HomeMy WebLinkAboutDrainage Reports - 01/04/1994is
Final Storm Drainage Report
for
SILVER OAKS P.U.D., SECOND FILING
DECEMBER 1993
STEWART&ASSOCATES
Consuldn3 Engineers and Surveyors
103 South. IkZdvm SiAeef
F04t Co&&6, Coto4ado 80511
, * 3031482-9331
1i
TABLE OF CONTENTS
TOPICS
- Storm Drainage Report
- Erosion Report
COVER / LOCATION
YELLOW
- Erosion Control Design/Estimate PINK
- Times Of Concentration
Runoff Computations
- Hydraulic Design Information
- Referenced Attachments
•
BLUE
PURPLE
RED
GENERAL SITE CONDITIONS
•
This is the "Final Submittal" for Silver Oaks P.U.D.
Second Filing (the Filing), which is being developed by Tri-Trend
Inc. of Fort Collins. .The proposed improvements will involve the
continuation of single family home sites, in this previously
approved Preliminary Overall Drainage Plan for this medium density
residential development. Silver Oaks is, on the Northwest corner of
the intersection of Horsetooth and Taft Hill Roads. It is situated
in the South 1\2 of the Southeast 1\4 of section 28, Township 7,
Range 69 West, of the 6th P.M..
The site, 7.98 ac, is at the upstream end of the Spring
Creek Drainage Basin near the foothills. Adjacent land uses include
Olander Elementary. School and Silver Oaks First Filing to the
Southwest, and undeveloped areas to the Northwest of this proposed
Filing. On the North side are residential "ranchetts" with lot
sizes of approximately 5 acres. These home sites are not within
current Fort Collins. City Limits, and remain within Larimer
County's jurisdiction. East of this Filing is the newly constructed
detention pond and South Taft Hill Road; Rossborough Subdivision is
on the other side of South Taft Hill Road. Finally, on the South
are Silver Trails Drive and Bronson Street, both part of the First
Filing.
• /
Storm Drainage Report
. Silver Oaks P.U.D., Second
Page 2
HYDROLOGY
A detailed exhibit is included which was developed with the
First Filing to show the Overall Drainage Plan (ODP). It shows
basin patterns for historic, and conceptual developed conditions.
This ODP was approved on March 3, 1993 and outlined the future
storm drainage development for the entire Silver Oaks P.U.D. site.
All hydraulic and hydrologic design has been established using the
ODP concept as a basis, along with the City of Fort Collins Storm
Drainage Design Criteria and Construction Standards (SDDCCS). The
labeling of all developed basins included on the Second Filing
Grading, Erosion and Drainage Plan are consistent with the ODP,
along with hydraulic structures and design points pertinent to this
Filing.
The drainage area of this Filing includes 9.23 ac that
consists of five subbasins. The Rational Method was used to
establish direct runoff rates from these basins. Times of
concentration (TOC) and intensities were established by methods
identified in the SDDCCS.
A runoff coefficient of C=.50 was used for the developed
condition, the same used in the ODP. The results of this analysis
are shown on the spread sheets attached. There was a revision made
to the subbasin areas from those tabulated on the ODP, due to
errors in the ODP.
•
Storm Drainage Report
. Silver Oaks,P.U.D., Second
Page 3
A planimeter was used in establishing all basin areas. Planimeter
readings were repeated for the subbasins in the area of this
Filing, and errors in the areas used in the ODP were discovered.
The correct subbasin areas were incorporated into the spreadsheets
for this Filing. Although the area that encompasses the Second
Filing, basin IA-1 in the ODP, was underestimated in the ODP, most
of the basin areas comprising the First Filing were assigned
erroneously large areas. The downstream flows used to size drainage
structures are therefore approximately correct, and inlets and
pipes installed have adequate capacity for the revised flows.
TOC's ranged from a low of 5.0 min in basin IA -lc to the high
of 20.6 min in basin BL-1, both are the 100 yr. TOC. Total direct
runoff is 10.0 cfs for the minor event and 34.1 cfs for the major.
Noteworthy, is the fact that the subbasin contributing to the BL-1
pan includes a 1.29 ac area developed in the First Filing,
resulting in a contributing area for BL-1 of 1.64 ac. Two basins do
not drain to the storm sewer collection system, basins IA -lc and
IA -la. Basin IA -lc flows into the backlot swale N-1 toward
detention, and IA -lc flows overland/channelized into the existing
detention pond. Basins BL-1 and IA -lb are collected and conveyed by
the existing storm sewer system. B1-1 releases to inlet IC, while
basin IA -lb flows to inlet IA. Confirmation of all hydraulic
capacities will be shown in the Hydraulics section of the report.
•
Storm Drainage Report
• Silver Oaks P.U.D., Second
Page 4
HYDRAULICS
All hydraulic design criteria meet the SDDCCS. Catch
basins/inlets pertinent to this Filing are IA and IC as identified
in the ODP and shown on this GP. The piped storm drainage
conveyance system has been designed and installed as part of the
First Filing. Catch basins were sized and located so that
subsequent street developments will be easily accommodated.
Additionally, back- lot pan BL-1 was constructed as part of the
First Filing improvements. All of the aforementioned are indicated
on both the ODP and the detailed GP for this Filing.
Piping network capacities were established during the First
Filing, using software developed for the Urban Drainage and Flood
Control District, by University of Colorado, Denver. The title of
the package is "UDSEWER." The piped system was designed to carry
the 2 yr. design storms while the 100 yr. will be carried by
available street capacities. Design flows were established as shown
in the "Hydrology" section of the ODP and incorporated into the
hydraulic model. Revised hydrology for this Filing is within the
capacity established for all streets, collection inlets and pipes
(see attached ODP). Inlets of interest include IA and IC as shown
on the ODP. Design flows to these inlets calculated in the ODP are
5.8 cfs and 9.7 cfs respectively. Actual capacities are 7.1 cfs and
• 9.5 respectfully, and shown in the computational package attached.
