Laserfiche WebLink
4. Newly constructed open channels in HQW shall be designed <br /> and constructed with side slopes no steeper than 2 <br /> horizontal to 1 vertical if a vegetative cover is used for <br /> stabilization unless soil conditions permit a steeper slope <br /> or where the slopes are stabilized by using mechanical <br /> devices, structural devices or other acceptable ditch <br /> liners. In any event, the angle for side slopes shall be <br /> sufficient to restrain Accelerated Erosion, <br />5. Ground Cover sufficient to restrain Erosion must be <br /> provided for any portion of Land-Disturbing Activity in a <br /> HQW zone within 15 Working Days or 60 calendar days <br /> following Completion of Construction or Development, <br /> whichever period is shorter. <br /> <br />Storm Water Outlet Protection <br />Persons shall conduct Land-Disturbing Activity so that the post- <br />construction Velocity of the Ten Year Storm runoff in the <br />receiving watercourse to the Discharge Point does not exceed the <br />greater of: <br />1. The velocity established by the table in Paragraph (d) of <br /> this Section; or <br />2. The Velocity of the Ten Year Storm runoff in the receiving <br /> watercourse prior to the Land-Disturbing Activity. <br />If conditions (1) or (2) of this Subsection cannot be met, then <br />the receivin9 watercourse to and including the Discharge Point <br />shall be designed and constructed to withstand the expected <br />Velocity anywhere the Velocity exceeds the ~prior to Land- <br />Disturbing Activity" Velocity by ten percent (10%) . <br />ACceptable Management Measures - Measures applied alone or in <br />co~ination to satisfy the intent of this section are acceptable <br />if there are no objectionable secondary consequences. The NCSCC <br />recognizes that the management of Storm Water Runoff to minimize <br />or control downstream channel and bank Erosion is a developing <br />technology. Innovative techniques and ideas will be considered <br />and may be used when shown to have the potential to produce <br />successful results. Some alternatives are to: <br />1. Avoid increases in surface runoff volume and Velocity by <br /> including measures to promote infiltration to compensate <br /> for increased runoff from areas rendered impervious. <br />2. Avoid increases in Storm Water Runoff discharge Velocities <br /> by using vegetated or roughened swells and waterways in <br /> lieu of closed drains and high velocity paved sections, <br />3. Provide Energy Dissipaters at outlets of Storm Drainage <br /> Facilities to reduce flow Velocities to the point of <br /> discharge, These may range from simple rip-rapped sections <br /> to complex structures. <br />4. Protect watercourses subject to Accelerated Erosion by <br /> improving cross sections and/or providing Erosion-resistant <br /> lining. <br />Exceptions This rule shall not apply where it can be <br />demonstrated that storm water discharge Velocities will not <br />create an Erosion problem in the receiving watercourse. <br />The following is a table for maximum permissible Velocity for <br />Storm Water discharges: <br /> Maximum Permissible Velocities <br /> <br /> Feet/ Meters/ <br /> Second Second <br /> <br />Section 9 - <br /> <br />Material <br /> <br />Fine sand (noncotloidal) <br />Sandy loam (noncolloidal) <br />Silt loam (noncolloidal) <br />Ordinary firm loam <br />Fine gravel <br />Stiff clay (very colloidal) <br /> <br />2.5 0.8 <br />2.5 0.8 <br />3.0 0.9 <br />3,5 1.1 <br />5.0 1.5 <br />5,0 1.5 <br /> <br />Feet/ Meters/ <br /> <br />Material <br /> <br />Second Second <br /> <br />Graded, loam to cobbles <br />(noncolloidal) <br />Graded, silt to cobbles <br />(colloidal) <br />Alluvial silts (noncolloidal) <br />Alluvial silts (colloidal) <br />Coarse gravel (noncolloidal) <br />Cobbles and shingles <br />Shales and hard pans <br /> <br />1.5 <br /> <br />5.5 1.7 <br /> <br />3.5 1.1 <br />5.0 1.5 <br />6.0 1.8 <br />5.5 1.7 <br />6.0 1.8 <br /> <br /> <br />