HomeMy WebLinkAboutFOSSIL CREEK ESTATES PUD FIRST FILING FINAL - 50 92F - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI ':
J
Final Drainage and Erosion Control Report
for
FOSSIL CREEK ESTATES P.U.D. FIRST FILING
Fort Collins, Colorado
Prepared for:
FOSSII, CREEK PARTNERS
363 West Drake Road
Ft. Collins, Colorado 80526
11�11'T16A s ww YAL
Prepared by:
SHEAR ENGINEERING CORPORATION
Project No: 1318-01-92
Date: March, 1994
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
APPENDIX I
Stonn Drainage Calculations
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SHEAR ENGINEERING CORPORATION
DEVELOPED'SITE
PAGE t 2
PROJECT tPOSSIL CREEK FIRST
PROJ.NO. 11318-01-92 DATE? 03/31/94
FILE tFOSSILI BYR NED
NOTES 2INCLUDES 1/2 SHIELDS STREET
RUNOFF
SURFACE
CORP.
CHARACTERISTICS
AREA
C
C*A
(acres)
STREETS
ASPHALT
3.270
0.950
3.107
CONCRETE
0.000
0.950
0.000
GRAVEL
0.000
0.500
0.000
ROOFS
1.740
0.950
1.653
LAWNS SANDY SOIL
PLAT < 2%
0.000
0.100
0.000
AVERAGE 2 - 71
0.000
0.150
0.000
STEEP > 74
0.000
0.200
0.000
LAWNS HEAVY SOIL
FLAT < 21
0.000
0.200
0.000
AVERAGE 2 - 7%
8.020
0.250
2.005
STEEP > 7%
0.000
0.350
0.000
TOTAL AREA
13.030
6.765
C2
C10
C100
COMPOSITE C VALUE
0.519
0.519
0.649
USE
0.52
0.52
0.65
No Text
I I
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b
i; I,iv ��,
6u�¢u
LAwN PAU6�6rVT - Ltiw,� Ao,,slo�e.,
�i
li C.,-
= 0163
C,o = 0 ,, Cio o = 0,64,
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Oi�GT'�
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'1
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La�aN =
10 0 �� ..�,, P,Wb .51o,ve
CGog - 0.40
...
I,
li
i; ,
;; Com ostit�- I„ CZ
= 6,-3 c,,= 0135 G1QD= (3,44
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- d\$Z c -
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SHEAR ENGINEERING CORPORATION
PAGE 4 DEVELOPED FLOW TO •S•
PROJECT& FOSSIL CREEK FIRST PILING DATE 03/31/94
PROJ. NO.1318-01-92
BY HBO
FILEt FOSSILI
AREA (A). 11.83 ACRES SUB BASINIb INCLUDES 1.0 ACRES OFF SITE
RUNOFF CORP. (C)
2 YEAR
10 YEAR
200 YEAR
C 0.49
0.49
0.62
088 CALCULATIONS ON PAGE
3
TIME OF CONCENTRATION (TC)
OVERLAND TRAVEL TIME (Ti)
(1.87(1.1-CCf)*(L)"0.5)/(8)•0.33
LENGTH . 200 FEET
SLOPE
8.00 1
2 YEAR
10 YEAR
100 YEAR
C 0.25
0.25
_ 0.31
Ti (min). 21.32
11.32
10.49
TRAVEL TIME (Tt) .L/(60-V) FLOW TYPE
L (ft)
380 S
(1)
. 1.00
GUTTER
V (fps) .
2.00
Tt(min).
3.17
L (ft)
. 300 8
(1)
. 8.00
GUTTER
V (fps) .
5.60
Tt(min).
0.89
L (ft)
. 335 8
(t)
. 5.00
GUTTER
V (fps) .
4.50
Tt(min).
1.24
L (ft)
0 S
(t)
. 4.40
GUTTER
V (fps) .
0.00
Tt(min).
0.00
L (ft)
0 S
(1)
. 0.00
GUTTER
V (fps) .
0.00
Tt(min).
0.00
L (ft)
0 S
(1)
. 0.00
GUTTER
V (fps) .
0.00
Tt(min).
0.00
L (ft)
0 S
(1)
. 0.00
GUTTER
V (fps) .
0.00
Tt(min).
0.00
NOTE
ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL TRAVEL
TIME
(min) .
