6-17-24 Joint Workshop betweent the Commission snd Community Development Board Adopted MinutesMINUTES
Joint Workshop between the City Commission
and the Community Development Board
~' Monday, June 17, 2024 - 6:00 PM
City Hall, Commission Chamber
800 Seminole Road, Atlantic Beach, FL 32233
ATTENDANCE:
Present: Curtis Ford, Mayor - Seat 1
Bruce Bole, Commissioner - Seat 2 (District 1308)
Michael Waters, Commissioner - Seat 3 (District 1307)
Candace Kelly, Commissioner - Seat 4 (District 1306)
Jeff Haynie, Member
Harold Gear, Member
Jennifer Lagner, Member
Kirk Hansen, Chair
Richard Arthur, Member
Ellen Golombek, Vice Chair
Absent: Jessica Ring, Commissioner - Seat 5 (District 1312)
Gregory (Greg) Beliles, Alternate Member
Angela Farford, Member
Also Present: William B. Killingsworth, City Manager (CM)
Kevin Hogencamp, Deputy City Manager (DCM)
Jason Gabriel, City Attorney (CA)
Donna Bartle, City Clerk (CC)
Ladayija Nichols, Deputy City Clerk (DCC)
Steve Swann, City Engineer (CE)
Amanda Askew, Planning & Community Development Dir. (PCDD)
CALL TO ORDER
Mayor Ford called the meeting to order at 6:03 PM.
1. INTRODUCTIONS
Mayor Ford introduced Brian Icerman representing Jones Edmunds.
2. PUBLIC COMMENT
Mayor Ford explained the process for public comment and requested that Greg Powell be
allowed 10 minutes to speak since he has been working on data and reports that pertain to the
workshop discussion.
CC Bartle called speakers to the podium:
Commission Workshop
June 17, 2024
Greg Powell presented as detailed in a handout (which is attached hereto and made part of this
Official Record as Attachment A).
Bruce Andrews expressed concerns regarding flooding.
Chris Bettinger spoke about permeable pavement systems.
Ethan Henninger spoke about permeable pavement systems.
Karl Klein read a memo (which is attached hereto and made part of this Official Record as
Attachment B).
Lee Elmore asked questions about swales and stormwater remediation.
Kelly Elmore spoke about possible stormwater solutions.
Susanne Barker spoke about different means of resiliency.
Lisa Herrold spoke about the importance of environmental consideration.
Max Saxston shared information about artificial turf.
Kate Kettell spoke about permeable pavement systems.
Carol Schwarz provided suggestions for stormwater management.
Kendell King provided suggestions for stormwater management.
Linda Lanier provided suggestions for stormwater management.
Brinkley Harrell expressed concerns about stormwater management.
6-17-24 Attachment A
6-17-24 Attachment B
OVERVIEW: STORMWATER MANAGEMENT PROGRAM AND ONSITE
STORAGE HISTORY — STEVE SWANN, CITY ENGINEER
CE Swann presented as detailed in pages 3-16 of the agenda packet.
PCDD Askew presented as detailed in pages 17-23 of the agenda packet.
2. PRESENTATION — JONES EDMUNDS ENGINEERING AND CONSULTING
SERVICES
Mr. Icerman presented as detailed in a slideshow presentation (which is attached hereto and
made part of this Official Record as Attachment Q.
Commission Workshop
June 17, 2024
6-17-24 Attachment C
3. QUESTIONS AND DISCUSSION — CITY COMMISSION
Commissioner Kelly inquired about the maintenance of paver systems. Chris Bettinger
explained that studies have been completed to help explain how these systems work. He
explained that the easiest maintenance practice of these systems would be daily care. The
maintenance process for artificial turf was explained.
Commissioner Waters thanked Mr. Powell for his presentation and asked about the storage of
stormwater. Mr. Powell recommended determining what the goal is regarding how stormwater
is managed. He expressed that once this is determined, then a plan can be made based on this
goal. Mr. Icerman explained that his analysis of the stormwater storage was from a perspective
of coming up with their own calculations.
Commissioner Bole expressed that the City needs to look at this topic from a macro level view
so that decisions are inclusive.
Mayor Ford inquired about permeable systems. Mr. Bettinger explained how permeable pavers
dispel unwanted materials and how the systems are maintained.
Member Arthur inquired about potential funding issues. Mr. Icerman clarified that there were
more project needs than funding available. Member Arthur also asked about stormwater
drainage and different sections of Chapter 24. Mayor Ford asked if the City could identify any
coastal cities in FL with on-site residential stormwater retention.
Member Lagner asked if there was a list that explains where the City is with Capital
Improvement Projects (CIP). CE Swann mentioned that there is a list that can be provided.
Vice Chair Golombek inquired about water seals as they relate to permeable systems. Mr. Powell
explained that water seals being applied often will result in clogging. He explained the different
types of pavers and how they are maintained.
