01.15.2019 CDB Agenda Packet
CITY OF ATLANTIC BEACH
COMMUNITY DEVELOPMENT BOARD
REGULAR MEETING AGENDA
Tuesday / January 15, 2019 / 6:00 PM
Commission Chambers / 800 Seminole Road
1. Call to Order and Roll Call.
2. Approval of Minutes.
A. Minutes of the December 18, 2018 regular meeting of the Community Development
Board.
3. Old Business.
4. New Business.
A. ZVAR18-0020 PUBLIC HEARING (Sheila Powers)
Request for a variance as permitted by Section 24 -64, to increase the maximum length
allowed for a privacy screen/wall and to decrease the required side yard setbacks for
privacy screen/wall from 15 feet to 0 feet.
B. ZVAR18-0021 PUBLIC HEARING (Ruthie Wilcher Cody and Allen J. Cody III)
Request for a variance as permitted by Section 24 -64, to increase the maximum fence
height allowed in front yards from 4 feet to 6 feet to allow a 6 foot fence in the western
front yard of a double frontage lot.
C. Ordinance No. 90-19-238 PUBLIC HEARING
AN ORDINANCE OF THE CITY OF ATLANTIC BEACH, COUNTY OF DUVAL, STATE OF
FLORIDA, AMENDING CHAPTER 24, LAND DEVELOPMENT REGULATIONS; AMENDING
SECTIONS: 24-17, DEFINITIONS; 24-64, VARIANCES; 24-66, STORMWATER, DRAINAGE,
STORAGE AND TREATMENT REQUIREMENTS; 24-104, RESIDENTIAL SINGLE-FAMILY-
LARGE LOT; 24-105, RESIDENTIAL, SINGLE-FAMILY; 24-106, RESIDENTIAL, SINGLE-FAMILY;
24-107, RESIDENTIAL GENERAL, TWO-FAMILY; 24-108, RESIDENTIAL GENERAL, MULTI-
FAMILY; 24-115, RESIDENTIAL, SELVA MARINA; PROVIDING FOR CONFLICT; PROVIDING
FOR SEVERABILITY; PROVIDING AN EFFECTIVE DATE.
5. Reports.
6. Public Comment.
7. Adjournment.
All information related to the item(s) included in this agenda is available for review online at www.coab.us and at the City of Atlantic
Beach Community Development Department, located at 800 Seminole Road, Atlantic Beach, Florida 32233. Interested parties may attend
the meeting and make comments regarding agenda items, or comments may be mailed to the address above. Any
person wishing to speak to the Community Development Board on any matter at this meeting should submit a Comment Card located at the
entrance to Commission Chambers prior to the start of the meeting. Please note that all meetings are live streamed and videotaped. The video is
available at www.coab.us.
If any person decides to appeal any decision made by the Community Development Board with respect t o any matter considered at any
meeting may need to ensure that a verbatim record of the proceedings is made, including the testimony and evidence upon which any appeal
is to be based.
I n accordanc e wit h the American s with Disabilitie s Act and Section 286.26 of the Florida Statutes , persons with disabilities needin g
special accommodation s to participat e i n this meeting should contact the City not less than three (3) days prior to the date of this meeting
at the address or phone number above.
January 15, 2019 Community Development Board Agenda Packet Page 2 of 42
Minutes of the Regular Meeting of the
COMMUNITY DEVELOPMENT BOARD
December 18, 2018
1. CALL TO ORDER AND ROLL CALL
The meeting was called to order at 6:00 p.m. by Chair Lanier. Mr. Major, Mr.
Hansen, Mr. Tingen and Ms. Simmons were all present. Ms. Paul and Mr. Elmore
were absent. Also present were Director Shane Corbin, Principal Planner Derek
Reeves, Planner Brian Broedell, and the City Attorney, Brenna Durden representing
the firm Lewis, Longman and Walker.
2. APPROVAL OF MINUTES
A. Minutes of the November 20, 2018 Regular Meeting of the Community
Development Board.
Mr. Tingen motioned to approve the minutes. Mr. Hansen seconded the motion.
The motion carried unanimously.
3. OLD BUSINESS
There was no old business.
4. NEW BUSINESS
A. UBEX18-0002 PUBLIC HEARING (Julie Ann Weber)
Request for a use-by exception as permitted by Section 3-5, to allow the sale
of alcoholic beverages for on-premises consumption in accordance with
Chapter 3 of the code at 299 Atlantic Boulevard, Unit 1.
Staff Report
Planner Reeves explained that the property is located in an existing multi-unit
structure next to Ragtime Restaurant. The zoning and future land use for the
property is Central Business District. The business will be a men's apparel,
grooming products and gifts retail store in the front with a café in the back serving
beverages including coffee, tea, beer and wine.
Retail sales are permitted in the CDB, it is only the alcohol sales and consumption
that is being considered. There will not be any outdoor seating or exterior changes
other than signage.
Planner Reeves reminded the Board that they can recommend conditions be
placed on the use-by-exception. He said that the action tonight will be to
recommend approval or denial to the City Commission.
Applicant Comment
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Julie Weber of 124 14th Street introduced herself as one of the four people that
are opening the new store. She said they are excited to open a store at the Town
Center. Ms. Weber said that they believe creating an experience of shopping and
a café will draw people in. They will be a part of the valet parking.
Board Discussion
Mr. Tingen said that he had ex-parte with Ms. Weber. He asked her what the hours
will be. Ms. Weber said that they would be 10:00 a.m. to 7:00 p.m. with an earlier
close on Sunday. They would like to stay open on Friday and Saturday nights until
11:00 p.m. She added that they would like to stay open later on the nights of the
Art Walk and any special or private events. Ms. Weber said that an example would
be an Artist Pop-up or a business presentation.
Public Comment
Chair Lanier opened the floor to public comment. There was no public comment.
Motion
Mr. Hansen motioned to approve UBEX18-0002 due to fact that it is consistent
with the CBD. Ms. Simmons seconded the motion. The motion carried
unanimously.
B. ZVAR18-0018 PUBLIC HEARING (John Halverson)
Request for a variance as permitted by Section 24-64, to decrease the
required rear yard setback form 30 feet to 17 feet at 1861 Sea Oats Drive
in order to convert an existing screen room in a glass room.
This item was withdrawn by the applicant prior to the meeting, but after notices
were sent out.
C. ZVAR18-0020 PUBLIC HEARING (Shelia Powers)
Request for a variance as permitted by Section 24-64, to increase the
maximum length allowed for a privacy screen/wall and to decrease the
required side yard setbacks for privacy screen/wall from 15 feet to 0 feet.
The applicant for this item requested to defer this item to the January 15, 2019
meeting prior to the meeting. The item was deferred to that date.
5. REPORTS
A. CDB Land Development Regulations Workshop #2
Mark Shelton with Kimley-Horn Associates, 12740 Grand Bay Parkway, Suite 2350
in Jacksonville introduced himself. He said he was here to give an update on the
LDR rewrite.