5.30
TO .Ti+TOTAL TRAVEL TIME
2 YEAR
10 YEAR
100 YEAR
TO (min). 16.62
16.62
15.79
USE Tc
. 16.5
16.5
16.0
INTENSITY (I) (iph)
,
2 YEAR
10 YEAR
100 YEAR
I
2.05
3.60
5.80
NOTEt
INTENSITIES
TAKEN
FROM FIGURE
3-1
RUNOFF
(Q. CIA) (Cfe)
2 YEAR
10 YEAR
100 YEAR
Q
11.88
20.87
42.54
CONCLUDE&POR 240 RCP
MINIMUM SLOPE .
3.54
n.
0.013
FOR 30• RCP
MINIMUM SLOPE .
1.08
♦ n.
0.012
SHEAR ENGINEERING CORPORATION
PAGE 5 DEVELOPED FLOW TO •A•
PROJBCTt FOSSIL CREEK FIRST FILING DATE 03/31/94
PROJ. NO.1318-01-92
BY MEO
PILEt POSSILI
AREA (A). 23.03 ACRES SUS BASINIa 9Ib
RUNOFF COBF. (C)
2 YEAR 10 YEAR 100 YEAR
C . 0.42 0.42 0.53
ORB CALCULATIONS ON PAGE 3
TIME OF CONCENTRATION (To)
OVERLAND TRAVEL TIME (Ti)(1.87(1.1-CCf)*(L)"0.5)/(S)"0.33
LENGTH .
500 FEET SLOPE .
2.00 i
2 YEAR
10 YEAR
100 YEAR
C .
0.20
0.20
0.25
Ti (min).
29.94
29.94
28.28
TRAVEL TIME (Tt)
.L/(60*V)
FLOW TYPE
L (ft) .
650
S (1) .
1.20
PASTURE
V (fps) .
0.80
Tt(min).
13.54
L (ft) .
400
S (1)
0.80
GUTTER
V (fps) .
1.90
Tt(min).
3.51
L (ft)
700
S (1) .
5.00
GUTTER
V (fps) .
4.50
Tt(min).
2.59
L (ft) .
45
S (1)
4.44
PIPE
V (fps) .
10.00
Tt(min).
0.08
L (ft)
0
S (1)
0.00
GUTTER
V (fps) .
0.00
Tt(min).
0.00
L (ft) .
0
S (1) •
0.00
GUTTER
V (fps) .
0.00
Tt(min).
0.00
L (ft)
0
S (1) .
0.00
GUTTER
V (fps) .
0.00
Tt(min).
0.00
NOTEt ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL TRAVEL TIME
(min) .
19.72
To .Ti+TOTAL TRAVEL TIME
2 YEAR
10 YEAR
100 YEAR
To (min).
49.66
49.66
47.99
USE To .
49.5
49.5
48
INTENSITY (I) (iph)
2 YEAR 10 YEAR
I 1.05 1.89
NOTEt INTENSITIES TAKEN FROM FIGURE
RUNOFF (Q. CIA) (cfe)
2 YEAR 10 YEAR
Q 10.16 18.28
CONCLUDBtFOR 24• ADS N-12 MINIMUM SLOPE .
FOR 30• ADS N-12 MINIMUM SLOPE
100 YEAR
3.12
3-1
100 YEAR
39.08
2.41 1 n. 0.012
0.73 1 n. 0.012
FLOW SUMMARY FOR FOSSIL CREEK FIRST FILING
Sun
AREA C2 C10 C100 To
To
To
I2
I10
I100
Q2
Q10
Q100
BASIN
ac. min.
min.
min.
iph
iph
iph
cfe
cfe
cfe
Ib 11.83 0.49 0.49 0.62 26.50 16.50 16.00 2.05 3.60 5.80 11.88 20.87 42.54
Ia iIb 23.03 0.42 0.42 0.53 49.50 49.50 49.00 1.05 1.89 3.12 10.16 18.28 38.09
APPENDIX II
Backup diagrams and exhibits
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 -family 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.
I-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: 0.95
Asphalt................................................................................................
Concrete............................................................................................. 0.95
Gravel................................................................................................. 0.50
Roofs..........................................................................................................
Lawns, Sandy Soil:
Flat<2%.............................................................................................
Average2 to 7%..................................................................................
Steep>7%..........................................................................................
Lawns-, Heavy Soil:
Flat<2%.............................................................................................
_.• Average 2 to 7%..................................................................................
Steep>7%......... :................................................................................
