Taming the Alabama River Patrick Dobbs & Clay Campbell AMEC Environment & Infrastructure, Inc 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) Alabama River Alabama River near Montgomery 283,000260,000290, Alabama River Alabama River at Selma 284,000250,000280, Alabama River Alabama River near Millers Ferry 284,000na 87.0na Coosa River Coosa River at Jordan Dam near Wetumpka 234,000316,000208, na

8 Hydrology Results Comparison

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) 10218, , , , ,

12 Hydraulics – Parameters & Floodway  HEC-RAS Guidance  Contraction/Expansion coefficients  Ineffective area  Manning’s ‘n’ coefficient – Aerial imagery – Survey photos – Field visits  Floodway – similar to effective Stream NameLeft OverbankChannelRight Overbank MinimumMaximumMinimumMaximumMinimumMaximum Alabama River Coosa River

13 Calibration  March 1990 flood event  March 15 th – 16 th  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 HWMs  Within +/- 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 SourceRiver Station (miles)Location Historic Peak (Feet NAVD 88) Model Elevation (Feet NAVD 88) Difference (Feet NAVD 88) Alabama River152.9North Boulevard Alabama River143.4US Highway Alabama River Alabama River Alabama River102.4 R.F. Henry Lock and Dam Alabama River Alabama River Alabama River Alabama River Alabama River72.4 Louisville and Nashville Railroad Bridge Alabama River Alabama River Alabama River55.6Cahaba River Alabama River Alabama River Alabama River33.3Oak Creek Alabama River Alabama River Alabama River Alabama River Alabama River16.2Ellis Ferry Landing Alabama River Alabama River2.0Shell Creek

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 EffectiveRevised

23 Questions Patrick Dobbs & Clay Campbell AMEC Environment & Infrastructure, Inc.