The Storm Water Control Plan

Attention: SC DHEC's new Construction General Permit is effective as of January 1, 2013. All new and existing construction projects must comply with new permit provisions.


For SC DHEC's stormwater permit coverage applications and forms for construction activities, click here.

The purpose of the Storm Water Control Plan is to specify how the built project will incorporate site design characteristics, landscape features, and BMPs that minimize imperviousness, retain or detain stormwater, slow runoff rates, and reduce pollutants in post-development runoff. The Stormwater Control Plan must incorporate measures to treat stormwater runoff before it is discharged from the site; these treatment facilities must be designed to minimum criteria specified by the Storm Water Design Manual. The Storm Water Control Plan must also identify responsibility and a mechanism to ensure maintenance of the treatment facilities in perpetuity. Development of a Storm Water Control Plan must be coordinated and integrated with preparation of the site layout, landscaping, and drainage. The Stormwater Control Plan is separate from, and in addition to, a storm water pollution prevention plan which addresses requirements for erosion and sediment control and for pollution prevention measures during construction. The following items are storm water specific and do not reflect that of other department requirements

To contact your plan reviewer click here.

The Plan Package


The major components of the plan package for storm water review consists of:

The Storm Water Report

A Stormwater Report must be submitted with the Notice of Intent permit application to document compliance with the Stormwater Management Standards. The following checklist is NOT a substitute for the Stormwater Report (which should provide more substantive and detailed information) but is offered here as a tool to help the applicant organize their Stormwater Management documentation for their Report and for the reviewer to assess this information in a consistent format. As noted in the Checklist, the Stormwater Report must contain the engineering computations and supporting information set forth in Horry County Storm Water Manual. The Stormwater Report must be prepared and certified by a Registered Professional Engineer (RPE) licensed in the state of South Carolina. The Stormwater Report must include:

Summary table which includes:

  • CN designations
  • Peak inflows, peak outflows, and max pond water surface elevations for the 2, 10, 25 and 100yr storms.
  • Tailwater assumption

Narrative which includes:

  • A brief narrative describing stormwater management practices.
  • NRCS soil identifications and characteristics
  • Describe pre- and post-conditions and any flooding issues
  • Describe topographic and soil conditions
  • Upstream and down stream conditions (Flooding issues)
  • Existing tail water elev and any assumptions
  • An analysis and details for any streams that may be affected or within ½ mile radius of a water body listed on the 303D DHEC list or if a TMDL is established. If the project does not fall into these criteria then this shall be clearly stated in the narrative.
  • A general description of adjacent properties and existing structures located on surrounding properties.
  • Site acreage also pond area in (Ac Ft)
  • Narrative of 10% downstream analysis. Include pinch points and outfall conditions determining the effects from the project and any potential flooding.
  • Anticipated start and completion dates.
  • If using a feature which is sensitive to water table elevations state the water table elevation

Maps included are:

  • FEMA and Flood Zones
  • Project location
  • USGS quadrangle sheet (show project location, route runoff from site to nearest water body)
  • Wetland permit or certification letter if required
  • Map of 10% down stream analysis map with points of interest.
  • Map to show off site drainage through or onto the site

Supporting documents included are:

  • Lake maintenance agreement For a blank copy click Here
  • Off site temporary easement agreements for outfalls (may not be required)
  • Adjacent property owner’s agreement for new point discharge onto adjacent property that was not previously natural (may not be required)
  • If an infiltration system used: Geotech report

Site Hydrology:

