HomeMy WebLinkAboutFOSSIL CREEK ESTATES PUD PRELIMINARY - 50 92D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTv
Preliminary Drainage and Erosion Control Report
for
FOSSIL CREEK ESTATES P.U.D.
Fort Collins, Colorado
Prepared for:
FOSSIL CREEK PARTNERS
363 West Drake Road
Ft. Collins, Colorado 80526
Prepared by:
SHEAR ENGINEERING CORPORATION
Project No: 1318-01-92
DATE: September, 1993
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
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SHEAR ENGINEERING CORPORATION
PAGE 3
FOSSIL CREEK ESTATES DATE 09/07/93
HISTORIC FLOW FROM SUBBASIN I TO Ai TIME 1237 HOURS
PROJ. N0.13t8-01-92
FILE NAME FOSSIL BY MEO
AREA (A)= 17.32 ACRES
RUNOFF COEF. (C)
2 YEAR 10 YEAR 100 YEAR
CCf = 0.25 0.25 0.31
PASTURE WITH HEAVY SOILS AND AVG TO STEEP SLOPES (REF TABLES 3-3 & 3-4)
TIME OF CONCENTRATION (TO
OVERLAND TRAVEL TIME (TO
LENGTH = 500 FEET
2 YEAR
CCf = 0.25
Ti (min)= 18.97
(1.870.1-CCf)*(0^0.5)/(S)^0.33
SLOPE = 6.70 %
10 YEAR 100 YEAR
0.25 0.31
18.97 17.63
TRAVEL TIME (TO=L/(60*V) FLOW TYPE
L (ft) = 275 S (%) = 4.20 LAWN
L (ft) = 280 S (%) = 2.90 LAWN
L (ft) = 200 S (K) = 4.10 GUTTER
L (ft) = 175 S (%) = 1.19 GUTTER
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
Tc =Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)= 27.82 27.82 26.48
USE Tc = 28 28 26.5
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 1.50 2.70 4.45
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (0= CCfIA) (cfs)
2 YEAR 10 YEAR 100 YEAR
0 = 6.50 11.69 23.89
V (fps) =
1.50
Tt(min)=
3.06
V (fps) =
1.20
Tt(min)=
3.89
V (fps) =
4.05
Tt(min)=
0.82
V (fps) =
2.70
Tt(min)=
1.08
TOTAL TRAVEL
TIME
(min) =
8.85
CONCLUDE: COMPARE THIS FLOW TO Ai WITH THE DEVELOPED FLOW TO THE SAME POINT
SHEAR ENGINEERING CORPORATION
PAGE 4
FOSSIL CREEK ESTATES DATE 09/07/93
HISTORIC FLOW FROM SUBBASIN II TO Aii TIME 1233 HOURS
PROJ. N0.13t8-01-92
FILE NAME FOSSIL BY MEO
AREA (A)= 52.25 ACRES
RUNOFF COEF. (C)
2 YEAR 10 YEAR 100 YEAR
CCf = 0.25 0.25 0.31
PASTURE WITH HEAVY SOILS AND AVG TO STEEP SLOPES (REF TABLES 3-3 & 3-4)
TIME OF CONCENTRATION (Tc)
OVERLAND TRAVEL TIME (TO (1.87(1.1-CCf)*(L) 0.5)/(S)^0.33
LENGTH = 450 FEET SLOPE = 2.40 Y.
