HomeMy WebLinkAboutFRONT RANGE COMMUNITY COLLEGE, PARKING LOT EXPANSION - SITE PLAN ADVISORY REVIEW - 10-06 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPond Spillway Calculations
Worksheet for Broad Crested Weir
Project Description
Worksheet Spillway Calcs
Type Broad Crested Weir
Solve For Crest Length
Input Data
Discharge
216.1 cfs --�
Headwater Elevation
5,064.20 ft -�
Crest Elevation
5,063.20 It
Tailwater Elevation
5,060.00 ft
Crest Surface Type
Gravel
Crest Breadth
5.0 ft
Q 5?I« WAY
To? of BERM
Results
9CQU[RED
Crest Length
22.0 ft-1
Headwater Height Above Crest
1.00 ft
Tailwater Height Above Crest
-3.20 ft
Discharge Coefficient
3.00 US
Submergence Factor
1.00
Adjusted Discharge Coefficient
3.00 US
Flow Area
72.0 ft'
Velocity
3.00 fills
Wetted Perimeter
74.0 ft
Top Width
72.0 ft
7revious ?ond
_
QV114WAY _
INpIo%v
6�EsT LENGTH
k + Currev,4 fond
1 Ki?lo w
gi.8c-P + I(6, 3 c'5
= 216. I AS
To? of 3eRNl
So6y.Z ----
_ t
(,o
CkesT exe v,
,�- 7z'
PMk
Project Engineer: Kevin Tone
j:\...\flowmaster\1352c pond spillway.fm2 JVA, Inc FlowMaster v7.0 [7.0005]
03/08/06 10:56:40 AM 0 Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Page 1 of 1
OPTIONAL CONCRETE WING WALL (TYP.)
K. AND PAO (END OF PAD i0 MATCH
` END OF WING WALL)
I Ls 3.-6.
I 1'
I � � (MIN.) 6- 6"
6" TRASH RACK 3/8' ROUND OR
51%51' GRATING iWt$iED CROSS
3/8'16' BOLT TO HOLD� �� (3/8' ROUND OR 1'13/8'
HINGE IN PUCE, 2 I/4' `\ ` A B TWISTED CROSS D BEARING
FROM EDGE OF GRATE . �\ EARS A7 3' O.C., BAR
(TYP. OPP, SIDE) ��� WEARER 70 11AT
BEARING BARS
'S AT
l `
3
A
F. ..
®I�gRR�R�RI�R�RRRRmail/I
�'�RRRRRRRRRRRRRRMRRtl
RRRRRRRLIRRRRRRRR�won
RsonsommooRRRRo�\RRR
tl�R��RRRRRRRsRRRoRRB
�R�RO\RRRRRORRR
���RRR�RRRRRR�RRtl
RORRRRRRR�R�RRtl
MRRRMMENEM
RRq
RR
RlRRn
MEMRE�Rn
\R�MENEM
MENEM
_
t / � -t L"
C \'/ L L
y�i\/ ROW CONTROL
WELL SCREEN TN 93 PATE
STEEL FOREEOVAL) LESS A B PLAN
D
L
TRASH RACK
ELEV. C
0
03 (NOTE 5) 4 R 3
Ln 3/8'16' THREADED BOLT 1
CELEV, B TO FASTEN GRATE DOWN
L
O
WELL SCREEN NO. 93
D (U.S, RATER $iNNLEss _
STEEL OR EQUAL)
C 4 FLOW CONTROL
CONCRETE PAD WITH USE 3T` 10 PLATEY PLATE OF OPTIONAL WING WALLS 100-YEAR OUTLET
DOWEL WITH USE OF
CONCRETE PAD
3/8'16' BOLT TO HOLD
HINGE IN PUCE, 2 1/4-
FROM EDGE OF GRATE SPILL ELEV.
(TYP. OPP. SIDE)
#4012"
3 1/2-
I1 1/2"
KEY
PIPE
STEEL CHANNEL FORMED
INTO CONCRETE SIDES
Wo
� 1 1
3/8'.1" FLAT
BAR HOLDING
FRAME
WELL SCREEN
NO. 93 (U.S.