Mr. Shelton said that drafting of amendments has begun. Part of the research
involved going to other municipalities to see what they have done and looking at
the American Planning Association techniques and tools.
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Mr. Shelton said that they divided the "hot" topics into categories: lot of record,
nonconforming issues, design and dimension issues, city-wide parking issues and
central business issues.
He said he heard that the lot of record definitions were in question. Mr. Shelton
said that they believe the code has good definitions. He said that it didn't need to
be changed and is actually pretty clear. Kimley-Horn thinks the application of the
dividing and joining of lots could be clarified through the use of graphics to go
along with the text. They are proposing to show something that illustrates the
before and after view of what they're trying to prevent.
In regards to nonconforming issues, enlarging nonconforming structures is always
a big issue in every code. He said it will help to add graphics to the existing
language.
Next, Mr. Shelton addressed voluntary and involuntary demolition. He said that
the code as it exists can be streamlined and clarified in regards to voluntary
demolition. For involuntary demolition they would like to add "that all permits
have to be received and reconstruction must be completed within 3 years of the
event that caused the destruction".
Mr. Tingen asked if for clarification on the demolition differences. Mr. Shelton said
that if it is a natural event that causes the demolition then it can go back to the
former state. That is what the code currently has and Kimley-Horn is
recommending they keep that. This was discussed further.
Mr. Shelton said that they found design and dimensions issues in the code that
they think may have been left over from years ago. One example was that
architectural style, colors and materials be the same. He said that today you can
make materials look like whatever you need. Design projections lacks a good
definition. Kimley-Horn has come up with a good definition which they will
continue to work on and they will add graphics to clarify. He said that the driveway
part of code needs clarification.
The city-wide parking issue has need for changes. He suggested clarifying the
shared parking language, adding motorcycle parking credit, bicycle parking credit,
etc. In regards to central business issues he gave examples from Delray Beach that
he felt could benefit Atlantic Beach. Mr. Shelton talked about different types of
parking options and the pros and cons of metered or paid parking. Director Corbin
gave an update of the status of the Parking Committee's progress in regards to
paid parking.
Mr. Shelton told the Board that now is the time to consider if they want to add
any new uses to the code. He gave examples that Neptune Beach allows but the
City of Atlantic Beach does not. The Board discussed this further.
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The last topic was the landscaping in the CBD. Kimley-Horn is proposing some
changes to allow more redevelopment potential.
Mr. Shelton said that the next time the Board sees him he will have proposed
language and a draft re-write. They will see a permitted use table for uses and lot
requirements. There might also be a parking table. He said that they still want to
hear from the Board and get as much input as possible. Mr. Shelton said this was
their 8th workshop and they will be back in January and February. He reminded
the Board about the web-site which has updated information for them to read.
Ms. Lanier asked for clarification on Kimley-Horn's recommendation for splitting
lots. Mr. Shelton said they are recommending that they define a single developed
parcel and make sure that nonconformity isn't created while splitting a lot.
B. Impervious Surface/Stormwater Retention Code Change Discussion
Director Corbin told the Board that the City Commission has asked Staff to address
this issue. Director Corbin explained that Jones-Edmunds presented a study in
November where they found additional runoff volume due to the rate of
additional impervious surface coverage. This added stress to the local drainage
features. This increases maintenance by the City due to wear and tear.
Director Corbin pointed out that the code goes on to say that the Director can
wave requirements. There isn't clear language saying that Staff can give
inspections. Director Corbin gave an example of homeowner making landscaping
changes that ended up unknowingly interfering with approved drainage plans.
There is no way for Staff to go back and inspect. This is just one example of changes
that can cause an adverse effect and this is happening on a larger scale throughout
the City.
He showed the Board a timeline that shows the impervious surface for residential
has gone back and forth beginning in 1982 with 35% and went from
implementation to elimination and then added back at 50%. Exemptions were
added later.
The direction the Commission gave Staff was to eliminate the 50% credit for
impervious pavers, the exemption for pools and the grandfathering of taking
down a home and allowing the same footprint for the new structure. Some square
footage will be allowed for a small utility building to be added to a back yard
without having an engineer involved and a stormwater management plan. The
Commission wants to remove the waiver for the Director of Public Works and
require a homeowner who wants relief to be required to come before the CDB
and request a variance. They also want to strengthen the language to allow Staff
to do inspections on private property if they feel there is a need or an issue.
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At a later meeting the Commission asked that in addition to this they want to add
a requirement to reduce the total impervious surface ratio for residential from
50% to 45%. He said that Staff is currently working on a red-line draft and they
plan to bring it to the Board at the next meeting.
Ms. Simmons asked if all pavers were equal. Director Corbin said there is some
type of channel lock system. Ms. Simmons asked about looking at alternative ideas
from other cities.
Mr. Major asked to clarify whether Edmund-Jones said that the City cannot build
the way it has been and they should reduce the amount of impervious surface.
Director Corbin said his understanding is that if the City continues to build out at
50% along with the credits then the City is going to do damage to the existing
system because you increase the flow rate and there will be a need for more
maintenance along with more flooding. Mr. Major asked if Edmund-Jones looked
at whether there was anything that could be done to maintain or increase the
impervious surface. Director Corbin said they did not. He said that the report from
Edmund-Jones will be made available to the Board and the public.
Ms. Durden suggested that the 150 sq. ft. allowance be made a one-time option
with a five year limitation. She said that by making it available with a variance then
we shouldn't allow for a waiver by the Commission any longer. Ms. Durden also
wanted to see some type of reprobation requirement of either one or two pages
being recorded that would include a document on the front page with the text and
a drawing on the second page which is placed into the public records. This would
be a tool for other owners to do a title search where they would come across this
document and they will know that an existing swale is mandatory to be there and
serves a purpose. Ms. Simmons asked if it would be like a deed restriction. Ms.
Durden said it would be. Mr. Tingen agreed that this would be a great idea.
6. PUBLIC COMMENT
There was no public comment.
7. ADJOURNMENT
Ms. Lanier announced that Mr. Tingen is now a permanent member of the Board.
Mr. Hansen motioned to adjourn the meeting at 7:25 p.m. Mr. Major seconded
the motion. The motion carried unanimously.
_______________________________________
Linda Lanier, Chair
_______________________________________
Attest
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AGENDA ITEM 4.A
CASE NO. ZVAR18-0020
Request for a variance as permitted by Section 24-64, to increase the maximum
length allowed for a privacy screen/wall and to decrease the required side yard
setbacks for a privacy screen/wall from 15 feet to 0 feet at 1946 Beachside
Court.
