Agenda - Public Works Committee - 03/20/2012

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163 Lane Description As shown on Exhibit 11, a low area exists south of 163rd Lane and east of Wolfram Street. The low area does not have a piped outlet to County Ditch #3. During a majority of the year, stormwater runoff infiltrates into the soil. However, during early spring when the ground is frozen and during periods of heavy rainfall, water levels have risen to levels that cause flooding of adjacent properties. Alternatives The following alternatives address the water elevation in the low area. Alternative 1 In this alternative, an outlet pipe would be installed from the low area to County Ditch #3, as shown on Exhibit 12. The outlet pipe will not be installed at the bottom of the low area, rather, it will be installed at an elevation that would allow smaller stone events to continue to infiltrate into the soil. The outlet pipe invert is proposed at an elevation of 872.0, which is the approximate elevation of a 3 -inch rainfall event. The following table summarizes the 100 -year HWL's, the detention time above an elevation of 873.0 and estimated costs to construct each outlet pipe: As shown, the area may continue to flood during large stone events; however, the duration of flooding will be much shorter. Tables 19 through 21 include the individual costs for this alternative. It is proposed to directionally drill the pipe as shown on Exhibit 12 as opposed to open cutting a trench. A trench would require excessive cuts in the surrounding area. The outlet pipe will be approximately 700 feet long. Cleaning the pipe will require access on both ends of the pipe. Alternative 2 Alternative 2 included draining the low area east to a ditch system in Elmcrest Park. This alternative was reviewed and deemed not feasible. There is not enough difference in elevation from the low area to the ditch in Elmcrest Park. Detention Time Above Elevation 873 During a Outlet Pipe 100 -Year 100 -Year Storm Event Size HWL (hours) Estimated Cost Existing 874.8 23.4 N/A 12" 874.3 6.2 $68,640 15" 874.0 2.9 $74,305 18" 873.8 1.5 $80,795 163 Lane Description As shown on Exhibit 11, a low area exists south of 163rd Lane and east of Wolfram Street. The low area does not have a piped outlet to County Ditch #3. During a majority of the year, stormwater runoff infiltrates into the soil. However, during early spring when the ground is frozen and during periods of heavy rainfall, water levels have risen to levels that cause flooding of adjacent properties. Alternatives The following alternatives address the water elevation in the low area. Alternative 1 In this alternative, an outlet pipe would be installed from the low area to County Ditch #3, as shown on Exhibit 12. The outlet pipe will not be installed at the bottom of the low area, rather, it will be installed at an elevation that would allow smaller stone events to continue to infiltrate into the soil. The outlet pipe invert is proposed at an elevation of 872.0, which is the approximate elevation of a 3 -inch rainfall event. The following table summarizes the 100 -year HWL's, the detention time above an elevation of 873.0 and estimated costs to construct each outlet pipe: As shown, the area may continue to flood during large stone events; however, the duration of flooding will be much shorter. Tables 19 through 21 include the individual costs for this alternative. It is proposed to directionally drill the pipe as shown on Exhibit 12 as opposed to open cutting a trench. A trench would require excessive cuts in the surrounding area. The outlet pipe will be approximately 700 feet long. Cleaning the pipe will require access on both ends of the pipe. Alternative 2 Alternative 2 included draining the low area east to a ditch system in Elmcrest Park. This alternative was reviewed and deemed not feasible. There is not enough difference in elevation from the low area to the ditch in Elmcrest Park.