Entire Design Manual - Greenville County

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Floodplain Study General Criteria All floodplain studies shall follow the guidelines and procedures as set forth by FEMA and the County. The following general criteria and requirements have been established to help clarify the procedures related to performing a floodplain study in Greenville County. The project must be consistent with applicable State and Federal regulations. A professional engineer registered in the State of South Carolina shall prepare all studies. The following hydraulic computer models for floodplain development in Greenville County are recommended but is not limited to: HEC-RAS WSPRO The floodplain analysis shall include the 10-, 50-, 100-, and 500-year, 24-hour storm events. Hydrologic analyses should utilize the current land use conditions based on the most updated data within the desired watershed. FEMA only allows for consideration of existing conditions in the watershed. The County can require particular models to be based on built out conditions for its own purposes, but FEMA will not accept these future conditions in the FEMA submittal. Volume as well as peak flow shall be evaluated. Limits of the 100-year floodplain for the pre-development and post-development conditions shall be shown on the site plan. Backwater conditions, local obstructions, bridges, culverts, and storm water conveyance systems shall be considered. Digital data shall have the following characteristics: Horizontal Datum: NAD83 (1994) Coordinate System: SPC Lambert Zone 3900 Vertical datum: NAD88 Units: International Feet Data capture methods must result in new data meeting national horizontal and vertical accuracy standards, which are scale dependent. In 1997, the County was mapped at three different scales, 1- inch = 100-feet (100 scale), 1-inch = 200-feet (200 scale), and 1-inch = 400-feet (400 scale). Horizontal accuracy standards are approximately (+/-) 2.5-feet, +/- 5.0-feet, and (+/-) 10.0-feet, respectively for each mapping scale. Vertical accuracy is (+/-) one half of the contour interval for a given area. Therefore, the vertical accuracy standards are (+/-) 2.0-feet for the 100 and 200 scale and (+/-) 4-feet for the 400 scale. New data should not significantly exceed the above standards. All proposed work within Unnumbered A zones must be accompanied by hydrologic and hydraulic modeling. Calculated flood boundaries shall be submitted in a digital format that is compatible with Greenville County’s GIS. Greenville County, South Carolina January 2013 Storm Water Management Design Manual 3-18
Each permit must include: Floodplain Study Submittal Criteria Applicants Name Address where the work will be done Correct tax map I.D. number Subdivision name if applicable A type of development must be chosen. If the work being done falls into “other”, please elaborate in the comments section. Under “Flood Zone” all properties that have floodplains must check either “No. A or A Zone”. The No. A zones are floodplain areas that have had a detailed study performed and a base flood elevation is known. The base flood elevation in A Zones have been approximated. Under “Location in relation to Floodway/Floodplain”, all properties that have floodplains must chose “inside adopted floodplain”. In the comments section, if the work to be done includes a structure, make a note as to whether the structure is located within the floodplain. The application must be signed and stamped by a South Carolina Registered Engineer or Surveyor and the applicant must sign the application. Hydrologic and hydraulic analyses must be contained in a report describing the study methodology, a listing of all assumptions (e.g., rationale for Manning’s ‘n’ values, reasons for revising hydrology, source of topographic information and land use), bridge and cross section data, and a brief description of the project. All projects being submitted to FEMA must have a completed FEMA MT-1 or MT-2 form as appropriate. These forms can be obtained from the following. FEMA website: www.fema.gov FEMA Region IV 3003 Chamblee Tucker Road Atlanta, Georgia 30341 (770.220.5400) The South Carolina Department of Natural Resources Flood Mitigation Program 2221 Devine Street, Suite 222 Columbia, South Carolina 29205 (803.734.9103) 3.3.7 Storm Water Facility Ownership and Maintenance Ownership All permanent storm water management facilities shall be privately owned and maintained unless Greenville County accepts the facility for County ownership and maintenance. The owner of all private facilities shall grant the County a perpetual, non-exclusive easement that makes the facility accessible Greenville County, South Carolina January 2013 Storm Water Management Design Manual 3-19
Page 1 and 2: GREENVILLE COUNTY STORM WATER MANAG
Page 3 and 4: 3.10.1 Purpose ....................
