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<br /> '-' � streams. Carrboro also has standards for intermittent�strea
<br /> 6" ., , ➢khereas the Cotmty does not.
<br /> - ---�.- --.._.., _ ._ mm ;.._ . 021 -
<br /> A-13 l ;i
<br /> y m, Retention a, iRuno6 6nom Industniat Sites - On sites developed j
<br /> } Retention
<br /> in. .tn-ial purposes 4...e„, we .znuatving the manu6actun'tg, _€_
<br /> pnaceea.ing, creating, nepaiiatg, renovating, painting, etean.ing,
<br /> on asaembVng o6 goods, menchand.iae, on equipment), retention an
<br /> ' detention anew, meeting the standards set 6onth .in subsection j.
<br /> ' shctU be abed to ifdune that nwto66 .ia retained on the site be6ane
<br /> being nelea.aed. The punpase 06 this requirement .c4 to insure that,
<br /> not on,ey meet the standard set 6oath in subsection 9a. be met,
<br /> but aLsa a mechanism mitt be pnav-.des to sa6eguand the to tenshed —
<br /> aga.inet the, spULa:ge 06 toxic on dungevwud dubs.tances. ,
<br /> s
<br /> Section 9 Permanent Downstream Protection of Stream Banks and Channels
<br /> I
<br /> i Provision shall be made for permanent protection of off-site stream banks
<br /> and channels from the erosive effects of increased velocity and volume of
<br /> stormwater runoffiresulting from land-disturbing activities.
<br /> ti
<br /> a.. Cant/tot a6 V.L6change - pnoviaons shale be made bon the cannot 06 i.
<br /> dtannwaten discharges ban the .types 06 development as speci.6.Ged i
<br /> below. A6texi development 06 the .site, the peak d,idchange 06
<br /> starumuaten nuno66 nesutt.ing 6nom a. ten-yeah, atanm shale be no
<br /> gneatee. than :that which wouCd nesu.lt 6nom a ten-yeah atom; on the. 1
<br /> Esame site. pn.ion to development. This nequ.i.ement shaft apply to: 1
<br /> 1 i
<br /> i 1. Commenc o2, .industntat, o66%ce, and inati.tutional developments
<br /> 2. Matti.-6am•ty. Atsidentiat devetopme.nts o6 mane .then JO units
<br /> { 3. S.thg..e-6a:ni.Cy detached nes.identiat developnents where mane •than. •
<br /> 3 eats are to be created.
<br /> I
<br /> i b. Control of Velocity - stream banks and channels downstream from any
<br /> an -disturbing activity shall be protected from increased degradation
<br /> I by accelerated erosion caused by increased velocity of runoff from a
<br /> land-disturbing activity. The land-disturbing activity shall be
<br /> { planned and conducted such that the velocity of stormwater runoff in
<br /> (( the receiving lwatercourse at the point of discharge resulting from
<br /> Ia 10-year storm i after development shall not exceed the greater of:
<br /> (i) the velocity as determined from the table in (F) of this rule, or
<br /> (ii) the velocity in the receiving watercourse determined for the
<br /> 10-year storm prior to development.
<br /> ! If conditions (1) and (ii) of this paragraph cannot be met, the channel
<br /> below the discharge point shall be designed and constructed to withstand
<br /> the expected velocity.
<br /> 1) Acceptable Management Measures - measures applied alone or in
<br /> combination to satisfy the intent of this subchapter are acceptable '
<br /> if there are no, objectionable secondary consequences. Innovative
<br /> techniques and ideas will be considered and may be used when shown
<br /> to have the potential to produce successful results. Some alternatives
<br /> are to:
<br /> (i) avoid increaI ses in surface runoff volume and velocity by
<br /> including measures to promote infiltration to compensate for
<br /> increased runoff from areas rendered impervious;
<br /> (ii) avoid increases in stormwater discharge velocities by using , '
<br /> vegetated or roughened swales and waterways in lieu of closed i
<br /> drains and high velocity paved sections; j
<br /> (iii) provide energy dissipaters at outlets of storm drainage
<br /> facilities to reduce flow velocities at the point of discharge;
<br /> these may range from simple rip rapped sections to complex }a
<br /> structures;1
<br /> iv) protect watercourses subject to accelerated erosion by improving
<br /> cross sections and/or providing erosion-resistant lining.
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