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Stream morphology and hydrology

Stream morphology and hydrology. Hydraulic geometry. Typical at a station values (midwestern streams). b = 0.25 f = 0.4 m = 0.35. B = aQ b h = cQ f U = kQ m. Typical downstream values. b = 0.5 f = 0.4 m = 0.1. Hydrology short overview. Stream records Flow duration curves

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Stream morphology and hydrology

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  1. Stream morphology and hydrology

  2. Hydraulic geometry Typical at a station values (midwestern streams) b = 0.25 f = 0.4 m = 0.35 B = aQb h = cQf U = kQm Typical downstream values b = 0.5 f = 0.4 m = 0.1

  3. Hydrology short overview • Stream records • Flow duration curves • Flood frequency curves • Importance of short-lived (<< 1 day) rare events (“flashiness”)

  4. Example: Anoka discharge record

  5. Flow duration curve

  6. Note: daily Q values do not capture true maxima For small basins (< 100 km^2), 15 min max Q can be ~10x annual daily max Q

  7. Flow duration curve

  8. Flood frequency (return period) Note: Find annual max on water year basis

  9. If gage data are not available… • USGS regional curves: multiple regression of flood frequency on basin area, other variables • Gage analysis: estimation based on discharge records from nearby basins, correcting for basin area • Literature: “prediction in ungaged basins”

  10. USGS regional curves

  11. USGS regional curves

  12. USGS regional curves

  13. USGS regional curves Minnesota Region D: Lorenz et al. USGS 2009-5250 Q1.5 = 0.892 DAREA0.778 SLOPE 0.422 (LAKE+1)-0.29 ROFF1.144 Q2 = 1.58 DAREA0.785SLOPE 0.436(LAKE+1)-0.328 ROFF 1.011 Q5 = 4.62 DAREA0.795SLOPE 0.453(LAKE+1)-0.392 ROFF 0.78 Q10 = 7.98 DAREA0.799SLOPE 0.456(LAKE+1)-0.419 ROFF 0.671 Q50 = 19.9 DAREA0.803SLOPE 0.455(LAKE+1)-0.458 ROFF0.507 Q500 = 48.9 DAREA0.803SLOPE 0.449(LAKE+1)-0.488 ROFF0.376 Qn = discharge with return interval n in years (cfs) DAREA = drainage area (sq. miles) SLOPE = channel slope (feet / mile) LAKE = area covered by lakes (as % of drainage area, 0=1%) ROFF = generalized mean annual runoff (in) Note: analogous reports also available for estimating low-flow statistics

  14. Mean annual runoff

  15. Estimating flow duration curve in ungaged basins • Assuming there is a gaged basin nearby (similar climate, vegetation, rock type, etc): • Plot Q/Q2 vs % time exceeded for the gaged basin • Estimate Q2 for the ungaged stream assuming Q2 = bankfull Q • Estimate other % time exceeded for a given Q by multiplying the Q/Q2 value from the gaged curve by the Q2 value for the ungaged stream

  16. Example Q/Q2

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