Commissioner Bole expressed the importance of the City adhering to its own rules.
Vice Chair Golombek explained why this meeting was requested and encouraged the
Commission to take the timeline of when Chapter 24 needs to be submitted into consideration
when making changes.
Mayor Ford encouraged everyone to think about exactly what the City wants as it pertains to
stormwater management. Commissioner Bole added that the budgeting needs for projects are
important as well.
Member Gear inquired about permeable assets. Mr. Icerman explained that pools have not been
looked at; however, based on math, stormwater calculations would be treated as a post recent
rain events since stormwater designs are meant to be completed after these events.
Commission Workshop
June 17, 2024
Mayor Ford expressed that he would like to have more citizens engaged at the next meeting.
ADJOURNMENT
The meeting adjourned at 8:36 PM
Attest:
Donna L. Bartle, City Clerk
Date Approved. %1,92L,202-11
Curtis Ford, Mayor
Commission Workshop
June 17, 2024
Attachment A to
6-17-24 Minutes
COAB STORMWATER WORKSHOP
Monday June 17, 2024, 6:00 PM
Gregory Powell, PhD, PE
Good evening! For the Record:
1. Name: Gregory Powell
2. Address: 1871 Selva Marina Drive, Atlantic Beach, FL. 32233
3. 1 have lived at this address for over 30 years.
4. BS(1972), ME(1975), Ph.D.(1980) in Engineering, from the University of Florida.
5. Licensed Professional Engineer in Florida since 1982 (PE No. 31165).
6. Worked for over 40 years as a consulting engineer specializing in Civil, Environmental and Water
Resources Engineering.
7. 1 have testified as an expert in administrative hearings and in court over 15 times on subjects
including: Hydraulics, Hydrology, Water Quality, Water Supply, Stormwater Management, and
Wastewater Disposal.
8. 1 am now semi -retired, and I am here representing myself as a property owner in COAB.
If time will allow, there are a number of issues with the current Chapter 24 stormwater regulations that
are TECHNICALLY INCORRECT, and in my professional opinion, they are NEITHER REASONABLE nor
APPROPRIATE.
However, before I address those issues, I would like to start with three aspects of the Chapter 24
Stormwater Regulations that are foundational, and in my opinion are REASONABLE AND APPROPRIATE.
1. The OBJECTIVE of the Chapter 24 Regulations:
a. As discussed in the Storm Water Master Plan, developed by CDM, as far back as 2012
(SWMP 2012), the objective of the stormwater regulations is to control EXCESS stormwater
runoff from IMPERVIOUS surfaces.
b. EXCESS runoff is the increased runoff from an IMPERVIOUS surface, when compared to
runoff from a typical PERVIOUS area (SWMP, 2012).
c. It's clear from the language of the code cited in this document that there shall be no
increase in the rate or volume of flow from development or redevelopment of a lot.
d. It is also clear from the history of development in Atlantic Beach, and other places, that
unregulated development leads, over time, to increases in the percent impervious area,
which increases offsite stormwater runoff, which can lead to localized flooding.
e. This OBJECTIVE is both REASONABLE AND APPROPRIATE.
f. My concerns are not with the OBJECTIVE, but with the IMPLEMENTATION.
2. The DESIGN STORM EVENT required by Chapter 24.
a. The design storm required is a 25 -year, 24-hour event with a rainfall depth of 9.3 inches.
b. This design storm is commonly used in stormwater analysis and regulation.
c. In my professional opinion it is REASONABLE AND APPROPRIATE.
Page 1 of 5 COAB Stormwater Workshop 6/17/24
Attachment A to
6-17-24 Minutes
3. The DEFINITION OF IMPERVIOUS SURFACE (Section 24-17)
a. The first sentence of this definition is CORRECT.
b. An IMPERVIOUS SURFACE is a surface that prevents the entry of water into the soil.
I will not be presenting any calculations today to support my conclusions. However, I have provided
them, in the past to City staff and would be happy to provide them to others that wish to review them.
Now, I would like to discuss my concerns with the Chapter 24 stormwater regulations.
1. The expanded definition of Impervious Surface in Chapter 24 is TECHNICALLY INCORRECT after
the first sentence.
a. While it is true that some surfaces made of concrete, asphalt, brick, or plastic are
effectively impervious, the definition should NOT be based on the materials of
construction -- It should be based on the infiltration rate of the material.
b. There are many products made from concrete, asphalt, brick, and plastic that are partially
or effectively PERVIOUS. Examples include:
i. Permeable Pavers,
ii. Porous Pavers or "Turf Blocks",
iii. Permeable Concrete or Asphalt,
iv. Pervious Pavers, and
v. Artificial Turf.
c. To exclude these products based solely on the material of construction is a significant
stormwater management mistake that is UNREASONABLE AND INAPPROPRIATE.
d. In Northeast Florida, rainfall events with an intensity of 4.0 inches/hour have a return
period of 100 -years (US Department of Commerce, Weather Bureau, Technical Paper No.
