Conceptual Pond Layouts
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Memo
.. 11.. Bonestroo
R Rosene
"1\11 Anderlik &
. \J. Associates
Engineers & Architects
Project Name: Pond LL-P7.5
Client: City of Chanhessen
To: Lori Haak, Water Resource Coordinator
File No: 393-02-128
From: John Smyth, Project Manager
Date: June 7, 2004
Re: Conceptual Pond Layouts
Conceptual grading plans for the proposed Pond LL-P7.5 have been prepared and are provided as an
attachment to this memo. This memo describes the configuration of the proposed cells, provides analysis and
response to comments, and provides projected tree loss for consideration.
Background
The 1994 Channhassen Surface Water Management Plan (SWMP) lays out the concept for a four cell pond
identified as LL-P7.5. The intent of the pond was to provide water quality treatment of waters discharging to
Lotus Lake. The pond was not identified to provide significant rate controls. A two cell pond, identified as LL-
P7.3 was also identified as treating some upstream areas. Pond LL-P7.3 has been installed in accordance with
the SWMP.
The contributing drainage areas were reviewed and confirmed. The existing configuration of Pond LL-P7.3 was
also confirmed. The sites for the proposed pond LL-P7.5 were then reviewed. During this examination, it
became apparent that a development ('The Frontier") was constructed after the preparation of the SWMP in the
location of the two cells that were to be located the furthest upstream. The conflicts posed by these homes and
associated utilities will not allow the construction of the two upstream cells as proposed in the SWMP.
An alternative concept was developed, showing a four cell water quality pond over the existing drainage
channel on a lot owned by the Frontier Trail Homeowners Association that provides access to Lotus Lake. The
preliminary concept identified proposed pond sizes and shapes. Subsequent meetings with the Association and
City Staff requested changes to the proposed pond footprints to minimize disruption to the lot.
Response to City Staff and Homeowners Association Comments
The attached concept grading plans provide details about the revised proposal for the pond system. City staff
and Homeowners Association comments were used to prepare the different layouts. The downstream cell,
identified as Cell D, has been reduced in size to minimize disruption to the beach lot on all of the layouts. The
comments provided by the City and Homeowners Association are summarized in italics and the analysis and
response follows the comment.
Ponds should stay as close to the alignment as possible and maintain parking and turning around for the
Homeowners Association: All cells are kept as close to the existing channel as possible and within drainage
and utility easements with the new concept plans. I am not positive what portion they utilize as a turn around,
however we have addressed this under the discussions of Option Band C
Reconfigure Pond Cell A to maximize use of City Easement: The City owns an existing drainage and utility
easement along Frontier Trail. The boundaries of this easement are provided on the conceptual drawing. The
City requested that Pond Cell A be enlarged to cover this easement. Unfortunately, due to the existing contours
Bonestroo, Rosene, Anderlik and Associates, Inc.
www.bonestroo.com
51. Paul Office:
2335 West Highway 36
SI. Paul, MN 55113
Phone: 651-636-4600
Fax: 651-636-1311
Milwaukee Office:
1516 West Mequon Road
Mequon, WI 53092
Phone: 262-241-4466
Fax: 262-241-4901
Rochester Office:
112 ih Street NE
Rochester, MN 55906
Phone: 507-282-2100
Fax: 507-282-3100
Willmar Office:
205 5th Street SW
Willmar, MN 56201
Phone: 320-214-9557
Fax: 320-214-9458
St. Cloud Office:
3721 23"' Street S
SI. Cloud, MN 56301
Phone: 320-251-4553
Fax 320-251-6252
Grayslake Office:
888 East Belvidere Road
Grayslake, IL 60030
Phone: 847-548-6774
Fax: 847-548-6979
Memo
..11.. Bonestroo
R Rosene
"1\11 Anderlik &
1\J1 Associates
Engineers & Architects
in the area on the adjacent property, this cell cannot be enlarged significantly onto the existing easement. As
an alternative, the normal water level of the Cell could be raised, but this would require the construction of a
berm at the downstream end of the pond and along the easement to keep the water contained within the lake
lot and easement. The construction of this berm would offset any gains in water quality storage volume and
thus expansion was determined not a feasible option.
