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HomeMy WebLinkAboutSW8970104_Historical File_20010920Michael F. Easley, Governor William G. Ross, Jr., Secretary North Carolina Department of Environment and Natural Resources Ls' September 20, 2001 Mr. W. Christopher Stephens, President Landmark Developers, Inc. PO Box 4127 Wilmington, NC 28406-4127 Gregory J. Thorpe, Ph.D., Acting Director Division of Water Quality Wilmington Regional Office Subject: ' Permit No. SW8 970104 Modification Magnolia Greens Master Plan High Density Subdivision Stormwater Project Brunswick County Dear Mr. Stephens: The Wilmington Regional Office received a complete modification to the Stormwater Management Permit Application for Magnolia Greens Master Plan on August 7, 2001. Staff review of the plans and specifications has determined that the project, as proposed, will comply with the Stormwater Regulations set forth in Title 15A NCAC 2H.1000. We are forwarding Permit No. SW8 970104 Modification, dated September 20, 2001, for the construction of the project, Magnolia Greens Master Plan. This permit shall be effective from the date of issuance until October 4, 2009, and shall be subject to the conditions and limitations as specified therein. Please pay special attention to the Operation and Maintenance .requirements in this permit. Failure to. establish an adequate system for operation and maintenance of the stormwater management system will result in future compliance problems. If any parts, requirements, or limitations 'contained in this permit are unacceptable, you have the right to request an adjudicatory hearing upon written request within thirty (3 0) days following receipt of this permit. This request must be in the form of a written petition, conforming to Chapter 150B of the North Carolina General Statutes, and filed with the Office of Administrative Hearings, P.O. Drawer 27447, Raleigh, NC 27611-7447. Unless such demands are made this permit shall be final and binding. If you have any questions, or need additional information concerning this matter, please contact Linda Lewis, or me at (910) 395-3900. Sincerely, t-:—k C `1 Rick Shiver Water Quality Regional Supervisor RSS/:arl S:1WQSISTORMWATIPERMIT\970104.APR cc: Davis Fennell, P.E. Delaney Aycock, Brunswick County Inspections Linda Lewis Wilmington Regional Office Central Files N.C. Division of Water Quality 127 Cardinal Drive Extension Wilmington, N.C. 28405 (910) 395-3900 Fax (910) 35D.2004 0, Customer Service 800-623-7748 State Stormwater Management Systems Permit No. SW8 970104 Modification STATE OF NORTH CAROLINA DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES DIVISION OF WATER QUALITY STATE STORMWATER MANAGEMENT PERMIT HIGH DENSITY DEVELOPMENT In accordance with the provisions of Article 21 of Chapter 143, General Statutes of North Carolina as amended, and other applicable Laws, Rules, and Regulations PERMISSION IS HEREBY GRANTED TO Landmark Developers, Inc. Magnolia Greens Master Plan Brunswick County FOR THE construction, operation and maintenance of 2 wet detention ponds and a low density subdivision with a curb outlet system in compliance with the provisions of 15A NCAC 2H .1000 (hereafter referred to as the "stormwater rules') and the approved stormwater management plans and specifications and other supporting data as attached and on file with and approved by the Division of Water Quality and considered a part of this permit. This modified permit shall be effective from the date of issuance until October 4, 2009 and shall be subject to the following specified conditions and limitations: I. DESIGN STANDARDS 1. This permit is effective only with respect to the nature and volume of stormwater described in the application and other supporting data. Stormwater Management measures are 2 wet detention ponds and a curb outlet system for the uncollected low density portions of the project. 2. This stormwater system has been approved for the management of stormwater runoff as described on page 3 of this permit, the Project Data Sheet. The subdivision is permitted for a total of 1019 lots. The built -upon area permitted to date is: 226 single family lots @4,000 ft2 each for Sections 1-9; 76 lots @3,500 ft2 each for Sections 11 & 12; the Clubhouse @4.2 acres which drains to the pond permitted under SW8 990628; Tract N (Section 8) is permitted for 21 lots @4,000 ft2; and Tract D is permitted for 67 lots @4,000 ft2; Patio Homes I Tracts E and O (Sections 8, 9, and 10) are permitted under SW8 981008 for 941ots @4,000 Wand 6 lots @5,000 ft2; the West Commercial Area is permitted under SW8 980807 for 3.93 acres of built -upon area. The Fairway Villas is permitted for 6.24 acres under SW8 990628; Lanvale Townhomes is permitted for 9.75 acres under SW8 990947; and Patio Homes III is permitted for 75 lots @3,500 ft2; Future development includes the East Commercial Area @10.57 acres; 190 Multi -family units @1,200 ft2 each (Tract P); and 236'single family lots @4,000 ft2 each (Tracts B, C &D). Total proposed BUA is 158.13 acres. 3. Approved plans and specifications for this project are incorporated by reference and are enforceable parts of the permit. The project must maintain an overall density of 30% of less. PA State Stormwater Management Systems Permit No. SW8 970104 Modification DIVISION OF WATER QUALITY PROJECT DATA SHEET Project Name: Magnolia Greens Master Plan Permit Number: SW8 970104 Modification Location: Brunswick County Applicant: Mr. W. Christopher Stephens, President Mailing Address: Landmark Developers, Inc. PO Box 4127 Wilmington, NC 28406-4127 Application Date: August 7, 2001 (Modification complete) Receiving Stream/Classification: Jackey's Creek (CFR 18-77-3) Sturgeon Creek (CFR18-77-1) Classification of Water Body: "C Sw" POND 1 POND 5 Drainage Area, acres: 151.6 26.2 Pond Depth, feet: 7 7.5 Permanent Pool Elevation, FMSL: 18 17 Total Impervious Surfaces, ft2: 1,767,801 366,850 Lot B IJA, ft2: 845,084 209,299 Roads/Parking, ft2 453,902 119,920 Sidewalk, ft2 121,100 28,919 Patio Homes I, ft2: 268,000 ------ Maintenance Building, ft2: ------- 8,712 SW8 991136, ft2: 79,715 ------ Offsite Area entering Pond, ft2: none, per Engineer Required Surface Area, ft2: 68,309 9,864 Provided Surface Area, ft2: 82,200 11,137 Required Storage Volume, ft3: 160,046 32,269 Provided Storage Volume, ft3: 183,796 32,334 Temporary Storage Elevation, FMSL: 20.1 19.4 Controlling Orifice: 2 @4" cp each 2" cp pipe Kj State Stormwater Management Systems Permit No. SW8 970104 Modification 4. The project must maintain 30% low density on an overall basis. 