Agenda - Public Works Committee - 08/18/2020

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Public Works Committee 5.2. Meeting Date: 08/18/2020 By: Bruce Westby, Engineering/Public Works Title: Consider Recommendation to City Council Authorizing Requests for Quotes for 5751 164th Lane Drainage Improvements, Improvement Project 19-17 Purpose/Background: Purpose: The purpose of this case is to consider a recommendation to City Council authorizing Requests for Quotes for 5751 164th Lane Drainage Improvements, Improvement Project 19-17. Background: The property owner at 5751 164th Lane first contacted Staff regarding drainage concerns on May 11, 2019. According to the property owner, stormwater runoff from the drainage ditch in City right-of-way in front of their house has been flowing directly across their property in a shallow swale for decades without any drainage easements in place. The property owner claimed that during the winter of 2018/19 the outer edge of the 14-foot by 16-foot floating concrete slab supporting their attached enclosed patio, which is directly adjacent to the drainage swale running across their property, lifted approximately 6-inches. Staff has not been provided with any evidence that the lifting of the slab actually occurred that winter, such as before and after pictures, but the lifting of concrete slabs can/does occur if/when the soils underneath a slab are subjected to numerous freeze -thaw cycles during the course of a winter. After the property owner contacted Staff with their concerns, Staff began working to develop plans to route the stormwater runoff from the public right-of-way through ditches and storm sewer culverts and pipes located within City right-of-ways and drainage easements, instead of across the private property in a swale. After collecting topographic survey and working with the private utilities, including Northern Natural Gas who owns and operates two high pressure gas lines that traverse the private property and the ditches in City right-of-way, Staff completed plans and recommends constructing the improvements this fall to ensure no further claims of damage to private property will be received. Existing drainage infrastructure includes a culvert crossing under 164th Lane located just west of the driveway to 5751 164th Lane. Runoff from the south side of 164th Lane flows though this culvert, which empties into the drainage ditch in front of 5751 164th Lane, and is then routed through a swale on the private property as mentioned earlier. As shown in the attached plans, the drainage improvements proposed with this project involves re -grading the ditch on the south side of 164th Lane and adding a new culvert under 164th Lane at the western lot line of 5751 164th Lane where a drainage and utility easement currently exists and is the intended route for conveying stormwater runoff from this stretch of 164th Lane to the pond to the north. This project will require the replacement of the driveway culvert at 5800 164th Lane. Northern Natural Gas owns an 80' wide easement which crosses 5751 diagonally and contains two high pressure gas mains. City Staff has had to work with Northern Natural in the design of these plans to avoid conflicts with these gas mains, and has received Northern Natural's approval of the plans with some contingencies which have been built into the plans.