HomeMy WebLinkAboutDrainage Reports - 10/24/1994 (2)FINAL DRAINAGE REPORT
FOR
LINDIMER SUBDIVISION
JULY 12, 1994
STEWART & ASSOCIATES, INC.
103 SOUTH MELDRUM STREET
FORT COLLINS, COLORADO 80521
303/482-9331
STEWART&JkSSOCIATES
Consulting Engineers and Surveyors
July 12, 1994
Mr. Basil Hamdan
Storm Water Utility
City of Fort Collins
P.O. Box 580
Fort Collins, Colorado 80522
Dear Basil:
The following is the revised final drainage report for Lindimer Subdivision
which is located on Birmingham Drive in the Southeast I of Section 27, Township
7 North, Range 69 West of the 6th P.M. The site contains 4.30 acres and is
at the very south end of the Spring Creek Basin. It is bounded on the west
by the existing Rossborough Subdivison, on the northeast by the Pleasant Valley
and Lake Canal and on the south by an existing horse stable. The site slopes
gently from southwest to northeast to the Pleasant Valley and Lake Canal.
Since the historic drainage has discharged into the Canal, the runoff actually
flows into the Foothills Drainage Basin, via the Canal, rather than into Spring
Creek.
Mr. Willis Smith of the Pleasant Valley and Lake Canal Company has signed
Sheets 1 and 5 of the Utility Plans giving approval to continue to discharge
into the Canal at the calculated two year historic runoff rate.
It is proposed to detain the difference between the 100—year developed
flows and the two—year historic flows. The present site is an existing grass
pasture. The proposed use is for a fifteen lot single—family detached
residential subdivision.
The calculated allowable discharge rate is 0.85 cubic feet per second.
Due to not detaining the rear yards of Lots 4, 5, 6 and 7, the discharge rate
has been reduced by 0.13 c.f.s. This change was required due to having to
raise the discharge pipes and the bottom of the two detention ponds. The
original pipes were found to be lower than the high water line of the Pleasant
Valley and Lake Canal. The developed 2—year, 10—year and 100—year flows are
2.86, 5.03 and 11.47 cubic feet per second respectively. The required detention
volume is 17,886 cubic feet. The storm water will be detained in two detention
ponds. Pond "A" for Sub —Basin "A" will have a volume of 12,448 cubic feet
and a discharge rate of 0.54 cubic feet per second. Pond "B" for Sub —Basin
"A" will have a volume of 5,840 cubic feet and a discharge rate of 0.18 cubic
feet per second.
James H. Stewart
and Associates. Inc.
103 S. Meldrum Street
P.O. Box 429
Ft. Collins, CO 80522
303/482-9331
Fax 303/482-9382
Lindimer Subdivision
Page 2
It is proposed to carry the runoff to the two proposed detention ponds
on the surface in the Birmingham Drive gutter and in two concrete pans. The
site was divided into two sub —basins, "A" and "B", which each have a detention
pond. The ponds are located in drainage easements in the rear of rather deep
lots. They will be maintained by the Lindimer Subdivision Homeowners
Association. Refer to the Protective Covenants for greater detail on the
maintenance responsibilities. The ponds will each discharge into the Pleasant
Valley and Lake Canal through a pipe laid through an earthen berm. Side yard
fences will not be allowed in the detention ponds. The owners will be allowed
to fence the rear of the detention ponds with a 6.0 foot high open —type fence
that allows water to flow through or under. A variance is requested for
freeboard for the detention ponds. Pond "A" has only 2% over the required
capacity, and Pond "B" has 2% greater capacity than the required. All of the
adjacent residences will have greater than 18 inches of freeboard.
Construction activities or homes should not create adverse hazards to
the irrigation ditch. The Pleasant Valley and Lake Canal is presently bordered
by numerous subdivisions as it traverses the City of Fort Collins. The
developer and builder will be responsible for keeping construction materials
out of the ditch. The quality of storm water runoff from existing developments
entering the ditch has not been an issue in the past. In the large storms,
the ponds will fill up and the turf in the rear yards will be able to filter
out some oils. In the minor storm or for nuisance flows, the filtering will
not happen since the flow will remain in the concrete pan. The City of Fort
Collins has not required treatment of storm water from residential developments.
This development is on the high side of the ditch so there should not
be seepage onto these lots. Seepage will only occur on the east, or low side,
where the headgates are located. There was no ground water encountered in
the soils report although the investigation was done before the irrigation
season. All of the ditch access is on the east side of the ditch.
The only offsite flows that enter the site are from the rear yards of
four lots in Rossborough, Third Filing, which are adjacent to Lots 11 through
15. That offsite flow will continue to sheet flow across Lots 11 through 15.
There are drainage easements between these lots. The runoff from the stable
property to the south drains east to the ditch and doesn't enter this site.
The site has a moderate wind erodibility and a high rainfall erodibility.
