The following policies apply to hydrologic modeling methodology used in drainage studies submitted to the town. When applicable, exceptions to these policies may be made in writing at the discretion of the Town Engineer under special conditions.
(A) Peak runoff and volume calculations shall be performed, at a minimum, for the 2-, 10-, and 100-year return periods, in conjunction with all drainage reports for private developments and public works projects. The 24-hour duration storm shall be used for all watersheds modeled using the unit hydrograph method.
(B) Peak runoff and volume calculations shall be performed for both existing and proposed conditions. Proposed condition peak runoff flow rates for the 2-, 10- and 100-year 24-hour storms shall not exceed the existing conditions runoff flow rates for the respective storms. A statement to this effect must be either in the Final Drainage Report or on the improvement plans. The hydrologic modeling for the project must demonstrate that this requirement is met. Refer to § 152.61(A) for the only exception to this policy.
(C) It is the policy of the town that increases in runoff volume be allowed to percolate into the ground as much as possible. This may be accomplished with either detention basins designed to maximize detention time for the more frequent storms, in-channel check basins or improvement of on-site watershed initial abstraction. Soil conditions on the site must be conducive to percolation. Refer to §§ 152.60 - 152.62 for policies regarding detention/retention requirements and basin times.
(Res. 1637, passed 2-28-02; Am. Res. 2272, passed 5-17-07; Am. Ord. 714, passed 5-17-07; Am. Res. 2871, passed 9-17-15; Am. Ord. 872, passed 9-17-15)