(A) Upstream. Drainage flowing onto the site from upstream areas must be managed and accommodated. Alterations to flow paths which impound or slow down water will not be allowed unless it can be shown that the upstream system can accommodate the change. Proposed rates, volumes, velocities, and duration of flow may be requested in order to document that any impacts are nonexistent or insignificant.
(B) Downstream.
(1) To the extent possible, existing drainage areas and discharge points from the site should be maintained post-development and concentrated flows onto neighboring properties should be avoided or mitigated. The downstream conveyance system (natural or structural) must be able to accommodate, to the nearest major receiving waterbody, increased volumes caused by development.
(2) If diversions from existing drainage areas and alterations to discharge points are proposed, the responsible party shall provide additional documentation (rates, volumes, velocities, duration of flow, and the like) to demonstrate that the downstream conveyance system can accommodate the change. The responsible party shall provide evidence of easements or other agreements concerning water flow if a plan involves increased impervious or directing concentrated runoff from onto a neighboring property.
(3) If diversions from existing drainage areas, alterations to discharge points, increased duration of flow, or additional runoff volumes are proposed, the responsible party shall provide additional documentation (rates, volumes, velocities, duration of flow, and the like) to demonstrate that the downstream conveyance system can accommodate the change. The responsible party shall provide evidence of mitigation, easements or other agreements concerning water flow if a plan involves increased impervious or directing concentrated runoff from onto a neighboring property.
(Ord. 99-2022, passed 6-28-22)