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Memo-Wetland Alteration Supporting Memo 7-27-16 Memorandum TO: Terry Jeffery CC: Bill Coffman FROM: Mark Rausch, PE DATE: July 27, 2016 SUBJECT: Foxwood – Wetland Permit Application Wetland Avoidance Sequencing Support ____________________________________________________________ Kjolhaug Environmental Services (KES) has assembled the Wetland Permit Application for the Foxwood development project. KES has identified the following three alternatives for wetland avoidance for the project: 1. No build 2. Creation of a development that does not have a road connection to the property to the south 3. 100’ easterly shift of the roadway alignment to cross at the wetland minimum width point Alternatives (1 and 2) are straight forward with the explanation provided in the KES permit application. KES has identified that alternative 3 would result in a less functional and potentially less safe roadway. This memo provides additional support of the KES statement. The City of Chanhassen’s “Foxwood” development approval has required the extension of public right of way including watermain be provided to the property south of the existing Wilson Nursery property. The roadway extension does requires impact to a narrow waterway between two larger wetland cells. The waterway is a swale conveying overflow drainage from west to east from wetland 4 (identified as 4 in the KES delineation report) to wetland 3. The connecting swale has been defined as wetland by KES and they have chosen to include the swale as part of the wetland 3 complex. The main cells of wetlands 3 and 4 are at significantly different elevations with wetland 4 at a much higher elevation of 894.5, and wetland 3, 14’ lower at 880.4. The distance between the main cells of wetlands 3 and 4 is as close as 194 feet limiting the amount of space available to construct a roadway in-between the two. The City desires this proposed roadway extension as it will provide an alternate local connector from TH 101 (Great Plains Blvd) to Powers Boulevard. The roadway connection will be a minor collector which is defined by the City of Chanhassen as: Foxwood Wetland Permit Application Support Memo Page 2 of 2 “Minor collectors are streets or roadways providing travel between local streets and the arterial roadway network, or serving multifamily development or neighborhood centers or services such as fire stations, parks or schools.” As this roadway is to be a minor collector it serves a greater functional purpose than the lesser local roadway classification. A minor collector roadway design typically includes greater visibility by limiting horizontal roadway curves and/or having lesser rates or curvature for any necessary horizontal curves. As designed and aligned the roadway requires only one 250’ radius horizontal curve through the wetland impact area. This design provides excellent sightlines through this curving segment of roadway that is also at a low point sag curve ending the road stretch dropping at 6% elevation from the north. A shift of the roadway easterly in attempt to find a ‘narrower’ segment of the wetland connection swale would require the addition of 2 more horizontal road curves and those curves would be required a rate of curvature less than the currently proposed 250’ radius. The addition of more and tighter horizontal curves would reduce sightline visibility through this stretch of road reducing the potential safety of the roadway. The additional curves and tighter rate of curvature would also result in lesser traffic flow efficiency reducing the functionality of the minor collector. The significant elevation difference between the two wetlands creates a challenge in aligning the proposed roadway extension between the 2 wetlands. The roadway does need to be set at an elevation above the estimated high water level of the higher wetland 4 to prevent potential road flooding. The significant elevation difference between the wetlands results in a grading challenge when aligning the roadway closer to wetland 3. The closer the road is to Wetland 3, the greater the extension of fill/embankment is needed on the wetland 3 side of the roadway. The proposed roadway elevation must be maintained to prevent flooding from wetland 4 and since wetland 3 is 14’ lower than wetland 4, locating the roadway closer to wetland 4 reduces the necessary grading impact to the wetland area on the wetland 3 side of the road. To limit the potential wetland impact, the City could allow modifications to their typical design standards. The City could allow: 1. A modified road section 2. Elimination of sidewalk requirement 3. Negative boulevard slope grading from the proposed back of curb 4. Allow retaining walls within public easement or right of way The current design includes a 31’ curb back to back roadway width with a sidewalk on 1 side of the road and 2% positive slope right of way boulevard. The City could explore reducing the roadway width to 28’ back to back and eliminate the sidewalk in the area to reduce the roadway “footprint” through the impact area. The City could allow ‘negative’ slope grading and retaining wall construction within the right of way to limit the amount of wetland impact resulting from grading the roadway to the required elevation.