Culverts are used to convey storm water in an open channel, natural or man-made, through an embankment such as a roadway.
(A) Design.
(1) Storm frequencies. Surface run-off used for selecting the culvert shall be determined by using the following storm frequencies:
(a) Design for 25 years.
(b) Check for 50 years to meet maximum allowable headwater elevations.
(c) Determine for 100 years to check building impacts.
(d) Driveway pipes are the responsibility of the property owner and should be sized for a storm of at least ten years frequency. Each driveway pipe need not be formally designed except when the headwater approaches the maximum allowable.
(B) Data design and submission. Culverts will be designed by the methods, nomographs, and the like found in "Hydraulic Charts for the Selection of Highway Culverts - Highway Engineering Circular No. 5, 1965" and "Capacity Charts for the Hydraulic Design of Highway Culverts - Highway Engineering Circular No. 10, 1965", published by the U.S. Department of Transportation, Federal Highway Administration.
(C) Type of culvert flow. All culverts will be reviewed for both inlet control and outlet control. The assumption resulting in the higher headwater elevation will govern.
(D) Headwalls. All culverts except driveway pipes will be constructed with headwalls according to the requirements of these criteria.
(E) Allowable headwater elevations. Maximum headwater or any water surface:
(1) For a 100-year storm, shall be two feet below the lowest opening in any building affected by the storm;
(2) For a 50-year storm, shall be one foot below the top of bank or embankment on the upstream end of the culvert;
(3) For a driveway pipe, shall be no higher than the roadway shoulder at the ditch or the driveway sag, whichever is lower.
(4) Depressed culvert inlets (dropped channels) may be used except for driveway pipes.
(F) Minimum cover. The minimum cover for culverts except driveway pipes shall be two feet from bottom of roadway base material to the top of pipe. Driveway pipes will be constructed according to applicable standard drawings.
(G) Erosion control. Outlet velocity will determine the erosion control needed at the culvert outlet. Height of protection along the slope shall be the outlet depth of water in the culvert for a 25-year storm plus two feet. Specially designed energy dissipators may be used with the approval of the Village Engineer.
(Ord. C-604, passed 9-8-86)