Storm Drainage Report
Silver Oaks P.U.D., Second,
Page 5
Flows to these points, based on the Second Filing basin
delineations, are 5.9 and 9.8 cfs in minor events. These flows
represent the peak flow rates to these specific inlets from their
entire tributary areas. Inlet IC is 3 percent over design capacity
0.3 cfs, this overage of capacity does not pose a concern as it
will move to the east and be collected in inlet IA. Inlet IA has an
available capacity in a 6-ft inlet of 7.1 cfs, following this phase
6.2 cfs will be directed towards it, this inlet is adequate. No
subsequent improvements will affect these specific inlet flows.
Though flow to inlets IA & IC modestly exceeds the original design
flows calculated from the ODP, the 6-ft and 8-ft existing inlets
require no modification.
The only new construction being undertaken during this Filing
will be a backlot swale N-1, which will release directly into the
existing detention pond. Geotech fabric as shown on the GP is
proposed to protect the pond bank. The swale for N-1 will be 15-ft
wide and 1.35-ft deep. Earthen slopes will be at the slopes 4:1
and 5:1 within the easement. The capacity of the pan will retain
the major event within the easement section. Under drains will be
provided to control nuisance flows in "flatter" areas of the swale.
Thus, all SDDCCS hydraulic capacity criteria are met. Additionally,
back lot pan BL-1 meets pertinent design standards also.
•
Storm Drainage Report
• Silver Oaks P.U.D.
Page 6
DETENTION REQUIREMENTS
No specific detention modifications will be required as part
this Filing. Detention designed, and constructed in the First
filing has been sized in a way that includes the area of the Second
Filing.
CONCLUSIONS
This Second Filing of Silver Oaks P.U.D. will not deviate in
concept from the approved Overall Drainage Plan of March 1993.
Basin configurations have been refined with the final gradir)g plan,
this has direct runoff to the existing inlets IA and IC developed
to there final conditions. The facilities constructed as part of
the First Filing provide adequate storm drainage conveyance
throughout. No modification will be necessitated by the Second
Filing.
Should any questions arise during your review of this report
please do not hesitate in contacting Alex Evonitz or myself at your
earliest convenience.
Respectfully, •,.P�ou„R(%Ty`.,
GIsTck-. 5ee r
Richard A. Rutherfor , P.E. & L.S. :*1 c O O `
• a O ,
:o $:\siloaks2.rpt
•" F.
•
EROSION CONTROL REPORT
The Second Filing of Silver Oaks P.U.D., ±7.9 ac, is a single
family development that falls in the area of high rainfall
erodibility and moderate wind erodibility. Following is the
construction sequence for which erosion control will be provided.
Construction of the detention pond in the First Filing will
act as a sedimentation basin. The first scheduled activity will be
the installation of gravel curb inlet filters at inlets IA and IC
as shown on the Grading Plan. Additionally, straw bale dikes will
be placed at the release points of pans BL-1 and the newly
constructed N-1. A third straw bale dike will be placed at the
outlet of the existing detention facility ensuring an effectiveness
above the performance standard.
Street rough cuts will be next in the sequence of activities.
Those gravel filters will provide the primary method of erosion
control during the preliminary earth work and subsurface 'utility
installations. All points of direct runoff concentration will be
provided with erosion protection. The final earthwork activity will
be the overlot grading required for the design grades to be
realized. This will expose approximately 5.8 ac to wind and
rainfall erosion. Seasonal temporary vegetation will be cultivated
to minimize wind and rainfall erosion.
Road base and asphalt will be the next scheduled construction.
This will aid significantly in reducing the erosion potential. It
is at this point that the straw bale dikes in the back lot pans
• will begin providing protection for rainfall erosion.
Erosion Report
• Silver oaks, Second
Page 2
The final gravel filter in the detention facility will further
enhance system performance. Wind erosion will be addressed by use
of furrowed contours in all areas of overlot grading. Surface
conditions for both wind and rainfall erosion will see a benefit
from this final methodology. The last point is that rainfall
erosion will be near the end of its primary season of concern,
while the wind erosion controls will be more important.
Should questions arise regarding this erosion control plan
please do not hesitate in contacting us.
J
S
/ CONSTRUCTION SEQUENCE
PROJECT: -e5llL�P-I' .Djw-S,� STANDARD FORI1 C
SEQUENCE. FOR 19 �Q/�
4 ONLY COMPLETED BY: h"�`c DATE: 12—I 1'`_->
ficate by use of a bar line or symbols when erosion control measures will be installed.
Major modifications to an approved schedule may require submitting a new schedule for
approval by, the City Engineer.
YEAR MONTH
----
----
OVERLOT GRADING ' -
WIND EROSION CONTROL
i
Soil Roughing
Perimeter Barrier
Additional Barriers
Vegetative Methods
Soil Sealant
Other
.RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers I.•
Sand Bags
Bare Soil Preparation
Contour Furrows
Terracing
Asphalt/Concrete Paving
Other
I
VEGETATIVE:
Permanent Seed Planting
Mulching/Sealant
Temporary Seed Planting
Sod Installation -
Nettings/Mats/Blankets
Other
STRUCTURES: INSTALLED BY l��yt ra ng7�
------------------------ --- I ----------I
MAINTAINED BY Q,
VEGETATION/MULCHING CONTRACTOR
DATE SUBMITTED IZ - APPROVED BY CITY OF FORT COLLINS ON
HOF-C:1989
Effectiveness Calculation
.
SLandar d Form B
rProject:
Stewart
By: Stewart & Associates Completed: N-0
I 10 S
03 S. Meldrum
FortCollins,
ort CollColorado 80521 Date:
-Control
Erosion
-Factor
P - -Factor
'Comments..
Method
Value •
Value
T-, t
L)
1, o
Z,
I'D
6,A2p,L14?(- rJL
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por lip
P-6-
0
HDI/SF-B:1989
STEWART&406SOCIATES 103 S. PH 482-93 DRF X F4882 9 COLLINS, CO 80521
ConsultingEngineers and Surveyors
• By: �i�� Date: Client: %r //-ter �' Sheet No. _ of
�x �r
Project: J'
Subject: 6 - -5'I
X GS
/ GO�U`�TG'GjIG'�J GISTS
� U c
A
0;
JAN-11-93 NON 13i09
0125
NORTH ANERICAN GREEN FAX NO. 8670247
NORTH AMERICAN GREEN
FLEXIBLE CHANNEL LINTERS
Developed for extreme slopes, high -discharge channels, and applica-
tions requiring semi -permanent to permanent protection and vegetal
reinforcement. The coconut and nylon flexible channel liners consist of
heavy duty, UV stabilized netting and a uniformly consolidated coconut
or nylon fiber matrix for Superior erosion control performance.
