Item 13-H Stormwater Management and Flood Damage Prevention (TC)
LAND DEVELOPMENT ORDINANCE - TEXT AMENDMENTS – Round 13
Item 13H STORMWATER MANAGEMENT AND FLOOD DAMAGE PREVENTION
Town Council Meeting – January 14, 2010
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BACKGROUND |
The proposed amendments provide consistency with changes in the FEMA floodmaps and existing requirements of the NC Division of Water Quality pertaining to Stormwater Management.
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PROCESS AND ACTIONS TO DATE |
Town Council Public Hearing
The Town Council public hearing was held on October 22, 2009. There were no comments or discussion on this item at the public hearing.
Planning and Zoning Board Work Session
The proposed amendments were presented at the Planning and Zoning Board work session on November 9, 2009. There was some concern that allowing urban transition buffers to be included within the boundaries of some individual lots would result in higher residential densities. It was pointed out that this would only apply where the lot is less than five acres and the subdivision contains fewer than 10 lots with no homeowners association to assume ownership of the buffer.
Changes Since Planning and Zoning Board Work Session
None
Staff Recommendation
Staff recommends approval of the proposed amendment.
Planning and Zoning Board Meeting and Recommendation
On December 21, 2010, the Planning and Zoning Board recommended approval of the proposed amendment by a vote of 7-0. .
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PROPOSED TEXT AMENDMENT |
4.4 Overlay Zoning Districts
TABLE 4.4-5: MAXIMUM IMPERVIOUS SURFACE LIMITS: HIGH DENSITY OPTION
4.4.6 Watershed Protection Overlay
(G) Engineered Stormwater Control Structures…
(8) Inspections for Stormwater Control Structures and Release of Financial Security
7.2 Landscaping , Buffering and Tree Protection
7.2.14 Urban Transition Buffer Regulations……
(G) Exclusion of Urban Transition Buffer from Lots
Generally, no single-family lots created through a site and/or subdivision plan may encroach upon any required or established UTB, except that single-family lots platted prior to July 27, 2000 shall be exempt from Urban Transition Buffer requirements. However, sSingle-family lots platted after July 27, 2000 may encroach upon a required or established UTB when all of the following conditions are met:
(1) The total area of a parcel under single ownership is not greater than five (5) acres and ……;
(2) The proposed subdivision consists of fewer than ten (10) lots and has no homeowners association;
(3) There is no other reason for the formation of a homeowners association ……
(4) The area of the UTB is subject to a permanent conservation easement or other legal instrument ……..
TABLE 7.2-6 TOWN OF CARY GENERAL AND SPECIALIZED UTBs
7.3 Stormwater Management
7.3.1 Purpose…
7.3.2 Nitrogen Reduction Requirements…
7.3.3 Peak Runoff Control…
7.3.4 Allowable Best Management Practices…
7.3.5 Maintenance of Best Management Practices….
7.3.6 Illegal Discharges to the Storm Sewer System….
7.3.7 Town of Cary NPDES Phase II Post Construction Runoff Controls for Walnut Creek Watershed / Middle Creek Watershed / Crabtree Creek Watershed
To meet the requirements of the Town of Cary NPDES Phase II Permit any new development or redevelopment in the Walnut Creek, Middle Creek, or Crabtree Creek Watershed not exempted pursuant to Section 7.3.2(B) must meet either the low density or high density option requirements described below. New development or redevelopment in the Swift Creek or Jordan Lake Watersheds must meet the requirements of Section 4.4.6 of the LDO. For purposes of this Section 7.3.7, impervious surface area shall be calculated pursuant to Section 4.4.6(D)(2) of the LDO and the provisions of Section 4.4.6(G) of the LDO shall apply to all engineered stormwater control structures.
(A) Low Density Projects, having no more than two dwelling units per acre or no more than 24% impervious surface area for all residential and non-residential development, shall transport stormwater runoff by vegetated conveyances to the maximum extent practicable.
(B) High Density Projects, having more than two dwelling units per acre or more than 24% impervious surface area for all residential and non-residential development, shall implement stormwater control measures that comply with each of the following standards:
(1) The stormwater control measures shall control and treat the difference between the pre-development and post-development conditions for the 1 year 24 hour storm. Runoff volume drawdown shall be a minimum of 24 hours, but not more than 120 hours.