2 YEAR 10 YEAR 100 YEAR
CCf = 0.25 0.25 0.31
Ti (min)= 25.26 25.26 23.47
TRAVEL TIME (TO=L/(60*V) FLOW TYPE
L (ft) = 500 S (Y.) = 8.40 LAWN
L (ft) = 585 S (Y.) = 3.90 LAWN
L (ft) = 370 S M = 1.90 LAWN
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
Tc =Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)= 42.32 42.32 40.53
USE Tc = 42 42 41
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 1.18 2.10 3.45
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q= CCf IA) (cfs)
2 YEAR 10 YEAR 100 YEAR
Q = 15.41 27.43 55.88
V (fps) =
2.00
Tt(min)=
4.17
V (fps) =
1.45
Tt(min)=
6.72
V (fps) =
1.00
Tt(min)=
6.17
TOTAL TRAVEL
TIME
(min) =
17.06
CONCLUDE:TOTAL FLOW TO CONCENTRATION POINT DOWNSTREAM OF SUBASIN II
COMPARE WITH FLOW CAUSED BY DEVELOPMENT OF SITE TO SAME POINT
SHEAR ENGINEERING CORPORATION
PAGE j
DATE 09/07/93
TIME 1245 HOURS
FILE NAME FOSSIL
BASIN I HISTORIC
PROD. NO.1318-01-92
BY MEO
FLOW SUMMARY
2 YEAR
10 YEAR
100 YEAR
CCF
0.25
0.25
0.31
Tc
28
28
26.5
I
1.50
2.70
4.45
A
17.32
17.32
17.32
Q
6.495
11.691
23.893
NOTES:
BASIN II HISTORIC
2 YEAR
10 YEAR
100 YEAR
CCF 0.25
0.25
0.31
Tc 42
42
41
I 1.18
2.10
3.45
A 52.25
52.25
52.25
Q 15.41
27.43
55.88
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SHEAR ENGINEERING CORPORATION
PAGE $
FOSSIL CREEK ESTATES DATE 09/07/93
DEVELOPED FLOW FROM SUBBASIN I TO Ai TIME 1248 HOURS
PROD. N0.1318-01-92
FILE NAME FOSSIL BY MEO
AREA (A)= 16.23 ACRES
RUNOFF COEF. (C)
2 YEAR
CCf = 0.41
SEE PAGE 6
TIME OF CONCENTRATION (TO
OVERLAND TRAVEL TIME (Ti)
LENGTH = 200 FEET
2 YEAR
CCf = 0.20
Ti (min)= 12.24
10 YEAR 100 YEAR
0.41 0.51
(1.87(1.1-CCf)*(L)A0.5)/(S)AO.33
SLOPE = 7.50 Y.
10 YEAR 100 YEAR
0.20 0.25
12.24 11.56
TRAVEL TIME (Tt)=L/(60*V) FLOW TYPE
L (ft) = 410 S (%) = 7.50 GUTTER
L (ft) = 300 S (K) = 4.00 GUTTER
L (ft) = 185 S (Y.) = 3.50 GUTTER
L (ft) = 80 S (%) = 2.00 PIPE
L (ft) = 300 S M = 2.00 GRASSED SWALE
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
Tc =Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)= 18.61 18.61 17.93
USE Tc = 19 19 18
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 1.90 3.35 4.85
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (0= CCf IA) (cfs)
2 YEAR 10 YEAR 100 YEAR
O = 12.64 22.29 40.14
V (fps) =
4.60
Tt(min)=
1.49
V (fps) =
4.00
Tt(min)=
1.25
V (fps) =
3.80
Tt(min)=
0.81
V (fps) =
3.00
Tt(min)=
0.44
V (fps) =
2.10
Tt(min)=
2.38
TOTAL TRAVEL
TIME
(min) =
6.37
SHEAR ENGINEERING CORPORATION
PAGE q
FOSSIL CREEK ESTATES
DATE 09/07/93
DEVELOPED FLOW FROM SUBBASIN II TO Aii TIME 1239 HOURS
PROD. NO.1318-01-92
FILE NAME FOSSIL
BY MEO
AREA (A)= 53.34 ACRES
RUNOFF COEF. (C)
2 YEAR
10 YEAR 100 YEAR
CCf = 0.37
0.37 0.47
SEE PAGE 6
TIME OF CONCENTRATION (TO
OVERLAND TRAVEL TIME (TO
(1.87(1.1-CCf)*(L)^0.5)/ WO.33
LENGTH = 450 FEET
SLOPE = 2.40 Y.