MAY 1984 3-4
0.95
0.10
0.15
0.20
0.20
25
0.35
DESIGN CRITERIA
PAGE 1
Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
A. Location:
1. Fossil Creek Estates P.U.D. First Filing is located in the Northeast one -quarter (1/4)
of Section 10, UN, R69W of the 6th P.M., Latimer 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. First Filing 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.
a. 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.
b. The property to the west is currently being considered for development.
c. 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 corner
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 6 x10 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. First Filing property covers approximately 13.03
acres, including the South Shields Street 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.
2. There is approximately 60 feet of relief across the property from the southwest
corner of the site to the northeast.
3. Fossil Creek Estates P.U.D. First Filing will consist of the development of 38 single
family residences including the necessary infrastructure to service these lots.
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 —CCI) DI/2
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) C,
2 to 10 1.00
11 to25 1.10
26 to 50 1.20
51 to 100 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, cfs
A =Total Area of Basin, acres
C, = 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 ana!ysis. This procedure is detailed in the Urban Storm Drainage
Criteria Manual, Volume 1, Section 4.
MAY 1984 3-5 DESIGN CRITERIA
DRAINAGE CRITERIA MANUAL
RUNOFF
5C
3C
F- 20
z
w
U
cc
W
10
z
w
a
OJ 5
to
w
cc 3
0
U 2
cc
w
I-
3
1
.5
I
►I�� I
1
I
����
INNER
■NNE
soon
WINNE
WAM
WA
II
OR
MENEM
-►��M
■11
M
MEMOS
ME
C►..N.....mmmo........
FAME
NNE
NONNI�
........ME
' •0 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
No Text
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
TABLE 4
CIRCULAR PIPE FLAW CAPACITY
Full Flow (cubic feet per second)
Mannings "n"= 0.012
Dia. *Conv. % Slope (feet per 100 feet)
(in.) Factor 0.02 0.05 0.10 0.20 0.35 0.50 0.75 1.00 1.25 1.50 1.75 2.0 2.5 5.0 10.0 20.0
(c.f.s.)
3 0.957 0.014 0.021 0.030 0.043 0.057 0.068 0.083 0.096 0.107 0.12 0.13 0.14 0.15 0.21 0.30 0.43
4 2.062 0.029 0.046 0.065 0.092 0.122 0.146 .0.179 0.206 0.231 0.25 0.27 0.29 0.33 0.46 0.65 0.92
5 3.738 0.053 0.084 0.118 0.167 0.221 0.264 0.324 0.374 0.418 0.46 0.49. 0.53 0.59 0.84 1.18 1.67
6 6.079 0.086 0.136 0.192 0.272 0.360 0.430 0.526 0.608 0.680 0.74 -0.80 0.86 0.96 1.36 1.92 2.72
8 13.091 0.185 0.293 0.414 0.585 0.774 0.926 1.134 1.309 1.464 1.60' 1M 1.85 2.07 2.93 4.14 5.85
10 _ 23.74 0.34 0.53 0.75 1.06 1.40 1.68 2.06 2.37 2.65 2.91 3.14 3.36 3.75 5.31 7.61 10.61
12 38.60 0.55 0.86 1.22 1.73 2.28 2.73 3.34 3.86 4.32 4.73 5.11 5.46 6.10 8.63 12.21 17.26
15 69.98 0.99 1.56 2.21 3.13 4.14 4.95 6.06 7.00 7.82 8.57 9.26 9.90 11.06 15.65 22.13 31.30
18 113.80 1.61 2.54 3.60 5.09 6.73 8.05 9.86 11.38 12.72 13.94 15.05 16.69 17.99 25.45 35.99 50.89
21 171.65 2.43 3.84 5.43 7.68 10.16 12.14 14.87 17.17 19.19 21.02 22.71 24.28 27.14 38.38 54.28 76.77
24 245.08 3.47 5.48 7.75 10.96 14.50 17.33 21.22 24.51 27.40 30.02 32.42 34.66 38.75 54.80 77.50 109.60
27 335.51 4.74 7.50 10.61 15.00 19.85 23.72 29.06 33.55 37.51 41.09 44.38 47.45 53.05 75.0 106.1 160.0
30 444.35 6.28 9.94 14.05 19.87 26.29 31.42 .38.48 44.44 49.68 54.42 58.78 62.84 70.26 99.4 140.5 198.7
36 722.57 10.22 16.16 22.85 32.31 42.75 51.09 62.58 72.26 80.79 88.50 95.59 102.19 114.25 161.6 228.5 323.1
42 1089.9 15.41 24.37 34.47 48.74 64.5 77.1 94.4 109.0 121.9 133.5 144.2 154.1 172.3 243.7 344.7 487.4
48 1556.1 22.01 34.80 49.21 69.59 92.1 110.0 134.8 155.6 174.0 190.6 205.9 220.1 246.0 348.0 492.1 695.9
* Conveyance Factor = (1.486 x R2/3 x A) / n
APPENDIX III
Stuffer Envelope
Drainage and Erosion Control Plan
PAGE 2
Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
L GENERAL LOCATION AND DESCRIPTION:
B. Description of Property: (continued)
4. 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. First Filing ranges from approximately 360' at the creek's
intersection with South Shields Street, to approximately 890' at its furthest distance
from Fossil Creek Estates P.U.D. First Filing.
5. The Scenic Knolls Ditch , traverses the southern boundary of the project. The ditch
line generally defines the southern boundary of Fossil Creek Estates P.U.D. First
Filing. Refer to the Final Drainage and Erosion Control Plan in Appendix III of this
report.
a. All drainage analysis assumes that during larger storm events, the irrigation
ditch over flows its bank.
H. DRAINAGE BASINS AND SUB -BASINS:
A. Major Basin Description:
Fossil Creek Estates P.U.D. First Filing 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.
4. One irrigation ditch lateral, the Scenic Knolls Ditch, is located along the southern
property line of the project as mentioned in Item LBA above. Discussions are
continuing concerning lining of the Scenic Knolls Ditch.
B. Sub -Basin Description:
1. 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.
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Fossil Creek Estates P.U.D . First Filing
Final Drainage and Erosion Control Report
H. DRAINAGE BASINS AND SUB --BASINS:
B. Sub -Basin Description (continued):
2. There is some offsite runoff conveyed through and around the site. Offsite
developed flows have been included in all drainage calculations. Refer to exhibit 'A'
in Appendix I for the offsite contributing areas.
3. The western half of the South Shields R.O.W. will contribute storm water runoff to
Fossil Creek Drive.
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 conform to the requirements of the City of
Fort Collins Erosion Control Reference Manual.
B. Development Criteria Reference and Constraints:
1. Development of this area was considered in the Fossil Creek Drainage Study,
prepared ;by Simons Li 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. First Filing because of its proximity and relationship to the Fossil Creek
Drainageway in accordance with the City of Fort Collins Master Plan and the Fossil
Creek Master Drainageway Planning Study.
3. South Shields Street bounds Fossil Creek Estates P.U.D. First Filing to the east.
Development of Fossil Creek Estates P.U.D. First Filing 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 constraints to the South
Shields Street new Right -of -Way (20' west of the current 30' Right -of -Way; total
50' R.O.W.) and the easternmost lots located adjacent to the South Shields Street
Right -of -Way.
a. 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.
b. Slope easement acquisition from the City of Fort Collins will also be required
due to the existing topography along the north side of Fossil Creek Drive at the
intersection with South Shields Street.
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Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
B. Development Criteria Reference and Constraints: (continued)
5. Wetland area identification and documentation is also a design constraint in the
layout of the street and drainage system and the lot layout. Separate wetland studies
have been prepared in association with the planning of the project.
6. Groundwater considerations and underground conveyance to the Fossil Creek
channel remains a major design issue. A groundwater interceptor and conveyance
system has been designed with this project.
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:
1. 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.
IV DRAINAGE FACLLIW 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. First Filing and west of
South Shields Street, maintaining discharge points at, or near, historic 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. First
Filing.
PAGE 5.
Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
A. General Concept: (continued)
2. There is some offsite contributing runoff to the site (refer to exhibit'A' included in
Appendix I). This offsite contributing area, which includes one half (1/2) of the
South Shields Street R.O.W. and portions of the property to the south and west,
was utilized in calculations for developed peak flows.
3. Ground water will be intercepted in a subdrain system constructed with the storm
and sanitary sewer system. The groundwater will be conveyed in a subdrain to the
proposed storm sewer at the intersection of Fossil Creek Drive and South Shields
Street where it will be conveyed via the storm sewer to Fossil Creek. (Refer to
sheets 4 and 6 of 19 of the Utility Plans).
4. Appendix II contains all tables, charts and figures referenced in the calculations for
storm sewer design, and developed runoff peak flow quantities.
B. Specific Details:
1. The street system will convey the runoff to concentration points in the street
system.
2. Runoff will be conveyed from the street system, to the main channel of Fossil Creek
via a combination storm sewer and open channels. The outlet to Fossil Creek will
be located at the northwest corner of the intersection of Fossil Creek Drive and
South Shields Street. This storm sewer will also convey groundwater intercepted
by the subdrain to Fossil Creek.