5. The runoff from the curbed streets in the low density portions of this project are proposed to be treated in curb outlet swales. Each swale as shown on the approved plans denoted with a "WQ", must be a minimum of 100' long, with a 5:1 or flatter side slope, a longitudinal slope not more than 5%, and have a dense vegetated cover. 6. The higher density portions of the project, such as multi -family areas, the clubhouse, parking areas, or where a discrete collection system exists, are proposing to treat runoff in wet detention ponds. The clubhouse drainage, 221,300 W, is treated in the Fairways Villas Pond 1, permitted under SW8 990628. II. SCHEDULE OF COMPLIANCE 1. No homeowner/lot owner/developer shall fill in, alter, or pipe any drainage feature (such as swales or curb outlet swales) shown on the approved plans as part of the stormwater management system without submitting a revision to the permit and receiving approval from the Division prior to construction. 2. The permittee is responsible for verifying that the proposed built -upon area does not exceed the allowable built -upon area. Once the lot transfer is complete, the built -upon area may not be revised without approval from the Division of Water Quality, and responsibility for meeting the built -upon area limit is transferred to the individual property owner. 3. The uncollected portions of the low density subdivision are served by a Curb Outlet System. The swales are generally located between lots, and must be maintained with a stable, vegetated 5:1 sideslope, be a minimum of 100' long, have a longitudinal slope of 5% or less, maintain a dense, vegetated cover, and be able to carry the peak flow from a 10 year storm in a non -erosive manner. 4. The following items will require a modification to the permit: a. Any revision to the approved plans, regardless of size. b. Project name change. C. Transfer of ownership. d. Redesign or addition to the approved amount of built -upon area. e. Further subdivision of the project area. f. Filling in, altering, or piping of any vegetative conveyance shown on the approved plan. 5. The Director may determine that other revisions to the project should require a modification to the permit. 6. The Director may notify the permittee when the permitted site does not meet one or more of the minimum requirements of the permit. Within the time frame specified in the notice, the permittee shall submit a written time schedule to the Director for modifying the site to meet minimum requirements. The permittee shall provide copies of revised plans and certification in writing to the Director that the changes have been made. 7. The stormwater management system (ponds and curb outlet swale system) shall be constructed in it's entirety, vegetated and operational for it's intended use prior to the construction of any built -upon surface. During construction, "erosion shall be kept to a minimum and any eroded areas of the system will be repaired immediately. 4 State Stormwater Management Systems Permit'No. SW8 970104 Modification 9. Upon completion of construction, prior to issuance of a Certificate of Occupancy, and prior to operation of this permitted facility, a certification must be received from an appropriate designer for the system installed certifying that the permitted facility has been installed in accordance with this permit, the approved plans and specifications, and other supporting documentation. Any deviations from the approved plans and specifications must be noted on the Certification. 10. Decorative spray fountains will not be allowed in the stormwater treatment system. 11. If the stormwater system was used as an Erosion Control device, it must be restored to design condition prior to operation as a stormwater treatment device, and prior to occupancy of the facility. 12. Prior to transfer of ownership from the permittee to a third party such as an HOA, the stormwater management systems must be inspected by DWQ personnel, and determined to be in compliance with all permit conditions. Records of maintenance activities will be required. 13. The permittee shall at all times provide the operation and maintenance necessary to assure the permitted stormwater system functions at optimum efficiency. The approved Operation and Maintenance Plan must be followed in its entirety and maintenance must occur at the scheduled intervals including, but not limited to: a. Semiannual scheduled inspections (every 6 months). b. Sediment removal. C. Mowing and revegetation of side slopes of the pond and the swales. d. Immediate repair of eroded areas. e. Maintenance of side slopes in accordance with approved plans and specifications. f. Debris removal and unclogging of outlet structures, orifice devices, catch basins and piping. g. Access to the outlet structures and swales must be available at all times. 14. Records of maintenance activities must be kept and made available upon request to authorized personnel of DWQ. The records will indicate the date, activity, name of person performing the work and what actions were taken. 15. This permit shall become voidable unless the facilities are constructed in accordance with the conditions of this permit, the approved plans and specifications, and other supporting data. 16. A copy of the approved plans and specifications shall be maintained on file by the Permittee for a minimum of ten years from the date of the completion of construction. 17. All runoff from the impervious surfaces of the clubhouse / pro shop area, including parking lots, roads, buildings, and pool decks, must drain into the "Golf Pond" permitted under SW8 990628. Pond #3, as shown on the Master Plan, is no longer a stormwater treatment pond. 18. Each curb outlet swale must be located in an easement wide enough to completely contain the required 5:1 side slope back to natural ground. W State Stormwater Management Systems Permit No. SW8 970104 Modification 19. Prior to the sale of any lot, deed restrictions must be recorded which limit the built -upon area per lot to the amount as shown on the Project Data Sheet, per Section I, Part 2. The recorded statements must follow the form: a. "The maximum built -upon area per lot in this section is *see below square feet. This allotted amount includes any built -upon area constructed within the lot property boundaries, and that portion of the right-of-way between the front lot line and the edge of the pavement. Built upon area includes, but is not limited