HomeMy WebLinkAboutSite Certifications - 08/26/2016301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com
August 10, 2016
City of Fort Collins
281 N. College Avenue
Fort Collins, CO 80522
RE: Lakeview Subdivision
Detention Pond Certification
Dear Staff:
This letter is to verify detention pond volume and positive drainage for the detention pond constructed
at Lakeview Subdivision. The pond was surveyed in August 10, 2016 by Northern Engineering Services;
an as‐built topographic exhibit is attached.
The detention pond was originally designed with the Lakeview Subdivision, in accordance with
agreements with staff, with infiltration basins to treat small storm events with high frequency. After
construction, it was found that groundwater was seasonally high and higher than found in design of the
subdivision causing stormwater to pool in the bottom of the pond without the benefit of infiltration.
Although the ponding effect mentioned above would be advantageous for downstream water quality,
the Lakeview Subdivision residents and City requested that the pond be regraded with positive slope to
the outfall of the pond. This has been accomplished through the installation of concrete pans as shown
on the attached exhibit.
As currently constructed, this detention pond has adequate water quality and stormwater storage per
the attached stage storage calculations. The pan also has positive slope from the concrete forebay
structures to the pond outlet structure to the southeast of the pond.
Please feel free to contact me with any questions you may have.
Sincerely
NORTHERN ENGINEERING
Ryan Banning, PE
Project Manager
Lakeview Subdivision
665-002 Volume per King Survey Field Data 5-12-15
Fort Collins, Colorado Revised bottom by NES 8-10-16
R. Banning Date:8/11/2016
Pond No.:N/A
B3-3 ASBUILT VOLUME OKAY!!
100-yr
4.39 acft 4967.30 ft.
Design Storm WQCV
Required Volume=16772 ft 4962.44 ft.
Contour
Elevation (Y
values)
Contour
Area Depth SWMM Stage Incremental Volume Total Volume Total Volume
ft ft.ft ft ft acre-feet
4,960.70 0 0.00 0 0 0 0
4,961.00 942 0.30 -1.44 94 94 0.00
4,962.00 15800 1.00 -0.44 6860 6954 0.16
4,963.00 29778 1.00 0.56 22400 29354 0.67
4,964.00 33547 1.00 1.56 31612 60966 1.40
4,965.00 37272 1.00 2.56 35358 96324 2.21
4,966.00 41563 1.00 3.56 39359 135683 3.11
4,967.00 42843 1.00 4.56 42159 177842 4.08
4,967.70 45686 0.70 5.26 30949 208791 4.79
Design Point
Design Storm
Require Volume=
Stage - Storage Calculation
Project Number:
Project Location:
Calculations By:
Required Volume Water Surface Elevation (WSE)
4,962.00
4,963.00
4,964.00
4,965.00
4,966.00
4,967.00
4,968.00
4,969.00
-50000 0 50000 100000 150000 200000 250000
Co
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Cummulative Volume, cu. ft.
8/11/20161:46 PM
D:\Projects\665-002\Dwg\As-Builts\Drainage Cert\
665-002__Detention Pond_SWMM ASBUILT Revision.xlsm\Stage_Storage
EAST D
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ELDORADO
SPRINGS
SECOND FILING
SILVERWOOD VILLAGE
SECOND FILING
GE
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CHRIST CENTER
COMMUNITY CHURCH
FG=73.10
TF=73.77
A
LOT 30
FG=73.61
TF=74.28
A
LOT 29
FG=72.55
TF=73.22
A
LOT 31
FG=72.25
TF=72.92
A
LOT 32
FG=71.94
A
LOT 33
FG=72.08
TF=72.75
A
LOT 14
FG=72.38
TF=73.05
A
LOT 13
FG=72.68
TF=73.35
A
LOT 12
FG=72.98
TF=73.65
A
LOT 11
FG=73.28
TF=73.95
A
LOT 10
FG=73.57
TF=74.24
A
LOT 9
FG=73.99
TF=74.66
A
LOT 8
FG=74.81
TF=75.48
A
LOT 7
FG=74.83
TF=75.50
A
LOT 6
FG=74.71
TF=75.38
A
LOT 5
FG=75.26
TF=75.93
A
LOT 4
FG=75.76
TF=76.43
A
LOT 3
FG=76.75
TF=77.42
A
LOT 2
FG=77.15
TF=77.82
A
LOT 1
FG=76.96
TF=77.63
B
LOT 24
FG=76.55
TF=77.22
B
LOT 25
FG=75.81
TF=76.48
B
LOT 26
FG=74.58
TF=75.25
B
LOT 27
FG=73.90
TF=74.57
B
LOT 28
FG=75.86
TF=76.53
B
LOT 39
FG=74.46
TF=75.13
B
LOT 38
FG=73.45
TF=74.12
B
LOT 37
B
LOT 36
FG=74.15
A
LOT 41
FG=75.63
TF=76.30
A
LOT 40
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LEGEND:
NOTES:
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
before you dig.Call
R
A-A
NORTH
G1
G2
KEYMAP
MATCHLINE-SEE SHEET G2
NOTE: ALL PROPOSED STREETS ARE PRIVATE
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24" HDPE
@ 0.50%
PR
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LOT 22LOT 23
TRACT B
EASTBOROUGH
INLET 1-1
STA 10+36.53
N: 117490.59
E: 200786.17
FES 1
STA 10+00.00
N: 117483.56
E: 200822.01
4945
4950
4955
4960
4965
4970
4975
4980
4985
4990
4945
4950
4955
4960
4965
4970
4975
4980
4985
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PRIVATE STORM SEWER
TRACT B
ELDORADO
SPRINGS
SECOND FILING
LOT 20
LOT 19
LOT 18
SANITARY LINE A
SEE SHEET SS1
BROOKWOOD DRIVE
11.26 LF
18" HDPE
@ 0.84%
34.28 LF 18" HDPE @ 0.50%
OUTLET 2-1
STA 10+45.55
N: 117446.64
E: 201225.58
FES 2
STA 10+00.00
N: 117401.14
E: 201227.67
12'' DOME GRATE
STA 10+34.28
N: 117435.39
E: 201226.09
ST 2
4945
4950
4955
4960
4965
4970
4975
4980
4985
4990
4945
4950
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4960
4965
4970
4975
4980
4985
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10+0011+0011+50
34.28 LF
18" HDPE
@ 0.50%
PRIVATE STORM SEWER
2.00
1.50
1.25
6" CURB
@ SPILL
ELEV
12" DOME
GRATE
ON RISER
PIPE
@ 100-YR
WSEL
FRONT OF
WALL @
SPILL ELEV
OPEN
FRONT
@ 100-YR WSEL
18"X18"X4"
CONC
PAD
KEYMAP
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LEGEND:
NOTES:
W
G
T
E/T/C
ST
S
W
SS
E
W
INLET SCHEDULE
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
before you dig.Call
R
PROFILE SCALE:
NORTH
STORM SEWER 1
ST1
PROFILE SCALE:
STORM SEWER 2
ST2
NORTH
RELIEF OUTLET DETAIL
(REDUCES FREQUENCY OF SPILL ABOVE 100-YEAR EVENT)
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