HomeMy WebLinkAboutDrainage Reports - 11/05/1993STORMWATER REVIEW COPY
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FINAL DRAINAGE AND
EROSION CONTROL STUDY
FOR
817 SYCAMORE STREET
FORT COLLINS, COLORADO
1 October 29, 1993
Mr. Glen Schlueter
City of Fort Collins
Utility Services Stormwater
' 235 Mathews Street
Fort Collins, Colorado 80522
RE: Dolores Williams project Duplex site on Sycamore Street
' Drainage and Erosion Control Analysis
PROJECT NO.: 594-001
Dear Glen:
This letter report is in regard to the Dolores Williams. project at
' 817 Sycamore Street, and in response to earlier City comments and
concerns with on -site developed runoff. The project consist of the
construction of two duplex residential units, paving a portion of
t an existing alley, and providing parking for 4 vehicles. More
particular the site is lots 13 and 14 of the West Side Addition in
the City of Fort Collins. This site is also located within the Old
' Town Drainage Basin.
Drainage Concepts
' As mentioned above, this site is located within the Old Town
Drainage Basin. The Stormwater Utility Department has requested
that on -site detention be provided with this development. Attached
' are calculations of the existing and developed peak .flow rates for
this project. A detention pond has been designed in the northeast
corner of the site to provide detention for the difference between
the 2 year historic and the 2 year developed condition, as well as
' the difference between the 100 year historic and the 100 year.
developed condition. The F.A.A. method for determining pond size
was utilized.
' A outlet weir release structure will be constructed that will limit
offsite flows to 0.30 cfs for the 2 year event, and 1.11 cfs for
' the 100 year event, which are the peak flow rates for the historic
condition. A berm will also be constructed to provide an"additional
0.5' freeboard. The rational method was used to determine all
runoff values.
0
' The City Stormwater Utility policy for detention is that storage be
provided for the difference between the 2 year historic and the 100
' year developed.' A. variance is requested to deviate from the
standard policy and to allow the detention pond to function as
described above. This variance is requested due to the relative
size and impact of this project, existing flat topography in.the
area, and the lack of any storm sewer in the immediate area.
There is relatively little offsite flows associated with this lot.
t Direction of flows for the lot to the east of this project is
directed to the north and east of the existing and proposed alley.
The proposed grading of this project .will direct developed flows
' heading towards the detention pond. A relative high point towards
the southwest corner of this project tends to split the flows from
this lot to the north and south, so a small portion of this project
will be draining to the southwest, as existing. No impervious
' surfaces will be in this small area draining to the southwest
undetained. A small portion of the lot to the west of this project
drains towards this project, and has been included in the basin
calculations.
' Copies of all drainage calculation have been included as
attachments to this letter.
' Erosion Control
This site falls within the Moderate Rainfall trodibility Zone and
the Low Wind Erodibility Zone, as defined by the City of Fort
' Collins Erodibility Zone maps.
Per the attached calculations for erosion protection, the required
' performance standard for this site has been determined to be
approximately 78%. With the erosion control measures shown on the
plans, and the attached calculations, this site can achieve a
' performance standard of over 76%. Although this is 1.8% below the
required performance standard, I believe that the City of Fort
Collins Erosion control standards will be, for all intents and
purposes, achieved. Given the relative size of the project, the
' construction schedule should be short, and the time of exposure to
erosion should be minimal.
' Copies of the Erosion Control calculations have been included as
attachments to this letter. A separate letter has been sent to your
office regarding this clients obligation for a erosion control
' security deposit.
Conclusion
In conclusion, this site will conform to the requirements of the
,City Stormwater Utility for Drainage and Erosion Control. All.
construction should conform to the City of Fort Collins Standards
and Specifications.
Thank you for your time and consideration of this submittal.
Sincerely,
RBD Inc. Engineering Consultants
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DETENTION POND SIZING BY FAA _METHOD
=====_________________
DEVELOPED BY
' JAMES C.Y. GUO, PHD, P.E.
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF COLORADO AT DENVER
------------------------------
EXECUTED ON 10-29-1993 AT TIME 1103:09
PROJECT TITLE: 817 SYCAMORE STREET DUPLEX SITE 2 YEAR STORM
**** DRAINAGE BASIN DESCRIPTION
' BASIN ID NUMBER = 1.00
BASIN AREA (acre)= 0.48
RUNOFF COEF = 0.55
DESIGN RAINFALL STATISTICS
DESIGN RETURN PERIOD (YEARS) = 2.00
'INTENSITY(IN/HR)-DURATION(MIN) TABLE IS GIVEN
DURATION 5 10 20 30 40. 50 60 80 100 120 150 180
INTENSITY 3.2 2.6 1.9 1.5 1.3 1.1 1.0 0.8 0.7 0.6 0.5 0.4
***** POND OUTFLOW CHARACTERISTICS:
MAXIMUM ALLOWABLE RELEASE RATE _ .3 CFS
' OUTFLOW ADJUSTMENT FACTOR = .85
AVERAGE RELEASE RATE _ .255 CFS
AVERAGE RELEASE RATE = MAXIMUM RELEASE RATE * ADJUSTMENT FACTOR.
