(A) When storm sewer construction is permitted, storm sewers shall be designed to flow full, using Manning's Formula with 0.013 as the roughness coefficient unless otherwise approved by the Village Engineer. If a storm sewer is designed with a constantly submerged outfall, the sewer shall be designed using the "hydraulic gradient" with a maximum allowable water level elevation at the top of the street curb.
(B) The rational method shall be employed when computing storm runoff. The storm system shall be designed with "positive street and swale drainage" such that in the event of a complete storm system failure, storm water runoff will be directed overland to the storm water detention area in a manner to minimize property damage due to flooding. The runoff coefficient used in the rational method shall be the weighted average for the proposed tributary watershed based on a c-value of 0.95 for all impervious areas (paved or hard surfaced areas of all types and buildings) and a c-value of 0.45 for all pervious areas.
(C) Storm sewers shall be designed to flow full and have a minimum velocity of three feet per second and shall not exceed ten feet per second. A ten-year storm shall be used for design purposes.
(D) In areas where curb and gutter and storm sewers are approved, inlets shall be installed so that the distance between each inlet shall not exceed 400 feet and each inlet shall drain a maximum street gutter length of 400 feet. Where the inlet is located at a low point, additional inlets may be required by the Village Engineer. No more than two inlets shall be interconnected. Inlets shall be so located that storm water runoff will not "pond" greater than the top of the street curbs. Depressed street crowns to facilitate drainage will not be permitted. A four-inch perforated underdrain tile shall be installed at all street sag and undercut locations.
(E) Yard inlets shall be placed where required by the Village Engineer.
(F) The minimum size storm sewer shall be 12 inches in diameter, and the minimum size inlet connection shall be ten inches in diameter.
(G) Unless otherwise approved by the Village Engineer, storm sewers shall be reinforced concrete pipe conforming to ASTM C76 minimum Class III with O-ring joints conforming to ASTM C443. All inlet connections shall be concrete sewer pipe, ASTM C14 for extra strength pipe. Refer to Appendix D following this chapter.
(H) Minimum cover shall be generally three feet zero inches for all storm sewers unless special precautions are taken to protect the pipe, as approved by the Village Engineer.
(I) All manholes, inlet manholes, inlets and catch basins, and headwalls shall be designed in accordance with the standard details of the village. A two-inch wide non-hardening butyl rubber mastic of minimum thickness one-quarter of an inch shall be installed between all manhole sections and adjusting rings for all storm sewer structures lying in pavement. All castings shall be made in the U.S.A. with U.S.A. materials.
(J) Connections to sanitary sewers or existing agricultural drainage systems (tiles) will not be permitted for any new developments. All developments will utilize separate drainage systems to avoid disruption or overloading of the existing agricultural tile drainage system. Any field tile systems cut during the process of land development must be reconnected or rerouted as approved by the Village. Connection of existing agricultural drain tiles to new storm water management systems may be approved if proper allowance for flows from said tiles is incorporated in the new system design.
(Ord. 04-02, § 158.022, passed 4-5-04)