HomeMy WebLinkAboutCOLLEGE EIGHT THIRTY - FDP - FDP160002 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTELOPED RUNOFF SUMMARY T. LE
DESIGN
BASIN
TOTAL
2-yr T�
10-yr
100-yr
Qz
Quo
QIoo
POINT
ID
AREA
Cz
CIO
C,00
(min)
T`
Tc
(cfs)
(cfs)
(cfs)
(acres)
min
min
A
A
1 0.32
1 0.84
1 0.84
1 1.00
1 5.0
1 5.0
5.0
1 0.77
1 1.31
1 3.20
D:IProjects1574-0061DrainageWydrology1574-006 Rational-Calcs_Proposed.xlsxlSummary Table
DEVELOPED RUNOFF COMPUTATIONS
:eb2e 5-4
Rational Method Equation:
aarfaaM N8l000 eSWJWMcz aosoaaMr ragas
Project: College Eight Thirty
Q — Cj (C,)(li)(lA)
s= at® Period Frequency Feeto=
Calculations By: A. Reese
l
r9"='� G
Date: January 13, 2016
From Section 3.2.1 of the CFCSDDC
2 to 10 1.00
11 to 25 1.10
26 to 50 1.20
51 to 100 1.25
Rainfall lntenSitV:
Note: The product of C time Cr shell not exceed 1.00
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design
Criteria (CFCSDDC), Figure 3.1
2-yr
30-yr
100-yr
i
Intensity,
Intensity,
Intensity,
Flow,
Flow,
Flow,
Design
Basin(s)
Area, A
T`
T`
T°
C2
CIO
C1oo
i2
i10
iloo
Q2
Q10
Q1oo
Point
(acres)
(min)
(min)
(min)
(in/hr)
(in/hr)
(in/hr)
(cfs)
(efs)
(cfs)
A
A
0.32
5.0
5.0
5.0
0.84
0.84
1.00
2.85
4.87
9.95
0.77
1.31
3.20
D:VlrojectsZ74-0061DrainageViydrology1574-006 Rational-CaICs Proposed.xlsxorect-Runoff
T. 1.87(1.1-C*Cf)�
= V/ I
t = L / 60V
'� = TI + T, (Equation RO-2) I
'elocity (Gutter Flow), V = 208v (Equation RO-4)
'elocity (Swale Flow), V = 155�
TOTE: C,alue for Overland flwrs over grassy wdaces; C = 0.25
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Table 3-4
AASSDEGL MZ=W s=QU=LT AD=Md=2 FACTOna
storm Retorn Pariod FreQaancy Factor
Isears) C.
2 to 10 1.00
11 to 25 1.10
26 to 50 1.20
51 to 100 1.25
Note: The product of C times Cf shall not exceed 1.00
Project: College Eight Thirty
Calculations By: A. Reese
Date: January 13, 2016
Overland Flow
Gutter Flow
Swale Flow
Time Of concentration
Design
C*C
C*C,
C*C
Length,
Slope,
T,
T,
T,
Length,
Slope,
Velocity,
Tt
Length,
Slope,
Velocity,
T,
2-yr
10-yr
100-yr
Point
Basin
Is Length
(2-yr
(10-yr
(100-yr
L
S
2-y7
10•y�
100-y7
L
S
V
(min)
L
S
V
(r"I")
T.
T,
T,
>500'?
Cf(2- O)
Ca1.00)
C,=1.25)
(ft)
(%)
(min)
(min)
(min)
(ft)
(%)
(ft/s)
(ft)
(%)
(ft/s)
(min)
(min)
(min)
D:IProjectsl574-0061DrainageViydmlogyt574-006 Rational-Calcs Proposed.XIUITc-2-N_&_100-yv
DEVELOPED COMPOSITE
% IMPERVIOUSNESS
AND
RUNOFF COEFFICIENT CALCULATIONS
CHARACTER OF SURFACE:
Streets, Parking Lots, Roofs, Alleys, and Drives:
Asphalt...............................................................................................
Concrete.............................................................................................
Gravel................................................................................................
Roofs.................................................................................................
Concrete Pavers ....................................................................................
Lawns and Landscaping
SandySoil..........................................................................................
Clayey Soil..........................................................................................
