Stormwater Management Standard Forms (Low Density)

Stormwater Phase II Post - Construction (LOW DENSITY)

• Limit amount of built-upon surfaces per the most current state rules and local ordinances.
• No collection system - (limited piping-only enough to get under a road, no inverted crown streets)
• Sheet flow stormwater
• No area of the project of such high-density that runoff threatens water quality (example: pocket of high density)

What makes up a complete low-density application package?

• One paper set and one electronic set (PDF Format) of layout & grading plans with road details and a swale drainage map for curb outlet systems. Unrelated plan sheets such as water/sewer profiles or details are not necessary.
• One paper (original) completed application with supplement(s), (SW401-Low Density, or SW401-Curb Outlet, or SW401-Grassed Swale)

Review Procedures -

• Original signature required on applications and supplemental documents, NO COPIES ACCEPTED.
• Submit correct supplements (low density and/or curb outlet supplement) and grass swale supplement (no low density supplements needed for projects that do not propose to subdivide and sell lots)
• Built upon areas must be reported in square feet in Section III.6 of the application.
• Section III.6 of application must be completed.
• Provide correct signature for owner. If corporation, imited Liability Corporation, etc - must be designated on the NC Secretary of State website as having authority.

Calculations:

• Top of page 2 of low-density supplement. For non-subdivision projects, a supplement form is not required and the calculations in Section III.6 of the application will suffice.
• Wetlands, the applicant must calculate the site area to be used in the BUA per lot calculation by the following the calculation methods outlined in the wetlands policy.
• For curb outlet systems, swale velocity calcualations are required, to include the individual swale drainage area, the buil-upon area within each drainage area, and the Rational C-value calculated for each drainage area.
• If pocket of high-density is formed, the application must include an engineered control suitable or the classification of the receiving waters.

Plans:

• Plan sheet should be kept to a minimum.  The plan set should consist of 1 - 4 sheets with the following information provided:
  • Developer/Project Name
  • Engineer Name and Engineering Firm
  • Legend containing all of the symbols used on the plans.
  • North Arrow
  • Location Map with nearest intersection of two major roads shown. Major road is any 1, 2, or 3 digit NC, US or interstate highway.
  • Scale - Standard Engineering Scale
  • Date
  • Revision number and date, if applicable
  • Original contours, proposed contours, spot elevations, finished floor elevations, pipe inverts, swale inverts, etc.
  • Existing drainage (piping, swales, ditches, ponds, etc.), including off-site.  Include a map delineating the offsite drainage areas.
  • Property/Project boundary lines, bearing & distances.
  • Mean High Water Line, or Normal High Water line if applicable.
  • Drainage easement location and width.
  • Wetlands, whether they are disturbed or not, are delineated, or provid a note on the plans that none exist. Provide a copy of the wetlands delineation map signed by the Corp of Engineers, or include a copy of the unsigned delineation map that was submitted to the Corp of Engineers.
  • Details for the roads, parking area, cul-de-sac radii, sidewalk widths, curb and gutter, all dimensions and slopes. Note, if dimensions are face of curb to face of curb (FC-FC) or back of curb to back of curb (BC-BC).
  • The drainage area for each curb outlet swale is clearly delineated and numbered to match up to the calculations and supplement. Only swales that actually receive road runoff have to be curb outlet swales with 5:1 side slopes. Delineation is best done as a separate plan sheet.
  • A curb outlet swale detail noting the 5:1 or flatter side slopes, the 100’ minimum length and the type of grass to be planted on the side slopes.
  • A level spreader is provided at the end of all swales that will drain into wetlands or surface waters. Level spreader O & M is provided.