to, structures, asphalt, concrete, gravel, brick, stone, slate, and coquina, but does not include raised, open wood decking, or the water surface of swimming Pools." b. "The covenants pertaining to stormwater regulations may not be changed or deleted without concurrence of the State." C. "Alteration of the drainage as shown on the approved plan, including the curb outlet swales, may not take place without the concurrence of the State." d. "Each lot shall maintain a minimum of 30' of vegetated buffer between any impervious surface on the lot and surface waters." * The Permittee will fill in the built -upon area associated with each lot in the section per the BUA limits I. as listed in Section Part 2 this permit, and as shown on the summary table on the approved Master Plan. 20. A copy of the recorded deed restrictions for each section must be submitted to the Division within 30 days of the date of recording the plat, and prior to selling lots in that section. The recorded copy must bear the signature of the Permittee, the deed book number and page, and stamp/signature of the Register of Deeds. III. GENERAL CONDITIONS 1. This permit is not transferable. In the event there is a desire for the facilities to change ownership, or there is a name change of the Permittee, a "Name/Ownership Change Form" must be submitted to the Division of Water Quality accompanied by appropriate documentation from the parties involved, such as a copy of the deed of trust. Other supporting materials, such as a signed Operation and Maintenance plan in the case of engineered systems, will also be required. The project must be in good standing with DWQ. The approval of this request will be considered on its merits and may or may not be approved. 2. Failure to abide by the conditions and limitations contained in this permit may subject the Permittee to enforcement action by the Division of Water Quality, in accordance with North Carolina General Statute 143-215.6A to 143-215.6C. 3. The issuance of this permit does not preclude the Permittee from complying with any and all statutes, rules, regulations, or ordinances which may he imposed by other government agencies local, state, and federal) which have jurisdiction. 4. In the event that the facilities fail to perform satisfactorily, including the creation of nuisance conditions, the Permittee shall take immediate corrective action, including those as may be required by this Division, such as the construction of additional or replacement stormwater management systems. 0 State Stormwater Management Systems Permit No. SW8 970104 Modification 5. The permit may be modified, revoked and reissued or terminated for cause. The filing of a request for a permit modification, revocation and reissuance or termination does not stay any permit condition. 6. Permittee grants permission to staff of the DWQ to access the property for the purposes of inspecting the stormwater facilities during normal business hours. 7. The approved plan set consists of the September 18, 2001, revised Master Plan, Patio Home I site plan with Pond 1 details, Pond 5 detail sheet, and the Clubhouse Site Plan. The permittee will swap out the required plans and replace outdated sheets with the revised ones. The permittee shall notify the Division of any changes in project name, ownership, or mailing address. Permit issued this the 20th day of September, 2001. NORTH CAROLINA ENVIRONMENTAL MANAGEMENT COMMISSION Gregory J. Thorpe, Ph.D., Acting Director Division of Water Quality By Authority of the Environmental Management Commission Permit Number SW8 970104 Modification fi State of North Carolina Department of Environment and Natural Resources Division of Water Quality STORMWATER MANAGEMENT PERMIT APPLICATION FORM This form may be photocopied for use as an original I. GENERAL INFORMATION: 1. Applicant's name (specify the name of the corporation, individual, etc. who owns the project): Landmark Developers, Inc. 2. Print Owner/Signing Official's name and title (person legally responsible for facility and compliance): W. Christopher Stephens, President 3. Mailing Address for person listed in item 2 above: 5022 Wrightsville Ave. Suite 102 City: Wilmington State: NC Zip: 28403 Telephone Number: (910 ) 392-7201 4. Project Name (subdivision, facility, or establishment name - should be consistent with project name on plans, specifications, letters, operation and maintenance agreements, etc.): Magnolia Greens 5. Location of Project (street address): NC HYW. 17 City: Leland 6. Directions to project (from nearest major intersection): County: Brunswick Located along the north right-of-way on hyw. 17 approx. 1000 ft northeast of the Hyw. 17 and Lanvale Road intersection. 7. Latitude: 34-12-40 Longitude 8. Contact person who can answer questions about the project: Name: Chris Stephens H. PERMIT INFORMATION: 78-01-47 Telephone Number: (919) 392-7201 of project 1. Specify whether project is (check one): New Renewal X Modification 2. If this application is being submitted as the result of a renewal or modification to an existing permit, list the existing permit number SW8 970104 And its issue date (if known) 28 April 2000 Form: SWU-101 Version 3.99 Page 1 of 4 3. Specify the type of project (check one): X Low Density High Density Redevelop General Permit Other 4. Additional Project Requirements (check applicable blanks): CAMA Major X Sedimentation/Erosion Control 404/401 Permit NPDES Stormwater Information on required state permits can be obtained by contacting the Customer Service Center at 1-877-623-6748. III. PROJECT INFORMATION 1. In the space provided below, summarize how stormwater will be treated. Also attach a detailed narrative (one to two pages) describing stormwater management for the project. Overall project employs low density stormwater measures wherever possible. Pockets of high density and other areas unsuitable for low density measures will be provided enhanced treatment via. wet detention ponds. 2. Stormwater runoff from this project drains to the Cape Fear River basin. 