HomeMy WebLinkAboutDrainage Reports - 11/02/1993 (2)STORMWATER REVIEW COPY
Final Appmved Report
2 3 Dde
FINAL STORM DRAINAGE
AND
EROSION CONTROL REPORT
COBBLESTONE CORNERS
PREPARED
FOR
DUNLAP - SEIER
c/o ROBB, BRENNER AND BRELIG, INC.
PREPARED
BY
STEWART & ASSOCIATES, INC.
103 SOUTH MELDRUM STREET
FORT COLLINS, COLORADO 80521
303/482-9331
OCTOBER 27, 1993
FINAL STORM DRAINAGE
AND
EROSION CONTROL REPORT
COBBLESTONE CORNERS
SITE LOCATION AND DESCRIPTION:
Cobblestone Corners is located in the Southeast 'a of the Northeast ; of
Section 34, Township 7 North, Range 69 West, of the Sixth P.M., Fort Collins,
Colorado. The site lies to the west of South Shields Street and is about one —
quarter (',—) mile south of West Horsetooth Road. The net site consists of five
(5) acres which is presently pasture land.
The site is located in the Foothills Drainage Basin. Historic drainage
on the site is from west to east and then north along the.west borrow ditch
of South Shields Street.
The existing borrow ditch along the west side of South Shields Street
has a high point about 300 feet south of Wabash Street. From this high point,
it drains north to Horsetooth Road.
The Pleasant Valley and Lake Canal Ditch, which runs from north to south,
lies about 400 feet west of the site. The area between the site and the
Pleasant Valley and Lake Canal Ditch is pasture land, and it drains from west
to east and will be a source of offsite flow through the Cobblestone Corners
site. There will be no offsite flow from the large lots in Skyline Acres,
a subdivision located north of Cobblestone Corners, and there also will be
no offsite flows from the south.
PROPOSED DEVELOPED SITE:
City of Fort Collins Storm Drainage Design Criteria shall be used for
design of site drainage. The proposed development will be a planned unit
development of duplexes and four—plexes. Storm water runoff will be carried
in the private driveway and swales from west to east through the development
and then into a detention pond at the east end of the site. The Foothills
Basin Drainage Master.Pl.an indicates detention facilities are to be used in
this area and that outflow is to be north to the Shields and Horsetooth
intersection. There..is an existing 36—inch storm sewer extended about 300
feet south of Horsetooth Road on the west side of Shields Street.
The Cobblestone Corners site is included in the Preliminary Master Drainage
Study For Mountainridge P.U.D., prepared by RBD in 1992. This.study shows
the Cobblestone Corners site draining north along Shields to Horsetooth, as
we have done and as the Foothills Study proposed. A copy of the proposed
Mountain Ridge development is included with this report.
The detention pond is designed to contain the runoff volume difference
between the 2—year historic flow and the 100—year developed flow for the gross
area of the site, which is 5.50 acres, including half of Wabash Street. The
pond release rate is the 2—year historic runoff, which is 1.21 c.f.s. The S
release will be through.a restricted outlet and then.piped to the west borrow
ditch of South Shields Street.
Cobblestone Corners/Page 2
Some minor regrading of approximately 400 feet of this ditch to the north
of the site will be necessary to provide a positive outfall. This regraded
borrow ditch shall be reseeded with rye grass and straw mulched. Runoff from
the north half of Wabash Street will enter the detention pond through a concrete
sidewalk culvert located'in the north curb line and 35 feet west of Shields
Street. This culvert location west of the curb return was necessary so that
the gutter flow line would not be below the detention pond high water line.
A 15—inch concrete culvert will be placed in the west borrow ditch of Shields
Street .under the Wabash to Shields connection. This culvert will carry borrow
ditch flows which drain north from the high point located about 300 feet south
of Wabash Street. This culvert is sized to carry the existing 10—year flow
from the offsite undeveloped basin lying south of the centerline of Wabash
Street. This pipe is proposed to be temporary, since the developed flows south
of Wabash Street are proposed to be carried south to a future detention pond.
Offsite flows from the 4.8 acre undeveloped tract lying west of Cobblestone
Corners will run between lots in drainage easements to Cobble Court, which
will carry the flow to the detention pond. The quantity of this offsite flow
is 1.25 c.f.s..,for a 2—year storm and 4.8 c.f.s. for a 100—year storm. The
Mountain Ridge plan proposes that developed flows from this area will be
directed to the southeast to a regional detention pond.
Overflow of the detention pond will be at the northeast corner of the
pond and will be into the west borrow ditch of Shields Street. A grass —lined
spillway will be constructed at the overflow site. The high water elevation
of the pond will be a minimum of 2.5 feet below the lowest building opening.