  • Size of Areas (Acreage)
  • Post-development is less than pre-development by 20%  (for projects over 5 acres) Note: Post- vs pre-discharge rates are based on point discharges and not accumulative site discharge.
  • CN designations calculated avg. or designation
  • Soils information (type, special characteristics, perk rate if a perk system is used, water table if dry pond is used)
  • Proper rainfall intensities used for 2, 10, 25,100 yr storms –Use NOAA 14 charts (Click Here)
  • Correct Peaking factors used (256 pre, and 323 post)
  • Volume Hydrographs for SCS 24 hr
  • 10, 25, 100 yr peak inflow/outflow and max water elevation of ponds (note on drawing as well)
  • Drainage nodes
  • Provide Basin and node map
  • Design calculations for culverts and storm sewers
  • Design calculations, cross sections and method of stabilization of existing and planned channels (include temporary linings) 10 yr storm velocities of 5fps
  • Design calculations and construction details of energy dissipaters below culverts and storm sewer outlets (for rip-rap aprons, include stone sizes (diameters) and apron dimensions)
  • Inlets not to handle more than 1 acre
  • Time of concentration
  • Tail water conditions (elevations of outfall ditch match and tail water condition should reflect an existing 25 yr event in the ditch if using a static condition)
  • Dry ponds drain between 24 – 72 hrs
  • Emergency spillway designed to 100 yr storm
  • Soil information below culvert and storm sewer outlets
  • Design calculations and construction details to control ground water, i.e. seeps, high water table, etc.
  • Wet Storm water basins trap the first ½ inch of storm run off and release over 24 hrs. Dry basins will trap the first 1-inch and finished releasing between 24-72 hrs. (Show calculations)
  • Water Quality Calculations for sediment basins and/or other BMPs (use correct graph to show 80% Efficiency)
  • Sediment basins required for 10 acres or more and show calculations for 80% efficiency
  • 10 % down stream analysis
  • Required retention calcs

The Stormwater Management Report shall document compliance with each of the Stormwater Management Standards as provided in the Horry County Stormwater Manual and Horry County ordinances.

NOI Information

This form can be filled out online at the DHEC website by following this link. A mapping tool for assisting with NOI completion may be found here. Please submit a copy of this form along with the other documents as part of the Plans Package.

Also, complete and submit the DHEC Plan Review Checklist when submitting the plan package.

For a list of SC DHEC Stormwater Design Aids and Technical Documents, click here.

Storm Water Pollution Prevention Plan (SWPPP)

A Storm Water Pollution Prevention Plan (SWPPP) identifies structural and non-structural controls that will be put in place to minimize negative impacts, caused by offsite storm water discharges, to the environment. The purpose of these controls is to minimize erosion and run-off of pollutants and sediment. A SWPPP establishes procedures for minimizing the potential for pollutants to be carried away in storm water discharges. These procedures emphasize the use of Best Management Practices (BMPs) to provide the flexibility to address varying sources of pollutants. A SWPPP must describe the site characteristics and list the pollutants that could impact storm water quality. The plan must also identify pollution prevention measures designed to minimize the discharge of pollutant laden storm water. For a SWPPP template from SC DHEC, click here. The SWPPP is required to be onsite or readily accessible upon request. The Inspector will request this document during inspections to verify it is current. The SWPPP must include:

  • Narrative
  • Stormwater Management and Sediment Control
  • Reporting forms and logs of inspections
  • Sequence of construction
  • Site features and sensitive areas (Buffer zones)
  • Sources of pollution
  • BMPs
  • Maps
  • Engineering report
  • Construction site plans
  • Non-Numeric effluent limits
  • Management of non-stormwater discharges
  • (TMDL) Documentation of permit eligibility related to Total Maximum Daily Loads

Preliminary / Final Plat

Preliminary / Final Plat is a plat with easements and legal boundaries. These plans include the following:

  • All Easements labeled Public or Private
  • Proper easement widths (check for both pipe and ditches)
  • Lake maintenance easement to be 12 feet from NWL if the slopes are 5:1, 12 feet from top of bank if 3:1
  • Note to the effect: “Prohibit all fences and structures, which would interfere with access to the easement areas and/or the maintenance function of the drainage system.”
  • Engineer's or Surveyor's Seal
  • Wetland limits
  • If back of lot drainage is sloped at a 5:1, drainage easement can be a minimum of 20 feet from back property line. If slope is greater standard ditch easement widths apply
  • Ponds shall be located in Common areas rather than on individual lots in residential areas.
  • Note: all activities, including activities by individual lot owners, will be carried out in
    accordance with the approved Stormwater Management and Sediment Control Plan for the subdivision.

Additional information may be required by the County Engineer as deemed necessary to adequately document the conditions of the road and drainage systems.