(2) Engineered stormwater control structures shall be designed to achieve a minimum of 85% average annual removal for Total Suspended Solids (TSS).
7.5 Flood Damage Prevention
7.5.2 Applicability
(B) Exemptions
(1) All new residential construction and substantial residential improvements proposed on a parcel of land that has no buildable area outside the Special Flood Hazard Area or Future Conditions Flood Hazard Area, and that was recorded prior to June 1978, shall be exempt from the requirements for residential construction set forth in this section, but shall be developed in strict accordance with the requirements for non-residential construction.
(2) Residential subdivisions submitted for review prior to May 10, 2001, shall be exempted from the requirements prohibiting the platting of lands located within Special Flood Hazard Areas and Future Conditions Flood Hazard Areas, provided the section subdivision complies with the requirements in place prior to May 10, 2001.
(3) Site and/or subdivision plans submitted prior to May 10, 2001, shall be exempted from the special use permit for filling in the flood fringe portion of Special Flood Hazard Areas or Future Conditions Flood Hazard Areas. and all new residential construction or substantial residential improvements proposed on a platted lot that is located within the Special Flood Hazard Area or Future Flood Conditions Hazard Area, but was not so located at the time it was platted, shall be exempt from the requirement to obtain a special use permit for filling in the flood fringe portion of the Special Flood Hazard Area or the Future Conditions Flood Hazard Area but shall submit a floodplain development permit application. An engineering study must be performed to determine whether an adverse impact will result from filling in the flood fringe portion of the Special Flood Hazard Area or Future Conditions Flood Hazard Area and must be submitted with the floodplain development permit application. For purposes of this Section 7.5.2, an “adverse impact” includes, but is not limited to, a reduction of floodplain storage greater than 10%, an increase in 100-yr average channel velocities greater than 10%, or the potential for aggravating a known existing drainage problem as determined by the Town of Cary Floodplain Administrator. If an adverse impact will result, the construction or improvements must meet the requirements for new non-residential construction and substantial improvements to non-residential construction contained in Section 7.5.3(C) and (D)(2).
7.5.3 Development Restrictions and Related Standards in and Near Special Flood Hazard Areas and Future Conditions Flood Hazard Areas
(G) Additions/Improvements to Pre-FIRM Existing Structures
(1) For Aadditions and/or improvements to pre-FIRM structures located within the Special Flood Hazard Area or Future Flood Conditions Hazard Area when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(a) not a substantial improvement, the addition and/or improvements must be designed to minimize flood damages and must not be any more non-conforming than the existing structure.
(b) a substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction contained in Section 7.5.3(C) and (D).
(2) Additions to post-FIRM structures located within the Special Flood Hazard Area or Future Flood Conditions Hazard Area with no modifications to the existing structure other than a standard door in the common wall shall require only the addition to comply with the standards for new construction contained in Section 7.5.3(C) and (D).
(3) Additions and/or improvements to post-FIRM structures located within the Special Flood Hazard Area or Future Flood Conditions Hazard Area when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(a) not a substantial improvement, the addition and/or improvements only must comply with the standards for new construction contained in Section 7.5.3(C) and (D).
(b) a substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction contained in Section 7.5.3(C) and (D).
(4) For either a pre-FIRM or post-FIRM structure located within the Special Flood Hazard Area or Future Flood Conditions Hazard Area , Wwhere an independent perimeter load-bearing wall is provided between the addition and the existing building, the addition(s) shall be considered a separate building and only the addition must comply with the standards for new construction contained in Section 7.5.3(C) and (D).
Chapter 12, Section 12.4 (Other Key Terms Defined)
BUILT-UPON AREA
See IMPERVIOUS SURFACE AREA
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IMPERVIOUS SURFACE AREA
Any hard-surfaced, man-made area that allows little or no infiltration of precipitation into the soil. Impervious surface areas include that portion of a development project that is covered by buildings; areas paved with concrete, asphalt or brick; gravel road; recreation facilities such as tennis courts; patios, driveways, and streets. “Impervious surface area” does not include slatted decks.
