Stream morphology and hydrology. Hydraulic geometry B = aQ b h = cQ f U = kQ m Typical at a station...
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Transcript of Stream morphology and hydrology. Hydraulic geometry B = aQ b h = cQ f U = kQ m Typical at a station...
Stream morphology and hydrology
Hydraulic geometry
B = aQb
h = cQf
U = kQm
Typical at a station values (midwestern streams)
b = 0.25
f = 0.4
m = 0.35
Typical downstream values
b = 0.5
f = 0.4
m = 0.1
Hydrology short overview
• Stream records
• Flow duration curves
• Flood frequency curves
• Importance of short-lived (<< 1 day) rare events (“flashiness”)
Example: Anoka discharge record
Flow duration curve
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
Flow duration curve
Flood frequency (return period)
Note: Find annual max on water year basis
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”
USGS regional curves
USGS regional curves
USGS regional curves
USGS regional curves
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)
Minnesota Region D: Lorenz et al. USGS 2009-5250
Note: analogous reports also available for estimating low-flow statistics
Q1.5 = 0.892 DAREA0.778 SLOPE 0.422 (LAKE+1)-0.29 ROFF 1.144
Q2 = 1.58 DAREA0.785 SLOPE 0.436 (LAKE+1)-0.328 ROFF 1.011
Q5 = 4.62 DAREA0.795 SLOPE 0.453 (LAKE+1)-0.392 ROFF 0.78
Q10 = 7.98 DAREA0.799 SLOPE 0.456 (LAKE+1)-0.419 ROFF 0.671
Q50 = 19.9 DAREA0.803 SLOPE 0.455 (LAKE+1)-0.458 ROFF 0.507
Q500 = 48.9 DAREA0.803 SLOPE 0.449 (LAKE+1)-0.488 ROFF 0.376
Mean annual runoff
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
Example Q/Q2