FILTER STAINLESS
STEEL OR
EQUAL)
ITAINLESS STEEL ANCHOR BOLTS OR
NTERMITTANT WELDS ON TOP AND SIDES
WELLSCREEN
SECTION A -A
/4 HOOP
METAL OR
CONCRETE
PIPE
12- / / -
UP
1
CLR Ir
11 LL
4% 1 jA 4%
SECTION D-D
Wp
WATER DUALITY (WO)
HOLE (TYP), SEE
TABLE
a
1/4' (MIN,) THICK
c STEEL FLOW CONTROL
PLATE
p (TYP) `STNNLE55 STEEL
ANCHOR BOLT (TYP.)
FLOW CONTROL PLATE
SECTION B-B
—
LEGEND
A A SECTION LINE A -A (ARROWS
f4012'
p
PRINT IN DIRECTION SECTION
O.C.
IS WEWEO)
ABBREVIATIONS
CLR. CLEARANCE TYP. TYPICAL
DIA. DIAMETER Wo MOTH OF CONCRETE OPENING
ELEV. ELEVATION VIP WIDTH OF PLATE
INV, INVERT WO WATER DUALITY
d4 DIAGONAL
MAX. MAXIMUM Ls LENGTH OF STRUCTURE
(TYP.)
MIN. MINIMUM Ws MOTH OF STRUCTURE
O.C. ON CENTER X NUMBER
DPP, OPPOSITE 0 AT
O.C.
.GENERALNOTES
--------------------
I. CONCRETE SHALL BE CLASS B. MAY BE CAST -IN -PUCE OR PRECAST.
2 REINFORCING BARS SHALL BE EPDXY COATED AND DEFORMED, AND SHALL
HAVE A MINIMUM i' CLEARANCE.
]CLLR,
3, STEPS SHALL BE PROVIDED WHEN VERTICAL DIMENSION EXCEEDS Y-6'
AND SHALL BE IN ACCORDANCE WITH A SHTO M 199.
4. ALL TRASH RACKS SHALL BE MOUNTED USING STAINLESS STEEL HARDWARE AND
PROVIDED WON MINCED AND LOCKABLE OR BOLTABLE ACCESS PANELS
RACKS 5. TRASH SHALL BE STAINLESS STEEL. ALUMINUM, OR STEEL. STEEL TRASH
RACKS SHALL BE HOT OIP GALVAN12E0 AND MAY BE HOT POWDER POINTED
AFTER GALVANIZING. 1' CIR
f 4012'
L I-'4012- ,1p
i-#4LO12" 14018-
557 TAMPER
SECTION C-C 5/8'PPROOF BOLTS
~u WATER QUALITY OUTLET STRUCTURE _ P FA SIDE)
J
TITS
1/4 THK PLATE
26•
RESTRICTOR PLATE DETAIL
ELEV. A POND INV.
5058.5 FT
ELEV. B WOCU ELEV
50613 FT
ELEV. C
5062.3 FT
SPILL ELEV.
5063.2 FT
Dro 12' MIN.
2.8 FT
Ls
5.0 FT
WS
5.0 FT
Wo
18 IN
HOLE CIA,
1-1/8 IN
WO
OF ROWS
8
OF COLUMNS
5
0
_
0
O
0
0�
O
0000
a
0
OOO
0
IB
— WOCV ELEV.
5061.3
6 PI-1/8'
10 02'
INV 5058.5
L9
PERFORATED PLATE DETAIL
Flow Capacity of a Riser (Inlet Control)
Project: FRCC
Basin ID: Larimer Campus
Layer
00000
$d
layer3
0 0 0 0 0
Numberofholes
Layer
0 0 0 0 0n
inearLlayer
Layer 1
0 0 0 0 0 U
YFImY
Design Information (Input):
Diameter of holes
d =
2.000 in.
Number of holes per layer
n =
5
Number of layers
NL =
2
Vertical distance between layers
h =
4.00 in.
Orifice discharge coefficient
Co =
0.61
Total opening area at each layer
A. =
15.7080 sq in
Ao = 0.1091 sq ft
Calculation of Collection Capacity
The starting water surface elevation must be> the central elevation of the first layer.