2 YEAR
10 YEAR 100 YEAR
CCf = 0.20
0.20 0.25
Ti (min)= 26.74
26.74 25.26
TRAVEL TIME (Tt)=L/(60*V) FLOW TYPE
L (ft) = 300 S W
L (ft) =
= 5.30 GUTTER V (fps) =
Tt(min)=
340 S (%)
L (ft) =
= 1.00 GUTTER
2.00
2.83
200 S (%)
L (ft) =
= 6.00 GRASSED SWALE V (fps) =
3.80 Tt(min)= 0.88
400 S (Y.)
L (ft)
= 3.00 LAWN/WETLANDS V (fps) =
1.20 Tt(min)= 5.56
= 370 S (%)
NOTE:
= 1.90 LAWN/WETLANDS V (fps) =
.m
100 Tt(min)= 6.17
ALL VELOCITIES TAKEN FROM FIGURE 3-2 TOTAL TRAVEL
TIME (min) = 16.52
Tc =Ti+TOTAL TRAVEL TIME
2 YEAR
10 YEAR 100 YEAR
Tc (min)= 43.26
43.26 41.78
USE Tc = 43
43 42
INTENSITY (I) (iph)
2 YEAR
10 YEAR 100 YEAR
I = 1.15
2.08 3.40
NOTE: INTENSITIES TAKEN
FROM FIGURE 3-1
RUNOFF (Q= CCf IA) (cfs)
2 YEAR
10 YEAR 100 YEAR
O = 22.70
41.05 85.24
CONCLUDE:INCREASE IN RUNOFF
CAUSED BY DEVELOPMENT OF SITE ONLY
UPSTREAM DEVELOPMENT ALSO TO BE CONSIDERED FOR PIPE AND INLET
SIZING
SHEAR ENGINEERING CORPORATION
PAGE IO
DATE 09/07/93 PROJ. NO.13Y8-01-92
TIME 1257 HOURS BY NED
FILE NAME FOSSIL
FLOW SUMMARY
BASIN I
HISTORIC
BASIN I
DEVELOPED
2 YEAR
10 YEAR
100 YEAR
2 YEAR
CCF
0.25
0.25
0.31
CCF
0.41
Tc
28
28
26.5
Tc
19
I
1.50
2.70
4.45
I
1.90
A
17.32
17.32
17.32
A
16.23
0
6.495
11.691
23.893
O
12.64
BASIN
II HISTORIC
BASIN
II DEVELOPED
2 YEAR
10 YEAR
100 YEAR
2 YEAR
CCF
0.25
0.25
0.31
CCF
0.37
Tc
42
42
41
Tc
43
I
1.18
2.10
3.45
I
1.15
A
52.25
52.25
52.25
A
53.34
0
15.41
27.43
55.88
O
22.70
DEVELOPED BASIN SUMMARY
SUBBASIN
UPSTREAM
ONSITE
DOWNSTREAM
TOTAL
ac
ac
ac
ac
I
0.47
12.69
3.07
16.23
II
13.69
32.78
6.87
53.34
TOTALS
14.16
45.47
9.94
69.57
HISTORIC
BASIN SUMMARY
SUBBASIN
UPSTREAM
ONSITE
DOWNSTREAM
TOTAL
ac
ac
ac
ac
I
0.47
13.50
3.35
17.32
II
13.69.
31.69
6.87
52.25
TOTALS
14.16
45.19
10.22
69.57
10 YEAR
100 YEAR
0.41
0.51
19
18
3.35
4.85
16.23
16.23
22.29
40.14
10 YEAR
100 YEAR
0.37
0.47
43
42
2.08
3.40
53.34
53.34
41.05
85.24
PAGE 1
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
L GENERAL LOCATION AND DESCRIPTION:
A. Location:
1. Fossil Creek Estates is located in the Northeast one -quarter (1/4) of Section 10,
T6N, R69W of the 6th P.M., Larimer County, Colorado.
2. More specifically, it is located on the southwest corner of the intersection of South
Shields Street and Fossil Creek Drive. It is approximately 1.0 mile south of
Harmony Road and 1.0 mile north of Trilby Road.
3. Fossil Creek Estates P.U.D. is bounded on the East by South Shields Street.
Nittman M.R.D. (County M.R.D.) is directly across South Shields Street east of this
project. It is bounded on the north, south and west by currently unplatted
properties. The property to the north is owned by the City of Fort Collins and will
be maintained as City open space. This property will not be developed. The
property to the west is currently being considered for development. The property to
the south is unplatted and to our knowledge, is not being seriously considered for
development at this time. Clarendon Hills is located immediately northeast of this
site at the northeast comer of South Shields Street and Fossil Creek Drive.
4. The site is located within the Fossil Creek Basin as defined by the City of Fort
Collins Stormwater Basin Map. Fossil Creek flows generally in an easterly
direction. Flows west of South Shields Street are conveyed under South Shields
Street via a recently constructed 6x10 reinforced concrete box culvert. This box
culvert was constructed as part of the South Shields Street widening project in
association with the Clarendon Hills development. The box culvert is located
approximately 380 feet north of the project site. The culvert is sized with upstream
development in mind as noted in the Fossil Creek Drainage Study prepared by
Simons Li Associates, May, 1982.