The C125 flexible channel liner features a 10090 Coconut fiber
matrix sewn between two heavy duty, UV stabilized nets. The
heavy duty construction and high performance coconut fiber
matrix of the C125 provides increased durability, longevity,
and effectiveness required for protecting high -discharge chan-
nels and other difficult -to -stabilize sites.
3116� Ili S.;n'3.d':T•'Cu6>;w",....,,kiiG;Y"-'v";1v(
A composite channel lining consisting of C125/ve elation sideslo es ,
9- p ' The P300 was used to establish and telrifeme the gran stands pro -
and aconcrete low -Row bottom provides acost-effective, aesthetic tecting the banks of this pemfanenf stream. High -velocity discharges
alternative to rtprap. The North American Green Erosion Control Plan '{ will damage esfablished grasses without supplemental root protection
Software System was used in designing the composite fining for opti- and ruin ornament provided by the P300,
count channel Scour protection.
11
P. 05
The P300 flexible channel liner features a 100% recycled
nylon fiber matrix sewn between an extra heavy duty, UV sta.
bilized top net and a heavy duty UV stabilized bottom net. The
P300 is a non -degradable blanket designed to provide tempo-
rary protection of high -discharge channel surfaces until vege-
tation establishment, and permanent reinforcement of vegeta-
tion after maturity,
rue rvutnr Hmarican careen trosron Control Plan Software System pro-
vides computer -assisted design of materials for slope erosion protec-
lion and channel scour resisfance. The computer programs arc based
on laboratory and field research Involving erosion control blanitels,
vcgstation, and rtprap, utilizing a ehannei lining selection procedure
developed by the Federal Hiyhwaav Administration. The North American
Green Scfht'are System ComeS romplete with a comprehensive design
Surel_ock� Staple Gun
Use of the Sure Lock staple glue
makes staple placement quick
and simple. The patented,
spring -operated design and
extended handle of the Sure.
Lock staple gun eliminate con-
stant bending and stooping
involved in staple placement by
hand. The SureLock is the most
cost-effective method for
Installing North American Green
blankets, as well as other materi-
als and geotextiles that must be
anchored to the ground.
Distributed By:
JAN-11-93 NON 13:08 NORTH ANERICAN GREEN FAX NO. 8670247 P,03
EffeClive 2120189
NORTH
AMERICAN
GREEN
MATERIAL SPECIFICATIONS CATEGORY I
P300 Permanent Channel and shore lining shall be a machine -produced mat of 100o/0
recycled nylon fiber.
The blanket shall be of consistent thickness with the nylon fiber, evenly
distributed over the entire area of lire mat. The blanket shall be Covered on the
top with black polypropylene netting having ultraviolet additives to reduce
breakdown, approximate 1/2 inch x 1/2 inch mesh size. The bottom net shall also
be UV stabilized polypropylene, with a 5/8 inch x 5/8 Inch mesh size. The
blanket shall be sewn together with polyester thread.
Nylon fiber channel and shore lining shall be P300 as manufactured by
North American Green, or equivalent. Nylon fiber channel and shore lining shall
have the following properties:
Material Content
Recycled Nylon Fiber
Netting
Thread
Physical Specifications (Roll)
Width
Length
Weight
Area
L
100%
(.80 Ib/y2) (.436 kg/m2)
One side heavyweight UV stabilized
(5.0 Ibs/1,000 sq It approx wt)
One side heavyweight UV stabilized
(3.0 Ibs/1,000 sq it approx wt)
100% Polyester Black
6.5 feet (2m)
83.5 feet (25.4rn)
48 Ibs + 10% (21.8 kg)
60 sq yd (50m2)
•
i
Rainfall Performance Standard Evaluation
Project: 5rt- e-z 8n14-Standard Form A
By: Stewart & Associates Completed: r�
103 S. Meldrum
Fort Collins, Colorado 80521 Date:
Developed
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Erodibility
Zone
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Adapted from Bureau of Public Roads Nomograph (' I
Yo ��
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CJ
0
STEWART&, ,SSOCIATES 103 S. PH. 482-93 1 Ff X 48z 9 80LLINS, CO 80521
Consulting Engineers and Surveyors
By: —At'J— Date: �' 1 C Sheet No. of
g "1 `J - 1 � Client: 1 tZ � - �t,.l.
Project: C.Jr!> 0�'�-5
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H
GUTTER CAPACITY TABLE FOR VAIABLE STREET SLOPES AND CROSS SLOPES
2 YR EVENT WILL BE EXAMINED
FOR: SILVER OAKS P,U.D. DEVELOPED BY: TRI-TREND, INC.
BY: STEWART AND ASSOCIATES
THEORETICAL CAPACITY Q = .56 (Z/ n) (S) ^.5 (y) ^ 8/3
VARIABLES AND DEFINITIONS: Q = THEORETICAL GUTTER CAPACITY (cis)
0.42 = y (DEPTH OF FLOW AT FACE OF GUTTER, feet)
0.016 = n (MANNINGS ROUGHNESS COEFFICIENT)
S = SLOPE OF CHANNEL( feet / feet)
Z = RECIPROCAL OF CROSS SLOPE, ( 1 / cross slope(ft / it))
Florll Infirm fnm/ ,. n f...... Ql....... n...:_.___ ram_:._ :_ a 1.
