(A) Drainage systems shall be designed to maximize dispersed flow through vegetated areas and minimize channelization of flow.
(B) Stormwater that cannot be released as dispersed flow shall be transported by vegetated conveyances. A minimal amount of non-vegetated conveyances for erosion protection or piping for driveways or culverts under a road shall be allowed by the permitting authority when it cannot be avoided. Vegetated conveyances shall meet the following requirements:
(1) Side slopes shall be no steeper than 3: 1 (horizontal to vertical) unless it is demonstrated to the town that the soils and vegetation will remain stable in perpetuity based on engineering calculations and on-site soil investigation: and
(2) The conveyance shall be designed so that it does not erode during the peak flow from the ten-year storm as demonstrated by engineering calculations.
(C) Low density projects may use curb and gutter with outlets to convey storm water to grassed swales or vegetated areas. Requirements for these curb outlet systems shall be as follows:
(1) The curb outlets shall be designed such that the swale or vegetated area can carry the peak flow from the ten-year storm at a non-erosive velocity.
(2) The longitudinal slope of the swale or vegetated area shall not exceed 5%, except where not practical due to physical constraints. In these cases, devices to slow the rate of runoff and encourage infiltration to reduce pollutant delivery shall be provided.
(3) The swale's cross-section shall be trapezoidal with a minimum bottom width of two feet.
(4) The side slopes of the swale or vegetated area shall be no steeper than 3:1 (horizontal to vertical).
(5) The minimum length of the swale or vegetated area shall be 100 feet; and
(6) Low density projects may use treatment swales designed pursuant to the Drainage Manual in lieu of the requirements specified in divisions (C)(1) through (5) above.
(Ord., passed 5-11-09; Am. Ord., passed 1-13-20; Am. Ord., passed 9-13-21)