HomeMy WebLinkAboutDrainage Reports - 09/30/2015 (2)City of Ft. Collins A e lans
Approved By
Date So z*
September 15, 2015
Mr. Basil Hamdan
City of Fort Collins
Storm Water Utility
700 Wood Street
Fort Collins, CO 80522
iNTER1V T CONSULTING GROU P
Re: The Colony at Rigden Farm, Lot 2 Minor Amendment - Storm Drainage Report
Dear Basil,
Please accept the following letter on behalf of Schuman Companies, Inc. to demonstrate the
site's compliance with the previously approved Final Drainage Report for The Colony at Rigden
Farm, as prepared by JR Engineering dated January 16, 2006. Please note that a separate erosion
control / stormwater management report has been prepared for this project; erosion control is not
addressed in this letter. Also included with this letter are the standard operating procedures for
the proposed rain garden and storm drain system.
INTRODUCTION
This site was subdivided in 2005 and is legally known as The Colony at Rigden Farm Lot 2,
being a replat of Rigden Farm Filing 1. The site is 1.34 acres and is bounded on the north by
Custer Drive, the west by Kansas Drive, and the south and east by The Willow Subdivision. The
site was initially developed in 2006 when the parking lot and utility improvements where
constructed for a proposed multifamily development. The building was not constructed at the
time of the site improvements. This minor amendment is for the approval of a new multifamily
building and associated walk and utility connections to the existing improvements. All detention
and water quality requirements for this site have been met by the overall Rigden Farm
development.
EXISTING CONDITIONS
As previously mentioned, the site currently has an existing driveway entrance and parking lot on
the southern and eastern portion of the site. All runoff from the existing parking lot is conveyed
via curb and gutter to an existing Type C inlet located in the southeast corner of the site
(designated as design point 4). The flow captured in this Type C inlet is conveyed south via an
existing pipe system to Water Quality Pond 2 which was designed with Rigden Farm Filing One.
Mr. Basil Hamdan
September 15, 2015
Page 2 of 3
The northwestern portion of the site was over lot graded when the site improvements were
constructed in 2006 in preparation for the building footprint. This area is currently vacant and
covered with native grasses. There is a slight high point in the center of this vacant area and all
existing runoff drains from the high point equally in all directions.
PROPOSED DEVELOPMENT
The proposed improvements consist of a 12,300 square foot building footprint and associated
walks connecting the primary entrances of each unit to the existing parking lot or public right-of-
way. There is also a proposed trash enclosure that will be located in a median of the existing
parking lot.
Per previous conversations with Basil Hamdan on this project regarding low impact development
(LID), this project is not required to _ provide pervious pavers since the parking lot was
constructed in 2006. It is proposed to provide two rain gardens - one on the east side of the
building and one on the west side - that will capture and treat a minimum of 50% of the roof area
of the new building. This will satisfy the current City code that states 50% of all new impervious
area must undergo some form of LID treatment. Overflow from these raingardens will be routed
through a private 12-inch storm system that will connect to the existing Type C inlet located in
the southeast corner of the site.
BASIN DESCRIPTIONS
The Final Drainage Plan for the Colony at Rigden Farm dated January 16, 2004 divided the site
into four drainage basins (basin 101-104). Lot 2 consisted of a portion of basin 101 and all of
basin 104. For the purpose of this letter, a small portion of the roof area in basin 101 will be
relabeled as 101 a. Basin 104 will remain as previously shown. Please see the attached Drainage
Basin Map.
Runoff from basin 101 will flow overland both to the west and to the north where it will be
intercepted by existing curb and gutter in Kansas Drive and Custer Drive respectively. This
runoff is ultimately conveyed east of the site along Custer Drive.to an existing sump inlet which
conveys flows south to the existing Water Quality Pond 1 designed with Rigden Farm Filing
One.
