taming the alabama river
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Taming the Alabama River. 2012 Alabama Water Resources Conference. Patrick Dobbs & Clay Campbell AMEC Environment & Infrastructure, Inc. Objective & Scope. Develop a more accurate model Utilize new data Address scientific opinion about effective model Produce regulatory products - PowerPoint PPT PresentationTRANSCRIPT
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Taming the Alabama River
Patrick Dobbs & Clay CampbellAMEC Environment & Infrastructure, Inc.
2012 Alabama Water Resources Conference
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Objective & Scope
Develop a more accurate model Utilize new data Address scientific opinion about effective model
Produce regulatory products Produce non-regulatory (Risk MAP) products
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Cottrell Landing LOMR
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USGS Profile Estimate
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Alabama River Watershed
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Upper Alabama Watershed
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Historic Flooding
Flooding Source Site Name
Peak Discharges (cfs) Peak Elevation (ft NAVD 88)
1961 1979 1990 1961 1979 1990
Alabama River
Alabama River near Montgomery
283,000 260,000 290,000 158.5 152.5 154.5
Alabama River
Alabama River at Selma 284,000 250,000 280,000 119.9 116.9 118.7
Alabama River
Alabama River near Millers Ferry
284,000 na na 87.0 na na
Coosa River Coosa River at Jordan Dam near Wetumpka
234,000 316,000 208,000 182.1 189.3 na
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Hydrology Results Comparison
5000 7000 9000 11000 13000 15000 17000 19000 21000 23000225000
250000
275000
300000
325000
350000
375000 1% Annual Chance Event Results Comparison
FIS
USGS SIR 2007-5204
AMEC Study
Gage Maximum
5% Confidence Limit
95% Confidence Limit
Drainage Area (sq. mi.)
1% A
nnua
l Cha
nce
Disc
harg
e (c
fs)
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Hydraulics Method and Analysis
Alabama-Coosa River - From the Millers Ferry Lock and Dam to the Jordan Dam 187 miles 6 counties State Capital 12 river
crossings–12 main bridges–22 relief bridges
1 dam – R. F. Henry Lock and Dam
162 cross-sections HEC-RAS 4.1.0
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Survey
Road/deck elevations were collected Field verification
Deck thickness Bridge width Rail height Piers
–Number of–Width
Sloping abutments
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Hydraulics - Boundary Conditions
Known WSEL were set at the Millers Ferry Lock and Dam based on a headwater rating curve from the USACE WCM
Recurrence Interval (%) Discharge (cfs)
Water Surface Elevation (feet NAVD 88)
10 218,000 83.24 253,000 85.72 278,000 87.51 303,000 88.7
0.2 358,000 91.7
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Hydraulics – Parameters & Floodway
HEC-RAS GuidanceContraction/Expansion
coefficients Ineffective areaManning’s ‘n’ coefficient
–Aerial imagery–Survey photos–Field visits
Floodway – similar to effective
Stream Name Left Overbank Channel Right OverbankMinimum Maximum Minimum Maximum Minimum Maximum
Alabama River 0.05 0.11 0.03 0.038 0.04 0.12Coosa River 0.07 0.12 0.037 0.045 0.07 0.12
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Calibration
March 1990 flood event March 15th – 16th
8 to 13 inches of rain Most recent large flood event to affect the Upper Alabama Watershed Affected homes
–Near Montgomery ~ 500 –Near Millbrook ~ 200 to 250–Dallas County ~ 1,700
Represents floodplain characteristics of recent history–Development–Clearing and grubbing–Dam construction–Channel maintenance
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Calibration vs. High Water Mark Elevations
23 HWMsWithin +/- 0.5’ of 17 HWMs;
+/- 1.0’ of 19 HWMs; +/- 2.0’ of all HWMs
Calibrated by adjusting Manning’s ‘n’ values All values are within the
acceptable range presented in HEC-RAS Hydraulic Reference Manual (USACE, 2010)
Flooding Source River Station (miles) LocationHistoric
Peak (Feet NAVD 88)
Model Elevation
(Feet NAVD 88)
Difference (Feet NAVD
88)
Alabama River 152.9 North Boulevard 158.1 158.3 0.2
Alabama River 143.4 US Highway 31 154.5 155.0 0.5
Alabama River 138.0 152.0 152.7 0.7
Alabama River 107.4 138.4 138.8 0.4
Alabama River 102.4 R.F. Henry Lock and Dam 135.5 135.9 0.4
Alabama River 99.8 134.6 134.5 -0.1
Alabama River 96.5 132.7 132.8 0.1
Alabama River 89.7 128.4 130.0 1.6
Alabama River 75.7 120.5 121.8 1.3
Alabama River 72.4Louisville and
Nashville Railroad Bridge
119.1 119.6 0.5
Alabama River 72.2 118.5 119.6 1.1
Alabama River 65.5 115.8 115.5 -0.3
Alabama River 55.6 Cahaba River 110.4 110.5 0.1
Alabama River 52.6 108.8 108.7 -0.1
Alabama River 36.4 99.1 99.5 0.4
Alabama River 33.3 Oak Creek 97.9 98.0 0.1
Alabama River 31.5 97.0 96.6 -0.4
Alabama River 28.0 94.7 93.8 -0.9
Alabama River 20.5 90.7 90.6 -0.1
Alabama River 18.9 89.9 90.1 0.2
Alabama River 16.2 Ellis Ferry Landing 89.3 89.6 0.3
Alabama River 14.0 87.0 88.9 1.9
Alabama River 2.0 Shell Creek 83.5 83.8 0.3
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Calibration vs. High Water Mark Elevations
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Results
Revised 1% WSELs are on average 2.6 feet below the effective WSELs
Greatest difference occurs just south of Montgomery ~5 feet below the effective
Calibration to HWMs justify the difference between revised and effective BFEs
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1% Comparison to Effective
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Base Floodplain Comparison – Selma, AL
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Base Floodplain Comparison – Montgomery, AL
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Base Floodplain Comparison – Wetumpka, AL
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Stakeholder Involvement/Expectations
Stakeholders USACE USGS Alabama Power Company Counties/Municipalities bordering the river
Expectation - Lower BFEs due to 2008 USGS publication
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Cottrell Landing
Effective Revised
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Questions
Patrick Dobbs & Clay CampbellAMEC Environment & Infrastructure, Inc.