Runoff
Coefficient
Percentage
Impervious
Project: College Eight Thirty
Calculations By: A. Reese
Date: January 13, 2016
2-year Ct = 1.00 10-year C, = 1.00 100-year C, = 1.25
0.95
100
0.95
90
0.50
40
0.95
90
0.40
22
0.15
0
0.25
0
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Desi n Criteria and Construction Standards, Table 3-3. % Im ervious taken from UDFCD USDCM, Volume I.
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
Po
�� Imp erv.
A
13,997
0.32
0.00
0.03
0.23
0.00
0.05
0.02
0.84
0.84
1.00
75.7
TOTAL ONSITE
13,997
0.32
0.00
0.03
0.23
0.00
1 0.05
0.02
0.84
0.84
1.00
75.7
D.,Wrojectsl574-0061DrainagetHydrology1574-006 Rational-Calcs Pmposed.xlsxlc-Values
"ISTING RUNOFF SUMMARY TAP'
DESIGN
BASIN
TOTAL
2-yr T`
10-yr
100-yr
Q2
Q+o
Q+oo
AREA
C z
C +o
C
ciao
T`
T`
POINT
ID
(min)
(cfs)
(cfs)
(cfs)
(acres)
(min)
(min)
A
A
0.32
1 0.95
1 0.95 1
1.00
5.0
5.0
5.0
0.87
1 1.49
3.20
D:IProjectsl574-0061DrainageWydrology1574-006 Rational-Calcs_Existing.xlsxlSummaryTable
EXISTING RUNOFF SUMMARY TABLE
Sable 3-4
Rational Method Equation:
w.:sacmm =Ta0o Fla QM= xoaoaTNM: VACT=
Project: College Eight Thirty
Q— Cf
a Period ►reGoenoS Feet=
Calculations By: A. Reese
lC/lZ/l`4/
Date: January 13, 2016
From Section 3.2.1 of the CFCSDDC
2 to 10 1.00
11 to 25 1.10
26 to 50 1.20
51 to 100 L.25
Rainfall Intensity:
Note: The product of C time CZ ahall not erteed 1.00
Rainfall Intensity taken from the City of Fort Collins Storm
Drainage Design Criteria (CFCSDDQ,
Figure 3.1
2-yr
10-yr
100-yr
Intensity,
Intensity,
Intensity,
Flow,
Flow,
Flow,
Design
Basin(s)
Area, A
T,
T.
Tc
Cz
CIO
Ctoo
iz
i10
iloo
Qz
410
4100
Point
(acres)
(min)
(min)
(min)
(in/hr)
(in/hr)
(in/hr)
(cfs)
(Cfs)
(cfs)
A
A
0.32
5.0
5.0
5.0
0.95
0.95
1 1.00
2.85
4.87
9.95
0.87
1.49
3.20
cv
D:Vc�rojectst674-0061DrainageViydrologyl574-006 Rational-Calcs_Exisfing.xlsxlDirect-Runoff
EXISTING RUNOFF SUMMARY TABLE
Overland Flow. Time of Concentration:
1.87(1.1 — C * Cf ) 'V /T
Table 3-4
Project: College Eight Thirty
T —
PAXTOM aISx�
Calculations
: Reese
I
� VMQUMWT nwWMZNT
FACIMe
Date: January 13, 2016
Gutter/Swale Flow. Time of Concentration:
atom Re Period rzaqizency
hector
Tf = L / 60V
Isaare)
C.
T, = T, + TI (Equation RO-2)
2 to 10
1.00
11 to 25
1.10
Velocity (Gutter Flow), V = 20•S'4 (Equation RO-4)
26 to 50
1.20
Velocity (Swale Flow), V = 15S
51 to 100
1.25
Note: The product of C times Cf shall
not exceed 1.00
NOTE: C-value for wetland flows suer grassy surfaces: C = 0.25
Overland Flow
Gutter Flow
Swale Flow
Time of Concentration
Design
Basin
C*Cf
C*Cf
C*
Len Length,
Slope,
TI
TI
TI
Length,
Slope,
Velocity,
Tf
Length,
Slope,
Velocity,
Ti
2-yrT(min)
-yr
Point
Is Length
(2•yr
(10-yr
(100-yr
L
S
2-yr
10-yr
100-yr
L
S
V
L
S
V
T�I
F(m!n)r
>500'7
Cf=1.00)
Cf=1.00)
Cf=1.25)
(ft)
(%)
(min)
(min)
(min)
M
(%)
(Ws)
(mini
(f)
(%)
(ft/s)
(min)
(min)
A
A
No
0.25
1 0.25
1 0.31
1 26
5.0
4.7
1 4.7
1 4.4
1 0
0.0
0.00
N/A
0
0.0
0.00
N/A
5.0
1 5.0
1 5.0
D:IPrgwst574-0O61D2inagevbdrology1574-006_Rabonal-Calm Ecisfing.x1v%Tc-2-yr 8 100-yr
EXISTING RUNOFF SUMMARY
TABLE
CHARACTER OF SURFACE:
Sheets, Parking Lots, Roofs, Alleys, and Drives:
Asphalt...............................................................................................