Enter water surface elevations in ascending order.
star
B 4SE
FLOW
ketmE
WQCV
ELEV,---,
506f,3
Water
Surface
Central Elevations of Layers of Holes in feet
La er 1 La er 2 Layer 3 La er 4 Layer 5 La er 6 La er 7 La er 8 La er 9 La er 10
Flow
Elevation
5058.56 5058.831 1 1 1 1
Rate
ft
(input)
Collection Capacity for Each Layer of Holes in cfs
cfs
5058.60
0.17
0.00
0.17
5058.80
0:29
0.00
0.29
5059.00
0.38
0.22
0:60
5059.20
0.45
0.33
0.78
505 40
0.51
0.41
0:92
5059.60
0.56
0.47
1.04
5059.80
0.61
0.53
1.14
5060.00
0.66
0.58
1
1.24
5060.20
0.70
0.631
1.33
5060.40
0.74
0.67
1.41
5060.60
0.78
0.72
1.49
5060.80
0.82
0.75
1.57
5061.00
0.85
0.79
1.64
5061.20
.0.88
0.83
1.71
5061.401
0.92
0.86
1.78
5061.60
0.95
0.89
1.84
5061.80
0.98
0.93
1.90
5062.00
1.01
0:96
1.96
LID-Detention_v1.03a, Riser 3/7/2006, 12:46 PM
JVA, Incorporated
Job Name: FRCC Larimer
1319 Spruce Street
Job Number: 1352c
Boulder, CO 80302
Date: 02/06/06
Ph: 303.444.1951
By: PPM
Fax:303.444.1957
FRCC Larimer Campus Phase 1 Parking Volume &
WQCV Calculations
TOTAL
Area sf)
I %la
I %Iwq
9892801
72.0
1 68.0
from Figure ND-1
Extended Detention Basin - EDB UDFCD
Figure EDB-2
WQCV = a ' (0.911^3-1.191^2 + 0.781)
40 hour drain time a = 1.0
Iwq = 0.68
WQCV= 0.27 watershed inches
Design Volume = (WQCV /12) *Area ` 1.2)
Design Volume = 0.605 ac-ft
REQUIRED1 26342 ft"3
Water Quality Outlet Structure
Plate Design:
Inv = 5058.5
Hwq= 5061.3
Dwq= 2.80 ft
Area per row:
Ao=Design Volume / K40
K40 = 0.013 " Dwq^2 + 0.22'Dwq - 0.10 K40= 0.62
Ao= 0.98 in^2
Figure 5 Hole Diameter = 1.12 (1-1/8")
nc = 1
nr = 8
Steel Plate Thickness= 3/8"
AREA = Current Lots (not accounted
for) + New Lots + Future Lots
WOCV ELEV.
5061.3
10 02'
NV 505B.5
18
244
PERFORATED PLATE DETAIL
0
0
0
0
o
0
0000
I-?
000
0
JVA, Incorporated Job Name: FRCC-Larimer
1319 Spruce Street Job Number: 1352C
Boulder, CO 80302 Date: 03/02/06
Ph: 303.444.1951 By: XT
Fax: 303.444.1957
FRCC - Larimer Campus
Orifice Plate using Headwater above opening and
Previous Pond Release Rate' = 6.12 cfs
Current Pond Release Rate" = 13.63 cfs
Q=cA(2gH)A.5 C= 0.65 Q2 allowable release rate= 19.746 cfs
Water Surface Elev 5063.20
Inv Elev 5058.50
Determine the Height of the Plate to release Allowable Flow
Using the 18" RCP pipe for Area that passes Qallowable
Q=cA(2gH)A.5 C= 0.65
Q 19.75 cfs Assume Dia
c 0.65
Hhe d 5.31
Dia
Needed Area 1.64 sf 1.45 ft 17.36 in
Hole diameter needed in order to
discharge the allowable release rate.
USE 14-1/2" Hole Diameter
NOTES:
From Landmark 1997
" For Conservative Design, Allowable Release Rate =
Historic 2-year runoff rate for 22.7 acre study area.
14.53 in
I" CLR
(TYP)
18"
5/8"¢ SST TAMPER 14-1/2"
PROOF BOLTS
(TYP EA SIDE)
1 I
i I
1/4" THK PLATE I I 1
O O
26"
RESTRICTOR PLATE DETAIL
1352c Drainage Calcs.xls
5o 6+s cn
TO of
Qor' 0 'bCfu"
5709! . 5063.
l oo `(R.
vJ5£l,
5062.
