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I I I I I I I I I I I I I I I I I I I 2,11,02 Section 3 - Hydraulic and Water Quality Analyses Hydraulic Analyses Regional Stonnwater Treatment Locations There are thirteen proposed potential regional ponds in Arden Hills that were identified in a 1999 comprehensive drainage study by BRW Inc. (Dames and Moore Group Company). TCAAP property was not considered or modeled as part of this Plan, Two ponds within TCAAP, P-1 and P-l3, will be completed as part of the reconstruction of TH 96, and will not be discussed in this Plan. Figure II shows the approximate locations of the proposed regional ponds. They are mostly located in natural low lands or inlets to lakes. It should be noted that the City would need to further investigate the proposed regional pond locations with respect to jurisdictional wetlands and regulatory restrictions that may affect the construction of these facilities. Even though the BRW, Inc. study and this Plan evaluate the proposed construction of regional ponds, other stormwater treatment best management practices (such as infiltration BMP' s) will be addressed in the feasibility study stage. The Minnesota Urban Small Sites EMP Manual (Metropolitan Council, 2001) outlines a three-step process to select a BMP or combination of BMP's for sites less than five acres, This process looks at stormwater treatment suitability, physical feasibility factors, and community and environmental factors, Summary Discharge Data HydroCAD@ modeling was completed for the eleven proposed regional ponds. At this stage the ponds are only concepts, and therefore the modeling consisted of the drainage districts identified in the 1999 comprehensive drainage study by BRW, Inc. and the proposed concept pond. The concept pond was assumed to be rectangular in shape, with a ten-foot shelf below the normal water level, side slopes of 3:1 everywhere else, and a depth of six feet. Appendix E includes pond design standards for the City, The 5, 10, and 100-year, 24-hour, storms were run, using antecedent moisture conditions II. The results ofthese models can be seen in Appendix F. The 100-year design storm was used to calculate a peak height of the pond and to determine if any potential damage or flooding could occur at the neighboring structures. Only one pond as calculated from this modeling, P-12, has the potential for flooding the low point on North Hamline Avenue and City of Arden Hills, Minnesota Local Stormwater Management Plan A-ARDEN0101.00 Page 24 e e e