13 - Agreement with Nash for cost sharing of improvements - Johnson Woods Creek

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Item No. 13 R�� EN R", 1, MT TO: Mayor & City Council Grayson Path, City Manager FROM: Carla Easton, PE, Engineering & Community Development Director SUBJECT: JOHNSON WOODS BANK STABILIZATION — GARY NASH AGREEMENT DATE: July 27, 2020 BACKGROUND: The Johnson Woods Sewer & Drainage Improvement project was recently completed as part of the 2013 Bond Fund for Water and Sewer Improvements. The project included replacement of sanitary sewers as well as erosion protection along the drainage channel running from Lamar Avenue to Clark Lane, located between Johnson Woods Drive and 31St St SE. AECOM and Hayter Engineering Inc. prepared the construction drawings and specifications, and the work was completed by RBIS construction company. The work was accepted in February of this year. Gary and Rebecca Nash own lots 3 and 4, Block B of the Merry -Glen Addition located at 645 Johnson Woods Drive. Their home and swimming pool backs up to the drainage channel, which is within a 25 feet wide drainage and utility easement along their east property line. The channel has a natural bend along the Nash property, and due to the high water volumes and velocities, the area is prone to erosion of the channel bank through the years. Approximately 20 years ago, Mr. Nash built a wall along a portion of the creek bend. The wall was made from bags of concrete and rebar, called a sackrete wall, and it showed no signs of movement or failure during the Johnson Woods Sewer and Drainage project. The field decision was made by the design engineer as well as Mr. Nash that the wall would remain in place, and a new gabion basket wall would be constructed through the remaining part of the creek bend to appropriately protect the back from further erosion. The gabion wall was construction according to this plan and has held up nicely. However, the sackcrete wall is now a weaker section along the bend of the creek than the area reinforced by gabion baskets, and during spring rains the sackcrete wall did not hold up to the high velocity in the creek. The sackcrete wall was undermined, and has slid down into the creek where it is now an obstruction.