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A. Drainage areas, including areas draining from off -site onto or adjoining the project <br />B. Design storm runoff: based on the type of facility and storm frequency listed in Section <br />5.4. <br />C. 100 — year runoff sheet flow pattern. <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 />H. For bridge designs the 100-year WSEL must be shown on the plans and the low chord of <br />the bridge must be a nunirmm of eighteen inches above the 100-year WSEL. <br />5.2.2 Detailed drainage calculations shall be submitted with the construction plans. <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. A dedicated easement must be provided at the terminus to allow the 100-year <br />event to sheet flow to the ultimate outfall. In no instance will plans be approved without specific <br />detail as to how the 100-year event will sheet flow from the development to the outfall without <br />adversely impacting structures. <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 />If the 25-year WSEL is not available then use 80% of the ultimate channel height. In areas which <br />are tidally influenced the mean high tide elevation will be used unless it is lower than the 25-year <br />WSEL, in which case the higher value will be used. In instances where the 25 year WSEL in the <br />receiving channel is lower than the top of pipe then the top of pipe shall be used as the starting <br />point for HGL calculations. <br />5.2.5 The location of detention facilities required by these standards shall generally be in the vicinity of <br />the lowest point of the property being developed. The city engineer has authority to make <br />exceptions in the event that the runoff is conveyed via underground storm sewer facilities that <br />accommodate the 100 year discharge. <br />5.3 USE OF PREVIOUSLY DESIGNED AND INSTALLED INFRASTRUCTURE <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 />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 />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 />5.4 STORM FREQUENCY, RUNOFF AND DATUM <br />A. Storm Frequency <br />Stormwater Criteria Page 2 of 10 <br />