The following conditions are required for storm water runoff control facilities.
(A) The peak discharge from the detention/retention basin shall be controlled by a release outlet structure and shall not be greater than a pre-development peak runoff rate based on a two-year, ten-year, 25-year and 100-year storm frequency at the discharge point.
(B) The outlet structure shall be sized to accommodate flow equal to the 100-year storm post-development discharge. The routing of the outlet structure shall be shown based on a 100-year storm frequency.
(C) The emergency spillway shall be designed to prevent flowing during a 100-year storm event, unless the principle spillway has become blocked. Erosion protection and any necessary energy dissipation shall be provided for spillways and any receiving watercourse. Spillways shall not be placed over a dam. Vegetated emergency spillways shall be embedded in in-situ soils.
(D) The dam elevation shall not be less than one foot above the 100-year storm storage and overflow elevation.
(E) Detention basins shall be fully discharged within 36 hours after the storm event.
(F) (1) The detention basin shall be the first item of construction and shall be designed to function as a sediment basin throughout construction.
(2) The basin design must be checked for capacity due to additional runoff generated by disturbed site conditions.
(G) (1) The detention basin shall be easily accessible for maintenance.
(2) All basins shall be designed and constructed with side slopes no greater than 3:1 (three feet horizontal per on foot vertical).
(3) Fencing may be required by the approving agency when warranted by the location of the detention basin.
(Ord. 012-118, passed 10-8-2012)