The existing ground cover is very good pasture, grass. Due.to the flat condition
of the site, there will be no overlot grading and, therefore, only the street
area will be disturbed. The two detention basins will be constructed prior
to the beginning of any earthwork. Pock filters will be placed on the discharge
pipes to create sedimentation basins.
To the best of my knowledge all design complies with the city of Fort
Collins Storm Drainage Criteria.
Lindimer Subdivision
Page 3
The runoff calculations, the
and drainage plan are included as
questions regarding this site or
Sincerely,
Richard A. Rutherford, P.E. & L.S
President
jrr
enclosures
detention pond mass diagram
a part of this report. If
this report, please call.
and the grading
you have any
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'STEWART&O6SOCIATES 10 82 9 3DIRUM, FAX FORT gOLLINS, CO 80521
Consulting Engineers and Surveyors
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RAINFALL PERFORMANCE STANDARD EVALUATION
--------------------------------------------------------
PROJECT: G /N D/M E,e SOIL 0IV IJ/o.v STANDARD FORM A
COMPLETED BY: g k DATE:
------------------------------------------------------------
DEVELOPED ERODIBILITYI
SUBBASIN ZONE
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HDI/SF-A:1939
(! 4;
EFFECTIVENESS CALCULATIONS
--------
PROJECT: Li�v oin� e,e .j'� sprvi.r� -=--------=---------------
o u STARUARU FORM B
COMPLETED BY: ��,e UATE: L ¢
Erosion Control
C-Factor
P-Factor.
Method
-------------------------------
Value
Value Comment
p,a C 6 Cameo v N
---------------------------
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--- PS ----------------
MAJOR SUB AREA
----------------------------
________________
BASIN
-----
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BASIN
(Ac)
CALCULATIUNS
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CONSTRUCTION SEQUENCE
PROJECT: LiA)viMEre .ru1sDiV1 ien) STANDARD FORM C
SEQUENCE. FOR 19 13 ONLY COMPLETED BY: ' r2 A;C DATE: G >t f3
indicate by use of a bar line or symbols when erosion control measures will be installed.
Major modifications to an approved schedule may require submitting a new schedule for
approval by,the City Engineer.
YEAR
MONTH
--------------------
OVERLOT GRADING
WIND EROSION CONTROL
Soil Roughing
Perimeter Barrier
Additional Barriers
Vegetative Methods
Soil Sealant
Other
RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers
Sand Bags
Bare Soil Preparation
Contour Furrows
Terracing
Asphalt/Concrete Paving
Other
VEGETATIVE:
Permanent Seed Planting
Mulching/Sealant
Temporary Seed Planting
Sod Installation
Nettings/Mats/Blankets
Other
STRUCTURES: INSTALLED BY
I J I FI MIA I I J I J
I----------------------------------
VEGETATION/MULCHING CONTRACTOR
DATE SUBMITTED
'DI/SF-C:1989
MAINTAINED BY
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APPROVED BY CITY OF FORT COLLINS ON
STEWART& SSOCWES
Consulting Engineers and Surveyors
June 16, 1994
Mr. Willis Smith
Pleasant Valley and Lake Canal Co.
2904 West Vine Drive
Fort Collins, Colorado 80521
Dear Mr. Smith:
This is regarding the storm water detention ponds in Lindimer Subdivision that
discharge into the Pleasant Valley and Lake Canal. We will be raising the .bottom
of the ponds and the outlet pipes to be higher than the high water line of the canal.
The rear yards of Lots 4, 5, 6 and 7 are adjacent to the canal; however, we had
designed a swale to carry the runoff from the rear yards to the detention ponds.
Due to the raising of the ponds, we are requesting approval to allow the rear yards
of the four lots to sheet flow into the canal without detention.
The area of the rear yards is 0.28 acres. The historic two-year runoff rate
is 0.13 cubic feet per second, and the developed two-year runoff rate is 0.35 cubic
feet per second. It is difficult to force the runoff in a swale to flow to the ponds
with a very flat percentage of slope.
In the major storm, there are two overflow structures that would allow controlled
spillways from the canal. One of the structures is just upstream from the Lindimer
Subdivision at Chelsea Court and Downing Court. The overflow structures will
help mitigate small areas that are allowed to flow into the canal undetained.
We have enclosed a copy of the Grading, Drainage and Erosion Control Plan for
Lindimer Subdivision that has the area included in the request shown in red. Thank
you for considering this request. If it is acceptable, please sign below.
Sincerely,
6L a. 62wztl�
Richard A. Rutherford, P.E. .& L.S.
President
jrr
cc: Mr. Mark Linde
Approved by:4�___/
Pleasant Valley and Lake Canal Co.
James H. Stewart
and Associates, Inc.
103 S. Iveldrum Street
P.O. Box 429
Ft, Collins. CO 80522
303/462.9331
Fax 303/482-9382
Date: : ,b - / -7—(7Y
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