DESIGN CONSTANTS
CHANNEL REDUCTION
SLOPES FACTOR
0.0045 0.50
1 /CROSS SLOPE h / ft
50.000� 1 % 0
THEO.GUTTE REDUCED
CAPACITY cfs CAPACITY cis
11.580 5.79
.. �.J._v„.r„u u VVIIJ\IVVII
1 /CROSS SLOPE (tt / ft)
40.000 = Z = 1 .025
-1 =
THEO.GUTTE REDUCED
CAPACITY cis CAPACITY (cfs
9.264 4.63
VII VlQ11UQ1UJ
1 / CROSS SLOPE (ft / it)
33.330 = Z = 1 0:
-- _ - --�-
THEO.GUTTE REDUCED
CAPACITY cfs CAPACITY (cf
7.719 3.8E
0.0050
0.65
12.207
7.93
9.765
6.35
8.137
5.2f
0.0060
0.80
13.372
10.70
10.697
8.56
8.914
7.1,
0.0070
0.80
14.443
11.55
11.555
9.24
9.628
7.7(
0.0080
0.80
15.440
12.35
12.352
9.88
10.293
&Z
0.0090
0.80
16.377
13.10
13.102
10.48
10.917
8.7:
0.0100
0.80
17.263
13.81
13.810
11.05
11.507
9.21
0.0110
0.80
18.105
14AB
14.484
11.59
12.069
9.6E
0.0120
0.80
18_911
15.13
15.128
12.10
12.606
10.0E
0.0130
0.80
19.683
15.75
15.746
12.60
13.121
10.5C
0.0140
0.80
20.426
16.34
16.341
13.07
13.616
10.8E
0.0150
0.80
_ 21.143
16.91
16.914
13.53
14.094
11.27
0.0160
0.80
21.836
17.47
17.469
13.98
14.556
11.64
0.0170
0.80
22.508
18.01
18.006
14.41
15.004
12.00
0.0180
0.80
23.161
18.53
18.528
14.82
15.439
12.35
0.0190
0.80
23.795
19.04
19.036
15.23
15.862
12.69
0.0200
0.80
24.413
19.53
19.531
15.621
16.274
13.02
0.0210
0.78
25.016
19.51
20.013
15.61
16.676
13.01
0.0220
0.77
25.605
19.72
20.484
15.77
17.068
13.14
0.0230
0.76
26.180
19.90
20.944
15.92
15.40
17.452
13.26
0.0240
0.72
26.744
19.26
21.395
17.827
12.84
0.0250
0.68
27.295
18.56
21.836
14.85
18.195
12.37
0.0260
0.66
27.836
18.37
22.268
14.70
18.555
12.25
0.0270
0.64
28.366
18.15
22.693
14.52
18.909
12.10
0.0280
0.61
28.886
17.62
23.109
14.10
19.256
11.75
0.0290
0.58
29.398
17.05
23.518
13.64
19.596
11.37
0.0300
0.54
29.900
16.15
23.920
12.92
19.931
10.76
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STEWART&ASSOCIATES 103 S. PH 82-93 1 FAX FORT
COLLINS, CO 80521
Consulting Engineers and Surveyors
By: Date: 1— C3 client: '(RI -" kfZEHQ INC- Sheet No. of �
• Project: SI l,\CER UNKS PNA5e C)N27 CCNSTRIACfIC>N
Subject: IzzRM CDI-L.Fx'gpri MDDsL `�cNEMAT(
ens
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� � NOTES
* Catch basins are modeled as single manholes with specific
design flows, based on the Rational Method Spread Sheet design
points.
* A11 design sizing assumes a fully developed Silver Oaks.
• * Manhole #5 is a "dummy" used for modeling purposes.
* All interconnecting piping is 15" at 1% slopex >:v-i'r ZE 1K
* Sewer and manhole numbering correspond to "UDSEWER."
----------
REPORT OF STORM SEWER SYSTEM DESIGN
USING UDSEWER-MODEL 10-19-1992
DEVELOPED
BY
JAMES C.Y. GUO ,PHD, PE
DEPARTMENT OF CIVIL ENGINEERING, UNIVERSITY OF COLORADO AT DENVER
IN COOPERATION WITH
URBAN DRAINAGE AND FLOOD CONTROL DISTRICT
DENVER, COLORADO
*** EXECUTED BY STEWART AND ASSOCIATES (FT
COLLINS-COLORADO)............................
ON DATA 12-02-1993 AT TIME 13:51:04
*** PROJECT TITLE :
Silver oaks,Second Filing, Comparing to the original ODP
*** RETURN PERIOD OF FLOOD IS 2 YEARS
*** SUMMARY OF HYDRAULICS AT MANHOLES
-------------------------------------------------------------------------------
MANHOLE CNTRBTING
RAINFALL
RAINFALL DESIGN GROUND
WATER COMMENTS
ID NUMBER AREA * C
DURATION
INTENSITY PEAK FLOW ELEVATION
ELEVATION
MINUTES
INCH/HR CFS
FEET
FEET
-------------------------------------------------------------------------------
3.00 0.00
0.00
0.00 18.80
26.48
24.30 OK
2.00 0.00
0.00
0.00 28.60
24.05
22.60ZZ.SSOK
1.00 0.00
0.00
0.00 36.60
23.15
21.6421.f30K
5.00 0.00
0.00
0.00 36.60
22.75
21.40 OK
OK MEANS WATER ELEVATION
IS LOWER THAN GROUND ELEVATION
�rciC�iN r�
- VA�U�S
�Kt�l"1=_'ME _.tiDP---P_iZ'E
51���1N
*** SUMMARY OF SEWER HYDRAULICS
• NOTE: THE GIVEN FLOW DEPTH -TO -SEWER SIZE RATIO= .9
-------------------------------------------------------------------------------
SEWER
MAMHOLE
NUMBER
SEWER
REQUIRED
SUGGESTED
EXISTING
ID NUMBER
UPSTREAM
DNSTREAM
SHAPE
DIA(HIGH)
DIA(HIGH)
DIA(HIGH)
WIDTH
-------------------------------------------------------------------------------
ID NO.
ID NO.
(IN) (FT)
(IN) (FT)
(IN) (FT)
(FT)
20.00
3.00
2.00
ROUND
22.84
24.00
0.00
0.00
10.00
2.00
1.00
ROUND
31.12
33.00
0.00
0.00
50.00
1.00
5.00
ROUND
32.74
33.00
0.00
0.00
DIMENSION UNITS FOR ROUND AND ARCH SEWER ARE IN INCHES
REQUIRED DIAMETER WAS DETERMINED BY SEWER HYDRAULIC CAPACITY.
SUGGESTED DIAMETER WAS DETERMINED BY COMMERCIALLY AVAILABLE SIZE.
