2a. Acquisition of 6921 Yuma Drive, Carver Beach 1 1
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CITYOF
i
CHANHASSEN
''';14. ' 690 COULTER DRIVE • P.O. BOX 147 • CHANHASSEN, MINNESOTA 55317
(612) 937 -1900 • FAX (612) 937 -5739
Action by City Administrztor
Endorsed,_ U PUjA
MEMORANDUM t ��;':,r__` —'
Reia tc a
TO: Don Ashworth, City Manager ezc:,��
Dat, Sui.,; tte., to CommissloA
FROM: Paul Krauss, Planning Director pate su:.mitted to Council
1 DATE: January 21, 1993 � ..
1 SUBJ: Potential Acquisition of Property Located At 6921 Yuma Drive, Carver Beach
1 Staff's involvement with this property originated with the owner's request for variances to make
this lot buildable. The parcel in question is a lot of record that is severely impacted by the
I location of a wetland, public rights -of -way, `and utility lines which result in unusually small
usable area. While theoretically buildable with variances, significant questions have been raised
regarding on -site soil conditions, flood elevations and other matters pertaining to the low and wet
I nature of this parcel. Given these factors, plus conversations individually with a number of
members of the City Council, we thought it might be prudent to offer you some input regarding
potential acquisition of this property by the city for water retention and ponding.
1 As the Council is aware, the city's Surface Water Management Program is proceeding towards
undertaking several construction projects this spring. One of the project areas where we have
I already completed significant investigation includes the parcel in question. Thus, we are readily
able to present to you information regarding how this lot fits into the city's drainage and water
quality protection program. I might add that 1 believe having this type of planning available is
I another example of the wisdom of the city's investment and commitment to this program. In
an attached memorandum, the Assistant City Engineer details how this parcel may reasonably fit
into the city's storm water and water quality efforts. What we have concluded in general is that
I there is some short term benefit in providing an ability to create an additional water
impoundment area. At some point in the future when area streets in Carver Beach are improved
and provided with curb, gutter and storm sewer, the importance of this site will increase. At that
1 point, we will be able to direct substantial quantities of storm water into impoundment basins that
could be constructed on this site which would result in a net improvement in water quality for
water flowing out to Lotus Lake. The Carver Beach area offers few opportunities to obtain open
1 land for water protection purposes. This site represents one of the few remaining undeveloped
parcels that could reasonably be put to this use. In summary, it may be reasonable for the city
to consider acquisition of this property should the opportunity arise.
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PRINTED ON RECYCLED PAPER
1
Don Ashworth
January 21, 1993
I Page 2
While we would encourage the City Council to look into this option, one note of caution is in
' order. As the Council is aware from staff's comments during budgetary reviews of the past two
years, we believe that the SWMP program is under funded. We have agreed that the program
needs to demonstrate its utility to the community by offering a number of successes and we are
prepared to do so. However, as originally outlined, this program would have generated enough
funds for acquisition of individual parcels. Unfortunately, this is not the case and SWMP
funding levels are going to be sorely pressed to meet the demands of undertaking the projects
' we have committed to in 1993. Therefore, it is staff's recommendation that if City Council
wishes to proceed with acquisition of this property, that we look into utilizing some other source
of funds so that the 1993 SWMP fund can continue unimpeded.
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CITYOF
CHANHASSEN
690 COULTER DRIVE • P.O. BOX 147 • CHANHASSEN, MINNESOTA 55317
(612) 937 -1900 • FAX (612) 937 -5739 1
MEMORANDUM 1
TO: Paul Krauss, Planning Director 1
FROM: Dave Hempel, Assistant City Engineer 1 (4 4
�
DATE: January 21, 1993
SUBJ: Potential Acquisition of Property in Carver Beach for Storm Water Quality 1
Purposes, Carver Beach Lots 2919 -2943 and Lots 2877 -2897
File No. PW -201F
1
As requested, staff has reviewed the potential usage of the above - referenced lots for
additional storm water ponding facilities in the Carver Beach neighborhood. Back in 1
September of 1992 the City authorized the report on storm water quality improvements for
Lotus Lake and Lake Riley drainage areas. The report was prepared by Bonestroo, Rosene,
Anderlik & Associates (BRA) which described a number of storm water improvements.
One of the projects includes modifying the wetland which encroaches upon the subject
parcel. I have attached three excerpts from the report on storm water quality improvements
prepared by BRA. These excerpts describe modifications to a wooded natural depression
to improve storm water quality prior to discharging into Lotus Lake.
•
The report on page 28 (Attachment No. 2) proposes improvements at this ponding location 1
(subject site) may not have as substantial an impact on storm water quality as the other
ponds proposed downstream However, from a cost - effectiveness standpoint, the proposed
improvements at this location (LL-P10.14) are less expensive than the other proposed
improvements. As described on excerpt page 30 (Attachment No. 3), the existing pond LL-
P10.14 is a natural depression and contains heavy vegetation with no ponding water and is
considered a natural wetland.
The proposed ponding improvements include construction of an earth berm of
approximately three to eight feet in height across the southerly portion of the wetland.
Construction of the berm would also include an outlet structure to control the water
elevation to approximately three feet in depth. The proposed high water elevation for a
100 -year storm event is calculated at 929.0 feet. According to City ordinance, the house
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to 41 PRINTED ON RECYCLED PAPER
111
Paul Krauss
January 21, 1993
Page 2
would have to be a minimum of two feet above the 100 -year storm event or three feet above
the water table, whichever is greater.
