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.