3. A ten (10) foot type R inlet is to be constructed at Sta. 53+15.36 (South Shields
Street stationing) in a continuous grade condition on the south side of the median
island near the intersection of Fossil Creek Drive and South Shields Street (refer to
sheet 6 of 19 of the Utility Plans).
a. This inlet will intercept a majority of the storm water runoff from the south side
of Fossil Creek Drive and the ofsite contributing area south of Fossil Creek
Drive.
b. The majority of the storm water that is not intercepted by this inlet will be
intercepted by the 10' type 'R' inlet on the north side of Fossil Creek Drive (see
item 4).
c. Refer to the grading plan (sheet 16 of 19 of the Utility Plans), the plan and
profile for Fossil Creek Drive (sheet 12 of 19 of the Utility Plans), and the
Storm sewer profile (sheet 6 of 19 of the Utility Plans).
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Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
B. Specific Details: (continued)
4. A ten foot (10) type 'R' inlet is to be constructed in a continuous grade condition at
Sta. 52+75.03 (South Shields Street stationing) on the north side of Fossil Creek
Drive (refer to sheet 6 of 19 of the Utility Plans).
a. This inlet will intercept a portion of the storm water runoff from the site.
b. It will also intercept some of the storm water runoff from the western half of
South Shields Street and the off site contributing area to the south.
c. Refer to the grading plan (sheet 16 of 19 of the Utility Plans) , the storm sewer
profile (sheet 6 of 19 of the Utility Plans)., and the plan and profile for Fossil
Creek Drive (sheet 12 of 19 of the Utility Plans).
5.. Forty five (45� lineal feet of 24" RCP Class III will connect the two inlets in Fossil
Creek Drive.
a. The slope of the pipe is 4.44%.
b. The peak 100 year flow to the inlet is 42.54 cfs. Refer to page 4 in the drainage
calculations.
c. The pipe has a capacity of 47.62 cfs based on Mannings equation using a
Mannings 'n' value of 0.013 as suggested by the City of Fort Collins Storm
Drainage Criteria Manual.
6. One hundred and twenty (120') lineal feet of 30" ADS N-12 will convey the storm
water and the runoff from the sub drain to Fossil Creek from the northern inlet.
a. The slope of the pipe is 1.0%.
b. The peak 100 year flow to the inlet is 38..08 cfs. Refer to page 4 in the
drainage calculations.
c. The pipe has a capacity of 44.44 cfs based on Mannings equation using a
Mannings 'n' value of 0.012 as suggested by the Advanced Drainage Systems
Technical Note No. 2.109 (88) dated June 1,1988.
d. Refer to table 4 attached in Appendix H.
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. at
the South Shields Street design low point. 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. First Filing.
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Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
V. EROSION CONTROL:
A. General Concept
Permanent and temporary erosion control measures will be provided with
construction.
a. The temporary measures will include;
L silt fence along downstream property lines.
I hay bale barriers in swales.
iii. Gravel filters at storm sewer inlets.
These measures will effectively reduce the amount of soil erosion potential
created during the construction of the project.
b. The permanent treasures will include rip rap aprons at all storm sewer outfalls,
particularly at Fossil Creek. These will effectively reduce the amount of soil
erosion potential and bank erosion created by storm water runoff from the site.
c. Erosion control device maintenance, both onsite and offsite, will retrain the
responsibility of the developer until the subdivision is completely developed.
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 will be the higher of the following determinations.
* 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.
L The estimated security deposit for the entire 13.03 acres would be $0,772.50
(13.03 X 500.00 X 1.5). Reseeding cost estimates have been provided by
the City's Storm Water Utility and are based on recent experience.
* The cost to provide the actual erosion control device improvements noted on the
Drainage and Erosion Control Plan. Refer to sheet 17 of 19 of the Utility Plans.
PAGE 8
Fossil Creek Estates P.U.D. First Filing
Final Drainage and Erosion Control Report
VI. CONCLUSIONS:
A. Compliance with Standards
1. All drainage analysis has been performed in accordance with 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 and generally accepted practices.
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. First Filing 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.
3. There are major irrigation facilities that will be affected by the development of
Fossil Creek Estates P.U.D. First Filing. An irrigation ditch noted along the south
boundary (the Scenic Knolls Ditch) is considered as a major design factor with the
design of Fossil Creek Estates P.U.D. First Filing. Easements and possible ditch
improvements are being discussed with users of the ditch. This however, has no
immediate affect on drainage, erosion control or wetlands considerations.
VII REFERENCES:
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