LOCATION 1946 Beachside Court
APPLICANT Sheila Powers
DATE January 8, 2019
STAFF Brian Broedell, Planner
STAFF COMMENTS
The applicant is Sheila Powers, the owner of 1946 Beachside Court. In May of this year, a “stop work
order” was placed on the property by one of the city’s building inspectors for replacing a fence without a
permit. At the time of the “stop work order”, a 6
foot fence with 2 feet of open lattice attached to
the top of it was already installed along the entirety
of the rear lot line and portions of both side lot
lines. The applicant then applied for a permit to
keep the existing 6 foot fence with 2 feet of open
lattice but was denied for exceeding the maximum
6 foot height allowed for fences in side and rear
yards, as restricted by Section 24-157(b).
The applicant has expressed that the intent of the
fencing and lattice is to create privacy in their
backyard, which is limited due to the raised
elevation of the neighboring property behind the
applicant’s. Section 24-157(d) of the city code
allows vertical structures intended for privacy
such as trellises, screens, partitions or walls up to
8 feet in height and 12 feet in length, provided
such structures are not located in the front yard and
meet applicable side yard setbacks. The applicant
is requesting a variance from this section to allow
for a privacy screen that is longer than 12 feet and
does not meet the applicable side yard setbacks.
January 15, 2019 Community Development Board Agenda Packet Page 9 of 42
ANALYSIS
Section 24-64(b) (1) provides that “applications for a variance shall be considered on a case-by-case basis,
and shall be approved only upon findings of fact that the application is consistent with the definition of a
variance and consistent with the provisions of this section.” According to Section 24-17, Definitions, “[a]
variance shall mean relief granted from certain terms of this chapter. The relief granted shall be only to
the extent as expressly allowed by this chapter and may be either an allowable exemption from certain
provision(s) or a relaxation of the strict, literal interpretation of certain provision(s). Any relief granted
shall be in accordance with the provisions as set forth in Section 24-64 of this chapter, and such relief may
be subject to conditions as set forth by the City of Atlantic Beach.”
Section 24-64(d) provides six distinct grounds for the approval of a variance:
(1) Exceptional topographic conditions of or near the property.
The applicant states that deck in the backyard of the property behind them is approximately 9 feet,
6 inches off the property line and elevated approximately 4 feet from grade. The applicant states that
this results in no privacy in the backyard for the applicant.
(2) Surrounding conditions or circumstances impacting the property disparately from nearby
properties.
The applicant states that the deck on the property to the rear, 1949 Seminole Road, is constructed
within 9 feet, 6 inches of the property line and violation of the 20 foot rear setback, resulting in no
privacy for the applicant.
(3) Exceptional circumstances preventing the reasonable use of the property as compared to other
properties in the area.
(4) Onerous effect of regulations enacted after platting or after development of the property or after
construction of improvements upon the property.
(5) Irregular shape of the property warranting special consideration.
(6) Substandard size of a lot of record warranting a variance in order to provide for the reasonable
use of the property.
January 15, 2019 Community Development Board Agenda Packet Page 10 of 42
REQUIRED ACTION
The Community Development Board may consider a motion to approve ZVAR18-0020, request for a
variance as permitted by Section 24-64, to increase the maximum length allowed for a privacy screen/wall
and to decrease the required side yard setbacks for a privacy screen/wall from 15 feet to 0 feet at 1946
Beachside Court (Lot 26, Block 1, Beachside), upon finding this request is consistent with the definition
of a variance, and in accordance with the provisions of Section 24-64, specifically the grounds for approval
delineated in Section 24-64(d) and as described below.
A variance may be granted, at the discretion of the Community Development Board, for the
following reasons:
(1) Exceptional topographic conditions of or near the property.
(2) Surrounding conditions or circumstances impacting the property disparately from nearby
properties.
(3) Exceptional circumstances preventing the reasonable use of the property as compared to
other properties in the area.
(4) Onerous effect of regulations enacted after platting or after development of the property or
after construction of improvements upon the property.
(5) Irregular shape of the property warranting special consideration.
(6) Substandard size of a lot of record warranting a variance in order to provide for the
reasonable use of the property.
Or,
The Community Development Board may consider a motion to deny ZVAR18-0020, request for a
variance as permitted by Section 24-64, to increase the maximum length allowed for a privacy screen/wall
and to decrease the required side yard setbacks for a privacy screen/wall from 15 feet to 0 feet at 1946
Beachside Court (Lot 26, Block 1, Beachside), upon finding this request is not consistent with the
definition of a variance, or it is consistent with one or more of the grounds for denial of a variance, as
delineated in Section 24-64(c), described below.
No variance shall be granted if the Community Development Board, in its discretion, determines
that the granting of the requested variance shall have a materially adverse impact upon one (1) or
more of the following:
(1) Light and air to adjacent properties.
(2) Congestion of streets.
(3) Public safety, including traffic safety, risk of fire, flood, crime or other threats to public
safety.
(4) Established property values.
(5) The aesthetic environment of the community.
(6) The natural environment of the community, including environmentally sensitive areas,
wildlife habitat, protected trees, or other significant environmental resources.
(7) The general health, welfare or beauty of the community.
Variances shall not be granted solely for personal comfort or convenience, for relief from
financial circumstances or for relief from situation created by the property owner.
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AGENDA ITEM 4.B
CASE NO. ZVAR18-0021
Request for a variance as permitted by Section 24-64, to increase the maximum
fence height allowed in front yards from 4 feet to 6 feet to allow a 6 foot fence
in the western front yard of a double frontage lot.
LOCATION 1880 George Street
APPLICANT Ruthie Wilcher Cody and Allen J. Cody III
DATE January 3, 2018
STAFF Brian Broedell, Planner
STAFF COMMENTS
The applicants are Ruthie Wilcher Cody and Allen J. Cody III, the owners of 1880 George Street which
consists of two platted lots of record. The southern lot has an existing single family home while the
northern lot is currently vacant. Both lots have frontage on both George Street on the east and Park Street
on the west, making them “double frontage lots” as defined by the City’s Code. Section 24-84 of the Code
states that “On double frontage lots, the required front yard shall be provided on each street…” The
required front yard is defined as the area extending across the full width of the lot, extending from the
front lot line to the 20 foot front building setback.
The applicant is proposing to install a 6 foot fence on the northern, vacant lot along the western and
northern lot lines. However, Section 24-157 limits maximum fence heights in front yards to 4 feet. Since
both the western and eastern sides of this lot are considered front yards, the proposed fence would exceed
the maximum height allowed.
Proposed 6 foot fence
(alowed)
Required
front yards
Variance
requested
for section
in red
January 15, 2019 Community Development Board Agenda Packet Page 19 of 42
ANALYSIS
Section 24-64(b) (1) provides that “applications for a variance shall be considered on a case-by-case basis,
and shall be approved only upon findings of fact that the application is consistent with the definition of a
variance and consistent with the provisions of this section.” According to Section 24-17, Definitions, “[a]
variance shall mean relief granted from certain terms of this chapter. The relief granted shall be only to
the extent as expressly allowed by this chapter and may be either an allowable exemption from certain
provision(s) or a relaxation of the strict, literal interpretation of certain provision(s). Any relief granted
shall be in accordance with the provisions as set forth in Section 24-64 of this chapter, and such relief may
be subject to conditions as set forth by the City of Atlantic Beach.”
