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9 <br /> d 4- <br /> Section 9 - Permanent Downstream Protection of Stream Banks and <br /> Channels <br /> Provision shall be made for permanent protection of off-site <br /> stream banks and channels from the erosive effects of increased <br /> velocity and volume of stormwater runoff resulting from <br /> land-disturbing activities. <br /> a. Control of Velocity - stream banks and channels downstream <br /> from any Land-disturbing activity shall be protected from <br /> increased degradation by accelerated erosion caused by <br /> increased velocity of runoff from a land-disturbing activi <br /> ty. The land-disturbing activity shall be planned and <br /> conducted such that the velocity of stormwater runoff in the <br /> receiving watercourse at the point of discharge resulting <br /> from a 10-year storm after development shall not exceed the <br /> greater of: <br /> (i) the velocity as determined from the table of permissi- <br /> ble velocity for stormwater in 3) , or <br /> (ii) the velocity in the receiving watercourse determined <br /> for the 10-year storm prior to development. <br /> If conditions (i) and (ii) of this paragraph cannot be met, <br /> the channel below the discharge point shall be designed and <br /> constructed to withstand the expected velocity. <br /> 1) Acceptable Management Measures- measures applied alone <br /> or in combination to satisfy the intent of this <br /> subchapter are acceptable if there are no objectionable <br /> secondary consequences. Innovative techniques and ideas <br /> will be considered and may be used when shown to have <br /> the potential to produce successful results. Some <br /> alternatives are to: <br /> (i) avoid increases in surface runoff volume and <br /> velocity by including measures to promote infil- <br /> tration to compensate for increased runoff from <br /> areas rendered impervious; <br /> (ii) avoid increases in stormwater discharge velocities <br /> by using vegetated or roughened swales and water- <br /> ways in lieu of closed drains and high velocity <br /> paved sections; <br /> (iii) provide energy dissipators at outlets of storm <br /> drainage facilities to reduce flow velocities at <br /> the point of discharge; these may range from <br /> simple rip-rapped sections to complex structures; <br /> (iv) protect watercourses subject to accelerated <br /> erosion by improving cross-sections and/or provid- <br /> ing erosion-resistant lining. <br />