belle view/new alexandria/river towers-flood risk management status update

106
Public Meeting Belle View/New Alexandria/River Towers Flood Risk Management Study Status Update October 25, 2012

Upload: fairfax-county

Post on 07-Jul-2015

565 views

Category:

News & Politics


0 download

DESCRIPTION

Belle View/New Alexandria/River Towers-Flood Risk Management Status Update Public Meeting October 25, 2012

TRANSCRIPT

Page 1: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

Public Meeting

Belle View/New Alexandria/River Towers

Flood Risk Management Study Status Update

October 25, 2012

Page 2: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

2

Purposes of Meeting

• Review the Belle View/New

Alexandria/River Towers flood risk

management study

• Initiate a discussion with residents about

the alignment of a flood wall/levee

• Start to create consensus among

residents about the best location of the

proposed floodwall/levee

Page 3: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

3

Agenda

• Welcome

• Presentation by the U.S. Army Corps of

Engineers (Corps)

• Question/Answers and Feedback

• Final Steps

Page 4: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

4

Communities are at Risk of Flooding

*1% annual chance flood is the flood that has a 1% chance of occurring in any

given year, sometimes referred to as the 100-year flood

1% Annual

Chance

Floodplain*

Based on

Storm Surge

Elevation 11.2

ft (NGVD29)

Page 5: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

5

Flood Inundation Areas to Elev. 14 Ft.

• Sea Level Rise

will increase

chance of

flooding

• Floods higher

than the 1%

chance flood

DO occur

Page 6: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

6

Elevation Data

• Many low openings/first floors: elevation

6-11 feet

• Majority of ground elevation is 8-9 feet in

Belle View, 4-9 feet in New Alexandria

• 2% annual chance (50 year/Hurricane

Isabel) storm surge: 9.6 feet

• 1% annual chance (100 year) storm

surge: 11.2 feet

• 0.2% annual chance (500 year) storm

surge: 16.2 feet

Page 7: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

7

Previous Study

• Completed Feb 2008 – Flood Damage Reduction

Analysis for Belle Haven Watershed (by Corps)

– Fairfax County requested that Corps conduct a study to

evaluate various flood damage reduction alternatives to

determine if they are technically feasible

– Conducted under technical services program; was not a

Corps project study authorized by Congress

– County asked Corps to conduct preliminary economic

analysis to determine if a project might meet the federal

economic justification requirements

– Evaluated alternatives to protect entire study area, and

New Alexandria/Belle View independently

Page 8: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

8

Project Goals and Objectives

• Goal

– Provide adequate flood risk management

measures that are technically feasible and

financially prudent for the safety of communities

• Objectives

– Examine various alternatives for reducing flood

risk and damages – primarily from storm surge

– Minimize risk to the community

– Minimize environmental impacts

– Incorporate needs/desires of the communities to

the degree possible

Page 9: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

9

2008 Study - Most Cost Effective, Plan 1b

• Preliminary concept plan assumed top of

levee/floodwall at elevation 12.0’ (0.8’

above 1% annual chance elevation; no risk

and uncertainty analysis was conducted;

cannot say will provide “100-year

protection” and no sea level rise

considered)

• Approx. 6600 feet long; 4-6 feet above

ground

Page 10: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

10

Plan 1b (2008 Study) - Levee/Floodwall Alternative

Page 11: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

11

Plan 1b (cont.)

• Requires 2 closure structures – along Belle

Haven Road and Belle View Blvd

• Minimizes impacts to wetlands

• Impacts many trees

• Is partially located on NPS and River Towers

property

• Requires 1 pumping station

• Estimated costs Plan 1b - Levee/Wall 12’

– Construction Cost = $12.7M

– Benefit to Cost Ratio (BCR) = 2.5

– Current cost and BCR: $13.7M and 2.2

Page 12: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

12

NPS Concerns Regarding Plan 1b

• Impact to GW Memorial Parkway

• Impact to trees

• Impact to view/aesthetics

• Would prefer project to be off their

property (if on federal property, need NEPA

process, Congressional authorization, etc.)

