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Conceptual Pond Layouts - 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 NWL SECTION o TYPICAL 3 7 ¿> ~ Bonestroo Rosene 3 Anderlik & 1\J1 Associates Engineers & Architects 1 EXHIBIT -- ..' s . CONCEPT GRADING PLAN Option A - CITY OF CHANHASSEN 0 00 - . . CITY OF LL-P7.5 Scale in feet CHANHASSEN K:\393\39302128\Cad\Dwg\39302128Fl04>dwg JUNE 8, 2004 NWL SECTION o TYPICAL 3 7 ~ Bonestroo Rosene 8 Anderlik & . \j. Associates Engineers & Architects 7: CONCEPT GRADING PLAN Option B EXHIBIT 2 . -- N CITY OF CHANHASSEN o 00 * ~cole in feet W yE CITY OF LL-P7.5 CHANHASSEN K:\393\39302128\Cad\Dwg\39302128Fl04.dwg JUNE 8, 2004 s NWL SECTION o TYPICAL 3 7 A ~ Bonestroo Rosene 8 Anderlik & . \j. Associates Engineers & Architects . CONCEPT GRADING PLAN - Option C EXHIBIT 3 N CITY OF CHANHASSEN o 00. ~cole In feet w .. E CITY OF LL-P7.5 CHANHASSEN K:\393\39302128\Cod\Dwg\39302128Fl04.dwg JUNE 8, 2004 s ". 7 -. ~ Bonestroo Rosene ~ Anderlik & . \J. Associates Engineers & Architects .. "". I CONCEPT GRADING PLAN Option A - TREE LOSS EXHiBIT 4 - - N CITY OF CHANHASSEN o 00 . CITY OF LL-P7.5 Scale in feet W E CHANHASSEN K:\393\39302128\Cod\Dwg\39302128F104.dwg JUNE 8, 2004 s ". 7 ~ Bonestroo -=- Rosene ~ Anderlik & . ~. Associates Engineers & Architects . CONCEPT GRADING PLAN Option B TREE LOSS EXHIBIT 5 - N CITY OF CHANHASSEN o 00. I CITY OF LL-P7.5 Scale in feet W . E CHANHASSEN K:\393\393021 28\Cod\Dwg \393021 28F1 04.dwg JUNE 8, 2004 s 7 ~ Bonestroo Rosene ~ Anderlik & . ~. Associates Engineers & Architects \ -- CONCEPT GRADING PLAN - Option C TREE LOSS EXHIBIT 6 N CITY OF CHANHASSEN o 00. CITY OF LL-P7.5 Scale ~n feet W . E CHANHASSEN K: \393\393021 28\Cod\Dwg\393021 28F1 04.dwg JUNE 8, 2004 s r