3. Total Project Area: 916.5 acres 4. Project Built Upon Area: 17.25 % 5. How many drainage basins does the project have? 3 6. Complete the following information for each drainage area. If there are more than two drainage areas in the project, attach an additional sheet with the information for each area provided in the same format as below. Basm Information Drainage Area I Drainage Area 2 Receiving Stream Name See attached sheet Receiving Stream Class Drainage Area Existing Impervious* Area Proposed Impervious* Area Impervious* Area (total) knper-v-iuus Surface Area Drainage Area 1 Drainage Area 2 On -site Buildings On -site Streets On -site Parking On -site Sidewalks Other on -site Off site Total: Total: lmperveuuy ureu is uejineu us sne uum upun area inczuazng, our nor amzrea ro; ouzzazngs, roaas, parking areas, sidewalks, gravel areas, etc. Form: SWU-101 Version 3.99 Page 2 of 4 Complete the following information for each drainage basin. If there are more than two drainage basins in the project, attach an additional sheet with the information for each basin provided in the same format as below. Basm Information Pond# I Clubhouse -To 5W8 990626 Receiving Stream Name Jackey5 Creek Jackey5 Creek Receiving Stream Class C-SW C-5W Drainage Basin Area 15 1.3 AC 13.32 AC Existing Impervious* Area 0 5F 0 5F Proposed Impervious* Area I ,7G7,50I 5F 2 1 2,914 5F % Impervious* Area (total) 26.8 36.7 l viousSurface Arrea Pondal€1 Clubhou5e—To 5W8 990626 On -site Buildings 1, 165,320 5F 28,750 5F On -site Streets 476,430 5F 57,593 5F On -site Parking 0 5F 79,375 5F On -site Sidewalks 126,05 15F I 1 ,964 5F Other on -site 0 5F 35,202 5F Off site 0 5F 0 5F Total: 1 ,767,801 5F E= 212,914 5F Basm Information Pond#5 Overall Low Density Receiving Stream Name 5tur eon Creek 5tur eon/ Jackey5 Creek Receiving Stream Class C-5W C-5W Drainage Basin Area 26.2 AC 916.5 AC Existing Impervious* Area 0 5F 0 5F Proposed Impervious* Area 366,850 SF 155.13 AC Impervious* Area (total) 32.1 17.25 lnrpmious Surface Area Pond#5 OveraA Low Density On -site Buildings 218,01 1 5F 84.17 AC On -site Streets I 19,9205E 33.42 AC On -site Parking 0 SF 28.96 AC On -site Sidewalks 28,9 19 5F 0 AC Other on -site 0 5P 1 1.57 AC Off site O Sf 0 AC Total: 366,850 SF E= 1 58. 13 AC Basin Infomation Receiving Stream Name Receiving Stream Class Drainage Basin Area Existing Impervious* Area Proposed Impervious* Area OYO Impervious* Area (total) Impervious* Surface Area On -site Buildings On -site Streets On -site Parking On -site Sidewalks Other on -site Off site Total: Page 2A of 4 7. How was the off -site impervious area listed above derived? N/A IV. DEED RESTRICTIONS AND PROTECTIVE COVENANTS The following italicized deed restrictions and protective covenants are required to be recorded for all subdivisions, outparcels and future development prior to the sale of any lot. If lot sizes vary significantly, a table listing each lot number, size and the allowable built -upon area for each lot must be provided as an attachment. 1. The following covenants are intended to ensure ongoing compliance with state stormwater management permit number SW8 970104 as issued by the Division of Water Quality. These covenants may not be changed or deleted without the consent of the State. 2. No more than * * square feet of any lot shall be covered by structures or impervious materials. Impervious materials include asphalt, gravel, concrete, brick, stone, slate or similar material but do not include wood decking or the water surface of swimming pools. 3. Swales shall not be filled in, piped, or altered except as necessary to provide driveway crossings. 4. Built -upon area in excess area of the permitted amount requires a state stormwater managementpermit modification prior to construction. 5. All permitted runoff from outparcels or future development shall be directed into the permitted stormwater control system. These connections to the stormwater control system shall be performed in a manner that maintains the integrity and performance of the system as permitted. **244 lots @ 4000 SF, 6 lots @ 5000 SF, 46 lots @ 1200sf in Sections 1-10; 76 lots @ 3500 SF in Sections 11&12. 67 lots @ 4000 SF in Patio 1, 57 lots @ 6000 sf in Phases 3&4; By your signature below, you certify that the recorded deed restrictions and protective covenants for this project shall include all the applicable items required above, that the covenants will be binding on all parties and persons claiming under them, that they will run with the land, that the required covenants cannot be changed or deleted without concurrence from the State, and that they will be recorded prior to the sale of any lot. V. SUPPLEMENT FORMS The applicable state stormwater management permit supplement form(s) listed below must be submitted for each BMP specified for this project. Contact the Stormwater and General Permits Unit at (919) 733-5083 for the status and availability of these forms. Form SWU-102 Wet Detention Basin Supplement Form SWU-103 Infiltration Basin Supplement Form SWU-104 Low Density Supplement Form SWU-105 Curb Outlet System Supplement Form SW-106 Off -Site System Supplement Form SWU-107 Underground Infiltration Trench Supplement Form SWU-108 Neuse River Basin Supplement Form SWU-109 Innovative Best Management Practice Supplement Form: SWU-101 Version 3.99 Page 3 of 4 VI. SUBNHTTAL REQUIREMENTS Only complete application packages will be accepted and reviewed by the Division of Water Quality (DWQ). A complete package includes all of the items listed below. The complete application package should be submitted to the appropriate DWQ Regional Office. Please indicate that you have provided the following required information by initialing in the space provided next to each item. • Original and one copy of the Stormwater Management Permit Application Form • One copy of the applicable Supplement Form(s) for each BUT • Permit application processing fee of $420 (payable to NCDENR) • Detailed narrative description of stormwater treatment /management • Two copies of plans and specifications, including: -Development/Project name -Engineer and firm -Legend -North Arrow -Scale -Revision number & date -Mean high water line -Dimensioned property / project boundary -Location map with named streets or NCSR numbers -Original contours, proposed contours, spot elevations, finished floor elevations -Details of roads, drainage features, collection systems, and stormwater control measures -Wetlands delineated, or a note on plans that none exist -Existing drainage (including off -site), drainage easements, pipe sizes, runoff calculations -Drainage areas delineated -Vegetated buffers (where required) VIL AGENT AUTHORIZATION If you wish to designate submittal authority to another individual or firm so that they may provide information on yo behalf, please complete this section: Designated agent (individual or firm): Cape Fear Engineering, Inc. Mailing Address: 5040 New Centre Drive, Suite D City: Wilmington State: N.C. Phone: (910) 790-8584 Fax: (910) 790-8583 VIH. APPLICANT'S CERTIFICATION Zip: 28403 I, (print or type name ofperson listeJ in Ge eral Inforwalon, item 2) W. Christopher Stephens certify that the info lion inclu is permi ication form is, to the best of my knowledge, correct and that the project will be cons c d ' co a roved plans, t the required deed restrictions and protective co 'll e o , and a proposed p ' ctZIth the requirements of 15A NCAC 2H .100 Signature: / Date: Form: SWU-101 Version 3.99 Page 4 of 4 co 1, � rN-I O a a �a 'GJ O 9 r- 0 of tn 9 � acc Ur7t�oC Ob ,V-W0 :y "-<z j0 H H z U P 00� �zO z �yWW mu a) ecu U 0-0 +�• a) 0 0 as � C3 cd r+ 0 o��'�� CA O U' y t"-+ O ►ter i O ¢, O C a O a) cd b cd O Z U cC O 'O �, O 0 tea), •C G U � w y a) C7 c .d �'; rU. i U U' °i a O � O U '~ C/] bA ~ �' w O N w O m C W U W o in a� w> y °'*" y8'oast�, � ca � o 0 z tip to 0 [•� cd >W Cc,IT,ao u Ctdo ib a tw �. ° W-a O C .