Z
O
Q
5061.!
w
50611
W
wacv
w >
VQ
co
LL
w
5060.!
M
(q W
w LL
W
a
3
5059.t
5058.!
STAGE VS. STORAGE
Detention Pond —
i-
ggq�Sc'F
11531 � c�
I
I
1
�
v zuuuu y.
Neui Re? -
UoI-WQCV
4000U 60000
POND VOLUME (CF)
80000 y 100000 y
T 'rvlous Re?.
Vol -too
Plrk�t o �g �-f
(moo rim
Nfw Re7J
vJQCv +
Wevious R71
Vol- too
lm;: c:
TOTAL
Vo-r i Cam.
t= v-t�z OoMr_o
�'� JVA, Incorporated
I11\!!. /! 11 1319 Spruce Street Job Name: FRCC-Larimer
`J ` J �`' I I1 Boulder, CO 80302 Job Number: 1352C
_ Ph: 303.444.1951 Date: 03/02/06
Fax: 303.444.1957 By: XT
POND VOLUME CALCULATION
WEIGHTED
INCREMENTAL
CUMMULATIVE
AREA
AVG AREA
VOLUME
VOLUME
ELEVATION
DEPTH
S.F.
S.F.
C.F.
C.F.
5058.5
50
0.5
151
76
76
5059.0
252
1.0
846
846
921
5060.0
1,439
1.0
14,322
14,322
15,243
5061.0.
27,205
1.0
36,439
36,439
51,682
5062.0
45,672
1.0
54,358
54,358
106,039
5063.0
63,043
0.2
63,642
12,728
118,767
5063.2
64,240
4.7
TOTAL CUBIC FEET
118,767
2.73 ac-ft
STAGE/STORAGE
STAGE
CUM VOL(CF)
CUM VOL(AF)
5058.5
0
0
5059:0
'76
0.002
5060.0
921
0.021
5061.0
15,243
0.350
5062.0
51,682
1.186
5063.0
106,039
2.434
5063.2
118,767
2.727
Volume
Ac-Ft
Surface Elev
Depth
PREVIOUS POND
Required Vol-100*
88975 cf
2.04 ac-ft
5064.00*
4.00 ft
Provided Vol-100*
89833 cf
2.06 ac-ft
5064.00"
4.00 ft
CURRENT POND
New Required Vol-WQCV
26342 cf
0.60 ac-ft
5061.30
2.80 ft
Previous Req Vol-100* +
115317 cf
2.65 ac-ft
5063.15
4.65 ft
Current Req. Vol WQCV
Total Volume Provided
118767 cf
2.73 ac-ft
5063.20
4.70 It
* Includes WQCV
** From Landmark 1997
JVA, Incorporated
1319 Spruce Street
Boulder, CO 80302
Ph: 303.444.1951
Fax: 303.444.1957
TABLE 2
Job Name: FRCC Larimer
Job Number: 1352c
Date: 02/06/06
By: PPM
FRCC Larimer Campus Parking Project 2006
Developed Storm Drainage System Design (Rational Method Procedure)
Design Storm Developed -10 YEAR Cf= 1.25 C100 values are determined from a weighted imperviousness on Table 1
Direct Runoff
Total
Runoff
c
N r
U
N
(„)
_tt:
Y
U
C9C
d
U
E
C
O
J
N O
0 2
7 CDC
In 0 O
3 0
X U ..
«.`
U
w
«Q
U
=
(7
H
W
C
`_'
(1)
(2)
(3)
(4)
1 (5)
(6)
(7)
1 (8)
(9)
(10)
(11)
(12)
(13)
(14)
ou ery
Portion of
Site Outfall
Site
at East
22.71
0.69
0.87
18.3
19.64
1 2.90
1 56.97
18.3
19.64
1 2.90
56.97
Water Quality Area
Design Storm Developed -100 YEAR Cf= 1.25 C100 values are determined from a weighted imperviousness on Table 1
Direct Runoff
Total Runoff
C
C
C
c
o
a
g
E 76
o
c
d
U
E
a 'vim
c d
U
E
E
m
¢
L
cf0
«�
Q
c
W U
U
U
C7
(1)
(2)
(3)
(4)
(5)
1 (6)
(7)
(8)
1 (9)
10)
(11)
(12)
(13)
(14)
Southerly
Portion of
Site Outfall
Site
at East
22.71
0.69
0.87
18.3
19.64
5.92
116.30
18.3
19.64
5.92
116.30
1352c Drainage Caics.xls
Water Quality Area
JVA, Inc.
