Building Resiliency in Transportation FacilitiesFDOT currently reviewing status of existing backflow devices
6 new WaPro valves have been installed as of 8/2020. Appeared to be bypassed by infiltration
Some seem to function; some may need maintenance; some may be bypassed with groundwater Issues can range from barnacles, trash,
rebalancing of the gate to ensure closure, etc.
23
Outfall Location Backflow Prevention Type Street Pipe Size Head to
Open Gate (In.)
Balboa In Line Flap Gate (Unknown Type) Balboa 24" 1.3 Franklin In Line Flap Gate (Unknown Type) Franklin 54" 2.8 Sheridan CheckMate Valve Sheridan St 15" 11.3 Sherman CheckMate Valve Sherman St 30" 22.5 New Hampshire CheckMate Valve New Hampshire St 30" 22.5 Collidge CheckMate Valve Coolidge St 30" 22.5 Taft CheckMate Valve Taft St 36" 27 Mckinley CheckMate Valve Mckinley St 24" 18 Connecticut CheckMate Valve Connecticut St 60" 45 Minnesota CheckMate Valve Minnesota St 36" 27 Johnson CheckMate Valve Michigan St 30" 22.5 Buchanan CheckMate Valve Buchanan St 24" 18 Indiana CheckMate Valve Indiana St 24" 18 Pierce CheckMate Valve Pierce St 30" 22.5 New York CheckMate Valve New York St 30" 22.5 Arizona CheckMate Valve Arizona St 24" 18 Tyler CheckMate Valve Polk St 30" 22.5 VanBuren CheckMate Valve VanBuren St 42" 31.5 VanBuren CheckMate Valve SR A1A 36" 27 Oregon CheckMate Valve Oregon St 30" 22.5 Madison Wapro Madison St 30" 4.7 Jefferson Wapro Jefferson St 28" 3.5 Azalea Wapro Azalea Ter 28" 3.5 Bouganvilla Wapro Bouganvilla Ter 42" 6.7 Bouganvilla Ross 70 HFV-A Flap Gate-30" Crocus Ter 24" 1.3 Bouganvilla In Line Flap Gate (Unknown Type) Daffodil Ter 24" 1.3 Foxglove Ross 70 HFV-A Flap Gate-24" Eucalyptus Ter 24" 1.3 Foxglove Wapro Foxglove Ter 34" 5.5 Foxglove Ross 70 HFV-A Flap Gate-24" Greenbriar Ter 18" 0.95 Foxglove Ross 70 HFV-A Flap Gate-30" Hyacinth Ter 24" 1.3 Magnolia Wapro Magnolia 48" 7.1 Magnolia Ross 70 HFV-A Flap Gate-19"X30" Iris Ter 14"X23" 0.82
SR A1A Tidal Flooding Study - Back Flow Preventer SummaryBackflow Preventers
King Tide Field Results
King Tide Field Review Summary
Location
Measurement
Measurement
3/10/20
5/6/20
Seawall Section
Outfall Location
Balboa
Balboa
24"
1.3
Franklin
Franklin
54"
2.8
Sheridan
Crocus Ter
Daffodil Ter
Eucalyptus Ter
Greenbriar Ter
Hyacinth Ter
Iris Ter
Average Runoff (cfs)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
$ 9,480,000.00
Devices work better in dry weather but require head to open during rain events that coincide with high tides
Pressure head to open the device can range from 3” to 7” for the WaPro valves and up to 32” for the CheckMate Valves
MHHT (0.58 NAVD) + 7” = 1.16 NAVD – or about 4” over avg inlet elevation
24
Backflow Preventers
Existing seawalls range from about 2 NAVD to over 5 NAVD
Areas at elevation below 2.7 NAVD allowed King Tide flooding (Oct 2019 King Tide was 2.64 NAVD)
*
*
25
Seawalls
Some areas are missing seawalls and are generally low areas (below 2 NAVD) A quarter are adjacent to FDOT
R/W,
26
Seawalls
27
County Park
FDOT R/W