25). Furthermore, most "typical" PERVIOUS surfaces in Atlantic Beach have an infiltration
rate that is less than 4.0 inches/hour.
e. Consequently, if test data or manufacturer's specifications confirm a long-term infiltration
rate greater than or equal to 4.0 inches/hour, it should be classified as 100% PERVIOUS.
f. I have personally conducted tests on pervious pavers and found the infiltration rates to be
well above 4 inches/hour even after subjecting them to mud flows and applying water seal.
g. A suggestion for correcting the definition of Impervious Surface is provided below:
i. In the 2nd sentence, insert the word "may" before the word "include".
ii. Insert the following sentence between the 2nd and 3rd sentences. "Construction
products or the surface materials that may be impervious, as discussed above, can
be classified as PERVIOUS, if test results or manufacturer specifications confirm
that the long-term infiltration rate is greater than or equal to 4.0 inches/hour, and the
base or lining is not impervious"
iii. Delete the last sentence. This statement about pools is incorrect (see #5 below).
2. Chapter 24 regulations should be based on the Curve Number (CN) Method, NOT on a "modified"
rational method, because the CN method is more accurate and justifiable.
a. The CN method is now the required procedure by many municipal and regional authorities
I
[Handbook of Hydrology, Maidment (1983)].
Page 2 of 5 COAB Stormwater Workshop 6/17/24
I
Attachment A to
6-17-24 Minutes
b. The CN method has largely replaced the rational method for calculating runoff volumes
and peak runoff rates for several reasons:
i. Literature values used with the rational method depend on storm intensity, duration
and other drainage basin factors that require significant judgement, rather than
justifiable or measurable data - it may be simple, it can be very inaccurate.
ii. The CN method incorporates many of the physical characteristics (i.e., land cover,
soil characteristics, and storm depth) that determine the runoff volume.
iii. Consequently, the CN method is much more accurate and justifiable.
iv. Also, peak runoff rates and the impact of onsite storage can be determined from CN
methods. The procedures are discussed in Urban Hydrology for Small Watersheds
(USDA, Technical Release -55, 1986).
c. Since the objective is to determine the onsite storage needed to control excess runoff
from impervious surfaces, the more accurate CN method should be used.
d. Then, the results can be easily converted to a simple modified rational formula for
regulatory simplicity.
3. The CN for atypical pervious surface in AB
a. Using soil data for Atlantic Beach from the Natural Resources Conservation Service (NRCS
web soil survey), I determined that a typical pervious surface in AB (i.e., upland, grassed
open space in good to fair condition) has a CN of 65.
b. Jones/Edmunds used the CN method in Attachment 1 to the SWMP Update (October 2018)
and found the same exact value for typical pervious area in AB.
c. I recommend that this CN -value (65) for atypical pervious area in AB, along with the
standard CN for an impervious surface (98), be incorporated into Chapter 24, for clarity and
consistency.
4. The Chapter 24 "modified" rational formula used to determine onsite storage is NOT CORRECT.
a. Using the standard CN method, the calculation shows that the AB Code requires a property
owner to install more than twice the onsite storage as is necessary to meet the stated
objective to control the excess runoff from impervious surfaces.
b. This error in Chapter 24 can be easily corrected by changing the constant at the beginning
of the formula [Redline, Sec 24-89 (c)(9)] from 0.92 to 0.44.
c. Furthermore, while it is true that the SWMP objective requires limiting both excess runoff
volume and peak discharge rate, the CN methods in TR -55 show conclusively that if the
onsite storage volume criteria is met, the peak discharge rate criteria also will be met.
d. Consequently, there is no need to regulate peak discharge separately, and appropriately,
the AB code does not provide a formula for calculating peak discharge.
5. Classifying all swimming pools as 50% impervious is INCORRECT, ARBITRARY AND UNJUSTIFIED.
a. At best, this pool credit was based on consensus of the AB City Commission, with input
from staff. The credit was NOT backed by sound science or engineering.
b. Infinity pools have little or no freeboard and should be considered 100% IMPERVIOUS.
Page 3 of 5 COAB Stormwater Workshop 6/17/24
Attachment A to
6-17-24 Minutes
c. Standard swimming pools use a surface skimmer to remove floating debris and the
skimmer is usually installed between 4.5 and 5.5 inches below the deck or coping. This
defines the normal water level and the pool's freeboard.
d. If the pool freeboard is at least 4.3 inches, which is the case for most standard pools,
runoff from the pool during the design storm event will be no more than from a typical
pervious area in Atlantic Beach (i.e., the pool will not cause any excess runoff). Therefore,
the pool should be considered 0% IMPERVIOUS.
e. If for some reason, a pool's normal freeboard (PFB) is less than 4.3 inches, calculation of
PERCENT IMPERVIOUS is simple and straightforward.