Grading And Drainage Plan

Site Plans (General observations)

  • Engineers Seal
  • Can each phase stand on its own hydraulically if no other phase is built?
  • Size of Areas (Acreage)
  • Emergency spillway to pass the 100yr event and not installed on fill (if unavoidable it must be paved)
  • Adjoining lakes, streams, or other major drainage ways
  • Existing and planned drainage patterns (include off-site areas that drain through project
  • 1 ft minimum freeboard on all ponds from the 25yr water level
  • Include Landscape Plan and check if it is encroaching on an easement.
  • Note : The land disturbing activity will be accomplished pursuant to the concept plan and the county has the right to conduct on-site inspections.
  • Note: Final inspections will not be conducted until a final as-built has been submitted to the county.
  • Note: Prohibit all fences and structures which would interfere with access to the easement areas and/or maintenance function of the drainage system.
  • All channels cannot be greater than 3 ft in depth otherwise it needs to be piped.
  • Velocity in a ditch can not exceed 5ft/s.
  • The design surface runoff across lots shall not have erosive velocities.
  • Legend
  • Show Avg. bottom, Normal water level, 25yr and 100 yr water level, TOB elev., Area if storage in Ac Ft on all ponds
  • Average depth of pond dry or 4 ft. for aquatic line
  • Minimum of (2)  12" by 18" “No Swimming Allowed” signs along with the international symbol to be posted in the pond itself at a height visable from the shoreline at a maximum of every 250 feet of pond circumference Click here for an example
  • Utility lines (how creek crossings will be handled and details, note fill, cover and seed after each day, if water is encountered it is to be filtered for sediments prior to discharging back into creek.
  • Directional arrows should be shown on the plan for each planned lot in the subdivision to show the drainage direction. The direction of flow cannot be changed without a revision to the plan.
  • Trash racks and safety grates on weir structures
  • Existing and proposed contours 25 feet outside of all property lines and further if county deems necessary for clarity.
  • Show drainage flow patterns for sheet flow
  • Show spot elevations for swales
  • Discharge has a 15 ft buffer to property line/ Slopes & Embankments 20 ft.
  • FFE of buildings 1’ above roadway  
General Information

  • North arrow
  • Scale (not to exceed 1:100)
  • Property lines
  • Legend
  • Planned and existing buildings location and elevations
  • Planned and existing roads location and elevations
  • Lot and/or building numbers
  • Limits and acreage of disturbed area
  • Streams, lakes, ponds, drainage ways, dams
Storm Water Structure Details

  • Show Pipe detail
  • Show catch basin detail (frames fully supported on box wall or structural top.
  • Provide detail of pond banks 5:1 slope or a 3:1 slope with a littoral shelf
  • Outfall structure details with dimensions and design elevations.
  • Swale detail not to exceed 2 feet at a 3:1 slope
  • Ditch detail not to exceed 3 feet at 3:1 slope All roadside and outfall ditches deeper than thirty-six (36) inches shall be piped.
  • Note: All Structures are to meet SCDOT standards
  • 12" sump on all catch basins with drain holes on bottom.
  • Minimum size box 2’ X 2’
  • Emergency spillway detail
Drainage Profiles

  • Profiles provided for the 25 yr HGL (starting tail water at 25 yr elev and grades stays below the inlet grate)
  • Match all pipe sofits not inverts.
  • Provide pipe data (Slope, Type, Size, Length)
  • Catch basin data. (Grate elev., Sump elev. Size of box, type of box, pipe inverts)
  • Existing and proposed surface grade.
  • Length of pipes not to exceed 400 ft
  • Provide 25 yr HGL with its tale water in the pond or outfall at its 25 yr event elev.
  • If the HGL in the CB is too close to determine if HGL is out of the box on the profiles, provide HGL elev. in the CB data.
  • Provide profiles to show tops and toes for all ditches over 1 ft in depth

Additional information may be required by the County Engineer as deemed necessary to adequately document the condition of the road and drainage systems.

Sediment and Erosion Control Plan

Erosion Control Notes

  • Standard Notes (OCRM) For a copy click here
  • Mud and soil removed from public road daily
  • Construction sequence related to sedimentation and erosion control (include installation of critical measures prior to initiation of the land-disturbing activity and removal of measures after areas they serve have been permanently stabilized, within 30 days)
  • Maintenance requirements during construction
  • Person responsible for maintenance during construction and where records are kept
  • No use of the words “as directed by” or as conditions warrant”
  • Maintenance schedule, description and procedures for permanent structures
  • As-built to be supplied to the county prior to final inspection (and certified by a either a PE or PLS in South Carolina)
  • Must have the statement:” The land disturbing activity will be accomplished pursuant to the Concept Plan and that the County has the right to conduct on-site inspections.”
  • Sediment traps not to be used for over 5 acres and provide 1800 cubic ft per acre
  • Double silt fence if buffer is less than 10 feet from a wetland
  • Silt fence not to be used in areas of concentrated flows. 