Runoff from basin l0la will be conveyed to the rain garden located west of the building. All
runoff that doesn't infiltrate back into the ground will be conveyed via pipe system to the
existing Type C inlet in the southeast corner of the site identified as design point 4 in the Final
Drainage Report for the Colony at Rigden Farm.
Runoff from basin 104 will be conveyed via overland and gutter flow to the existing Type C inlet
at design point 4. Runoff from a portion of the proposed roof will be conveyed to the rain garden
located east of the building. All runoff in the rain garden that doesn't infiltrate back into the
ground will be conveyed via pipe system to design point 4. The flow is then conveyed south via
an existing pipe system to Water Quality Pond 2 which was designed with Rigden Farm Filing
One.
Mr. Basil Hamdan
September 15, 2015
Page 3 of 3
The proposed building footprint has been reduced by approximately 500 sf as compared to the
previous building footprint approved with the Final Drainage Report for the Colony at Rigden
Farm. The proposed walk connections to the buildings are of equal square footage to the walks
approved with the original plan. The proposed design maintains the original basin boundaries
with the exception of basin 101. A portion of the roof that was intended to go.to design point 1
will now be re -directed to the rain garden on the west side of the building and ultimately to
design point 4. As previously mentioned, this basin has been designated as basin 101a. The 10-
yr flow from basin 101 a is 0.2cfs and the 100-yr flow is 0.5cfs. According to the original report,
the existing 21-inch pipe that conveys runoff from design point 4 has a capacity of 14.9cfs. The
original flow directed to this pipe was 9.2cfs so the additional 0.5cfs from basin 101 a will have
no adverse impact to the storm system downstream. Thisadditional flow is considered
negligible to the overall design of Water Quality Pond 2 designed with Rigden Farm Filing One.
I trust that I have been able to address your concerns. If you have any questions or comments
please contact me at (970) 460-8487.
Sincerely,
4 "4t4
Skylar Brower, P.E.
Colorado Professional
Engineer No. 44248
Attachments
Drainage Basin Map
Hydrologic Calculations
Rain Garden Sizing
LID Exhibit
Standard Operating Procedures
Reviewed By:
Robert Almirall, P.E.
Colorado Professional
Engineer No. 33441
or'q.P
G/ST
33441
�o:kN :,.
S��ON* AL •EaG
i
----------..------W------------------- a---- I
am
[ 71JW161D
Fti
q
.SST
r
I I
I
11
j �
i
101
I I
I
see as7 I
I
I
'----
I
I
I
I
---,
j )T
,
I r
I
'
I
L
I
I
I
I
I
I
I
I
I
I
s
CIISTE�p DRlI/B `\� �a
\ _
492
491➢29 INp \ \ \ \
T9 �
101D ,
II aoe aa7 , .
*I
ME
Emrnv4WnPnLUA1
AbLTmen
ei.
_�».
E.»na.m
�.�.
�nA�P.
DPn�[.:�
AMw Pryakx 6MRr
nRwM tybtruwf
L+m b-'•
h (0. ;pry, CIWRI
rtex:nP,Dter
_
-
IIIIIIIIIIIIIIIIIIII.IIIIIIIIIIIIIIIIIIIIIII.
•Vxil+:erErtr RG•
eWWctf
-
Iw balsa ryl+vul'
-
-
mFRw Dirum•
_---
0.y4e
• •I +qb .sal mn
I+Wriab
+ IIUWIeO.MF+mnylq
.
•ps[N
.TPw+ry SRGR PIwnl.y
A nine ay
lrtew0l ul
ftx ml. xtlyn"CA
.
+MWla+n
A nme ILIA.
/t ut BRrmernI
xtNnlDW
-
+rexfdryPo+IaIR
InRe6w:beiyie+MWY.s
A tlNaW
irtewllut ORm.Wr41R
x[NnrD
FF=4930.15 • \ i i / \ /
r---II r--- ' I I I 1 I 1W / i_I_ I \ 9� Y \" �.\ \/
r \\\\ IN \\./
1 I I a 03
,4930
a81o0. _ I ' I I _ I I I •: I I / / \\\/ /� J / .