Pool Freeboard >4.3 inches: %IMPERVIOUS = 0%
Pool Freeboard <4.3 inches: %IMPERVIOUS = [1-(PFB (inches)/4.3 inches)]* 100
6. Artificial Turf, which AB previously considered pervious, is now being classified as impervious.
a. The OF/IFAS paper, mentioned in the Comprehensive Plan Presentation, did not call
artificial turf either IMPERMEABLE or IMPERVIOUS. As discussed above (issue #1), artificial
turf should be classified on its ability to infiltrate water.
b. I have seen data from artificial turf manufacturers (independent testing labs) that show
infiltration rates exceeding 500 inches/hour.
c. The OF/IFAS paper relied on other studies, which are not directly applicable to AB for
SEVERAL reasons:
Just one example, the authors point out that this experimental setup is most
appropriate for TEMPERATE climate conditions. Atlantic Beach is considered
HUMID SUBTROPICAL. There are several other reasons why this study is NOT
APPLICABLE.
ii. The depth(small) and duration(short) of the simulated rainfall events.
iii. The relatively small plots, and high simulated slopes when compared to AB.
d. The redline version of Chapter 24 states that artificial turf is prohibited within the dripline
of regulated tree. This statement is NOT JUSTIFIED OR JUSTIFIABLE. Even if the
impervious character of artificial turf were somehow justified, it would NOT justify the
prohibition. There are numerous examples of truly impervious surfaces within the dripline
of regulated trees that have been in place for years without an adverse impact to the tree.
7. Professional Engineering Certification
As a Professional Engineer, I would suggest that permit applications, submit with plans and
specifications, signed, and seated by a Florida PE should be reviewed by a PE.
I would suggest the following language be included in Chapter 24:
If a Professional Engineer (PE), licensed in the State of Florida, provides the COAB with a signed
and sealed engineering report for an onsite stormwater management system (including
necessary plans, specifications, and calculations), and certifies that the system meets the
objectives and requirements of Chapter 24, only the City Engineer, or a licensed engineer under
the City Engineer's responsible charge, shall review the plans and approve/disapprove the
permit. Furthermore, If the COAB chooses not to review the plans within a reasonable time
Page 4 of 5 COAB Stormwater Workshop 6/17/24
Attachment A to
6-17-24 Minutes
(TBD), the permit should be automatically approved. However, if the City Engineer requests
further information from the PE, the review clock stops until the PE responds.
This is not intended to preclude a property owner from providing the COAB with the necessary
information for a permit. It is intended to ensure that the work of a licensed Professional Engineer
is reviewed by a similarly qualified engineer.
B. One Last Point. One of the unintended consequences of overreach when establishing
regulations is that the citizens begin to ignore them, request more and more exceptions, or may
even litigate. I can attest to the fact that some of this is happening in AB with respect to the
stormwater regulations.
a. Regulations must be based on sound science and good engineering practices.
b. To gain acceptance by those regulated, they must be APPROPRIATE, JUSTIFIED, AND
CONSISTENT.
THANK YOU FOR LISTENING TO MY CONCERNS.
ANY QUESTIONS?
Page 5 of 5 COAB Stormwater Workshop 6/17/24
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Attachment A to
6-17-24 Minutes
Onsite Storage
(Based on Excess Runoff)
8.56 COAB Code requires
more than twice the
onsite storage as is
required to meet any of
the SWMP OBJECTIVES
4.
2.33
Design Storm COAB Code SWMP Objective SWMP Objective Peak
Volume Rate
1.25
WQ Control
Attachment A to
6-17-24 Minutes
Hydrologic Soil Group & Areas For
Atlantic Beach
Data Source: NRCS, Web Soil Survey, 5/13/2023
Area of Interest: Intercoastal Marsh to Ocean,
Hanna Park to Atlantic Blvd.
Map Unit
Area (ac)
HSG
7
8.5
A
14
257.4
C
22
19.3
B
24
24.2
A
29
36.2
A
32
489.4
B
33
1.7
B
35
113.2
B
36
78.3
A
42
4.3
A
49
20.7
B
58
24.9
B
62
23.3
B
71
753.6
B
Total Area =
1855
% of Area
Total A =
151.5
8%
Total B =
1446.1
78%
Total C =1
257.4
14%
Typical Pervious Area CN = 65
All A/D Soils Aassigned HSG = B.
All HSG D Soils Dropped to be Conservative
(i.e., to minimize runoff from the Typical Pervious Area).
