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6 Shadowmere Addition CITY OF CHANHASSEN 90 City Center Drive, POBox 147 ChanhiWen, Minnesota 55317 Phone 612.9311900 General Fax 612.9315739 Engineering Fax 612.9319152 DubHe Safety Fax 612.934.2524 Wéb www.ci.chanhassen.mn.us &, MEMORANDUM TO: Mayor City Council FROM: Lori Haak, Water Resources Coordinator DATE: November 8,2000 RE: Acquisition of Lot 11, Block 1 Shadowmere Addition - 500 Bighorn Drive BACKGROUND Shadowmere is a subdivision consisting of27 single-family residential lots on the west side of Lotus Lake. The subdivision received final plat approval from the Chanhassen City Council on August 17, 1987. Lot 11 is an L-shaped riparian lot in the northeast comer of the subdivision that has not yet been developed. The lot is approximately 33,840 square feet (0.78 acres) in size, During the City review process, Lot 11 Wás deemed buildable. The purpose of this memorandum and presentation is to determine whether staff should pursue acquisition of the above parcel due to the factors outlined below. Existing Features Lot 11 contains a storm water pond that was constructed in conjunction with the subdivision and a creek that runs along the north side of the lots north of Bighorn Drive. The lot has approximately 85 feet oflakeshore. According to City maps, the area closest to the Bighorn Drive cul-de-sac may meet the criteria for a bluff (a rise of at least 25 feet above the toe of the bluff and the grade of the slope ITom the toe of the bluff to a point 25 feet or more above the toe of the bluff averages 30% or more). ANALYSIS In July 2000, the owner of this parcel approached the City ofChanhassen to inquire about the setbacks that structures upon the lot are required to maintain. Investigation revealed that a principal structure (such as a home) on Lot 11 would have to meet at least the following requirements: I. The principal structure must meet a 75' setback ITom the Ordinary High Water Level (OHW) of Lotus Lake (896.3); e City O(Cbilllbassf1l. A frowin[ community with cleau li1kes, (fuality schools. a channinf downtown, thrivinfr businesses. and betl/ltifùl fHtrks. A çrreat ,.,Iaee to /;1'(, work. and n{¡¡lI November 8, 2000 Page 2 2. The low opening ofthe principal structure must be at least 2' above the 100-year elevation for the pond, the overflow elevation for the creek or the OHW for Lotus Lake, whichever is greater. It appears that this would require a large amount of fill; 3. No structure (except a driveway) may be located within the drainage and utility easement that encompasses at least 50% of the lot; 4. Structures must maintain a 50' setback from the centerline of the creek that runs across a portion of the property; and 5. Structures must maintain all standard setbacks (30' front yard, 10' side yard). (There is no setback requirement from storm water basins.) If the area closest to the Bighorn Drive cul-de-sac is bluff, any structures are prohibited on the bluff and must be set back at least 30 feet from the top, toe and side of the bluff. It should be noted that, at the time of final plat approval, a 50' setback from the centerline ofthe creek was not mentioned. However, the staff report from May 13, 1987 states "the plat has identified a 'creek slope line' through Lots 1 through 11. This is the applicant's self imposed setback to be included in private covenants. However, it is necessary to retain a drainage easement over the area so that no building activity occurs below this line." According to plans on file, the creek slope line is just over 50' from the center ofthe creek. Applying the now- standard 50' setback from the centerline of the creek would not be more constraining than what was originally approved. Once the above requirements are met, there is just enough room to place a 60' by 60' house pad on the lot. Access to the lot could only occur between the storm water pond (on the west) and the eastern property line. Any driveway would be located almost entirely within the drainage and utility easement. "Lots]] and ]2, I think some of us that have been down there long enough wi1l see that that's very, very low ground. If you're going to get a house in there you're going to have to be building, I would say build up I I and 12. Basically when you build up you have to have some major consideration on the run-off going over in the property directly north from there. My concerns are basically the same as the people who talked ahead of me. The fact that the run-off and drainage wi1l have a problem on that creek." Roger Smith, 606 Carver Beach Road, Chanhassen City Council Meeting minutes, June I, 1987 The above excerpt from the City Council minutes suggests two things about Lot 11: 1. The lot is very low and probably does not have soils suitable for building; and 2. If the building pad is built up to meet City standards, the path of storm water runoff from the lot should be considered. According to conversations between the property owner and City staff, a considerable amount of soil correction may be necessary to achieve an acceptable building pad on