HomeMy WebLinkAboutDrainage Reports - 05/08/1987Drainage Report
for the
Oak Ridae Estates
■��INC
1 Engineering Consultants
2900 South College Avenue
Fort Collins, Colorado 80525
' 303/226-4955
' May 8, 1987
' Mr. Bob Smith
Storm Drainage Department
' City of Fort Collins
P.O. Box 580
Fort Collins, Colorado 80522
' RE: PINE RIDGE SUBDIVISION
Dear Bob:
' We are pleased to submit to you this final drainage report of the
Pine Ridge Subdivision.
' Please call if you have any questions.
Sincerely,
owutt�0 I RE�j'�i, ,
i,
RBD, Inc. go % .0 A °• y°;rid;'%
o• 1P M F�19�' .
10060
Stan A. Myers, P.E. 9�;
Project Manager '�F•.
amNA�tua a
' Brian H. Cole
Project Engineer
' Other Offices: Vail, Colorado 303/476-6340 • Colorado Springs, Colorado 303/574-3504
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DRAINAGE REPORT
FOR THE
PINE.RIDGE SUBDIVISION
PREPARED FOR:
EVERITT COMPANIES
3000 SOUTH COLLEGE AVENUE
FORT COLLINS, COLORADO 80525
PREPARED BY:
RBD, INC. ENGINEERING CONSULTANTS
2900 SOUTH COLLEGE AVENUE
FORT COLLINS, COLORADO 80525
INDEX
INTRODUCTION
PAGE
LOCATION 1
DESCRIPTION 1
DESIGN PROCEDURE 1
DESIGN APPROACH 1
CONCLUSIONS AND RECOMMENDATIONS 2
REFERENCES 3
APPENDIX
KEY MAP Al
2 YEAR DEVELOPED CALCULATIONS A2
100 YEAR DEVELOPED CALCULATIONS A3
100 YEAR HISTORIC CALCULATIONS A4
SUMP INLET A5
CONCRETE PIPE INLET CONTROL A6
CONCRETE PIPE OUTLET CONTROL A7
DETENTION VOLUME, MASS DIAGRAM METHOD AS
SUBCRITICAL FLOW AROUND BENDS IN
CHANNELS/SWALES A9
n
INTRODUCTION
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Location
The Pine Ridge Development is located on South Lemay Avenue, just
north of St. Elizabeth Seton Catholic Church. More specifically
this site is located in the Southwest Quarter of Section 6,
Township 6 North, Range 68 West of the 6th P.M. of Larimer
County, Colorado.
Description
' As this property currently exists, many small buildings, a house
and horse corrals occupy the area. A ridge exists on this site
being highest on the northwest corner and dropping at 0.5% to 1%±
' to the southeast. This ridge creates flows to two directions, to
the northeast at 2%+ and to the southwest at 5%+. Slopes are
covered with natural grasses.
' This site when developed will be occupied by 15 single family
lots which will face the cul-de-sac located on the site, (see
Drainage Plan).
' DESIGN PROCEDURE
All of the design flows were calculated using the rational method
' (see City of Fort Collins Storm Drainage Design Criteria and Con-
struction Standards). Because this is a residential area, the
minor storm is considered a 2 year storm and the major storm is
' considered a 100 year storm, according to City of Fort Collins
criteria. The calculations for these design storms are in the
Appendix.
DESIGN APPROACH
The drainage from this site will be in two directions as ex-
plained above. Basin D-2, which represents the area draining to
the northeast, is the smaller of the two basins. This basin,
will have a lesser impact on offsite areas because it will be
' smaller than its corresponding historic basin (H-2). Discharge
from this basin will sheet flow offsite. These flows will not be
concentrated, therefore no detention will be required for this
basin. The second basin (D-1) will represent most of the
developed area for this site. Calculations for the 2 year and
100 year developed storms (in Appendix) show that flows will be
within acceptable limits for gutter and street capacities. These
flows will be carried in the street finally exiting at two
proposed 5 foot type "R" inlets located just south of design
point D1. These inlets have been sized for the 2 year storm (see
Appendix). The inlets are located at the low points of the curb
and gutter. During the 100 year storm, flows will overtop the
South inlet and flow offsite to the south. These flows will be
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carried in a Swale, shown on the Drainage Plan, to the pond.
Support calculations are on the Drainage Plan with superelevation
calculations in Appendix.
Detention for basin D-1 will be required because the developed
discharge exceeds the discharge generated historically. The
detention pond will be an enlargement of the pond that detains
storm water for St. Elizabeth Seton Catholic Church P.U.D. This
pond will be re -graded to handle the additional 19,075 ft
required. This volume plus the design volume (67,914 ft3) from
the St. Elizabeth Seton Catholic Church P.U.D. Drainage Report,
by James H. Stewar,3t and Associates, gives a total detention
volume of 86,989 ft .
The release rate from the detention pond have been calculated and
checked in several ways (see Appendix). Outfall flows were cal-
culated based on as -built survey information obtained at the time
of this report. Flows through the outfall pipe were checked
using nomographs for outlet and inlet control with an inlet check
using the orifice equation. This pipe was sized in the above
mentioned report by James H. Stewart and Associates.
The berm for this pond will not be raised, as was suggested in
the preliminary drainage report. In order to preserve it's ex-
isting landscaping, the pond will be graded larger in area, not
in depth (see Plan in Pocket). This approach leaves the emergency
spillway at the same elevation it was before re -grading.
