HomeMy WebLinkAboutDrainage Reports - 04/18/2012I
December 13, 2011
Mr. Wes Lamarque
City of Fort Collins
Storm Water Utility
700 Wood Street
Fort Collins, CO 80522
/NTERWBBT = C O N S U
%ony orrt-Collins Prov Plans
Approved By
bate- 4 =1 R-12.
Re: Liberty Common Charter School — Storm Drainage Report
Dear Wes,
Please accept the following letter report on behalf of the Liberty Common Charter School to
demonstrate the site's compliance with the previously approved Final Drainage Reports for
Rigden Farm Filing One and Filing Six, as prepared by JR Engineering and the Drainage Letter
for Pioneer Charter School dated August 20, 2003, as prepared by Interwest Consulting Group.
City comments dated November 28, 2011 have been addressed in this letter.
INTRODUCTION
This site is legally known as Tract E of Rigden Farm Filing One. It contains 4.72 acres and is
bounded on all four sides by existing city roadways, namely being Custer Drive, Kansas Drive,
Limon Drive and Minnesota Drive. The site is bisected by a previously constructed storm
drainage channel/detention pond which is referred to as Pond 217. The design for this pond was
included as part of the Filing One Drainage Report and was constructed with that Filing. This
pond was amended and is only for conveyance and detention. The original stage -storage table is
attached for reference. There are three ponds in series which drain from west to east (Ponds 216,
217 and 218) which were modeled using EXTRAN and SWMM. All detention and water quality
requirements for this site have been met by the overall Rigden Farm development.
Rigden Farm Filing Six updated the basins in the vicinity of this pond based upon anticipated
ultimate development; however, the original pond sizing (stage -storage) was not altered. Filing
Six did update the SWMM model using the updated basin information; however, the EXTRAN
model was not re -run with that Filing. Excerpts from the Filing Six report are attached for
reference.
The Filing Six updated SWMM model shows that the peak storage of Pond 217 during a 100-
year storm event is 2.2 acre-feet. The Pioneer Charter School Drainage letter interpolated from
the original stage -storage curve to determine a new 100-year water surface elevation for the pond
during the ultimate development. By interpolating from the original stage -storage curve, it was
' Mr. Wes Lamarque
December 13, 2011
Page 2 of 4
' determined that the new 100-year water surface elevation `for the pond during ultimate
development is 4924.0. The pond was modified as part of that project.
' EXISTING CONDITIONS
The site currently has an existing building and parking lot on the southern portion. A drainage
channel/ pond exists through the middle of the site as do the inlet and outlet culverts. The
northern portion is vacant.
■ The site drains in three distinct directions and these general basin lines have been maintained
with the proposed development and in conformance with the Ultimate Development basin
' delineations as shown in the Rigden Farm Filing Six Final Drainage Report.
PROPOSED DEVELOPMENT
' The proposed development is phased and consists of an approximately 6,200 square foot school
addition in phase 1 with approximately 15,500 square feet possible in a future phase for a total of
21,700 square feet. The site will also include a play field, future parking areas and a
reconfigured drainage/detention area. The existing parking lot south of the channel will remain
in its current configuration
' Portions of the existing pond are to be re -graded with this development. During phase one, the
northwest portion of the pond will be re -graded. Because the proposed phase two building
' expansion causes a pinch point in the detention pond, during phase two the pond will be split by
a retaining wall into two and connected via a 30-inch reinforced concrete pipe. The southeast
corner of the pond will also be re -graded in order to contain the 100-year WSEL. A portion of
' the existing drainage easement will be vacated and a proposed Drainage Easement is shown for
this area to contain the 100-year WSEL.
' Attached are the previously approved stage -storage calculations and the calculations with the
proposed improvements. The storage is shown to be equal to or greater than the previously
approved design. Therefore, we request that the pond volume (2.2 ac-ft) be deemed in
' substantial conformance with the approved design.
Although water quality for the site is downstream, low impact development (LID) is in use for
' this development via the 3' by 3' filter channel along the bottom of the pond thereby managing
stormwater as close to its source as possible.
' The existing pedestrian bridge is to be relocated during phase two. The bottom chord of the
bridge is to be set at a minimum elevation of 4925.0 in order to free span the proposed 100-year
WSEL and provide 1' of freeboard above the 100-year WSEL of 4924.0.
' Mr. Wes Lamarque
December 13, 2011
' Page 3 of 4
BASIN DESCRIPTIONS
The site is divided into three basins, the southern (Basin 1), the middle (Basin.2) and the
northern (Basin 3).
