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

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2. INTRODUCTION 2.1 Authorization The preparation of this report was authorized by the Ramsey City Council on October 27th, 2015. 2.2 Project Overview Ramsey is located on the Anoka Sand Plain where soils are generally sandy and free draining, but 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 throughout the City. Several residents attended Public Works Committee meetings in September and October of 2014 to discuss their issues and request assistance from the City. The Committee then directed staff to update the City's comprehensive stormwater model and to prepare a feasibility report to explore options for addressing the resident's concerns. Based on this direction, staff analyzed drainage areas for three of the hardest hit areas that reported flooding in 2014. These areas, in order of priority, were Gibbon Street north of 173rd Avenue, 162nd Lane West of Ramsey Boulevard, and 156th Lane East of TH 47. On March 31st, 2015, Staff reviewed their findings with the Public Works Committee. At that time it was determined that it would be cost -prohibitive to address these and similar drainage concerns throughout the City. It was also confirmed that the Gibbon Street area experienced the most significant issues. Staff was therefore directed to research solutions for the drainage issues identified in this area. Options for effectively draining low-lying, land -locked areas include installing gravity storm sewer to drain water to other areas at lower elevations, installing storm sewer lift stations to pump the water to a higher elevation where it can then flow to lower elevations via gravity sewers or ditches, pumping the water with portable pumps and flexible hosing to other locations where it can flow to lower elevations via gravity sewers or ditches, or by promoting infiltration by constructing infiltration basins, ponds or trenches. Unfortunately, it is typically not an option to pump water elsewhere in Ramsey due to the relatively flat terrain and extensive distance between grade breaks. The other options typically require installing thousands of feet of sewer and purchasing numerous, and often large, easement areas, and/or installing lift stations, all of which can cost hundreds of thousands of dollars (or more) per area. Feasibility Report Gibbon Street and 173rd Avenue Drainage Improvements City of Ramsey Project No. 16-88 Page 2