CONCLUSIONS AND RECOMMENDATIONS
Flows from both the 2 year and 100 year developed storms will
pass through this site in a controlled and safe manner.
Other conclusions and recommendations are as follows:
1. The grading of this site should be in agreement with the
drainage and grading plan to promote positive overland and
street flows within the guidelines of F.H.A.
2. Flows leaving this site will flow, as shown on the drainage
plan, to 2-5 ft. type "R" inlets placed at the street low
points. Any flows over the capacity of these inlets will
overtop the curb and inlet at this point and flow to the
detention pond.
3. The detention pond for the St. Elizabeth Seton Catholic
Church wi311 be re -graded to accommodate a total volume of
86,989 ft as shown on plan in pocket.
I
REFERENCES
1. Pine Ridge Preliminary Drainage Report, by RBD, Inc. Jan.
1987.
2. St. Elizabeth Seton Catholic Church P.U.D. Drainage Report,
by James H. Stewart and Assoc., Inc. 1984.
3. Storm Drainage Design Criteria and Const Standards, by the
City of Fort Collins, May 1984.
4. Hydraulic Charts for the Selection of Highway Culverts, by
the Hydraulic Branch, Bridge Division, Office of Eng., Fed.
Highway Ad., Dec., 1965.
5. Standard Handbook for Civil Engineers, Third Edition, by
Frederick S. Merritt, 1983.
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APPENDIX
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SUMP INLET
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Figure 5-2
NOMOGRPAH FOR CAPACITY OF CURB OPENING INLETS IN SUMPS, DEPRESSION DEPTH 2-
Adapted from Bureau of Public Roads Nomograph
MAY 1984
DESIGN CRITERIA
A5
CONCRETE PIPE INLET
CONTROL
ISO
10,000
168
8,000 EXAMPLE
(I)
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Protecting
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6 To use scab (2) or (3) Protect
21
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D and 0 scabs, or reverse as
6
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Q= 877% CAS
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12
HEADWATER
DEPTH
,FOR ..
CONCRETE PIPE
CULVERTS
'
HEADWATER SCALES 261
BUREAU
OF PUBLIC
ROADS JAN. 1963 REVISED MAY 1964 WITH
INLET
CONTROL
A6
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CONCRETE PIPE OUTLET CONTROL
2000
N
a
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0 .4
IsW SIOpe $ems --
IOOO a = SUBMERGED OUTLET CULVERT FLOWING CULL
f J NW • N♦ h0-LSO
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800 120 For ouuet Crown not suemerged, oomputs NW by .6
methods described in the design procedure
600 108 HW : S,-'7
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500 96 11oc 1 14g50me D, t`-mP OE P,�•El
1.0
400 84 H = NYV ��1pt l_ so
300 72 41 : 6 . ab
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HEAD FOR
CONCRETE PIPE CULVERTS
FLOWING FULL
BUREAU OF PUBLIC ROADS BAN. 1963 n a 0.0 12
6.86:0
A7
N�
DETENTION
^'
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VOLUME
0ME
..
����� ��N���������
�� � DIAGRAM 0����N_�
___m1���w�m�om�o ���N�����NNm���kN��N METHOD
DATE: �7')—'6^-87
PROJECT:
N�
(]AKR{DGE ESTATES
JOB NUM8ER: 035~016
DESIGN ENGINEER: BC
BASIN DE5IGNATION
0�
DETERMINE ExISTING Q FOR
2
YEqR=STORM
HI5TORIC RUNDFF COEFFICIENT
N�
BASIN SLOPE: 5
.25
PERCENT
BASIN LENGTH 500
FEET
AREA: 4.87 ACRES
HIST TC = 1,87*(1.1�( 1
*
25
N�
26,30562
MINUTES
HISTORIC RAINFALL INTENSITY:
1.622553
INCHES/HOUR
HISTORlC OUTFALL: 1.975458
CUBIC FEET PER
SECOND ,
—
DETERMINATION OF DETENTION POND
VOLUME FOR DEVELOF'ED
CONDITIONS
N�
DEVELOPED STORM : 100
YEAR STORM
�
DEVELOPED RUNOFF COEFFICIENT
�
^45
CCFAC
4. 87 = 2.739375
N�
DU�ATION GROSS VOL.
OUTFLOW VOL.
DETENTION VOL.
HIN CU. FT.
CU^ FT"
CU FT
5 7494,93
11538,25
592.6373
1185.275
69022^3
'7
1035^
m�
15 14694.01
1777.912
1291�^'
30 20315.21
45 24407.B3
3555.824
5333,737
1675~^^9
1907'^~9
N�
60 25739.17
7111.649
1862'^�2
90 810"14
27
106647 7.
1714'^ ~6
N�
120 28401.84
180 30768.66
14223.3
1417�^�4
21334.95
9433~`�5
34318.89
42669.89
~8351^'^
REQUIRED DETENTlON VOLUME IS
19074,09
CU. FT OR
^
m�
�3788| ACRE FEET
NOTE: AREA INCLUDES HALF OF U EMAY AVENUE FROM THE
HIGH POINT STA. 40+15 TO
STA. 46+00
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Engineering Consultants OAK RIDGE ESTATES
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