/
LEGEND
� Xxx/ EXISTING MINOR CONTOUR
�xn% EXISNNGMAIORCOWOUR
�XIf%If/ PROPOSED MINOR CONTOUR
,400w/ PROPOSED MAJOR CONTOUR
PROPOSED DRAINAGE BASIN DIVIDE UNE
PROPOSEDDIRECTIONOF
OVERLAND FLOW
:WAGE BASIN NUMBER
a 1 .•/ AS INCOEFFICIENTIICOM
RAINAGEBASINAREA
,I DESIGNPOINT
O® CONCRETEWASHOUT
OSILTFENCE
■
OOWATTLE INI_f:TPROTECTION
�O --.,* GRAVELSAG
_ ----1
________________________________ I i 1► W /\\ i` NOTES:
p• I II1IIj f11 I _ �AIp / / \ \v
_
I. CONCRETE WASHOUT LOCATION TO BE DETERMINED IN
14I Ii� I 1 I I I I I e9T9- ' _ .9TB- 4D1A / // /� \ // <\ ../ THE FIELD.
2. CONTRACTOR TO ESTABLISH PERIMETER PROTECTION
A NGTHEUM FDSTURB
\ ItLO ITS I ANCETOLIMrr ACCESSTO
u �Po----------,h�-------__-� 9b -\ J J� \ / // / `� / / THEAENEROM ENTERING
TION U LIC RIGCTORTAY
/ \ / / / / SEDIMENT FROM ENTERING THE PUBLIC RIGHT OF ICE
O LIMIT
THROUGH THE USE OFATRACKOUT CONTROL DEVICE (EX.
1 \ \ �\ /y RUMBLE MA) OR OTHER APPROVED METHOD.
I i I I / /1 \ / 3. THE DOWNSTREAM INLET ON THE SOUTH SIDE OF
_ _ CUSTER DRIVE JUST WEST OF THE ROUNDABOUT MAY BE
�- 4 \ REQUIREDTO RECEIVE INLET PROTECTION IF GRAVEL BAG
I / / I I � / /1b / �� \\ ATPROPERTV LINE IS NOT ADEQUATELY MAINTAINED.
PROV. COR1lEnR /
I 1441621.b7 / a L 4 A. / \ \ /
_-----
I 313004SW
m
LL_ r-,LJ_
I _ I_I
DRAINAGE SUMMARY TABLE
Design
Polm
Tributary
Sub enin
_ _
Area
lac)
C (21
_
C (10)
__ __
C (100)
_ __ .._ _
tc (2)
tt (10)
_ _ _
(min)
tt 1100)
_ _
(min) __
O(2)tot
_ _
- (do)
O(10)tot
0(100)tot
DRAINAGE
� _-�..
STRUCTURE
---MEMARKS
(C1W)
-
_
(CIS) _
(min)
101
0.99
0.46
0.46
0.57
12.7
12.7
12.7
0.8
1.4
3.6
loin
0.06
0.53
0.53
0.67
5.0
5.0
5.0
0.1
0.2
0.5
102
0.61
0.511
0.58
0.73
5.3
5.3
5.0
1.0
1.7
4.4
103
0.24
0.62
0.62
0.77
12.2
122
9.6
0.3
0.5
1.5
004
0.6%
0.69
0.69
0.86
1 6.5
1 6.5
5.6
1.6
2.7
72
-�
L I I
L1
I rJ
O N
U O O
- W O m
W Z)
W
tE Z 0 -
IL °
CI a Q-JN
i 0 (9Ou C>
a U W (Ij m
Z JjzLj
IL F -1O
I NjUa
U p ¢
�O
CALL UTIUTY NOTIFICATION
CENTER OF COLORADO
ry
N
x
Q
811
q
-
z
m
)
L" 2-9USINESS DAYS N ADVANCE
\
q
W
W
BEFORE YOU DID GRADE. OR EXCAVATE
m
O
FOR ME MARNING a UNDOCRWND
MEMBER UMIMS
a
y
V
CITY OF FORT COLLINS. COLORADO
.