Page 5 and 6: 8.4.2 Design of Riprap Channel Lini
Page 7 and 8: LIST OF TABLES Table Name Page# Tab
Page 9 and 10: Figure 8-10 Subsurface Draiange Cap
Page 11 and 12: Standard Drawing WQ-08 Standard Dra
Page 13 and 14: ACRONYMS AND ABBREVIATIONS AASHTO A
Page 15 and 16: Chapter 1. INTRODUCTION 1.1 Purpose
Page 17 and 18: Effects of Urbanization on Watershe
Page 19 and 20: Utilize nontraditional lot designs
Page 21 and 22: South Carolina Storm Water Manageme
Page 23 and 24: Nothing in the Storm Water Manageme
Page 25 and 26: Chapter 2. STORM WATER MANAGEMENT R
Page 27 and 28: Technical Report The technical repo
Page 29 and 30: The Greenville County Storm Water P
Page 31 and 32: Chapter 3. PLAN SUBMITTAL 3.1 Storm
Page 33 and 34: flooding or water quality or other
Page 35 and 36: Plan. However, concurrence in the c
Page 37 and 38: interfere with access to the easeme
Page 39 and 40: Agency, and does not require prepar
Page 41 and 42: 3.3.3 Storm Water Management Design
Page 43 and 44: Design details and computation for
Page 45 and 46: of the Clean Water Act; Description
Page 47: 1. Restrict or prohibit uses that a
Page 51 and 52: water in storm water management fac
Page 53 and 54: 3.4 Digital Submittal Requirements
Page 55 and 56: 3.5.3 Incomplete Storm Water Manage
Page 57 and 58: Final Storm Water Management Site P
Page 59 and 60: 2. The owner has obtained applicabl
Page 61 and 62: 2. Upgrade of Existing Detention or
Page 63 and 64: standards. The following conditions
Page 65 and 66: Chapter 4. EASEMENTS 4.1. Purpose A
Page 67 and 68: left hand corner of the plat. No ot
Page 69 and 70: equired, only the SCS Method or oth
Page 71 and 72: Description of Area Runoff Coeffici
Page 73 and 74: The SCS CN Method begins with a rai
Page 75 and 76: Use Figure 5-1 (Composite CN) if th
Page 77 and 78: 5.2.3.3. Factors Affecting the Time
Page 79 and 80: Diversion, Swales, Paved gutters, R
Page 81 and 82: T c : Time of concentration (T c )
Page 83 and 84: Mild slopes less than 2 percent. Si
Page 85 and 86: 484 300 t/Tt q/qu Q/Qp q/qu Q/Qp 3.
Page 87 and 88: triangular approximation, k r = t r
Page 89 and 90: 5.6.2 Normalized Peak Flow Rate If
Page 91 and 92: Rainfall-runoff calculations carrie
Page 93 and 94: Chapter 6. HYDRAULICS 6.1. Open Cha
Page 95 and 96: 6.1.3 Momentum Equation The momentu
Page 97 and 98: Type of Flow Media Min Normal Max N
Page 99 and 100:
The hydraulic radius (R) for a trap
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Rearrangement of the continuity equ
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Water quality and channel protectio
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all three equations should be utili
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6.3.4 Critical Depth in Culverts Wh
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Select entrance coefficient K e fro
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Type of Structure and Design of Ent
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Therefore, Inlet Control prevails a
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6.4.3 Flow Through a Rock Ditch Che
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Stage (m) Flow Length (m) Unit Flow
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6.5.1.4 Pipe Size The minimum pipe
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where backwater effects created fro
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2) Knowing the channel dimensions,
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Table 6-5. Maximum Permissible Velo
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Chapter 7. STORM WATER DETENTION DE
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Evaluate the control structure outl
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6. Access: Maintenance access shall
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4. Access Port: Access to the subsu
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asin area. In calculating runoff vo
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equirements, The downstream propert
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times gully erosion is formed on th
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8.2. Purpose This chapter of the De
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8.3.2 Alternative Erosion Preventio
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Manning’s n of matting: 0.025 Sid
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**If side slopes were less than 3:1
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V S = Y D W * 43,560 Where V S is t
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If construction of a particular sit
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are located Appendix F and include:
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must be obtained. For Greenville Co
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Solution: Part (a) 1. Estimate the
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If the ditch check ratio intersects
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8.7.4.1 Silt Fence Design Aid Ratio
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B. 1. A Cecil D 15 topsoil is 0.006
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A sediment storage volume shall be
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Chapter 9. WATER QUALITY 9.1. Water
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lakes (US EPA, 1997). Such nutrient
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Table 9-4. Event Mean Concentration
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Event mean pollutant concentrations
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Permanent water quality ponds and d
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only the permanent pools of storm w
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9.7. Non-Structural Water Quality C
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A ( K T ) = cd I [( ) − K] Where:
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General Structural Control Sand Fil
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BMP TSS TP TN Estimated Pollutant R
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Limited Structural Control Vegetate
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equired water quality standard. For
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Chapter 10. LOW IMPACT DEVELOPMENT
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Minimize imperviousness by reducing
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10.1.1.5.1 Residential Residential
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Maximize sheet flow Modify/ lengthe
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Table 10-3. LID Techniques for use
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from infiltration. The results of t
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volume control, needed to maintain
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Table 10-4. Site Constraints of LID
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Chapter 11. STREAM PROTECTION AND R
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advantages. Vegetated measures prov
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Frequency of bank-full flow based o
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with geotextiles and geogrids suppl
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Date and location of the site inspe
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Failure to comply with the storm wa
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on the property, and payment of all
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