Agenda - Public Works Committee - 06/18/2019

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Public Works Committee 5.2. Meeting Date: 06/18/2019 By: Bruce Westby,Engineering/Public Works Title: Update on Drainage Concern Findings at 17290 Germanium Street NW Purpose/Background: Purpose: The purpose of this case is to update the Public Works Committee on Staff's findings related to drainage concerns previously expressed by the owner of real property at 17290 Germanium Street NW. Background: In 1992,the property owner built a home on the property, and then in 1998 a garage was built in the southwest corner of the property.A new garage was subsequently built in 2005 after the original garage was destroyed by fire. The home was constructed north of an existing depression that can hold slightly less than a foot of water during heavy rain events. The garage was constructed within a low area of the lot with the garage door facing toward a private property to the south which was used to access Germanium Street approximately 300-feet to the west. In 2017, construction began on the Covenant Meadows residential development,which included construction of a new public street, 172nd Lane NW,which abuts the south property line of 17290 Germanium Street NW.During construction of this development,the property owner contacted City Staff and the developer on numerous occasions to request modifications to the new driveway installed between his garage and 172nd Lane NW. The property owner also requested some grading modifications around the garage to prevent drainage from entering the property from the north and west. On more than one occasion,the property owner stated there were existing standing water issues on this property. On November 13,2018,the property owner at 17290 Germanium Street NW,Mr.Rick Aberle, informed the City Council of his concerns that runoff from the Covenant Meadows development was flooding his property. On December 18,2018,Mr.Aberle attended the Public Works Committee meeting to again present his concerns that runoff from the Covenant Meadows development is flooding his property.Also in attendance were City Engineer Bruce Westby, Senior Engineering Technician Mike McDowall, Civil Engineer IV Leonard Linton,and the developer of Covenant Meadows,Mr.Eric Thomsen. After much discussion, consensus was reached that Mr. Thomsen would complete the driveway improvements including grading and two eight-inch culverts, and Mr.Aberle provided his permission for Staff to enter his property to collect topographic data along his west property line and around and adjacent to his garage and driveway. A copy of the meeting minutes is attached,which includes detailed discussion from the meeting on pages 6 through 9. Based on the consensus reached at the Public Works Committee meeting on December 18,2018,Engineering Staff obtained survey grade topographic data along the west edge of Mr.Aberle's property in December 2018, and along the south edge of the property in April 2019. Staff then reviewed this data and arrived at the following findings. .Before Covenant Meadows was developed(pre-development), 11.125 acres of land drained onto Mr. L..- Aberle's property from the north and west, contributing 3.1 cubic feet per second of runoff from a 100-year storm event. .After Covenant Meadows was developed(post-development), 1.306 acres of land drain onto Mr.Aberle's property from the north and west, contributing 0.75 cubic feet per second of runoff from a 100-year storm