B. Description of Property:
1. The Fossil Creek Estates P.U.D. property covers approximately 45.19 acres,
including the existing westernmost South Shields Street 30' Right -of -Way. A
majority of the site is predominantly open pasture land covered with native
vegetation. The property generally slopes in a northerly / northeasterly direction.
The southern property line traverses an existing ditch which follows an existing
ridge line. The west boundary lies approximately 100 feet west of an existing west
ridge line. There is approximately 60 feet of relief across the property from the
southwest corner of the site to the northeast. .
2. Fossil Creek Estates P.U.D. will consist of the development of 130 single family
residences including the necessary infrastructure to service these lots.
3. The main Fossil Creek channel lies immediately north of Fossil Creek Estates
P.U.D. The distance of the Fossil Creek main channel flowline from Fossil Creek
Estates P.U.D. ranges from approximately 360' at the creeks intersection with
South Shields Street, to approximately 890' at its furthest distance from Fossil
Creek Estates P.U.D.
APPENDIX II
Backup diagrams and exhibits
No Text
• 3.1.6 Runoff Coef nts
The runoff coefficients to be used with the Rational Method referred to in Section 3.2
"Analysis Methodology" can be determined based on either zoning classifications or the
1. types of surfaces on the drainage area. Table 3-2 lists the runoff coefficients for the various
types of zoning along with the zoning definitions. Table 3-3 lists coefficients for the different
kinds of surfaces. Since the Land Development Guidance System for Fort Collins allows land
development to occur which may vary the zoning requirements and produce runoff coeffi-
cients different from those specified in Table 3-2, the runoff coefficients should not be based
solely on the zoning classifications.
The Composite Runoff Coefficient shall be calculated using the following formula:
C = (EC,A,)/At
,_i.
Where C = Composite Runoff Coefficient
C,=Runoff Coefficient for specific area A;
A, = Area of surface with runoff coefficient of C,
n = Number of different surfaces to be considered
A, = Total area over which C is applicable; the sum of all A,'s is equal to A,
Table 3-2
RATIONAL METHOD RUNOFF COEFFICIENTS FOR ZONING CLASSIFICATIONS
Description of Area or Zoning
Coefficient
Business: BP, BL........................................................................................
0.85
Business: BG, HB, C..................................................................................
0.95
......................................
Industrial: IL, IP ..:..................... ............................
0.85
Industrial: IG...............................................................................................
0.95
Residential: RE, RLP..................................................................................
0.45
Residential: RL, ML, RP.............................................................................
0.50
Residential: FILM, RMP..............................................................................
0.60
Residential: RM, MM..................................................................................
0.65
Residential: RH..........................................................................................
0.70
Parks, Cemeteries......................................................................................
0.25
Playgrounds...............................................................................................
0.35
RailroadYard Areas...................................................................................
0.40
UnimprovedAreas......................................................................................
0.20
Zoning Definitions
R-E Estate Residential District — a low density residential area primarily in outlying
areas with a minimum lot area of 9,000 square feet.
R-L Low Density Residential District — low density residential areas located throughout
the City with a minimum lot area of 6,000 square feet.
R-M Medium Density Residential District — both low and medium density residential
areas with a minimum tot area of 66,000 square feet for one -family or two-family
dwellings and 9,000 square feet for a multiple family dwelling.
R-H High Density Residential District— high density residential areas with a minimum lot
area of 6,000 square feet for one -family or two-family dwellings, 9,000 square feet
for a multiple family dwelling,.and 12,000 square feet for other specified uses.
R-P Planned Residential District — designation of areas planned as a unit (PUD) to pro-
vide a variation in use and building placements with a minimum lot area of 6,000
square feet.
R-L-P Low Density Planned Residential District — areas planned as a unit (PUD) to permit
variations in use, density and building placements, with a minumum lot area of 6,000
square feet.
MAY 1984 3-3 DESIGN CRITERIA
R-M-P Medium Density Planned Residential District — designation for medium density
areas planned as a unit (PUD) to provide a variation in use and building placements
with a minimum lot area of 6,000 square feet.
R-L-M Low Density Multiple Family District— areas containing low density multiple family
units or any other use in the R-L District with a minimum lot area of 6,000 square feet
for one-farnily or two-family dwellings and•9,000 square feet for multiple -family
dwellings.
M-L Low Density Mobile Home District — designation for areas for mobile home parks
containing independent mobile homes not exceeding 6 units per acre.
