2B, Valentine Park Drainage Analysis Review

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• E-3C�L.T41'�.,I �. M �N K , ! Nam® • Consulting Engineers &Surveyors 12224 NicolletAvenue•Burnsville,MN 55337 Phone(952)$90-0509 o Fax(952)690-3065 www,bolton-menk.com November 2, 2010 Mr.Terry Maurer, P.E. Public Works Director City of Arden Hills Arden Hills, MN 55112 RE: Engineering Review for Valentine Park Drainage Analysis City of Arden Hills,Minnesota Mr. Maurer: We have reviewed the drainage analysis prepared by WSB&Associates on February 9,2009 for the Valentine Park sub-watersheds of the City of Arden Hills (City). In addition, we performed a site visit on September 22, 2010 to compare the hydrologic model assumptions with the existing conditions observed within the Valentine Park sub-watersheds. The drainage analysis,completed by WSB,provided three options for mitigating the localized flooding within Valentine Park. Per our scope of services we reviewed: "Option#1 —Maintain Park Facilities with Improved Drainage and Storm Water Treatment", found on page 8 of the drainage analysis,the data and results of the XPSWMM model, the practicality of the proposed stormwater system layout,and the apparent cost to value relationship of the overall improvements. Bolton &Menk, Inc. only reviewed the XPSWMM model results. The model itself was not provided for review. THE XPSWMM MODEL Based on the hydrologic model information that was provided in the drainage analysis it appears that the model parameters and assumptions were properly identified using the standard of care appropriate for an analysis of this type and scale_ When we compared the model assumptions with the existing conditions observed within the sub-watersheds it appears that the existing conditions are accurately reflected in the hydrologic model. The model identified localized flooding within the Glenview Avenue and the Crystal Avenue drainage networks for the 5-, 10-,and 100-yr, 24-hr storm events. This flooding was identified in the report, but we believe it is important to note that given that the area has been identified in the City's Pavement Management Program(PMP) for reconstruction, there are options available to the City,within the PMP, that will have a significant impact on downstream(Valentine Park)flooding. It is widely accepted that on urban sites,controlling stormwater at the source is more efficient,cost- effective,and sustainable than the alternative,end of pipe treatment. The City has the opportunity to implement street reconstruction Best Management Practices(BMPs)such as reduced pavement width, biofiltration, bioinfiltration, and other means of volume control and water quality in the PMP that would significantly reduce the downstream flooding at Valentine Park and meet the Rice Creek Watershed District abstraction requirements. This approach would be similar to Option#3 in the drainage analysis accompanied with additional hydrologic model evaluation.