HomeMy WebLinkAboutDrainage Reports - 12/07/1994'3
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Final Drainage and Erosion Control Report
for
COURTYARDS AT MIRAMONT P.U.D., SECOND FILING
Fort Collins, Colorado
Prepared for:'
ALBRECHT HOMES
4836 South College Avenue Suite 1(
Fort Collins, Colorado 80525
Prepared by:
SHEAR ENGINEERING CORPORATION
Project No: 1410-01-94
DATE: October, 1994
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
PAGE 1
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
The Courtyards at Miramont P.U.D., Second Filing is contained within an area considered
with the Amended Oak/Cottonwood Farm Overall Drainage Study. More specifically, this
is the area which contributes storm water runoff to Detention Pond #313 as defined in the
Amended Oak/Cottonwood Farm Overall Drainage Study. Although this report has been
specifically prepared for the Courtyards at Miramont P.U.D., Second Filing, several known
proposed projects, adjacent to this one, are considered with this report because of the direct
relationship to the projects, all of which contribute to detention pond #313 which will be
detailed with final design parameters in this report. The projects considereddand referenced
in this report include:
* Oak Hill Apartments P.U.D.
* Miramont Fitness and Tennis Center
* The Cottages at Miramont P.U.D.
* The Courtyards at Miramont P.U.D., First Filing
The Oak Hill Apartments P.U.D. Final Drainage and Erosion Control Report is being
prepared simultaneously with this proposal by RBD Inc., Consulting Engineers. Final
conclusions which relate to the Oak Hill Apartments P.U.D. have been closely coordinated
with RBD, Inc. and included in this report. Reference to conclusions presented with the
Final Drainage and Erosion Control Report for the Oak Hill Apartments P.U.D. will be
clearly identified in this report when referenced.
The Final Drainage and Erosion Control Report for Miramont Fitness and Tennis Center
was submitted on September, 1994 and is currently being reviewed by the City of Fort
Collins Storm Water Utility. The report has been prepared by Water, Waste & Land, Inc.
Final conclusions which relate to the Miramont Fitness and Tennis Center have been
closely coordinated with Water, Waste & Land, Inc. and included in this report. Reference
to conclusions presented with the Final Drainage and Erosion Control Report for Miramont
Fitness and Tennis Center will be clearly identified in this report when referenced.
The Cottages at Miramont P.U.D. has been submitted to the City of Fort Collins as a
Preliminary submittal only. Final conclusions which relate to the Cottages at Miramont
P.U.D. are based primarily on preliminary data and assumptions.
The Amended Oak/Cottonwood Farm Overall Drainage Study is being prepared by RBD
Inc., Consulting Engineers simultaneously with this proposal. The Amended
Oak/Cottonwood Farm Overall Drainage Study is the primary reference for the storm water
management design for Courtyards at Miramont P.U.D., Second Filing. Reference to
conclusions presented with the Amended Oak/Cottonwood Farm Overall Drainage Study
will be clearly identified in this report when referenced.
PAGE 2
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
L GENERAL LOCATION AND DESCRIPTION:
A. Location
Courtyards at Miramont P.U.D., Second Filing is generally located in the East One
Half (1/2) 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., Second Filing is located on the
east side of Boardwalk Drive, approximately three quarters (3/4) of a mile South of
Harmony Road. The project is east of the Upper Meadow at Miramont and west of
the Collinwood assisted living facility (Oakridge West P.U.D. First Filing).
3. Courtyards at Miramont P.U.D., Second Filing is bounded on the west by
Boardwalk Drive, and on the north and south by currently unplatted properties.
Refer to the Preliminary Drainage and Erosion Control Plan in the stuffier envelope
of this report for location of the following described properties.
a. The property to the North, which also borders on Boardwalk Drive has been
submitted for final review to the City of Fort Collins as Oak Hill Apartments
P.U.D.
b. Directly northeast of the site, is unplatted property which has been submitted to
the City of Fort Collins as a preliminary proposal known as the Cottages at
Miramont P.U.D.
c. North of the Cottages at Miramont P.U.D. property, is unplatted property which
has been submitted to the City of Fort Collins as a final proposal known as
Miramont Fitness and Tennis Center.
d. To the South is unplatted, vacant property which is not currently being
considered for development. This area is identified on the Miramont Amended
Overall Development Plan (O.D.P.) for possible use as a park or as multi -family
development. The City of Fort Collins appears to be purchasing the property
for use a park. Preliminary park layouts have been prepared.
B. Description of Property
1. The 10.1436 acre site (Courtyards at Miramont P.U.D., Second Filing) is currently
vacant land covered with native vegetation. There is an existing irrigation/detention
pond located within the limits of the 10.635 acre site.
a. The pond is designated as pond #313 of the Amended Oak/Cottonwood Farm
Overall Drainage Study.
b. This pond will be located within the limits of a tract which will be defined as
Tract D on the final plat of the Courtyards at Miramont P.U.D., Second Filing.
Tract D will remain under separate ownership.
c. The pond tract (Tract D) has an area of approximately 1.974 acres.
PAGE 3
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
L GENERAL LOCATION AND DESCRIPTION:
B. Description of Property (continued)
d. The existing detention pond was constructed based on the original
Oak/Cottonwood Farm Overall Drainage Study. It was constructed in
association with the Upper Meadow at Miramont, Second Filing.
e. Preliminary Pond volume requirements and water surface elevation data were
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.
f. RBD, Inc. has certified the actual detention pond volume for detention pond
#313. They have also updated actual detention pond volume requirements with
the Amended Oak/Cottonwood Farm Overall Drainage Study based on actual
contributing areas determined by final design. Possible modifications to
detention pond #313 are considered with this report.
2. 46 single family homes are proposed within the limits of the Courtyards at
Miramont P.U.D. This includes the first two (2) lots which have been platted with
the Courtyards at Miramont P.U.D., First Filing and the 44 lots being platted with
the Second Filing.
II. DRAINAGE BASINS AND SUB -BASINS:
A. Major Basin Description
1. The Courtyards at Miramont P.U.D., Second Filing is located in the McClelland -
Mail Creek Drainage 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).
B. Sub -Basin Description
1. The Courtyards at Miramont P.U.D., Second Filing is contained within Basin 208
of the Amended Oak/Cottonwood Farm Overall Drainage Study Plan.
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Courtyards'at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
II. DRAINAGE BASINS AND SUB -BASINS:
B. Sub -Basin Description (continued)
2. Storm water from the projects to the north, are conveyed to the existing
irrigation/detention pond. Design of the Courtyards at Miramont P.U.D., First and
Second Filings will facilitate the routing of storm water from the Cottages at
Miramont P.U.D., the Miramont Fitness and Tennis Center and the Oak Hill
Apartments P.U.D. sites according to the requirements of the Amended
Oak/Cottonwood Farm Overall Drainage Study.
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.
a. The Amended Oak/Cottonwood Farm Overall Drainage Study indicates that
maximum allowable release rates for this area are as follows:
* 0.20 cfs/acre for the 10-year storm
* 0.50 cfs/acre for the 100-year storm.
The total required detention volumes, as well as the allowable release rate for
detention pond #313, have been, summarized and are presented in subsequent
sections of this report, as well as on the Drainage and Erosion Control Plan located
in Appendix III (stuffer envelope) of this report. These summaries are consistent
with the final conclusions presented in the Amended Oak/Cottonwood Farm
Overall Drainage Study and the Final Drainage and Erosion Control Study for Oak
Hill Apartments P.U.D.
III 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 Drainage and Erosion Control Plan.
2. Supplemental drainage design criteria specified in the Amended Oak/Cottonwood
Farm Overall Drainage Study was also utilized.
3. Erosion control measures and design conform to the requirements of the City of
Fort Collins Erosion Control Reference Manual.
PAGE 5
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
III DRAINAGE DESIGN CRITERIA:
B. Development Criteria Reference and Constraints
1. The following drainage reports were considered in the final drainage design and
calculations for Courtyards at Miramont P.U.D., Second Filing:
a. Oak/Cottonwood Farm Overall Drainage Study; RBD, Inc.; dated May 4, 1992;
RBD Project No: 504-001
b. Amended Oak/Cottonwood Farm Overall Drainage Study; RBD, Inc.; dated
August 16, 1994; RBD Project No: 504-001.
c. Preliminary Drainage Report for Oak Hill Apartments P.U.D.; RBD, Inc.; dated
February 7, 1994; RBD Project No: 088-010.
d. Final Drainage and Erosion Control Report for Oak Hill Apartments P.U.D.;
RBD, Inc.; dated May, 1994; RBD Project No: 088-010.
e. Preliminary Drainage and Erosion Control Report for Courtyards at Miramont
P.U.D. (Phases I-V) and The Cottages at Miramont P.U.D. (Phase VI); Shear
Engineering Corporation; Project No: 1410-01-94; Dated: March, 1994.
f. Final Drainage and Erosion Control Report for Miramont Fitness and Tennis
Center; Water, Waste and Land; dated September 12, 1994; WWL Project No:
402.
g. Master Drainage Study for the Oakridge Business Park
h. Drainage and Erosion Control Report for Oakridge West P.U.D. First Filing
2. The allowable storm water release rates for the 10 and 100-year storms, consider
the maximum allowable release rates per acre of 0.20 cfs for a 10-year storm and
0.50 cfs per acre for a 100-year storm as discussed in the Amended
Oak/Cottonwood Farm Overall Drainage Study, and the actual contributing area.
3. Downstream improvements have been completed within the Oakridge development
to accept a maximum storm water runoff of 119 cfs (0.50 cfs per acre) from the
Oak/Cottonwood Farm site according to the report titled "Master Drainage Study
for the Oakridge Business Park". Detention requirements for the McClellands
Master Drainage Basin have been established to be 0.20 cfs/acre for the minor, or
10-year storm event, and 0.50 cfs/acre for the major, or 100-year storm event.