JVA, Incorporated
Job Name: FRCC Larlmer
1319 Spruce Street
Job Number: 1352c
Boulder, CO 80302
Date: 02106/06
Ph: 303.444.1951
By: PPM
Fax: 303.444.1957
FRCC Larimer Campus Parking Project 2006
Developed Composite Runoff Coefficient & Time of Concentration Calculations
%I
Type of Land Surface Conveyance Coefficient Cv
Location: Fort Collins, Colorado
Open Space
10.00
Heavy Meadow
2.5
Minor Design Storm: 10
Gravel
50.00
Tillagelfeld
5
Major Design Storm: 100
Landscaping
10.00
Short Feature and lawns
7
SOIL TYPE: C 8 D (assumed)
Pavements
95.00
Nearly bare ground
10
Roof
95.00
Grassed waterway
15
Playground
25.00 .
Paved areas and shallow paved swales
20
Art. Turf
25.00
Basin Design Data
e
a
c N
rn�
01 o
3 u
Runoff Coeffs
Initial Overland Time (Q
4=0.395(1.1•Cs)L1QS'r'
Travel Time (t,)
t,=Lengtht(Velocity x 60)
F Computed
I.
Urbanized Check
4
Final
Basin
Aos Agovel Ar Awe Arcot p`Tv,t '4Total ATot,i
Uppermost Slope A
Length Slope Velocity 4
Time of
Conc
Total
Length V(L1180)+10
Min t, =
Name
Design Point
(SO (sf) (Sf) (so (sf) (SO (Sf) (ac)
s¢ E
C2 C5 C10 C100
Length (R) (No) (min)
(it) (°h) C,. (fps) (min)
6+t,=t,
(ft) (min.)
5min
ou e y
Portion of
Site Outtall a[
1
1
Site
East
0 0 267.343 721,937 0
0 989,280
22.71
72.0
0,51 0.55
0.59
0.69
300
1.0
17.5
1200 1.00 20 2.0 10.0
27.5
1500
18.3
18.3
1352c Drainage Calm.xls
JVA, Incorporated Job Name: FRCC Larimer
1319 Spruce Street Job Number: 1352c
Boulder, CO 80302 Date: 02/06/06
Ph: 303.444.1951 By: PPM
Fax: 303.444.1957
TABLE 2
FRCC Larimer Campus Parking Project 2006
Storm Drainage System Design (Rational Method Procedure)
Design Storm HISTORIC - 2 YEAR Cf= 1 C100 values are determined from a weighted imperviousness on Table 1
Direct Runoff
Total
Runoff
c
d
C
C
U
�
m
C
.O76
D_
C
N
U
.�
.�
E
Q
o
u
o
❑
❑
o:
U
u
U
C!
