1 of 39

LaSalle Avenue Corridor Resiliency Plan�

Courses of Action (COAs) – Mitigation Measures

Carroll E. Collins, AICP

Uday Khambhammettu, P.E., CFM

December 07, 2021

2 of 39

OVERVIEW

Introductions
Study Area
Purpose and Need / Goals and Objectives
H&H Methodology and Assumptions
Existing Conditions Review
Courses of Action (COAs) Review
Mitigation Measures

Phases
Project Costs

Conclusion – Next Steps

3 of 39

STUDY AREA

1.5-mile segment (shown in red)

LaSalle Gate to Mercury Boulevard

Serves ~ 30% to 35% of JBLE-Langley AFB traffic
Traverses bridge vulnerable to rising seas and storm surge
LaSalle Gate has potential to flood due to elevation/proximity to Southwest Branch of Back River

LaSalle Gate

Mercury Blvd

LaSalle Ave

JBLE - Langley

Nealy Ave

Tide Mill Ln

Armistead Ave

King St

4 of 39

PURPOSE AND GOALS

Purpose and Need:

Focus resources on prioritized resiliency improvements to sustain accessibility to/from JBLE-Langley due to multiple forces of water (i.e., storm surge, tidal action, stormwater, and groundwater)

Goals and Objectives:

Mitigate risk to the Air Force and public safety
Sustained mission readiness, national security, and resiliency
Protect economic resources

5 of 39

H&H MODEL METHODOLOGY

Rainfall Conditions

(NOAA Atlas 14 2000)

Storm Event	Precipitation
10-Year	5.53 in
25-Year	6.83 in
50-Year	8.05 in
100-Year	9.35 in

Tailwater Conditions

(assuming 1.5’ of SLR since 1970 by 2018 per HRPDC guidance)

Event Scenario	May 2021 Tailwater
Current Tailwater	3.6’ NAVD 88
3’ SLR	5.1’ NAVD 88 (3.6’ NAVD 88 + 1.5’)
4.5’ SLR	6.6’ NAVD 88 (3.6’ NAVD 88 + 3’)

* Future = Scenarios that will occur with OR without intervention

6 of 39

8 of 39

EXISTING CONDITIONS REVIEW

Many houses and roads located within or near the study area are impacted by inundation in the 100-year storm event

Tailwater (TW) Scenario	Houses Impacted	LaSalle Ave Impassable	Mercury Blvd Impassable
3.6’ TW	118	No	No
5.1’ TW	435	No	Yes
5.6’ TW	631	No	Yes
6.6’ TW	1210	Yes	Yes

9 of 39

COA EVALUATION CRITERIA

Maintains Installation Accessibility (Critical Corridor Resiliency)
Impact on JBLE-Langley Gate Operations
Mitigates/Reduces Impact of Forces of Water impact on Residential Community/Built Environment
Mitigate Risk to JBLE-Langley Mission Readiness and Public Safety
Protects Economic Resources
Order of Magnitude Preliminary Cost Estimate

10 of 39

COURSES OF ACTION (COA)

COA 1 No Action (Existing and Future Conditions)

COA 2 Mitigation measures to protect transportation infrastructure to and from the installation

COA 3 Mitigation measures to protect primary transportation infrastructure in the study area

COA 4 Mitigation measures to protect primary transportation infrastructure in the study area and Riverdale Neighborhood

11 of 39

PROPOSED MITIGATION MEASURES

LASALLE AVE

MERCURY BLVD

TIDE MILL LN

RAISING LASALLE AVENUE

7,8,9

REPLACING LASALLE BRIDGE (NORTH)

LASALLE NORTH FLOODWALL

LASALLE SOUTH FLOODWALL

BACKRIVER FLOOD GATE

BACKRIVER PUMP STATION

MERCURY BLCD FLOOD GATE, REPLACING MERCURY BLVD BRIDGE, MERCURY BLVD PUMP STATION

BOX CULVERTS WITH SLUICE GATES

NEWMARKET CREEK FLOOD GATE

LASALLE AVENUE CORRIDOR RESILIENCY PLAN

12 of 39

PROPOSED MITIGATION MEASURES

RAISING LASALLE AVENUE

REPLACE LASALLE BRIDGE (NORTH)

LASALLE NORTH FLOOD WALL

LASALLE SOUTH FLOOD WALL

BACKRIVER FLOOD GATE

BACKRIVER PUMP STATION

BOX CULVERT AND SLUICE GATE (NORTH)

BOX CULVERT AND SLUICE GATE (SOUTH)