Tables.xlsx Table 1 1 of 5 6/14/2024
Attachment A to
6-17-24 Minutes
Hydrologic Soil Group (HSG) & Areas
For Atlantic Beach
Data Source: NRCS, Web Soil Survey, 5/13/2023
Area of Interest: Atlantic Beach Municipal Boundaries.
Map Unit
Area (ac)
HSG
7
8.5
A
14
257.4
C
24
24.2
A
29
36.2
A
32
489.4
B
36
78.3
A
42
4.3
A
58
24.9
B
71
753.6
B
Total Area =
923.2
% of Area
Total HSG A =
151.5
16%
Total HSG B =
514.3
56%
Total HSG C =
257.4
28%
Typical Pervious Area CN = 65
All A/D Soils Further Evaluated: Based on Drainage Class,
Surface Texture, Wet Season Depth To Water Table, and Hydric
Rating. All HSG D Soils Dropped to be Conservative (i.e., to
minimize runoff from the Typical Pervious Area).
Tables.xlsx Table 2 2 of 5 6/14/2024
Attachment A to
6-17-24 Minutes
Estimate of Runoff and Onsite Storage Coefficients
Based on Standard Curve Number Method.
Atlantic Beach Design Storm = 9.3 inches (25 -year, 24-hour)
Required Onsite Storage Volume = CAR 12 cu, ft, Reference: AB Municipal Code Sec. 24-68(b)(9)
seasonable Vaiue for C = 0.97-0.53 = 0.44 NOT 0.92, a, : sed in AB Municipal Code
The rational or the modified -rational methods are designed to predict peak discharge rate.
IDF Curves for Jacksonville, FI show that a 9.3 inch rainfall would have a duration of at least 24 hours.
SCS CN method uses a hydrograph method and is based on 24 hour rainfall events.
SCS CN method is more appropriate for calculating runoff volumes.
CONCLUSION: The AB Municipal Code is requiring home owners to install more than twice the onsite storage
volume necessary to control runoff from the regulated impervious area during the design storm event.
Reference HEC -HMS Technical Reference Manual (USACE)
Tables.xlsx Table 3 3 of 5 6/14/2024
Typical
Pervious
Impervious
RUNOFF CALCULATION
Area
Area
Average CN for Area
65
98
Soil Storage (inches)
5.4
0.20
Initial Abstraction (]a] (inches)
1.1
0.04
Total Runoff (inches)
4.97
9.06
Equivalent Runoff Coefficients
0.53
0.97
Required Onsite Storage Volume = CAR 12 cu, ft, Reference: AB Municipal Code Sec. 24-68(b)(9)
seasonable Vaiue for C = 0.97-0.53 = 0.44 NOT 0.92, a, : sed in AB Municipal Code
The rational or the modified -rational methods are designed to predict peak discharge rate.
IDF Curves for Jacksonville, FI show that a 9.3 inch rainfall would have a duration of at least 24 hours.
SCS CN method uses a hydrograph method and is based on 24 hour rainfall events.
SCS CN method is more appropriate for calculating runoff volumes.
CONCLUSION: The AB Municipal Code is requiring home owners to install more than twice the onsite storage
volume necessary to control runoff from the regulated impervious area during the design storm event.
Reference HEC -HMS Technical Reference Manual (USACE)
Tables.xlsx Table 3 3 of 5 6/14/2024
Attachment A to
6-17-24 Minutes
Runoff Coefficient required to Keep Peak Discharge from
Impervious Area equal to Peak Discharge from Pervious Areal
25 -Year 24 -Hour Depth = 9.3 inches Runoff
Pervious CN = 65 Qp = 4.97 inches
Impervious CN = 98 Qi = 9.06 inches
Rainfall Distribution = Type III Qi-Qp = 4.09 inches
Pervious la = 1.077 inches Table 4.1 TR -55
Pervious la/P = 0.1158
Impervious la = 0.041 inches Table 4.1 TR -55
Impervious la/P = 0.0044
Peak Discharge Coefficients: Pervious Impervious
Co = 2.471685 2.457317
C1 = -0.51846 -0.52206
C2 = -0.16808 -0.18188
Time of Concentration = 0.5 hr Min=0.1, Max = 10
Unit Peak Discharge qu = 409.7562 csm/in 396.268846 csm/in
qo = Qp*qu(p) = 7.3E-05 cfs/ft2 Peak Pervious Unit Outflow Rate
qi = Qi*qu(i) = 1.29E-04 cfs/ftz Peak Impervious Unit Inflow Rate
qo/qi = 0.567173
Vs/Vr = 0.25
Onsite Storage Volume (ft) = 0.25 * P(inches)*Imp Area(ft2)/12
To Control Peak Runoff Rate the coefficient should be = 0.25
To Control Runoff Volume the coefficient should be = 0.44
The RO Coefficient in the AB Code = 0.92
Conclusion: If you control RO volume, you will control peak runoff rate
Note 1: Calculation Method from Urban Hydrology for Small Watersheds, TR -55, USDA, June
1986.