FOR A NEW SEWER, FLOW WAS ANALYZED BY THE SUGGESTED SEWER SIZE; OTHERWISE,
EXISITNG SIZE WAS USED
-----------------------------------------------------------------------------
SEWER
DESIGN
FLOW
NORMAL
NORAML
CRITIC
CRITIC
FULL FROUDE
COMMENT
ID
FLOW Q FULL
Q
DEPTH
VLCITY
DEPTH
VLCITY VLCITY NO.
NUMBER
------------
CFS
CFS
FEET
FPS
FEET
FPS
FPS
20.0
7-----------------------------------------------------------------
18.8
21.5
1.45
7.72
1.56
7.15
5.98 1.17 V-OK
10.0
28.6
33.5
1.95
6.34
1.77
7.07
4.82 4,1(,0.83 V-OK
50.0
36.6
37.5
2.20
7.19
2.02
7.85
6.16 Gz.x 0.83 V-OK
FROUDE NUMBER=O
INDICATES
THAT A
PRESSURED FLOW OCCURS
----------------------------------------------------------------------
SEWER
SLOPE
INVERT
ELEVATION
BURIED
DEPTH
COMMENTS
ID NUMBER
UPSTREAM
DNSTREAM
UPSTREAM
DNSTREAM
---------------------------------------------------------
%
(FT)
(FT)
(FT)
(FT)
------------
20.00
0.90
22.74
20.25
1.74
1.80
OK
10.00
0.40
19.40
18.55
1.90
1.85
OK
50.00
0.50
18.95
18.83
1.45
1.17
OK
OK MEANS BURIED DEPTH IS GREATER THAN REQUIRED SOIL COVER OF 1 FEET
•
***
SUMMARY
OF HYDRAULIC GRADIENT LINE ALONG SEWERS
---------------------------------------------------
SEWER
SEWER
SURCHARGED
CROWN ELEVATION
ID
NUMBER
LENGTH
LENGTH
UPSTREAM
DNSTREAM
FEET
FEET
FEET
FEET
---------------------------------------------------
20.00
277.00
20.90
24.74
22.25
10.00
213.00
152.83
22.15
21.30
50.00
25.00
0.00
21.70
21.58
----------------------------
WATER ELEVATION FLOW
UPSTREAM DNSTREAM CONDITION
FEET FEET
----------------------------
24.30 22.60 JUMP
22.60 2-2.f5b21.64 SUBCR
21.64 Z k,& , 21. 40 SUBCR
PRSS'ED=PRESSURED FLOW; JUMP=POSSIBLE HYDRAULIC JUMP; SUBCR=SUBCRITICAL FLOW
***'SUMMARY OF ENERGY GRADIENT LINE ALONG SEWERS
-----------------------------
UPST MANHOLE SEWER
SEWER MANHOLE ENERGY FRCTION
ID NO ID NO. ELEV FT FT
-----------------------------
20.0 3.00 25.23 1.86
10.0 2.00 23.22 0.69
50.0 1.00 22.44 0.90
----------------------------------------------
JUNCTURE LOSSES
DOWNST MANHOLE
BEND
BEND
LATERAL
LATERAL
MANHOLE
ENERGY
K COEF
LOSS FT
K COEF
LOSS FT
ID
FT
----------------------------------------------
0.25
0.14
0.00
0.00
2.00
Z', b.22
0.25
0.09
0.00
0.00
1.00
22.44
0.25
0.15
0.00
0.00
5.00
21.40
BEND LOSS =BEND K* VHEAD IN SEWER.
LATERAL LOSS= OUTFLOW VHEAD-JCT LOSS K*INFLOW VHEAD
FRICTION LOSS=O MEANS IT IS NEGLIGIBLE OR POSSIBLE ERROR DUE TO JUMP.
FRICTION LOSS INCLUDES SEWER INVERT DROP AT MANHOLE
NOTICE: VHEAD DENOTES THE VELOCITY HEAD OF FULL FLOW CONDITION.
A MINIMUM JUCTION LOSS OF 0.05 FT WOULD BE INTRODUCED UNLESS LATERAL K=O.
FRICTION LOSS WAS ESTIMATED BY BACKWATER CURVE COMPUTATIONS.
0
Final Ap r ved Report
Final Storm. Drainage..Report -3 �/IL.3
Silver Oak$.P.U.D.
" jY7
February 1993
STEWART&ASSOCATES
Consulting Engineers and Surveyors
103 Sotdh RePrl um st,w-et
fob Co22inz, Catonado 80521
3031482-9331
EXECUTIVE SUMMARY
The following is presented in a bullet list form to aid in your
review of the residential project for Tri-Trend,Inc..
- Spring Creek Drainage Basin is our location
- 133 single family units and 16 patio home lots
- 9.2 cfs is our historic release rate
8.4 cfs historic from 38.16 ac
3.3 cfs directly released Olander school
<1.1 cfs> undetained 100yr from 1.03 ac
<1.4 cfs> undetained 100yr from .74 ac
9.2 cfs- Total Allowable release rate
- Olander School has a release rate of 3.3 cfs
- this 3.3 will be carried as street flow into this newly
developed detention basin in Silver Oaks
- the only offsite contributing area, the Olander Elementary
School site,'is controlled
- all adjacent properties have been considered as part of our
review of the grading plan
- no sump areas have been created as a result of our grading
- all adjacent parcels have been improved
- discharge from the detention area is directed as it has been
historically, east under S.Taft Hill Road into Rossboroughs'
swale
- point discharge will be maintained and unmodified
- free board of .8-ft. has been provided with 110 %
capacity of required detention, (variance requested)
Should additional questions arise that are not answered as part of
the text of the detailed report please do not hesitate in calling
for clarification of design concepts.
TABLE OF CONTENTS
TOPICS
- Executive Summary
- Storm Drainage Report
- Erosion Report
- Erosion Control Design
- Times Of Concentration
Runoff Computations
- Hydraulic Design Information
- Street Gutter Capacity 2 & 100 yr.
- Detention Design
- Referenced Attachments
i�
COVER / LOCATION
PINK
waigreia
PURPLE
YELLOW
GRAY
RED
GENERAL SITE CONDITIONS
This is the "Final Submittal" for Silver Oaks P.U.D.,
which is being developed by Tri-Trend Inc. of Fort Collins. The
proposed improvements will involve single family and patio home
sites, resulting in a medium density residential development.