Concrete.............................................................................................
Gravel................................................................................................
Roofs.................................................................................................
Concrete Pavers ....................................................................................
Lawns and Landscaping
SandySoil..........................................................................................
Clayey Soil..........................................................................................
Runoff
Coefficient
Percentage
Impervious
Project: College Eight Thirty
Calculations By: A. Reese
Date: January 13, 2016
2-year G = 1.00 10-year C, = 1.00 100-year c, = 1.25
0.95
100
0.95
90
0.50
40
0.95
90
0.40
22
0.15
0
0.25
0
Runoff Coefficients are taken from the City
of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
A
13,997
0.32
0.00
0.24
0.08
0.00
0.00
0.00
0.95
0.95
1.00
90.0
TOTAL ONSITEI
13,997
1 0.32
0.00
1 0.24
0.08
1 0.00
0.00
1 0.00
0.95
0.95
1.00
90.0
D:IProjects1574-0061Drainageftdrology1574-006 RatfonalCalcs Existing. xlsxlGValues
EXISTING PROPOSED
o �
d • 4 • . • / . I .. iT (UTi'���
• I � p p p fI}[ r -r�.�, Ilppp���
a
ll
• rI}3f .l II
• I • D
o -
c ,
� o a
w f 1 z � --- I Z
D r
0
z w� °
<
o, LLj
a
w
uj
(7 i'
I6
J , _ _�• J
J_,. .a •.� �__ _.
O Ab -
d Dr
j e
• • .4 ad • ♦ >� . as
LOCUST STREET LOCUST STREET
SURFACE
AREA (SF)
%IMPERV
IMPERV.
AREA (SF)
ROOFTOP -;�� 3,438
100%
3,438
CONCRETE 10,559
100%
10,559
ASPHALT 0
100%
0
LANDSCAPE 0
0%
0
SURFACE
AREA (SF)
%IMPERV.
IMPERV.
AREA (SF)
ROOFTOP
9,879
100%
9,879
CONCRETE
1,385
100%
1,385
ASPHALT
0
100%
0
PAVERS
2.076
40%
630
LANDSCAPE 657
0%
0
TOTALS 13,997 TOTAL= 13,997
TOTALS 13.997 TOTAL= 12,094
DEsa:iPrroN
EXISTING VS. PROPOSED
NORTHERN
COLLEGE EIGHT THIRTY
IMPERVIOUS AREA
ENGINEERING
FORT COLLINS
of ,�
sU-
DRAWING
COLORADO
A. REESE
1 =3a
S K-C 1
OnsE
PHOJEcr
301 N. !boas Wed. Suite 100
PHONE: 970.221.4158
JANUARY 13,2016
574-006
Fart Wlins, Col a 80521
w .na ii,wrginwnrgc
■V NORTHERN
ENGINEERING
Although stormwater quantity detention is not required, stormwater quality mitigation will be addressed by
both temporary and permanent Best Management Practices (BMPs). During construction, the Contractor
will follow the appropriate and applicable City of Fort Collins standards for erosion and sediment control.
Since more than 10,000 sf of the project site will be disturbed, a comprehensive Stormwater Management
Plan will be prepared for this project at Final Design. Post construction water quality and erosion control
will be achieved by a fully established and stabilized site. All areas disturbed during construction will
receive permanent hardscape, landscape, or building structure.