4. RBD, Inc. has completed the re-evaluation the Oak/Cottonwood Farm Overall
Drainage Study to consider the final design of the Courtyards at Miramont P.U.D.,
First and Second Filings, the Cottages at Miramont P.U.D., the Miramont Tennis
Center and Oak Hill Apartments.
PAGE 6
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
III DRAINAGE DESIGN CRITERIA:
B. Development Criteria Reference and Constraints (continued)
5. The preliminary drainage design for Oak Hill Apartments P.U.D. indicated a 22'
wide (minimum) drainage channel located at the southwest corner of the Oak Hill
Apartment P.U.D. site. This channel would convey storm water to the existing
irrigation/detention pond which is located adjacent to the limits of the Courtyards at
Miramont P.U.D., Second Filing site.
a. This storm water would need to be conveyed under the entry private drive to the
Courtyards at Miramont P.U.D. site. Storm sewer pipe conveyance has been
considered as an alternative to the open channel specified with the Oak Hill
Apartments P.U.D. preliminary drainage report. Final design of the Oak Hill
Apartments P.U.D. now considers storm sewer along Boardwalk Drive instead
of the open channel alternative.
6. The property to the east, Collinwood (Oakridge West P.U.D. Fast Filing), is
developed and limits the amount of grading that can be performed along the east
property line of the Courtyards at Miramont P.U.D., Second Filing and the future
Cottages at Miramont P.U.D.
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 II for reference), in conjunction with the
"Rational Method" for detertnining peak flows at various concentration points.
D. Hydraulic Criteria
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.
IV DRAINAGE FACILITY DESIGN:
A. General Concept
1. Storm water from the Courtyards at Miramont P.U.D., First and Second Filings, the
Cottages at Miramont P.U.D., the Oak Hill Apartments P.U.D. and the Miramont
Fitness and Tennis Center, will be conveyed to the existing irrigation/detention
pond #313 via a combination of open channel conveyance, gutter conveyance and
storm sewer conveyance.
PAGE 7
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
A. General Concept (continued)
2. The existing irrigation/detention pond (Pond #313) will be provided with an outfall
pipe and outlet structure designed to restrict flows according to the allowable
release rates defined in the Amended Oak/Cottonwood Farm Overall Drainage
Study and based on the total contributing area to the pond.
a. The preliminary design of the detention pond outfall pipe was represented on
the "Detention Pond 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,
Project No. 504-003. A portion of the design alignment of the outfall pipe is
adjusted to facilitate the development occurring adjacent to the detention pond
(Pond #313).
b. The detention pond outlet pipe will be constructed with the Courtyards at
Miramont P.U.D., Second Filing and will convey release waters from pond
#313 to an open channel along the west side. of South Lemay Avenue (refer to
the Amended Oak/Cottonwood Farm Drainage Study and Plan).
c. The storm water will then be conveyed via the South Lemay Avenue open
channel to the existing triple culvert (3-36" RCP) which conveys storm water
under South Lemay Avenue to the Oakridge development. Storm water will not
be conveyed into pond #340 defined with the Amended Oak/Cottonwood Farm
Overall Drainage Study, but directly to the existing culvert.
i. It is our understanding, that the South Lemay Avenue open channel will be
replaced by a 36" storm sewer pipe in the future by others.
d. The final detention pond #313 outfall requirements are identified in the
Amended Oak/Cottonwood Farms Overall Drainage Study. The pond outfall
storm sewer plan and profile design has been included with the final utility
plans for Courtyards at Miramont P.U.D., Second Filing. The outfall restriction
structure has also been designed and incorporated with the final utility plans for
Courtyards at Miramont P.U.D., Second Filing.
B. Specific Details:
Specific design details and final design calculations have been provided with this
submittal of the Final Drainage and Erosion Control Report and Utility Plans for the
Courtyards at Miramont P.U.D., First and Second Filings.
PAGE 8
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
2. The existing irrigation/detention pond, which will service the Courtyards and
Cottages at Miramont P.U.D., the Oak Hill Apartments P.U.D. and the Miramont
Fitness and Tennis Center, is identified on the Amended Oak/Cottonwood Farm
Overall Drainage Study as pond #313.
a. The pond was originally designed and constructed in conjunction with the
Upper Meadow at Miramont P.U.D., Second Filing.
Reference: "Detention Pond 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, Project No. 504-003.
ii. Preliminary detention pond volume requirements were based on the
original Oak/Cottonwood Farm Overall Drainage Study; RBD, Inc.; dated
May 4, 1992; RBD Project No: 504-001.
iii. Final detention pond requirements have been determined based on actual
contributing design areas and are presented in the most current Amended
Oak/Cottonwood Farm Overall Drainage Study. Detention pond
requirements are also summarized in this report.
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 irrigation/retention pond. The ultimate pond would act as
an irrigation/detention pond. The following represents summary data which
was presented on the "Detention Pond and Erosion Control Plan" for Upper
Meadow at Miramont P.U.D., Second Filing (Sheet 1 of 1).
i. The interim pond is proposed to have 6.7 acre feet of irrigation volume.
ii. The ultimate pond is proposed to have 2.7 acre feet of irrigation volume.
iii. The ultimate pond is proposed to have 4.0 acre feet of detention volume.
c. The Amended Oak/Cottonwood Farm Overall Drainage Study indicates a 4.60
acre-foot detention requirement based on the SWMM model. Refer to the
Amended Oak/Cottonwood Farm Overall Drainage Study and the Appendix of
the Final Drainage and Erosion Control Study for the Oak Hill Apartments
P.U.D.; Sheet 10 - Site Hydrology.
d. The existing pond detention storage volume is 4.20 acre-feet based on actual
volume verification provided by RBD, Inc. Consulting Engineers. Refer to the
Appendix of the Final Drainage and Erosion Control Study for the Oak Hill
Apartments P.U.D.; Sheet 10 - Site Hydrology.
PAGE 9
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
e. Detention pond #313 will require additional volume due to actual volume
requirement determination. Additional detention pond grading requirements to
provide the additional volume are shown on the Final Grading Plan, Sheet 11 of
13 of the,Utility Plans for Courtyards at Miramont P.U.D., Second Filing. The
pond expansion has provided 4.75 ac-ft of detention storage volume. The
detention pond design stage -storage curve is included in Appendix A of this
report. A summary of detention pond data is presented on the Drainage and
Erosion Control Plan in Appendix III of this report.
f. The detention pond will also act as an irrigation facility for this site, the open
space greenbelt areas on the west side of Boardwalk Drive, and for future
development to the south and east. A pump house and necessary infrastructure
is under construction to distribute the irrigation water as needed.
i. Construction of the pump house will not be associated with the Courtyards
at Miramont P.U.D., Second Filing.
ii. Maintenance of the detention/irrigation pond will be the responsibility of the
owner of the tract on which the pond is located. This includes the pump
house.
3. The maximum allowable storm water release rates for the 10 and 100-year storms,
are 6.50 and 16.2 cfs respectively. This is based on the actual contributing area and
the maximum allowable release rates per acre.
4. An outlet structure has been provided for pond #313 to restrict the 10 and 100-year
storm event release rates to 6.50 and 16.2 cfs respectively. This structure will be
constructed with the Courtyards at Miramont P.U.D., Second Filing.
a. The outlet consists of a Type 2 box structure with the following components:
i. 12" orifice at elevation 66.50
1 16' broad crested weir, which is the top of the box structure, at an
elevation of 69.38
iii. 24" ADS N-12 outlet pipe with a slope of 0.40%.
PAGE 10
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
5. An emergency overflow weir has been provided near the extreme southwest corner
of the pond. The final emergency overflow was location was preferred by the the
City of Fort Collins Park and Recreation Department, future owners of the property
south of the Courtyards at Miramont P.U.D., Second Filing.
a. The emergency overflow has an outfall elevation of 69.85 and consists of the
following :
i. A 10' x 10' rip rap weir with a slope 0.5%; grassed.
ii. Grassed banks with 4:1 side slopes
d. The flow capacity of the weir at various depths is presented on page 15 of the
calculations for different elevations above the overflow elevation.
e. Storm water overflow will be conveyed overland to either Boardwalk Drive
further downstream, or to the major drainage channel on the north side of
Boardwalk Drive downstream.
i. Downstream emergency overflow conveyance will initially consist of sheet
flow on the park property with no defined conveyance channelization.
I The final emergency overflow conveyance design is to be provided to , and
approved by the City of Fort Collins Parks and Recreation Department.
This conveyance is to be incorporated into the preliminary design for the
park which has been provided by Parks and Recreation. This emergency
overflow conveyance design must be approved prior to Phase 3 construction
of the Courtyards at Miramont P.U.D., Second Filing.
f. The detention pond water surface elevations for the 10 and 100-year storm
events are 69.00 and 69.74 respectively. These elevations are based on the
respective release rates. Refer to the detention pond stage -storage curve in
Appendix I of this report.
5. A storm sewer will be provided for the detention pond outfall. The storm sewer
will convey detention pond #313 release waters to the existing open channel along
the west side of South Lemay Avenue (refer to the Amended Oak/Cottonwood
Farm Drainage Study and Plan).
a. The 24" ADS N-12 pipe has a capacity of 15.5 cfs with HW/D = 1.0 (slope =
0.40%).
b. The 24" ADS N-12 pipe has a pressure flow capacity of 16.86 cfs with
hydraulic gradient of 0.56% from the pond high water elevation of 69.74 to the
outfall at the Lemay Avenue open channel.
PAGE 11
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
c. The storm sewer will be constructed in association with this project. Refer to
the Utility Plans for Courtyards at Miramont P.U.D., Second Filing.
