<div class="chunk-title">Sec. 31-8. - Design and performance standards.</div>
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            <p class="incr0">
               (a)
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            <p class="content1">
               Except as provided in subsection (b)(2) and (c)(1) of this section, 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 using the procedures in the latest edition
               of the USDA, Natural Resources Conservation Service's "National Engineering Field
               Handbook," or other acceptable calculation procedures.
               </p>
            		
            <p class="incr0">
               (b)
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               <span class="ital">HQW zones.</span> In high-quality water (HQW) zones the following design standards shall apply.
               </p>
            		
            <p class="incr1">
               (1)
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            <p class="content2">
               <span class="ital">Limit on uncovered area.</span> Uncovered areas in HQW zones shall be limited at any time to a maximum total area
               of 20 acres within the boundaries of the tract. Only the portion of the land-disturbing
               activity within an HQW zone shall be governed by this section. Larger areas may be
               uncovered within the boundaries of tract with the written approval of the director
               upon providing engineering justification with a construction sequence that considers
               phasing, limiting exposure, weekly submitted self-inspection reports, and a more conservative
               design than the 25-year storm.
               </p>
            		
            <p class="incr1">
               (2)
               </p>
            		
            <p class="content2">
               <span class="ital">Maximum peak rate of runoff protection.</span> Erosion and sedimentation control measures, structures, and devices within HQW zones
               shall be planned, designed and constructed to provide protection from the runoff of
               the 25-year storm which produces the maximum peak rate of runoff as calculated according
               to procedures in the United States Department of Agriculture Natural Resources Conservation
               Service's "National Engineering Field Handbook" or according to procedures adopted
               by any other agency of this state or the United States or any generally recognized
               organization or association.
               </p>
            		
            <p class="incr1">
               (3)
               </p>
            		
            <p class="content2">
               <span class="ital">Sediment basin design.</span> Sediment basins within HQW zones shall be designed and constructed according to the
               following criteria:
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               a.
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               Use a surface withdrawal mechanism, except when the basin drainage area is less than
               one acre;
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               b.
               </p>
            		
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               Have a minimum of 1,800 cubic feet of storage area per acre of disturbed area;
               </p>
            		
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               c.
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               Have a minimum surface area of 325 square feet per cfs of the 25-year storm (Q25)
               peak flow;
               </p>
            		
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               d.
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               Have a minimum dewatering time of 48 hours;
               </p>
            		
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               e.
               </p>
            		
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               Incorporate three baffles, unless the basin is less than 20 feet in length, in which
               case two baffles shall be sufficient.
               </p>
            		
            <p class="b2">
               Upon a written request of the applicant, the director may allow alternative design
               and control measures in lieu of meeting the conditions required in subparagraphs (3)b
               through (3)e of this subsection if the applicant demonstrates that meeting all of
               those conditions will result in design or operational hardships and that the alternative
               measures will provide an equal or more effective level of erosion and sediment control
               on the site. Alternative measures may include quicker application of ground cover,
               use of sediment flocculants, and use of enhanced ground cover practices.
               </p>
            <p class="incr1">
               (4)
               </p>
            		
            <p class="content2">
               <span class="ital">Grade.</span> Newly constructed open channels in HQW zones shall be designed and constructed with
               side slopes no steeper than two horizontals to one vertical if a vegetative cover
               is used for stabilization unless soil conditions permit a steeper slope or where the
               slopes are stabilized by using mechanical devices, structural devices or other acceptable
               forms of ditch liners proven as being effective in restraining accelerated erosion.
               In any event, the angle for side slopes shall be sufficient to restrain accelerated
               erosion.
               </p>
            		
            <p class="incr1">
               (5)
               </p>
            		
            <p class="content2">
               <span class="ital">Ground cover.</span> Ground cover sufficient to restrain erosion must be provided for any portion of a
               land-disturbing activity in a HQW zone within 15 working days or 60 calendar days
               following completion of construction or development, whichever period is shorter.
               </p>
            		
            <p class="incr0">
               (c)
               </p>
            		
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               <span class="ital">Sewershed areasâ€”Sherrills Ford District.</span>
               </p>
            		
            <p class="incr1">
               (1)
               </p>
            		
            <p class="content2">
               <span class="ital">Existing development.</span> Existing development is not subject to the requirements of this section; existing
               development shall be considered to be any impervious surfaces created prior to, or
               for which a vested right has been established, as of the effective date of this chapter
               July 1, 2005. However, redevelopment and expansion of any development shall be subject
               to the requirements of this section.
               </p>
            		
            <p class="incr1">
               (2)
               </p>
            		
            <p class="content2">
               <span class="ital">General requirements.</span> Prior to developments of any tract of land over one acre in size, the applicant or
               financially responsible party for the proposed project shall conduct surveys for threatened
               or endangered species in the project area. The required surveys, or a statement that
               none are present, shall be submitted along with the erosion and sedimentation control
               plan.
               </p>
            		
            <p class="incr1">
               (3)
               </p>
            		
            <p class="content2">
               <span class="ital">Floodplain preservation.</span> No new development disturbing over one acre shall, after the effective date of this
               chapter July 1, 2005, encroach in to floodplains designated in the Sherrills Ford
               District that are on the most recent FEMA flood insurance rate maps (FIRMs).
               </p>
            		
            <p class="b2">
               An additional 25-foot setback shall be preserved from the landward edge of the protected
               floodplain areas, and diffuse flow shall be maintained across forested floodplain
               areas both during and after land-disturbing activities impacting one or more acres.
               </p>
            <p class="incr2">
               a.
               </p>
            		
            <p class="content3">
               Single-family residential lots may incorporate ground-level improvements within the
               required setback. No additional fill or structures will be allowed within the setbacks.
               </p>
            		
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               b.
               </p>
            		
            <p class="content3">
               Commercial, industrial and multifamily developments are allowed to encroach into the
               25-foot setback when additional BMPs are employed to capture and treat stormwater
               expected from the two-year storm.
               </p>
            		
            <p class="incr2">
               c.
               </p>
            		
            <p class="content3">
               Where required, the utilization of BMPs shall be subject to approval of the county
               utilities and engineering department. The county recognizes that stormwater treatment
               and control is an evolving science, and will entertain site-specific proposals for
               use and implementation of BMPs. For purposes of this section, water-dependent structures
               and public projects where no practical alternative exists, and other non-habitable
               structures are exempt from the requirements of this section.
               </p>
            		
            <p class="historynote0">
               (Ord. No. 2008-18, 11-17-2008; Ord. No. 2021-10, 10-18-2021)
               </p></div>