There are no existing stormwater BMP's currently on -site. In order to bring the site into compliance with
the Low Impact Development Standards adopted by the city, water quality mitigation and permeable
pavers will be provided on -site. Water quality treatment will occur through a variety of methods. The first
method is the use of a raised bio-retention area (Stormwater Planter Boxes) along the west side of the
building that intercepts runoff from rooftop downspouts on the west side. These planter beds will have an
engineered section designed to remove particulates and contaminants from the runoff. While most minor
events are expected to infiltrate into the ground, a subdrain is provided to drain the Planter Boxes should it
become overburdened. The underdrain will outfall directly into the existing inlet located at Locust Street
and College Avenue.
There will also be an area of permeable pavers installed on the northeast corner of the project site. This
area of pavers will treat not only the exposed parking areas, but also the rooftop drainage by routing runoff
into the paver subbase. A subdrain and monitoring basins will be provided for the paver subbase that ties
into the same system as the Planter Boxes. The subdrain will have a water quality control structure that
will slow the release of stormwater from the paver subbase and promote infiltration as well as to increase
contact time across the surface area of the subbase.
The City LID requirements specify that no less than 25% of all new paving shall be treated using
permeable paving technique. In the case of this project, 2,076 sf of permeable pavers will be provided,
which is 100% of the total 2,076 sf of new paving in parking areas, which far exceeds the requirement.
The City LID requirements also specify that no less than 50% of any new impervious areas must be treated
using LID techniques. The combination of treatment provided by the Permeable Pavers and Stormwater
Planter will treat 11,068 sf of impervious area on the site, which is 82.67% of the new impervious areas
proposed with the project, which again far exceeds the amount required by city code. A separate LID
Conformance Report and Exhibit have been provided to document LID compliance.
To summarize, the proposed grading concept closely matches existing elevations and drainage patterns.
Existing site imperviousness has decreased from the existing condition, and a variance to the requirement
to provide onsite detention using a 2-year historic release rate will be requested. Stormwater quality has
been provided, and exceeds the city requirements for Low Impact Development paving and treatment.
Therefore, it is my professional opinion that College Eight Thirty satisfies all applicable stormwater criteria.
Please do not hesitate to contact me if you have questions or require additional information.
Sincerely,
Andrew Reese
Project Engineer
Nicholas W. Haws, PE LEED
Project Manager AP
enc.
W INORTHERN
ENGINEERING
Drainage Letter Report
Date: January 13, 2016
Project: College Eight Thirty
Fort Collins, Colorado
Attn: Stormwater Staff
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
Dear Staff:
Project No. 574-006
This letter serves to address the stormwater impacts of the College Eight Thirty project. The project is a
redevelopment of the Schrader's Country Store located on the northeast corner of College and Locust
Street. The site currently consists of rooftop, concrete walks, and asphalt parking areas. On -site drainage
currently flows out from the building to the adjacent streets. Once it reaches the streets, water flows south
on College, then is directed east along Locust. The total impervious area of the existing site is
approximately 13,997 square -feet. The existing percent impervious for the entire site is 90.0%.
The proposed redevelopment will remove the existing structures from the site and replace them with a
mixed -use building. In addition to the new building, the parkways will be modified to meet current Land
Use Code requirements, including sidewalks and landscaping that is not currently present or poorly
defined. An area of pavers is also proposed at the northeast corner of the site, which is the only area of
exposed pavement within the property line. Existing drainage patterns will generally be followed. The total
impervious area of the proposed redevelopment is roughly 13,340 square -feet. When the impervious value
of 40% for pavers is considered, the effective impervious area decreases to 12,094 square feet and the
proposed percent impervious for the entire site decreases to 75.7%. An exhibit depicting existing and
proposed impervious areas has been provided.
The site is located in the Old Town Drainage Basin. Historically, on -site detention has not been required
so long as there is no increase in impervious area. Since the redevelopment does not propose an increase
in runoff, detention would not have been required. However, changes to City policy now require that a
project that is being completely redeveloped must provide onsite detention with a 2-yr historic release rate.
However, a variance may be justified if the site has been paying fees for the higher imperviousness.
Verification of the fees paid to date is underway, however the current assumption is that the site has been
paying the higher fees, and will therefore be exempt from the 2-year release and onsite detention
requirements.
There are no regulatory floodplains associated with the project.
301 N. Howes Street, Suite 100, Fort Collins, CO 80521 1 970.221.4158 1 www.northernengineering.com