6. Storm water will then be conveyed via the existing South Lemay Avenue open
channel directly to the existing triple culverts (3-36" RCP) located near the
intersection of Lemay Avenue and Boardwalk Drive. It is our understanding, that
the South Lemay Avenue open channel will be replaced by a 36" storm sewer pipe
in the future by others.
a. The Amended Oak/Cottonwood Farm Overall Drainage Study indicates that
during final design of Detention Pond #340, the hydraulics of the connection
from the detention pond to the existing 36" culverts under Lemay Avenue will
need to be determined to ensure that the 0.50 cfs per acre release rate is not
exceeded.
b. The Amended Oak/Cottonwood Farm Overall Drainage Study also indicates
that Pond #340, as well as the storm discharge structure, will need to be
permanently designed when the area of the Overall plan known as the Hamlet is
developed (the Hamlet was defined as a part of the Miramont Phase 3
Preliminary Plan).
c. This storm discharge structure has not been designed with the Courtyards at
Miramont P.U.D., Second Filing.
7. A 10' type R inlet will be required at the intersection of Boardwalk Drive and the
private Drive for the Courtyards at Miramont P.U.D. This structure has been
installed in association with the Courtyards at Miramont P.U.D., First Filing.
a. The 100-year peak flow to the 10' type R inlet (design point F) is 13.64 cfs.
8. A storm sewer has been proposed adjacent to Boardwalk Drive and the Courtyards
at Miramont P.U.D. to extend from the Oak Hill Apartments P.U.D. to the existing
detention pond. This storm sewer is sized to facilitate the drainage design
requirements for the Oak Hill Apartments P.U.D. and a portion of the Courtyards at
Miramont P.U.D.
a. The peak flow from the Oak Hill Apartments will be 68.63 cfs according to the
Final Drainage and Erosion Control Study for Oak Hill Apartments P.U.D. A
36" RCP storm sewer will be constructed from the Oak Hill Apartment P.U.D.
peak discharge point to the inlet located at the intersection of Boardwalk Drive
and the Courtyards at Miramont P.U.D. private Drive. A portion of the 36"
RCP storm sewer was constructed in association with the Courtyards at
Miramont P.U.D., First Filing.
PAGE 12
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
i. The 36" RCP storm sewer has a design slope of 0.50% and a capacity of
47.20 cfs with a HW/D = 1.00. The pipe will be under pressure during a
100-year storm.
b. A 42" RCP storm sewer has been constructed from the type R inlet located at
intersection of Boardwalk Drive and the Courtyards at Miramont P.U.D. private
drive, to the existing detention pond. This portion of the storm sewer was
constructed in association with the Courtyards at Miramont P.U.D., First Filing.
i. The 42" RCP storm sewer has a design slope of 0.60% and a capacity of
77.90 cfs (Peak flow of 68.63 cfs from Oak Hill P.U.D.; 13.64 cfs from
Courtyards at Miramont P.U.D. These peak flows are based on different
Times of Concentration).
c. The Boardwalk Drive storm sewer, adjacent to the Courtyards at Miramont
P.U.D., is partially profiled with the Utility Plans for the Courtyards at
Miramont P.U.D., First Filing and partially with the Courtyards at Miramont
P.U.D., Second Filing. These design profiles were coordinated with RBD, Inc.
for the continuation of the storm sewer with the Oak Hill Apartments P.U.D.
The same storm sewer profile is presented on the final utility plans for Oak Hill
Apartments P.U.D.
9. Conveyance of storm water from the Miramont Fitness and Tennis center will be
provided via a storm sewer located in a twenty foot easement provided by the Oak
Hill Apartments P.U.D. An area inlet will be provided at the North property line of
Courtyards at Miramont. A storm sewer will then convey the storm water through
Tract A (open space) of the Courtyards at Miramont P.U.D., Second Filing and
thence under the Courtyards at Miramont P.U.D. private drive to the detention pond
#313.
a. The peak flow from the Fitness and Tennis Center is identified as 34.4 cfs
according to the Final Drainage and Erosion Control Report for Miramont
Fitness and Tennis Center.
b. A 30" ADS storm sewer will be provided in the Courtyards at Mimmont P.U.D,
Second Filing open space (Tract A) for the conveyance of peak flows from the
Tennis Center. The storm sewer is profiled with the Utility Plans for the
Courtyards at Miramont P.U.D., Second Filing.
i. The 30" ADS storm sewer has a design slope of 2.68% and a capacity of
68.3 cfs (HW/D=1.00).
PAGE 13
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IN DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
10. Maintenance of the open space areas within the limits of the Courtyards at
Miramont P.U.D., will be the responsibility of the developer until completion of the
project. A Homeowners Association would then assume maintenance
responsibilities for the open space areas.
11. Boardwalk Drive to the west of the Courtyards at Miramont P.U.D. is fully
constructed to collector standards (except the eastern detached sidewalk).
a. The Final 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
storm water 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.
12. The street capacity of the private drive is based on a flow depth of 0.90' above the
flow line elevation on the low side of the private drive. This allows for a flow up
to the top of curb on the high side of the road. Refer to Figures 1 and 2 enclosed in
Appendix 1.
a. Using a composite Mannings 'n' value of 0.021, the conveyance factor (C =
(1.486 A Wo)/n) for the private drive is 1,308.1.
b. The street capacity of the private drive can be determined by multiplying the
conveyance factor (C) by the square root of the street slope (ft/ft) (Mannings
Equation).
c. The minimum street capacity based on the street slope of 0.005 ft/ft is 92.5 cfs.
d. The peak flow (Q100) to the low point at the end of the private drive
(Concentration Point B) is 32.37 cfs.
13. Storm water from the rear of lots 33-41 sheet flows undetained to the future park
property to the south. The developed peak flow from this area was found to be less
than the historic peak flow to the southeast corner of the property. This historic
peak flow assumes that pond 313 is constructed. Refer to pages 18 and 19 and
exhibit G in Appendix I.
a. The historic peak flow was found to be 6.7 cfs.
b. The developed peak flow from the rear of lots 33-41, is 2.2 cfs.
PAGE 14
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
IV DRAINAGE FACILITY DESIGN:
B. Specific Details: (continued)
14. Storm water from the rear of lots 28-32 flows to the existing detention pond on the
Collinwood property.
a. The detention pond is designed for a larger amount of impervious area than was
actually built with Oak Ridge West P.U.D.
b. We have determined that the composite 'C' factor for the existing conditions at
the site are significantly less than those calculated by RBD, Inc. as part of the
Grading and Drainage Plan for Oakridge West P.U.D., First Filing. Refer to
pages 10-12 in the drainage calculations. The comparison is as follows:
i. C=0.49 for current conditions for 100-year storm
I C=0.70 by RBD for original design conditions for the 100-year storm
c. Therefore, the detention pond should have sufficient capacity to store the small
amount of runoff from the rear of lots 28-32.
V: EROSION CONTROL DESIGN CRITERIA:
A. Regulations
1. Design Criteria from the City of Fort Collins Erosion Control Reference Manual
were utilized.
VI. EROSION CONTROL FACILITY DESIGN:
A. General Concept:
1. Courtyards At Miramont P.U.D., Second Filing lies within the Moderate Wind
Erodibility Zone per the City of Fort Collins Erodibility Zone Map.
a. According to the criteria of the City of Fort Collins Erosion Control Reference
Manual for Construction sites, the Erosion control performance standard has
been calculated and appropriate erosion control measures identified for the
control of erosion during and after construction.
2. Erosion control measures are specified on the Drainage and Erosion Control Plan
attached in Appendix III (stuffer envelope). 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 ofsite and offsite, will remain the
responsibility of the developer until the subdivision is totally developed.
PAGE 16
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
VIL EROSION CONTROL SECURITY DEPOSIT (continued):
I The $650.00 per acre for re -seeding sites of less than 10 acres was quoted
to us by the City of Fort Collins Storm Water Utility staff.
2. The erosion control security deposit amount required for this project will be
$11,343.75. See the Erosion Control Security Deposit Requirements document
located in Appendix III (stuffer envelope).
3. The erosion control security deposit is reimbursable.
VM. VARIANCE FROM CITY STANDARDS
A. Variance from City of Fort Collins requirements
1. There will be no requests for variances from Storm Drainage Design Criteria.
IX. 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., Second
Filing.
2. The erosion control measures specified will effectively reduce erosion potential
during construction.
PAGE 15
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
VI. EROSION CONTROL FACILITY DESIGN:
B. Specific Details
1. Haybale dikes will be provided in channel sections upstream from storm sewer
pipes.
2. Silt fencing or haybales will be provided around the disturbed portion of the
perimeter of the pond.
3. Gravel filters will be provided at all inlets.
4. Permanent erosion control devices will consist of Rip rap aprons at all storm sewer
outfalls. See the Drainage and Erosion Control for apron dimensions and Rip rap
sizes.
VII. EROSION CONTROL SECURITY DEPOSIT:
A. An erosion control security deposit is required in accordance with City of Fort Collins
policy (Chapter 7, Section C : SECURITY; page 7.23 of the City of Fort Collins
Development Manual). In no instance shall the amount of the security be less than
$1000.00.
1. According to current City of Fort Collins policy, the erosion control security deposit
is figured based on the larger amount of 1.5 times the estimated cost of installing
the approved erosion control measures or 1.5 times the cost to re -vegetate the
anticipated area to be disturbed by construction activity.
a The cost to install the proposed erosion control devices for the Courtyards at
Miaomont P.U.D., Second Filing is $ 7,562.50. 1.5 times this estimate is $
11,343.75.
i. unit prices have been provided by Connell Resources.
b. Based on current data provided by the City of Fort Collins Storm Water Utility,
and based on an actual anticipated net affected disturbed area during
construction of the Courtyards at Miramont P.U.D., Second Filing
(approximately 8.66 acres) we estimate that the cost to re -vegetate the disturbed
area will be $5,629.00 ($650.00 per acre x 8.66 acres). 1.5 times the cost to re -
vegetate the disturbed area is $8,443.50.
i. The 8.66 acres is the actual area of the Courtyards at Miramont P.U.D.,
Second Filing housing project. The area of Tract B (the existing detention
pond; 1.974 acres) has been deducted from the overall platted area of 10.635
acres.