Page 13: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

13

River Towers Concerns Regarding Plan 1b

• Impacts to Dykes Marsh

• Impacts to River Towers property

• Impacts to view/aesthetics

• Impact of pump station on their property

• Requested that the project be moved off

their property

Page 14: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

14

Community Concerns Regarding Plan 1b

• Impacts to view/aesthetics & trees

• Impacts to Dyke Marsh

• Impacts to private property

• Level of protection & want it to fix the

problem

• FEMA certification & the need for

insurance

• Global warming/sea level rise

• Environmental impacts

Page 15: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

15

Study Progress

• 2009 – County conducted field survey and

tree survey for study

• 2010 – 2012 – Development and evaluation of

new alternatives – Team identified various new alignments

– Coordinated alignments with NPS and made revisions

– Investigated portable flood barriers

– Developed concept plans, costs and benefits for the new

plans

– Completed a preliminary sea level rise analysis

– Coordinated with community leaders

Page 16: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

Previous and New/Modified Floodwall/Levee Alignments

Page 17: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

17

Height of Protection Overview

• 1% annual chance flood elevation (100-yr

elevation based on storm surge) = 11.2 feet

• FEMA - for certification of project (no flood

insurance requirement), FEMA requires the

project be 3 feet higher than the 1% annual chance

elevation = 14.2 feet

• CORPS – for Corps built projects, wall must be

built higher than the design event to account for

risk and uncertainty (varies per project, but for the

1% annual chance flood design, typically 3-4 feet

higher than the 1% annual chance flood elevation)

plus sea level rise must be considered = 14.2-15.2

feet + SLR consideration

Page 18: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

18

Height of Protection (Cont.)

• Sea level rise predictions by the year 2100 – Based on historic rate = 1 foot

– Based on Intergovernmental Panel on Climate Change (IPCC) study = between 0.6 - 1.9 feet

– Based on National Research Council (NRC study) = between 1.5 – 4.7 feet

• Height of floodwall/levee has not been decided; initially top of protection at elevation 12 feet has been used for concept plan so that is can be compared with original plan. However, 3 heights of protection will eventually be evaluated and compared for the final alignment; higher protection is recommended to account for risk and uncertainty and sea level rise

Page 19: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

19

Corps’ Vegetation/Tree Setback

Requirements

• Trees can adversely impact floodwalls and levees and

cause the flood protection system to fail

• Vegetation/tree-free zone (except grass) extends 15 feet

on each side of a floodwall

• If a large tree has the potential to damage the wall if it

overturns, then it should be removed. General rule of

thumb - trees should be a minimum distance of half their

height from a floodwall

• County surveyed trees along potential alignments;

arborist preliminarily identified highest priority trees

based on species/condition

• Tree setback will be based on tree height and risk; we are

currently showing a 40-foot setback

Page 20: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

Alternative

Floodwall/Levee

Alignments

Page 21: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

21

Boulevard View South (South of Belle View Blvd)

• Alternative BVS1 – Wall along eastern edge

of Boulevard View (original alignment)

• Alternative BVS2 – Wall along center of

Boulevard View

• Alternative BVS3 – Wall along western

edge of Boulevard View

Page 22: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

22

Boulevard View South

Page 23: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

23

Alternative BVS1

Page 24: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

24

Boulevard View South

Looking South

Page 25: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

25

Concept View of BVS1 Looking South

Floodwall Elevation 12 Feet

Wall approximately 4 feet high

Page 26: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

26

Concept View of BVS1Looking South

Floodwall Elevation 14.5 Feet

Wall approximately 6.5 feet high

Page 27: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

27

Alternative BVS2

Page 28: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

28

Alternative BVS3

Page 29: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

29

Revised Alternative BVS3

Page 30: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

30

Concept View of BVS3 Looking South

Floodwall Elevation 12 Feet

Wall approximately 4 feet high;

Revised BVS3 wall would be constructed

further west, closer to BV buildings

Page 31: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

31

Concept View of BVS3 Looking South

Floodwall Elevation 14.5 Feet

Wall approximately 6.5 feet high;

Revised BVS3 wall would be constructed

further west, closer to BV buildings

Page 32: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

32

Boulevard View South

Looking West

Page 33: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

33

Concept View of BVS3 Looking West

Floodwall Elevation 12 Feet

Wall approximately 4 feet high;

Revised BVS3 wall would be closer to buildings

Closure structure for access

Page 34: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

34

Concept View of BVS3 Looking West

Floodwall Elevation 14.5 Feet

Wall approximately 6.5 feet high;

Revised BVS3 wall would be closer to buildings

Page 35: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

35

Sample Closure Structures

Page 36: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

36

Page 37: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

37

Page 38: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

38

Page 39: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

39

Boulevard View Central

(From Belle View Blvd north to Old Towne Rd)

• Alternative BVC1 – Wall along eastern edge of

Boulevard View (original alignment)