F
U
w
C7
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
Site
:7.72
Outfall at
1
0.00
Eas
22.71
0.20
0.20
18.3
4.54
1.70
7.72
18.3
4.54
1.70
Design Storm HISTORIC - 10 YEAR Cf= 1 C100 values are determined from a weighted imperviousness on Table 1
Direct Runoff
Total
Runoff
c
m
'U
o
O_
0
O
E
U
$
'0
a2m
c
U
E
Q
u
y
co
U
U
C
H
w
U
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
Historic -
Southerly
Site
Portion of
I
Ouffall at
1
Site
East
1
22.71
1 0.20
1 0.20
1 18.3 1
4.54
1 2.90 1
13.17
1 18.3 1
4.54
2.90
13.17
Design Storm HISTORIC - 100 YEAR Cf= 1 C100 values are determined from a weighted imperviousness on Table 1
Direct Runoff
Total
Runoff
C
C
c
m
U
N
O
C
L14)
Q
c
o
omm
❑
m❑
of
U
U
U
f-(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(13)
(14)
-Fistoric -
Southerly
Site
Portion of
Outfall at
Site
East
22.71
0.20
0.20
18.3
4.54
5.92
26.89 1
18.3
1 4.54 1
5.92
1 26.89
1352c Drainage Calcs.xls
JVA, Incorporated Job Name: FRCC Larimer
1319 Spruce Street Job Number: 1352c
Boulder, CO 80302 Date: 02/06/06
Ph: 303.444.1951 By: PPM
Fax: 303.444.1957
FRCC Larimer Campus Parking Project 2006
Historic Composite Runoff Coefficient & Time of Concentration Calculations
% I
Type of Land Surface Conveyance Coefficient Cv
Location: Fort Collins, Colorado Open Space
10.00
Heavy Meadow
2.5
Minor Design Storm: 10 Gravel
50.00
Tillage/field
5
Major Design Storm: 100 Landscaping
10.00
Short Pasture and lawns
7
SOIL TYPE: C & D (assumed) Pavements
95.00
Nearly bare ground
10
Roof
95.00
Grassed waterway
15
Playground
25.00
Paved areas and shallow paved swales
20
Art. Turf
25.00
Basin Design Data
a y
ar
L ,Q
2
3 E
Runoff
Coeff
Initial Overland Time (Q
,rp 113
t;=0.395(1.1-Cs)L S'
Travel Time t
(�)
t,=Length/(Velocity x 60)Urbanized
I. Computed
4
Check
t�
Final
Basin
Aos Agravei Als Avave %{root ATurt Arotal Arotal
Uppermost Slope 4
Length Slope Velocity t,
Time of
Conc
Total
Length F=(L/180)+10
Min t, _
Name
Design Point
(5f) A (So (Sf) (So (Sf) (so (ac)
e o
C
Length (ft) (%) (min)
(ft) N C, (fps) (min)
t;+t,=t�
(ft) (min.)
5min
istoric -
Southerly
Portion of
Site Outfall at
Site
East
0
0
989,280
0
0
0
989,280
22.71
10.0
0.20
300
1.0
28.6
1200
1.00
20
2.0
10.0
38.6
1500
18.3
18.3
1352c Drainage Calcs.xls
, I r•.
ti6.S e�6 0 6 V)
1-4
FF
9 lr
F 870 SV
FF c 15, ccr
Fc
87"0 FF
970
870-
- &c.o
18 17 - 16 15-
95
I
1
•,
u I `
I Q.
a
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7,6
FINAL DRAINAGE STUDY AND EROSION CONTROL REPORT
FOR
THE FRONT RANGE COMMUNITY COLLEGE ADDITION
LARIMER CAMPUS
Prepared For:
The Front Range Community College
4616 South Shields
Fort Collins, CO 80527
April 30, 19%
Project No. DAVP-5J1D-01-303A1
CONSULTING ENGINEER
Landmark Engineering Ltd.
3521 West Eisenhower Boulevard
Loveland, Colorado 80537
FRCC Larimer Campus — State Project No. FR070518
March 30, 2006
Page 3 of 3
vegetated ditch leaving the vegetation intact. This allows the existing trees, shrubs and cattails in
the ditch to thrive and assist with the water quality enhancement.
For this project, the 22.7-acre southerly area has been analyzed in order to provide with water
quality features. As shown by the attached calculations, historic runoff patterns were analyzed
for this area, and it was found that the total historic runoff rates at 20% impervious before the
existing campus was built were 13.2 CFS and 26.9 CFS for the 10-year and 100-year storm
events, respectively. Developed runoff patterns were analyzed for this area, and it was found
that the total developed runoff rates at 72% impervious will be 56.9 CFS and 116.3 CFS for the
for the 10-year and 100-year storm events, respectively. Utilizing these results, a required water
quality capture volume (WQCV) of 26,342 CF was calculated for this area. The proposed outlet
structure is based on outlet details provided by the City staff and includes a water quality plate
and well screen. The release rate at the WQCV elevation (2.8' deep) is calculated at 1.71 CFS,
which includes a base flow of 1 CFS for release of nuisance flows in the ditch, using Urban
Drainage and Flood Control District flow capacity worksheet. An armored forebay is included at
the main 36" RCP outfall into the pond to collect silt and trash before the runoff can enter the
pond.
