HomeMy WebLinkAboutSite Certifications - 08/29/2013LR�Opgm
ENGINEERING
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Letter
238 WALNUT STREET, SUITE 200
FORT COLLINS. CO 80524
970.420.5345 of Transmittal:
TO:
JAY BARBER (CITY OF FORT COWNS STORMWATER)
FROM:
JOHN GOOCH
DATE:
AUGUST 29, 2013
PROJECT. •
OPIUM CREEK FARM NORTH. FIUNC NO.3
C
PROJECT NO:
600-005
RE:
DRAINAGE CERTIFICATION
We are transmMnr the following:
✓ 1 copy (signed & sealed) of the Drainage Certification
THANK YOU,
JOHN GOOCH, PE
ASPEN ENGINEERING
CC: FILE
SC GROUP INVESTMENTS
ENGINEERING
May 29, 2013
Mr. Jay Barber
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522
Re: Drainage Certification for Spring Creek Park (Spring Creek Farms North Filing No. 3)
Dear Mr. Barber,
The purpose of this letter is to provide the grading certification for Spring Creek Farms North Filing No. 3,
which is located southwest of the Police Facility in Fort Collins, Colorado.
Aspen Engineering reviewed the record survey, prepared by Edmonds Land Surveying, Inc. on August 16,
2013, and also visited the site on several occasions between August 17t' and August 27, 2013. Based on the
provided record survey and visual observation, Aspen Engineering asserts that the proposed grading appears to
meet the intent of the approved grading and drainage plan, with the exception of some of the contouring along
the west bank of Pond 200 being steeper and located further west than shown in the approved plans. Aspen
spoke with and provided Wes Lamarque an exhibit showing the asbuilt contours versus the proposed contours
for Pond 200 to confirm the slight difference in contouring was acceptable. Mr. Lamarque confirmed the pond
contours were acceptable.
Aspen has provided the asbuilt rating curve for Pond 200, which provides for a water quality/detention volume
of 2.51 acre-feet at elevation 4940.15, versus the proposed detention volume of 2.37 acre-feet at elevation
4940.05. It's important to note that because the west side of the park/pond was required to be raised 1.20' to
accommodate City of Fort Collins cover requirements over the two 18" storm sewer pipes, the free -board (top
of weir) elevation of the pond was increased from 4940.05 up to 4940.50. Accordingly, the flowline elevation
of the overflow weir was also raised from 4939.70 to 4940.15, thus maintaining the 0.35' of weir height per the
approved plans. This change has little to no impact on the park/pond, with the exception of the pond volume
capacity increasing, which is a benefit to future development adjacent to the park/pond (west of Joseph Allen
Drive). Please refer to Exhibits 'A' and 'B' for the asbuilt Pond 200 contours and the asbuilt rating curve.
Grading within the park/pond area appears to provide positive conveyance of storm water to the southeast
comer of the park/pond, in accordance with the approved grading and drainage plan. Grades within the
park/pond area vary from approximately 1.2% to 28%, thus providing positive conveyance of stormwater runoff
to the proposed water quality/ detention pond outlet structure, located in the southeast comer of the park/pond.
The water quality/ detention pond outlet structure appears to have been constructed correctly and meets the
intent of the approved plans and detail for the structure. Please refer to Exhibit `C' for asbuilt information on
the structure.
Overall, the grading and.drainage for Pond 200 appears to meet the intent of the approved plans for the Spring
Creek Farms Filing No. 3 project, with Aspen submitting this certification for the City of Fort Collins' records.
Please do not hesitate to contact me with any questions.
Sincerely,
FtYA
``OZ51
1-19-13
JOHN GOOCH, PE
ASPEN ENGINEERING
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Spring Creek Park Asbuilt.Rating Curve 8-29-13.txt
SPRING CREEK FARMS NORTH FILING NO. 3
Pond 200 ASBUILT RATING CURVE
JRG 8-29-13
PROPOSED 100-YR VOLUME = 2.37 ACRE-FEET at ELEVATION 4940.05
PROVIDED 100-YR VOLUME = 2.51 ACRE-FEET AT ELEVATION 4940.15
THE 100-YR VOLUME OF 2.51 ACRE-FEET FOR POND 200 is achieved at elevation
4940.15.
COVER REQUIREMENTS OVER THE TWO 18" RCP PIPES REQUIRED THE WEST..SIDE-OF THE
PARK/POND
BE RAISED UP, THUS INCREASING THE FREE-BOARD•ELEVATION FROM 4940.05 TO
4940.50..THEREFORE,
THE 100-YEAR WSEL INCREASED FROM 4940.05 TO 4940.1, THUS MAINTAINING THE 0.35'
OF
FREEBOARD CALLED FOR IN THE APPROVED PLANS.
s
THE 2.51 ACRE-FEET ASBUILT VOLUME WILL BE CARRIED FORWARD IN THE DESIGN FOR
THE SPRING CREEK
FARMS NORTH FILING NO. 4 PROJECT AS THE STORAGE CAPACITY OF POND 200.
#units=Elevation,ft,Area,it2,voluine,acft,volume,acft
# Elev
Area
Cumml Avg Cumml
Conic
# ft -
ft2
acft acft
4940.5000
42601.8423
2.8661
2.8319 2 S�jkr=i D
4940.0000
39468.0272
2.3951
2.36�
4939/.0000
34683.7275
1.5440
1.5105 0 ggga�5
4938.0000
29788.0447
0.8039
0.7712
4937,.0000
15838.8974
0.2802
0.2558 ,
4936.0000
.4164.8610
0.0506
0.0406
4935.0000
189.2940
0.0006
0.0004
4934-.7200
1.6710
.ti
0.0000
0.0000
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