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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 January 15, 2019 Community Development Board Agenda Packet Page 3 of 42 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. January 15, 2019 Community Development Board Agenda Packet Page 4 of 42 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. January 15, 2019 Community Development Board Agenda Packet Page 5 of 42 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. January 15, 2019 Community Development Board Agenda Packet Page 6 of 42 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 January 15, 2019 Community Development Board Agenda Packet Page 7 of 42     January 15, 2019 Community Development Board Agenda Packet Page 8 of 42 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. January 15, 2019 Community Development Board Agenda Packet Page 11 of 42 January 15, 2019Community Development Board Agenda PacketPage 12 of 42 January 15, 2019Community Development Board Agenda PacketPage 13 of 42 January 15, 2019Community Development Board Agenda PacketPage 14 of 42 January 15, 2019Community Development Board Agenda PacketPage 15 of 42 January 15, 2019Community Development Board Agenda PacketPage 16 of 42 January 15, 2019Community Development Board Agenda PacketPage 17 of 42     January 15, 2019 Community Development Board Agenda Packet Page 18 of 42 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. January 15, 2019 Community Development Board Agenda Packet Page 20 of 42 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. January 15, 2019 Community Development Board Agenda Packet Page 21 of 42 January 15, 2019Community Development Board Agenda PacketPage 22 of 42 January 15, 2019Community Development Board Agenda PacketPage 23 of 42 January 15, 2019Community Development Board Agenda PacketPage 24 of 42 January 15, 2019Community Development Board Agenda PacketPage 25 of 42     January 15, 2019 Community Development Board Agenda Packet Page 26 of 42 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 January 15, 2019 Community Development Board Agenda Packet Page 27 of 42 Page 2 of 2 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.