a
UTILITY PLAN APPROVAL
APPROVED:
CITY ENGeIEER
DAIS
CHECKED BY:
WATER n WASTEWATER UIE11Y
DAIS
CHECKED BY:
S1g01WAlFR UIMY
DAIS
CHECKED BY:
PARNS a RECREATION
DAIS
PROD. NO. 123J1.1
CHECKED BY:
IRAmc DKRNEER
DALE
4 OF 7
CHECKED BY:
NANRAL RESOURCES
DAIS
A
:3
O
`
Q
W
5
ac
d
L
O
a
N m
� C
U
y
t N
ZF
W
tl
oU
LL
U
LL
c
W
o 'A
U i
0
LL
° E
LL c
o
Z ¢
F N
C
14
C
¢ C
O
M
c
� E
O O
U
O
E
E
m
c
cr
N
Z
2 0°
O0
v
c
zza
and
OU
o a 0
¢ ¢
coc
G
�OOiN
o
n
00
E
w N
O'
N IO
N
O O
c Ummm
�m
In
� o
U
o0000
A
O Q
T
a
so
U c
m
N N
O n
� N
s
t0 _q
a -
N
N C
m 3
m �
J
W W
W
a
r
a
r
O
¢ ¢
LL
N
6
¢
J J
w w
W
a
w
W
¢
O
O
¢ ¢
z
¢ ¢
w
t
w w
t t
a a
x x
N
LL
N N
LL LL
r r
¢ ¢
O O
O
O O
z z
co
LL m
LL LL
O
2 U
w
Q'�'
d
O
N N..
O O
O O
¢
w
a
Q
N
0
4
5
J
> ug
¢
s
o
0 0
0 0
a =
c7
LL Q
W¢
O
N
0 d
m N
W Q
y
N
O d
N O
O a
N
U
J
f
O
n
O n
N 0
O N
N 0
J 4
z 3
N
a
A N
m d
y N
0
Q
W
O
N �
N Z
Q 0
LL Q
R �
Z
pZ
W
N Z
O
U
LL
O
W
2
F-
E
LL
C
O
�co
11
U
E
0
N
Y
Q
W
¢
n
O m
N N
E
LL
n
m a
m
#
N
-
m
V
0
= Q
N t N
m
U ¢
F
u �
m
O m
N m
V #
3
co
o�oide
p
r E
J
LL
moo
soa
Wm
x
¢
C m
o
0 0
0 0
p
W
N OO
�
o
0 0
0 0
0
0 0
0 0
~
c
av'nncni
F .^.
a
m m
� m
O
O O
O O
0 o m
c � a
J
O
Z
m
m m
N m
a
O
N N
t0 b
J
¢
O
O O
O O
7
Q W
�
Z
_ F
m
d � N
o
0 0
0 0
z
m
o
0 0
0 0
m
m
N
Z
m
0 Z
m�wo
N C
O a
E
U
E
IY
A
w
Q
g
w
n
oo�om
J
m
lV
Ui i(i
Oi i(i
Z ~
E
LL
n
n a
m T
O
N
C �
fV lV
E v
mu
O..
