SR-A1A Tidal Flooding Study Presented by James Poole, FDOT & David Boyer, Scalar Consulting Group Inc.

May 27, 2021 Project Introduction  One of the roadway segments identified for a resiliency study in the Broward MPO’s 2045 metropolitan transportation plan is this segment of SR A1A in Hollywood.  The catalyst for the study was recurring flooding.  The Study area extends from Southbound ramp tie down just south of Hallandale Beach Boulevard to the south end of SR-A1A bridge just north of Dania Beach Boulevard  Study Status: Study Area  Existing Conditions Report submitted to FDOT on July 8, 2020  Alternatives Report submitted to FDOT on August 28, 2020  FDOT Programing of three pump station began in December 2020

Begin End Project Project

2 Tidal Elevation Basics

 Mean High High Water (MHHW) – The average of the higher high-water height of each tidal day observed - 0.53 NAVD  Mean High Water (MHW) – The average of all the high-water heights observed - 0.38 NAVD  Mean Tide Level (MTL) – The arithmetic mean of mean high water and mean low water - (-) 0.87 NAVD

3 Sea Level Rise Data

 October 2019 King Tide elevation - 2.64 NAVD  October 2020 King Tide elevation - 2.51 NAVD

4 Sea Level Rise Data

 Sea Level Rise (SLR) applied to MHHW (NOAA intermediate values for project site)  2.13 – Year 2040  4.96 – Year 2070

5 Existing Conditions

 Existing Conditions Report - Identify and evaluate:  Field observations

 Flooding observed  Seawalls  Low road elevations  Potential overflow locations  Storm sewer systems

 Locate outfalls

 Contributing areas

 Land use  Overland flow weirs  Create model of system

6 Tidal Flooding Observations  Overflow of low sidewalk/park areas  Overflow of low seawalls  Backflow through storm sewer systems  Infiltration though leaky pipes

 Occurs both at night and during the day October 2020 King Tide Flooding on SR-A1A From a low seawall and over a sidewalk

May 2020 King Tide Flooding on SR- A1A at Harrison Street – 10 PM October 2019 King Tide Flooding on SR-A1A 7 Tidal Flooding Observations

 Evidence of upwelling or groundwater affecting tidal flooding observed with study  Side streets have low points adjacent to SR- A1A Average grate elevation is 0.88 NAVD October 2020 King Tide Flooding on SR-A1A (North American Vertical Datum of 1988) From a low seawall and over a sidewalk  MHHW – 0.53 NAVD = 0.35’ freeboard

SR-A1A at Azalea Street – October 2020 8 Tidal Flooding Observations

Overtopping of low areas with no Overtopping of low seawalls seawalls and interconnected low areas

9 Flooding – Backflow through Storm Systems

Leak at joint at a manhole

12 Flooding – Flow through Leaky Seawalls

Vertical seam where the walls join not sealed

13 Flooding – Collapsed or Damaged Seawalls

15 Hydrological Modeling

 Received High Resolution LiDAR data from FDOT  Lidar accuracy: +/- 3” to 7  Received as-built data and CADD files from on-going FDOT projects along corridor

 Determined pipe and invert data, designation of pipe types and pipes that have been lined, and identified pipes with installed back flow prevention

16 Hydrological Modeling

 Data processed/refined and imported into ICPR4 (modeling software)  Digital Elevation Model and CADD data are inputs to GIS for data manipulation and ICPR4 model development  Storm sewer systems appear adequate for storm flows, but inlets are too low relative to tide stages  Flooding from tidal waters

17 Project Results

 Alternatives Report:  Review of existing devices  Proposed remedies:  Prevention

 Raise low seawalls

 Construct new seawalls where none exist  Attenuation

 Repair or replace backflow preventers

 Repair or replace leaking structures

 Pump stations to remove tidal flows  Restoration

 Raise, reconstruct low side streets

 Raise, reconstruct SR-A1A

21 Backflow Preventers

 Flap gates exist on most outfalls throughout the corridor

5 – Ross 70 HFV-A Flap Gates 3 – In-line Flap Gates

6 - new WaPro valves installed 8/2020 18 – CheckMate Valves

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