Regional Analysis of LowFlow in Western WA - PowerPoint PPT Presentation

1 / 26
About This Presentation
Title:

Regional Analysis of LowFlow in Western WA

Description:

Choose a flow characteristic to estimate (Q7,10) ... Surficial geology (% coarse material). Base-flow recession time constant, t. 8 ... – PowerPoint PPT presentation

Number of Views:47
Avg rating:3.0/5.0
Slides: 27
Provided by: KenG93
Category:

less

Transcript and Presenter's Notes

Title: Regional Analysis of LowFlow in Western WA


1
Regional Analysis of Low-Flow in Western WA
  • Presented by Ken Eng1 and Chris Curran2

1USGS, NRP, WRD, BRR-ER Reston, VA2USGS, WAWSC,
Tacoma, WA May 23, 2008
2
Regional Analysis of Low-flowin Western
Washington
  • Decide on a list of candidate index sites.
  • Select relevant basin characteristics.
  • Choose a flow characteristic to estimate (Q7,10).
  • Run correlation analysis (MOVE, etc) to estimate
    Q7,10 at simulated misc. sites.
  • Test different scenarios for index-site
    selection.
  • Develop regression model to estimate Q7,10 at
    ungaged or future miscellaneous sites.

3
Index site
4
Index site
5
Index-site selection
  • Natural, unaltered flow.
  • No significant storage (lakes, ponds).
  • No significant contribution from snowmelt.
  • Q7,10 cannot equal zero (correlation analysis).
  • More than 10 years of continuous daily-streamflow
    record.
  • Must have overlapping record (correlation only).
  • Only USGS gages considered.

6
USGS index gages used in the correlation analysis
7
Basin characteristics
  • Drainage area (StreamStats).
  • Geographic proximity.
  • Mean-annual precipitation (StreamStats).
  • Surficial geology ( coarse material).
  • Base-flow recession time constant, t.

8
Base-flow Recession Time Constant, t
  • Tau describes how fast base-flow recedes

Large t
Small t
Time
  • Many ways to estimate t e.g., Brutsaert and
    Nieber, 1977 Eng and Brutsaert, 1999 Eng and
    Milly, 2007, Brutsaert, 2008.

9
Base-flow Recession Time Constant, t
  • Estimated t from pair of measurements

Single
Paired
Day 8
No t can be estimated for a single value.
Qt
QtDt
Dt5 days
10
Regional low-flow correlation analysis
  • Done using a Matlab script written by Ken
  • Uses the daily-streamflow records for all index
    gages.
  • Simulates a miscellaneous site by using an index
    site.
  • Extracts the recession segments of hydrograph.
  • Randomly picks a daily flow (or pairs) and treats
    it as a miscellaneous measurement.

11
Regional low-flow correlation analysis
  • Runs each scenario with a user-defined
    combination of basin characteristics and number
    of miscellaneous measurements.
  • Determines best index site (similar A,G,P,t,S)
  • Performs Q-ratio, MOVE, base-flow correlation
  • Calculate estimates of Q7,10 and compares this
    with the known value of Q7,10, records error.
  • Repeated 500 times.

12
Low-flow correlation analysis
73
13
Low-flow correlation analysis
14
Summary for correlation analysis
  • Minimum 4 measurements for Q-Ratio.
  • Using t reduces RMSE by roughly 10.
  • MOVE and base-flow correlation will underestimate
    (more conservative).
  • Q-Ratio may overestimate (undesirable for low
    flow).

15
Recommendations based on correlation analysis in
western Washington
  • Q-Ratio (lt8) and/or MOVE (gt8) methods.
  • Minimum 4 measurements (paired for t).
  • 3 day minimum wait between paired meas.
  • Wait 6 days until after peaks, check a nearby
    gage hydrograph to ensure recession
  • Make measurements during base-flow season

16
Regional regression analysis
  • Different from correlation analysis
  • Uses basin characteristics.
  • Uses index gages
  • Can use discontinued sites.
  • Miscellaneous measurements can be used.
  • More accurate Q7,10 benefits regional regression
    model.

17
USGS index gages used in analyses
18
Regional regression models using A, P, t
19
Regional regression analysis
20
Regional regression analysis
  • Summary for regression models
  • 8 pairs - 60 of potential reduction in RMSE.
  • Diminishing returns after 8 pairs.
  • Recommendations
  • Use A, P, and t.
  • Maximum of 8 paired measurements.
  • Minimum of 4 paired measurements.

21
Optimizing the Low-flow Networkin Western
Washington
What types of miscellaneous sites do we still
need?
22
Optimizing the Low-flow Networkin Western
Washington
  • Fill spatial gaps in the existing network.
  • Use StreamStats to identify potential locations
    for miscellaneous sites.
  • Balance location with operational concerns.

23
Future Miscellaneous Sites
  • Correlation analysis versus regional regression
    to estimate Q7,10 for miscellaneous sites
  • Correlation
  • Gambling, based on best single index site
  • Lengthy, need measurements
  • Regression
  • Robust
  • Simple
  • Recommendation regional regression models to
    estimate Q7,10 at future miscellaneous sites.

24
Summary of What to do for a Study
  • For estimating Q7,10 at current miscellaneous
    sites
  • Run a correlation analysis to estimate Q7,10 at
    current miscellaneous sites.
  • Use A, P and t as criteria to select index site.
  • Use Q-ratio for lt 8 pairs of measurements or MOVE
    (gt 8) to estimate Q7,10.
  • Need minimum of 4 singles/pairs.

25
Summary of What to do for a Study
  • Develop regional regression model to estimate
    Q7,10 at future sites.
  • Use A, P, and t.
  • Use all continuous and current miscellaneous
    sites.
  • Use t (at least 4 pairs).
  • Application of regional regression model.
  • Make measurements at a stream of interest.
  • Compute t from all pairs and average.
  • Find A and P for the site (StreamStats).
  • Place into regression model to calculate Q7,10.

26
References
  • Brutsaert, W. and J. L. Nieber (1977),
    Regionalized drought flow hydrograph from a
    mature glaciated plateau, Water Resour. Res.,
    13(3), 637-643.
  • Brutsaert (2005), Hydrology An Introduction,
    Cambridge University Press, 605.
  • Brutsaert (2008), Long-term groundwater storage
    trends estimated from streamflow records
    Climatic perspective, Water Resour. Res., 44,
    W02410.
  • Eng K. and W. Brutsaert (1999), Generality of
    drought flow characteristics within the Arkansas
    River basin, J. Geophys. Res., 104(D16),
    19,435-19,441.
  • Eng, K. and P.C. D. Milly (2007), Relating
    low-flow characteristics to the base flow
    recession time constant at partial record stream
    gauges, Water Resour. Res.,43, W01201.
Write a Comment
User Comments (0)
About PowerShow.com