• Alternative BVC2 – Move Boulevard View to the

west; wall along eastern edge of Boulevard View

• Alternative BVC3 – Wall on west side of Boulevard

View

• Revised Alternative BVC3 – Wall on west side of

Boulevard View south of I Street; north of I Street

– shift road west and wall on east side

Page 40: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

40

Boulevard View Central

Page 41: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

41

Alternative BVC1

Page 42: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

42

Boulevard View Central Looking

Southeast Along Road Near H Street

Page 43: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

43

Concept View of BVC1 Looking Southeast

Floodwall Elevation 12 Feet

Wall approximately 3 feet high

Page 44: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

44

Concept View of BVC1 Looking East

Floodwall Elevation 14.5 Feet

Wall approximately 5.5 feet high

Page 45: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

45

Boulevard View Central Looking West

Page 46: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

46

Concept View of BVC1 Looking West

Floodwall Elevation 12 Feet

Wall approximately 3 feet high

Page 47: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

47

Concept View of BVC1 Looking West

Floodwall Elevation 14.5 Feet

Wall approximately 5.5 feet high

Page 48: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

48

Alternative BVC2

Page 49: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

49

Alternative BVC3

Page 50: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

50

Revised Alternative BVC3

Page 51: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

51

Page 52: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

52

Page 53: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

53

Page 54: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

54

Page 55: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

55

Page 56: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

56

Boulevard View North

(From Old Towne Rd to Belle Haven Rd)

• Alternative BVN1 - Wall behind houses

along NPS property (original alignment)

• Alternative BVN2 – Wall behind houses on

private property

• Alternative BVN3 – Wall runs along Old

Towne Rd and 10th Street; 7 houses

outside protection

Page 57: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

57

Boulevard View North

Page 58: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

58

Alternative BVN1

Page 59: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

59

Alternative BVN2

Page 60: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

60

Boulevard View North

BVN1 and BVN2 - Wall would run

near existing fence (existing wood

fence is approx. 4’4” high)

Page 61: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

61

Alternative BVN3

Page 62: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

62

Page 63: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

63

Page 64: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

64

Page 65: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

65

Page 66: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

66

Page 67: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

New Alignment –Floodwall along

GWMP

67

Page 68: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

68

Page 69: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

69

Southern Area

(near River Towers)

• Alternative S1 – Levee/wall along south

side of River Towers (original alignment)

• Alternative S1A – Levee/wall along south

side of River Towers closer to building

• Alternative S2 – Wall adjacent to Belle View

Condo north of West channel

• Alternative S3 – Wall along southern curb

of BV parking lot north of West channel

• Alternative S4 – Wall along northern curb

of parking lot south of West channel

Page 70: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

70

Southern Area

Page 71: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

71

Alternative S1

Page 72: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

72

Looking South from River Towers

Page 73: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

73

Concept View of S1 Looking South

Levee Elevation 12 Feet

Levee approximately 7 feet high

Page 74: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

74

Concept View of S1 Looking South

Levee Elevation 14.5 Feet

Levee approximately 9.5 feet high

Page 75: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

75

New Alignment - Alternative S1A

Page 76: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

76

Looking West Behind Eastern River Tower

Page 77: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

77

Looking South Behind Eastern

River Tower

Page 78: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

78

Looking West Behind Center River Tower

Page 79: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

79

Looking South Behind Center River Tower

Page 80: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

80

Alternatives S2, S3, and S4

Page 81: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

81

Alternative S2 – Western Part

Page 82: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

82

Southern Area Looking East Between Belle View Condo and West Channel

Page 83: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

83

Concept View of S2 Looking East

Floodwall Elevation 12 Feet

Wall approximately 4 feet high

Page 84: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

84

Concept View of S2 Looking East

Floodwall Elevation 14.5 Feet

Wall approximately 6.5 feet high

Page 85: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

85

Alternative S3 – Western Part

Page 86: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

86

Concept View of S3 Looking East

Floodwall Elevation 12 Feet

Wall approximately 4 feet high

Page 87: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

87

Concept View of S3 Looking East

Floodwall Elevation 14.5 Feet

Wall approximately 6.5 feet high

Page 88: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

88

Alternative S4 – Western Part

Page 89: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

89

Southern Area Looking Northwest

across West Channel

Page 90: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

90

Eastern Part of Alternative S2, S3, S4

Page 91: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

91

Southern Area (Eastern Part) Looking

North from River Towers

S2, S3 and S4 - Wall would replace existing fences

Page 92: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

92

Southern Area (Far Eastern Part)