Basin 1 is comprised of the southern half of the school building, the proposed south phase H
building expansion and the entire existing parking area. This basin drains to the south toward
Custer Drive where it is intercepted and conveyed via curb, gutter and storm drainage pipes to
' the Water Quality ponds located north of the Foothills Regional Channel. Portions of this basin
sheet flow over the existing Custer Drive sidewalk in accordance with the LCUASS. The
remaining concentrated areas are conveyed under the sidewalk via proposed channels and/or
' sidewalk chases to the flow line of Custer Drive.
Basin 2 is comprised mainly of Pond 217, the northern half of the school building and the
proposed north phase I and H building expansions, the southwest half of the proposed parking lot
and the field area north of the channel. Pond 217 discharges to the east under Minnesota Drive
via an existing storm culvert and into Extended Detention (Water Quality) Pond 218 prior to
being released into the Foothills Regional Channel.
The majority of Basin 3 drains to the north to Limon Drive via proposed sidewalk chases and
' curb cuts and runoff is conveyed in the existing storm drainage system to pond 218 which is just
east of this site. This basin consists of the northeast half of the proposed parking lot and the
existing sidewalk.
' Filing Six similarly utilized an "Ultimate Development" condition for the basins that make up
the School site. All the area contained within the site was assumed to be Commercial or Multi -
Family with an imperviousness of 70% used for the middle basin (SWMM Sub basin 583) and
90% for both the north and south basins (SWMM Sub basins 584 and 58) for an average site
imperviousness of 0.79. The actual imperviousness of the site is 0.51, with a composite C Factor
' of 0.62. Therefore, it is requested that the site be deemed in substantial conformance with the
previously approved Final Drainage Reports.
EROSION CONTROL
Erosion and sedimentation will be controlled on -site by use of silt fences, culvert inlet protection,
' a gravel construction entrance, and seeding and mulch. The measures are designed to limit the
overall sediment yield increase due to construction as required by the City of Fort Collins.
During overlot and final grading the soil will be roughened and furrowed perpendicular to the
' prevailing winds.
During the performance of the work required by these specifications or any operations
' appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor
shall furnish all labor, equipment, materials, and means required. The Contractor shall carry out
proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust
' nuisance that has originated from his operations from damaging crops, orchards, cultivated.
' Mr. Wes Lamarque
December 13, 2011
' Page 4 of 4
fields, and dwellings, or causing naissance to persons. The Contractor will be held liable for any
' damage resulting from dust originating from his operations under these specifications on right-
of-way or elsewhere.
' It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights -of -
way unless so approved by the Director of Engineering in writing. Wherever construction
vehicles access routes or intersect paved public roads, previsions must be made to minimize the
' transport of sediment by runoff or vehicles tracking onto the paved surface. Stabilized
construction entrances are required with base material consisting of 6" coarse aggregate. The
contractor will be responsible for clearing mud tracked onto city streets on a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Silt fence will
require periodic replacement. Maintenance is the responsibility of the contractor.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation shall
not be considered established until a ground cover is achieved which is demonstrated to be
mature enough to control soil erosion to the satisfaction of the City Inspector and to survive
severe weather condition.
I trust that I have been able to address your concerns. If you have any questions or continents
please contact me at (970) 674-3300 Ext: 106.
Sincerely,
/ l.rrlM�1� OPP�O R���
Robert Almirall, P.E. , a
Colorado Professional Engineer 33441 33441 �=
Interwest Consulting Group �¢
Attachments
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3 OWNER/CONTRACTOROFCORADOCISRE GENERAL
FOR OBTAINMGA
STATE OF COLORADO COPHE. GENERAL PERMIT
• \\\ y � � \ /AySp % I / APPLCATION-STORMWATER DISCHARGES ASSOCIATED WITH
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CONSTRUCTION ACTIVITY PRIOR TO CONSTRUCTION (NPDES
1 PERMIT). THE OWNER/CONTRACTOR SHALL PROVIDETHE CITY
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ASSOCIATED E ERALNATEPERMR. SEE ORED TAILS. CONTROL
TRACTA NOTES ON THE GENERAL NOTES PAGE FOR MORE DETAILS.