The proposed pond will have a new maximum 100-year volume of approximately 118,760 CF,
which is an increase of approximately 28,930 CF over the volume of the current pond. This
volume is based on a water surface at the proposed spillway elevation. Additional volume over
the 118,760 CF is provided within the one foot of freeboard to the top of the proposed berm. In
addition, an engineered/armored spillway has been incorporated into the pond which has the
capacity to convey the total 100-year flow to the downstream ditch.
CONCLUSIONS
In summary, this project was designed to improve numerous drainage conditions at the FRCC
site. The existing pond, which has an unsafe berm and lacks water quality features, will be
rebuilt and consolidated with a new larger water quality/detention pond. The new pond will
detain approximately 28,930 CF more than the existing pond. The previous release rate for the
existing northerly pond was designed with an allowable release rate of 6.12 CFS per the
Landmark report. The new pond will now capture both the southerly and northerly portion of the
site and has a limited release orifice which has a conservatively -designed allowable release rate
of 7.72 CFS. The lushly vegetated ditch will remain in tact and will be improved by redirecting
sediment -laden tributary runoff from the ditch to the forebay and water quality basin via an
upgraded storm system.
Please note that this drainage analysis was prepared under my direct supervision. JVA, Inc.
understands that the City of Fort Collins does not and will not assume liability for drainage
facilities designed by others. If you have any questions or comments regarding this drainage
letter submission, please feel free to call us to discuss.
JVA, INCORPORATED
Xavier Torrents
Design Engineer
0 Re
*sees*.
`v��S R H,y ••F9�Q
Mtn
i 37146
Charles R. ger IV, .E. #37
Associate/P t Manager ���•.,�������,.•`�`
FRCC Larimer Campus — State Project No. FR070518
March 30, 2006
Page 2 of 3
portion of the site flows directly to this ditch or is conveyed via a storm drainage system
to the ditch at the east end of the site. There is an 8" diameter PVC outlet pipe at the
westerly, upstream end of the ditch. The beginning point of this pipe could not be found;
however, it is our understanding based on discussions with FRCC and City staff that this
pipe is an outfall line for a groundwater underdrain system somewhere to the west. It is
our understanding that direct rainfall runoff does not enter this 8" pipe. Further to the
west and tributary to the ditch there are two right-of-way outfall pipes that release runoff
from Shields Street.
All runoff from the southerly portion of the site and the Sheilds Street right-of-way tributary to
the vegetated ditch exits the site without detention or significant water quality enhancement.
This existing condition is potentially hazardous and detrimental to the environment and
downstream waterways.
DEVELOPED (PROPOSED) DRAINAGE
The proposed development consists of a minor expansion of Lot 1 and paving of gravel parking
Lots 2 and 5 as shown on the attached Figure 1 - Drainage Map and referenced JVA storm
system plans. Site construction will include demolition of an existing asphalt road, removal of
wheel stops, demolition of storm sewer, minor regrading, realignment of the Shields Street
intersection, replacement of a Type R inlet with a double Type 13 surface inlet near the library,
public sidewalk reconstruction, and all associated utility infrastructure work. As shown on the
drainage map, a future lot was discussed during the recent design process (Lot 7 at the south side
of the site); however, this lot will not be built as a part of this project nor in the foreseeable
future. To produce a more conservative design, the construction of Lot 7 was included in the
attached runoff calculations.
For drainage design of this project, an existing large 22.7-acre study area has been delineated by
JVA as shown on the drainage map. As discussed above, this area currently drains overland to
the existing vegetated ditch, or to an inlet/storm pipe system that conveys runoff directly to the
existing vegetated ditch. This ditch runs through the southerly portion of the site from west to
east and then flows directly offsite without detention.
The motivation of our design is to improve the water quality of the runoff from the site and
provide as much detention as possible for the 22.7-acre study area. To accomplish this, it is
necessary to reshape and redesign the existing pond with more volume and a new updated water
quality enhancement outlet structure, as is typically required by the City of Fort Collins. The
proposed pond as shown on JVA's plans will now capture the previously undetained runoff
from the southerly portion of the site by encompassing the east end of the existing vegetated
ditch. In addition, water quality enhancement will be provided to both the northerly and
southerly portions of the site where none existed before.