S2, S3 and S4 - Wall would extend along this area

Page 93: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

93

Closure Structures/Increased Risk

• The more closure structures a project has,

the higher the risk of possible failure

• Original alignment (S1, BVS1, BVC1, BVN1)

= 2 road closures

• Innermost alignment (S2, BVS3, BVC3,

BVN3) = approx. 50 closures (roads,

sidewalks, and driveways)

Page 94: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

Evaluation of New Plans

Page 95: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

New Plan 1

• BVN3, BVC3, BVS3,

S1a

• No impacts to NPS

property

• River Towers within line

of protection; project on

River Towers property

• Houses near 10th St.

outside line of protection

• Estimated cost: $26.5 M

• BCR 1.2

Page 96: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

New Plan 2

• BVN3, BVC3, BVS3, S2

• No impacts to NPS

property

• River Towers and houses

near 10th St. outside line

of protection

• Not on River Towers

property

• Estimated cost: $31.4 M

• BCR 1.0

Page 97: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

New Plan 3

• BVN3, BVC3, BVS3, S4

• No impacts to NPS

property

• River Towers and

houses near 10th St.

outside line of protection

• S4 section on River

Towers property

• Estimated cost: $28.6 M

• BCR 1.1

Page 98: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

New Plan 4

• BVN1, BVC3, BVS3,

Sa1

• On NPS and River

Towers property

• All structures are within

line of protection

• Estimated cost: $22.5 M

• BCR 1.4

Page 99: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

New Plan 5

• GWMP, Sa1

• On NPS and River

Towers property

• All structures are within

line of protection

• Estimated cost: $35.2 M

• BCR 0.9

Page 100: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

100

Challenges

• Except for original plan (that will have major impact

to NPS trees), all BCR’s are less than 1.4

• Majority of alternatives would include numerous

closure structures that County would be

responsible for maintaining and closing

• Innermost alignments would impact Boulevard View

– many large trees in front of condos would have to be removed

– roadway would have to be realigned in sections

– significant impact to utilities

Page 101: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

101

Challenges (Cont’d)

• BVN3 would not protect houses near 10th street;

many challenges with aligning wall down 10th

street

• Alignments off of River Towers property

– plans are more expensive

– cross roads and tributary, cross utilities, may need

additional pump station

– RT property would be outside line of protection and would

be flooded if floodwaters were higher than elev. 11-12 ft.

(HVAC, elevators, utilities, parking lots, etc.)

– would need to leave one closure gate open for emergency

vehicles; would have to close just before flooding

Page 102: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

102

Challenges (Cont’d)

• GWMP alignment

– has less impacts to trees and utilities and less

closures than other alignments (however closures will

be large)

– road will be partially closed during/after closure

installation

– project cost will be high

– will have significant review process due to NPS land

(Congressional approval, NEPA, etc.), and may likely

be considered an “impairment”, which would prevent

the construction of the project

Page 103: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

103

Potential Next Steps

• Based on feedback from public, County may select

a project alignment for further analysis and design

• Corps will develop, evaluate and compare concept

plans for the selected alignment for 3 different

heights of protection and County will select a final

height of protection

• If alignment impacts NPS property, formal NEPA

process will be initiated concurrently

• Corps will develop more detailed design for the final

project

• Depending on many factors, the earliest project

construction would occur would be 4-5 years after

completion of 65% design

Page 104: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

104

Minimize Your Flood Risk!

• Purchase flood insurance, even if you are not

required to

• Sign up for flood alerts through the County’s

RiverWatch Program (www.fairfaxcounty.gov/cean)

• Move critical and valuable items from the basement

or the first floor (documents, old photographs,

computer, etc.)

• Consider elevating new utilities when they are being

installed since they are expensive to replace (hot

water heater, air conditioning/heating unit)

• Have an evacuation plan for you and your family

Page 105: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

105

For More Information Contact:

Donald Demetrius, P.E., PhD., Chief

Watershed Projects Evaluation Branch, Stormwater Planning

Division

Fairfax County Department of Public Works and Environmental

Services

12000 Government Center Parkway

Fairfax, VA 22035

703-324-5500, TTy 711

[email protected]

Presentation will be available on-line at:

http://www.slideshare.net/fairfaxcounty

Page 106: Belle View/New Alexandria/River Towers-Flood Risk Management Status Update

Questions?

Thoughts?

Concerns?