Section 24-64(d) provides six distinct grounds for the approval of a variance:
(1) Exceptional topographic conditions of or near the property.
The applicant stated that people are constantly walking across their property to George Street or to
the Donner Park and are littering on their property. A 6 foot fence would prevent trespassers from
entering their property.
(2) Surrounding conditions or circumstances impacting the property disparately from nearby
properties.
(3) Exceptional circumstances preventing the reasonable use of the property as compared to other
properties in the area.
(4) Onerous effect of regulations enacted after platting or after development of the property or after
construction of improvements upon the property.
(5) Irregular shape of the property warranting special consideration.
(6) Substandard size of a lot of record warranting a variance in order to provide for the reasonable
use of the property.
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REQUIRED ACTION
The Community Development Board may consider a motion to approve ZVAR18-0021, request for a
variance as permitted by Section 24-64, to increase the maximum fence height allowed in front yards from
4 feet to 6 feet to allow a 6 foot fence in the western front yard of a double frontage lot, upon finding this
request is consistent with the definition of a variance, and in accordance with the provisions of Section
24-64, specifically the grounds for approval delineated in Section 24-64(d) and as described below.
A variance may be granted, at the discretion of the Community Development Board, for the
following reasons:
(1) Exceptional topographic conditions of or near the property.
(2) Surrounding conditions or circumstances impacting the property disparately from nearby
properties.
(3) Exceptional circumstances preventing the reasonable use of the property as compared to
other properties in the area.
(4) Onerous effect of regulations enacted after platting or after development of the property or
after construction of improvements upon the property.
(5) Irregular shape of the property warranting special consideration.
(6) Substandard size of a lot of record warranting a variance in order to provide for the
reasonable use of the property.
Or,
The Community Development Board may consider a motion to deny ZVAR18-0021, request for a
variance as permitted by Section 24-64, to increase the maximum fence height allowed in front yards from
4 feet to 6 feet to allow a 6 foot fence in the western front yard of a double frontage lot, upon finding this
request is not consistent with the definition of a variance, or it is consistent with one or more of the grounds
for denial of a variance, as delineated in Section 24-64(c), described below.
No variance shall be granted if the Community Development Board, in its discretion, determines
that the granting of the requested variance shall have a materially adverse impact upon one (1) or
more of the following:
(1) Light and air to adjacent properties.
(2) Congestion of streets.
(3) Public safety, including traffic safety, risk of fire, flood, crime or other threats to public
safety.
(4) Established property values.
(5) The aesthetic environment of the community.
(6) The natural environment of the community, including environmentally sensitive areas,
wildlife habitat, protected trees, or other significant environmental resources.
(7) The general health, welfare or beauty of the community.
Variances shall not be granted solely for personal comfort or convenience, for relief from
financial circumstances or for relief from situation created by the property owner.
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CITY OF ATLANTIC BEACH
COMMUNITY DEVELOPMENT BOARD
STAFF REPORT
AGENDA ITEM 4.C
ORDINANCE 90-19-238
AN ORDINANCE OF THE CITY OF ATLANTIC BEACH, COUNTY OF
DUVAL, STATE OF FLORIDA, AMENDING VARIOUS PROVISIONS
RELATED TO MAXIMUM IMPERVIOUS SURFACE LOT COVERAGE,
STORMWATER AND DRAINAGE MANAGEMENT REQUIREMENTS
AND APPROVAL PROCEDURES IN CHAPTER 24, LAND
DEVELOPMENT REGULATIONS; AMENDING SECTIONS: 24-17,
DEFINITIONS; 24-64, VARIANCES; 24-66, STORMWATER, DRAINAGE,
STORAGE AND TREATMENT REQUIREMENTS; 24-104, RESIDENTIAL
SINGLE-FAMILY-LARGE LOT; 24-105, RESIDENTIAL, SINGLE-
FAMILY; 24-106, RESIDENTIAL, SINGLE-FAMILY; 24-107,
RESIDENTIAL GENERAL, TWO-FAMILY; 24-108, RESIDENTIAL
GENERAL, MULTI-FAMILY; 24-115, RESIDENTIAL, SELVA MARINA;
PROVIDING FOR CONFLICT; PROVIDING FOR SEVERABILITY;
PROVIDING AN EFFECTIVE DATEDATE
DATE January 8, 2019
STAFF Shane Corbin, Director of Planning and Community Development
STAFF COMMENTS
In January of 2018, the City Commission participated in an all-day strategic planning session where
priorities were developed for the year. One of the priorities that came out of the session was to “review
land development regulations, including the maximum impervious surface ratio, to ensure that new
development is suited in scale and character to the existing neighborhoods.” Staff moved forward with a
full update to the Land Development Regulations with the assistance of consultants Kimley-Horn and the
Northeast Florida Regional Council. However, impervious surface was put on hold in order to allow a
separate project, the Stormwater Master Plan, to be completed by engineering consultants Jones Edmunds.
In October 2018, Jones Edmunds completed an Impervious Area Drainage Impact Analysis on a
residential drainage basin east of Sherry Drive as part of their Stormwater Master Plan. This basin was
chosen because it contains several larger parcels with relatively low existing impervious surface and
redevelopment potential. The following assumptions were used to create local-scale hydraulic models for
build-out scenarios in the basin:
Existing Conditions Model
40 percent impervious with maintained on-site storage
50 percent impervious with maintained on-site storage
40 percent impervious with unmaintained on-site storage
50 percent impervious with unmaintained on-site storage
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The analysis compared flood stages between the existing conditions model and the four scenarios. The
results showed that:
1. Local-scale flooding will worsen under the scenarios with higher impervious surface.
2. Additional runoff stresses drainage infrastructure that have met or exceeded their capacities.
3. Systems at or exceeding capacity are prone to nuisance flooding.
4. Surface flooding will occur more frequently and at greater depths as impervious increases.
5. Additional stress on the system will cause more flooding and more frequent maintenance.
On October 22, 2018 the Drainage Impact Analysis results and the City’s impervious surface requirements
were discussed at a City Commission meeting. At that meeting, staff was directed to amend various code
provisions to help address the findings in the analysis. Specifically, staff was directed to eliminate
reduction credits for pools, pervious pavers, previous structures, and additions up to 400 sq. ft. when
calculating onsite stormwater storage for new development. In addition, the provision allowing the
Director of Public Works to administratively waive stormwater requirements would be replaced with a
standard variance process.
On November 26, 2018 the issue was discussed again at a City Commission meeting where staff was
directed to reduce the allowed impervious surface in all residential zoning districts from 50% to 45%.