There.are grassed drain swales proposed in the open spaces along the north
side of the project and south of Lots 13 through 18. These swales are on slopes
of l percent and 1.7 percent. These grassed swales in the open areas will
be maintained by the Cobblestone Corners homeowners' association, and, since
-there will be very little runoff in these swales (the most water will be from
irrigation), no concrete pans are to be installed.
EROSION CONTROL:
The site is located in a moderate rainfall erodibility zone and also in
a moderate wind erodibility zone.
The detention pond will be used as a sediment trap and, immediately after
grading of the detention pond and streets, a gravel filter shall be placed
over the pond outlet.-,..The..existing vegetation, which amounts to about 90
percent ground cover,; will be left on Lots 1 through 14. The detention pond
area will be seeded with annual rye grass and straw mulched immediately after
grading and installation of the sediment trap.
The rainfall erosion control procedures and installation of curbs will
provide adequate wind erosion control.
Th' 'nage and osio�Control Report was prepared by: %`��•• °•��'rys'd
Phillip Robinson, P.E. & L.S.
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PH. 482-9331 FAX 482-9382
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PH. 482-9331 FAX 482-9382
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VELOCITY IN FEET�PER SECOND
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FIGURE 3-2. _.ESTIMATE OF AVERAGE FLOW VELOCITY, FOR
USE WITH THE RATIONAL FORMULA.
MOST FREQUENTLY OCCURRING "UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFERENCE: "Urban Hydrology For Small Watersheds" Technical
Release No. 55, USDA, SCS -Jan. 1975.
5 -1-84
URBAN DRAINAGE & FLOOD CONTROL DISTRICT
-.COMPUTATIONS
Stewart & Associates,, Inc., m s. mELDRum st Ft. Collins, CO 80521 (303) 482-9331
Date /435JClient:— TZQ n 10a , Se Jer- Sheet No. of
Chkd By:— Date— Project:— C uales -ie Cor-1 L.A/abojrA
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RAINFALL ,PERFORMANCE -STANDARD
EVALUATION'
PROJECT:
coggL�$iONE
cURivERS
P(JD
STANDARD FORM
COMPLETED
-----------------------------f-----------------------`-j------
BY: p!(z
DATE: 30
DEVELOPED
ERODIBILITY
Asb
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SUBBASIN
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EFFECTiVEIIESS CALCULATIOIIS
--------------------------------------------------------------=--------
PROJECT: C•OODLESTONE CORNERS Pv0 STANDARD FORM a
COMPLETED 0Y: p/ N DATE: 0 3
Erosion Control
C-Factor
P-Factor.
Method
Value
Value Comment
------------- ---------------------------------------------
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to __..-
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------------------------------
MAJOR PS. SUB AREA
---------------------------------------
BASIN
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BASIN
(Ac)
CALCULATIOIIS
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--------------------------------------- --------------------------------i
IIU I /SF-0: 1909
CONSTRUCTION SEQUENCE
PROJECT:. C0axrFSTonie orz 1�'5 wr7 STANDARD FORM C
SEOUENCE. FOR 1993-9¢ ONLY: COMPLETED BY: PJ)z GATE: 30 3
Imitate by use of m 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 93 ?4-
----------------------- MONTH,* S ._ o n
OVERLOT GRADING / D 1 s I F I NI
M s I T I
__ _� T7._-__t�--- T---- T_--- ----T----I
-
WIND EROSION CONTROL
Soil Roughing
Perimeter Barrier
Additional Barriers
Vegetative Methods
Soil Sealant
Other curbs
RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers
Sand Bags
B.are Soil Preparation.'
Contour Furrows
Terracing
Asphalt/Concrete Paving
Other
VEGETATIVE:
Permanent Seed Planting
Mulching/Sealant
Temporary Seed Planting
Sod Installation
Nettings/Mats/Blankets
Other
.--------------------------------1____�
I I
T
t
a
iTRUCTURES: INSTALLED BY MAINTAINED BY
'EGETATION/MULCHING CONTRACTOR ,>
IATE SUBMITTED APPROVED BY CITY OF FORT COLLINS ON
IDI,-C:1989
STEWART&ASSOCIATES 103 PH. S. 3 DRUM,FAX FORT COLLINS, CO 80521
82
Consulting Engineers and Surveyors
By: p) R Date: 1 4 3 Client: D U n low - se l er- Sheet No. _ of
Project. Co �>b )es +c he_ C o E5 .
Subject:__ �ros)on �G^�►o[ CaS'f
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