PAGE 17
Courtyards at Miramont P.U.D., Second Filing
Final Drainage and Erosion Control Report
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 Overall Drainage Study; RBD, Inc.; dated May 4, 1992;
RBD Project No: 504-001
5. Amended Oak/Cottonwood Farm Overall Drainage Study; RBD, Inc.; dated
August 16, 1994; RBD Project No: 504-001.
6. Final Drainage Report for Oak Hill Apartments P.U.D.; RBD, Inc.; dated May 2,
1994; RBD Project No: 088-010.
7. Final Drainage and Erosion Control Report for Oak Hill Apartments P.U.D.;
RBD, Inc.; dated May, 1994; RBD Project No: 088-010.
8. Preliminary Drainage and Erosion Control Report for Courtyards at Miramont
P.U.D. (Phases I - V) and The Cottages at Miramont P.U.D. (Phase VI); Shear
Engineering Corporation; Project No: 1410-01-94; Dated: March, 1994.
9. Final Drainage and Erosion Control Report for Miramont Fitness and Tennis
Center; Water, Waste and Land; dated 'July 18, 1994 WWL Project No: 402.
10. "Detention Pond 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,
Project No. 504-003
11. Master Drainage Study for the Oakridge Business Park; RBD, Inc.; dated
September, 1990.
APPENDIX I
Storm Drainage Calculations
Erosion Control Calculations
P;s[
r
C OUr�\, r�(r` ' ^ 1�1 \(.'�'10 •,� V
•� {'ice\c.i_,.�C. �.,4.\G!I�''.110'•l�
PREPARED DY tn6(
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2-
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7[
t C
II
FLOW SUMMARY FOR COURTYARDS AT MIRAMONT SECOND FILING
DESIGN SUB AREA C2 C10 C100 Tc Tc Tc I2 I10 I100 Q2 Q10 Q100
POINT BASIN 2 YR 10 YR 100 YR
ac. min. min. min. iph iph iph cfe c£e cfe
1fR1111R f41f 111f tfR ttf tf tttRt ttkRR RtMRf RtRRf RR♦Rf RRf tf ftltf f1t4t tRftf tf tft ftRff
B Ib 5.51 0.71 0.71 0.89 12.50 0.00 12.50 2.34 4.15 6.60 9.15 16.24 32.37
H (2) Ih 6.57 0.72 0.72 0.90 15.00 15.00 15.00 2.14 3.75 6.06 10.12 17.74 35.83
P (3) if 2.34 0.53 0.53 0.67 5.00 5.00 5.00 3.29 5.64 8.70 4.08 6.99 13.64
OPPSITB Ioo 0.10 0.58 0.58 0.73 5.00 5.00 5.00 3.29 5.64 8.70 0.19 0.33 0.64
OFPSITE Io 1.17 0.58 0.58 0.73 5.00 5.00 5.00 3.29 5.64 8.70 2.23 3.83 7.43
A Ia 3.93 0.51 0.51 0.64 5.00 5.00 5.00 3.29 5.64 8.70 6.59 11.3 21.88
NOTES:
1: TAKEN FROM INFORMATION PREPARED BY RED, Inc. FOR OAK HILL APARTMENTS
2: SUB BASIN Ih CONSISTS OF THE PROPOSED TENNIS CENTER AT MIRAMONT AND SMALL PORTIONS
COURTYARDS AT MIRAMONT AND THE OAK HILL APARTMENTS
3: SUB BASIN If IS THE CONTRIBUTING AREA TO THE INLET CONSTRUCTED WITH FIRST PILING
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SHEAR ENGINEERING CORPORATION
PAGE 4A FLOW TO CONCENTRATION POINT B
FROM SUBBASIN Ib
PROJECT: COURTYARDS AT MIRAMONT AT MIRAMONT DATE 10/05/94
FILE: MIRARUN PROJ. NO.1410-01-94
NOTES: BY MEO
AREA (A)- 5.510 ACRES
RUNOFF CORP. (C)
2 YEAR
10 YEAR
100
YEAR
C . 0.71
0.71
0.89
SEE PAGE 4
TIME OF CONCENTRATION (Tc)
OVERLAND TRAVEL TIME (Ti)
NOT APPLICABLE
LENGTH 0 FEET
SLOPE
0.00 k
2 YEAR
10 YEAR
100
YEAR
C 0.00
0.00
0.00
Ti (min)- 0.00
0.00
0.00
TRAVEL TIME (Tt)-L/(60*V)
FLOW TYPE
L (ft) = 270 S (t) -
1.00
GUTTER
V
(fps) -
2.00
Tt(min)-
2.25
L (ft) - 250 S (t) =
2.00
GUTTER
V
(fps) -
2.80
Tt(min)-
1.49
L (ft) - 210 S (t) -
4.00
GRASSED SWALH V
(fps) -
3.00
Tt(min)-
1.17
L (ft) - 226 S (t) -
1.12
GUTTER
V
(fps) -
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Tt(min)-
1.79
L (ft) - 526 S (t)
- 0.50
GUTTER
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(fps) -
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Tt(min).
5.84
L (ft) = 0 S (t)
- 0.00
GUTTER
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(fps) -
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Tt(min)-
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L (ft) - 0 S (t)
- 0.00
GUTTER
(fps), -
0.00
Tt(min).
0.00
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL TRAVEL
TIME
(min) =
12.54
Tc-Ti+TOTAL-TRAVEL TIME
2 YEAR
10 YEAR
100
YEAR
Tc (min)- 12.54
12.54
12.54
USE Tc - 12.5
12.5
12.5
INTENSITY (I) (iph)
2 YEAR
10 YEAR
100
YEAR
I = 2.34
4.15
6.60
NOTE: INTENSITIES TAKEN
FROM FIGURE 3-1
RUNOFF (Q= CIA) (cfe)
2 YEAR
10 YEAR
100
YEAR
Q = 9.15
16.24
32.37
CONCLUDE:INSTALL: CURB OPENING TO HANDLE Q100
9
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SHEAR ENGINEERING CORPORATION
SUB BASIN If BREAKDOWN
PAGE 6
PROJECT :COURTYARDS AT MIRAMONT
PROJ.NO. :1410-01-94 DATE: 07/28/94
LOCATION :PORT COLLINS BY: HBO
PILE :MIRAMONT
NOTES - :FINAL
RUNOFF
SURFACE CORP.
CHARACTERISTICS AREA C C+A
(acres)
STREETS
ASPHALT 0.350 0.950 0.333
CONCRETE 0.000 0.950 0.000
GRAVEL 0.000 0.500 0.000
ROOFS 0.690 0.950 0.656
LAWNS SANDY SOIL
PLAT < 2% 0.000 0.100 0.000
AVERAGE 2 - 7% 0.000 0.150 0.000
STEEP > 7t 0.000 0.200 0.000
LAWNS HEAVY SOIL
FLAT < 2% 1.300 0.200 0.260
AVERAGE 2 - 7% 0.000 0.250 0.000
STEEP > 7% 0.000 0.350 0.000
TOTAL AREA 2.340 1.248
C2 C10 C100
COMPOSITE C VALUE 0.533 0.533 0.667
USE 0.53 0.53 0.67
SHEAR ENGINEERING CORPORATION
PAGE 7 DEVELOPED FLOW TO P
FROM SUB BASIN If
PROJECT: COURTYARDS AT MIRAMONT DATE 07/28/94
SECOND FILING PROD. NO.1410-01-94
BY MEO
FILE: MIRAMONT
AREA (A). 2.34 ACRES SUB BASIN If
RUNOFF CORP. (C)
2 YEAR 10 YEAR 100 YEAR
C = 0.53 0.53 0.67
SEE SPREAD SHEET ATTACHED ON PAGE 6
TIME OF CONCENTRATION (TO FORT COLLINS FORMULA
OVERLAND TRAVEL TIME (Ti)(1.87(1.1-CCf)*(L)"0.5)/(S)^0.33 NOT APPLICABLE
LENGTH = 0 PERT SLOPE = 1.00 i FLOW IN GRASS SWALE INITIALLY
2 YEAR 10 YEAR 100 YEAR
C = 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 (i) = 1.00 GRASSED SWALE V (£pa) = 1.60 Tt(min)= 1.56
L (ft) = 150 S (i) - 0.60 GUTTER V (fpe) = 1.60 Tt(min)= 1.56
L (ft) = 155 S M - 2.00 GUTTER V (fpa) = 2.80 Tt(min)= 0.92
L (ft) = S (4) . V (fpe) = Tt(min)= 0.00
L (ft) = S (6) = V (fpe) = Tt(min). 0.00
L (ft) = S (i) . _ _.. V (fpe).'= Tt(min). 0.00
L (ft) S (6) _ V (fpe) = 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 5.64 8.70
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q. CIA) (cfe)
2 YEAR 10 YEAR 100 YEAR
Q = 4.08 6.99 13.64
CONCLUDE:INSTALL 5 TYPE 'R' INLET
NOTE: 5 FOOT OPENING WITH 10 FOOT BOX AS PIPE IS OFFSET
INSTALL 135 LF OF 42 r RCP 0 0.6 t ,
n = 0.013 Qcap . 77.92 CPS
NOTE: PIPE IS OVERSIZED FOR DEVELOPED FLOWS FROM UPSTREAM PROJECT
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20
21
22
20
24
25
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21
e : ccuiiur. 20
SHEAR ENGINEERING CORPORATION
PAGE 9 DEVELOPED FLOW TO H
FROM SUB BASIN Ih
PROJECT: COURTYARDS AT MIRAMONT DATE 08/12/94
SECOND FILING PROJ. NO.1410-01-94
BY MEO
FILE: MIRAMONT
AREA (A)= 6.57 ACRES SUB BASIN Ih
RUNOFF COEF. (C)
2 YEAR 10 YEAR 100 YEAR
C = 0.72 0.72 0.90
SHE PAGE 8
TIME OF CONCENTRATION (Tc) FORT COLLINS FORMULA
OVERLAND TRAVEL TIME (TO (1.87(1.1-CCf)*(L)A0.5)/(WO .33
LENGTH -HA FEET SLOPE -NA i
2 YEAR 10 YEAR 100 YEAR
C =
Ti (min). 15.20 15.20 15.20
Ti TAKE FROM FINAL DRAINAGE REPORT FOR TENNIS CENTER TO DESIGN POINT 'B' ON THEIR PLANS
TRAVEL TIME (Tt) =L/(60*V) FLOW TYPE
L (ft) = 210 S (4) = 1.00 PIPE V (fps) = 6.00 Tt(min)= 0.58
L (ft) = S (i) = V (fps) = Tt(min)= 0.00
L (ft) = S (%) _ _ V (fps) = Tt(min)= 0.00
L (ft) = S (i) = V (fps) = Tt(min)= 0.00
L (ft) = S-(4) = V (fps) _ Tt(min)= 0.00
L (ft) = S (t) _ V (fps) 'T Tt(min)= 0.00
L (ft) = S M = V (fps). = Tt(min)= 0.00
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2 TOTAL TRAVEL TIME (min) = 0.58
Tc =Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)- 15.78 15.78 15.78
USE Tc = 15.00 15.00 15.00
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 2.14 3.75 6.06'
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q= CIA) (cfe)
2 YEAR 10 YEAR 100 YEAR
Q = 10.12 17.74 35.83
NOTE: APPROXIMATELY 34 CPS IS ALREADY IN UPSTREAM PIPE FROM TENNIS CENTER
CONCLUDE:INSTALL 351.93 LF OF 30 " ADS-N12 ® 2.36%
INSTALL AREA INLET AT 'H' IN SUMP CONDITION .