Note2: Lot size = 0.5 acres
L = 209 ft
n = 0.35
2 -yr 24 -hr Depth = 4 inches
Land slope = 0.02 ft/ft
tc = 0.5 hr
Tables.xlsxTable 4 4 of 5 6/14/202412:44 PM
Attachment A to
6-17-24 Minutes
Tables.xlsx, Tab: Table 5 5 of 5 6/14/2024 12:44 PM
Pool Pervious Credit Tablet
Design Storm Volume = 9.3 Inches
Pervious Area CN = 65
Impervious CN = 98
Typical Pervious Area Runoff = 4.97 Inches
Impervious Area Runoff = 9.060 Inches
Total Pool
Pool
Pool
Pool
Freeboard'
Runoff
Pervious
Percent
(inches)
(inches)
Credit (%)
Impervious
Comments
50.24
9.060
0%
100%
Example: infinity pools
1.0
8.30
19%
81%
2.0
7.30
43%
57%
Interpolate between values, if
2.3
7.00
50%
50%
nessary.
3.0
6.30
67%
33%
4.0
5.30
92%
8%
4.3
4.97
100%
0%
100% Pervious, No Extra Credit
5.0
4.30
116%
-16%
Pervious credit values above
100% or negative percent
impervious values represent extra
storage credit that could be used
to offset other impervious areas.
(See Example Below3)
6.0
3.30
141%
-41%
7.0
2.30
165%
-65%
8.0
1.30
190%
-90%
9.0
0.30
214%
-114%
10.0
-0.70
239%
-139%
11.0
-1.70
263%
-163%
12.0
-2.70
287%
-187%
1 Based On Curve Number Method
2 Vertical distance between normal pool water level and overflow elevations.
3 Example: If pool freeboard is 8.0 inches, impervious area credit would equal:
0.90 x Pool Area.
Tables.xlsx, Tab: Table 5 5 of 5 6/14/2024 12:44 PM
S.
Attachment A to
6-17-24 Minutes
Procedure used by Gregory Powell, PhD, PE to Evaluate Pervious Paver
Permeability. (Paver #1)
Step 1: Obtained pervious paver from local distributor.
Step 2: Built plexiglass container to enclose pervious paver and sealed all sides with silicone sealant.
Step 3: Tested the containment seal around the paver and added sealant to the bottom edge of
paver adjacent to plexiglass.
Step 4: Tested the new (clean) pervious paver (n=8). The 959'% LCL of the permeability was
inches/hour.
Step 5: Flushed over a gallon of muddy water through the paver and carefully removed the 1/2 inch
of mud that had accumulated on the surface.
Step 6: Tested the "poorly maintained" paver (n=3). The 95% LCL of the permeability was
inches/hour (5 times the AB 100 year storm intensity is 4 inches/hour).
Step 7: Dryed the "poorly maintained" paver for two days (no additional cleaning) and retested
(n=6). The 95% LCL for permeability was inches/hour (not statistically different from first muddy
test).
Step 8: Washed off the surface of the paver with tap water and let it dry for two days. Applied
Thompson's Water Seal with spray applicator, as suggested on label, and let paver dry for two days.
Step 9: Tested pervious paver after applying Thompson's Water Seal (n=5). The 95% LCL of the
permeability was ; : inches/hour.
Calculation of Permeability:
The pervious paver/containment frame:
Length = 7.75 inches
Width = 3.125 inches
PP Surface Area = 24.22 sq.in
4 cups of water = 57.75 cu. inches
t(sec) = time to infiltrate 4 cups of water
Permeability (in/hr)= (57.75(cu.in.)*3600(sec/hr)/(t(sec)*24.22(in^2))
Conclusion: Permeability of "poorly maintained" pervious paver was at least 21 inches/hour or
7.4% of the new (clean) value. Even if the final permeability of the poorly maintained Pervious
Paver were only 1.5% of the value when new, it would still infiltrate a 1 -hour 4" storm, which is a
100 year storm event. This is consistent with EPA NPDES (EPA -832 -F -21-031W, December 2021)
assessment of pervious pavers (https://www.epa.gov/npdes).
Attachment A to
6-17-24 Minutes
Pervious Paver #1 Data
Volume = 4 cups of clean water
Trial Time (sec) Inches/hr
1 17.3 496 Leaks observed, data not used
2 16.8 511 leaks observed, data not used
3 16.2 530 Leaks observed, data not used
4 15.2 565 Leaks observed, data not used
Added silicone sealant to bottom of seam around edge of paver.