Proposed are 133 single-family and 16 patio home lots on the
38.16 acre (ac) property. Silver Oaks is on the Northwest corner of
the intersection of Horsetooth and Taft Hill Roads. It is situated
in the South 1\2 of the Southeast 1\4 of section 28, Township 7,
Range 69 West, of the 6th P.M..
The site is at the upstream end of the Spring Creek
Drainage Basin near the foothills. Adjacent land uses include
Olander Elementary School to the southwest, and undeveloped area to
the northwest. On the north side are residential "ranchetts" with
lot sizes of approximately 5 acres. These home sites are not within
current Fort Collins City Limits, and remain within ,Larimer
County's jurisdiction. East of the site is South Taft Hill Road
with Rossborough Subdivision on the other side of the road.
Finally, on the South is West Horsetooth Road with Timber Ridge
Mobil Home Park on the other side of West Horsetooth.
0
Storm Drainage Report
Silver Oaks P.U.D.
Page 2
HYDROLOGY
Overall Drainage Plan -
A detailed set of exhibits have been included for your
use in understanding how basins were configured for historic, and
developed conditions. The Overall Drainage Plan (ODP) has been
developed as part of this submittal to establish how best to
integrate phase one with subsequent development activities. In
reviewing the developed site conditions bear in mind the ODP. All
hydraulic and hydrologic design has been established using the ODP
as a basis, along with the City Of Fort Collins Storm Drainage
Design Criteria and Construction Standards (SDDCCS). The labeling
of all historic and developed basins is included as well as
locations of hydraulic structures and design points.
Currently, this portion of Spring Creek Basin consists of
three historic sub -basins totaling 44.96 ac. This total is the sum
of the 38.16 ac of the current Silver Oaks proposal, 5.03 ac of
future commercial development and 1.77 ac of undetained runoff
area. The Rational. Method yields a total 2 yr initial historic
runoff of 8.4 cfs from the developed 38.16 ac. The 5.03 ac future
commercial site produces .6 cfs in a 2 yr event while the 1.03
acres developed of Silver Oaks that discharges onto the commercial
site yields 1.1 cfs in a major (100yr) storm. Only .74 ac in the
• northwest corner of Silver Oaks will truly remai undetained. h�
major event on this developed area results in ,,7 cfs of runoff to
the northwest, a reduction to current unimproved conditions.
Storm Drainage Report
Silver Oaks P.U.D.
Page 3
These historic undetained runoffs are based on a time of
concentration TOC(100 yr) of 44.8 min., from historic basin "C"
(Exhibit D). The design TOC's were established for the developed
conditions by considering each inlet as a basis of design. This
resulted in a total of five individual basin segments as shown on
the Grading Plan (GP sheets 6&7).
Reiterating, .74 ac. will remain undetained following
development,'5.03 ac. of commercial property in the southeast will
be required to develop onsite detention for itself and 1.03 ac of
undetained Silver -Oaks area that will flow onto the commercial
area. Finally, 38.16 ac. will be detained as designed in this
report. Further detail on how'discharge rates from the detention
area were established will be included in the detention portion of
this report.
The ODP model includes a series of design points for inlets
and cross pans, (refer to exhibit "A", ODP for the locations of
these points). Many points in phase one are integrated into the ODP
to facilitate a consistent program of storm water management.
•
0
Storm Drainage Report
Silver Oaks P.U.D.
Page 4
Phase Specific Drainage -
Phase One of Silver Oaks includes 12.87 ac. of single
family residential, with 25.29 ac. remaining in an "as is"
condition. The one exception to the "as is", comes in the from of
a temporary drainage swale to be constructed on the east end of the
first phase of Silver Oaks Drive. This swale will allow for
conveyance of 3.4 cfs (2 yr.), and 12.2 cfs (100 yr.) runoff
volumes to the developed detention area. These flows are generated
from the 4.89 developed acres west of Auntie Stone St. that are
part of phase one. Following the completion of subsequent phases of
Silver Oaks, these flows will be directed in the future extension
of Silver Oaks Drive to inlet IA, located in the north flow line of
Bronson St. just West of the proposed detention pond as shown on
the ODP. Catch basin IA will be built as part of phase one of the
development. During the interim period the swale provides
additional capacity to convey cutoff overland flows moving
generally in the northeast direction, into the new detention
facilities which will be constructed with phase one.
•
Storm Drainage Report
Silver Oaks P.U.D.
Page 5
HYDRAULICS
Overall Drainage Plan -
All hydraulic design criteria are in compliance with the
SDDC. Catch basins/inlets are identified as IA...IE and Taft, while
street pans are designated as P-1... P-5. The piped storm drainage
.conveyance system will be designed and installed as part of phase
one. Catch basins are sized and located in such a manner that
subsequent street developments will be easily accommodated.
Additionally, four back lot pans BL-1... BL-4 will be included as
part of the phase one improvements. They are indicated on both the
ODP and the detailed GP for phase one. Subsequent phases may
require additional site specific details (back lot pans... etc).
Piping network capacities were established using software
developed for the -Urban Drainage and Flood Control District, by
University of Colorado, Denver. The title of the package is
"UDSEWER". Included in the output is a detailed listing of design
parameters for hydraulic constraints. The piped system was designed
to carry the 2 yr. design storm while the 100 yr. will be carried
by available street capacities. Design flows were established as
indicated in the "Hydrology" section of the report and incorporated
into the hydraulic model. Olander Elementary does contribute
• 3.3 cfs to inlet IE and has been included in the hydraulic design
of the attending structures.
Storm Drainage Report
Silver Oaks P.U.D.
Page 6
Phase Specific Drainage -
A series of four, 2-foot surface drainage pans as
previously mentioned, will be installed to minimize concerns over
areas between lots becoming swamped due to the low slope of back
lot drainage. Solid fencing will. be incorporated, but only above
the computed high water surface elevation of a specific pan. The
locations of these pans are shown on the ODP and details are
included as part of the phase one GP. Recall that the entire piped
storm water conveyance system is going to be installed in phase
one.
