HomeMy WebLinkAboutCOURTYARDS AT MIRAMONT PUD - PRELIMINARY - 54-87N - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPreliminary Drainage and Erosion Control Report
for
COURTYARDS AT MMAMONT P.U.D.
Fort Collins, Colorado
Prepared for
ALBRECHT HOMIES
4836 South College Avenue Suite 10
Fort Collins, Colorado 80525
Prepared by:
SHEAR ENGINEERING CORPORATION
Project No: 1410-01-94
® DATE.: March, 1994
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
I hereby state that this Preliminary Report for the Drainage and Erosion Control design of
"Courtyards at Arramont P.U.ID.", was prepared under my direct supervision in accordance
with the provisions of the City of Fort Collins Storm Drainage Criteria Manual for the owners
thereof.
Brian W. Shear, P.E.
Registered Professional Engineer
State of Colorado No: 20262
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PAGE 1
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
INTRODUCTION:
Courtyards at Miramont P.U.D. is one of three (3) projects currently being considered
for development in what is- known as Parcel Q of the Oak/Cottonwood Farm
Amended Development Plan prepared by Cityscape Urban Design, Inc. with a last
date of revision being July 10, 1992. The other two (2) proposed projects are Oak Hills
Apartments P.U.D. and Mimmont Tennis Center, both of which have been submitted to
the City of Fort. Collins as Preliminary submittals.
We have coordinated the storm drainage design of the Courtyards at Miramont P.U.D.
with the other two (2) projects in order to produce a safe and aesthetically pleasing
neighborhood. Coordination of the drainage design is especially important as the
Courtyards at Miramont P.U.D. is the primary location for storm water management
facilities for the three projects.
The Oak/Cottonwood Farm O.D.P. Drainage Study is the primary reference for the
storm water management design for Courtyards at Mi wnont P.U.D. The City of Fort
Collins has required that this study be re-evaluated to include the three (3) projects
mentioned above. At the time of this preliminary submittal, the Amended
Oak/Cottonwood Farms O.D.P. Drainage Study had not been completed.
L GENERAL LOCATION AND DESCRIPTION:
A. Location
1. Courtyards at Miramont P.U.D. is generally located in the Northeast 1/4 of Section
1, Township 6 North, Range 69 West of the 6th P.M., City of Fort Collins, County
of Larimer, State of Colorado.
2. More specifically, Courtyards at Miramont P.U.D. is located. on the East side of
Boardwalk Drive approximately three quarters of a mile South of Harmony Road.
It is east of the Upper Meadow at Miramont and west of the Collinwood assisted
living facility.
3. Courtyards at Miramont P.U.D. is bounded on the West by Boardwalk Drive, on the
north by vacant land.
a. The property to the North, which also borders on Boardwalk Drive has been
submitted for preliminary review as Oak Hill Apartments P.U.D.
b. The other property to the North, which is located at the western terminus of
Rule Drive, has been submitted for preliminary review as Miramont Tennis
Center.
To the South is vacant land which is currently being considered for use as park land
by the City of Fort Collins Parks and Recreation Department.
PAGE 2
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
I. GENERAL. LOCATION AND DESCRIPTION:
B. Description of Property
1. The 12.86 acre site is currently vacant land covered with native vegetation
2. There is an existing irrigation / detention pond located within the limits of the 12.86
acre site.
a. The pond is designated as pond 313 of the Miramont Overall Drainage Plan.
b. The pond will be defined within a tract which will be platted with the Courtyards
at Miramont project, however will remain under separate ownership.
c. The pond tract has an area of approximately 1.97 acres.
d. This pond was built based on the original Oak/Cottonwood Farms Overall
Drainage Study and in association with the Upper Meadow at Miramont,
Second Filing.
e. Pond volume and water surface elevation data was provided on the Utility Plan
titled "Detention Pond and Erosion Control Plan" for Upper Meadow at
Miramont P.U.D., Second Filing, prepared by RBD, Inc., dated June 7, 1993,
RBD Project No. 504-003. We understand that this data may change with the
required amendment to the Oak/Cottonwood Farm Overall Drainage Study.
3. 46 single family homes are proposed within the limits of Phases I - V, along with
the necessary infrastructure to serve them. Phase VI and Phase VII are planned for
single family homes as well, but at a future date and with a slightly different
concept..
