HomeMy WebLinkAboutDrainage Reports - 01/16/1992DRAINAGE INVESTIGATION
A BUILDING REMODEL
LOCATED AT
203 WEST MYRTLE STREET
FORT COLLINS, COLORADO
Prepared for
EAST -WEST IMPORTS
203 WEST MYRTLE STREET
FORT COLLINS, COLORADO 80521
APRIL 1991
Project No. HYD-052-90
(Revised May 1%4994
-Acutiw�r�
STORMWA(i
RECEIVED-
JAN 15 1992
PREPARED BY:
Messner Engineering Associates
150 East 29th Street, Suite 225
Loveland, Colorado 80538
Telephone: (303) 663-2221
Fin(:! An..roved Report
{ Date -J-
Civil and Environmental Engineering Consultants
Engineering Associates
April 9, 1991
Project No. HYD-052-91
Mrs. Choko Oshima
East -West Imports
203 West Myrtle
Fort Collins, Colorado 80521
Dear Mrs. Oshima,
The enclosed report represents the results of the drainage investigation performed for
the proposed addition and remodeling of your building located at 203 West Myrtle Street
in the City of Fort Collins, Larimer County, Colorado.
This investigation was based upon the proposed site development and building
construction plans; existing reports and plans for adjacent properties; on -site
observations; and topographic information obtained on -site. The investigation was
performed in accordance with the criteria established in the City of Fort Collin's "Storm
Drainage Design Criteria and Construction Standards".
Thank you for the opportunity to be of service to you. If you should have any questions,
please feel free to contact this office.
�� •° 'Y
Dennis 53
�.��
MESSNE 'B �" �a Associates
DRM/mkm
(Revised per City of Fort Collins review comments dated May 14, 1991)
Enclosures
Civil and Environmental Engineering Consultants
150 E. 29th Street, Suite 225 Loveland, Colorado 80538 Telephone: (303) 663-2221
TABLE OF CONTENTS
Letter of Transmittal
Table of Contents
Scope
Site Description
Existing Conditions
Proposed Development
Conclusions and Recommendations
Letter Requesting Variance to On -site
ii
Detention Requirement (Added 4-26-91)
EXHIBITS
Vicinity Map
Original Conditions Exhibit
Existing Conditions Exhibit
Proposed Construction Exhibit
Calculations (Revised 5-16-91)
Architectural Site Plan (Added 5-16-91)
ii
SCOPE
The following report represents the results of a drainage investigation performed for a
proposed remodel and addition to an existing structure located on the North 90 feet of the
West 65 feet of Block 106 of Harrison's Addition to the City of Fort Collins, Larimer
County, Colorado.The investigation was performed for East - West Imports. The purpose
of this investigation is to determine the effects of the proposed development on the area's
existing drainage conditions and to determine the improvements, if any, and the
appropriate sizing for proposed improvements so that it may be incorporated with the
construction of the project. The conclusions and recommendations presented in this
report are based upon the proposed building construction and site redevelopment plans;
grading and drainage construction plans and reports for existing adjacent facilities;
on -site observations; and the available topographic information. The analysis was
performed in accordance with the City of Fort Collins' "Storm Drainage Design Criteria
and Construction Standards".
SITE DESCRIPITION
The property is located at the southwest corner of the intersection of West Myrtle Street
and South Mason Street. The address is 203 West Myrtle Street.The site is rectangular in
shape and contains approximately 0.37 acres. The site's East-West dimension is 65 feet
and its North -South dimension is 90 feet. The site is located in the OLD TOWN
DRAINAGE BASIN.
EXISTING CONDITIONS
The site is presently zoned B-G General Business District. The existing structure located
on the site was originally a single family residence (Please refer to Original Conditions
Exhibit.) A succession of changes in useage of the structure and the exterior site have
occurred since the property was originally occupied in 1977. No physical changes have
been made to the structure since that time. The structure is presently used as a retail
sales outlet for imported products. Several modifications have been made to the exterior
portion of the property during this time (Please refer to Existing Conditions Exhibit.) The
following is a list of modifications in chronological order:
1. The gravel surfaced areas between the sidewalks and the curb and gutter adjacent
to both streets has been removed and replaced with asphalt surfacing.
2. The gravel driveway, concrete walks and some "lawn" area located at the
southerly side of the property have been removed. Raised wooden decks and a
flagstone surfaced area have been constructed to provide an outdoor seating area
for the restaurant located in the adjacent property to the south.
3. A portion of the "lawn" area along the west side of the structure has been removed
and replaced with asphalt surfaced parking places. This was done at the same
time that an asphalt access drive was constructed on the adjacent property to the
west.
