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URS MEMORANDUM Thresher Square 700 Third Street South Minneapolis, MN 55415 Phone: (612) 370-0700 Fax: (612) 370-1378 To: Debra Bloom! Assistant Copy: Public Works Director, City of Roseville Duane Schwartzi Public File: Works Director, City of Roseville Kristine Giga/ City of Roseville 31810177 From: Frank Ticknor/ URS ff Date: December 5, 2006 Subject: City of Roseville Charlie Pond Stormwater Modeling Project Project Summary and Results The purpose of this memorandum is to document the data and results produced for an existing condition drainage study performed for the entire drainage area and storm sewer system associated with Charlie Pond in the City of Roseville. In addition to the existing condition model, the City of Roseville requested additional modeling of possible modifications to the Storm Sewer System. Summarized below are the background and scope of services provided by URS for this modeling project, the existing condition drainage study results, and the modeling results for the possible adjustments to the storm sewer system. BACKGROUND & SCOPE OF SERVICES For many years, concern has been raised about periodic flooding in the watershed of Charlie Pond during high intensity rain events. The City of Roseville has performed a number of improvements to address flooding in areas such as Avon Street, Millwood A venue, and Victoria Street. Also, the City of Roseville, iu cooperation with the City of Shoreview, constructed two ponding facilities immediately north of Charlie Pond, which provide extra stormwater storage and increased water treatment prior to discharge to Lake Owasso. The City of Roseville has analyzed the Charlie Pond watershed in a variety of different formats over the past 20 years. As indicated above, numerous modifications and additions have been made to the storm sewer system within the watershed. This has resulted in the necessity to re-evaluate the system as a whole. The City of Roseville hired URS Corporation to prepare a detailed hydrologic model to help clarify how stormwater is conveyed through the watershed. Due to the complexity of the Charlie Pond watershed, the City of Roseville determined that the XPSWMM software was best suited for the analysis of the Charlie Pond watershed. XPSWMM is a comprehensive software package used for the analysis and design of stormwater, sanitary, or river systems. It simulates natural rainfall-runoff processes and the performance of engineered systems that control water resources. XPSWMM is a dynamic unsteady flow model rather than a steady state or standard step model, which means the program is capable of delivering results far more accurately and 10f6