ORDINANCE NO. BL2014-910

An Ordinance amending Chapter 15.64 of Title 15 of the Metropolitan Code pertaining to stormwater management regulations for infill development.

BE IT ENACTED BY THE COUNCIL OF THE METROPOLITAN GOVERNMENT OF NASHVILLE AND DAVIDSON COUNTY:

Section 1. Section 15.64.010 of the Metropolitan Code is hereby amended by
adding the following new definitions:

“Infill (regulated residential)” means the creation of 800 to 15,000 square feet of additional net impervious area (IA) for a residential dwelling(s) through new development, redevelopment, or rehabilitation in existing neighborhoods.

“Impervious area (IA)” means the portion of a parcel of property that is covered by any material, including without limitation roofs, streets, sidewalks and parking lots paved with asphalt, concrete, compacted sand, compacted gravel or clay, that substantially reduces or prevents the infiltration of storm water. Impervious area shall not include natural undisturbed surface rock.

“Lot” means a tract, plot or portion of a subdivision or parcel of land intended as a unit for the purpose, whether immediate or future, for transfer of ownership or for building development.

Section 2. Section 15.64.130 of the Metropolitan Code is hereby amended by deleting subsection A. and substituting with the following new subsection A.:

A. Single-family to two-family individual residential dwellings in any given area that do not alter a drainage channel, do not alter the natural ground elevation or vegetation by an amount greater than specified in the technical guidelines to be issued by the metropolitan department of water and sewerage services, or do not meet the definition of regulated residential infill;

Section 3. Title 15 of the Metropolitan Code is hereby amended by adding the following new Section 15.64.131:

15.64.131 Infill development – Applicability and requirements.

A. No project shall add impervious area without meeting the requirements of this section, unless otherwise specifically exempt from regulation pursuant to this section.

B. There shall be three tiers of infill development for projects that are subject to infill regulation by this section:

1. Tier I - Projects creating between 800 and 2,500 square feet of net additional IA and with the total lot IA exceeding 30.0% must treat, by means of capture of the first inch of rainfall runoff, an IA equal to the net increase of IA.

2. Tier II - Projects creating between 2,500 and 8,000 square feet of net additional IA, without regard to total lot IA percent must treat, by means of capture of the first inch of rainfall runoff, an IA equal to the net increase of IA.

3. Tier III – Projects creating between 8,000 and 15,000 square feet of net added IA, without regard to total lot IA percent, must treat, by means of capture of the first inch of rainfall runoff an IA equal to the net increase of IA. Additionally, the project design must insure there is not an increase in the 10-year storm peak flow from the site, and be certified by a professional engineer.

C. Construction projects that meet the definition of regulated residential infill shall include provisions for the management of the first inch (1”) of rainfall runoff from an impervious area equal to the net added impervious area; and shall not be exempt from the provisions of Section 15.64.120 concerning prohibition of increase in the degree of flooding.

D. Prior to the net addition of at least 800 square feet of impervious area or issuance of a building permit, a sufficient development plan and supporting information required by the latest version of the regulated residential infill guidance document shall be submitted to and approved by the metropolitan department of water and sewerage services.

E. The net added impervious area shall be calculated by subtracting the IA present in the aerial photography data obtained by Metro in March 2014 from the proposed post-development IA and maintaining the original property boundary as the regulated project boundary, regardless of subdivision, re-plat, horizontal property regime, or any other modification of property boundaries by deed or plat.

F. The owner/developer of a project meeting the definition of regulated residential infill shall endeavor to treat the first 1” of rainfall runoff from net added impervious area using methods from the regulated residential infill guidance document. If this treatment proves impractical, analysis of the downstream management system to identify adequate drainage per the regulated residential infill guidance document or improving downstream drainage to mitigate a known flooding problem with assistance from a professional engineer may be considered for all or part of the 1” treatment requirement.

G. The metropolitan department of water and sewerage services shall have the authority to offer additional runoff volume reduction measures and incentives. Refer to the latest version of the regulated residential infill guidance document for details.
H. Notwithstanding other provisions of this section to the contrary, excluded from infill regulation are projects that:
(1) add less than 800 square feet of net new IA,
(2) add more than 15,000 square feet of net new IA,
(3) are on lots larger than 40,000 square feet, or
(4) are on lots with a grading permit previously filed with the metropolitan department of water and sewerage services, as long as the post-construction IA conforms to the original grading plan.

I. Projects on lots larger than 40,000 square feet may seek infill classification on a case-by-case basis.

Section 4. This Ordinance shall take effect from and after its enactment, the welfare of The Metropolitan Government of Nashville and Davidson County requiring it.

Sponsored by: Burkley Allen , Emily Evans , Jason Holleman , Peter Westerholm , Sean McGuire

LEGISLATIVE HISTORY
Introduced:	October 7, 2014
Passed First Reading:	October 7, 2014
Referred to:	Public Works Committee
Passed Second Reading:	October 21, 2014
Passed Third Reading:	November 4, 2014
Approved:	November 5, 2014
By: