.4 cfs
• 30Q585.7 cfs
• Harmonic mean..394 cfs

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http//water.usgs.gov/osw/lins/streamflowtrends.ht
ml
Figure 1. Number of streamgages, out of a total
of 395, with statistically significant (plt0.05)
trends for the 50-year period 1944-1993
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Definition

• Standardized departure (normalize data)

• Compute the mean of a set of time series values
• Subtract the mean from each value
• Compute the standard deviation of 2)
• Divide each value by the standard deviation

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http//ks.water.usgs.gov/Kansas/pubs/reports/dmw.g
rl.v29.pdf
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USGS in cooperation with WVDEP

• Evaluate low-flow trends in WV
• Quantify variability of selected low-flow
  statistics
• Develop a procedure to manage periods of
  gaging-station records and trends in low flow for
  estimating low-flows on ungaged streams
• Compute selected station statistics

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PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE
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PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE
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PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE
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PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE
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Regional analysis of standardized departures

• Added 5 stations located outside of the State to
  the 15 WV stations
• Conducted principal component analysis and
  correlation analysis that determined 3 regions
  and removed 3 stations from consideration

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PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE
Lower Plateaus
Upper Plateaus
Eastern Panhandle
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Summary
PRELIMINARY, SUBJECT TO REVISION, DO NOT QUOTE

• The value of low-flow statistics are sensitive to
  the period of record at a station and the
  climatic changes over that period
• The sensitivity of low flow statistics to climate
  change decreases with increasing streamflow
• Climatic changes affecting low flows have
  regional characteristics

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Questions

• Jeffrey B. Wiley
• U.S. Geological Survey
• 11 Dunbar Street
• Charleston, WV 5301
• [phone] X234
• jbwiley_at_usgs.gov