DETENTION REQUIREMENTS
Overall Drainage Plan -
The 4.8 ac-ft of required detention will be provided
in the northeast portion of the Silver Oaks development. Detention
sizing for a developed 38.16 ac. site major event has been provided
at this time. A storage volume of 4.8 ac-ft was required with an
allowable release rate of 9.2 cfs. The 9.2 cfs was established
using appropriate historic TOC and corresponding intensities. This
7.�1?- I@EuAt e- Frm
total 2 yr release is made up of 8.4 cfs ('38.16 ac) plus 3.3 cfs
(Olander detention release), minus undetained (100yr) total of (1.1
+1.4 cfs), yielding a total allowable release rate of 9.2 cfs. This
facility is sized to. accommodate future phases of Silver Oaks
• P.U.D.. The area of the detention is approximately 1.6 ac.
resulting in a High Water Surface Elevation (HWSE) of 5121.7-ft..
A variance for the .8-ft detention freeboard is requested.
Storm Drainage Report
Silver Oaks P.U.D.
Page 7
The detention pond will outf all to an existing 18-in rc pipe in the
northeast corner of the detention area (see GP), which crosses
under Taft Hill Road and conveys flows to the 40-ft Rossborough
drainage way along the east side of the road. Field data indicates
grading that will allow a maximum capacity of 20.0 cfs with the
HWSE indicated. Development upstream of this historic release point
has eliminated the concern of tail water at our discharge piping.
The original Rossborough design was for all undetained flow to
overtop Taft Hill and be collected in the swale. This can no longer
occur in light of the Taft Hill improvements. This historic point
of release will be maintained as our control structure and
supplemented with an orifice plate to allow for a maximum allowable
release rate. Please reference the "Mass Diagram Table" and graph
in the report for details of the required design storage.
The commercial area has two possible outlets; first through an
existing 15-in. pipe crossing Taft Hill, flowing east, south of
Bronson identified in the City's "Taft Hill/Horsetooth Road
Intersection" Drainage Report (May 89). The second possibility is
to utilize the 18-in exiting the detention area. We are assuming
that these release points for'the commercial site will be under
scrutiny in the future. This design will not allow storm runoff to
enter the detention area from the undeveloped commercial site.
Rather, a berm will be constructed at top elevation 5124.0 and
direct flows into the catch basin south of Bronson on Taft Hill .
Storm Drainage Report
Silver Oaks P.U.D.
Page 8
Downstream concerns have been addressed by insightful planning
in the "Drainage Report Rossborough Subdivision" (April 79), and
confirmed in the May 89 "Drainage Report Taft Hill Road/Horsetooth
Road Intersection", prepared by the City, Development
Services/Engineering. Both referenced bodies of work clearly
indicate the ability of the 40-foot "Drainage Way" to handle all
major events from the developed tributary area at the up stream end
of the Spring Creek Basin (please reference the attached excerpts).
The detailed GP shows a 4-foot concrete drainage pan to be
built in the detention pond capable of carrying nuisance flow to
the 18-inch outlet piping. Grading within the detention pond is
being dictated by existing grades for the discharge piping into the
Rossborough Swale, and the naturally occurring "flat" topography.
The surrounding topography will best be suited with a top of bank
elevation 5222.5-ft. as the minimum grade around the detention
pond.
The construction of the Silver Oaks detention facilities will
improve conditions for adjacent property owners by controlling
release rates in the northwest quadrant of the Horsetooth and Taft
Hill intersection.
Storm Drainage facilities in this development, will be
maintained by a "Home Owners Association" to be established as part
• of a future development agreement with the City.
Storm Drainage Report
Silver Oaks P.U.D.
Page 9
INTERIM STORM DRAINAGE SUMMARY
The focus of phase one will be on the south and west
portions of the Silver Oaks P.U.D.. Development of the onsite
detention will control the storm runoff from the undeveloped
25.29 ac. as well. .as the phase one improvements. The natural
topography of this site lends itself to our selection of the
current development area. On the north the flows off site will be
cut off by the east -west ditch used to direct flows from the east
end of Silver Oaks Drive into the detention area, thus resulting in
a significant reduction in flows leaving the site in that general
direction. Flows moving in a easterly direction toward S.Taft Hill
Road will be collected and detained within our newly established
detention area. The existing grades adjacent to the south side of
Bronson Street will be modified with a low berm (± 1.0-ft.) to a
top elevation of 5124.0. This will retain and direct a major storm
into the existing curb inlet on the west side of Taft Hill Road,
south of Bronson. Further consideration to the 2.1 cfs generated in
the 100 yr storm will garner consideration during review of a
proposal of development for the 5.03 ac commercial site. Runoff to
the south has not been a concern for this site topography. Looking
to the west we have a developed basin in the form of Olander
Elementary School. Discharge is at a point west of Auntie Stone
• Drive at the south flow .line of the newly developed Bronson Drive.
0
Storm Drainage Report
Silver Oaks P.U.D.
Page 10
The discharge rate as identified by the March 89 Final Drainage
Report for Olander Elementary is 3.3 cfs, and has been included in
all design considerations for Bronson Street and the detention
area.
Please reference excerpts from the aforementioned final
drainage reports for additional details as required. Should
questions arise during your review of this report please do not
hesitate in contacting Alex Evonitz or myself for further
clarification.
lD�-•tom-fi�r�/ ( A
Richard A. Rutherford, P.E. & L.S.
S n hall",
502
c:\wp51\siloak.rpt
EROSION CONTROL REPORT
Silver Oaks, First Filing, is a 12.87 acre single-family
residential development. During Phase One construction, a total of
17.92 acres will be disturbed due to construction of Phase One
lots, temporary swales and the attendant detention facility. The
following is the sequence of construction for which erosion must be
controlled.
The first construction that will take place is the rough cuts
for the streets. The lots will not be over lot graded since there
are no large cut or fill activities planned for the site. Each lot
will be graded after the foundations are completed. This will leave
8.92 acres undisturbed. There are pans planned for back lot
drainage. The swales for the pans will be rough cut at the same
time the streets are being established. Straw bale barriers will be
placed in the swales, and the swales seeded. Those bale barriers
will remain in place until any disturbed areas are reseeded and the
vegetation established.