Qcap = 68.26 cfe PIPE OVERSIZED BECAUSE UPSTREAM PIPE FROM TENNIS
CENTER IS 30• 0 0.60% Qcap = 34.42 CPS
INV. 0 POND = 70.00 GRATE ELEVATION = 82.50
INV. OUT 0 'H' = 78.30
INV. IN 0 'H' = 78.50
r rrtxxrtxrrtttxrxrrrtrt trxxxxrtrxttxxttrrrtrrttxt*rt ttrrrttrttt trr
p P\C,e 10
April 22, 1994
Project No. 1366-01-93
Glen Schlueter, Civil Engineer
City of Fort Collins Storm Water Utility
P.O. Box 580
Ft. Collins, Colorado 80522
Re: Collinwood; Ft. Collins, Colorado
Dear Glen,
Enclosed please find the composite 'C' factor calculations. you requested for Collinwood. We
have compared the runoff coefficient calculations to those shown on the Grading and Drainage
plan for Oakridge West P.U.D., First Filing with the existing conditions that are shown on the
City of Fort Collins aerial photo having a date of photography of April 8, 1993. The Grading
and Drainage plan for Oakridge West P.U.D., First Filing was prepared by RBD, Inc.; latest
revision. date, October 3, 1988.
We have determined that the composite 'C' factor for the existing conditions at the site are
significantly less than those calculated by RBD, Inc. as part of the Grading and Drainage Plan for
Oakridge West P.U.D., First Filing. The comparison is as follows:
* 0.49 for current conditions for 100 year storm
* 0.70 by RBD for original design conditions for the 100 year storm
The smaller runoff coefficient can be attributed to the fact that the site has not been fully
developed in accordance with the original site plan. Several buildings and additional parking
areas that are shown on the approved plans for Oakridge West P.U.D., First Filing have not been
built as of this time.
As you will note in the attached calculations and spreadsheets the small additions being added to
two (2) of the buildings have an insignificant effect on the composite factor. It changes from
0.492 to 0.493. We estimate that the roof area of the additions will cover approximatley 0.02
acres.
If you havejulther comments or questions, please call at 226-5334.
l`rrian W. Shear, P�
Shear Engineering Corporation
BWS / jmb
attachments
cc: Baldwin Construction
Bruker-Brown Architects
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
f P(7c AI
SHEAR ENGINEERING CORPORATION
COMPOSITE •C' FACTOR EXISTING CONDITIONS
PAGE t 1
PROJECT :COLLINWOOD
PROJ.NO. t1366-01-93 DATER 04/22/94
PILE :COLLIN BY: HBO
RUNOFF
SURFACE CORP.
CHARACTERISTICS AREA C C*A -
(acree)
STREETS
ASPHALT 1.270 0.950 1.207
CONCRETE 0.540 0.950 0.513
GRAVEL 0.000 0.500 0.000
ROOFS 1.490 0.950 1.416
LAWNS SANDY SOIL
PLAT < 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
PLAT < 24 9.500 0.200 1.900
AVERAGE 2 - 7k 0.000 0.250 0.000
STEEP > 7% 0.000 0.350 0.000
TOTAL AREA 12.600 5.035
C2 -CIO " C100
COMPOSITE C VALUE 0.393 0.393 0.492
USE 0.39 0.39 0.49
RED VALUE 0.56 0.56 0.70
u
P AGE vZ
SHEAR ENGINEERING CORPORATION
COMPOSITE 'C' FACTOR DEVELOPED CONDITIONS
PAGE 2
PROJECT :COLLINWOOD
PROJ.NO. t1366-01-93 DATE: 04/22/94
PILE tCOLLIN BY: HBO
NOTE ROOF AREA INCREASES VERY SLIGHTLY
DUB TO 3 SMALL ADDITIONS
LAWN AREA DECRESES BY LIKE AMOUNT
RUNOFF
SURFACE CORP.
CHARACTERISTICS AREA C C*A
(acres)
STREETS
ASPHALT 1.270 0.950 1.207
CONCRETE 0.540 0.950 0.513
GRAVEL 0.000 0.500 0.000
ROOFS 1.510 0.950 1.435
LAWNS SANDY SOIL
PLAT < 2t 0.000 0.100 0.000
AVERAGE 2 - 7% 0.000 0.150 0.000
STEEP > 7t 0.000 0.200 0.000
LAWNS HEAVY SOIL
PLAT < 2% 9.480 0.200 1.896
AVERAGE 2 - 7% 0.000 0.250 0.000
STEEP > 7% 0.000 0.350 0.000
TOTAL AREA 12.800 5.050
C2 CIO C100
COMPOSITE C VALUE 0.395 0.395 0.493
USE 0.39 0.39 0.49
CONCLUDE: THE ADDITIONS HAVE VERY LITTLE AFFECT ON THE 'C' PACTOR
THE DETENTION PONDS WERE SIZED USING TUB LARGER 'C' VALUE
CALCULATED BY RED WITH PLANS FOR OAKRIDGE WEST PIRST PILING
LAST REVISED 10/3/88
,
\ \.
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PREPARED 3Y\G
N DATE •�
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SHEAR ENGINEERING CORPORATION
PAGE 14 DEVELOPED PLOW TO A
FROM SUB BASIN Is
PROJECT: COURTYARDS AT MIRAMONT DATE 09/16/94
SECOND PILING PROD. NO.1410-01-94
BY MEO
PILE: MIRAMONT
AREA (A)- 3.93 ACRES SUB BASIN Is
RUNOFF CORP. (C)
2 YEAR 10 YEAR 100 YEAR
C = 0.51 0.51 0.64
SEE BASIN BREAKDOWN ON PAGE 13
TIME OF CONCENTRATION (Tc) PORT COLLINS FORMULA
OVERLAND TRAVEL TIME (Ti)(1.87(1.1-CCf)*(L)A0.5)/(W0.33 NOT APPLICABLE
LENGTH 0 FEET SLOPE = 1.00 • FLOW IN GRASS SWALE INITIALLY
2 YEAR 10 YEAR 100 YEAR
C = 0.20 0.20 0.25
Ti (min)- 0.00 0.00 0.00
TRAVEL TIME (Tt)=L/(60*V) PLOW TYPE
L (£t) = S (t) = V (fps) - Tt(min)= 0.00
L (ft) . S (t) - V (fps) - Tt(min)- 0.00
L (ft) - S (t) = V (fps) = Tt(min)= 0.00
L (£t) = S (t) = V (fps) _ .Tt(min)- 0.00
L.(ft) . S (t) . V (fps) . Tt(min). 0.00
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) = 0.00
Tc -Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min). 0.00 0.00 0.00
USE Tc = 5.00 5.00 5.00
Tc ASSUMED TRAVEL PATH FROM ANY WHERE IN SUBASIN IS VERY SHORT DISTANCE
TO POND AND WILL BE REDUCED AS POND RISES
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 3.29 5.64 8.70
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q. CIA) (cfe)
2 YEAR 10 YEAR 100 YEAR
Q . 6.59 11.30 21.88
L CONCLUDE:THIS CALCULATION IS FOR REFERENCE ONLY
Drainage Notes
Courtyards at Miramont, P.U.D.
Albrecht / Miramont / DrgNotes
Detention Pond Summar
*Bottom of Pond elevation
= 62.0
Top of Berm elevation
= 70.0
Overflow spillway elev.
= 69.85
Irrigation W.S. elevation
= 66.50
Top of outlet structure
= 69.38
100 year W.S. elevation
= 69.74
10 year W. S. elevation
= 69.00
*Irrigation Volume
= 2.7 ac-ft
Detention Volume Provided at elev. 69.85
= 4.75 ac-ft
*Detention Volume Required
= 4.6 ac-ft
Total Contributing Area
to Pond
= 32.39 acres
100 year release rate
= 16.2 cfs
(Based on release rate of 0.5 cfs/acre of
contributing area)
10 year release rate
= 6.5 cfs
(Based on release rate of 0.2 cfs/acre of
contributing area)
*Information taken from Final Drainage and
Erosion Control Report for the Oak Hill
Apartments P.U.D.: prepared RBD, Inc:
Project No. 088-010: Dated May 2, 1994.
September 27, 1994
v
FACE 15
SHEAR ENGINEERING CORPORATION
OUTLET STRUCTURE FOR POND 313
PROJECT:
COURTYARDS AT MIRAMONT DATE: 10/06/94
PROJECT NO
1410-01-94 BY HBO
PROJECT LOCATION
:FORT COLLINS
NOTES:
OUTLET STRUCTURE FOR POND 313
FILE NAME:
MIRAOUT
INPUT FOR OUTLET STRUCTURE
STRUCTURE TYPE:
2
WEIR TYPE
BROADCRESTED
LOWER ORIFICE DIAM.
(ft) =
1.00
WEIR LENGTH (ft) =
16.00
LOWER ORIFICE INV.
(ft) =
66.50
WHIR INVERT (£t) =
69.38
LOWER ORIFICE COEF.
(Cl) =
0.65
WHIR CORP. (Cw)
2.60
UPPER ORIFICE DIAM.(ft)
=
NA
TOP OF BERM (ft) =
70.00
UPPER ORIFICE INV.
(ft) =
NA
INIT. DELTA (ft) =
1.50
UPPER ORIFICE COBF.
(Cu) =
0.65
DELTA HEAD (ft) =
0.25
2 YR. RELEASE RATS
(cfe) =
NA
EMERGENCY OVER PLOW
10 YR RELEASE RATE
(cfe) =
6.48
WEIR TYPE
BROADCRESTED
100 YR RELEASE RATE
(c£e)=
16.20
WHIR LENGTH (ft) =
10.00
OUTLET PIPE DIAM. (ft)
=
2.00
WHIR INVERT (ft)
. 69.85
PIPE SLOPE (4)
-
0.40
WHIR CORP. (Cwo)
= 2.60
MANNINGS n
=
0.012
f err+ree f!!r+l+! r:a
trrr
♦OUTPUTf
etlf++r+ rif r♦rir
ferrtrf!
rirl++ri
PIPS AREA (SF) =
3.14
WETTED PERIMETER
6.28
FEET
HYD. RAD (FT) =
0.500
FEET
RA2/3 0.6298
OUTLET PIPE CAPACITY
15.50
CPS WITH HW/D =
1.00
LOWER ORIFICE AREA
(A) =
0.7054
SQUARE FEET
UPPER ORIFICE AREA
(A) =
0.0000
SQUARE FEET
-�
+ti+rtr trrtf+! tiitiit
tOUTPUr*
tl+lrit irtrftt
rtrlf if
if rirft
rrtrrr+
fi+lf+f
f14k11f
ilf ilf+
OVERFLOW
SPILLWAY
HEAD
HEAD
HEAD
SUB
HEAD
ELEV. OVER
LOWER
OVER
UPPER OVER
WEIR
TOTAL
OVER
WEIR
TOTAL
SLEV.
LOWER
ORIFICE
UPPER
ORIFICE WHIR
FLOW
FLOW
WHIR
PLOW
FLOW
ORIFICE
IFLOW
ORIFICE
PLOW
ft ft
cfe
ft
cfe ft
cfe
cfe
ft
cfe
cfe
ft
66.50 0.00
0.00
0.00
0.00 0.00
0.00
0.00
0.00
0.00
0.00
66.50
68.00 1.50
5.02
0.00
0.00 0.00
0.00
5.02
0.00
0.00
5.02
68.00
68.25 1.75
5.42
0.00
0.00 0.00
0.00
5.42
0.00
0.00
5.42
68.25
68.56 2.00
5.79
0.00
0.00 0.00
0.00
5.79
0.00
0.00
5.79
68.50
68.75 2.25
6.15
0.00
0.00 0.00
0.00
6.15
0.00
0.00
6.15
68.75
69.00 2.50
6.48
0.00
0.00 0.00
0.00
6.48
0.00
0.00
6.48
69.00
69.25 2.75
6.79
0.00
0.00 0.00
0.00
6.79
0.00
0.00
6.79
69.25
69.50 3.00
7.10
0.00
0.00 0.12
1.73
8.83
0.00
0.00
8.83
69.50
69.75 3.25
7.39
0.00
0.00 0.37
9.36
16.75
0.00
0.00
16.75
69.75
70.00 3.50
7.66
0.00
0.00 0.62
20.31
27.97
0.15
1.51
29.48
70.00
70.18 3.68
7.86
0.00
0.00 0.80
29.77
37.63
0.33
4.93
42.55
70.18
70.25 3.75
7.93
0.00
0.00 0.87
33.76
41.69
0.40
6.58
48.27
70.25
trl+t+r rrtr+ir
r: rrrrf
rtrrttr
trt rtrt ♦lrf+l+
rrtrttt
f+l+err
trlfl+t
trtrtfr
f♦+fl+f
r!lfrrt
ORIFICE EQUATION: CA(29H)A1/2
WEIR PLOW EQTN. :
CWLH^3/2
? RGe. 16
J
0
SHEAR ENGINEERING CORPORATION
OUTLET STRUCTURE FOR POND 313
PROJECT: COURTYARDS AT MIRAMONT DATE: 10/06/94
PROJECT NO 1410-01-94 BY Moo
PROJECT LOCATION :FORT COLLINS
NOTES: OUTLET STRUCTURE FOR POND 313
FILE NAME: MIRAOUT
CHECK FOR 100 YEAR WATER SURFACE ELEVATION Qreleaoe- 16.20 cfa
START AT HLEV. = 69.735 FEET
DELTA HEAD . 0.001 FEET
HEAD HEAD HEAD SUB
ELEV. OVER LOWER OVER UPPER OVER WEIR TOTAL
LOWER ORIFICE UPPER ORIFICE WEIR FLOW FLOW
ORIFICE FLOW ORIFICE FLOW
ft ft cfo ft cfo ft cfo cfo
...... ...... ...... ...... ...... ...... ...... ......
69.735 3.235 7.369 0.000 0.000 0.355 8.799 16.168 +++
69.736 3.236 7.370 0.000 0.000 0.356 8.836 16.206 +++
69.737 3.237 7.371 0.000 0.000 0.357 8.874 16.244
69.738 3.238 7.372 0.000 0.000 0.358 8.911 16.283
69.739 3.239 7.373 0.000 0.000 0.359 8.948 16.321
•** = approximate 100 year water surface elevation
CHECK FOR 10 YEAR WATER SURFACE ELEVATION
START AT ELEV. = 69.000 FEET
DELTA HEAD . 0.001 FEET
Qreleaoe= 6.48 cfs
HEAD
HEAD
HEAD
ELEV.
OVER
LOWER
OVER
UPPER
OVER
LOWER
ORIFICE
UPPER
ORIFICE
WHIR
ORIFICE
FLOW
ORIFICE
FLOW
ft
ft
cfs
ft
cfo
ft
69.000
2.500
6.478
0.000
0.000
0.000
69.001
2.501
6.479
0.000
0.000
0.000
69.002
2.502
6.480
0.000
0.000
0.000
69.003
2.503
6.482
0.000
0.000
0.000
69.004
2.504
6.483
0.000
0.000
0.000
**** = approximate
10 year
water surface elevation
SUB
WHIR
TOTAL
FLOW
FLOW
cfs
c£s
0.000
6.478
0.000
6.479
0.000
6.480 ****
0.000
6.482
0.000
6.483
NO.
PAGE ��
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CONSTRUCTION SEQUENCE
PROJECT: COURTYARDS AT MURAMONT FIRST FILING
STANDARD FORM C
SEQUENCE FOR 19 ONLY COMPLETED BY:MEO/Shear Engineering Corp.
Indicate by use of a bar line or symbols when erosion control measures will be installed. Major modifications
to an approved schedule may require submitting a new schedule for approval by the City Engineer.
Year 194 95
Month O N D J F M A M J J A S O
OVERLOT GRADING ***
WIND EROSION CONTROL
*.Soil Roughening
***
RAINFALL EROSION CONTROL
STRUCTURAL:
* Sediment Trap/Basin
***
* Inlet Filters
*** ***
* Straw Barriers
*** ***
* Silt Fence Barriers
*** ***
* Asphalt/Concrete Paving
***
VEGETATIVE:
* Permanent Seed Planting
* Sod Installation
*** *** ***
0
*** *** ***
STRUCTURES: INSTALLED BY: OWNER MAINTAINED BY: OWNER
VEGETATION/MULCHING CONTRACTOR: OWNER
DATE PREPARED: 1O/5/94 DATE SUBMITTED:10/7/94
APPROVED BY THE CITY OF FORT COLLINS ON:
RAINFALL PERFORMANCE STANDARD EVALUATION
PROJECT: Cori ra\s•r�r,o,+�GaNa t ,\',^'S STANDARD FORM A
COMPLETED BY: rn6 a DATE: 2�
DEVELOPED
ERODIBILITY
Asb
Lsb
Ssb,
Lb
Sb
PS
SUBBAgIN
ZONE
(ac)
(ft)
M
(feet)
M
M
T o0
I�d���. <
,�
40
► 0/0
3C5
I.3
.v00
1/
-t4
MARCH 1991 8-14 DESIGN CRITERIA
EFFECTIVENESS CALCULATIONS
PROJECT: Gaar? Y{ ,\ L Ih,ra,., ,•; C Sec oNu\ ��\�.,� STANDARD FORM B
COMPLETED BY: M 6 o DATE: z) 4
Erosion Control C-Factor P-Factor
Method Value Value Comment
�3greGrooH% I,U 114 14°USC�
SuA 0,el \,u
S1a Fca..e I,u p,r,
I'}UU;Q.1171i...1 O.U�,GIZO1 SCL �'ln,T4hy(. G'1C.V I:.Y�J1)j
MAJOR
PS
SUB
AREA
BASIN
($)
BASIN
(Ac)
CALCULATIONS
—7c6;So
316
I ,bo - (l.S$ t 3,%�) 3 5
G= golxI,S`t) } (1-0 v3 'A`3$TIl1I. f 63ZJ2
-Yp
7
knCC
+
(0,3-7x,IS)]xlou
�00
o.ltic
Sub\ = o.\
C= olx,l 7 0l
G�E.I2ALL CGlf��'U�1 i E
�2,8�
MARCH 1991 B-15 DESIGN CRITERIA
Table 813 C-Factors and P-Factors for Evaluating EFF Values.