Proposed ORDINANCE 90-19-238 reflects all of the changes requested by the City Commission on
October 22 and November 26. Staff is recommending the addition of a 50% threshold for redevelopment
before requiring on-site stormwater storage. The purpose if this would be to enable property owners to
make significant improvements without trigging stormwater requirements. However, complete rebuilds
would trigger full on-site stormwater requirements.
January 15, 2019 Community Development Board Agenda Packet Page 28 of 42
ORDINANCE NO. 90-19-238
AN ORDINANCE OF THE CITY OF ATLANTIC BEACH,
COUNTY OF DUVAL, STATE OF FLORIDA,
AMENDING CHAPTER 24, LAND DEVELOPMENT
REGULATIONS; AMENDING SECTIONS: 24-17,
DEFINITIONS; 24-64, VARIANCES; 24-66,
STORMWATER, DRAINAGE, STORAGE AND
TREATMENT REQUIREMENTS; 24-104, RESIDENTIAL
SINGLE-FAMILY-LARGE LOT; 24-105, RESIDENTIAL,
SINGLE-FAMILY; 24-106, RESIDENTIAL, SINGLE-
FAMILY; 24-107, RESIDENTIAL GENERAL, TWO-
FAMILY; 24-108, RESIDENTIAL GENERAL, MULTI-
FAMILY; 24-115, RESIDENTIAL, SELVA MARINA;
PROVIDING FOR CONFLICT; PROVIDING FOR
SEVERABILITY; PROVIDING AN EFFECTIVE DATE.
NOW, THEREFORE, BE IT ENACTED BY THE CITY COMMISSION ON
BEHALF OF THE PEOPLE OF THE CITY OF ATLANTIC BEACH, FLORIDA:
SECTION 1. Regulation Amended. Section 24-17 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
Impervious surface shall mean those surfaces that prevent the entry of water
into the soil. Common impervious surfaces include, but are not limited to,
rooftops, sidewalks, patio areas, driveways, parking lots, swimming pools, and
other surfaces made of concrete, asphalt, brick, plastic, or any surfacing material
with a base or lining of an impervious material. Wood decking elevated two (2) or
more inches above the ground shall not be considered impervious provided that
the ground surface beneath the decking is not impervious. Pervious areas beneath
roof or balcony overhangs that are subject to inundation by stormwater and which
allow the percolation of that stormwater shall not be considered impervious areas.
Swimming pools shall not be considered as impervious surfaces because of their
ability to retain additional rainwater, however, decking around a pool may be
considered impervious depending upon materials used. Surfaces using pervious
concrete or other similar open grid paving systems shall be calculated as fifty (50)
percent impervious surface, provided that no barrier to natural percolation of
water shall be installed beneath such material. Open grid pavers must be installed
on a sand base, without liner, in order to be considered fifty (50) percent
impervious. Solid surface pavers (e.g., brick or brick appearing pavers as opposed
to open grid pavers) do not qualify for any reduction in impervious area,
regardless of type of base material used. Unless otherwise and specifically
provided for in these land development regulations, or within another ordinance,
or by other official action establishing specific impervious surface limits for a
particular lot or development project, the fifty (50) percent impervious surface
limit shall be the maximum impervious surface limit for all new residential
January 15, 2019 Community Development Board Agenda Packet Page 29 of 42
development and redevelopment. In such cases where a previously and lawfully
developed residential lot or development project exceeds the fifty (50) percent
limitapplicable impervious surface limit required by the zoning designation,
redevelopment or additions to existing residential development shall not exceed
the pre-construction impervious surface limit, provided the stormwater and
drainage requirements of section 24-66 are met.
SECTION 2. Regulation Amended. Section 24-64 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
A variance may be sought in accordance with this section. Applications for a
variance may be obtained from the community development department. A
variance shall not reduce minimum lot area, minimum lot width or lot depth, and
shall not increase maximum height of building or impervious surface area as
established for the various zoning districts. Further, a variance shall not modify
the permitted uses or any use terms of a property.
SECTION 3. Regulation Amended. Section 24-66 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
(a) Topography and grading. All lots and development sites shall be constructed
and graded in such a manner so that the stormwater drains to the adjacent
street, an existing natural element used to convey stormwater (see section 22-
303, definitions: Stormwater management system), or a city drainage structure
after meeting onsite storage requirements, as set forth within this section. The
city shall be provided with a pre-construction topographical survey prior to
the issuance of a development permit and a post-construction topographical
survey prior to the issuance of a certificate of occupancy. Elevations in all
topographic surveys will be referenced to NAVD 1988. Said surveys shall be
prepared by a licensed Florida surveyor, and the requirement for either or both
surveys may be waived by the director of public works if determined to be
unnecessary.
Except as required to meet coastal construction codes as set forth within a
valid permit from the Florida Department of Environmental Protection; or as
required to meet applicable flood zone or stormwater regulations as set forth
herein, the elevation or topography of a development or redevelopment site
shall not be altered.
(b) Onsite storage. The An applicant shall be required to provide onsite storage,
such that there is no increase in the rate or volume of flow to offsite, from
every developed or redeveloped parcel, and for any addition or modification
that increases the impervious surface area on a developed lot by ten (10)
percent or four hundredone hundred fifty (400150) SFsquare feet, whichever
is smaller and provide documentations and calculations to demonstrate
compliance. When fifty (50) percent or greater of any residential parcel’s
impervious surface is removed for redevelopment, those parcels shall not
January 15, 2019 Community Development Board Agenda Packet Page 30 of 42
receive credit or “grandfathering” for impervious surfaces when calculating
delta volumes. Development projects previously permitted by the St. Johns
River Water Management District (SJRWMD), which have an in-compliance
retention or detention system that collects and controls runoff, are exempt,
however a copy of the Engineer's Certification of As-Built Construction to the
SJRWMD must be submitted to the city before issuing building permits for
individual lot construction may begin. The requirement for onsite storage may
be waived by the director of public works if storage is determined to be
unnecessary or unattainable. If onsite storage is required for new development
or redevelopment, an as-built survey, signed and sealed by a licensed Florida
surveyor, documenting proper construction and required volume of the storage
system, must be submitted to the director of public works prior to permit
closeout or issuance of a certificate of occupancy. For an under-ground
system, a notarized letter from the general contractor, along with red-lined
plans and construction photographs, will be sufficient to document proper
construction.
Volume calculations for additions of impervious surface greater than 150 sf
on lots that shall require onsite storage after [the effective date of this
ordinance] and should shall be based on the difference in runoff volume
generated by the new impervious area ("delta volume") and would be
calculated by: with the following calculation:
V = CAR/12, where
V = volume of storage in cubic feet,
A = area of the lot in square feet,
R = 25-year and 24-hour rainfall depth (9.3 inches) over the lot area,
and
C = runoff coefficient, which is 0.6 for the fifty (50) percent maximum
imperviousness, 0.4 for twenty-five (25) percent imperviousness, and
0.2 for zero (0) percent imperviousness.