COMPUTATION OF POND SIZE
-----------------------------------------------------
RAINFALL RAINFALL INFLOW OUTFLOW REQUIRED
DURATION INTENSITY VOLUME VOLUME STORAGE
MINUTE INCH/HR ACRE -FT ACRE -FT ACRE -FT
----------------------------------------------------
' 0.00 0.00 0.00 0.00 0.00
5.00 3.22 0.01 0.00 0.00
10.00 2.57 0.01 0.00 0.01
15.00 2.22 0.01 0.01 0.01
' 20,00 1.87 0,01 0.01 0.01
25.00 1.68 0.02 0.01 0.01
30.00 1.49 0.02 0.01 0.01
35.00 1.37 0.02 0.01 0.01
40.00 1.25 0.02 0.01 0.00
45.00 1.17 0.02 0.02 0.00
-------------------------------------------------
THE REQUIRED POND SIZE = 6.938384E-03 ACRE -FT
'THE RAINFALL DURATION FOR TIE ABOVE POND STORAGE= 15 MINUTES
-------------
DETENTION POND SIZING BY FAA METHOD=====______
DEVELOPED BY - ..
' DAMES C.Y. GUO, PHD, P.E. -
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF COLORADO AT DENVER
EXECUTED ON 10-29-1993 AT TIME 11:28:37 ..
' PROJECT TITLE: 817 SYCAMORE STREET DUPLEX SITE 100 YEAR STORM EVENT
**** DRAINAGE BASIN DESCRIPTION
' BASIN ID NUMBER = 1.00
BASIN AREA (acre)= 0.48
RUNOFF COEF = 0.55
DESIGN RAINFALL STATISTICS
DESIGN RETURN PERIOD (YEARS) = 100.00
'INTENSITY(IN/HR)-DURATION(MIN) TABLE IS GIVEN
DURATION 5 10 20 30 40 50 60 80 100 120 150 180
.INTENSITY 9.0 7.3 5.2 4.2 3.5 3.0 2.6 2.1 1.7 1.5 1.2 1.0
POND OUTFLOW CHARACTERISTICS:
MAXIMUM ALLOWABLE RELEASE RATE = 1.12 CFS
' OUTFLOW ADJUSTMENT FACTOR = .86
AVERAGE RELEASE RATE = .9632 CFS
AVERAGE RELEASE RATE = MAXIMUM RELEASE RATE * ADJUSTMENT FACTOR.
COMPUTATION OF POND SIZE
-----------------------------------------------------
RAINFALL RAINFALL INFLOW OUTFLOW REQUIRED
DURATION INTENSITY VOLUME VOLUME STORAGE
MINUTE INCH/HR ACRE -FT ACRE -FT ACRE -FT
-----------------------------------------------------
0.00 0.00 0.00 0.00 0.00
5.00 9.00 0.02 0.01 0.01
10.00 7.30 0.03 0.01 0.01
15.00 6.25 0.03 0.02 0.01
20.00 5.20 0.04 0,03 0.01
25.00 4.70 6.04 0.03 0.01
30.00 4.20 0.05 0.04 0.01
35.00 3.85 0.05 0.05 0.00
40.00 3.50 0.05 0.05 0.00
' 45.00 3.25 0.05 0.06 0.00
----------------------------------------------
THE REQUIRED POND SIZE = 1.447417E-02 ACRE -FT
THE RAINFALL DURATION FOR THE ABOVE POND STORAGE= 15 MINUTES
1
RBD INC. ENGINEERING CONSULTANTS
WEIR SECTION FLOW DATA
OUTLET WEIR STRUCTURE SYCAMORE STREET DUPLEX SITE
WEIR COEF.
3.200
STA ELEV
0.0 2.00
2.6 1.35
4.6 1.35
4.6 0.80
4.8 0.80
4.8 1.35
6.8 1.35
9.4 2.00
ELEVATION
DISCHARGE
(feet)
(cfs)
.........
...•.....
0.80.
0.0
0.90
0.0
1.00
0.0
1.10
0.1
1.20
0.1
1.30
r
0.2� Z ale r'' ED c �L olV b.3 c+ s @ S��o1.30
1.40
0.4
1.50
1.1 n
1 `1;-- 1>Ez-\r-1=l,
1.60
2.3-"-�
1.70
3.8
1.80
5.6
1.90
7.9
2.00
10.5
1
1
1
1
1
1
1
1-
1
1
1
1
1
1,
1
1
1
1
1
RAINFALL PERFORMANCE STANDARD EVALUATION
PROJECT: STANDARD FORM A
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COMPLETED BY: �j r��e nss DATE: lc, 3I , 93
DEVELOPED
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MARCH 1991
8.14 DESIGN CRITERIA
EFFECTIVENESS CALCULATIONS
PROJECT: Il_L11�MS '0UPt�?C S1� STANDARD FORM B
COMPLETED BY: g. <14-)0-Ties DATE:
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SEQUENCE FOR 19 9B ONLY COMPLETED BY: DATE:
Idicate 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
ffproval by the City Engineer.
YEAR
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U I I I I ll I I I I 7 I I I
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BLOT GRADING
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I
Soil Roughening
Perimeter Barrier
Barriers
'Additional
Vegetative Methods
Soil Sealant
Other
iAINFALL 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/Hate/Blankets
Other
CTURES: INSTALLED BY MAINTAINED BY
TATION/MULCHING CONTRACTOR
SUBMITTED APPROVED BY CITY OF FORT COLLINS ON
MARCH 1991 8-16 DESIGN CRITERIA
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FORT COLLINS STREET DEPARTMENT 221 6750
DOLORES WILLIAMS
817 SYCAMORE STREET
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