5
6
23.5
25.0
365 Filling pore spaces, data not used
343 Filling pore spaces, data not used
7
29.0
296 Stable values
8
29.8
288 Stable values
9
28.9
297 Stable values
10
32.4
265 Stable values
11
29.3
293 Stable values
12
29.9
287 Stable values
13
29.5
291 Stable values
14
27.8
309 Stable values
Count
8
8
Average Day 2
29.6
291 in/hr
Std Dev Day two
1.30
12.32
STD ERR of Mean
0.46
4.36
95%UCL
31.9
283 95%LCL of new Pervious Paver
15
210
41 After flushing muddy water through Paver
16
301
29 After adding more mud to the top of Paver
17
297
29
Count
3
3
Average=
269
33
STD Dev =
51
7
Std Err of Mean =
29.7
4.1
95%UCL=
356
95%LCL poorly maintained Pervious Paver
Page 1 of 2
Attachment A to
6-17-24 Minutes
18
251
34 Scraped off the excess mud from top of paver.
19
296
29 No washing
20
285
30 dryed-out the muddy paver for two days
21
270
32
22
250
34
23
235
37
Count
6
6
Average=
265
33
STD Dev =
23
3
Std Err of Mean =
10.4
1.3
95%UCL=
285
95%LCL poorly maintained Pervious Paver
After drying for 2 days
After washing off top of paver with water (no pressure) and letting paver dry for two days.
Applied Thompson Water seal to top of paver and let dry.
24 68 126
25 68 126
26 70 123
27 72 119
28 71 121
Count
5
5
Average=
70
123
STD Dev =
2
3
Std Err of Mean =
0.8
1.4
95%UCL=
72
120 95%LCL After Thompsons Water Seal
Conclusion: Even if the final permeability of the poorly maintained Pervious Paver were only
1.5% of the value when new, it would still infiltrate a 1 -hour 4" storm, which is a 100 year storm.
Page 2 of 2
Pervious Paver #2
Area 9.5 in X 6.25 in = 59.38 in^2
4 cups of water = 57.75 in^3
New Clean Water Test Paver #2
Trial
Time (sec)
inches/hr
1
15
233
2
16
219
3
16
219
4
15
233
5
15
233
6
16
219
7
14
250
8
15
233
Count
8
8
Average
15
230
S.D.
0.71
10.85
Std Err Mean
0.25
3.84
95%UCL
16
237
95%LCL
15
223
Attachment A to
6-17-24 Minutes
Notes: flushed over 2 gallons of muddy
water through paver, rinsed off excess
mud (no pressure cleaning) and let dry
for 2 days.
Test of Dirty Paver #2
Trial Time (sec) inches/hr
1 36 97
2 39 97
3 41 90
4 41 85
5 38 8S
6 37 92
7 38 95
8 36 92
Count
8
8
Average
38
92
S.D.
1.98
4.69
Std Err Mean
0.70
1.66
95%UCL
40
95
95%LCL
37
89
Notes: Rinsed off surface of paver
and let dry for a day. Applied water
seal with spray bottle and let dry
before test.
Thompson's Test of Paver #2
Trial Time (sec) inches/hr
1 44 80
2 45 80
3 44 78
4 43 80
5 45 81
6 42 78
7 39 83
8 40 90
Count
8
8
Average
43
81
S.D.
2.25
3.95
Std Err Mean
0.80
1.40
95%UCL
44
84
95%LCL
41
78
Conclusions:
4.0 inches/hour is a 100 -year return interval for Northeast Florida (COAB)
When new, the paver has a permiability of 223 inches/hour (more than 55 times the 100 -year rainfall intensity).
After pouring more than two gallons of muddy water through the paver the permeability is still atleast 89 inches/hour (22 times
the 100 -year rainfall intensity).
After rinsing the surface of the dirty paver, letting it dry, and applying Thompson's Water Seal to the paver the permeability was
still 78 inches per hour (almost 20 times the 100 -year rainfall intensity)
Page 1 of 1
Attachment B to
6-17-24 Minutes
Dear Mr. Williams,
I received your 02/16/2021 email and it's appended report from your stormwater
supervisor "Matt." It is telling that Matt's first comment is to make an unwarranted
accusation against the citizen who made the complaint: "There was a slight impediment
at the entrance to the swale where it appears the homeowner piles their yard waste, we
opened that up and got it flowing faster." If Matt had carefully examined the "waste"
removed when the swale was "opened... and flowing faster," he might have noted that it
is a slurry of mud and leaves. (I can furnish photos.) This is typical of what is washed
from 19' Street, down the west lane of Oak Circle, every time it rains. And it typically
accumulates at the entrance to the swale, blocks it, and floods the street. In fact a
considerable amount of 19' Street's stormwater is drained to the swale via Oak Circle.
