1C, Update on Erosion Correction Project

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Consulting Engineers & Surveyors ` 12224 Nicollet Avenue a Burnsville,MN 55337 Phone(952)890-0509*Fax(952)890-8065 www.bolton-menk.com MEMORANDUM Date: August 27,2009 To: Greg Hoag,City of Arden Hills Public Works Director From: Marcus A.Thomas,P.E. Subject: Keithson Drive Trail Drainage On August 11, 2009,you and I met with Ron Nelson(4504 Keithson Drive)to discuss the drainage of the City's existing trail along Mr.Nelson's rear property lot line. This trail is located adjacent to and immediately east of the rear property line. At this meeting,Mr.Nelson discussed and showed us evidence of water coming off of the trail and eroding his lawn and mulch garden,both of which are located along a 4H:1 V(approx.)slope coming down from the trail. The trail sits approximately five to six feet higher than the average elevations of the rear property. The trail was constructed approximately thirteen years ago and is in fair condition. It exhibits signs of deterioration such as settling,heaving in the vicinity of tree roots,cracking,and edge degeneration. There is also evidence of previous crack sealing maintenance. The overall condition of the trail in this area is such that frequent and continued maintenance will be required to extend its useful service life. In the absence of continued maintenance, the trail could be expected to deteriorate to a poor and potentially unsafe condition within about five years. The purpose of our meeting was to review the problems associated with the existing drainage,as described above,and to discuss potential solutions to the problems. In general we discussed three possible approaches to eliminating the erosion problems on Mr.Nelson's property which are associated with the trail drainage. They include: 1. Construct a bituminous curb along the west side of the existing trail to prevent the trail from draining into the subject property. 2. Reconstruct the existing trail at new elevations and grades to prevent it from draining into the subject property. 3. Construct a tiered retaining wall system within the subject property and elevate the rear property grades such that the yard drains toward the trail as opposed to the trail draining toward the yard. Upon further consideration of option 1,we recommend against this approach. Given the deteriorating condition of the existing trail,it is not expected that a new bituminous curb constructed adjacent to the trail will stay in place and connected to the trail. More likely,the curb would separate and tip away from the trail, causing a hazard and increased maintenance needs. Option 2 would involve reconstructing about 150 feet of the trail in order to prevent it from draining onto the subject property. Currently the trail tips toward the property causing water to flow down the sloping back yard. If reconstructed,the trail could be tipped to the east,toward the flatter grades on the opposite side of the trail, and the water routed away from the subject property. This would also provide the City with a new trail segment in place of the aged existing trail. We estimate the cost of the trail DESIGNING FOR A BE7 ER TOMORROW Balton&Menk is an equal opportunity employer