(A) Drainage patterns should be designed to prevent erosion, maintain infiltration and recharge of local seeps and springs, and attenuate the harm of contaminants collected and transported by stormwater. Overland sheet flow and natural drainage features and patterns shall be maintained to the greatest extent reasonably possible and the dispersion of run-off back to sheet flow shall be the primary objective of drainage design where possible, depending on volumes and velocities of run-off for the development, as opposed to concentrating flows in storm sewers and drainage ditches.
(B) Construction of enclosed storm sewers and impervious channel linings are permitted only when the city on the basis of competent engineering evidence, concludes that such storm sewers or impervious linings are protective of water quality.
(C) If storm sewers are deemed necessary as specified above, the applicant shall design the drainage system to mitigate its harmful impact on water quality by using structural devices or other methods to prevent erosion and dissipate discharges from outlets wherever practicable, and by loading discharges to maximize overland flow through buffer zones or grass line swales.