Erosion Control Details

  • Location of temporary and permanent measures
  • Concrete wash out detail (locate the washout on the plans)
  • Construction drawings and details for temporary and permanent measures
  • Silt fence detail
  • Construction Entrance
  • Filter fabric under all stone (CE, Check dams, rock weirs)
  • Show a horseshoe shape rip rap berm in front of all low-level outlets during construction.
  • Wetland crossing details if used
  • Provide details for dewatering onsite (ponds, inlets, and ditches)
  • Hay bales not allowed
  • Provide Individual lot erosion control plan/detail (include silt fence and IP)
  • Show rip rap pipe spillway detail with formula or table.
  • Inlets go to basin and protected properly
  • Stockpiled topsoil or subsoil location 

Vegetative stabilization details

  • Areas and acreage to be vegetative stabilized to a 70% stand of grass
  • Requirements for temporary ground cover
  • Planned vegetation with details of plants, seed, mulch, fertilizer
  • Rates for seed, fertilizer and mulch
  • Specifications for permanent and temporary vegetation
  • Method of soil preparation
  • Rye grass not permitted. 

Additional information may be required by the County Engineer as deemed necessary to adequately document the condition of the road and drainage systems.

Landscape Plan

  • No landscape to be found in drainage easements
  • No berms over pipe.
  • No landscape in swales
  • Berms are to have a slope of 3:1 and stabilized

Additional information may be required by the County Engineer as deemed necessary to adequately document the condition of the road and drainage systems.

Preliminary As-Built Plan Requirements

Prior to completing the installation of the asphalt and curbing and prior to a proof roll inspection scheduling a preliminary "as-built" plan signed and sealed by a professional registered in South Carolina shall be submitted to the Horry County Engineering Department for review and approval. The purpose of this plan is to ensure the pipe and catch basin structures are located in the proper place as well as installed at the proper elevations to avoid disturbance of a final finished product in the asphalt and curbing. In the as-built plan the registered professional shall state: 

  • The facilities have been constructed as shown on the Preliminary As-built Plan, and 
  • The facilities meet the approved Stormwater Management and Sediment Control Plan and specifications or achieve the function for which they were designed. 

Also, the minimum information to be provided on the Preliminary As-built Plans shall include the following: 

  • Boundary, phase and lot lines. 
  • Lot numbers and street names.
  • Drainage structures which are installed within a road right-of-way with elevations.
  • Drainage pipes installed within a road- right-of-way with size, material, length, slope and invert elevations.
  • Ponds or lakes with average bottom, top of bank and water surface elevations, (Note top of bank is to be 1 foot above 25 year storm event elevation of pond)
  • Pond elevation data : (Normal, 25 and 100 year storm elevation)

Additional information may be required by the County Engineer as deemed necessary to adequately document the condition of the road and drainage systems.

As-Built Plan Requirements

Upon completing the installation of the stormwater management facilities included in the Stormwater Management and Sediment Control Plan, an "as-built" plan signed and sealed by a professional registered in South Carolina shall be submitted to the Horry County Engineering Department for review and approval. The as-built plan must be submitted prior to any final inspection scheduling. In the as-built plan the registered professional shall state: 

  • The facilities have been constructed as shown on the "as-built" plan, and 
  • The facilities meet the approved Stormwater Management and Sediment Control Plan and specifications or achieve the function for which they were designed. 

Also, the minimum information to be provided on the "as-built" plans shall include the following: 

  • Boundary, phase and lot lines. 
  • Lot numbers and street names.
  • Easements.
  • Road locations with centerline stationing and curve data.
  • Road centerline elevations at 100-foot intervals.
  • Drainage structures with elevations.
  • Drainage pipes with size, material, length, slope and invert elevations.
  • Ponds or lakes with average bottom, top of bank and water surface elevations, (Note top of bank is to be 1 foot above 25 year storm event elevation of pond)
  • 25 and 100 year storm elevation of pond
  • The Acre/feet of storage in a 25 year rain event
  • Any control structures shall be shown in detail with key-way dimensions and stage elevations. If structure is off site include a note of its location. 
  • Drainage ditches and swales, with elevations at 100-foot intervals and critical locations.

Additional information may be required by the County Engineer as deemed necessary to adequately document the condition of the road and drainage systems.

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