� ° rUn 40 w; .� > U U U ° ,a 0> O� -a �' O N c3 woo era' > _� c ° Uooa .� w-s W [� 4-4 P-4 + U v .�-i N '+Or +2 y U cd" 0 .� of � n n 0 N I q 0 cd 'b 1P H III ,,•'•• ,•`'`,,�'�� a w o r .� 2x O • U • H � oH O W H � u m 0 h n n O N a o M� LLL777 O (� 144 O LL y N -O cC O ai IOD� U cd Q" P� P� o QpQ Qi �/" � 4� �.r 4ti Fr ° " O 0 0 .D I A R� rl W W C"+ N +.. o y 0 y N O .� P� Q '., .. 04 N ° �� °' °' C. 0 ow.0 Qom, o z � p p �d ., N O N o 5 M y� � �Po �~��� en §� ,� r-10W ° y N�-A � . ced QN pb4J Z \ ".dO -d E" u o b �i �$° 'o0 W] O z C.O U v^v Nvw %O Z 'gyO en vO v*� � a ° , ,�c) cd 00 P��m ¢Q Q vZ o , c Q ¢, E-+ > 0 MPv"U ai cd y �UU Z Z Z• A S', w'b8b UcP 0 g0 O En w m p ,cbdU� A PL4 aao ." c�O+O ¢, M. v •�_pOaQ0 U N "t O LN Z, C`)jW� g 2 W W O N i p /~V� naD too 0 PL4 _0 �. 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'O b�A �d r y .Sy" O U >> v1 ~ b�D U •.�--� v M m F+' N v� ..V., i, v " N 64 ,Q 6b C", 'U ti N r0i V .� W Cp N O �'. >� N O a) �' i+ O >> IYi cd 0 a) �7 �.0 Id o 0 O vJ Cd O'�ram.+ bAn; 0.�� O y is 'b y o .a aoi rimv1 �.. �.+ m Q as O cOi 914 P-+ _ as c 00 An N M. I� . I;r • � s �: 0 Q •:��: • 45�1 CAPE FEAR 5040 New Centre Dnve, Suite D 250 North Church St. Wilmington, N.C. 28403 Spartanburg, SC 29306 TEL (910) 790-8584 TEL (884) 598-8801 FAX (910) 790-8583 FAX (884) 596-8802 www. cape fearen_q. com Engineering, Inc. P:\230\230-28 TO: NCDENR WATER QUALITY SECTION ATTENTION LINDA LEWIS TV `� L 3 02001 Transmittal DATE: August 30 2001 PROJECT NO: 230-28 RE: MAGNOLIA GREENS 9 & 10 SW8 981008 Quantity Drawing No. Description 1 Response to Add -info: SW8 981008 1 Response to Add -info: SW8 970104 REMARKS Linda: Per my phone message and e-mail, please replace the add -info submitted on August 7, 2001 with the attached package. Please ignore the August 7,2001 submittal. CC: File CAP EA Engineering, Inc. CNfI/SSr��/fF.U51 Zi9A0v'g21C Signed K. DAVIS FENNELL, PE 1Admin\STORMWTR\trans3OAUGOI-LEWIS.doc CAPE FEAR `= . Engineering, Inc. August 30, 2001 Linda Lewis NCDENK Water Quality 127 Cardinal Drive Ext. Wilmington, NC 28403 Re: Magnolia Greens Master Plan Stormwater Project No. SW8 970104 Dear Ms. Lewis: RECEIVED AUG 3 0 2001 DWQ PROD # Please find enclosed the response to your request for additional information for the above referenced project: I . The Wet Detention Basin Supplement, DC51gnei-5 Certification, and sealed designed calculations for Pond# I , 015 Submitted in a previous revision that went statutory, are attached. 2. See item I. 3. No other plan sheets have been revised. Pond# I has not been revised, for this revision or the revision that went statutory. No new details for Pond# I are nece55ary. Only the plan view Stormwater Master Plan has been revised. Please attached the revised plan to the 5heet5 that you already have to form a new approved plan set. 4. The master plan summary has been revised. 5. The vicinity map has been revised. We have also deleted the road stub to future development in this drainage basin and replaced it with 2 51ncjle- family lots at 5,000 SF of BIJA. Also attached are duplicate copies of a revised page 2A of the application and revised Low Density Supplement. I trust this information to be Sufficient for your review. If you have any clue5tion5, comments, or require additional information regarding this matter, please contact this office. T;.I k yo , CA% . K. Davi5 Fenn II, PE Cc: Chris Stephens, Landmark file (230-3 1 "30") 5040 New Centre Or., Suite D - WiImineton, NC 28403 - TEL: (910) 790-6584 - FAX. (910) 790-8583 250 worth Chuch Street - 5partanburg, SC 29306 - TEL: (664) 596-8801 - FAX. (864) 596-8802 �Of N OD a h N~ r" poi' � P s� s� z Z o ,3 W c Q Q 0 Z V N Q 0 . J Q- O i 0 - i ks N '1 WET POND DATA SHEET SECTIONS 9/ 10 AT MAGNOLIA GREENS POND#9-1 DRAINAGE AREA (Ad) = IMPERVIOUS AREA (Ai): BUILDINGS: ROADS: SIDEWALKS: OTHER ON -SITE: TOTAL: PERCENT IMPERVIOUS (1): I Ad/Ai = 3 2.7 1 % 2G.9 ACRES 2.89 ACRES , �to«ttatntrrtr�Q�oD�bO( 1. 13 ACRES +`'Q.�� CARd�' .°�Q F"Sys''•. 0.30 ACRES o pss�oy 9 4Q 4.48 ACRES SEAL 5.80 ACRES 024908 r r'f•, �' �N�► �' S FENS °rrrrttttsoef,r POND# I SHALL BE 7DEEP AND DESIGNED TO REMOVE 90% TSS. SA/DA= I.1813% REQUIRED SURFACE AREA AT PERMANENT POOL: SAREQ.= 0.3I777 AC. = 13842 SF 5URFACE AREA PROVIDED AT PERMANENT POOL (EL. 2 1)= I G843 SF y....................................................................................................................... SA PROV'D= I G843 > 13842 =5A R.EQ'D OK •.........................................................................................................................: MINIMUM REQUIRED VOLUME (SIMPLE METHOD BY TOM SCHUELER): Rv=0.05+0.009*(I) Kv= 0.344424 VOLUME= I "*Rv*Ad = 0.77208 AC -FT = 33G32 FT" 3 VOLUME PROVIDED AT TEMPORARY POOL: A SF 23 IG843 24 19329 25 21792 2G 245GG INCREM. TOTAL. VOL. (CO VOL. (CF) 0 0 1808G 1808G 205GO.5 38G4G.5 23 179 G 1825.5 POND#9- 1 DATA 5HEET PAGE I OF 3 REV: AUGUST, 2001 5ET TEMP. POOL ELEVATION: REQ'D EL.= 24.783GG *-5AY 25.3 VOL. PROV'D = 409G5 CF .................................................................................................................... VOL. PROV'D= 409G5 > 33G32 =VOL. REQ'D OK ....................................................................................................................:.....: FOREBAY 51ZING: PERMANENT POOL VOLUME: INCREM. TOTAL J. 5A (Sf), VOL. (M VOL. (CF) I 5127 0 0 17 G349 5738 5738 18 7712 7031 127G9 19 9209 84G1 21229 20 10542 1002G 31255 21 12715 11780 43035 21 .G4 14025 8558 51592 <-- REQ'D 5A 22 14750 5179 5G772 23 IG843 15797 725G8 REQ'D VOLUME = 20% TOTAL = 10318 CF <-- BASED ON PROVIDING THE MINIMUM REQUIRED SURFACE AREA, CALCULATE 20% OF CHECK FOREBAY VOLUME: MINIMUM BASIN VOLUME. INCREM. TOTAL EL 5F VOL. (CF) VOL. 19 1521 0 0 20 2029 1775 1775 21 2GO4 23 1 G.5 4091.5 22 324G 2925 701G.5 23 3950 3598 1OG14.5 PROV'D VOLUME = .......................................................................................................................... I OG 14.5 CF %4' DEEP FOREBAY) ' VOL. PROV'D= ......................................................................................................................... I OG 14.5 = 10318 =VOL. REQ'D OK s . POND#9-1 DATA 5HEET PAGE 2 OF 3 REV: AUGUST, 2001 ORIFICE SIZING: REQ'D DRAWDOWN TIME = 2-5 DAY5 Q2= O. ! 