Agenda - Public Works Committee - 01/18/2022

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Storm Water Management Storm water management concepts were developed to maintain existing drainage patterns and preserve the conveyance and flood storage capacity of the existing site. Storm water runoff west of Center Street is generally planned to flow north from Sunwood Drive and to a large future regional pond proposed on the north side of Ramsey Parkway. The outlet for this regional pond will most likely be extended along the future Yoffie Street, where an existing 30-inch arch pipe has been extended into the study area from Sunwood Drive. The upstream watershed associated with the regional pond is depicted on Figure 13 in Appendix B. The existing hydraulic model was reviewed to allow for the analysis of storm water within The COR area. Preliminary storm water management conditions and requirements were then developed to determine the elevations required for building pads in the area. The sub -watersheds were modeled using future land use conditions to generally size the regional storm water basin. The basin was sized to ensure proposed discharge rates were equal to existing flow rates. The pond was also reviewed with respect to potential storm sewer depths and potential aesthetic park function. The pond footprint used in the analysis is as shown in The COR Parks + Public Places, December 2015. The normal water level was determined by using the elevation of the outlet pipe located near Sunwood Drive. Additional design parameters and regional storm water management planning should be further refined as the areas begin to develop. Figures 10-13 show the general shape and location of the pond used in the analysis. No cost estimating was performed related to construction of the pond for this analysis. Along with the final pond configuration, proposed construction methodologies, including the requirement for pretreatment of all stormwater (public and private) prior to discharge to the regional pond, are currently being considered by the City. The COR is located within a Drinking Water Supply Management Area. Because of this, the required infiltration (1 inch over all new impervious area) is provided by the City in a regional infiltration basin. Developers then pay a share of the cost for creation of the regional facility. An analysis was performed to determine the benefits and costs associated with construction of a bioretention basin in the median area of Ramsey Parkway. The benefits associated with a bio-retention basin include: water quality improvements, potential traffic calming and creation of a landscaping feature within this area of The COR. The City has decided to proceed with construction of the biofiltration basin in the median from Center Street to Xenolith Street, and will likely continue the construction to Zeolite Street. The alignment of Veterans Drive is proposed to provide a 5-acre infiltration area on the south side of Veterans Drive to follow the 2003 Wetland Mitigation Plan and allow regional infiltration of the storm water. No sizing or modeling was performed on this infiltration basin as part of this report. Additional analysis should be performed prior to constructing Veterans Drive. Prepared by: Bolton & Menk, Inc. ADDITIONAL PUBLIC INFRASTRUCTURE ANALYSIS The COR Analysis [ R16.114924 Page 9