This delta volume (post V minus pre-V in cubic feet) must be stored at least
one (1) foot above the wet season water table and below the overflow point to
offsite (in many cases this may be the adjacent road elevation). As an option,
and as approved by the director of public works, the owner of the parcel to be
developed or redeveloped may implement, at the applicant's cost, offsite
storage and necessary conveyance to control existing flood stages offsite.
When fifty (50) percent or greater of any residential parcel’s impervious
surface is removed for redevelopment after [the effective date of this
ordinance], those parcels shall have a pre-V of zero (0) for volume
calculations.
(c) Floodplain storage. There shall be no net loss of storage for areas in the 100-
year floodplain, where a floodplain elevation has been defined by either the
Federal Emergency Management Agency (FEMA) on flood insurance rate
maps (FIRMs), the 1995 Stormwater Master Plan, the Core City project, or
January 15, 2019 Community Development Board Agenda Packet Page 31 of 42
the 2002 Stormwater Master Plan Update (e.g., Hopkins Creek), or the 2018
Stormwater Master Plan Update. Site grading shall create storage onsite to
mitigate for filling of volume onsite. This storage is in addition to the storage
required for the increase in impervious surface area. The applicant shall
provide signed and sealed engineering plans and calculations documenting
that this "no net loss" requirement is met.
(d) Stormwater treatment. For all new development or redevelopment of existing
properties, excluding single- and two-family uses, where construction meets
limits for requiring building code upgrades, stormwater treatment shall be
provided for a volume equivalent to either retention or detention with
filtration, of the runoff from the first one (1) inch of rainfall; or as an option,
for facilities with a drainage area of less than one hundred (100) acres, the
first one-half (½) inch of runoff pursuant to Chapter 62-25, Florida
Administrative Code (FAC). No discharge from any stormwater facility shall
cause or contribute to a violation of water quality standards as provided in
Section 62.302 of the Florida Administrative Code. This treatment volume can
be included as part of the onsite storage requirement in item d(2) [subsection
(b)] of this section.
(e) NPDES requirements. All construction activities shall be in conformance with
the city's National Pollutant Discharge Elimination Systems (NPDES) permit,
in addition to the requirements of the water management district and the
Florida Department of Environmental Protection. NPDES requirements
include use of best management practices (BMPs) prior to discharge into
natural or artificial drainage systems. All construction projects of one (1) acre
or more require a stand-alone NPDES permit. Site clearing, demolition and
construction on any size site may not commence until site inspection and
approval of the proper installation of a required best management practices
erosion and sediment control plan is completed.
(f) Enforcement. Subsequent to approval of a property owner's final grading,
including onsite and/or floodplain storage and stormwater treatment, the
improvements shall be maintained by the property owner. Failure to maintain
the improvements will require restoration upon notification by the director of
public works, within a stipulated time frame. If restoration is not timely
completed, the city shall have the right to complete the restoration, and the
city's actual cost incurred, together with a charge of one hundred (100) percent
of said costs to cover the city's administrative expenses, shall be charged to
the owner.
(g) Minor waiversVariances to impervious surface area limits. The director of
public works shall have the authority to waive the impervious surface area up
to five (5) percent of the established limit upon demonstration by the property
owner or applicant that preceding stormwater standards shall be maintained
and upon showing of good cause and need for the increased impervious
January 15, 2019 Community Development Board Agenda Packet Page 32 of 42
surface area which shall be based upon the inability to meet limits due to site
constraints or pre-existing conditions. Any reduction shall be calculated based
upon the total square footage of lot area and the square footage of the allowed
impervious surface area. For example, on a seven thousand five hundred
(7,500) square foot lot, the allowed impervious surface area is three thousand
seven hundred fifty (3,750) square feet, and the maximum impervious surface
area permitted to be waived in accordance with this provision is one hundred
eighty-seven and one-half (187.5) square feet. Variances to impervious
surface limits shall be subject to the provisions in Section 24-64. Impervious
surface requirements shall not be eligible for relief via waivers from the city
commission.
SECTION 4. Regulation Amended. Section 24-104 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
(f) Building restrictions. Additional building restrictions within the RS-L zoning
district shall be:
(1) Maximum impervious surface: Fifty Forty-five (5045) percent.
(2) Maximum building height: Thirty-five (35) feet.
SECTION 5. Regulation Amended. Section 24-105 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
(f) Building restrictions. Building restrictions within the RS-1 zoning district
shall be:
(1) Maximum impervious surface: Fifty Forty-five (5045) percent.
(2) Maximum building height: Thirty-five (35) feet.
SECTION 6 . Regulation Amended. Section 24-106 of the Code of Ordinances of the City
of Atlantic Beach, Florida, is hereby amended to read as follows:
(f) Building restrictions. Building restrictions within the RS-2 zoning district
shall be:
(1) Maximum impervious surface: Fifty Forty-five (5045) percent.
(2) Maximum building height: Thirty-five (35) feet.
SECTION 7. Regulation Amended. Section 24-107 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
(f) Building restrictions. The building restrictions for the RG zoning district shall
be:
(1) Maximum impervious surface: Fifty Forty-five (5045) percent.
(2) Maximum building height: Thirty-five (35) feet.
SECTION 8. Regulation Amended. Section 24-108 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
(f) Building restrictions. The building restrictions for the RG-M zoning district
shall be as follows:
(1) Maximum impervious surface: Fifty Forty-five (5045) percent.
(2) Maximum building height: Thirty-five (35) feet.
January 15, 2019 Community Development Board Agenda Packet Page 33 of 42
SECTION 9. Regulation Amended. Section 24-115 of the Code of Ordinances of the City of
Atlantic Beach, Florida, is hereby amended to read as follows:
(g) Building restrictions. The following building restrictions shall apply within
the R - SM z oning district:
(1) Maximum impervious surface: Fifty Forty-five (5045) percent.
(2) Maximum building height: Thirty-five (35) feet.
SECTION 10. Conflict. All ordinances, resolutions, official determinations or parts thereof
previously adopted or entered by the Cit y or any of its officials and in conflict with this
Ordinance are repealed to the extent inconsistent herewith.
SECTION 11. Severability. If a Court of competent jurisdiction at any time finds any
provision of this Ordinance to be unlawful, illegal, or unenforceable, the offending provision
shall be deemed severable and removed from the remaining provisions of this Ordinance which
shall remain in full force and intact.
SECTION 12. Effective Date. This ordinance shall take effect upon final reading and
approval.
PASSED by the City Commission on first reading this day of ___________, 2019.