This homeowner (and none other to my knowledge) has never piled any yard waste into
any part of the swale. (The other residents of Oak Circle can attest to this.) On the
contrary, before my recent coronary surgery, I have been clearing (by hand) both the
swale and the street for years -- though with little effect.
Matt is correct when he states: "The main issue lies in the road itself." Stonmwater
drainage (flooding) has been a serious problem on Oak Circle for as long as I have been
able to observe it (about 30 years). Some years ago (when, I can't recall), the City
attempted to mitigate the problem by digging up a narrow strip of the street's paving,
then repaving this strip, leaving a slight indentation down its length. It was not deep
enough, nor properly pitched, nor effective. I understand that this particular series of
rainstorms was unusual, but Oak Circle's flooding is chronic. We've been waiting for
Matt's long-term solution long enough. I beg the City to do more than "continue to keep
a close eye on this." Sincerely,
Karl Klein
Atlantic Beach 2018
Stormwater Master
Plan Update Recap
00.4m,
I;r�-17 Aal", ill-,XIAQ
Primary Focus
Attachment C to
6-17-24 Minutes
JonesEdmunds
Attachment C to
6-17-24 Minutes
Aquatic Gardens
JonesEdmunds'
ora KVA [e
Selected Test Area
iwaovv'�' Added "local -scale" detail to the
model in test Area
t w
Using U
Evaluated 4 Scenarios
g dated p
Model
• Compared Max Flood Depth
►� o �� x'.k Increases for Design Storm Events
Area of - - '.. ► it rT;
Existing Inlet`
Existing Culvert
+ _ -
ti if
FIs PIU46MKORNORKSl 9 11111ITYrlr VA role
Increased Basin Detail
AA
'' s► Increased Topographic Information
�" t ► Additional Hydraulic Detail
00Future Hydrologic Conditions
.. ..�_y
rawz
Attachment C to
6-17-24 Minutes
Impervious Impact Analysis
JonesEdmunds
Figure 4 Basin Impervious Area Increases for 40 Percent Impervious
//w w•�: w�:wwA C�ww �.:w
• Scenario 1 - 40 percent allowable impervious maintained on-site storage.
• Scenario 2 - 50 percent allowable impervious maintained on-site storage.
• Scenario 3 - 40 percent allowable impervious unmaintained on-site storage.
• Scenario 4 - 50 percent allowable impervious unmaintained on-site storage.
Figure 2 Basin Impervious Area Increases for 40 Percent Impervious Maintained
Scenario
Basin Impervious Area Increases for 50 Percent Impervious Maintained Figure 5
Scenario
o M
/ ncn.ouw WO 1W
t �/llri• ti
Basin Impervious Area Increases for 50 Percent Impervious
Unmaintained Scenario
n i5C Son
/ IMr new ti00 hH
Attachment C to
6-17-24 Minutes Jone,,,"ds1
Impervious Impact Analysis
Table 1
Maximum Flood Depth Increases from
Existing Conditions
Return Period
Scenario
Average
2 -Year
5 -Year 10 -Year
Scenario 1:
Maximum Flood Stage
Increase 40
Percent Impervious Maintained
1
1 1
1
(Inches)
Scenario 2:
Maximum Flood Stage
Increase 50
Percent Impervious Maintained
2
3 1
2
(Inches)
Difference (Inches)
1
2 0
1
Table 2
Maximum Flood Depth Increases from
Existing Conditions
Return Period
Scenario
Average
2 -Year
5 -Year 10 -Year
Scenario 3:
Maximum Flood Stage
Increase 40
Percent Impervious
3
3 1
2
Unmaintained (Inches)
Scenario 4:
Maximum Flood Stage
Increase 50
Percent Impervious
6
4 3
4
Unmaintained (Inches)
Difference (Inches)
3
1 2
2 _
Attachment C to
6-17-24 Minutes —'
Impervious Impact Analysis
JonesEdmunds
• More impervious area = More Runoff =
More Frequent/Intense Flooding
• On-site Storage Systems Need to Be
Maintained
8
Attachment C to
6-17-24 Minutes
JonesEdmunds
On-Site Storage Review
• Section 24-66 of the COAB code required on-site storage if
250 (400 in 2018) sq. ft. or more of impervious area was
added.
• The City had an existing spreadsheet method that was used
to calculate required storage volume.
• The City asked Jones Edmunds to:
• Review the spreadsheet assumptions.
• Develop a similar but independent approach.
• Compare results from the independent approach to the
City's method at the time.
PI
Attachment C to
6-17-24 Minutes
On -Site Storage Review
JonesEdmunds`
• Across 12 sample parcels, the independent
method required --10% more storage volume
on average.
• The City's method at the time produced
reasonable results.
• City codes and storage calculations have
changed slightly since the review was
completed.
10
Attachment C to
6-17-24 Minutes
JonesEdmundsl)