Acquisition of the subject parcel in Carver Beach may be of some benefit to the proposed
storm water improvement project. Part of the project will involve encroachment upon the
subject parcels where no drainage or utility easements exist. Eventually, if the City proceeds
with this project, the appropriate drainage utility easements will have to be acquired from
the existing property owners. Therefore, if the City was to outright purchase the lot at this
time, it would be at some cost savings down the road in lieu of acquiring the drainage /utility
easements at that time. In addition, the City would be able to utilize a portion of the lot
for pretreatment or sedimentation basin prior to discharging storm runoff into the wetland
area. This would provide a higher degree of water quality treatment prior to discharging
storm runoff into the wetland.
The City storm water consultant, Mr. Ismael Martinez of Bonestroo, Rosene, Anderlik &
Associates (BRA), also has reviewed this proposal. Mr. Martinez has also indicated that a
portion of the lot may be utilized for future storm water treatment from the neighborhood
streets. The existing streets, Woodhill Drive and Yuma Drive, are currently built to rural -
type street construction without curb and gutter or storm sewer facilities. The drainage is
basically over land via streets and lawns. There is currently a small detention basin located
south of Woodhill Drive to accommodate most of the storm runoff from Woodhill Drive.
However, storm runoff from Yuma Drive is directly discharged into the natural wooded
wetlands adjacent to and over a portion of the subject property.
In conclusion, acquisition of this parcel would be of some benefit to the City in the long run.
A portion of the parcel could be utilized as a pretreatment pond prior to discharging runoff
into the wetland from Yuma Drive. Eventually the City will be required to acquire a
drainage easement over this parcel if the prescribed storm water improvements are to be
completed.
jms
Attachment: 1. Location map.
2. & 3. Excerpts from report on storm water quality
improvements dated September, 1992.
c: Charles Folch, City Engineer
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Scale in feet
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ATTACHMENT 1
comm. 39309
Water Quality Improvement Alternatives
Following the creation of a stormwater quality model for ultimate conditions in the
drainage area, the most effective locations for water quality improvements in the area were
determined. The main results of this initial analysis are as follows:
1. Water bodies LL- P10.11, LL- P10.14, and LL- P10.16 were identified as the best
locations for improvements. The direct drainage area to each of these ponds is 78.3 ;
acres, 23.4 acres, and 66.0 acres, respectively.
2. Because of the total drainage area to Pond LL- P10.16 (66 acres direct drainage +
260.7 indirect drainage), any improvements performed at this pond will have a
substantial impact in stormwater quality.
r
3. The second best location for improvements in terms of total phosphorus reduction was
Pond LL- P10.11. This pond has a total drainage area of 133.1 acres.
provements at Pond LL- P10.14 would not have as substantial an impact on
stormwater quality as Ponds LL- P10.16 and LL- P10.11. On the other hand,
improvements at LL- P10.14 are less expensive than those at Ponds LL- P10.16 and LL-
P10.11.
5. Excavation of Pond LL- P10.17 would be expensive. Nevertheless, Pond LL- P10.17
would provide direct treatment of an extra 19.7 acres and would add one more level
of treatment to the runoff coming from Pond LL- P10.16 before entering Lotus Lake.
The added benefit of raising the normal water level of Pond LL- P10.16 four feet instead
of three feet does not justify the extra cost of the higher and bigger earth berm needed to
39309IV - 28 - ATTACHMENT 2
pro pond LIrP10.11
: * Keep invert elevation of 48 -inch, RCP inlet 950 5 ft.) 949.8 ft.
• 24-inch outlet culvert at 950.5 �� event = 956.0 ft.
* High water level for 100 -y
* Total wet volume = 3.0 ac. ft.
* Skimmer structure at outlet.
Natural depression and channel heavily vegetated with no
Pond LL-P10.14 * p
ponding water. Natural wetland.
propo Pond LrP10.1
* Earthen berm from elevation 924 ft. to 932 ft. 927.0 ft).
18 -inch RCP outlet at elevation 927.0 =
New wet pond with 3 ft. of ponding water.
* High water level for 100 -year storm event = 929.0 ft.
* Total Wet Volume = 6.5 ac. ft.
Pond surface area = 2.4 Acres.
* Outlet skimmer structure.
E pond I,IrP10.16: * 18 -inch outlet culvert appproximate1' at 921.0 ft.
* High water level for 100 -year storm event = 925.6
* 200 - foot earth berm at 925.0 ft.
* Total wet volume = 1.8 ac. ft.
Pond surface area = 1.0 acres.
* Basement of lowest house = 938 ft.
Pond LIrP10.16: * 36 -inch outlet culvert at 924.0 ft.(NWL
= 92.0 ft).
Pra ryos� d * High water level for 100 -year storm event = 927.1 ft.
* Earth berm at 929 ft.
* Total wet volume = 11.2 ac. ft.
Pond surface area = 2.6 acres.
* Outlet skimmer structure.
Existi Pond I, IrP10.17:
* Natural channel into Lotus Lake.
* Man -made pond with 3.2 ac. ft. of wet volume, 0.8 acres of
p r o d I,I
.-- -- pond rP10.17• area and 4.0 ft. of average depth.
* Riprapped, broad - crested weir outlet into Lotus Lake.
* Submerged berm with vegetation to trap nutrients.
- 30 -
39309IV
ATTACHMENT 3
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