M-M Medium Density Mobile Home District — designation for areas of mobile home
parks containing independent mobile homes not exceeding 12 units per acre.
B-G General Business District — district designation for downtown business areas,
including a variety of permitted uses, with minimum lot areas equal to 1 /2 of the total
floor area of the building.
B-P Planned Business District — designates areas planned as unit developments to
provide business services while protecting the surrounding residential areas with
minumum lot areas the same as R-M.
H-B Highway Business District — designates an area of automobile -orientated busi-
nesses with a minimum lot area equal to 1/2 of the total floor area of the building.
B-L Limited Business District — designates areas for neighborhood convenience
centers, including a variety of community uses with minimum lot areas equal to two
times the total floor area of the building.
C Commercial District —designates areas of commercial, service and storage areas.
1-L Limited Industrial District —designates areas of light industrial uses with a minimum
area of lot equal to two times the total floor area of the building not to be less than
20,000 square feet.
I-P Industrial Park District —designates light industrial park areas containing controlled
industrial uses with minimum lot areas equal to two times the total floor area of the
building not to be less than 20,000 square feet.
I-G General Industrial District — designates areas of major industrial development.
T Transition District — designates areas which are in a transitional stage with regard
to ultimate development.
For current and more explicit definitions of land uses and zoning classifications, refer to the
Code of the City of Fort Collins, Chapters 99 and 118.
Table 3-3
RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE ANALYSIS
Character of Surface Runoff Coefficient
Streets, Parking Lots, Drives:
Asphalt................................................................................................ 0.95
95
Concrete............................................................................................. 0.
Gravel................................................................................................. 0.50
Roofs 0.95
..........................................................................................................
Lawns, Sandy Soil:
Flat <2% 0.15
Average2 to 7%°.................................................................................. 0.15
Steep >7% 0.20
..........................................................................................
Lawns-, Heavy Soil:
Flat<2%.............................................................................................. 0.25
..................................................................................
Average 2 to 7% 0.2
Steep >7%......... :................................................................................
0.35
MAY 1984 3-4 DESIGN CRITERIA
3.1.7 Time of Concentration
In order to use the Rainfall Intensity Duration Curve, the time of concentration must be
known. This can be determined either by the following equation or the "Overland Time of
Flow Curves" from the Urban Storm Drainage Criteria Manual, included in this report (See
Figure 3-2).
Tc =1.87 (1.1' iz
S Ili
Where Tc =Time of Concentration, minutes
S = Slope of Basin, %
C = Rational Method Runoff Coefficient
D = Length of Basin, feet
C, = Frequency Adjustment Factor
Time of concentration calculations should reflect channel and storm sewer velocities as well
as overland flow times.
3.1.8 Adjustment for Infrequent Storms
The preceding variables are based on the initial storm, that is, the two to ten year storms. For
storms with higher intensities an adjustment of the runoff coefficient is required because of
the lessening amount of infiltration, depression retention, and other losses that have a
proportionally smaller effect on storm runoff.
These frequency adjustment factors are found in Table 3-4.
Table 3-4
RATIONAL METHOD FREQUENCY ADJUSTMENT FACTORS
Storm Return Period Frequency Factor
(years) Cr
2 to 10 1.00
N 11 to25 1.10
26 to 50 1.20
51 to100 1.25
Note: The product of C times C, shall not exceed 1.00
3.2 Analysis Methodology
The methods presented in this section will be instituted for use in the determination and/or verification
of runoff at specific design points in the drainage system. These methods are (1), the Rational Method
and (2) the Colorado Urban Hydrograph Procedure (CUHP). Other computer methods, such as
SWMM, STORM, and HEC-1 are allowable if results are not radically different than these two. Where
applicable, drainage systems proposed for construction should provide the minimum protection as
determined by the methodology so mentioned above.
3.2.1 Rational Method
For drainage basins of 200 acres or less, the runoff may be calculated by the Rational
Method, which is essentially the following equation:
Q = C,CIA
Where Q = Flow Quantity, cis
A =Total Area of Basin, acres
Ct = Storm Frequency Adjustment Factor (See Section 3.1.8)
C = Runoff Coefficient (See Section 3.1.6)
I = Rainfall Intensity, inches per hour (See Section 3.1.4)
3.2.2 Colorado Urban Hydrograph Procedure
For basins larger than 200 acres, the design storm runoff should be analyzed by deriving
synthetic unit hydrographs. It is recommended that the Colorado Urban Hydrograph
Procedure be used for such analysis. This procedure is detailed in the Urban Storm Drainage
Criteria Manual, Volume 1, Section 4.