Treatment C-Factor
P-Factor
BARE SOIL
Packed and smooth................................................................ 1.00
1.00
Freshlydisked........................................................................ 1.00
0.90
Roughirregular surface ....................................................... 1.00
0.90
SEDIMENT BASIN/TRAP................................................................. 1.00
0.50111
STRAW BALE BARRIER, GRAVEL FILTER, SAND BAG ........................ 1.00
0.80
SILT FENCE BARRIER..................................................................... 1.00
0.50
ASPHALT/CONCRETE PAVEMENT ................................................... 0.01
1.00
ESTABLISHED DRY LAND (NATIVE) GRASS .......................... See Fig. 8-A
1.00
SODGRASS................................................................................. 0.01
1.00
TEMPORARY VEGETATION/COVER CROPS .................................... 0.45121
1.00
HYDRAULIC MULCH @ 2 TONS/ACRE........................................... 0.1013'
1.00
SOIL SEALANT....................................................................0.01-0.60141
1.00
EROSION CONTROL MATS/BLANKETS............................................ 0.10
1.00
GRAVEL MULCH
Mulch shall consist of gravel having a diameter of approximately
1 /4" to 1 1 /2" and applied at a rate of at least 135 tons/acre.............. 0.05
1.00
HAY OR STRAW DRY MULCH
After olantino orass seed, apply mulch at a rate of 2 tons/acre (minimum) and adequately anchor,
tack or crimp material into the soil.
Sloe %
1 to............................................................................. 0.06
1.00
6 to 10............................................................................. 0.06
1.00
11 to 15............................................................................. 0.07
1.00
16 to 20............................................................................. 0.11
1.00
21 to 25............................................................................. 0.14
1.00
25 to 33.............................................................................0.17
1.00
> 33.......................................................................... 0.20
1.00
NOTE: Use of other C-Factor or P-Factor values reported in this table must be substantiated by documentation.
(1) Must be constructed as the first step in overlot grading.
(2) Assumes planting by dates identified in Table 11-4, thus dry or hydraulic mulches
are not required.
(3) Hydraulic mulches shall be used only between March 15 and May 15 unless irrigated.
(4) Value used must be substantiated by documentation.
MARCH 1991 8-6 DESIGN CRITERIA
O
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PAGE 23
TABLE 5.1
APPENDIX II
Backup Diagrams and Exhibits
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
Table 4; Circular Pipe Flow Capacity
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 — designate$_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
Concrete............................................................................................. 0.95
Gravel................................................................................................. 0.50
Roofs.......................................................................................................... 0.95
Lawns, Sandy Soil:
Flat<2%.............................................................................................
Average2 to 7%..................................................................................
Steep>7%..........................................................................................
Lawns, Heavy Soil:
Flat<2%.............................................................................................
Average2 to 7%..................................................................................
Steep>7%......... :................................................................................
MAY 1984 3-4
0.10
0.15
0.20
0.20
0.25
0.35
DESIGN CRITERIA
3.1.7 Time of Concentration
In order to use the Rainfall Intensity Duration Curve, the time of concentration must be
M
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,) D "2
S3
Where Tc =Time of Concentration, minutes
S = Slope of Basin, %
C = Rational Method Runoff Coefficient
D = Length of Basin, feet
Ct = 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 1.0
11 t025 1.10
26 to 50 1.20
51 to 100 1.25
Note: The product of C times Cl 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 = CtCIA
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)
1 = 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 OESIGN CRITERIA
0
50
s
t- 20
Z
w
U
W
a 10
Z
w
a
O 5
U)
w
cc 3
O'
U 2
cc
w
H
3
1
5
.1
RUNOFF
aMNNNIIII■
A
V
■iNIpim
II///CI�1111I/
=MINI'
�M
MINI
����II�■i■■Ili
�
�
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■WAWAAMMO■■■■�
MEAN
C
:I
MMM
WN:::C�
.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
PORT COLLINS
RAINFALL INTENSITY CURVE DATA FOR CITY OF PORT COLLINS
PIG 3-1
NOVEMBER 1975
INTERPRETED DECEMBER 21, 1992 BY MARK OBERSCHMIDT
SHEAR ENGINEERING CORPORATION
DO NOT INTERPRET BEYOND ROW 40
2
5
10
25
50
100
TIME
YEAR
YEAR
YEAR
YEAR
YEAR
YEAR
rrvvrrrvvvvvrrvvvrrrrvvvr»rrvr»vvrv»vr»rrrrvv•vvrr»rrvvrry
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
0.06
1.24
1.52
1.84
2.18
2.43
40 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
120
0.57
0.80
1.00
1.18
1.40
1.57
- 115
0.54
0.78
0.96
1.14
1.33
1.50
120
0.52
0.76
0.91
1.10
1.19
1.44
ROWOFFSET
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
0
"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 1.11.
e. Welded joints shall be galvanized with a rust preventive paint.
I. 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.
The curb inlets shown in the Standard Details, pages D-7, 8, 12 & 13, 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 flow 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
INLET CAPACITY REDUCTION FACTORS
Percentage of
Drainage Condition Inlet Type Theoretical Capacity
Sump or Continuous Grade ........................................... CDOH Type R-Curb
Opening
5' 80%
10, 85%
15, 90%
Street — Sump 4' Curb Opening 80%
..............................................................
Street —Continuous Grade .......................................... 4' Curb Opening 80%
Parking Lots, Medians ................................................... IArea 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 and 5-6.
The standard curb -opening is illustrated by Figure 5-4 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
SX (Cross Slope)
STREET
S Longltudinal Slope)
SIDE
B f"1
A4� ov
0
Q L m
(Gutter Flow)
CARRY
OVER
Froude No. at This Pointj _ Fw
—
Q—QI ram'— — — — — i�3
Curb
W
QI B
(Intercepted Flow)
L•
( Length of Operrng)
A 4J PLAN
Original Gutter Line
W
JC P g
�
X
3IN
Gutter Depression at Inlet
0
°
SECTION A —A
C m
o a
.a o
as
8 u
SECTION B-B_ SECTION B-B
( Straight Cross .Slope) ( Fort- Collim Standard 60 Verticcl CaG)
NOTE: THE FORT COLLINS STANDARDS HAVE
GUTTERS WITH CROSS SLOPES STEEPER THAN SX.
FI GURE. 5-4
STANDARD CURB -OPENING INLET
MAY 1984
5-12 DESIGN CRITERIA
No Text
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APPENDIX III
Portions of the Overall Drainage Study for
Oak /Cottonwoods Farm - McClellands Basin
L.`
OVERALL DRAINAGE STUDY
OAK/COTTONWOOD FARM - McCLELLANDS BASIN
FORT COLLINS, COLORADO
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The Oak/Cottonwood Farm development is located in the southeast part
of Fort Collins, immediately south of Harmony Road and west of Lemay
Avenue. The Oak/Cottonwood Farm development consists of
approximately 271.7 acres occupying the east half of Section 1,
Township 6 North, Range 69 West, of the 6th Principal Meridian. See
the Overall Drainage Plan in the back pocket of this report. This study
will deal only with the area within the McClellands Basin, or all of the
area north of the Mail Creek Irrigation Ditch. The areas south of the Mail
Creek Irrigation Ditch will be addressed under a separate study.
B. Description of Property
The Oak/Cottonwood Farm site contains two existing churches and
assorted retail businesses along Harmony Road, and an existing
psychiatric hospital along Lemay Avenue. The remainder of the existing
site, prior to the start of construction of the single family developments,
consisted of cultivated farmland and natural grasses. The Mail Creek
Irrigation Canal runs across the center of the site from northwest to
southeast. Topography north of the Mail Creek irrigation canal is
generally sloping from northwest to southeast at approximately 1 .4% .
Topography south of the Mail Creek irrigation canal is generally sloping
from north to south at approximately 5.7%. Mail Creek and Fossil Creek
is located in the southern part of the development, generally running
from west to east. A small portion of the site, planned for residential
development, is located south of Mail Creek
Three separate single family developments have been designed and
construction started within the Oak/Cottonwood Farm development; The
Upper Meadow at Miramont First and Second Filings, and Castleridge
P.U.D.. Four other developments have been proposed within this Overall
development, and either Final or Preliminary plans submitted to the City
for review; Miramont Third Filing, Oak Hill Apartments, Tennis Center,
and the Courtyards at Miramoht. The developments mentioned above
have been shown schematically on the overall Drainage Plan included in
I.. i the back of this report. Reference should be made to each individual
Drainage reports for more specific detail associated with each project.
I
II. DRAINAGE BASINS
A. Major Basin Description
The Oak/Cottonwood Farm site lies within the McClellands Basin, the
Mail Creek Basin, and the Fossil Creek Basin per the vicinity map in the
appendix. The major basin delineations are also shown on the Overall
Drainage Plan.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
The City of Fort Collins Storm Drainage Design Criteria is being used for
the subject site.