yd
n
ou>o
m
U Z
w
J
n
V
IO N
N
N m
N CJ
Q
m �
O
N m
O O
V
O N
U
C
G
N
O<
0
O^
E
J
w
J
W
m
le le
m a
o
o
a
S
o
in
mm�o
m
U
O
m c
o
0 0
0 0
W
o
0 0
0 0
U
O �o �
66666
W
O
N N
M
J
W
L
ln�f
Z n
f
£
m
O O
m N
�-
E m
0
0 0
0 0
O a m
L
cU Z a
m
J v v
N
m n
m
U
o
0 0
0 0
O
V
J
Q
y�
m
O
7 m
of m
N m
m m
C
G G
C G
O
4E w
2
O m
No
Q� v
N
z
m N
m O
Qm
O
0 0
0 0
m
y
2
2 r
co
t7
m f
N O
m
t
�
3
U
Y LL
c
o
� O
= w
�
c m
w
mE
m
D
O
C
N
N N
N
N
� C
In
E
E
O
V N
N II
C
O
+ r
J
C_
>
`o E
U
E
U
E
to
c
O
E
n
7
II
(J
II
11
C
C
fi
c
d
BOA
Iz
0
¢Y
Q
W
¢
�0
O
H
v N
a d
¢
W
O
c
>
E c
¢
cc
O Y O
t o a
U
N
CD
�
O
M
t0
a3^it
N
O
in
0
in
I�
inm
O
10
C.9
N
N
N
N
N
c
n
O
M
N
N
O
E
Nun
L6
6
a
10
10
t0
U
o
0
0
0
0
0
Q
GMD
O
t0
N
GMO
O
O
O
O
O
LL
LL
O
c� H
z
° m
0
N
M
a
¢
� D
W
C
c
rn c
y O
d a
0
0
z
N
a
LL
LL
O
z
2
Y
Q
aw
0 Q
OW
x}
� o
W
J
Q
z
O
Q
x
11
N
Y
S
Q
W
2
0
r
o
O
r
O N
U
w
c
O
odr
a
o
U
c F
vi
a
ti
vi
a
E
N
ui
N
N
ID
U
WMWNM
a
l
Lq
f
W
U
o
0
0
o
c
-00000
LL
¢
� n
U
~ U
w
0
c
w O
o a
0
a
N
J
z
Z
LL
O
LL
LL
LL
0
z
Y
Q
W
aLU
Q
O>
UJ O
L
J
Q
z
O
H
Q
E
co
z
0p
0E-F _
< W a
u0
Oa0C
N
Y
Q
i
W
S
0
O m
p
N
a
N
N
Q
O U
fh
o
v
e
r
Od
r
_O y
U
¢
a
w
O
�
T
O H p
� o a
a
U
O in
�O
N
a
N
N
G
n
0
0
p
U
E
N
N
lA
f o
N
U
u000ro
U
o
0
0
0
0
Q N
w
O
O
O
f0
O
N
O
M
6
LL
LL
7
N O
N
M
Q
r
Q
U
W
O
y C
o a
d
7
U
LL
_0
E
0
w
N L N
\ L
V C U
Co
O) N co
r =C
U a)N cU
N 0— CD
v — �
4) C r
o2c`v
If II II
00
d
W
C
7
= U Q
a � �
W
O y �
0
p N
t0
N
Q
N
N
Q
O^ A
Q
N
h
N
h
_O
0
m
�
O
t7
t0
N Y
Q
O
O
O
r
S C
r
O
O
� E
u
�
N
N
6
w
O c
r�
O
M
N
N
Y E
N
N
N
N
N
iz C
r
O
N
N
N
4 [
N
N
N
N
N
$
�
N
le
h
I�
-q
U
O
O
O
O
O
V
o
0
o
c
c
d
CO
O
O
N
m
m
Q
O
O
O
O
O
C
d W
5 a
o
�
0
0
0
a o
0
f to
Ll
Design Procedure Form: Rain Garden (RG)
Sheet 1 of 2
Designer: sb
Company: Interwest Consulting Group
Date: August 18. 2015
Project: The Colony at Rigden Farms
Location: Root Drains
1. Basin Storage Volume
A)
Effective Imperviousness of Tributary Area. I,,
1 _
58.0
00
If 00 / if all paved and roofed areas upstream of rain garden)
B)
Tributary Area's Imperviousness Ratio (i = 1„/100)
0.580
C)
Water Quality Capture Volume (WQCV) for a 12-hour Drain Time
WQCV _
0.18
watershed inches
(WQCV= 0.8' (0.91- i'- 1.19' il+ 0.78 - i)
D)
Contributing Watershed Area (including rain garden area)
Area -
6.775
sq ft
E)
Water Quality Capture Volume (WQCV) Design Volume
VWU" =
104
cu ft
Vol = (WOCV ! 12) ' Area
F)
For Watersheds Outside of the Denver Region, Depth of
dF =
in
Average Runoff Producing Storm
G)
For Watersheds Outside of the Denver Region,
VWOCV OTHER =