MAY 1984 3-5 ' DESIGN CRITERIA
DRAINAGE CRITERIA ANUAL RUNOFF.
50
30
I- 20
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2 .3 .5 1 2 3 5 10 20
VELOCITY IN FEET PER SECOND
FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR
USE WITH THE RATIONAL FORMULA.
*MOST FREQUENTLY OCCURRING "UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFERENCE: "Urban Hydrology For Small Watersheds" Technical
Release No. 55, USDA, SCS 'Jan. 1975.
5 -1-84
URBAN DRAINAGE & FLOOD CONTROL DISTRICT
FORT COLLINS
RAINFALL INTENSITY CURVE DATA
FIG 3-1
NOVEMBER 1975
INTERPRETED DECEMBER 21, 1992 BY MARK OBERSCHMIDT
SHEAR ENGINEERING CORPORATION
2
5
10
25
50
100
TIME
YEAR
YEAR
YEAR
YEAR
YEAR
YEAR
***************************************************************
5
3.29
4.70
5.64
7.02
7.95
8.70
10
2.54
3.65
4.45
5.50
6.35
7.14
15
2.14
3.07
3.75
4.60
5.29
6.06
20
1.85
2.65
3.25
4.00
4.60
5.21
25
1.63
2.34
2.87
3.54
4.08
4.63
30
1.47
2.11
2.60
3.17
3.67
4.20
35
1.32
1.92
2.38
2.88
3.35
3.81
40
1.20
1.76
2.19
2.67
3.08
3.60
45
1.12
1.62
2.02
2.46
2.84
3.28
50
1.04
1.51
1.87
2.27
2.65
3.02
55
0.97
1.40
1.73
2.12
2.46
2.80
60
0.90
1.32
1.62
1.99
2.32
2.60
65
0.88
1.24
1.52
1.84
2.18
2.43
70
0.82
1.18
1.44
1.72
2.05
2.30
75
0.79
1.11
1.38
1.62
1.93
2.17
80
0.74
1.07
1.30
1.53
1.82
2.07
85
0.70
1.00
1.23
1.46
1.73
1.96
90
0.68
0.97
1.20
1.40
1.67
1.87
95
0.64
0.91
1.13
1.32
1.59
1.77
100
0.61
0.88
1.09
1.27
1.51
1.70
105
0.60
0.83
1.04
1.22
1.46
1.63
110
0.57
0.80
1.00
1.18
1.40
1.57
115
0.54
0.78
1.96
1.14
1.33
1.50
120
0.52
0.76
0.91
1.10
1.19
1.44
6
APPENDIX III
Stuffer Envelope
Drainage Plan; Historic Conditions
Preliminary Drainage and Erosion Control Plan
PAGE 2
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
L GENERAL LOCATION AND DESCRIPTION:
B. Description of Property: (continued)
4. Existing irrigation ditches traverse the southern boundary of the project. The ditch
line generally defines the southern boundary of Fossil Creek Estates P.U.D. The
Trilby lateral traverses a portion of the western section of the project. The Scenic
Knolls ditch traverses the central and eastern southern boundary of the project.
Refer to the Preliminary Drainage and Erosion Control Plan in the appendix of this
report.
U. DRAINAGE BASINS AND SUB -BASINS:
A. Major Basin Description:
1. Fossil Creek Estates P.U.D. is within the Fossil Creek Basin. Historic runoff
from the site is conveyed to Fossil Creek, west of South Shields Street.
Development of the site will not affect the general historic flow pattern.
2. The Fossil Creek Basin Study, which was prepared by Simons Li Associates in
May, 1982, considers future development west of South Shields Street. A 6 x10
reinforced concrete box culvert was recently constructed under South Shields Street
at Fossil Creek. The culvert was sized based on fully developed flows to South
Shields Street from the upstream reaches.
3. Fossil Creek is the only major drainageway within 100' of the property boundary.
B. Sub -Basin Description:
1. There are two sub -basins defined within the Fossil Creek Estates P.U.D. project
area. These sub -basins are well defined by an existing ridge which nearly parallels
South Shields Street. Refer to the the existing conditions plan located in the
appendix of this report.
