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7.4.3  General Erosion and Sedimentation Control Standards

All persons conducting land-disturbing activities shall take all reasonable measures to protect all public and private property from damage by such activities.  Any and all state and/or federal standards apply and must be met.  In situations where state and/or federal rules conflict with the provisions of this section, the more restrictive shall apply.  All land-disturbing activities, except for those exempted by Section 3.13.1 of this Ordinance, shall meet the following standards:

(A)     Conveyance Channels

(1)      Stream banks and drainageway channels downstream from any land-disturbing activity shall be protected from increased degradation by accelerated erosion caused by increased velocity of runoff from the land-disturbing activity.  The land-disturbing activity shall be planned and conducted such that the velocity of stormwater runoff in the receiving watercourse at the point of discharge resulting from a ten-year storm after development shall not exceed the greater of:

(a)      The velocity as determined from Table 7.4-1 below; or

(b)      The velocity in the receiving watercourse determined for the ten-year storm prior to development.

(2)      If the requirements of paragraph (1) above cannot be met, then the channel below the discharge point shall be designed and constructed to withstand the expected velocity.  Any channel stabilization activities involving stream bank stabilization may not be approved without the required state and/or federal permits.

(3)      Alternative and innovative measures to satisfy the intent of this paragraph (A), applied either alone or in combination, may be used if there are no objectionable secondary consequences and the applicant can demonstrate to the Stormwater Services Manager that such measures have the potential to keep stormwater discharge velocities from creating an erosion problem in the receiving watercourse.  Some alternative measures include:

(a)      Avoiding increases in surface runoff volume and velocity by including measures to promote infiltration to compensate for increased runoff from areas rendered impervious;

(b)      Avoiding increases in stormwater discharge velocities by using vegetated or roughened swales or waterways in lieu of closed drains and high-velocity paved sections;

(c)      Providing energy dissipators, which may range from simple rip-rapped sections to complex structures, at the outlets of storm drainage facilities to reduce flow velocities to the point of discharge; and/or

(d)      If the watercourse velocity is greater than 2.0 F.P.S., improving cross-sections and installing erosion-resistant linings.

(B)     Slopes Left Exposed

Slopes left exposed shall be planted or otherwise provided with ground cover, devices, or structures sufficient to restrain erosion within 15 working days (exclusive of days where seed bed preparation is not possible due to weather as determined by the Planning Director) or 30 calendar days after completion of any phase of grading whichever period is less.

(C)     Design Requirements

Erosion and sedimentation control measures, structures, and devices shall be planned, designed, and constructed to provide protection from the calculated maximum peak rate of runoff from the ten-year storm.  Runoff rates shall be calculated in accordance with the Town's Standard Specifications and Details Manual.  Calculations shall be submitted with the plans and shall be drafted and organized in a neat and readable manner.

(D)     Protective Cover Required

All uncovered areas shall be provided with protective cover unless the Planning Director has granted an extension of time, for good cause shown, upon written request of the developer or landowner.  This cover shall be installed within 15 working days (exclusive of days where seedbed preparation is not possible due to weather as determined by the Planning Director) or 90 calendar days following completion of any phase of grading, whichever period is shorter.  Ground cover is not required on cleared land forming the future basin of a planned reservoir.

(E)      Activity Near Watercourse

All land-disturbing activities near a lake or natural watercourse shall provide erosion and sedimentation control measures.  An undisturbed buffer may be used as an erosion/sedimentation control measure, provided that the undisturbed zone shall be of sufficient width to confine visible siltation within the 25 percent of the undisturbed zone nearer to the land-disturbing activity.  This requirement shall not apply to land-disturbing activities for the construction of facilities to be located on, over, or under a lake or natural watercourse.

(F)      Protection During Construction

During construction, soil erosion and sedimentation control practices and devices shall be employed that are sufficient to retain the sediment generated by the land-disturbing activity within the boundaries of the tract during construction upon and development of said tract in accordance with plans approved by the Town.

(G)     Compliance with Town Manual

In addition to the standards set forth in this section, all soil erosion and sedimentation control measures shall conform to the applicable minimum standards set forth in the Town's Standard Specifications and Details Manual.

Cary, NC Land Development Ordinance On-line VIC Version - This site last updated 3/4/2008

Note: This is not the official version of the Cary Land Development Ordinance