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CALL UTILITY NOTIFICATION
CENTER OF COLORADO
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II�._(PNA6E if)/ CONSTRUCTION ACTIVITY PRIOR TOCONSTRUCTION(NPDES ,J U
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NOTES ON THE GENERAL NOTES PAGE FOR MORE DETAILS. Z
4 TRASH LLUTANTORAGE.STO SELOCATETOILETSBAND SED ON HE SITE Q'
POLLUTANT SOURCES TO BE LOCATED BASED ON THE
COLORADO DISCHARGE PERMIT SYSTEM -STORMWATER O
` I_ _ _ ,� _ _ P _ __ •�` - iy / / -/ , /' I I \ \ CONSTRUCTION PERMIT STORMWATER MANAGEMENT PLAN
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1.10T21 I I I DRAINAGE SUMMARY TABLE ry -' D m
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I i 155 o EEI O B5 59 i V U
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PRELIMINARYCALL UTILITY NOTIFICATION
NOT FOR CONSTRUCTION CENTER of caoRAoo
II THE COLONY AT RIGDEN FARM \ \ / / 811 PROD. NO. 115002600
II II LOT O �� \ \� >' �\ // / \t >\J� 11
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MEMBER uTl1TIE6.
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Liberty Common Charter School
PROJECT NO: 1150-028-00
COMPUTATIONS BY: es
DATE: 10/26/2011
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
Landscape Areas
Runoff
%
coefficient
Impervious
C
0.95
100
0.95
96
0.95
90
0.25
0
Interwest Consulting Group
SUBBASIN
DESIGNATION
TOTAL
AREA
(ac.)
TOTAL
AREA
(sq.ft)
ROOF
AREA
(sq.ft)
PAVED
AREA
(sq.ft)
SIDEWALK
AREA
(sq.ft)
LANDSCAPE
AREA
(sq.ft)
RUNOFF
COEFF.
(C)
%
Impervious
1
1.55
67,610
9,142
25,066
6,885
26,517
0.68
59
2
2.48
108,234
28,755
11,785
7,244
60,450
0.56
41
3
0.69
29,963
0
15,276
6,015
8,672
0.75
70
Total
4.72
205,807
37,897
52,126
20,144
95,639
0.62
51
Equations
- Calculated C coefficients & % Impervious are area weighted
C=E(Ci Ai) /At
Ci = runoff coefficient for specific area, Ai
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
Cval and Imperviousness.xls
Pond 217 REVISED
Proposed Detention Pond - Stage/Storage
LOCATION:
LIBERTY COMMONS CHARTER SCHOOL
PROJECT NO:
1150-028-00
COMPUTATIONS BY: SMB
SUBMITTED BY:
INTERWEST CONSULTING GROUP
DATE:
12/12/2011
PROPOSED POND PHASE I !keen ezintinn hridnel
Surface
Incremental
Total
Total
Stage
(ft)
Area
(ft2)
Storage
(ac-ft)
Storage
(ac-ft)
Storage
(cubic feet)
17.20
0
0.00
18.00
3480
0.02
0.02
928
19.00
7408
0.12
0.14
6250
20.00
10825
0.21
0.35
15312
21.00
15216
0.30
0.65
28271
22.00
20055
0.40
1.05
45851
23.00
24897
0.51
1.57
68283
24.00
30157
0.63
2.20
95768
PROPOSED POND PHASE II W/ PIPE
Surface
Incremental
Total
i Total
Stage
(ft)
Area
(ft)
Storage
(ac-ft)
Storage
(ac-ft)
Storage
(cubic feet)
17.20
0
0.00
18.00
2106
0.01
0.01
562
19.00
5333
0.08
0.10
4158
20.00
8536
0.16
0.25:
11030
21.00
15414
0.27
0.52
22837
22.00
26524
0.48
1.00
43557
23.00
30796
0.66
1.66
72190
24.00
35422
0.76
2.42
105272
12-13-11 detention.xls
Detention Pond
Emergency Overflow Spillway Sizing
LOCATION: LIBERTY COMMONS CHARTER SCHOOL
PROJECT NO: 1150-028-00
COMPUTATIONS BY: SMB
SUBMITTED BY: INTERWEST CONSULTING GROUP
DATE: 12/12/2011 top of berm
Equation for flow over a broad crested weir
Q = CLH32 spill elevation
where C = weir coefficient = 2.6
H = overflow height
L = length of the weir
The pond has a spill elevation equal to the maximum water surface elevation in the pond
Design spillway with 1.0 ft flow depth, thus H = 1.3 ft
Size the spillway assuming that the pond outlet is completely clogged.
Pond
Q (100) = 40.0 cfs (peak flow into pond)
Spill elev =
24.00
ft = 100-year WSEL
Min top of berm elev.=
25.50
Weir length required: .
L =
10
ft
UseL=
1s
ft
v =
1.86
ft/s
spillway, 12-13-11 detentionAs
' _ unproYei
L�
P�Po
odeT for Rigden If revises the'basin parameters .
