Taming the Alabama River Patrick Dobbs & Clay Campbell AMEC Environment & Infrastructure, Inc. 2012 Alabama Water Resources Conference.

Taming the Alabama River

Patrick Dobbs & Clay Campbell

AMEC Environment & Infrastructure, Inc.

2012 Alabama Water Resources Conference

2

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

3

Cottrell Landing LOMR

4

USGS Profile Estimate

5

Alabama River Watershed

6

Upper Alabama Watershed

7

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

8

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

nn

ual

Ch

ance

Dis

char

ge

(cfs

)

9

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

10

Survey

Road/deck elevations were collected Field verification

Deck thickness Bridge width Rail height Piers

–Number of

–Width Sloping abutments

11

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

12

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

13

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

14

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

15

Calibration vs. High Water Mark Elevations

16

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

17

1% Comparison to Effective

18

Base Floodplain Comparison – Selma, AL

19

Base Floodplain Comparison – Montgomery, AL

20

Base Floodplain Comparison – Wetumpka, AL

21

Stakeholder Involvement/Expectations

Stakeholders USACE USGS Alabama Power Company Counties/Municipalities bordering the river

Expectation - Lower BFEs due to 2008 USGS publication

22

Cottrell Landing

Effective Revised

23

Questions

Patrick Dobbs & Clay Campbell

AMEC Environment & Infrastructure, Inc.