2. Historically, runoff from the site is conveyed overland, northerly and northeasterly
across the site to Fossil Creek. Runoff continues easterly in Fossil Creek under
South Shields Street, through a portion of Clarendon Hills, under Fossil Creek
Drive, continuing through the Fossil Creek drainage system to Fossil Creek
Reservoir. Refer to the Fossil Creek Major Drainage Basin Study for further detail
of the Fossil Creek drainage system.
3. There is minimal contributing offsite runoff conveyed through the site because of
the southernmost ridge defining the south Fossil Creek Basin boundary, and a ridge
near the west boundary of the development.
PAGE 3
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
III DRAINAGE DESIGN CRITERIA:
A. Regulations:
1. Storm drainage design criteria from the City of Fort Collins Storm Drainage
Criteria Manual were used.
2. Erosion control measures and design will conform to the requirements of the City of
Fort Collins Erosion Control Reference Manual.
B. Development Criteria Reference and Constraints:
Development of this area was considered in the Fossil Creek Drainage Study,
prepared by Simons I i Associates, May, 1982. The recent South Shields Street
widening project adjacent to Clarendon Hills considered the Fossil Creek study in
the design and installation of the drainage structures under South Shields Street.
2. 'Detention is not being considered with the development of Fossil Creek Estates
P.U.D. because of its proximity and relationship to the Fossil Creek Drainageway.
3. South Shields Street bounds Fossil Creek Estates to the east. Development of
Fossil Creek Estates will require the widening of South Shields Street to City of
Fort Collins Arterial standards. The existing South Shields Street grade will dictate
the ultimate grading restraints to the South Shields Street new Right -of -Way (20'
west of the current 30' Right -of -Way) and the easternmost lots located adjacent to
the South Shields Street Right -of -Way.
4. The property to the north of Fossil Creek Estates P.U.D. will be the major design
constraint in the design of the Fossil Creek Estates P.U.D. drainage infrastructure.
Coordination of the two sites will allow for an effective method of conveying runoff
to the box culvert at Fossil Creek.
a. The property directly to the north is currently owned by the City of Fort Collins.
The property for was purchased primarily for utilization as open space.
b. There are no conceptual design plans for the property to the north of Fossil
Creek Estates P.U.D. as we understand it. Further detail of the situation with
the property to the north is required prior to final drainage and utility design, if
available.
c. Easement acquisition from the City of Fort Collins will be required in order to
extend sanitary sewer service from the project to the existing sewer trunk main
adjacent to Fossil Creek . The sewer trunk main is owned by the South Fort
Collins Sanitation District.
S. Wetland area identification and documentation will also be a design constraint in
the layout of the street and drainage system and the lot layout.
PAGE 4
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
III DRAINAGE DESIGN CRITERIA:
B. Development Criteria Reference and Constraints: (continued)
6. Groundwater considerations and underground conveyance to the wetlands and the
Fossil Creek channel, are a major issue and design constraint.
C. Hydrological Criteria:
1. The Rainfall -Intensity -Duration curves for the Fort Collins area were used in
conjunction with the "Rational Method" for determining peak flows at various
concentration points.
2. The site is situated within the Fossil Creek Drainage Study area. The majority of
the improvements recommended by the study have been installed up to South
Shields Street. The design and installation of these improvements considered
development within the basin and therefore, no detention is proposed at this time.
3. The 2 and 100 year storms have been used in analyzing the effects of development
and providing recommendations for a storm drainage system which will adequately
convey peak flows to the major drainage system.
D. Hydraulic Criteria:
Street capacity references provided in the City of Fort Collins Storm Drainage
Criteria Manual and street capacity exhibits which were prepared by this office and
based on the Mannings equation, were used.
2. Storm sewer and drainage channel capacities were based on the Mannings
Equation. The Mannings coefficients are as suggested by the City of Fort Collins
Storm Drainage Criteria Manual.
3. Storm inlet capacities were based on the Allowable inlet Capacity charts and
Figures provided in the City of Fort Collins Storm Drainage Criteria Manual.
IV DRAINAGE FACILITY DESIGN:
A. General Concept:
1. Proposed drainage improvements will convey 100% of storm runoff to the main
Fossil Creek channel, north of Fossil Creek Estates P.U.D. and west of South
Shields Street, maintaining peak discharge points at, or near, historic peak discharge
locations. Runoff will continue to be conveyed to the 6' x 10' concrete box culvert
at Fossil Creek, approximately 380 feet north of Fossil Creek Estates P.U.D.