Minor changes were made to sub -basins 58, 5-6 66;.6
kgd-n O.D.P. model. Sub -basins 611; 01, and
ge-discharge rating curve for Detention Pond 216,.
and Detention Pond-269 was added in. Basin 64.
he Rigden 11. model is 3:1.5.9 acres, 0.7 acres less tha
s due ' to changes in .basin boundaries along Drat
the SWMM Model Sub -basin Delineation is includi
Drnnage;md Erosion Control Report.
INJ
SWM_
Basin HYld Area . =Ov"nd flow
eA
% Im Slope Basin DescripLan
Subbal
W' Path. G
-
(ff)AK
....
2981.0%
. Commertaal
581
3450 224 283
90% 0.8% Commert9al
582
7700 11 5 295
80% 2.0% :: Multi -tam' 8 CommercJal
583 .
400 2.5 267
70% ? . Moiti-taM
W,584
65.
2900 19.7 296
90% 1.5% Dense multi -Fa .
60
;1200 4.0 1d5
4900 55.1 134
10% 30% : Ad'acenY:to'it 1�m Anal
12%
67
10400 99.2 415-'
:`2.0% ? Adjacent3oRegioiial`£hannei . .,
671
2300 8 3 157
45% 2.0 Single.Faindy
68
2d00 _. 25.2 457 -
19% 10.0% Ad ac to FCRID
459, 2 0% :' s Ie:.Farmty
681
640 _a S.0 dO8 r;:
45% '.1.5% .- sin e:Fami
682
500 3.5 305
450A 15% Single.Famfiy
69
5800 53.5 402
45% " 1.9% ' ' Si e
b ;
68t
170D 3.9 100
31% 10.0°h ImaceffYo;FCRID
315:9 acLj
I-P
E
53 ' Pond Description
Sixponds will be provided for Rigden IL Two primary water quality/detention ponds-' be
located in the northeast and southeast comers of the site. Three water quality ponds 1wt11 be
=
located south of the Foothills Reg onal Channel. A detention pond wi11 be located
'
in thew'
Northwest Roads area.
A
'
F W- 6!m luality/detention Pond 216 will be north and east ofthe improved Drake and'ZegIer ':
Roads and water-quality/detention Pond 269 will be south ;of Rigden Parkwa
y and,west of
Ziegler Road. Both Ponds 216 and 269 will be large wet ponds with detention volume
' 4
available above the permanentwater sui face elevation. The detention have
ponds will water
Drainage and Erosion ContmI'Rgmrt
Pi.armgdeoFFiling Six Pagc I8
'
Dccemba 5 2001
971 133.0
1S
2
'
0 36.
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104.2": 5.1
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115 3 .- 429.9
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4.9
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3.9
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f
4.7
2 14.
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Proposed De&406
As Propose
'
LOCATION.
PIONI
PROJECT NO ,.::
I
CO-03
t COMPUTATIONS BY:
R AU
SUBMITTED BY:p
DATE '.
6/I6/21
V-1/3d_(A+g+'
=_
where
V -, V.o
de
T-
A- su
POND 217
;. Surf
.491725
.' =0
+ .-
_.4919.00
v :93;
I
492000 ..
, z1.26
..4921,00
154
F
492200
� 190
4923.00
,227
100-yr LM1+SEL
; 4924.00
2561
r to of berm4925:50
f F
.: rl .f
at
Proposed :pond Volume
atween;contours, ft
veer contours, ff
-ea.Of contour
44cremer al Total
Storage
Storage
tv
0.03
0 03
D.i7.
t.021
0 25..,
0 32 -
0.78
fl 40
1;_i&
0 56
221
a
_C
hp
_
•.y
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
L-Reconimended Runoff Coefficients from Table 3-3 of City 6fFort bollinsDesign Criteria
ecommended % n Storm Drainage Criteria Manual
Impec" from Urban
�Rqnoff
coefficient
impervious
Streets, parking lots,lasptia!Q;
'0:95,
:100
Sidewalks d6te).'
0 95 r
90
Landscape Areas:
P�l
TOTAL
TOTAL'ROOF
PAVED.-
SIDEWALK
LANDSCAPE
`RUNOFF
%..-DE8IGkATION-1.
-.AREA!
AREA
AREAAPMA
AREA
AREA
COEFF—:
1ri� rvkxis:
�11F i.4
0.57
1559
69F260
7,673; i
:.29,118
:4,37D_
28, 099'.
2A
.1.79
77,072_
--- 10,441
6,032
52 04
-4:0 47
3
23,5W
19, M
;:x34X
11,674
7 7";
7
4��
:.—Tatav
4.72
205,60'.
