HomeMy WebLinkAboutHARRIS BILINGUAL ELEM. SCHOOL EXPANSION - SITE PLAN ADVISORY REVIEW - 6-01 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT11
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1 1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
This site is located in the southeast portion of Old Town Fort Collins. The school site
encompasses nearly the entire block bounded by E. Elizabeth Street on the north, Smith
' Street on the east, Garfield Street on the south and Whedbee Street on the west. A small
gas station exists on the southwest corner of this block. See the location map in
Appendix A.
' 1.2 Description of Property
The entire school site consists of approximately 3.06 acres of land. The site has
1 buildings and pavement currently existing and the site slopes from the center (existing
school) to the existing streets on all sides. The slopes on each side vary from 2.8% on the
east where the playground was recently reconstructed to 20% on the north which is
covered in grasses and street trees.
The project will consist of a removing two existing buildings and expanding the existing
building to the west. Additional walks will service the new expansion and the existing
' parking lot on the south will be reconstructed.
1 2. DRAINAGE BASINS AND,SUB-BASINS
2.1 Major Basin Description
1 The proposed development lies within the Spring Creek Drainage Basin.
' 2.2 Sub -basin Description
Flow from this site will enter the streets on all four sides. Runoff in Smith Street will
flow north to Elizabeth and west to existing inlets at the intersection of Elizabeth and
Whedbee. Runoff in Garfield Street will flow west to Whedbee and north to the same
inlets. This storm system will convey the runoff north.
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TABLE OF CONTENTS
TABLEOF CONTENTS............................................................................................................... iu
1.
GENERAL LOCATION AND DESCRIPTION
'
1.1 Location...................................................................................................................1
1.2 Description of Property ............................................................................................
I
1
2.
DRAINAGE BASINS AND SUB -BASINS
2.1 Major Basin Description..........................................................................................I
3.
2.2 Sub -Basin Description.............................................................................................1
DRAINAGE DESIGN CRITERIA
'
3.1 Regulations..............................................................................................................2
3.2 Development Criteria Reference and Constraints...................................................2
3.3 Hydrologic Criteria..................................................................................................3
'
3.4 Hydraulic Criteria....................................................................................................3
4.
DRAINAGE FACILITY DESIGN
4.1 General Concept......................................................................................................3
'
4.2 Specific Flow Routing.............................................................................................3
4.3 Drainage Summary ..................................................................................................4
4.4 Variance Requests....................................................................................................4
5.
EROSION CONTROL
5.1 General Concept......................................................................................................5
6.
CONCLUSIONS
'
6.1 Compliance with Standards....................................................................................5
6.2 Drainage Concept....................................................................................................5
7.
6.3 Water Quality and Erosion Control Concept...........................................................6
REFERENCES....................................................................................................................6
APPENDICES
A Vicinity Map
B Hydrologic Computations & Erosion Control
C Figures and Tables
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1% North Star
1-I aft, design _
'
January 17, 2001
'
Basil Hamdan
City of Fort Collins Stormwater
700 Wood Street
1
Fort Collins, CO 80522-0580
RE: Final Drainage Report for Harris Bilingual Elementary School Expansion
Dear Basil,
I am pleased to submit for your review and approval, this Final Drainage Report for Harris
Bilingual Elementary School Expansion. I certify that this report for the drainage design of
Laurel Street Apartments was prepared in accordance with the criteria in the City of Fort Collins
Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Since
Patricia Kroetch, P
North Star Design, Inc.
ii
1194 W. Ash Street, Suite B Windsor, Colorado 80550
970-686-6939 Phone . 970.686-1188 Fax
FINAL DRAINAGE AND
EROSION CONTROL REPORT
HARRIS BILINGUAL ELEMENTARY
SCHOOL EXPANSION
Prepared for:
RB+B Architects
315 E. Mountain Ave, Suite 100
Fort Collins, CO 80524
Prepared by:
North Star Design, Inc.