94G29 C. 5 (FOR 2 DAY DRAWDOWN) Q5= 0.077852 CP5 (FOR 5 DAY DRAWDOWN) SELECT A 2" CIRCULAR ORIFICE, EL. 23.0' (PERM. POOL EL.) Q PROV'D= Cd*A*(2gh) ^ 1 /2 Q PROV'D= 0. 1 10589 WHERE: Cd= O.G A= 0.0218 5F g= 32.2 FP5/5 h= AVE. HEAD=(2.3'-1 Y 1 2)/2 1.11 ' .................................................................... Q2> 0.1 10589 >Q5 OK ..................................................................... DRAWDOWN TIME: TIME = VOLUME = 3.51957 DAYS Q PROV'D POND#9-1 DATA 5HEET PAGE 3 OF 3 REV: AUGUST, 2001 E BURY COURT ass I /O �0` Y'*� \0 ,-' O,9 �-9 /0 OTHER ON -SITE AREA - SWS 970104 ._ /OAT 5K LOTS ALLOCATED 5,000 SF OF BUA. ALL ,>r OTHER LOTS ALLOCATED 4, 000 SF BUA. 104.6 /04 .gyp /pq-s ♦ ♦` 5-41 oq,� ♦� sK , 8-42 \pP, coy /oq � q 9_/N q, q, Cl4 2 s .. -�3 /4 q` 8 :.fir:. • �• .8. : Cl- 9, .•f9s1' 3q, 133 q! ` ;•;•' ' 0 8 - 51 200 0 200 400 + 1 INCH = 200 ON -SITE SWS g81008 OTHER ON -SITE SWS g70104 ��ROADS/SW 62 057 SF ��ROADS/SW q5 258 SF LOT5 LOTS 21@4 000 SF 84,000 SF 15@4 000 5F 60,000 SF 2@5 000 5F 10,000 5F 8@2 500 5F 20,000 5F 11@2 000 5F 22,000 5F 10@2 000 5F 20,000 5F 4@2 500 5F 10 000 SF TOTAL LOTS 100,000 5F TOTAL LOTS 126,000 SF TOTAL OTHER 1g5,258 (4.48 5F AC) TOTAL ON-51TE 1881057 SF (4.32 AC) TOTAL IMPERVIOUS INVENTORY = 383 315 5F 8.80 AC), .f*ROAD5/5W REMAIN UNCHANGED. IMPERVIOUS COVERAGE OF ALL R0AD5/5W TAKEN FROM EXISTING PERMIT 5W8 0181008). 41 BESCRPTM REV.BY DAW CAPE FEAR Engineering, Inc. MWgEry NG9Ba0 ,a �a OEM nP � amp n o au am: rmw A9WMWM SPORMi Dm s a Mr. a alo MA�p+IOLIA gas PCM 94 CAPE FEAR Engineering, Inc. August 7, 2001 Linda Lewis NCDENR Water Quality 127 Cardinal Drive Ext. Wilmington, NC 28403 Re: Sections 9* 10 at Magnolia Greens Stormwater Project No. SW8 981008 Dear Ms. Lewis: RECEIVED AUG 3 0 2001 DWQ PROD # Please find enclosed the response to your request for additional information for the above referenced project: I . A section detail for Pond # 10 and outlet structure details have been added to the detail sheet. Two sets of the revised plan and details are attached. 2. Road sections details (and plan view details of the cul-de-sacs) have been added to the plan. Two sets of the revised plan and details are attached. 3. The areas within Magnolia Greens but outside of the SW8 981008 boundary are shown as "Other On -site Area" in the calculations. Pages 2 and 2A of the application have been revised and are attached (2 copies); 4. A plan view exhibit has been attached to the calculations delineating the. "On-91te area" and the "Other on -site area". An impervious breakdown is also included on the revised plan. 5. The pond outlet structure has been revised to show a single 2" orifice. Revised calculations and revised page I of the Wet Detention Basin Supplement are, attached. G. Pond side slope vegetation and wetland species for the G: I shelf have been added to the detail sheet. We have also deleted the road stub to future development and in this area we have added 2 lots at 5,000 SF of BLIA. These lots will be added to the master permit (5W8 970104), but are treated in Pond 9-1 . All necessary paperwork has been updated and is included in this revised submittal. I trust this information to be sufficient for your review. If you have any questions, comments, or require additional information regarding this matter, please contact this office. Thank you, K. Davis Fennell, PF Cc: Chris Stephens, Landmark file (230-3 1 "30") 5040 New Centre Dr., Butte D • Wllmineton,.NC 2&403 • TEL: (910) 790-6564 • FAX: (910) 790-8583 250 North Chuch Street • Spartanburg, SC 29306 0 TEL: (664) 596-6601 1 FAX (864) 59643802 c I 4 0 go E-0 LJt11.9 z p Z o w Q Q N � � CAPE FEAR Engineering, Inc. August 7, 2001 Linda Lewis NCDENR Water Quality 127 Cardinal Drive Ext. Wilmington, NC 28403 Re: Magnolia Greens Master Plan Stormwater Project No. SW8 970104 Dear Ms. Lewis: RECEIVED AUG 0 7 2001 PROJ # .SW ?q�U1()�-1L(DD Please find enclosed the re5pon5e to your request for additional information for the above referenced project: I . The Wet Detention Basin Supplement, Designers Certification, and sealed designed calculations for Pond# I , as Submitted in a previous revision that went Statutory, are - attached. 2. See item I . 3. No other plan sheets have been revised. Pond# I has not been revised, for this revision or the revision that went statutory. No new details for Pond# I are necessary. Only the plan view Stormwater Master Plan has been revised. Please attached the revised plan to the Sheets that you already have to form a new approved plan set. 4. The master plan summary has been revised. 5. The vicinity map has been revised. I trust this information to be Sufficient for your review. If you have any questions, comments, or require additional information regarding this matter, please contact this office. Thank y , K. Davi5 Fennell, PE Cc: Chris Stephens, Landmark file (230-3 1 "30") 5)40 New Centre Dr., Suite D • Wilmington, NC 26403 • TEL: (910) 790-6584 • FAX- (910) 790-6583 250 North Chuch Street - Spartanburg, SC 29306 • TEL: (864) 596-8801 • FAX, (864) 596-6602 RECEIVED AUG 0 7 2001 PROJ # 'W$ 4- Hop Ra�s ed Wet Pond Calculations 3AO C 00 SEAL 0249M `�CiIP1E�r '��.,. _ �S FEN _.��• EXISTING WET POND DATA 5HEET PATIO I AT MAGNOLIA GREEN5 POND# I PERMIT NO. 5W8 970104 ORA/NAGEAREA (Ad) = 1AWP' eR!/OU.S ARffA (Al).. BUILDINGS: ROADS: PARKING: 51DEWALK5: TOTAL: PHA5E 3 BASIN 3��� 13�� ORAINAGEAREA (Ad) _ /MPERf//OUS AREA (Ai) - BUILDINGS: ROADS: PARKING: SIDEWALKS: TOTAL: TOTAL DRAINAGE AREA (Ad) = TOTAL IMPERVIOUS PEKCENT IMPERVIOUS (1): I - Ad/Ai = 2G.82%a 141 . G ACRE5 25.55 ACRES 10.42 ACRES 0.00 ACRES 2.78 ACRES 38.75 ACRES 9.7 ACRES 1.20 ACRES 0.5 1 ACRES 0.00 ACRES 0. 12 ACRE-5 1.53 ACRE5 151.3 ACRES 40.55 ACRES POND# I SHALL BE 7DEEP AND DE51GNED TO REMOVE 90% T55. 5A/DA= 1.0438% REQUIRED SURFACE AREA AT PERMANENT POOL: 5Ap�EQ.