cu It
Water Quality Capture Volume (WQCV) Design Volume
H)
User Input of Water Quality Capture Volume (WQCV) Design Volume
VwOcv USER =
cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A)
WQCV Depth (12-inch maximum)
Dw c%, =
8
in
B)
Ram Garden Side Slopes (Z = 4 min., honz. dist per unit vertical)
(Use "0" if rain garden has vertical walls)
Z =
4.00
It / It
C)
Mimimum Flat Surface Area
AM,,, =
69
sq ft
D)
Actual Flat Surface Area
AActu.0 =
172
sq ft
E)
Area at Design Depth (Top Surface Areal
ATE, =
354
sq It
F)
Rain Garden Total Volume
VT=
175
cu ft
(VT= ((ATw + AAau,) / 2) ' Depth)
Choose One
3 Growing Media
(� 18" Rain Garden Growing Media
Other (Explain):
c.�� r%;�, a iz^w rk�1111 .. Qm,
4. Underdrain System Choose One
A) Are underdrains provided? Q YES
Q NO
B) Underdrain system orifice diameter for 12 hour dram time
i) Distance From Lowest Elevation of the Storage y= ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours V0112= N/A cu ft
iii) Orifice Diameter. 3/8" Minimum Do = N/A in
2015-07-06 Rain Garden Basin.xls. RG 8/18/2015, 1223 PM
Design Procedure Form: Rain Garden (RG)
Sheet 2 of 2
Designer: sb
Company: Interwest Consulting Group
Date: August 18. 2015
Project: The Colony at Rigden Farms
Location: Roof Drains
Choose One
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
YES
A) Is an impermeable liner provided due to proximity
QQ NO
of structures or groundwater contamination?
Choose One
6. Inlet / Outlet Control
Sheet Flow- No Energy Dissipation Required
A) Inlet Control
Concentrated Flow- Energy Dissipation Provided
7. Vegetation
C) Seed (Plan for frequent weed controF
Plantings
O Sand Grown or Other High Infiltration Sod
Choose One
8 Irrigation
0 YES
AI Will the rain garden be vngated?
O NO
Notes:
2015-07-06 Rain Garden Basin.xls, RG 818,2015, 12.23 PM
I
WEST I
1 — — _ -
II I
AM GARDEN
II
II
II II
I
NEW IMPERVIOUS AREAI
TREATED W/ LID —
� I
II r
II L
I�
1 50
SCALE: 1 ' = 50'
/% ' 1716 w. AM. Sins c
V Wlna.o� , cowraao $05W
Ph(970)674-3300
Fm (970)674-3303
I N T F R W E S T C O N S U L T I N G G R O U P
I
\ X
A as'
_ � R
It
o \
� s
EAST RAIN GARDEN
3
r L Li
LID BASIN AREA EXHIBIT
NEW IMPERVIOUS AREA: 14,612 Sf
MINIMUM AREA TO BE TREATED: 7,306 sf
BASIN AREA l - WEST RAIN GARDEN 3,825 Sf
BASIN AREA 2 - EAST RAIN GARDEN: 3, s
TOTAL AREA TREATED: 79650 sf
BASIN AREA 3 - NEW IMPERVISOUS
AREA NOT TREATED 6.962 Sf
BASIN AREA 4 - EXISTING
IMPERVIOUS AREA NOT INCLUDED
IN CA LC. 22,210 Sf
THE COLONY @ RIGDEN FARM
LID AREA EXHIBIT
DATE: 08,19/15