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<br />tl. lJeslgn storm runon; based on the type of facility and storm frequency listed in Section <br />5.4. <br />C. 100 - year runoff <br />D. Route of overland flow including the overflow to a drainage channel or detention facility <br />E. Water surface profiles for the 25-year and/or 100-year storms in the outfall channel. All <br />available information will be considered when making this determination. <br />F. Flow per inlet <br />G. Maximum ponding elevation <br /> <br />5.2.2 Detailed drainage calculations shall be submitted with the construction plans. <br /> <br />5.2.3 A lot grading plan should demonstrate that the finished grading plan will drain to approved <br />collection and discharge points and that the overland flow of water from adjacent properties will <br />not be impacted <br /> <br />5.2.4 The hydraulic gradient for the design storm may be shown on the construction drawings. <br />Calculations for the elevation for the hydraulic gradient shall be provided with the design storm <br />drainage calculations. The hydraulic gradient must be below the gutter line for the design storm. <br />The tailwater elevations based on a 25-year frequency in the outfall channel shall be used for <br />calculations of the hydraulic gradient. <br /> <br />5.3 USE OF PREVIOUSLY DESIGNED AND INSTALLED INFRASTRUCTURE <br /> <br />Situations where previously installed infrastructure is in place but not yet utilized to its design <br />capacity will be considered on a case by case basis. The developers engineer shall after <br />consultation with the City, prepare a report that: <br /> <br />a. outline the original design criteria <br />b. evaluates the impact of the original design on the receiving stream, adjoining <br />properties and/or the 100 year Floodplain. <br /> <br />Based on the report, the City Engineer may allow full or partial use of the previously installed <br />infrastructure and may require it to be supplemented with detention or other facilities. <br /> <br />5.4 STORM FREQUENCY, RUNOFF AND DATUM <br /> <br />A. Storm Frequency <br /> <br />All drainage improvements shall be designed for the following storm frequencies. <br /> <br />Tvpe of Facilitv <br />Road Side Ditches and Culverts <br />Storm Sewers <br />Ditches & Culverts Drainage 100 acres and more <br />Bridges <br />Creeks <br />Detention Facilities <br /> <br />3 year <br />3 year <br />25 year <br />100 year <br />I 00 year <br />Refer to Section 5.5 <br /> <br />B. Storm Runoff <br /> <br />Design flow of storm water runoff is to be calculated using the Rational Method. <br /> <br />The Rational Method is based on the direct relationship between rainfall and runoff, and <br />the method is expressed by the following equation: <br /> <br />Stormwater Criteria Page 2 of 10 <br />