M DRAINAGE BASINS AND SUB -BASINS:
A. Major Basin Description
1. Courtyards at Miramont P.U.D. is located in the McClellands Mail Creek Basin as
delineated on the City of Fort Collins Storm Water Basin Map.
a., The Basin fee rate for this basin is $ 3,717.00 per gross acre according to the
development fee section of the City of Fort Collins Development Manual.
b. Our understanding is that the above mentioned fees may be reduced with the
provision for detention. The amount of impervious area created by the
development may also affect these fees. (Please refer to 01/24/94 conceptual
review comments).
® PAGE 3
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
LI
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II. DRAINAGE BASINS AND SUB -BASINS:
B. Sub -Basin Description
1. Courtyards at Miramont P.U.D. is contained within Basin 208 of the
Oak/Cottonwood Farm Overall Drainage Plan.
2. Storm water from the north flows to the existing irrigation / detention pond.
Design of the Courtyards at Miramont must facilitate the routing of storm water
from the Tennis Center and the Oak Hill Apartment sites according to the
requirements of the Oak/Cottonwood Farm Overall Drainage Plan.
3. Our understanding from the review of the drainage reports available, is that
allowable storm water release rates are very strictly controlled in this area. The
Preliminary Drainage and Erosion Control Study for the Oak Hill Apartments
P.U.D. indicates that maximum allowable release rates for this area are 0.20
cfs/acre for the 10-year storm and 0.50 cfs/acre for the 100-year storm.
M DRAINAGE DESIGN CRITERIA:
A. Regulations
1. Design Criteria from the City of Fort Collins Drainage Criteria Manual were
utilized in the design and preparation of the preliminary Drainage and Erosion
Control Plan.
B. Development Criteria Reference and Constraints
1. The following drainage reports were considered in the drainage design and
calculations for Courtyards at Miramont P.U.D.
a. Oak Cottonwood Farms O.D.P. Drainage Study, prepared by RBD, Inc.; dated
May 4, 1992; RBD Project No 504-001.
b. Preliminary Drainage Report for Oak Hill Apartments P.U.D.; prepared by
RBD, Inc.; dated February 7, 1994; RBD Project No: 088-010.
c.. Preliminary Drainage Plan for Miramont Tennis Center; Water, Waste and
Land; dated November 1993; WWL Project No: 402.
2. Historically, this site drains from north to southeast under Lemay Avenue and
through Oakridge Development on the East side of Lemay Avenue. The
Preliminary Drainage and Erosion Control Study for the Oak Hill Apartments
P.U.D. indicates that downstream improvements have been completed within the
Oakridge Development to accept a maximum storm water runoff of 1.19 cfs from
the entire Oak/Cottonwood Farm development.
® PAGE 4
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
III DRAINAGE DESIGN CRITERIA:
B. Development Criteria Reference and Constraints (continued)
3. RBD, Inc. is currently re-evaluating the Oak/Cottonwood Farms O.D.P. Drainage
Study to take into account the development of the Courtyards at Miramont P.U.D.,
the Miramont Tennis Center and Oak Hill Apartments.
4. The preliminary drainage design for Oak Hill Apartments P.U.D. has a 22' wide
(minimum) drainage channel located at the southwest corner of the Oak Hill site
which conveys storm water to the existing irrigation/detention pond which is
located adjacent to the limits of the Courtyards at Miramont P.U.D. site.
a. This storm water will need to be conveyed under the entry private drive to the
Courtyards at Miramont P.U.D. site.
5. The property to the east, Collinwood, is developed and limits the amount of
grading that can be done along the East property line.
C. Hydrological Criteria
® 1. The Rainfall -Intensity -Duration curves for the City of Fort Collins were used
(Figure 3.3.1-1, attached in Appendix I for reference), in conjunction with the
"Rational Method" for determining peak flows at various concentration points.
2. Detention storage volume requirements will be based on the Cumulative Runoff
Method in accordance with The City of Fort Collins Criteria.
a. Release rates are to be based on the Amended Oak/Cottonwood Farms O.D.P.
Drainage Study or by the original Oak/Cottonwood Farm O.D.P. Drainage
Study. This is dependent on the timing of the final submittal for Courtyards at
Miramont P.U.D. and the completion of the Amended Oak/Cottonwood Farm
O.D.P. Drainage Study
3. The .2 and .100 year storms were utilized in the design of the storm water
management infrastructure in accordance with City of Fort Collins Drainage
Criteria Manual. In addition, the 10 year storm was studied in association with the
Oak/Cottonwood Farm O.D.P. Drainage Study restriction of 0.20 cfs per acre for a
10 year storm.
D. Hydraulic Criteria
1. Street capacity references provided in the City of Fort Collins Drainage Criteria
Manual and street capacity exhibits which were prepared by this office, based on
the Mannings equation, were utilized.
® 2. Storm sewer and drainage channel capacities are based on the Mannings Equation.
The Mannings coefficients are as suggested by City of Fort Collins Drainage
Criteria Manual.
® PAGE 5
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
IV DRAINAGE FACILITY DESIGN:
A. General Concept
1. Storm water will be conveyed to the imgation/detention pond via a combination of:
a. Flow in grassed swale(s).
b. Flow in gutter.
c. Flow in pipe.
2. The irrigation/detention pond will outfall to the south onto property that is currently
being planned for use as a park by the City .of Fort Collins Parks and Recreation
Department. The actual outfall will not be designed, or constructed with the
Courtyards at Miramont project.
a. It is our understanding that negotiations are currently in progress by the City of
Fort Collins to purchase the land to the south and develop it into a neighborhood
park.
b. The outfall may consist of storm sewer pipe which will convey the storm water
to detention pond 340 at the northwest corner of Lemay Avenue and Boardwalk.
® Drive (refer to the original Oak/Cottonwood Farms O.D.P. Drainage Study and
Plan).
c. The final pond outfall design will be provided with the Amended
Oak/Cottonwood Farms O.D.P. Drainage Study.
B. Specific Details:
1. Specific details will be provided with the submittal of the Final Drainage and
Erosion Control Report and Plan for Courtyards at Miramont P.U.D.
2. A 10' type R inlet will be required at the intersection of the private Drive for the
Courtyards at Miramont project with Boardwalk Drive. An 18" ADS storm sewer
would be required to convey the peak flows adjacent to Boardwalk Drive to the
detention f irrigation pond.
3. A 42" storm sewer has been considered adjacent to Boardwalk Drive to facilitate
the drainage design requirements for the Oak Hill Apartments P.U.D.
a. The 42" storm sewer will be constructed with the following understandings:
* The cost of the 42" storm sewer, from the 10' type R inlet, to the northern
boundary of the Courtyards at Miramont P.U.D., will be the responsibility of
the developer of the Oak Hill Apartments property.
® PAGE 6
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
* The difference in cost of a 42" RCP storm sewer from an 18" ADS storm
sewer for the length of storm sewer between 10' type R inlet to the pond,
will be the responsibility of the developer of the Oak Hill Apartments
property.
* The difference in cost of a 60" diameter storm sewer manhole from a 48"
diameter storm sewer manhole, will be the responsibility of the developer of
the Oak Hill Apartments property.
4. Maintenance of the detention/irrigation pond will be the responsibility of the owner
of the tract which the pond is contained.
5. Maintenance of the open space areas within the limits of the Courtyards at
Miramont, will be the responsibility of the developer until completion of the
project. A Homeowners Association would then assume maintenance
responsibilities for the open areas.
6. Boardwalk Drive to the west of Courtyards at Miramont is fully constructed to .
collector standards (except the eastern detached sidewalk).
a. The Preliminary Drainage and Erosion Control Study for the Oak Hill
Apartments P.U.D. indicates that developed runoff from Boardwalk Drive will
be conveyed southerly to an existing curb inlet across from Highcastle Drive.
The inlet will intercept the stormwater and redirect it into an open channel
parallel to Boardwalk Drive and thence to Detention Pond 340, located at the
Northwesterly corner of Lemay Avenue and Boardwalk Drive. The inlets, open
channel and pond 340 have already been constructed, and have accounted for
the portion of Boardwalk adjacent to Courtyards at Miramont P.U.D.
7. The Oak Hill Apartments, Courtyards at Miramont and the Tennis Center at
Miramont will contribute storm water to the existing irrigation/detention pond
located adjacent to the Courtyards at Miramont P.U.D. (referred to as pond 313 on
the Oak/Cottonwood Farms O.D.P. Drainage Plan).
a. Possible volume reconsiderations for the existing irrigation/detention pond
(Pond 313) may be made in the Amended Oak/Cottonwood Farms O.D.P.
Drainage Study being prepared by RBD, Inc. Should additional volume
requirements be determined, expansion of the existing pond would
tremendously effect the current design of the Courtyards at Milramont. P.U.D. as
represented. Downstream, and/or upstream detention volume alternatives are
available.
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PAGE 7
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details- (continued)
b. The existing irrigation/detention pond was constructed in 1993. The plans for
the pond indicate that the pond would first be constructed as an interim pond
which would be an irrigationlretention pored. The ultimate pond would act as
an irrigation/detention pond.
L The interim pond is proposed to have 6.7 ac.-ft of irrigation volume.
I The ultimate pond is proposed to have 2:7 ac.-ft. of irrigation volume.
Ili. The ultimate pond is proposed to have 4.0 ac: ft. of detention volume.
c. Should the existing irrigation / detention pond lack the storage volume to handle
the storm water created by the development of the three (3) project contributing
to the pond, several alternatives will be evaluated to provide additional storage,
including but not limited to:
i. An additional detention pond located on the proposed park property to the
South.
I An additional detention pond located at the southwest corner of Oak Hill
Apartments.
8. Release rates and final storage volumes will be based on the Amended
Oak/Cottonwood Farms O.D.P. Drainage Study which is currently being prepared.
by RBD, Inc.
a. Release rates and required storage volumes will be calculated by Shear
Engineering at final if the Amended Oak/Cottonwood Farms O.D.P. Drainage
Study is not completed at the time of final submittal for the Courtyards at
Miramont P.U.D. If the Amended Oak/Cottonwood Farms O.D.P. Drainage
Study is not completed, the release rate will be based on the Original
Oak/Cottonwood Farms O.D.P. Drainage Study or as recommended by the City
of Fort Collins Storm Drainage Utility.
9. The detention pond will also act as an irrigation facility for the site, the green space
on the West side of Boardwalk Drive, and the future park land to the south. A
pump house and necessary infrastructure will be constructed to distribute the
irrigation water as needed. Construction of the pump has will not be associated
with Courtyards at Miramont.
PAGE 8
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
V. EROSION CONTROL:
A. General Concept:
1. Courtyards At Miramont lies within the Moderate Wind Erodibility Zone per the
City of Fort Collins Zone Map.
a. Per the City of Fort Collins Erosion Control Reference Manual for Construction
sites, the Erosion control performance standard will need to be calculated and
appropriate measures taken to control erosion during and after construction at
the time of Final design..
2. Erosion control measures are specified on the Drainage and Erosion Control Plan
attached in Appendix I L These measures will effectively reduce the amount of soil
erosion potential created during the construction of the project.
a. Maintenance of erosion control devices, both onsite and offshe, will remain the
responsibility of the developer until the subdivision is totally developed.
3. An Erosion control security deposit will be required according to current City of
P Fort Collins policy as presented in the City of Fort Collins Development Manual.
a. The security deposit is based on one and one-half times the estimated cost to
reseed the actual affected property area during overlot grading activity.
Currently, security deposit estimates are based on $500.00 per acre to reseed
sites that are 10 or more acres. Reseeding cost estimates have been provided by
the City's Storm Water Utility and are based on recent experience.
i. The estimated security deposit for the entire 10.89 acre Courtyards at
Miramont P.U.D. site would be $8,167.50 (10.89 acres x 1.5 x
$500.00/acre).
i. The security deposit is reimbursed upon completion of erosion control
measures or completion of the project.
B. Specific Details
1: Temporary erosion control devices will consist of silt fence along the downstream
property lines, hay bale dikes in all swales, and gravel filters at all inlets.
Permanent erosion control devices will consist of Rip rap aprons at all storm sewer
outfalls. Erosion control devices are shown on the Preliminary Drainage and
Erosion Control Plan attached in Appendix IIL
PAGE 9
Courtyards at Miramont P.U.D.
Preliminary Drainage Report
VI. CONCLUSIONS:
A. Compliance with Standards:
1, All drainage design and calculations conform with the criteria and requirements of
the City of Fort Collins Storm Drainage Criteria.
2. Proposed erosion control measures conform with generally accepted erosion control
measures and the City of Fort Collins Erosion Control reference manual.
B. Drainage Concept:
1. The design of the drainage infrastructure effectively controls any increase in storm
water runoff due to the development of Courtyards at Miramont P.U.D.
2. The erosion control _measures specified will effectively reduce erosion potential
during construction.
VIL REFERENCES:
1. City of Fort Collins Storm Drainage Design Criteria Manual
2. Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual.
3. City of Fort Collins Erosion Control Reference Manual; prepared by
Hydrodynamics, Inc.; dated January 1991.
4. Oak/Cottonwood Farm O.D.P. Drainage Study; RBD, Inc„ dated May 4, 1992;
RBD Project No: 504-001
5. Preliminary Drainage Report for Oak Hill Apartments P.U.D.; RBD, Inc.; dated
February 7, 1994; RBD Project No: 088-010.
6. Preliminary Drainage Plan for Miramont Tennis Center, Water, Waste and Land;
dated November 1993, WWL Project No: 402.
7. "Detention Pond and Erosion Control Plan" for Upper Meadow at Miramont
P.UD., Second Filing (Sheet 1 of 1) prepared by RBD, Inc. dated June 7, 1993,
Project No. 504-003
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APPENDIX I
0 Storm Drainage Calculations
n
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SHEAR ENGINEERING CORPORATION
SUB BASIN Ic BREAKDOWN
PAGE 1
PROJECT
:COURTYARDS AT MIRAMONT
PROJ.NO.
:1410-01-94
DATE= 03/07/94
LOCATION :FORT COLLINS
SY: MEO
FILE
:MIRAMONT
NOTES
:PRELIMINARY
RUNOFF
SURFACE
CORP.
CHARACTERISTICS
AREA
C
C*A
(acres)
STREETS
ASPHALT
0.230
0.950
0.219
CONCRETE
0.110
0.950
0.105
GRAVEL
0.000
0.500
0.000
ROOFS
0.350
0.950
0.333
LAWNS SANDY SOIL
FLAT < 2%
0.000
0.100
0.000
AVERAGE 2 - 7%
0.000
0.150
0.000
STEEP > 71
0.000
0.200
0.000
LAWNS HEAVY SOIL
FLAT < 21
0.670
0.200
0.134
AVERAGE 2 - 7%
0.000
0.250
0.000
STEEP > 7%
0.000
0.350
0.000
TOTAL AREA
1.360
0.790
C2
C5
C10
C100
COMPOSITE C VALUE 0.581
0.581
0.581
0.726
USE
0.58
0.58
0.5.8
0.73
Ll
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SHEAR ENGINEERING CORPORATION
PAGE 2 DEVELOPED FLOW TO 'C'
PROJECT: COURTYARDS AT MIRAMONT
FILE: MIRAMONT
AREA (A)- 1.36 ACRES SUB BASIN Ic
RUNOFF CORP. (C)
2 YEAR 10 YEAR 100 YEAR
C - 0.58 0.5E 0.73
SEE SPREAD SHEET ATTACHED ON PAGE 1
DATE 03/07/94
PROJ. NO.1410-01-94
BY MEO
TIME OF CONCENTRATION (Tc) FORT COLLINS FORMULA
OVERLAND TRAVEL TIME (Ti)(1.87(1.1-CCf)+(L)"0.5)/(S)"0.33 NOT APPLICABLE
LENGTH a 0
FEET SLOPE a 1.00
%
FLOW IN GRASS SWALE INITIALLY
2 YEAR
10 YEAR
100 YEAR
C o 0.20
0.20
0.25
Ti (min)- 0.00
0.00
0.00
TRAVEL TIME (Tt)
-L/(60+V) FLOW TYPE
L (ft) - 150
S (t) - 1.00 GRASSED SWALE
V (fps) -
1.60 Tt(min)-
1.56
L (ft) - 150
S (t) - 0.60 GUTTER
V (fps) a
1.60 Tt(min)-
1.56
L (ft) - 155
S (t) - 2.00 GUTTER
V (fps) -
2.80 Tt(min)m
0.92
L (ft) -
S (t) -
V (fps) -
Tt(min)-
0.00
L (ft) -
S (t) -
V (fps) -
Tt(min)-
0400
L (ft) -
S (t) -
V (fps) -
Tt(min)-
0.00
L (ft) -
S (t) -
V (fps) -
Tt(min)-
0.00
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL TRAVEL
TIME (min) -
3.13
Tc -Ti+TOTAL TRAVEL TIME
2 YEAR
10 YEAR
100 YEAR
Tc (min)- 3.13
3.13
3.13
USE Tc - 5.00
5.00
5.00
INTENSITY (I) (iph)
2 YEAR
10 YEAR
100 YEAR
I - 3.29
S.b4
8.70
NOTE: INTENSITIES TAKEN FROM FIGURE
3-1
RUNOFF (Q- CIA) (cfe)
2 YEAR
10 YEAR
100 YEAR
Q - 2.60
4.45
8.64
CONCLUDE: INSTALL
5 TYPE IRI INLET
NOTE:
5 FOOT OPENING WITH 10 FOOT BOX AS PIPH IS OFFSET
INSTALL
135 IF OF 42
- RCP @
0.6 t
n a
0.013 Qcsp a 77.92
CFS
NOTEs
PIPE IS OVERSIZED FOR DEVELOPED FLOWS FROM UPSTREAM PROJECT
11
11
APPENDIX II
Backup Diagrams and Exhibits
is Fort Collins Storm Water Basin Map
Table 3-3; Rational Method Runoff Coefficients for Composite Analysis
Table 3=4; Rational Method Frequency Adjustment Factors
Figure 3-2; Estimate of Average Flow Velocity for Use with the Rational Formula
Figure 3-1; City of Ft. Collins Rainfall Intensity Duration Curve
Table 5-4; Inlet Capacity Reduction Factors
Table 5-4; Standard Curb -Opening Inlet
Figure 5-5; Standard Curb -Opening Inlet Chart
Figure 5-6; Increase in Interception of Compound Street
Table 3; Full Flow Coefficient Values Circular Concrete Pipe
Table 4; Circular Pipe Flow Capacity
11
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R-M-P
Medium Density Planned Residential District — designation for medium density
(PUD) to a variation in use and building placements
areas planned as a unit provide
with a minimum lot area of 6,000 square feet.
R-L-M
®
Low Density Multiple Family District = areas containing low density multiple family
or in the R-L District with a minimum lot area of 6,000 square feet
units any other use
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,
uses, with minimum lot areas equal to 1/2 of the total
including a variety of permitted
floor area of the building.
B-P
Planned Business District — designates areas planned as unit developments to
the surrounding residential areas with
provide business services while protecting
minumum lot areas the same as R-M.
H-6
Highway Business District — designates an area of automobile -orientated busi-
to 112 of the total floor area of the building.
nesses with. a minimum lot area equal
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
the total floor area of the building not to be less than
area of lot equal to two times
20,000 square feet.
I-P
Industrial Park District —designates light industrial park areas containing controlled
lot areas equal to two times the total floor area of the
®
industrial uses with minimum
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 11.8.
Table 3-3
RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE ANALYSIS
Character of Surface Runoff Coefficient
Streets, Parking Lots, Drives: 0.95
Asphalt .... ....
Concrete........................................................... ..... 0.50
Gravel................................................................................ 0:50
0.95
Roofs.:.........
.................
Lawns, Sandy Soil:
0.10
Flat <2% . _
........
,.......
0.15
Average2 to 7%.................................:...........
..........
0:20
Steep>7% ..•.................. ........ ..............................
.........,......
Lawns, Heavy Soil:
0:20
Flat<2% ........................................ ..
•. ,,,•,,,
0;25
Average2 to 7% .................. ...............................
................
0.35
Steep>7%.............................
.....:...
MAY 1984 3-4 DESIGN CRITERIA
® 0
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 —CC D112
S-
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 FACTOF
Storm Retum Period Frequency Factor
(years) C,
2 to 10 1.00
11 to 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
Cr = 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 CRITERO MANUAL
RUNOFF
prk
30
i— 20
z
ILI
0
cc
ILI
0. 10
z
Iu
a
0 5
N
ILI
cc 3
U
� 2
LiJ
Q
3
1
_®ttmilli
®Mttt1111/ems//
311111/�
ttt
FAN
►%Mill
.• I e®■ I
r
e %
�ttm'
ItMISNOMER
®tt
ttt���
s
AMWANNI/MYAMW
® a
������■®
IMin
FAWWAMMOMMMENE
NN
.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
No Text
E
11
FORT COLLINS
RAINFALL INTENSITY CURVE DATA FOR CITY OF FORT COLLINS
FIG 3-1
NOVEKBBR 1975
INTERPRETED DECEMBER 21, 1992 BY MARK OBERSCEMIDT
SHEAR ENGINEERING CORPORATION
DO NOT INTERPRET BEYOND RON 40
2
5.
30
25
50
100
TIME YEAR.
ittiitfffOf
YEAR YEAR YEAR YEAR YEAR
i if tftOf 4itifffff
5
if
3.29
4.70
iiiidfftitiiiftiiiiii4t4f
5.64
7.02
tiiiitti
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
140
1.76
2.19
2.67
3.09
3.60
45
1.12
1.62
2.02
2.46
2.84
3.28
50
1.04
1.51
1.67
2.27
2.65
3.02
55
0.97
1.40
1.73
2.12
2.46
2.80
60
0.90
1.32
2.62
2.99
2.32
2.60
65
0.68
1.24
1.52
1.84
2.18
2.43
70
75
0.82
0.79
1.18
1.11
1.44
1.38
1.72
1.62
2.05
1.93
2.30
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
1.07
95
0.64
0.91
1.33
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
2.46
1.63
110
0.57
0.00
1.00
1.18
1.40
2.57
115
0.54
0.76
0.96
1.14
1.33
1.50
120
0.52
0.76
0.91
1.10
1.19
1.44
•5.3.5 Grates for Pipes
Where a clear and present danger exists such as a siphon, a drop in elevation adjacent to a
sidewalk or road, a long pipe with one or more manholes, or at pipes which are near play
grounds, parks, and residential areas, a grate may be required. For most culverts through
embankments and crossing streets, grates will not be required.
When called for on the plans, grates shall meet the following requirements:
a. Grating shall be constructed of steel bars with a minimum diameter of 5/8". Reinforcing
bars shall not be used.
b. Welded connections shall be 1/4" minimum.
c. Spacing between bars shall normally be 6" unless site conditions are prohibitive.
d. All exposed steel shall be galvanized in accordance with AASHTO M 111.
e. Welded joints shall be galvanized with a rust preventive paint,
f. Grates shall be secured to the headwall or end section by removable devices such as
bolts or hinges to allow maintenance access, prevent vandalism, and prohibit entrance by
children.
'5.4 Inlets
Storm inlets shall be installed where sump (low -spot) conditions exist or street runoff -carrying
capacities are exceeded.
12 & 13
The curb inlets shown in the Standard Details, pages D-7, 8 , shall be used in all City Streets.
If larger inlets are required, the Colorado Department of Highways Type R Curb Inlet, Standard M-604-
12, shall be used. For drainageways other than streets (for example, parking lots, medians, sump
basins) an Area Inlet similar to the detail on page D-9 shall be used.
The outlet pipe of the storm inlet shall be sized on the basis of the theoretical capacity of the inlet, with
a minimum diameter of 15 inches, or 12 inches if elliptical or arch pipe is used.
All curb openings shall be installed with the opening at least 2 inches below the f low.line elevation. The
minimum transition length shall be 3'6" as shown on the standard details previously listed.
Because of debris plugging, pavement overlaying, parked vehicles, and other factors which decrease
inlet capacity, the reduction factors listed in Table 5-4 shall be utilized.
Table 5-4
fINLEETrPACITY REDUCTI
ONON FACTORS
Percentage of
Drainage Condition Inlet Type Theoretical Capacity
Sump or Continuous Grade ........ .............................. CDOH Type R-Curb
Opening
5' 800/0
10, 85%
15, 90%
Street —Sump 4' Curb Opening 80%
.............................................
Street —Continuous Grade ..•. 4' Curb Opening 80%
Parking Lots, Medians ....................................•••• Area Inlet 80%
The theoretical capacity of inlets in a low point or sump shall be determined from Figures 5-2 and 5-3.
The theoretical capacity of curb openings on a continuous grade shall be determined from Figures�5-4.