41.6142,
57.W9
:;13.702::
92.698
�.0.63
E ti qua ons
Calculated coefficients & %-Impervious are area weighted
QI
C (Cl.AJ) I At
Ci = runoff coefficient for specific area AI
v ni t- 44
Ai = areas ofsurFace with runoff :coeffident of d
n nmbof.dffent:ufaes t--wdr,_&
At - total area over is applicable: -the sUnn of 0 Ars
o
I, -
I
KM. 22 1 2
12-
V 1:
C -
val and Impervic=ew
100 SD 0 I.GO 200
SCALE: 1' - 100'
MATCHLINE - SEE SHEET 27
4 R$ a
KEYMAP
A e
L EO=
r
R6
10
DESIGN POINT
N k�ggNygap9
101
BASIN CRITERIA
CZ,
AREA IN ACRES
10A
5 �
r
N BOOM MEMBER BBB
H
BASIN BOUNDARY
ENKTNC PIPES
B"Off-)BBI-BIB
PROPOSED INLET AND PIPE
ri
^P
'
FLARED ENO SECTON
m
v'
■
SIDEWALK CULVERT
M
u
EROSION BALES
S
BI
PROPOSED INLET LOCATION
d
Q
ce
a _ as
- - ws- -
EKISTINC S' CONTOUR
..r
V °:a
- - -
EKISTINC V CONTOUR
(�
ry W F.
PROPOSED S' CONTOUR
PROPOSED V CONTOUR
-)(--
SILT FENCE
^
OINLET
PROTECTION
OCONSTRUCTION
ENTRANCE
L"
OSEDIMENT
TRAP
m
m
RIPRAP
APPROVED 100 M. FLOOD
PLAN LIMITS (2.89- RAINFALL)
BASIN DELINEATIONS ARE BASED ON FUTURE
DEVELOPMENT AND
BOUNDARIES MAY NOT
MATCH CONTOURS
SHOWN.
'O
m
a
I'mPXI D UMMA M PROM 9A•DM90M OF
>-
W
J
w a
o
z z
U
z
O
City of Fort Collins.Cdorodo
r o
LIMUTY PLAN APPROVAL
<
C APPROVED: F to-r-94
.Z .�
GIy E•R�.r 9...
w
CHECKED Y:—M.I:umµ
6mi
BY:
w
rw-lrss•e,.Ir
V.
QZ
CHECKED �� Lw¢ttL
-o
WWI, 9m.
<
CHECKED BY: 77
K
O
.nA a—i-- n.r.ilm oow
OF
CHECKED BY:
rNIIM EI,—CHECKED
FSHEET23
R3
BY: /�T.
0
C -3
1771
m 4e C W 'N4 ry
uli..M v
�j
Basin Summary
Basin
Area C
CIDD
Q100
1
1.59 067
0.84
13.25
2
1.79 ] 4
0.59
7,90
3_
1 34 81
1.00
13,331
1�
11
��\. , ''Ili • , , ,�.�' , ���
\IMIIIIr�` ..wa� fr t
i
l /
r r
.,.. I_ --I ,..
4
- X -
SILT FENCE
IF
INLET PROTECTION
OCONSTRUCTION
ENTRANCE
HOTM
T. SEE CONSTRUCTION NOTES ON SHEET 3.
2- ALL DISTURBED AREAS MUST BE SEEDED AND
MULCHED WITHIN 30 DAYS OF PROJECT START.
3. SEE SHEET 3 FOR EROSION CONTROL DETAILS
4. THE EXISTING STORM DRAINAGE CULVERTS N
THE CHANNEL WERE CONSTRUCTED NTH RIDDEN
FARM FILING ONE
5. THE OUTLET PROTECTION SHOWN WAS
DESIGNED WITH RIGOEN FARM FILING ONE AND IS
TO BE CONSTRUCTED NTH THIS PROJECT. BURY
RIPRAP WITH G• OF TOPSOIL AND SEED NTH
APPRO94ATE MIX RIPRAR CALCULATIONS ARE
FOUND IN THE FILING ONE VIAL DRAINAGE AND
EROSION CONTROL REPORT.
S. THE BOTTOM CHORD OF THE PEDESTRIAN
BRIDGE MUST BE ABOVE THE IGO YEAR WSEL OF
4924-0.
T. THE PEDESTRIAN BRIDGE ABUTMENTS MAY
NOT CONSTRICT THE CHANNEL TO THE EXTENT
OF REDUCING STORAGE VOLUME ON THE
DETENTION POND.
City o/ Fort Collins, Colorado
UTILITY PLAN APPROVAL
J
ZO O
or W 2
O
0' O
LLU
Z LU
W
w
(9O
�a 0
0
SHEET
C8
60F9