1 530 4.26, 3.84 530 2 250 1.93, 2.18 250 3 1065 3.86, 3.53 1065 4 195 2.77 195 5 1130 4.52 1130 6 1050 3.71 1050 7 130 4.48 130 8 1530 3.73, 3.23 1530 9 375 2.73, 2.54 375 10 1200 3.77 1200 11 3750 3.77 3750 12 830 3.77 830 13 50 4.52 50 14 1770 4.52, 4.02, 4.85 1770 15 270 5.02 270 16 650 4.48 650 17 1430 3.40 1430 18 80 2.9 80 19 720 3.4 720 20 460 4.77 460 21 1910 2.15 1910 22 380 varies, below 2 385 23 975 Varies 1750 24 705 4.19 705 25 240 varies, above 2.5 240 26 120 5.05 120 27 290 varies 360 28 470 5.36 470 29 465 varies 465 30 325 varies 460 31 250 varies 250 32 315 varies 440 33 730 varies 820 34 970 2.72, 2.31,1.90,2.44 970 35 270 varies 270 36 795 4.02 795 37 195 2.15 195 38 80 varies 80 39 120 varies 120 40 390 varies 390
Total 27460 Ft 17830 880 5170 4780 5.20 Mi
Low Seawall
Notes A portion collapsed Low Seawall
Low Seawall
Low Seawall
Private, Low Seawall
Loggerhead Park Area, Sheridan to Condos No seawall Leatherback Park Area, Douglas To Cody
Green Turtle Park Area, Cody to Green
No seawall, Allen to North of Perry
No seawall, Charleston to Pershing Kemps Ridley Park Area, Pershing to Custer No seawall, Custer to Meade Hawksbill Park Area, Meade to Allen
No seawall, Palm to Desoto Private, Low Seawall Private, Low Seawall Private, Low Seawall No seawall, Cambridge No seawall, North of Dania Beach
Seawall Level of Service Example
King Tide Field Results
King Tide Field Review Summary
Location
Measurement
Measurement
3/10/20
5/6/20
Seawall Section
7
130
4.48
130
23
975
Varies
975
8
1530
9
375
10
1200
3.77
1200
29
465
varies
465
11
3750
3.77
3750
30
325
varies
325
12
830
3.77
830
31
250
varies
250
13
50
4.52
50
32
315
varies
315
14
1770
15
270
5.02
270
34
970
17
1430
3.40
1430
37
195
2.15
195
21
1910
2.15
1910
1.67
Mi
23
975
Varies
1750
24
705
4.19
705
26
120
5.05
120
27
290
varies
360
28
470
5.36
470
29
465
varies
465
30
325
varies
460
31
250
varies
250
32
315
varies
440
33
730
varies
820
34
970
36
795
4.02
795
Total
27460
Ft
17830
880
5170
4780
5.20
Mi
780
Outfall Location
Balboa
Balboa
24"
1.3
Franklin
Franklin
54"
2.8
Sheridan
Crocus Ter
Daffodil Ter
Eucalyptus Ter
Greenbriar Ter
Hyacinth Ter
Iris Ter
Number
Average Runoff (cfs)
Mobilization and Contingency (30%)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
10
3
15'
$ 1,575,000.00
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Hallmark
29.5
Y
10
3
15'
$ 1,575,000.00
37.6
16.9
29.5
Wet well costs based on 12 month avg cost for 6-' J-7 <10' Manholes, each size increases by $1200 per foot diameter
34
Seacrest
15"
None
N
-
-
-
-
35
Hallandale
48"
Unknown
Y
36
Chelsea
60"
None
N
-
-
-
-
16.6
8.2
12.4
Pump cost based on several consultant estimates. $30000 for a 1 cfs pump, increase cost by $2500 per cfs
Total Systems
2
$ 32,500.00
3
$ 35,000.00
1
$ 30,000.00
4
$ 37,500.00
2
$ 32,500.00
5
$ 40,000.00
3
$ 35,000.00
6
$ 42,500.00
4
$ 37,500.00
7
$ 45,000.00
5
$ 40,000.00
10
$ 52,500.00
6
$ 42,500.00
7
$ 45,000.00
10
$ 52,500.00
Seawall construction is estimated to be $1M adjacent to FDOT R/W and $6M in Broward County park areas.