It is understood that the City requested the expansion of Pond Cell A to provide additional treatment. Rather
then expanding Pond Cell A another option to gain additional treatment involves creating another cell to the
ponding system. This would require constructing a berm at the upstream end of Pond Cell A to contain water
within the easement and would allow the development of a Pond Cell in this area that would maximize the City's
easement. Details are discussed later in this memo under Option C.
Consideration of Additional Treatment West of Frontier:
It was also noted that an investigation of potential sites upstream of this location on the west side of Frontier
Lane should be investigated for improving water quality. Flows from this direction already receive some
treatment in the ponds located west of Frontier Trail, identified as pond LL-P7.3. Using the 2' topographic
information for the area west of Frontier Trail, it appears that there may be one location near the western end of
the ravine that may provide adequate space to construct a water quality feature. However, without investigating
the area on the ground and determining the current ownership of the area, it appears the majority of the
watershed is developed single family with little opportunity for further treatment. If requested, we can
investigate this further and would want to review the grading plans for the area.
Concerns about the state and alignment of present channel as it outlet to Lotus Lake - Water Quantity
Benefits?
It should be noted that this proposed pond complex does not provide any rate control benefits to the channel
and was never intended as such. The ponds were proposed strictly as water quality ponds with large overflow
type outlets. The ponds will intercept any sediment heading towards the lake from any upstream eroding
channels, but will not provide any rate control benefits to any portions of the channel downstream of the ponds.
If rate controls are desired at this location, the ponds will need to be enlarged significantly.
Low-flow outlet pipes between ponds
Low flow outlets could be constructed between the ponds if desired. However, the current intent is that each
pond would overflow from one pond to the next. These details can be accommodated at the final design stage.
Pond Analysis
Several pond configurations were considered and are described as Option A, B, C and a combination of Option
A and C. It should be noted that proposed contours were developed utilizing 4-foot contours that were not
surveyed and as a result the grading should be considered rough and provided for purposes of comparison of
the options. Table 1 provides the total phosphorous and potential tree removal for each of the pond options.
The SWMP Goal is provided in the table as a reference for the different treatment options.
Bonestroo, Rosene, Anderlik and Associates, Inc. www.bonestroo.com
St. Paul Office: Milwaukee Office: Rochester Office: Willmar Office:
Office:
2335 West Highway 36 1516 West Mequon Road 112 7'h Street NE 205 5th Street SW
Road
SI. Paul, MN 55113 Mequon, WI 53092 Rochester, MN 55906 Willmar, MN 56201
Phone: 651-636-4600 Phone: 262-241-4466 Phone: 507-282-2100 Phone: 320-214-9557
6774
Fax: 651-636-1311 Fax: 262-241-4901 Fax: 507-282-3100 Fax: 320-214-9458
St. Cloud Office: Grayslake
3721 23"' Street S 888 East Belvidere
SI. Cloud, MN 56301 Grayslake, IL 60030
Phone: 320-251-4553 Phone: 847-548-
Fax: 320-251-6252 Fax: 847-548-6979
Memo
Ji]j Bonestroo
-=- Rosene
"1\11 Anderlik &
1\J 1 Associates
Engineers & Architects
Table 1. Summary of Total Phosphorous and Tree Removal with Each Option
Scenario Total P to Total % P Lbs PI Acre Projected Tree
Lake (Ibs/year) Removed RemovedN ear Removal
(acres)
SWMP Goal 40.6 72% 0.85 N/A
Initial Lake Lot Concept 47.1 67% 0.82 N/A
Option A 56.8 60% 0.65 1.4
Option B 59.0 55% 0.64 1.0
Option C 55.4 61% 0.66 1.2
Option C and A 52.9 63% 0.68 1.4 +
Initial Lake Lot Concept
This concept presents the removals as identified with the previous conceptual plan for the Lake Lot. As shown
in Table 1 this proposal nearly met the goals of the 1994 SWMP. This concept however provides the most
disruption to the area actively utilized by the Homeowners Association.