= 1.5792G94 AC. = G8792.98 51' SURFACE AREA PROVIDED AT PERMANENT POOL (EL. I8)= 82200 SF ...................................................................................................................... 5A PROV'D= 82200 > G5792.95 =5A REQU OK ........................................................................................................................:.: POND# I DATA 5HEET PAGE I OF 3 OCTOBER, 1999 MINIMUM REQUIRED VOLUME (SIMPLE METHOD BY TOM 5CHUELER): Rv=0.05+0.009*(I) Rv= 0.291358 VOLUME= I "*Rv*Ad = 3.G7392 AC -FT 10003G F T ^ 3 VOLUME PROVIDED AT TEMPORARY POOL: INCREM. TOTAL F-L 5A (5F) .VOL-(CD Vol- (CF) 18 52200 0 0 19 87223 84712 84712 20 92299 897G1 174473 21 97754 95027 2G9499 SET TEMP. POOL ELEVATION: REQ'D EL.= 19.8391 G5 .4—SAY 20.1 (AS -BUILT RIM EL.) VOL. PROV'D = 183975. 1 5 CF ........................................................................................................................ VOL. PROV'D= 183975. 15 > 100035.8 =VOL. REQ'D OK .......................................................................................................................... FOREBAY SIZING: PERMANENT POOL VOLUME: INCktM. TOTAL F1.. SA (5f) VOL,_(Cffl VOL, (CF) II 37079 0 0 12 39751 38415 38415 13 42481 4111G 79531 14 58384 50432.5 1299G3.5 15 G2953 GOGG8.5 19OG32 I G G7G44 G5298.5 255930.5 17 72444 70044 325974.5 18 52200 77322 40329G.5 REQ'D VOLUME = 20% TOTAL = 51 18G CF ---MIN. SURFACE AREA USE TH15 VOLUME TO SIZE FOREBAY. -4 - (20% TOTAL = 80000 CF) POND# I DATA 5HEET PAGE 2 OF 3 OCTOBER, 1999 CHECK FOREBAY VOLUME: INCREM. TOTAL EL.. SA-a5A-aD VOL (CF) VDI—f M 14 1311G 0 0 15 14837 13977 13977 10 1GG24 15731 29707 17 184GO 17542 47249 18 22200 20330 G7579 PROV'D VOLUME = G7579 CF (4' DEEP POREBAY) ........................................................................................................................ MAX. VOL. (80000) > PROV'D VOL. (G7579) > MIN. VOL. (5 1 18G) ........................................................................................................................... 'FOREBAY MEETS DESIGN CRITERIA ORIFICE SIZING: REQ'D DRAWDOWN TIME — 2-5 DAYS Q2= 0.92G 1332 CFS (FOR 2 DAY DRAWDOWN) Q5= 0.3704533 CFS (FOR 5 DAY DRAWDOWN) SELECT 2 x 4" CIRCULAR ORIFICE, EL. 18' (PERM. POOL EL.) Q PROV'D= 2'(Cd'A'(2gh)^ 1/2) WHERE: Cd= O.G A= 0.05727 SF g= 32.2 FPS/5 h= AVE. HEAD =(2. P-27 1 2)/2 = 0.9G7 Q PROV'D= 0.82G385 1 .................................................................. ; Q2> 0.82G3851 >Q5 OK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . a . . . . . . . . . . . . . . . . . DRAWDOWN TIME: TIME = VOLUME = 2.24141 DAYS Q PROV'D POND# I DATA 5HEET PAGE 3 OF 3 OCTOBER, 1999 North Carolina Department of Environment and Natural Resources Division of Water Quality Wilmington Regional Office Michael F. Easley, Governor William G. Ross, Jr., Secretary July 19, 2001 Mr. Chris Stephens, President Landmark Developers, Inc. PO Box 4127 Wilmington, NC 28406 �. MI.Pt, • NCDENR NORTH CAROLINA DEPARTMENT OF ENVIRONMENT AND NIQURAL RESOURCES Subject: REQUEST FOR ADDITIONAL INFORMATION Stormwater Project No. SW8 970104 Modification Magnolia Greens Master Plan Brunswick County Dear Mr. Stephens: The Wilmington Regional Office received a Stormwater Management Permit Application for Magnolia Greens Master Plan on May 14, 2001. A preliminary review of that information has determined that the application is not complete. The following information is needed to continue the stormwatcr review: 1. Please provide a new wet detention supplement for Pond 1, since the design parameters have changed. The last Pond 1 supplement I have was signed in October, 1999. If this pond was part of the last revision that went statutory, I need to have that information before a permit can issued. 2. Please provide revised, sealed calculations for the revision to Pond 1. 3. None of the other sheets associated with this plan set were submitted. Please specify if the sheets I already have are to be attached to this new Master Plan, to form the new approved plan set. Are any revisions to the Pond 1 details needed? 4. The Master Plan summary indicates that the 991136 revision, (Phases 3 & 4) which made Parcel B a patio home site instead of a multi -family site, is to be treated in a detention pond. The permit, issued on January 30, 2001, approved a 30% low density site with a curb outlet system, with a small portion of the project's runoff being treated by Pond 1. Please correct this on the Master Plan summary. 5. Please add the nearest major intersection to the vicinity map. 127 Cardinal Dr. Ext., Wilmington, North Carolina 28405 Telephone 910-395-3900 FAX 910-350-2004 An Equal Opportunity Affirmative Action Employer 50% recycled/10% post -consumer paper Mr. Stephens July 19, 2001 Stormwater Project No. SW8 970104 Modification Please note that this request for additional information is in response to a preliminary review. The requested information should be received by this Office prior to August 19, 2001, or the application will be returned as incomplete. The return of a project will necessitate resubmittal of all required items, including the application fee. If you need additional time to submit the information, please mail or fax your request for a time extension to the Division at the address and fax number at the bottom of this letter. The request must indicate the date by which you expect to submit the required information. The Division is allowed 90 days from the receipt of a completed application to issue the permit. The construction of any impervious surfaces, other than a construction entrance under an approved Sedimentation Erosion Control Plan, is a violation of NCGS 143-215.1 and is subject to enforcement action pursuant to NCGS 143-215.6A. Please reference the State assigned project number on all correspondence. Any original documents that need to be revised have been sent to the engineer or agent. All original documents must be returned or new originals must be provided. Copies are not acceptable. If you have any questions concerning this matter please feel free to call me at (910) 395-3900. RSS/arl cc: Sincerely, 4�� X�o Linda Lewis Environmental Engineer S:1WQSISTORMWATIADDINF01970104 Modification.JUL Linda Lewis Davis Fennell, P.E. 127 Cardinal Dr. Ext., Wilmington, North Carolina 28405 Telephone 910-395-3900 FAX 910-350-2004 An Equal Opportunity Affirmative Action Employer 50% recycled/10% post -consumer paper CAPE FEAR Engineering, Inc. 5040 New Centre Drive, Suite D 250 North Church St. Wilmington, N.C. 28403 Spartanburg, SC 29306 