1194 W. Ash Street, Suite B
Windsor, Colorado 80550
(970)686-6939
January 17, 2001
Job Number 138-03
t
' APPENDIX C
' FIGURES AND TABLES
L
1
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C
11
Cost Est
EROSION CONTROL COST ESTIMATE
Project: HARRIS ELEMENTARY
Prepared by: PPK
ITEM
IQUANTITY
JUNIT
COST/UNIT
TOTAL COST
Silt Fence
635
LF
$3
$1,905
Straw Bale Barrier
0
EA
$150
$0
Gravel Inlet Filter
0
EA
$150
$0
Construction Entrance
0
EA
$550
$0
Subtotal
Contingency (50%)
Total
$1,905
$953
$2,858
CITY RESEEDING COST
Reseed/Mulch
3.06
ACRE
$615
$1,882
Subtotal
Contingency (50%)
Total
$1,882
$941
$2,823
EROSION CONTROL ESCROW AMOUNT $2,858
Page 1
North Star Design, Inc
1194 W. Ash St. Suite B
Windsor, CO 80550
LOCATION: Harris Elementary School
ITEM: Water Quality Pond Sizing
COMPUTATIONS BY: ppk
SUBMITTED BY: North Star Design, Inc
From Urban Strom Drainage Criterial Manual, March 1969
(Referenced figures are attached at the end of this section)
Use 40-hour brim -full volume drain time for extended detention basin
Water Quality Capture Volume = WQCV = (required storage/12)'(tributary drainage area)
MAJOR
BASIN
Trib.
area
(ac)
%Imperv.
Req. Storage
(in. of runoff)
from Fig. 5-1
WQCV
(ac-ft)
Dwo
00
req. area/row
(in 2/row)
from Fig. 5-3
EX
3.06
34.0
0.15
0.038
PRO
3.06
36.0
0.16
0.041
1 /16/01
WQVOL.xIs
North Star Design, Inc.
1194 W. Ash St., Suite B
Windsor, CO 80550
RATIONAL METHOD PEAK RUNOFF (NEW IDF CURVE)
(100-YEAR)
LOCATION: Harris Elementary School
PROJECT NO: 138-02
COMPUTATIONS BY: ppk
DATE: 1/16/01
100-yr storm, Cir = 1.25
DIRECT RUNOFF
CARRY OVER
TOTAL
REMARKS
Des.
Point
Area
Design.
A
(ac)
C Cf
tc
(min)
1
(new)
(in/hr)
0 (100)
(cfs)
from
Design
Point
0 (100)
(cfs)
all00)tot
(ds)
1
EX1
0.74
0.49
5.0
9.95
3.57
3.57
2
EX2
0.95
0.50
11.2
7.37
1 3.51
1
3.51
3
EX3
1.07
0.62
5.0
9.95
6.65
6.65
4
EX4
0.29
0.57
5.0
9.95
1.67
1.67
15.40
Total -
1
PRO1
0.74
0.57
5.0
9.95
4.22
4.22
2
PR02
0.95
0.50
11.2
7.37
3.51
3.51
3
PR03
1.07
0.57
5.5
9.63
5.95
5.95
4
PRO4
0.29
0.79
5.0
9.95
2.32
2.32
16.00
Total
Q=CiA
Q = peak discharge (cfs)
C = runoff coefficient
I = rainfall intensity (in/hr) from IDF curve I = 75 / (10+ tcf"
A = drainage area (acres)
NOTE: Intensity based on Figure 3-1, 1999 (Regional Analysis)
FlowAs 0100
North Star Design, Inc.
1194 W. Ash St., Suite B
Windsor, CO 80550
RATIONAL METHOD PEAK RUNOFF (NEW IDF CURVE)
(10-YEAR)
LOCATION: Hams Elementary School
PROJECT NO: 138-02
COMPUTATIONS BY: ppk
DATE: 1/16/01
10-yr storm. Cf = 1.00
DIRECT RUNOFF
CARRY OVER
TOTAL
REMARKS
Design
Point
Tributary
Sub -basin
A
(ac)
C Cf
tc
(min)
i
(new)
(in/hr)
Q (10)
(cfs)
from
Design
Point
Q (10)
(cfs)
Q(10)tot
(cfs)
1
EX1
0.74
0.39
5.4
4.75
1.36
1.36
2
EX2
0.95
0.40
11.2
3.60
1 1.37
1
1.37
3
EX3
1.07
0.50
6.4
4.46
2.38
2.38
4
EX4
0.29
0.46
5.2
4.81
0.65
0.65
5.77
Total
1
PR01
0.74
0.46
5.0
4.87
1.65
1
1.65
2
PR02
0.95
1 0.40
11.2
3.60
1.37
1.37
3
PR03
1.07
0.46
6.8
4.36
2.15
2.15
4
PRO4
0.29
0.63
5.0
4.87
0.91
0.91
6.09
Total
Q=CtCiA
Q = peak discharge (cfs)
C = runoff coefficient
Cf = frequency adjustment factor
I = rainfall intensity (in/hr) from OF curve I = 46.7 / (10+ tc)01B'
A = drainage area (acres)
NOTE: Intensity based on Figure 3-1, 1999 (Regional Analysis)
Flow.xls Q10
North Star Design, Inc.
