2C, Townhouse Villages Drainage Issues

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and prevent flooding from a 100-year storm event,or an event similar to that experienced in July, 2011. The estimated cost for Option 6 is shown in Table 1. Option 6(Figure 7) This option looked at what improvements to the existing storm sewer system would be necessary to keep the pipes downstream of the southern low point from surcharging during a 100-year event. Approximately 865-feet of storm sewer pipe would need to be removed and replaced from the southern low point to the last manhole,prior to outletting into Pond 4. Extensive removal of existing driveways would be required,along with removal of recent improvements that occurred in 2011 Pavement Management Program. The estimated cost for Option 6 is shown in Table 1. Estimated Costs of Options Proposed construction costs for each option are summarized in the table below. These cost estimates are based upon public construction cost information. Estimated construction costs presented in the following table include a 20 percent contingency factor. Table 1-Cost Summary. -Option 1 - Berm&New Outlet from Pond 2 $17,400 -Option 2—Overflow Pipe from SE Low Point $20,300 Option 3—Diversion Pie $75,100 -Option 4—New Outlet Pipe from Pond 2 $59,000 -Option 5—New Outlet Pipe from SE Low Point $68,900 -Option 6—Increased Storm Sewer Pipe Size $100,800 Recommendations The most cost effective solution would be Option 5. This option would provide an alternative route for storm water to discharge from the southern isolated low point, without relying on the existing storm sewer pipe system to carry runoff away from this area of concern. The existing storm drainage system in this townhome development should be inspected on a regular basis to ensure that there is no blockage of the grates or in the storm sewer pipe that would cause water to backup during storm events. There is no emergency overflow adjacent to the two low points studied. Storm events greater than the 100-year design storm will continue to pose a flooding threat to adjacent homes, even if the proposed recommendation is constructed.