2. There is minimal offsite contributing runoff to the site due to the site's proximity to
the southern ridge line which defines the Fossil Creek Major Basin.
PAGE S
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
IV DRAINAGE FACILITY DESIGN:
A. General Concept: (continued)
3. The appendix contains all tables, charts and figures referenced in the calculations
for storm sewer design, street capacities and historic and developed runoff peak
flow quantities.
B. Specific Details:
1. The street system will convey the runoff which contributes to the street system, to
peak concentration points in the street system. Proposed street grades allow
adequate street conveyance capacities.
2. Runoff will be conveyed from the street system, to the main channel of Fossil Creek
via a combination storm sewer and open channels.
a. All runoff will be directed to the designated wetland areas as much as
reasonably possible on the project site.
b. A utility and drainage easement will be required adjacent to the west Right -of -
Way of South Shields Street, to be secured from the owners of the property to
the north, to facilitate drainage conveyance from the easternmost sub -basin to
Fossil Creek. The drainage design and easement will be defined based on the
future conditions for full arterial widening of South Shields Street adjacent to
the property to the north.
3. Runoff which is conveyed directly to South Shields Street, will ultimately be
conveyed to Fossil Creek with an inlet on the west side of South Shields Street.
This is depicted on the South Shields Street Widening Project plans which were
prepared by Intermill Land Surveying in conjunction with Clarendon Hills (Sta. 48
+ 16.46). Interim drainage conveyance will be provided with the development of
Fossil Creek Estates P.U.D.
V. EROSION CONTROL:
A. General Concept
Erosion control measures will be provided with construction. These measures will
include; silt fence along downstream property lines, hay bale barriers in swales, and
inlet filters at storm sewer inlets. These measures will effectively reduce the
amount of soil erosion potential created during the construction of the project.
a. Erosion Control device maintenance, both ofsite and offsite, will remain the
responsibility of the developer until the subdivision is completely developed.
This includes completion of housing and yard surfacing, which until completed,
contributes to erosion potential.
PAGE 6
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
V. EROSION CONTROL:
A. General Concept (continued)
2. An Erosion control security deposit will be required for each phase of construction
according to current City of Fort Collins policy as presented in the City of Fort
Collins Development Manual.
a. The security deposit is based on the cost to reseed the actual affected property
during overlot grading activity (Project Phasing). Currently, security deposit
estimates are based on $ 650.00 per acre to reseed sites between 1 and 10 acres
and $ 500.00 per acre to reseed sites greater than 10 acres.
i. The estimated security deposit for the entire 45.19 acres would be
$22,593.00.
b. Construction phasing has not been established at the time of preliminary
submittal. Phasing is being discussed.
VI. CONCLUSIONS:
A. Compliance with Standards
1. All drainage analysis has been performed according to the requirements of the City
of Fort Collins Storm Drainage Criteria Manual.
2. Erosion control considerations conform to the City of Fort Collins Erosion Control
Reference Manual.
3. Proposed drainage improvements generally conform with the recommendations of
the Fossil Creek Drainage Study.
B. Drainage Concept:
1. The proposed drainage design for Fossil Creek Estates P.U.D. is effective for the
control of storm runoff with little or no downstream effects.
2. The proposed development of the site was considered in the Fossil Creek Drainage
Study. The property to the north of Fossil Creek Estates P.U.D. is owned by the
City of Fort Collins and will remain undisturbed open space.
3. There are no major irrigation facilities that will be affected by the development of
Fossil Creek Estates P.U.D. The small irrigation ditch noted along the south
boundary (the Trilby lateral) will be considered as a major design factor with the
design of Fossil Creek Estates P.U.D. Easements and possible ditch improvements
are being discussed with users of the ditch. This however, has no immediate affect
on drainage, erosion control and / or wetlands considerations.
PAGE 7
Fossil Creek Estates P.U.D.; Ft. Collins
Preliminary Drainage Report
0
1. City of Fort Collins Storm Drainage Criteria Manual
2. City of Fort Collins Erosion Control Reference Manual
3. Fossil Creek Master Drainage Study, Simons Li Associates, 1982
4. South Shields Street Widening Project plans; Intermill Land Surveying; Approved by
the City of Fort Collins, December, 1991.
5. Clarendon Hills Drainage reports
APPENDIX I
Storm Drainage Calculations