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I. GENERAL CONDITIONS The design and capacity of a drainage system shall be predicated on the following conditions: QOn the basis of the runoff resulting from the selected design storm, the system shall dispose of surface runoff and subsurface water without damage to street facilities, structures or ground and cause no serious interruption of normal vehicular traffic. ORunoff exceeding the design storm must be disposed of with the least amount of interruption to normal traffic and minimum amount of damage to surrounding property. OSystem must have maximum reliability of operation with minimum maintenance and upkeep requirements. QSystem must be adaptable to future expansion, if necessary, with minimum additional cost. © Where sump conditions exist; a safety measure such as an over- - - low swale shall be provided to prevent flooding of adjacent lots in the event the design capacity of the closed conduit is exceeded. Floor levels of homes adjoining sumps shall be a minimum of 3 feet above low point on roadway. OFloor levels of homes abutting streams and open channels shall be a minimum of 3 feet above freeboard elevation computed at design flow. 0 In general, natural gullies, waterways, streams and tributaries shall not be replaced with a closed s y s t e m except at roadway crossings. © Roadway culverts and bridges shall be designed to pass the design flow under open channel hydraulic analysis with a minimum freeboard as specified in the attached freeboard chart. Multiple span road crossings shall have minimum clear spans of 30 -feet, unless otherwise permitted by the Chief Engineer. Where possible, the road- way shall be designed to form a sag vertical curve with a low point at the waterway crossing with minimum grades to confine and control overflow at the crossing.. Roadway culverts and bridges shall be designed to include only deck and roadway. Fill material shall not be used to meet roadway elevations above the deck. OOutlets for enclosed drains emptying into open channels shall be designed to point downstream at an angle of 45 °. OSubsurface drains shall be installed wherever recommended by the Design Engineer, or Chief Engineer, where ground water is en- countered, or may be present during wet weather. © Lots abutting streams and open channels with a drainage area greater than 100 acres shall be graded to drain towards the waterway. Pl