Option A
This option includes all four cells as proposed in the initial lake lot concept, except it reduces the size of Pond
ell D (Exhibit 1). As shown in Table 1, the reduced size of Pond Cell D has a negative impact on the total
phosphorous removal provided by the pond complex, however it also reduces the disruption of the area of the
beach lot actively utilized by the Homeowners Association. The tree removal anticipated for this option is
shown on Exhibit 4. We anticipate the removal of 1.4 acres of trees with this option.
Option B
This option shows the impact of not constructing Pond Cells Band C of the proposed ponding system. Each of
these cells is relatively small and would maintain a shallow depth of water. As such, they do not provide a
significant reduction in the total phosphorous reaching the lake when compared to the removal provided by the
two larger cells. Not constructing these cells will minimize the removal of trees, with a relatively minor impact
on the total phosphorous removals (3-4 Ibs per year). Pursuing this option would also allow the addition of
parking along the existing road as requested by Scott Maeyaert. The tree removal anticipated for this option is
shown on Exhibit 5, however it only considers impacts from ponds and does not consider adding parking which
may result in tree removal. We anticipate the removal of 1.0 acre of trees with this option.
Option C
This option shows the impacts of constructing Pond Cells A, D and E including the berm required to develop the
Pond Cell E. Pond Cell E would only treat flows arriving from the drainage swale coming from the south. Flows
from west of Frontier Trail would enter Pond Cell A at the locations of the two existing culverts. This option
would also allow the addition of parking along the existing road as requested by Scott Maeyaert. The tree
removal anticipated from the ponds with this option is shown on Exhibit 6. We anticipate the removal of 1.2
acres of trees with this option.
Bonestroo, Rosene, Anderlik and Associates, Inc. www.bonestroo.com
St. Paul Office: Milwaukee Office: Rochester Office: Willmar Office:
Office:
2335 West Highway 36 1516 West Mequon Road 112 7'h Street NE 205 5th Street SW
Road
S¡ Paul, MN 55113 Mequon, WI 53092 Rochester, MN 55906 Willmar, MN 56201
Phone: 651 -636-4600 Phone: 262-241-4466 Phone: 507-282-2100 Phone: 320-214-9557
6774
Fax: 651-636-1311 Fax: 262-241-4901 Fax: 507-282-3100 Fax: 320-214-9458
St. Cloud Office: Grayslake
3721 23"' Street S 888 East Belvidere
SI. Cloud, MN 56301 Grayslake, IL 60030
Phone: 320-251-4553 Phone: 847-548-
Fax: 320-251-6252 Fax: 847-548-6979
Memo
.. 11.. Bonestroo
R Rosene
"Iil'I Anderlik &
1 \J 1 Associates
Engineers & Architects
Option A and C
This option shows the impact of constructing all five of the cells (A,B,C,D,E). As would be anticipated,
construction of all five cells results in the highest water quality benefits to Lotus Lake, but at the cost of the
largest disturbance of trees on the site. The tree loss is projected to be slightly more then 1.4 acres.
Bonestroo, Rosene, Anderlik and Associates, Inc. www.bonestroo.com
St. Paul Office: Milwaukee Office: Rochester Office: Willmar Office:
Office:
2335 West Highway 36 1516 West Mequon Road 112 7'h Street NE 205 5th Street SW
Road
SI. Paul, MN 55113 Mequon, WI 53092 Rochester, MN 55906 Willmar, MN 56201
Phone: 651-636-4600 Phone: 262-241-4466 Phone: 507-282-2100 Phone: 320-214-9557
6774
Fax: 651-636-1311 Fax: 262-241-4901 Fax: 507-282-3100 Fax: 320-214-9458
St. Cloud Office: Grayslake
3721 23"' Street S 888 East Belvidere
SI. Cloud, MN 56301 Grayslake, IL 60030
Phone: 320-251-4553 Phone: 847-548-
Fax: 320-251-6252 Fax: 847-548-6979
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EXHIBIT
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. CONCEPT GRADING PLAN Option A
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CONCEPT GRADING PLAN Option B EXHIBIT 2
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. CONCEPT GRADING PLAN - Option C EXHIBIT 3
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CONCEPT GRADING PLAN Option A - TREE LOSS EXHiBIT 4
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. CONCEPT GRADING PLAN Option B TREE LOSS EXHIBIT 5
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CONCEPT GRADING PLAN - Option C TREE LOSS EXHIBIT 6
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