Another goal of the project is to protect the existing vegetated ditch. This ditch will not be
modified with this project. The plans require portions of the existing drainage ditch near the
work areas to be protected by silt fence. Any use of this swale by wildlife will not be hindered,
as the existing parking lot extents will not be changed along the swale. In addition, FRCC will
be improving the drainage characteristics near the existing drainage swale. Silt- and trash -laden
storm runoff from the existing large unpaved lots (Lots 2 and 5, which currently drain directly to
the existing drainage swale and leave the site undetained) will be rerouted via curbs, inlets and
storm pipes to the new consolidated water quality enhancement/detention facility. Furthermore,
no wetlands areas will be disturbed during this project. Proposed grading at the new water
quality enhancement/detention facility only requires the removal the berms at the sides of the
"'
NIncorporated
1319 Spruce Street
'
Boulder, CO 80302
March 30, 2006
Ph: 303.444.1951
Fax: 303.444.1957
Mr. Basil Harridan, Utilities- Stormwater Engineer
Toll Free: 877,444.1951
City of Fort Collins — Engineering Development Review
Web site:
281 N. College / 700 Wood Street
www.ivajva.com
Fort Collins, CO 80521
E-mail:
info®jvajva.com
RE: Drainage Summary Letter for
"Reconfiguration & Expansion Of Parking Lots And Traffic Flow Improvements"
Principals
State Project No. FR070518
David M. Houdeshell
Front Range Community College-Larimer Campus, Fort Collins CO
Robert B. Hurries
JVA Job No. 1352c
Thomas P. Skinner
Thomas S. Soell
Dear Mr. Hanldan:
Kevin A. Tone
As requested by the City of Fort Collins Public Works, JVA Inc. has prepared this
Cinders L. Ward
drainage summary letter regarding the proposed improvements and the existing and
developed drainage conditions for the above referenced parking lot project at Front
Structural Engineering
Range Community College Larimer Campus (FRCC) in Fort Collins, Colorado. We have
Daniel E. Cooke
attached the related storm and erosion control plan portions of the final construction plans
Mark C. Cormier
for the project for your information. We have also attached excerpts from the previous
Kathy A.Gilhooly
drainage report by Landmark Engineering dated April 30, 1996. and runoff and structure
Heidi M. Hall
design calculations by JVA, Inc.
Derek D. Henderson
Michael R. Hope
GENERAL LOCATION AND PROJECT DESCRIPTION
Craig M. Kobe
Front Range Community College proposes to pave two existing gravel/road base parking
Michael J. McDonald
lots and enlarge and consolidate the existing detention pond at the Larimer Campus
David M. Mier
within the City of Fort Collins. The parking lots and the detention pond expansion are
Derek M. Pedersen
bounded by Shields Street, Harmony Road and the existing Larimer Campus. The total
Thomas M. Smith
campus/library site is approximately 44.0 acres.
Sarah E. Watts
EXISTING DRAINAGE
Charles B. Wilkerson
The existing site slopes from west to east between two and seven percent. At the
Civil Engineering
northerly and northwesterly side of the campus, existing runoff travels to the east via an
Jon C. Driggers
existing swale and storm culverts along Harmony Road until it reaches an existing
Charles R. Hager
detention pond. An existing outlet structure releases the runoff into the easterly
Howard M. McHenry
downstream end of a vegetated ditch that runs from west to east through the southern
Carolyn A. Sullivan
portion of the site. Existing runoff rates and detention pond facility features were
Melissa F. Tolve
calculated in the Landmark report to be 99.8 CFS for the peak inflow and 6.12 CFS for
the peak outflow (release rate for the I00-year event). The 100-year required volume for
Administration
the existing pond was 88,975 CF and the actual volume of the existing pond was
Andrew P Krizman
calculated to be 89,833 CF.
During our site visits, it was noted that the 100-year outfall/top of structure elevation of
this existing concrete outlet structure is higher than the top of the existing berm that
forms the pond creating a hazardous condition. Furthermore, no water quality
enhancement orifice, well screen, or other features were noted, and there is no engineered
spillway present.
At the southerly side of the campus, there is an existing vegetated ditch that runs through
the site from west to east beside the existing parking areas. Runoff from the southerly
B 0 U L D E R I FORT COLLI N S I W I N T E R P A R K