Agenda - Council - 07/12/2016 - Laserfiche WebLink

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1. EXECUTIVE SUMMARY This Feasibility Report explores the construction of a proposed storm sewer outlet for a low- lying land -locked area along Gibbon Street, north of 1731" Avenue. The purpose of the outlet is to maintain lower groundwater elevations, which would benefit adjacent residential properties that previously experienced wet basements. Figure 1 in Appendix A shows the scope of the proposed improvements. Ramsey is located on the Anoka Sand Plain where soils are generally sandy and free draining. Areas of heavier soils that retain water and support wetland vegetation also exist within the City. Approximately 20% of Ramsey's surface area is classified as wetlands, some of which are isolated pockets, while the rest are loosely connected by channels or swales. Water levels in wetlands are generally static but do fluctuate over time. Water levels can drop during periods of less rainfall, and rise during periods of more rainfall, which is more apparent in isolated areas that do not readily drain. All isolated areas will overflow given enough precipitation. Early developments in Ramsey were most often constructed without evaluation of adjacent wetlands and overflow elevations. Storm water management consisted of ditches adjacent to rural roads with culverts and small dry detention areas. Storm water management requirements have increased over the years. Current requirements include infiltration of the first 1" of runoff from new impervious (pavement and roof tops) surfaces, with rate control for the 2, 10, and 100- year events. High water concerns are generally reported from these early developments. In 2014, high water was reported on several properties. Several residents attended Public Works Committee meetings that September and October to discuss their issues and to ask if the City could help. The Committee, with Council ratification, directed staff to update the comprehensive stormwater model and to prepare a feasibility report to explore options addressing their concerns. Staff analyzed the drainage areas for three of the hardest hit areas reporting flooding in 2014. These areas, in order of priority, included Gibbon Street north of 173rd Avenue, 162nd Lane West of Ramsey Boulevard, and 156th Lane East of TH 47. On March 31st, 2015, the Public Works Committee determined it would be cost -prohibitive to address these and similar drainage concerns throughout the City, and confirmed the Gibbon Street area was experiencing the most significant issues. Staff was therefore directed to research solutions for drainage issues within this area. On June 16th, four options for alleviating localized flooding issues in the Gibbon Street area were discussed with the Public Works Committee. Figure 2 in AppendixA shows the alignments of the four options. The Public Works Committee recommended that the City Council consider ordering a feasibility report to further refine option #4 for the Gibbon Street and 173rd Avenue drainage improvements, including an analysis and determination of estimated costs, available funding sources, and whether any City policies would need to be created or amended to construct the improvements. On October 27th, 2015, the City Council directed staff to prepare this Feasibility Report to further explore option #4. It is the recommendation of City staff that though City Project No. 16-88 is feasible and can be constructed in 2017, given the estimated cost of $325,000, and the small number of benefiting properties, the proposed improvements are not cost-effective and should only be constructed if benefiting properties are specially assessed for all or a significant portion of the improvements, and/or if external funding is available to fund all or a significant portion of the improvements. Feasibility Report Gibbon Street and 173rd Avenue Drainage Improvements City of Ramsey Project No. 16-88 Page 1