1194 W. Ash St., Suite B
Windsor, CO 80550
STANDARD FORM SF-2
TIME OF CONCENTRATION -100 YR
LOCATION: Hams Elementary School
PROJECT NO: 138-02
COMPUTATIONS BY: ppk
DATE: 1/16/01
100-yr storm Cf = 1.25
SUB43MIN
DATA
INITIAL /OVERLAND
TIME (tl)
TRAVEL TIME / GUTTER OR CHANNEL FLOW
(tt)
tc CHECK
(URBANIZED BASIN)
FINAL
to
REMARKS
DESIGN
POINT
SUBBASIN(s)
(1)
Area
(ac)
(2)
C
(3)
C'Cf
Length
(ft)
(4)
Slope
(%)
(5)
ti
(min)
(6)
Length
00
(7)
Slope
(%)
(8)
n
Manning
rough.
Val.
(f 1s)
(9)
n
(min)
(10)
tc =
It + It
(11)
Total L
(ft)
(12)
tc=(1/180)+10
(min)
(13)
(min)
(14)
1
EX1
0.74
0.39
0.49
132
20.0
4.7
0
1.00
0.016
2.0
0.00
4.7
132
10.7
5.0
2
EX2
0.95
0.40
0.50
220
2.8
11.4
0
1.00
0.016
2.0
0.00
11.4
220
11.2
11.2
3
EX3
1.07
0.50
0.62
85
3.9
5.0
0
1.00
0.016
2.0
0.00
5.0
85
10.5
5.0
4
EX4
0.29
0.46
0.57
135
17.0
4.3
0
1.00
0.016
2.0
0.00
4.3
135
10.8
5.0
1
PROI
0.74
0.46
0.57
132
20.0
4.0
0
1.00
0.016
2.0
0.00
4.0
132
10.7
5.0
2
PRO2
0.95
0.40
0.50
220
2.8
11.4
0
1.00
0.016
2.0
0.00
11.4
220
11.2
11.2
3
PR03
1.07
0.46
0.57
85
3.9
5.5
0
1.00
0.016
2.0
0.00
5.5
85
10.5
5.5
4
PRO4
1 0.291
0.631
0.791
135
17.0
2.5
01
1.001
0.0161
2.01
0.001
2.5
135
10.8
5.0
EQUATIONS:
tC=ti+tt
ti=[1.87(1.1-CCr)Lo.5]/S1r.1
tt = lNel.
Velocity from Manning's Eqquation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + it and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
FlowAs TOC-100
North Star Design, Inc.
1194 W. Ash St., Suite B
Windsor. CO 80550
STANDARD FORM SF-2
TIME OF CONCENTRATION -10 YEAR
LOCATION: Hams Elementary School
PROJECT NO: 138-02
COMPUTATIONS BY: ppk
DATE: 1/16/01
10-yr storm C/ = 1.00
SUB -BASIN
DATA
INITIAL /OVERLAND
TIME (U)
TRAVEL TIME / GUTTER OR CHANNEL FLOW
(tt)
tc CHECK
(URBANIZED BASIN)
FINAL
tc
REMARKS
DESIGN
POINT
SUBBASIN(s}
0)
Area
(ac)
(2)
C
(3)
Length
(6)
(4)
Slope
(%)
(5)
ti
(min)
(6)
Length
(it)
(7)
Slope
(%)
(8)
n
Manning
rough.
Vel.
(11/s)
(9)
it
(min)
(10)
tc =
ti + 8
(11)
Total L
(ft)
(12)
tc=(1/180)+10
(min)
(13)
(min)
(14)
1
EX1
0.74
0.39
132
20.0
5.4
0
1.00
0.016
2.0
0.00
5.4
132
10.7
5.4
2
EX2
0.951
0.40
220
2.8
13.3
0
1.00
0.016
2.0
0.00
13.31
220
11.2
11.2
3
EX3
1.071
0.50
85
3.9
6.4
0
1.00
0.016
2.01
0.00
6.4
85
10.5
6.4
4
EX4
0.29
0.46
135
17.0
5.2
0
1.00
0.016
2.0
0.00
5.2
135
10.8
5.2
1
PRO1
0.74
0.46
132
20.0
4.9
0
1.00
0.016
2.0
0.00
4.9
132
10.7
5.0
2
PRO2
0.95
0.40
220
2.8
13.3
0
1.00
0.016
2.0
0.00
13.3
220
11.2
11.2
3
PR03
1.07
0.46
851
3.9
6.8
0
1.00
0.016
2.0
0.00
6.8
85
10.5
6.8
4
PR04
1 0.291
0.6.