As previously stated, a restaurant is located on the adjacent property to the south. The
area immediately west of the site is an access driveway and residential rental property.
The main line of the Burlington Northern Railroad is situated in the center of Mason
Street along the eastern border of the site. The site and surrouding vicinity is relatively
flat and slopes gently from southwest to northeast toward Mason Street. Slopes range
1
EXISTING CONDITION (cont.)
from 0.5% to 2%. The site does not appear to receive run-off from the adjacent properties.
The runoff generated on the adjacent properties to the south and west appears to flow
overland to the north in the inverted crown section of the access driveway located at the
west side of the property. The runoff is discharged into the curb and gutter along the
south side of West Myrtle Street. The runoff that enters the gutter in West Myrtle Street
flows easterly to South Mason Street. A storm drain inlet is located to the west of the curb
radius at the southwest corner of the intersection of West Myrtle Street and South Mason
Street which intercepts the flow from the west. A storm drain inlet located to south of the
curb radius at the southwest corner of the intersection of West Myrtle Street and South
Mason Street which intercepts the flow from the south. The storm drain inlets are
connected to a 27 inch diameter storm drain that flows easterly in West Myrtle Street.
There are no current plans to modify or upgrade the City's storm drainage system for the
immediate vicinity.
PROPOSED DEVELOPME
The proposed development is to consist of the construction of additions to the east and
north sides of the existing structure. The balance of the existing structure is to be
remodeled throughout. The exterior seating area for the restaurant to the south is to be
retained. The parking area along the west side of the site is to be retained. (Please refer to
Proposed Construction Exhibit.)
The proposed construction is designed to be able to conform with the existing slope and
grades. The site will continue to drain to the intersetion corner of the adjacent streets.
The calculations made to determine the peak rate of storm runoff that will be generated
by the proposed changes on the site indicate that there will be virtually no change in the
intensity or amount of runoff due to the proposed construction. The site has limitations
on the space that is available to provide for onsite detention facilities. Therefore, due to
this limitation and the estimated negligible change in runoff, it is recommended that no
onsite drainage detention facilities be provided.
CONCLUSIONS AND RECOMMENDATIONS
1. The proposed development will retain the existing drainage patterns.
2. The site is located in the OLD TOWN DRAINAGE BASIN. The site is not
located within a designated floodway or flood plain.
3. All construction is to be performed in accordance with City of Fort Collins'
Standards and Specifications.
4. Onsite detention of stormwater is not recommended due to the limited area available
to physically develop fully sized facilities. The estimated peak rates of runoff for the
proposed construction indicate that there is to be virtually no change from the
present and past conditions.
5. The City of Fort Collins' Standards for temporary erosion control measures are
recommended to be incorporated with the construction activities. Specifically, a
silt fence to control mud from being washed onto the existing sidewalk and street is
recommended.
2
OS
Engineering Associates
April 26, 1991
Project No. HYD-052-91
Stormwater Utility
City of Fort Collins
235 Mathews
P.O. Box 580
Fort Collins, Colorado 80522-0580
Attn: Mr. Glen Schlueter
Re: Drainage Investigation for East-West Imports located at 203 W. Myrtle,
Fort Collins, Colorado
Dear Mr. Schlueter,
Per your review comments, this office has revised the subject drainage investigation
report and has performed additional calaculations to determine the affect, if any, by the
proposed remodel.
Based upon the calculations performed, I would anticipate virtually no change in the
drainage characteristics in this area due to the proposed construction. Therefore, on
behalf of the owner, I am requesting that a variance be granted to allow the project to
proceed without providing on -site detention. �,
Your earliest possible response to this request will be greatly appreciated. For your
information the owner's contractor is in the process of maldng a submittal for Building
Permit at this time. If you should have any questions, please feel free to contact this
office.
Respect .,Wtz`k °1 �d
1)enni ssne :bc`�
MESSN��,e� Associates
��p�n�nAmm►au��
DRM/mkm
Civil and Environmental Engineering Consultants
150 E. 29th Street, Suite 225 Loveland, Colorado 80538 Telephone: (303) 663-2221
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WEST MYRTLE STREET .
EXISTING INLETS
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ORIGINAL CONDITIONS EXHIBIT
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EXISTING CONDITIONS EXHIBIT
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PROPOSED CONSTRUCTION EXHIBIT
Client: EAST -WEST IMPORTS Project No.HYD-052-91
By: DRM Date: Apr. 9, 1991
(Revised 4-26-91)
Calculations for Drainage Investigation for 203 West Myrtle Street, City of Fort Collins,
Larimer County, Colorado
Total Site Area = Lot Area + Adjacent Street Area
_ (65 x 90) + (90 x 50) + (50 x 50) + (65 x 50)
= 5,850 + 4,500 + 2,500 + 3,250
= 16,100 sq. ft. = 0.37 ± acres
The proposed construction on the site is to consist of an addition to the east and the north
sides of the existing structure. The balance of the existing structure is to be remodeled.