the lot. Surface Water Management Plan (SWMP) The SWMP was developed as a "tool to protect, preserve and enhance [Chanhassen's] water resources. The plan identifies from a regional perspective the storm water quantity and quality improvements necessary to allow future development to take place and minimize its impact to downstream waterbodies" (page I-I). Lotus Lake is an aesthetic and recreational amenity to the November 8, 2000 Page 3 City of Chanhassen. The protection of the lake's water quality has been identified as important to the City Council, the residents ofChanhassen and the future of this community. Subwatershed According to the SWMP, this property lies within the LL-AIO subwatershed for Lotus Lake. The AlO subwatershed is Lotus Lake's largest subwatershed (over twice the size of the second largest subwatershed) with its all of its 355 acres draining to the lake. Sub- Size watershed Area (ac) Rank I 73.6 5 2 64.4 8 3 89.9 3 4 72.8 6 5 46.4 9 6 81.9 4 7 123.8 2 8 39.5 II 9 68.2 7 10 354.7 I II 46.3 10 Lotus Lake 237.7 TOTAL t,299.2 Almost all storm water from the subwatershed enters Lotus Lake through the creek running through Lot 11, Block I Shadowmere. Proposed Storm Water Management Components The SWMP proposes a storm water nutrient trap (LL-PI0.17) along the length of Bighorn Drive from Lot 6 through Lot 11. The specifications for the proposed pond are shown below. Normal Pond # Pond TVDe Water Level LL-P I 0.17 Nutrient Trap 900.0 feet Pond Area Wet Outflow P- P-Removal at NWL Volume Concentration Efficiency 0.8 acres 3.2 ac-ft 133 Dub 72.0% Since Lot 11 is only 0.78 acres in size, it would not be able to accommodate the entire pond as proposed in the SWMP. Acquisition of the lot would allow the current pond to be enlarged to accommodate more storm water. An enlarged (or additional) pond would allow nutrients and sediment from the creek and from runoff ITom Bighorn Drive to settle out prior to discharge into Lotus Lake. Following is a suggested prioritization for the proposed new sediment and nutrient traps in Lotus Lake. November 8, 2000 Page 4 Rankin!! First Second Third Fourth ImDrovement LL-P7.3, LL-P7.5 and LL-P3.2 LL-PIO.I7, LL-P9.2, LL-P6.6 and LL-P2.2 LL-P2.4 and LL-P6.7 LL-P2. I, LL-P2.5, LL-P8.1 and LL-P8.2 Pond LL-PI 0.17 has a suggested prioritization of second. Funding The Water Resources Coordinator budgets approximately $70,000 per year for the acquisition of properties related to the goals of the SWMP. Thus far this year, no other properties have been acquired, but a portion of the budget has been spent on property taxes. The estimated market value of this lot is $72,000. (The actual market value of the lot has not been determined. Likewise, the City has not yet contacted the owner to inquire about his asking price.) Funds needed in excess of the amount budgeted for the year 2000 would come from the general SWMP Fund (720). Since the SWMP Fund is supported by water quantity and water quality connection charges and storm water utility fees, this proposal would not affect the City's overall budget. If, after acquiring the lot, the City proposed the construction or enlargement of a storm water pond, the City would budget for the project in conjunction with the annual budget. Staff does not anticipate proposing a project for this location in 200 I. RECOMMENDATION Staff recommends the Council instruct staff to pursue acquisition of Lot II, Block I of Shadowmere for the following reasons: I) Lotus Lake is an aesthetic and recreational amenity to the City of Chanhassen. The protection of the lake's water quality has been identified as important to the City Council, the residents ofChanhassen and the future of this community. 2) The AIO subwatershed is Lotus Lake's largest subwatershed with its all of its 355 acres draining to the lake through Lot II, Block I Shadowmere. Acquisition of the lot would allow for the expansion of the existing storm water pond and/or the addition of another storm water pond. This would improve the quality of water being discharged into Lotus Lake. 3) The SWMP proposes a storm water nutrient trap (LL-PIO.l7) along the length of Bighorn Drive from Lot 6 through Lot 11. Acquisition of the lot would allow the City to address the goals of the SWMP. 4) Access to the buildable portion of the lot would have to occur between the storm water pond (on the west) and the eastern property line, The driveway would be located almost entirely within a drainage and utility easement and the 50' creek setback. 5) Due to the unique characteristics of the site, meeting City standards while maintaining aesthetics would be difficult. November 8, 2000 Page 5 6) According to conversations between the property owner and City staff, a considerable amount of soil correction may be necessary to achieve an acceptable building pad on the lot. ATTACHMENTS 1. Location map 2. Preliminary Plat for Shadowmere 3. Preliminary Utility and Easement Plan for Shadowmere 4. Preliminary Grading and Drainage Plan for Shadowmere 5. Lot Lay-Out Plan for Shadowmere 6. 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