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Resolution No 36-2021 - Adopting Revised Construction Standards and Specifications
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Resolution No 36-2021 - Adopting Revised Construction Standards and Specifications
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10/27/2021 9:20:49 AM
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Board of Public Works
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Resolutions
Document Date
10/26/2021
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SECTION 3 ā STORMWATER <br />22 <br />storage facility is dry within 48 hours of a 100-year storm event. All wet storage facilities (retention <br />basins) shall be designed to resume the designed water elevation within 48 hours of a 100 -year <br />storm event. The storage volume provided by a storage facility is a function of the water elevation. <br />A stage (elevation) storage table should be calculated using the average area method. The following <br />is a formula for the average area method. The interval between intermediate elevations should not <br />exceed one foot. <br />V= storage volume <br />š=āāš»(š“1+š“2) <br />2 āš»=Elevation2-Elevation1 <br />A= surface area at a given elevation <br />The cumulative storage should be calculated by summing the storage volume at each elevation. <br />For wet storage facilities, only the volume provided above the ordinary water level is considered <br />in the storage volume calculations. A stage storage table showing all storage above the ordinary <br />water elevation should be shown and the total volume of that storage should be equal to or greater <br />than the calculated storage volume required. <br />3-1.4 CALCULATION OF REQUIRED STORAGE VOLUME: STANDARD METHOD <br />Due to uncertainties of future development patterns and the associated proposed stormwater <br />quantity and quality management systems within a watershed, it is the policy of the City of South <br />Bend to discourage release of runoff from a new development or redevelopment other than by <br />infiltration up to the 100-year storm event. However, the City Engineer may approve a controlled <br />release from a storage facility when the engineer can show that the downstream receiving system <br />has adequate capacity to accept the calculated discharge from the storage facility. At no time shall <br />an increased rate of discharge be directed to a combined sewer system or storm sewers that drain <br />to combined sewers. <br />3-1.4 (a) CONTROL RELEASE CALCULATIONS <br />1.) The same hydrologic method shall be used for runoff peak determination for both pre - <br />developed and post-developed condition calculations. <br />2.) Recommended hydrologic methods <br />i.The Rational Method is acceptable for calculating peak flows when the total tributary <br />drainage area is 5 acres or less and the tributary drainage area has no existing <br />depressional storage. Runoff coefficients for analysis are shown in Table 2 and are <br />adopted from the INDOT Design Manual. <br />Table 2: Runoff Coefficients for Rational Method <br />Land Use Runoff <br />Coefficient <br />āCā <br />Park, Lawn, Grassy Area 0.2 <br />Residential Single Family 0.4 <br />Apartment or Multi-Unit 0.7 <br />Business, Commercial or Industrial 0.8 <br />Pavement 0.9
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