PASSED by the City Commission on second and final reading this ____ day of
____________, 2019.
CITY OF ATLANTIC BEACH
Ellen Glasser, Mayor
Attest:
Donna L. Bartle, City Clerk
Approved as to form and correctness:
Brenna M. Durden, City Attorney
January 15, 2019 Community Development Board Agenda Packet Page 34 of 42
08505-003-02 1
November 2018 Impervious Area Drainage Impact Analysis
TECHNICAL MEMORANDUM
Impervious Area Drainage Impact Analysis
TO: Scott Williams, Public Works Director
FROM: Brian Icerman, PE; Jarrod Hirneise, PE
DATE: November 8, 2018
SUBJECT: Impervious Area Drainage Impact Analysis
Jones Edmunds Project No. 08505-003-02
1 EXECUTIVE SUMMARY
The City of Atlantic Beach has experienced an increasing amount of impervious area on
residential lots, particularly in the area east of Sherman-Puckett Creek and south of Saturiba
Drive where larger lots are commonly being subdivided into multiple lots with additional
impervious area.
The City is concerned with how this increase in impervious area and runoff will impact the
existing stormwater collection system in these areas. The City’s development code currently
allows residential lots to be 50 percent covered by impervious area. We analyzed the impact of
increasing impervious coverage on the City’s stormwater collection system and how much of
that impact could be mitigated by reducing the allowable impervious area on residential lots to
40 percent.
Local-scale surface flooding worsens due to increases in runoff volume and runoff rate from
additional impervious surface coverage. The additional runoff adds stress to local-scale
drainage features that have already met or exceeded their hydraulic capacities. Systems that
are already at or exceeding capacity are prone to creating nuisance flooding.
Ultimately, surface flooding will occur more frequently and at greater depths as impervious
surface coverage increases. The additional stress on the drainage system will cause more
frequent instances of nuisance flooding in roadways and on private properties. With a
development code allowing 50 percent impervious area versus 40 percent, the City’s
stormwater system will require more frequent maintenance because of the displacement of
sediment created from increased flows and the deposition of that sediment in the stormwater
system.
January 15, 2019 Community Development Board Agenda Packet Page 35 of 42
08505-003-02 2
November 2018 Impervious Area Drainage Impact Analysis
2 INTRODUCTION
The City of Atlantic Beach has experienced an increasing amount of impervious area on
residential lots, particularly in the area east of Sherman-Puckett Creek and south of Saturiba
Drive where larger lots are commonly being subdivided into multiple lots with additional
impervious area. Additional impervious area reduces the ability for stormwater to infiltrate into
subsurface soil storage, increasing the volume and rate at which stormwater runoff is
generated. The City is concerned with how this increase in impervious area and runoff will
impact the existing stormwater collection system in these areas. The City’s development code
currently allows residential lots to be 50 percent covered by impervious area. We analyzed the
impact of increasing impervious coverage on the City’s stormwater collection system and how
much of that impact could be mitigated by reducing the allowable impervious area on
residential lots.
Jones Edmunds previously developed a hydrologic and hydraulic (H&H) model of the City’s
stormwater system using Streamline Technologies Inc. Interconnected Pond and Channel
Routing Version 4.03.02 (ICPR4) as part of the City of Atlantic Beach Stormwater Master Plan
Update project. The model was developed at the scale appropriate for evaluating potential
stormwater improvement projects that will be included in the City’s Capital Improvement Plan
(CIP). The original model did not contain enough detail to quantify the impacts of increasing
impervious areas on local-scale stormwater collection systems. To analyze the impacts of
redevelopment we selected a representative basin within the existing model, increase the
modeled level-of-detail within that basin, and run model simulations to show the impact of
increased impervious area on the stormwater system. The following sections outline the steps
taken to evaluate the impacts of additional impervious area, the results of the analysis, and
recommendations.
3 EXISTING CONDITIONS MODEL UPDATES
Figure 1 shows the representative area of interest (AOI) selected by Jones Edmunds from the
existing ICPR4 model to increase the model level-of-detail within. This area was selected
primarily because it contained several larger parcels with relatively low existing impervious
surface coverage that have potential to be redeveloped with significantly more impervious
surface coverage.
January 15, 2019 Community Development Board Agenda Packet Page 36 of 42
08505-003-02 3
November 2018 Impervious Area Drainage Impact Analysis
Figure 1 Study AOI
3.1 HYDROLOGIC UPDATES
Jones Edmunds subdivided this area into 22 local-scale stormwater basins with an average
contributing area of 0.84 acre. We characterized the hydrologic conditions in the new model
basins using TR-55 curve number methodology with directly connected impervious area (DCIA)
percentages.
We digitized the existing impervious surfaces using Nearmap’s high-resolution imagery
collected on May 4, 2018. City permit data was also reviewed from the previous 5 years for
parcel-specific permitted impervious area calculations and plans sets. We incorporated this
data into our impervious area dataset and calculations where available. The aerial imagery and
permit data were used to identify locations where pavers have been installed. According to City
development codes, pervious pavers are considered 50 percent pervious when calculating the
total impervious area of a parcel. We identified approximately 28,000 square feet of pavers in
the AOI, which is approximately 4 percent of the total impervious surface. After reviewing the
permit data provided by the City and determining that most of the pavers in the AOI were
permitted as 50 percent pervious, we decided to model all of the paver surfaces as if they were
50 percent pervious. We also considered pool footprints to be pervious based on current City
development codes.
We used the impervious surface spatial dataset to determine the unconnected and directly
connected impervious area percentages for each of the new basins. We developed a composite
curve number representing the hydrologic response from the non-DCIA area for the basins. We
used an open land curve number of 65 for all of the basins based on soil data obtained from
the Natural Resource Conservation Service’s (NRCS) Web Soil Survey.
January 15, 2019 Community Development Board Agenda Packet Page 37 of 42
08505-003-02 4
November 2018 Impervious Area Drainage Impact Analysis
3.2 HYDRAULIC UPDATES
Jones Edmunds added 26 nodes, 20 pipe links, and 34 overland flow weir links to model the
local-scale hydraulics in this area. The City’s stormwater asset database was used to determine
pipe shape, size, inverts, and material. We used a 5-foot by 5-foot digital elevation model
(DEM) created using the 2007 Florida Department of Emergency Management (FDEM) Light
Detection and Ranging (LiDAR) data to parameterize the overland flow weir connections and
assign stage-area relationships to the nodes.
4 FUTURE CONDITIONS HYDROLOGIC ANALYSIS
Jones Edmunds used the impervious surface spatial dataset, permit data, and Duval County
Parcels spatial data to estimate the existing impervious surface percentage of each parcel
within the AOI. We determined that approximately 35 percent of the parcels within the AOI
were at or above the 50 percent allowable impervious surface limit and approximately
70 percent of the parcels were above 40 percent impervious surface coverage in existing
conditions. The existing average impervious surface percentage was approximately 45 percent.
Section 24-66 of the City’s Land Development Code requires that the difference between the
pre-development and post-development volume of stormwater runoff be stored on-site for the
25-year storm event when 400 square feet or more of new impervious area is added to a
parcel. Assuming that the provided on-site storage facilities are maintained and in working
condition, this means that any additional runoff volume generated by new impervious area
should not impact the City’s drainage system if more than 400 square feet of new impervious
area is added. No on-site storage is required if less than 400 square feet of new impervious
area is added, and the additional runoff volume from the new impervious area will impact the
City’s stormwater system.