The existing outdoor seating area for the restaurant located at the south property line is
to be retained. The existing paved parking area along the west side of the site is to be
retained.
The following calculations have been performed in order to determine the peak rate of
runoff for three conditions. Those being: the condition at time of initial occupancy by
East - West Import; the present condition; and the condition after the proposed
construction is completed.
The existing zoning is B-G General Business District. Therefore, the 10 Year and 100
Year Storms have been considered for the Minor and Major storm events respectively.
INITIAL CONDITIONS
Rational "C" Factor = 0.15 for Landscaped Areas
" ft " = 0.50 for Gravel Surfaced Areas
ft it = 0.60 for Flagstone Surfaced Areas
ft = 0.95 for Concrete Sidewalks, Driveways, Patios, etc.
= 0.95 for Roofs
= 0.95 for Streets
Area covered by Landscaping (Lawn) = 4,175 sq. ft.
Area covered by Gravel Surfacing = 2,175 sq. ft.
Area covered by Flagstone Surfacing = 310 sq. ft.
Area covered by Roof = 1,750 sq. ft.
Area covered by Sidewalk, Driveways, Patios, etc. = 1,140 sq. ft.
Area covered by Street = 6.550 sq. ft.
Total Area=16,100 sq.ft.
Average "C" Factor =[(4,175x0.15)+(2,175x0.5)+(310x0.6)+(1,750x0.95)+(1,140x0.95)+
(6,5500.95)1-16,100
"C"avg = 0.675
Off -site Area contributing runoff = 0
Elevation difference across west side of site = 100.7 - 100.2 = 0.5 ft.
Distance from SW corner to NW corner at Street= 100± ft.
Slope = 0.5/100 = .005 ft./ft. = 0.5±%
Page 1 of 3
Client: EAST -WEST IMPORTS Project No.HYD-052-91
By: DRM Date: Apr. 9, 1991
(Revised 4-26-91)
INITIAL CONDITIONS cont.)
Time of Concentration determined by the formula
Tc = 1.8 (1.1 - CCf)4L,-(S)1/3
Tc = 1.8 [1.140.675 x1.0N100-(0.5)1/3 = 10.5 minutes
USE 10 minutes as Time of Concentration due to minimum time of concentration
specified in Urban Drainage and Flood Control District -Design Criteria
Rainfall Intensity, I, at Tc = 10 minutes
Iio = 4.40 in./hr.
Runoff, Q, determined by Q = CIACf
Qio = 0.675 (4.40) (0.37)(1.0) =1.10 c.f.s.
Qioo = 0.675(7.25) (0.37)(1.25) = 2.26 c.f.s.
EXISTING CONDITIONS
Area covered by Landscaping (Lawn)
Area covered by Wooden Deck
Area covered by Flagstone Surfacing
Area covered by Roof
Area covered by Sidewalk, Driveways, Patios, etc.
Area covered by Street and Asphalt Paving
Total Area
Iioo = 7.25 in./hr.
= 2,785 sq. ft.
= 290 sq. ft.
= 1,130 sq. ft.
= 1,750 sq. ft.
= 1,015 sq. ft.
= 9.130 sq. ft.
=16,100 sq.ft.
Average "C" Factor =[(2,785x0.15)+(290x0.5)+(1,130x0.6)+(1,750x0.95)+(1,015x0.95)+
(9,130x0.95)1-16,100
"C"avg = 0.779
Tc = 10 minutes (Based on Minimum allowable)
Iio ® 10 min. = 4.40 in./hr.
Qio = 0.779 (4.40) (0.37)(1.0) = 1.27 c.f.s.
Qioo = 0.779 (7.25) (0.37)(1.25) = 2.61 c.f.s.
PROPOSED CONSTRUCTION
Area covered by Landscaping (Lawn)
Area covered by Wooden Deck
Area covered by Flagstone Surfacing
Area covered by Roof
Area covered by Sidewalk, Driveways, Patios, etc.
Area covered by Street and Asphalt Paving
Total Area
Iioo Q 10 min. = 7.25 in./hr.
= 1,950 sq. ft.
= 470 sq. ft.
= 1,130 sq. ft.
= 2,445 sq. ft.
= 975 sq. ft.
= 9.130 so. ft.
=16,100 sq.ft.