After the streets are rough cut, the sanitary sewer system,
water lines and services will be installed. The aforementioned
construction will have disturbed a width of 75-ft along the roadway
alignments. The storm drainage system will be completed next. After
the pipes are laid and before the curb and gutter inlets are
constructed, straw bale barriers will be placed to filter out silt
from entering the piping system. The curb, gutter, sidewalks and
back lot drain pans will be the next element completed. After the
concrete is done, the inlets will be constructed, and rock filters
If
placed at the inlets will replace the bale barriers.
Silver Oaks Erosion Control
Page 2
At this point power, phone service, gas, and cable will be
installed. This will disturb an area of approximately 1.2 acres.
Following the completion of the utilities, the disturbed areas will
be reseeded with a temporary mulched crop. The streets will then be
based and surfaced as the final construction element.
aQ
Richard A. Rutherfor P.E.& L.S
C I
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--- e• ! 30 p 3 #0010t T 4m.wJI
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3? 33G 3JF 3L.8 38 IW/
GRAPHIC SCALE -FEET
�
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94� a� 31p �3�3 9 3��� 3T� nr ,���, t I.13x.9 d1. , •3� j � \� /� \. ° � � ps LS N
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bfPJYI RN¢ plNe tb 66
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,••3S..I..r..y.I.,.,....I I . FC \. 1 to.;nv 3x p -Ie / I Pony Te sE aE+uxnED
t'I•• • nyI•u f/..._. A� •� 4 \,� '� Z9% E ,I SAL .0.� A 1b OR4INAL OvIr 10T1
gW _Nby q,ll
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r
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i:YT.=
1
n0
SECTION VIEW
bill Not..
SILT FENCE
110 2S on or III III of porm
2 bounct III blow III son Nor
Iry,
CITY OF FORT COLLINS. COLORADO
NIMIJIM
STORM WATER UTILITY
.r owWronI
-ID sD
28
..,.,.
pTun ye/
TENPDRNC/ V&4ETAi IDry Ib A Y
nxzv IN ARFAd OF wEFwt
4x 01
P�
nA, WHHH
E
t.t
Fullt
V IiG
In�
YNF
V.
r u
�L
`lenE
Gf�acH FFnv„
IYYV Lvblc RNn i
0 1vL YK A
LIboL�l
flA I
UNDFh fJANN (E?AIL
AL 7rtxn • ur,vEE
f5n TIE `1.InT.Ifxy
I
Hx NDA
11 wool Wood 11 1 'IV. borrow
"I IWIM10aml
IF , ` \ m 50
il
I.MA 11 1zBi \ Na ON
,,..t„ �,�, t0 All_ a
.,a•Ab•or I
0.9-4T 2 \ ZA Zd.L
2
NININUM 9FT11119-l1 •••i, \ 1 2�2/'u
,.CBEs MWNTAITW WROIN SA6"Nf 1
6CMCIN-55
in
AYI 0" plxE s� D N
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n
0 �
TEMPORARY VEGETATION TABLE FOR epFIpN:DS Quit, as Pi4 I $ I% �� �l\
EROSION CONTROL 09K MNEI _
SPECIES L&S/AC PENCEM MUTEDD LBS/ [glTpxeYIDl1 6MRt+P�'6eb.F' b �[¢� �•
• 1 �'1 P3sa
ANNUAL 20 To% 14lB5 _ — brims- .
n
RYEGRASS perto OEMa.cw
WINTER tl W% 12 LBS
WHEAT --
��— BRONSON 57R T
TOTAL 28 I83lAC
RIIPF ZL
vxnk i)
"FuNPDRARY YE4HAEDN 1a EE TIMbP IN ALL ARERS Dt
(TIgRD,THIEl FILTER iO
---RNf (IRAOIN4 WNIHH 6M WEEKS OF4RAOIN4 MINIIYI
INEMAM p PLR CITY
5N`LOpryplTlpryy }y�MitlNb i
�1°Ot
�TMVDArtpS AT £'/JNI HIT
_ _ _
OBJECT: Liu. D•t lt`M`I`yL}1d
SIUOtM M;NLET
by
�ny,IS
butor .md.my.
n �mynoyln "unity" w,m44 t for
Npmml by In City slimily.
%w.5....
must
IF I'r'IP �N�S
IZ ��IyIDIVIv
----II�
WUI gMIE
o) o„^nC
fit,
owt
,�
MT5�41; EARN MTM
M1CO
-
NANVILIY
n
vI
D.
u s
Won Nn
. Now wEm.
Soy Corro�I,.,
Si L F,el
I
Onto
mmt.u..
t:.�i
Mrnbun
Tor"Is
2'4'•.,
t, Tyrry
4fy
YsNrll/c
afQICx AA
WERETATINE
�ntl,n iou
_
ly/WpummIn
._..— —
Cowiml If
1. IymNo MM Ml„w,w CURB INLET FILTER
OF FORT CO LURE, COLOMOO
xmm..nwmm,w e, a,-
CItt OFFORFCOWNi COLLIMDO
'�
iTOR\IV/tT ttu VTILITY
e, IMyaln,m
$TOgI4VATFR JMW
STMMES: IIDINLCO BT O.nvP'.i ni MIx1YNY xT
xXIN CONE
� :.
sumus®
Cost namyw.IW yti.
I- '�vi0
r
FI
IUETAT[Vii
COTE NnITTN 0 1-v ATImM Its CUT CO FEET Min 0
D-26
D-25
5111' FENCE v RE Irvb(µyEp tER NfIr Nlkyroy S
FOIE ME E11flul ISIWIx 6 t4R, SOun0AKY
I IMAAUELTNLxR FA
ArbEf III TLACE9 TIRE LHT
LVU:f $A Sfi shbi AT nEar N15TIN[1
LENxIn4 �) 5N£1 £RN
—SItSW,1 iE
PA—'+InWR6AI£ fiv
011 — GNNEL ylbftIL�l FILTEP.
V,TT — GFUN INAl 1
ZE1: — L' uNDNLFAaH PIfIn4
l Drainage Table
eN1
Area
02
tOD
N-ta
1.lm at
zo cis
7.0c1a
a-1D
1 247
z5
9.0
U1-1c
1 0.85
1A
3.7
N:-1
1 z45
2.0
S.1
BL-1
1.54
1.5
5.3
J
JOE MUMOIJM .L.X.A 1
6 of 7