NEWMARKET FLOOD GATE

MERCURY BLVD FLOOD GATE

REPLACING MERCURY BLVD BRIDGE

MERCURY BLVD PUMP STATION

NEWMARKET CREEK TRAIL

13 of 39

PHASE 1

LINE ITEM	LANE DIRECTION	PROJECT #
RAISING LASALLE AVENUE	NORTH & SOUTH	1
BOX CULVERTS AND SLUICE GATES	NORTH & SOUTH	10 & 11
NEWMARKET CREEK TRAIL	SOUTH ONLY	13

Legend

NORTHBOUND & SOUTHBOUND

SOUTHBOUND

NORTHBOUND

14 of 39

PHASE 2

LINE ITEM	LANE DIRECTION	PROJECT #
REPLACING LASALLE BRIDGE (NORTH)	NORTHBOUND & SOUTHBOUIND	2

Legend

NORTHBOUND & SOUTHBOUND

SOUTHBOUND

NORTHBOUND

15 of 39

PHASE 3

LINE ITEM	LANE DIRECTION	PROJECT #
LASALLE NORTH FLOOD WALL	SOUTH	3
LASALLE SOUTH FLOOD WALL (ALT 1)	NORTH	4
LASALLE SOUTH FLOOD WALL (ALT 2)	NORTH	4

LASALLE AVE

MERCURY BLVD

Legend

NORTHBOUND & SOUTHBOUND

SOUTHBOUND

NORTHBOUND

16 of 39

LASALLE SOUTH FLOOD WALL – ALTERNATIVE 1�Protects Base Accessibility Only

PROS

Protects accessibility to JBLE-Langley
Cost of Alternative 1 < Cost of Alternative 2
Requires minimal property acquisition
Minimizes tidal wetland impact

CONS

Leaves commercial and residential areas at risk to flooding in high tailwater events
Blocks secondary access to commercial areas on Mercury Boulevard

17 of 39

LASALLE SOUTH FLOOD WALL – ALTERNATIVE 2�Protects Amazon Facility, Multi-Family Housing, and Base Accessibility

PROS

Protects accessibility to JBLE-Langley
Protects commercial and residential property
Amazon could potentially help offset cost

CONS

Cost of Alternative 2 > Cost of Alternative 1
Requires property acquisition from private property owner
Creates substantial wetland impact costs

18 of 39

PHASE 4

LINE ITEM	LANE DIRECTION	PROJECT #
BACK RIVER FLOOD GATE	SOUTH	5
BACK RIVER PUMP STATION	SOUTH	6
MERCURY BLVD FLOOD GATE	NORTH	7
REPLACING MERCURY BLVD BRIDGE	NORTH	8
MERCURY BLVD PUMP STATION	NORTH	9

7,8,9

Legend

NORTHBOUND & SOUTHBOUND

SOUTHBOUND

NORTHBOUND

19 of 39

PHASE 5

LINE ITEM	LANE DIRECTION	PROJECT #
NEWMARKET FLOOD GATE	NORTH	12

Legend

NORTHBOUND & SOUTHBOUND

SOUTHBOUND

NORTHBOUND

20 of 39

CONSTRUCTION SEQUENCE: SOUTHBOUND

Legend

Phase 1

Phase 2

Phase 3

Phase 4

RAISING LASALLE AVENUE

NEWMARKET CREEK TRAIL

BOX CULVERTS AND SLUICE GATES

REPLACING LASALLE BRIDGE NORTH (SOUTHBOUND LANE)

LASALLE NORTH FLOOD WALL

BACKRIVER FLOOD GATE

BACKRIVER PUMP STATION

MERCURY BLVD

LASALLE AVE

TIDE MILL LN

21 of 39

CONSTRUCTION SEQUENCE: NORTHBOUND

MERCURY BLVD

Legend

Phase 1

Phase 2

Phase 3

Phase 4

Phase 5

7,8,9

RAISING LASALLE AVENUE

BOX CULVERTS AND SLUICE GATES

REPLACING LASALLE BRIDGE NORTH (NORTHBOUND LANE)

LASALLE SOUTH FLOOD WALL

MERCURY BLVD FLOOD GATE, REPLACING MERCURY BLVD BRIDGE, MERCURY BLVD PUMP STATION

NEWMARKET FLOOD GATE

LASALLE AVE

TIDE MILL LN

22 of 39

COURSE OF ACTION #1

MERCURY BLVD

TIDE MILL LN

Legend

Phase 1

Phase 2

Phase 3

Phase 4

Phase 5

COA #1: NO ACTION

COA #2: MITIGATION MEASURES TO PROTECT TRANSPORTATION INFRASTRUCTURE TO AND FROM THE INSTALLATION

COA #3: MITIGATION MEASURES TO PROTECT PRIMARY INFRASTRUCTURE IN THE STUDY AREA

COA #4: MITIGATION MEASURES TO PROTECT PRIMARY INFRASTRUCTURE IN THE STUDY AREA AND RIVERDALE NEIGHBORHOOD

COURSE OF ACTION #2

COURSE OF ACTION #3

COURSE OF ACTION #4

7,8,9

23 of 39

PROPOSED MITIGATION MEASURES

RAISING LASALLE AVENUE

REPLACE LASALLE BRIDGE (NORTH)