135
17.0
3.81
01
1.001
0.0161
2.01
0,00
3.8
135
10.8
5.0
EQUATIONS:
tc=ti+III
6 [1.87(1.1-CCr)L0.5)/S113
tt = L/Vel.
Velocity from Manning's Eqquation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of OF curves
FlowAs TOC-10
North Star Design, Inc.
1194 W. Ash St., Suite B
Windsor, CO 80550 RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Hams Elementary School
PROJECT NO: 138-02
COMPUTATIONS BY: ppk
DATE: 1/16/01
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storm Drainage Criteria Manual
Streets, parking lots (asphalt)
Sidewalks (concrete)
Roofs
Gravel
Lawns (flat 2-7%, sandy soil)
` Runoff
%
coefficient
Impervious
C
0.95
100
0.95
96
0.95
90
0.50
40
0.15
0
SUBBASIN
DESIGNATION
TOTAL
AREA
(ac.)
TOTAL
AREA
(sq.ft)
ROOF
AREA
(sq.ft)
PAVED
AREA
(sQ-ft)
SIDEWALK
AREA
(sq.ft)
GRAVEL
AREA
(sq.ft)
LANDSCAPE
AREA
(sq.ft)
RUNOFF
COEFF.
(C)
%
Impervious
EX1
0.74
32,182
5,320
0
4.263
0
22.599
0.39
28
EX2
0.95
41.504
3,256
0
9,707
0
28,541
0.40
30
EX3
1.07
46,780
3,680
12,541
4,110
0
26,449
0.50
42
EX4
0.29
12,823
3.639
0
1,286
0
7,898
0.46
35
EX Total
3.06
133.289
15,895
12,541
0
85,487
0.44
34
PR01
0.74
32,182
9,194
0
d3,248
0
19.740
0.46
35
PRO2
0.95
41,504
3,256
0
0
28,541
0.40
30
PR03
1.07
46,780
7,582
3.048
3,908
26,459
0.46
3PRO4
0.29
12,823
6,661
0
0
5,068
0.63
55
PRO Total
3.06
133,289
26.693
3,048
19,832
3,908
79.808
0.46
36
Eauations
- Calculated C coefficients & %, Impervious are area weighted
C=E(Ci Ai) /At
Ci = runoff coefficient for specific area, At
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
Flow.xls C"I
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APPENDIX B
' HYDROLOGIC COMPUTATIONS
EROSION CONTROL
11
.1
ULBERRY STREE
-TT
FT
W
O
ELIZABETH STREET
LAURE
57RE
Q
I
W
v
y
C�
SITE
I
VICINITY MAP
NOT TO SCALE
I
APPENDIX A
' VICINITY MAP
[1
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1
1
1
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1
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1
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6.3 Erosion Control Concept
Since the site is less than 5.0 acres, a NPDES permit is not required. During
construction, erosion control shall be maintained to minimize erosion on this site and
transport of silt downstream.
7. REFERENCES
1. City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March,
1986.
2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated March, 1969, and Volume 3 dated September,
1992.
Z
:11
6.
EROSION CONTROL
5.1 General Concept
This site lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort
Collins Zone Maps. The potential exists for silt movement from the site and into the
existing storm system during construction. Silt fence is being utilized to minimize this
potential during construction.
This project is an infill project and construction will utilize the majority of the site.
Because of this, most Best Management Practices (BMP's) are not effective and therefore
very few erosion control measures are being proposed. Most of the construction traffic
(concrete trucks, etc) will utilize the existing parking lot which is proposed to remain
until the majority of the building is constructed thus minimizing the possibility of mud
tracking. Silt fence is utilized around the areas of disturbance to minimize wind and
stormwater erosion. Watering of disturbed areas is being proposed to also minimize the
wind erosion. The erosion control escrow amount is $2858.
CONCLUSIONS
6.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
City of Fort Collins Storm Drainage Design Criteria Manual.
6.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provide for the detention and transmission of developed on -site runoff to the
existing streets and into the existing storm system. The impact of the development of this
site on existing downstream facilities is very minor and therefore on site detention is not
being proposed.
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit would be required.
W
Subbasin 3 contains the south quarter of the site including a smallportion of the proposed
' building expansion, the existing parking lot and the proposed main entry walks. Runoff
from this basin flows south to Garfield Street. Flows then continue west and into
Subbasin 4.
Subbasin 4 contains the west quarter of the site including the west half of the proposed
building expansion and the delivery entrance. Runoff from this basin flows west to
Whedbee Street. Flows then combine with runoff from Subbasin 3 and continue north to
' the existing inlet at the intersection of Elizabeth and Whedbee.