We developed hydrologic parameters for four future conditions build-out scenarios to simulate
the potential impacts of new impervious area on flood conditions in the AOI. For the first two
scenarios we assumed that all on-site storage facilities provided for new impervious area are
maintained and in working condition in perpetuity. If this is the case, the greatest impact to
the City’s stormwater system would occur if all lots with new impervious capacity added the
lesser of 400 square feet of new impervious or the remainder of their allowable impervious
area coverage and were not required to provide on-site storage.
Scenario 1 assumed that the allowable parcel impervious area was 40 percent with maintained
conditions, and Scenario 2 assumed that the allowable parcel impervious area was 50 percent
with maintained conditions. In the maintained 40 percent coverage scenario (Scenario 1), we
added approximately 13,500 square feet (0.3 acre) of impervious area to the AOI. This
increased the basin impervious percentages by approximately 2 percent on average with a
minimum increase of 0 percent and a maximum increase of 6 percent. In the maintained 50
percent coverage scenario (Scenario 2), we added approximately 28,500 square feet (0.65
acre) of impervious area to the AOI. This increased the basin impervious percentages by
approximately 4 percent on average with a minimum increase of 0 percent and a maximum
increase of 9 percent. Figures 2 and 3 show the spatial variation of basin impervious area
percentage increases. Basins with the larger percentage increases contain parcels with low
existing impervious percentages and basins with smaller percentage increases contain parcels
January 15, 2019 Community Development Board Agenda Packet Page 38 of 42
08505-003-02 5
November 2018 Impervious Area Drainage Impact Analysis
with high existing impervious percentages, which limited the amount of impervious area that
could be added.
Figure 2 Basin Impervious Area Increases for 40 Percent Impervious Maintained
Scenario
Figure 3 Basin Impervious Area Increases for 50 Percent Impervious Maintained
Scenario
January 15, 2019 Community Development Board Agenda Packet Page 39 of 42
08505-003-02 6
November 2018 Impervious Area Drainage Impact Analysis
For Scenarios 3 and 4 we assumed that all on-site storage facilities provided for new
impervious area were unmaintained and not in working condition. Currently, the City does not
have a program to inspect the on-site storage facilities to ensure that they are maintained and
kept in working condition. If these systems go unmaintained or are filled, the additional runoff
from the new impervious surfaces will not be retained on-site and will impact the City’s
stormwater system. The worst-case scenario for the City’s stormwater system would occur if
all on-site storage systems were not maintained and all of the parcels with new impervious
capacity in the AOI were built out to the maximum allowable impervious surface coverage.
Scenario 3 assumed that the allowable parcel impervious area was 40 percent with
unmaintained conditions, and Scenario 4 assumed that the allowable parcel impervious area
was 50 percent with unmaintained conditions. In the 40 percent coverage unmaintained
scenario (Scenario 3), we added approximately 32,500 square feet (0.75 acre) of impervious
area. This increased the basin impervious percentages by approximately 3.5 percent on
average with a minimum increase of 0 percent and a maximum increase of 16 percent. In the
50 percent coverage unmaintained scenario (Scenario 4), we added approximately 76,000
square feet (1.75 acre) of impervious area. This increased the basin impervious percentages
by approximately 9 percent on average with a minimum increase of 0 percent and a maximum
increase of 26 percent. Figures 4 and 5 show the spatial variation of basin impervious area
percentage increases. Basins with the larger percentage increases contain parcels with low
existing impervious percentages and basins with smaller percentage increases contain parcels
with high existing impervious percentages, which limited the amount of impervious area that
could be added.
Figure 4 Basin Impervious Area Increases for 40 Percent Impervious
Unmaintained Scenario
January 15, 2019 Community Development Board Agenda Packet Page 40 of 42
08505-003-02 7
November 2018 Impervious Area Drainage Impact Analysis
Figure 5 Basin Impervious Area Increases for 50 Percent Impervious
Unmaintained Scenario
5 HYDROLOGIC AND HYDRAULIC MODELING AND RESULTS
We simulated the FDOT 1-, 2-, 4-, 8-, and 24-hour storm events for the 2-, 5-, and 10-year
return periods for the five model scenarios:
Revised Existing Condition Model with Local scale elements modeled.
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.
We compared peak flood stages from the four hypothetical scenarios to the revised existing
conditions peak flood stages to determine how flood depths would be impacted by the
additional impervious area. Changes in peak flood stages varied spatially depending on how
much impervious area was added within the associated basin. Basins with lower impervious
area percentage increases experienced smaller flood peak stage increases and basins with
larger impervious area percentage increases experienced larger peak stage increases. Tables 1
and 2 summarize the maximum peak flood stage increases where surface flooding occurs in
the four scenarios compared to existing conditions for the 2-, 5-, and 10-year return periods.
January 15, 2019 Community Development Board Agenda Packet Page 41 of 42
08505-003-02 8
November 2018 Impervious Area Drainage Impact Analysis
Table 1 Maximum Flood Depth Increases from Existing Conditions
Scenario Return Period Average 2-Year 5-Year 10-Year
Scenario 1: Maximum Flood Stage
Increase 40 Percent Impervious Maintained
(Inches)
1 1 1 1
Scenario 2: Maximum Flood Stage
Increase 50 Percent Impervious Maintained
(Inches)
2 3 1 2
Difference (Inches) 1 2 0 1
Table 2 Maximum Flood Depth Increases from Existing Conditions
Scenario Return Period Average 2-Year 5-Year 10-Year
Scenario 3: Maximum Flood Stage
Increase 40 Percent Impervious
Unmaintained (Inches)
3 3 1 2
Scenario 4: Maximum Flood Stage
Increase 50 Percent Impervious
Unmaintained (Inches)
6 4 3 4
Difference (Inches) 3 1 2 2
As shown in Tables 1 and 2, local-scale surface flooding will worsen due to the increases in
runoff volume and runoff rate from additional impervious surface coverage. The additional
runoff adds stress to local-scale drainage features that have already met or exceeded their
hydraulic capacities. Systems that are already at or exceeding capacity are prone to creating
nuisance flooding. Our modeling assumes all stormwater structures and roadside swales
between structures are in a well-maintained condition. Any changes to this maintenance
condition could adversely impact the adjacent parcels.
Ultimately, surface flooding will occur more frequently and at greater depths as impervious
surface coverage increases. The additional stress on the drainage system will cause more
frequent instances of nuisance flooding in roadways and on private properties. More frequent
maintenance of the City’s stormwater system will be required because of the displacement of
sediment created from increased flows and the deposition of that sediment in the stormwater
system.
These results also show the importance of ensuring that on-site storage systems are
maintained in proper working condition. If these systems are not maintained or are removed,
impacts of additional impervious area on the City’s stormwater system will worsen.