LASALLE NORTH FLOOD WALL

LASALLE SOUTH FLOOD WALL

BACKRIVER FLOOD GATE

BACKRIVER PUMP STATION

BOX CULVERT AND SLUICE GATE (NORTH)

BOX CULVERT AND SLUICE GATE (SOUTH)

NEWMARKET FLOOD GATE

MERCURY BLVD FLOOD GATE

REPLACING MERCURY BLVD BRIDGE

MERCURY BLVD PUMP STATION

NEWMARKET CREEK TRAIL

24 of 39

BACK RIVER FLOOD GATE

Sluice Gates

Back River

ECF Flood Wall

LaSalle Avenue

25 of 39

BACK RIVER FLOOD GATE

Back River

Example Sluice Gate

Sluice Gates

ECF Flood Wall

LaSalle Avenue

26 of 39

NEWMARKET CREEK FLOOD GATE

Newmarket Creek

Crest Gates

LaSalle Avenue

27 of 39

NEWMARKET CREEK FLOOD GATE

Example Crest Gate

Crest Gates

Newmarket Creek

LaSalle Avenue

28 of 39

ROADWAY IMPROVEMENTS TYPICAL SECTION

29 of 39

PROPOSED MITIGATION MEASURES

LASALLE AVE

MERCURY BLVD

TIDE MILL LN

RAISING LASALLE AVENUE

7,8,9

REPLACING LASALLE BRIDGE (NORTH)

LASALLE NORTH FLOODWALL

LASALLE SOUTH FLOODWALL

BACKRIVER FLOOD GATE

BACKRIVER PUMP STATION

MERCURY BLCD FLOOD GATE, REPLACING MERCURY BLVD BRIDGE, MERCURY BLVD PUMP STATION

BOX CULVERTS WITH SLUICE GATES

NEWMARKET CREEK FLOOD GATE

LASALLE AVENUE CORRIDOR RESILIENCY PLAN

30 of 39

WETLAND PERMITTING POINTS OF INTEREST

31 of 39

Approximately 2.73 acres of permanent impact to tidal wetlands

This estimate includes a 20-foot temporary construction easement

IMPACTS OF RAISING LASALLE AVENUE

32 of 39

IMPACTS OF LASALLE NORTH FLOODWALL

Approximately 0.22 acres of permanent impact to tidal wetlands for floodwall placement

33 of 39

IMPACTS OF LASALLE SOUTH FLOOD WALL

Alternative 1

Approximately 1.73 acres of permanent impact to tidal wetlands and subaqueous bottom for floodwall placement

34 of 39

Approximately 3.46 acres of permanent impact to tidal wetlands and subaqueous bottom for floodwall placement

Approximately 5.06 acres of permanent conversion from tidal to non-tidal wetlands

Approximately 8.52 acres of total impact

IMPACTS OF LASALLE SOUTH FLOOD WALL

Alternative 2

35 of 39

Approximately 0.13 acres of permanent impact to tidal wetlands and subaqueous bottom for gate construction and placement

Lower wetland impacts are anticipated assuming construction easements can be placed in uplands, adjacent to the western stormwater feature

IMPACTS OF MERCURY BOULEVARD GATE

36 of 39

IMPACTS OF NEWMARKET CREEK AND BACK RIVER GATES

NEWMARKET CREEK GATE

BACK RIVER GATE

Approximately 0.32 acres of permanent impact to tidal wetlands and subaqueous bottom for gate construction and placement

At least 0.33 acres of permanent impact to tidal wetlands and subaqueous bottom for gate construction and placement

The full extent of impacts will depend on the floodwall alternative chosen

37 of 39

IMPACTS OF BOX CULVERTS AND SLUICE GATES

Approximately 500 square feet (0.01 acre) of permanent impact to tidal wetlands and subaqueous bottom for gate construction and placement

The wetlands depicted in red were impacted as part of Phase 2 and are not included in the impact estimate for Phase 4

38 of 39

NEXT STEPS

Select/Refine Preferred COA

Mitigation Measures
Phasing
Cost Estimates

Schedule and conduct Public Engagement
DRAFT Report Under Review

39 of 39

Thank you!

Uday Khambhammettu, P.E., CFM

uday.Khambhammettu@kimley-horn.com

Ph: (757) 355-6661

Carroll E. Collins, AICP

Carroll.collins@kimley-horn.com

Ph: (757) 213-8616