Agenda - Public Works Committee - 05/17/2016

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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 Appendix A shows the alignments of the four options presented including; Option#1: This option requires installing a pipe in an existing drainage and utility easement. The initial plan was to install approximately 800 feet of pipe by jacking to avoid large trees within the easement and cutting a deep trench through Iguana Street. This was determined to be infeasible after further investigation for the following reasons. The jacking pit would need to be placed in one wetland and the receiving pit and pipe fusing area would need to be in the second area. Both areas are over 400 feet from the nearest road. Access would require acquisition of additional easements. The fused pipe may tend to sink into the wetland prior to being pulled back. The City did a project in 2012 where the boring machine was placed on upland in an existing easement extending to the street. The welding of the pipe was done on planking extended from an existing road. The jacked length was approximately 800 feet. The total project cost was $160,000. The Gibbon street project would require additional easements and restoration of all disturbed lawn surfaces. Option#2: This option requires cleaning the existing County Ditch that runs north of this development. This option is not feasible because it would require lowering the existing surface area of some wetlands up to 2 feet which is not permitted under the Wetland Conservation Act. Option#3: This option considered the suggestion of the property owners at 17421 Gibbon Street NW for using a different set of drainage and utility easements to provide drainage to the west. This route is not feasible due to the presence of two high areas that would need to have pipe installed under them and because there is minimal elevation difference between the beginning and ending points which could ultimately result in backflow, making the situation worse. Option#4: This option considered extending storm sewer pipe south in the Gibbon Street right- of-way, then west along the 173rd Avenue right-of-way to provide positive drainage from the land-locked area to a County Ditch. This option appears to be feasible, though the location and elevation of existing small utilities along the route would need to be verified during final design, as would the normal water level of the existing wetland east of Gibbon Street. This option was estimated to cost $325,000, which does not include the acquisition of easements which are not anticipated but would need to be verified during final design. Upon reviewing Staff's findings for the four options, the Public Works Committee recommended the City Council order a feasibility report to further refine option#4, 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 a Feasibility Report to further explore option 94. The owners of 17421 Gibbon Street NW were among the residents that contacted the City in the spring of 2014 with high water concerns stating groundwater was coming up through their basement floor due to adjacent wetlands. Staff visited the site in 2014 and observed the adjacent wetlands were full and the surface water level was near the road two lots to the north. Staff is not aware of any water flowing over Gibbon Street in 2014. Staff is not aware of any surface water levels ever reaching the lowest openings of any homes in the area. Feasibility Report Gibbon Street and 173rd Avenue Drainage Improvements City of Ramsey Project No.16-88 Page 3