4.3 Drainage Summary
' The storm conveyance system is a surface system and has been designed for minimum
' maintenance. The City of Fort Collins will be responsible for maintenance of the existing
adjacent streets utilized as drainage conveyance. The drainage facilities located on this
site will be maintained by the owners of the site.
1
4.4 Variance Requests
' A variance is being requested to forgo the detention requirement for this site due to the
' increase rainfall criteria adopted by the City of Fort Collins in 1999. The amount of
increase to the runoff for this site (from the existing condition to the developed condition)
is approximately 0.60 cfs in the 100 year storm and when viewed in the context of the
' overall basin, this increase is very minor.
' A variance is also being requested for the requirement to provide water quality in the
form of extended detention. With the development of the expansion several measures are
' being proposed to minimize the impervious areas on site. Grass pavers are proposed
(instead of concrete) on each side of the walks on the south and west sides of the
1 building. Gravel pavers are proposed in the parking bays of the reconstructed parking
lot. On the all sides of the building, the roof drain discharge will flow across grassed
areas before reaching the streets. This will allow sediment to be removed from the runoff
prior to reaching the streets.
1
4
I
minor impact on downstream conveyances.
' 3.3 Hydrologic Criteria
Runoff computations were prepared for the 10-year minor and 100-year major storm
frequency utilizing the rational method.
All hydrologic calculations associated with the basins are included in Appendix B of this
report. Standard Form 8 (SF-8) provides time of concentration calculations for all sub -
basins. Standard Form 9 (SF-9) provides a summary of the design flows for all Sub -
basins and Design Points associated with this site.
' 3.4 Hydraulic Criteria
All hydraulic calculations within this report have been prepared in accordance with the
City of Fort Collins Drainage Criteria and are also included in Appendix C of this report.
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
Because the site sits on top of a hill, the runoff from this site flows in all four directions.
Flow will be directed to the existing streets on all sides of the site.
4.2 Specific Flow Routing
A summary of the drainage patterns within each basin is provided in the following
paragraphs.
Subbasin 1 contains the north quarter of the site including a portion of the proposed
building expansion and runoff from this basin flows north to Elizabeth Street. Flows then
continue west and into the existing inlet at the intersection of Elizabeth and Whedbee.
1 Subbasin 2 contains the east quarter of the site including the existing playground. This
basin will remain unaltered by the expansion. Runoff from Subbasin 2 flows to Smith
street on the east boundary of the site. The flow is combined with runoff from Subbasin
1 and flows to the existing inlet.
3
i
1 3.
DRAINAGE DESIGN CRITERIA
3.1 Regulations
This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage
Design Criteria Manual' specifications. Where applicable, the criteria established in the
"Urban Storm Drainage Criteria Manual" (UDFCD), 1984, developed by the Denver
Regional Council of Governments, has been used.
3.2 Development Criteria Reference and Constraints
1 The runoff from this site has been routed to conform to existing site constraints. Since all
of the adjacent streets surrounding the site and the main building on the site are already
constructed, there is very little room for variances from existing site conditions.
i
The streets and associated drainage systems surrounding the site exist. The nearest storm
' system is at the intersection of E. Elizabeth Street and Whedbee Street at the northwest
corner of this site. The existing school sits on top of a hill in the center of the site. No
offsite flows will enter this site.
The expansion proposed for this site is approximately 13,500 square feet. Some of this
' building will replace existing impervious area (two buildings, paved area and walks) but
there would still be a large increase in impervious area on this site. In order to offset the
impervious area created by this expansion several alternative pavements are being
proposed. In some of the walkways, grass pavers are proposed to reduce the potential
concrete area. In the parking lot, the stall areas are proposed to be gravel pavers to
reduce the existing asphalt area. In the service area on the south side of the expansion,
gravel will be utilized rather than concrete. These techniques minimize the potential
impact of the expansion and reduce the potential runoff from the site.
No detention is proposed for this site. The existing site (based on the rainfall criteria
adopted by the City of Fort Collins on March 26, 1999) generates approximately 5.77 cfs
runoff in the 10 year storm and 15.60 cfs in the 100 year storm event. The site as it is
proposed will generate approximately 6.09 cfs in the 10 year event and 16.00 cfs in the
100 year event. Because of the innovative techniques utilized on this site to reduce
impervious areas, the additional runoff in the 100 year event is only 0.4 cfs. This
increase, when viewed on a basin wide level, is very insignificant and will have a very
2