AG 1997 08 12 - Laserfiche WebLink

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constructed to withstand the expected velocity anywhere the velocity exceeds the "prior to development" velocity by 10%. Acceptable Management Measures - measures applied alone or in combination to satisfy the intent of this section are acceptable if there are no objectionable secondary consequences. The NCSCC recognizes that the management of stormwater runoff to minimize or control downstream channel and bank erosion is a developing technology. Innovative techniques and ideas will be considered and may be used when shown to have the potential to produce successful results. Some alternatives are to: Avoid increases in surface runoff volume and velocity by including measures to promote infiltration to compensate for increased runoff from areas rendered impervious. Avoid increases in stormwater discharge velocities by using vegetated or roughened swales and waterways in lieu of closed drains and high velocity paved sections. o Provide energy dissipaters at outlets of storm drainage facilities to reduce flow velocities to the point of discharge. These may range from simple rip-rapped sections to complex structures. Protect watercourses subject to accelerated erosion by improving cross sections and/or providing erosion-resistant lining. Exceptions - this rule shall not apply where it can be demonstrated that stormwater discharge velocities will not create an erosion problem in the receiving watercourse. The following is a table for maximum permissible velocity for stormwater discharges: Maximum Permissible Velocities Feet/ Meters/ Material Second Second Fine sand (noncolloidal) Sandy loam (noncolloidal) Silt loam (noncolloidal) Ordinary firm loam 2.5 0.8 2.5 0.8 3.0 0.9 3.5 1.1 12