TEL (910) 790-8584 TEL (864) 596-8801 FAX (910) 790-8583 FAX (864) 596-8802 www.capefeareng.com TO: NCDENR I WATER QUALITY SECTION ATTENTION LINDA LEWIS 6r on OP 0 ("o Transmittal . DATE: MAY 14, 2001 PROJECT NO: 230-09 RE: MAGNOLIA GREENS SW8 970104 Quantity Drawing No. Description 2 ORIGINAL + 1 COPY: APPLICATION 2 ORIGINAL + 1 COPY: LOW DESNITY SUPPLEMENT 2 COPIES: STORMWATER MASTER PLAN IRRCEIVED MAY t WQ b lr,6) REMARKS CC: File CAPE,f EAR Engineering, Inc. Signed?. K. DAVIS FENNELL. PE 11CAPE_FEARIDATAIPROJECT'S12301230-SW-MASTERItrans14MAY01-LEWIS.doc RECEIVED DEC 18 2oOO Calculations DWO PROD # 33( 00 For Phase III and IV at Magnolia Greens Proj. No. SW8 991136 11 /3/00 FESSI0 9 SEAL - 024908 Prepared By: Cape Fear Engineering 5040 New Centre Dr., Suite D NAlilmington, NC 28403 Tel: (910) 790-8584 Fax: (910) 790-8583 0 Magnolia Greens Phases III and IV Calculations (Swale #1) Cc Iio 0 Cc Composite rational runoff coefficient = (Impervious area* 0.95 + Pervious area * 0.15)/Drainage area = 0.38 137.2656 I10 = Rainfall intensity (infhr) = = 653 in.fhr (T. + 25.5) 0.8617 3 0.385 L Tc = Time of concentration (min) = H = 8.8 min 128 L = Length of run (ft) = 750 ft H = Elevation change (ft) = 5 ft Q = Flowrate (cfs) = CIA =15.47 cfs A = Area (acres) = 6.2 acres Depth Depth (ft) = y Use mannings equation to solve for y: Q— 1.49A*R 3 *SY=15.47cfs n n = Mannings roughness coefficient = 0.03 A = Cross sectional area of flow (sf) = (Bottom width * Depth) + (Side slope ratio Depth2) = 0 + 5y2 R = Hydraulic radius (ft) = A A P P = Wetted perimeter (ft) = Bottom width + 2 * Depth * 1 + Side slope ratio2 = 0 + 2y 1 + 52 : therefore R = 0.49y S = Longitudinal slope (ftfft) = 0.005 Reformulate mannings equation: e F !+p p 3 y 1- y =1.14 ft Velocity V = Velocity (fps) V = Q = 2.38 fps A Stormwater Calculations Page 1 Magnolia Greens Phases III and IV Calculations (Swale #2) Cc Ilo M Cc = Composite rational runoff coefficient = (Impervious area * 0.95 + Pervious area * 0.15)/Drainage area = 0.38 I10 = Rainfall intensity (in/hr) = 137.265608617 = 6.64 in.1hr (Tc + 25.5) L3 0.385 H Tc = Time of concentration (min) = 128 = 8.13 min L = Length of run (ft) = 650 ft H Elevation change (ft) = 4 ft Q = Flowrate (cfs) = CIA =16.66 cfs A = Area (acres) = 6.6 acres Depth Depth (ft) —y Use mannings equation to solve for y: Q— 1.49A*R 3 *S2 =16.66cfs n n = Mannings roughness coefficient = 0.03 A = Cross sectional area of flow (st) = (Bottom width * Depth) + (Side slope ratio Depth2)=0+5y2 R = Hydraulic radius (ft) = P P = Wetted perimeter (ft) = Bottom width + 2 * Depth * 1 + Side slope ratio2 = 0 + 2y 1 + 52 : therefore R = 0.49y S Longitudinal slope (ftfft) = 0.005 Reformulate mannings equation: s Q y ' 10.88 y =1.17 ft Velocity V = Velocity (fps) V = Q 2.43 fps A Stonnwater Calculations Page 2 Magnolia Greens Phases III and IV Calculations (Swale #3) M Iro 0 Cc Composite rational runoff coefficient (Impervious area* 0.95 + Pervious area * 0.15)/Drainage area = 0.29 I10 = Rainfall intensity (inUhr) = 137.2656o.s617 6.40 in.1hr (T� + 25.5) 3 0.385 L H Tc = Time of concentration (min) = 128 = 9.59 min L = Length of run (ft) = 750 ft H = Elevation change (ft) 4 ft Q Flowrate (cfs) = CM =15.04 cfs A = Area (acres) = 8.2 acres Depth Depth (ft) = y Use mannings equation to solve for y: Q-1.49A*R 3*SY=15.04cfs n n = Mannings roughness coeqz'cient : 0.03 A = Cross sectional area offlow (sf) = (Bottom width * Depth) + (Side slope ratio Depth2) = 0+5y2 R Hydraulic radius (ft) = P P = Wetted perimeter (ft) = Bottom width + 2 * Depth * 1 + Side slope ratio2 = 0 + 2y 1 + 52 : therefore R = 0.49y S = Longitudinal slope (ftfft) = 0.005 Reformulate mannings equation: ! f Q y 3 1 V.88 y =1.13 ft Velocity V = Velocity (fps) V = Q = 2.36 fps A Stormwater Calculations Page 3 Magnolia Greens Phases III and IV Calculations (Swale #4) Cc I10 R� Cc Composite rational runoff coefficient (Impervious area* 0.95 + Pervious area * 0.15)/Drainage area = 0.38 2656 I10 = Rainfall intensity (infhr) = 13 7.o.a6r� = 6.52 in.fhr (K + 25.5) - 0.385 Tc = Time o concentration = - H = f on (man) 128 8.85 man L = Length of run (ft) = 700 ft H Elevation change (ft) = 4 ft Q = Flowrate (cfs) = CIA =12.90 cfs A = Area (acres) = 5.2 acres Depth Depth (ft) = y Use mannings equation to solve for y: Q_ 1.49A*RZ3 *SY=12.90cfs n n = Mannings roughness coefficient = 0.03 A = Cross sectional area of flow (sf) = (Bottom width * Depth) + (Side slope ratio Depth Z) = 0 + 5y 2 R = Hydraulic radius (ft) _ A P P = Wetted perimeter (ft) = Bottom width + 2 * Depth * V1 + Side slope ratio = 0 + 2y 1 + sZ therefore R = 0.49y S = Longitudinal slope (ftfft) = 0.005 Reformulate mannings equation: 8 F Q y 3 10.38 y=1.07ft Velocity V = Velocity (fps) V = Q = 2.25 fps A Stormwater Calculations Page 4 Magnolia Greens Phases III and IV Calculations (Swale #5) Cc Iio M Cc = Composite rational runoff coefficient = (Impervious area * 0.95 + Pervious area * 0.15)/Drainage area = 0.41 137.2656 I,0 = Rainfall intensity (infhr) = o.ael� = 6.53 in.fhr (Te + 25.5) 3 0.385 L H Tc = Time of concentration (min) = 128 = 8.8 min L = Length of run (ft) = 750 ft H = Elevation change (ft) = 5 ft Q = Flowrate (cfs) CIA 15.69 cfs A = Area (acres) = 5.9 acres Depth Depth (ft) = y Use mannings equation to solve for y: Q_ 1.49A*RY *SY=15.69cfs n n = Mannirgs roughness coefficient = 0. 03 A = Cross sectional area of flow (sf) = (Bottom width * Depth) + (Side slope ratio Depth 2) = 0 + 5Y 2 R = Hydraulic radius (ft) = A A P P = Wetted perimeter (ft) = Bottom width + 2 * Depth * 1 + Side slope ratio = 0 + 2y 1 + 52 therefore R = 0.49y S = Longitudinal slope (fifft) = 0. 005 Reformulate mannings equation: s Q y 3 1110.88 y =1.15 ft Velocity V = Velocity (fps) V = Q = 2.37 fps Stormwater Calculations Page 5 O (A cn ID Co O W (n CO I CX) O Cf) Cl) oo CX) = o m- C = o m- C = o m- C mmmr D mr1rnr D rnrnmr- D D D � D � Z F- 7� U) I r- (A I r � CO c) � Cf)o � � v � v X D > D Z O Z —i O Z D D D D D C) r G7 r G7 ii a ii u m a ii ii u m n ii u u ii 0000 > ii 000-- > 000- > 0 j Ui J m o0 0- (A (A m �I O� CA �"� , m 0 � °' D J o -' 00 0° > `n 0 0 0o D n n C-) n n n n n W n n n n n n C)n n n N n n 0 n n Q n n n O (n (n co CO O C m O 40 -1 C o-4 m C� m m �D�z m r D m m �> m r D m >�z m o D .-.r(n I ..rcn X --I (nG —� m D --A m D --A D Z O `- Z 0 Z C D Gam') G7 n u n ii m ii ii n u m n u ii ii ii m ii N 0 0 > u 000 -' > 00 O O > CD -' Ui N o m CD N N 00 CJi a) O CA m cn CW O — O W -P O a) m D D D Q n n n n n n n n n CY) n n n n n n n n n n a n n n n n ❑ n ❑ n 4�k-