Other costs to be identified include: permitting and mitigation costs (mangroves)
environmental habitat and
possibly sea grasses
utility relocations, ownership, ties to existing ground may not be at right height, etc.
28
Seawalls
Drainage wells were reviewed. Based on existing permit data drainage wells require at least 1.6’ (19.2”) of head to overcome salinity density to move water
More head required than all but the larger CheckMate Valves
Not a viable alternative for most sites
29
Drainage Wells
Small pump stations are recommended to alleviate backflow device head and infiltration issues
Design to be upgradeable to accommodate larger pumping constraints as SLR continues
Estimate 18 small pump stations to minimize disruption to SR-A1A.
Range in size from 1 – 1 cfs pump to 3 – 10 cfs pumps
30
Stormwater Pump Stations
Pump station costs range from $210K to over $2M per station. Pump station costs only, does not include R/W, infrastructure updates, permitting, etc.
Storm sewer systems will have to be surveyed for sizes and inverts and for options to combine systems to document system storage
Prefabricated options exist
Stormwater Pump Stations
Since significant roadway reconstruction is required, it is recommended to not raise SR- A1A profiles until SLR warrants – potentially after 2050
Side streets were evaluated for profile raising
4 potential side streets appear viable to profile raising without major offsite impacts Harrison Street, Van Buren Street, Virginia Street
and Jackson Street
Other side streets will need more detailed evaluations including detailed field survey to define offsite impacts and feasibility
32
Van Buren Street during April 2020 King Tide Field Review
Raising Roadway Profiles
King and high tides are causing “Sunny Day” street flooding along the SR-A1A corridor in Hollywood, Florida
Tides are known to backflow through storm sewers, overtop low seawalls and overflow low boundary sidewalks
Flap gates are effective in some areas and not in others
Salt water appears to be degrading the storm sewer system and may be a cause of system leaking
Groundwater appears to be a major contributor due to the leaking systems (Even sanitary systems seem prone to infiltration)
Upwelling from a sanitary sewer, water valve riser, pavers, concrete pavement seams and between pavement and gutter edges has been observed
Flooding is large enough to spread along SR-A1A and cause street flooding at adjacent low areas not necessarily being flooded otherwise
33
Study Results
Low seawalls or no other tidal barriers appear to be the major cause of flooding in the area north of Sheridan Street
Outflow from inlets appears to be the major cause of flooding in the area south of Sheridan Street
Overtopping of sidewalks adjacent to SR-A1A from groundwater adjacent to the seawall south of Hollywood boulevard contributes to the street flooding
Installation of seawalls were none exist, raising low seawalls and installing stormwater pump stations is the preferred options to alleviate the flooding in the near future. Raising SR-A1A will be a future option as sea level rise warrants
34
Next Steps Existing conditions and alternatives reports have been completed. FDOT has
programmed seawall and pump improvements and is coordinating with partners on funding.
Evaluate existing backflow devices; maintenance & repair/replace, as necessary - Ongoing
Inspect and maintain per manufacturers or City’s maintenance schedule
Verify no issues from barnacles, trash, rebalancing of the gate to ensure closure, etc.
If flooding still occurs in areas behind inspected functioning valves – recommend an infiltration/leaking pipe assessment. Done along some of SR-A1A in the past
Coordinate seawall and/or other tidal barriers for areas not protected
City/County should review requiring all seawalls to be at least elevation 3.0 NAVD ASAP and to set elevations of 4.0 NAVD by 2040 and elevation 5 NAVD by 2050
Design/construct pump stations to alleviate backflow device head flooding
Re-evaluate effectiveness of recommendations every 10-years relative to SLR updates
35