5-5 an 5-5—
The standard curb -opening is illustrated by Figure 54 and is defined as having a gutter depression
apron W feet wide at the inlet opening which extends W feet upstream and downstream from the open-
ing, has a depression depth (a) equal to W/12 feet at the curb face, and a curb opening height (h) of at
least 0.5 feet. The graph as presented by Figure 5-5 is based on a depression apron width (W) equal to
2 feet and depression width (a) equal to 2 inches. The pavement cross-section is straight to the curb
MAY 1984 5-8 DESIGN CRITERIA
0
r.
SX .(Cross Slope)
STREET
-S Longitudinal Slope)
4
SIDE
B
A
1
°o
0
(Gutter Flow)
sm
(-
CARRYOVER
Froude No. at This
Point _ „ w
0 — 01 Izz` — — — —rng
W
01B
(Intercepted
A�
P LAN-
riginal Gutter
LineT55
Sx
wrO
3IN
Gutter Depression at Inlet
P
SECTION A -A
�m
oa
a G
N
J
SECTION - SECTION B_
-B
( Straight Cross Slope) ( Fort, Collins Stondord a Vertical C&G)
NOTE: THE FORT COLLINS STANDARDS HAVE
GUTTERS WITH CROSS SLOPES STEEPER THAN SX.
FIGURE 5-4-
STANDARD CURB -OPENING INLETL
MAY 1984
5-12
DESIGN CRITERIA
No Text
No Text
I
r:
i
I
TA
t
90
CONCRETE PIPE DESIGN MANUAL
TA13LE 3: FULL FLOW COEFFICIENT VALUES
CIRCULAR CONCRETE PIPE
D
A
R
Value ofC,=1.486xAx0'
Pipe
Area
Hydraulic
n
n=0.010
n=0.011
n=0.012
n=A.013
Diameter
(inches)
(Square
Feet)
Radius
(Feet)
8
0.349
0.167
15.8
14.3
13.1
12.1
10
0.545
0.208
2.8.4
25.8
23.6
21.8
12
0.785
0.250
46A
42.1
38.6
35.7
15
1.227
0.312
84.1
76.5
70.1
64.7
18
1.767
0.375
137
124
114
105
21
2.405
0.437
206
187
172
158
24
3.142
0.500
294
267
245
226
27
3.976
0.562
402
366
335
310
30
4.909
0.625
533
485
444
410
33
5.940
0.688
686
624
574
530
36
7.069
0750
867
788
722
666
9.621
0.875
1308
1189
1090
6
q16
48
12.566
1.000
1867
1698
1556
54
15.904
1.125
2657
2325
2131
1967
60
19.635
1.250
3385
3017
2821
2604
66
23.758
1.375
4364
3967
3636
3357
72
28.274
1.500
5504
5004
4587
4234
78
33.183
1.625
6815
6195
5679
5242
84
38.485
IJ50
8304
7549
6920
6388
90
44.170
1.875
9985
1078
83,21
7681
96
50.266
2.000
11850
10780
9878
9119
102
.56.745
2.125
13940
12670
11620
10720
108
63.617
2250
16230
14760
13530
12490
114
70.882
2.375
18750
17040
15620
14420
120
78.540
2.500
21500
19540
17920
16540
126
86.590
2.625
24480
22260
20400
18830
132
95.033
2.750
27720
25200
23100
21330
138
103.870
2..875
31210
28.370
26010
24010
144
113.100
3.000
34960
31780
29130
26890
TABLE 4
CIRCULAR PIPE FLAW CAPACITY
Full Flow (cubic feet per second)
mwmi,ngs "n"= 0.012
Dia. *Cony. %'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
O.� o
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 0.30 043
4 2.062 0.029 0.046 0:065 0.092 0.122 0.1460.179 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 1.73 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 7.51 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
.8 1.61 2.54 3.60 5.09 6.73 8.05 9.86 11.38 12.72 13.94 15.05 16.09 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 10. 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
F]j
E
APPENDIX III
Stuffer Envelope
Preliminary Drainage and Erosion Control Plan
Detention and Erosion Control Plan for Upper Meadow at Miramont
P.U.D. Second Filing Sheet 1 of 1, prepared by RBD, Inc., dated June 7,
1993
0