Page 2 of $
Client: EAST - WEST IMPORTS Project No.HYD-052-91
By: DRM Date: Apr. 9, 1991
(Revised 5-16-91)
PROPOSED CONSTRUCTION cont.)
Average "C" Factor =[(1,950xO.15)+(470xO.5)+(1,l30x0.6)+(2,445xO.95)+(975xO.95)+
(9,1300.95)1-16,100
"C"avg = 0.815
0.815 x 1.25 = 1.02 > 1.0 therefore, USE 1.0 for "C"avg Q 100Yr.
Tc = 10 minutes (Based on Minimum allowable)
5 w�'
ho Q 10 min. = 4.40 in./hr. hoo @ 10 min. = 7.25 in./hr.
Qio = 0.815 (4.40) (0.37)(1.0) =1.33 CS..s.
Qioo = 1.0 (7.25) (0.37)= 2.68 c.f.s.
Determine Volume if Detention were to be provided.
7
(Q2=0.675x251x0.37x1.0=0.62c.f.s.
Time
Qioo Proposed
Vol. Q Qioo
pis. ® 2 Yr.
Vol, as. Vol. Diff.
10 (min.)
2.68 (c.f.s.)
1,608 (cu.ft.)
0.62 (c.f.s.)
/
372 (cu.ft.)1,236 (cu.ft.T
15
2.22
1,998
0.62
558 ✓ 1,440 ✓
20
1.92
2,304 ✓
0.62
744 ✓ 1,560Z�
25
1.70
2,550
0.62
930 / 1,620 ✓
30
1.54
2,772 ✓
0.62
1,116 ✓ Ll:,65a6--�
40
1.30
3,120 ✓
0.62
1,488 ✓ 1,632
50
1.11
3,330 ✓
0.62
1,860 ✓ 1,470 ✓
60
0.96
3,456 v'--
0.62
2,232 ✓ 1,224 ✓
Therefore, a volume of 1,656 cu.ft wouldnbe detained if detention were to be provided.
Determine increase in depth of flow. OVE
Q1oo at initial development = 2.26 c.f.0'
Q1oo at proposed de
velopment = 2.68 c.f.s.✓
Q = 0.56 (Z/n) 4S(y)7From Section 4.2.2.2 - Theoretical Capacity y = [Q _ (0.56 VS/n)]"�
Z = 1/ Street Crown Slope = V 0.02 = 50
at Initial y = [2.26 - (0.56 x 50 x 40.005 / 0.016131$ = 0.223 ft.
at Proposed
p y = [2.68 = (0.56 x 50 x 40.005 / 0.016] 8 = 0.238 ft.
Therefore, the change in depth in the gutter flow is 0.015 ft. (0.18 inches)
Page 3 of 3
Drainage Summary for EAST - WEST IlVIPORTS located on the North 90
feet of the East 65 feet of Block 106 of Harrison's Addition to the City of Fort
Collins, Colorado
Existing Conditions:
Total Area = 0.134 ± acres Lot plus 0.236 ± acres adjacent Street R - 0 - W
Rational "C" factor: Cio= 0.779 Cioo = 0.779
(Proportioned by direct -area relationship)
Onsite Runoff: Q io= 0.46c.f.s. Qioo = 0.82 c.f.s.
Street Flows: Q io = 0.81 c.f.s. Qioo = 1.44 c.f.s.
Total Runoff: Q io = 1.27 c.f.s. Qioo = 2.26 c.f.s.
Developed Conditions: 111
Total Area = 0.134 ± acres Lot plus 0.236± acres adjacent Street R - 0 - W
Rational "C" factor: Cio= 0.815 Cioo = 0.815
Onsite Runoff:
Street Flows:
Total Runoff:
Q io = 0.48 c.fs.
Q io = 0.85 c.f.s.
Q io=1.33�c.f.s.
P�h�
Detention Summary:
Qioo = 0.97 c.fs.
Qioo = 1.71 c.f.s.
Q= 2.6�c.f.s.
,
uo I - -
On site detention facilities are NOT recommended. If detention were to be
provided, a volume of 1,656 cu. ft. would be desired.
Drainage Basin Statistics:
Gross Platted Area: 0.370 ± Acres
Gross Area Rational "C" Factor: C2 = 0.815 Cioo = 0.815
Net Platted Area: 0.134± Acres
Net Area Rational "C" Factor: C2 = 0.815 Cioo = 0.815
Onsite Detention: 0 c.f./ac.
Basin: OLD TOWN DRAINAGE BASIN
Streets: The increased rate of flow during the 100 Year Storm will increase
the depth of flow in the gutter by an estimated 0.18 inches.
(Revised 5-16-91, DRM)
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