B. Development Criteria Reference and Constraints
The portion of the Oak/Cottonwood Farm site within the McClellands
Basin historically drains southeasterly under Lemay Avenue and through
the adjacent Oakridge development. Downstream improvements have
been completed within the Oakridge development to accept a maximum
storm water runoff of 119 cfs (0.5 cfs per acre) from the
Oak/Cottonwood Farm site per the report titled "Master Drainage Study
for the Oakridge Business Park". Detention requirements for the
McClellands Master Drainage Basin have been established to be 0.20
cfs/acre for the minor, or 10 year storm event, and 0.5 cfs/acre for the
major, or 100 year storm event. Detention ponds ultimately designed for
the area of Oak/Cottonwood Farms within the McClellands Basin should
attempt to be designed to allow for multiple release rates to
accommodate both release requirements. The detention requirement for
the minor storm is not a requirements within the Oak/Cottonwood Farm
site (to be further explained later in the report).
C. Hydrological Criteria
The SWMM model, as acquired from the Urban Drainage and Flood
Control District, was utilized for lie portion of the Oak/Cottonwood Farm
site within the McClellands Basin. The adjacent Oakridge development
utilized SWMM modeling for the 10 year and 100 year storm events with
a different model for each storm event. Due to the number of existing
and proposed detention facilities within this portion of the subject site,
and the need to determine the size of the future detention ponds, a new
SWMM model was developed for the Oak/Cottonwood Farm site. The
2, 5, 10, 25, 50, and 100 year rainfall events, which were obtained from
the City of Fort Collins and required to be run by the City, were run for
a new single SWMM model developed for the site. The new SWMM
model was not. incorporated into the existing Oakridge site SWMM
model.
D. Hydraulic Criteria
All calculations with this report have been prepared in accordance with
the City of Fort Collins Storm Drainage Criteria.
E. Variances from Criteria
No variances are being sought for the Oak/Cottonwood Farm site.
IV. DRAINAGE FACILITY DESIGN - OVERALL DRAINAGE STUDY FOR
OAK/COTTONWOOD FARM
A. General Concept
As development continues to occurs within the Oak/Cottonwood Farm
site, the drainage concepts shown on the Overall Drainage Plan in the
back pocket of this report should be followed. Specific detention
requirements exist in the McClellands Basin, where as the Mail Creek
Basin and the Fossil Creek Basins allow for undetained storm water
runoff directly to Mail Creek and to Fossil Creek.
B. Specific Details
To the East of the Oak/Cottonwood Farm property, within the
McClellands Basin, is the Oakridge Business Park and Residential
Community. The appendix includes portions of the text from the Master
Drainage Study for the Oakridge Business Park. Three existing 36" pipes
lie beneath Lemay Avenue, approximately 3000 feet south of Harmony
Road, which in effect direct the Oak/Cottonwood Farm storm water
runoff to the Oakridge property. Within the Oakridge development, the
Storm Water Management Model (SWMM) was utilized to model the
3
anticipated storm water runoff. Within the Oakridge Master Drainage.
Study, SWMM modeled the proposed Oak/Cottonwood Farm
development with a 100 year developed storm water release rate of 0.5
cfs per acre. The Oakridge development 10 year SWMM model did not
include any site specific detention requirements for the Oak/Cottonwood
Farm development. This is due to the existing detention pond within the
Oakridge development and its ability to control and adequately bring the
10 year release rate within the McClellands Basin, at this location, to the
allowable 0.2 cfs per acre discharge. Thus the 10 year detention control
of 0.2 cfs per acre within the McClellands Basin is not necessary for the
Oak/Cottonwood Farm development.
The SWMM model developed for the Oakridge development consisted of
two different models, one model for the 10 year and one model for the
100 year storm events. The numbering scheme is different in the two
SWMM models. The City Stormwater Utility now requires that SWMM
models route the 2, 5, 10, 25, 50, and 100 year rainfall events. Due to
the differences in the Oakridge SWMM model elements for the different
storm events, and the complexity of the Oak/Cottonwood Farm
development, a new SWMM model has been developed, independent of
the Oakridge SWMM model, for the Oak/Cottonwood Farm development.
The new SWMM model utilizes the same hydrological assumptions and
criteria that the Oakridge SWMM model utilized, but the numbering of the
basins and elements has changed.
The Oak/Cottonwood Farm SWMM model study area was broken up into
sub -basins per the developments proposed in each sub -basins as shown
on the Overall Drainage Plan. Included in the appendix is a SWMM
schematic for the Oak/Cottonwood Farm development. In addition to the
SWMM schematic, the SWMM model numbers have been included on
the Overall Drainage Plan for ease of reference. The SWMM model
includes previously developed areas draining through the
Oak/Cottonwood Farm site as these areas also drain to the three existing
36" pipes under Lemay Avenue. Information was obtained on the
drainage characteristics of the existing developments within the SWMM
area modeled.,The SWMM model was calibrated using the basin widths
as a physical parameter, per the City of Fort Collins Stormwater Utility.
For the Pace Membership Warehouse, the Builders Square site and the
Steele's Market site numerous detention ponds exist on these properties.
The two basins defining these existing developments were not broken
down to show each of the numerous detention ponds on the sites. The
basins were calibrated to release runoff to the Oak/Cottonwood Farm
development at the projected design rates of these sites. For the
Collinswood Treatment Complex immediately north of the existing 36"
0
Pipes, the SWMM model was also calibrated to release runoff from this
property at a target design rate for the site.
Once the SWMM model was calibrated for the existing developments
within the study area, the study area was evaluated in reference to the
required 0.5 cfs per acre ,100 year storm event, release rate. Future
detention pond sites were planned with the Client to the best extent
possible in order to determine how the study area would drain. Each
detention pond system was modeled with a release rate of 0.5 cfs per
acre during a 100 year storm event.
The off -site residential neighborhood to the west of the Oak/Cottonwood
Farm site drains southeasterly and through the first planned development
in the Oak/Cottonwood Farm site. The extent of this off -site area was
estimated to be 14.75 acres per the Mail Creek Hydrologic Information
drawing by Water Engineering & Technology, Inc. dated 2-29-90. For
this report, it has been assumed that the separation between the Mail
Creek Basin and the McClellands Basin has been shown correctly on the
Mail Creek Hydrologic Information drawing. Per a conversation with the
City Stormwater Utility, it was learned that within the Mail Creek Basin
it was assumed during storm events that the Mail Creek Ditch is flowing
full and land above the Ditch will sheet flow storm water directly over
the Ditch and downstream to Mail Creek. Per a meeting with John Moen
(Ditch Rider of the Mail Creek Ditch) the Mail Creek irrigation ditch has
no available capacity for storm water runoff and during a storm event
storm water runoff sheet flows directly over the Mail Creek irrigation
ditch. This off -site storm water runoff from the 14.75 acres of existing
residential neighborhood only has a minor impact to the Oak/Cottonwood
Farm site and these off -site flows are collected in the First Filing
development as .discussed later in this report.
Included on the Overall Drainage Plan is a summary table of the proposed
detention ponds. their required capacities, and their maximum allowable
release rates (Summarized below). The detention pond capacities were
sized with the anticipated type of development contributory to the ponds
at the time of this report. As the development of these sites progresses
to final design, the SWMM model should be updated to finalize the size
of each detention pond per its final type of development. Outflow from
each pond shall utilize a rating curve based on the ultimate pond
configuration. The rating curves for detention ponds 321 (Associated
with Miramont First Filing), and.Detention pond 340 (Associated partly
with Miramont Second Filing) have been included in the model with this
update.
A
Minimum
Maximum
Detention Pond
Storage
Outflow
303
0.6 ac.ft
3.0 cfs
306
1.0 ac.ft
4.0 cfs
1
313 (Sc-% sedgy)
4.2 ac.ft
22.0 cfs
321 61� RB;D
3.5 ac.ft
7.0 cfs
322 ;1i4
2.1 ac.ft
11.0 cfs
340 +- eo
4.9 ac.ft
66.0 cfs
Detention ponds 322 and 306 have not been modeled with a rating
curve, but with a pipe outlet preliminarily sized to approximate a release
rate of 0.5 cfs per acre. As final design occurs around these ponds, a
rating curve should be built into the model to better approximate actual
conditions. The reader should be advised that with the insertion of a
rating curve into the model, the required minimum pond size can be
expected to be increased.
With this update, the SWMM model parameters for Basin 201 were
modified to reflect a higher impervious factor. This caused the require
storage volume of Existing pond 321, located between Miramont 1st and
2nd Filing to increase. A drainage certification has been performed on
Miramont 1 st Filing, and the actual volume of the pond constructed was
found to be approximately 3.8 ac.ft., or large enough to account for this
change in mode! parameters.
The model also shows a detention requirement for conveyance elements
301, 303, 307, and 311. The, following methodologies were applied
during the modeling of these conveyance elements:
Element 301 - Steele's sites (Basin 204)
Per the Harmony Market 3rd Filing drainage report, the designed
release rate at this location is 24 cfs. No SWMM model rating
curves are available for the detention ponds existing within this
basin. For the SWMM modeling herein, a conveyance element was
derived which modeled the maximum release rate of 24 cfs
occurring from this basin, and caused water over and above this
release rate to be detained at the upstream end of the conveyance
element. This way of modeling the existing facilities enables the
model to realize the intended release rate at this location so the
downstream system analysis can be completed utilizing the full
upstream impact. Per the SWMM Model output, the water
detained at conveyance element 301 is 1.3 ac.ft.. The actual
n
detention volume available within basin 204 based on field
verification is 3.4 ac.-ft.. Because the existing available volume
is greater than the required volume per the SWMM Model, this
method of modeling Basin 204 is adequate.
Element 307 - Pace and Builders Square (Basin 203)
Per the Harmony Market 2nd Filing drainage report, the designed
release rate at this location is 6 cfs. No SWMM model rating
curves are available for the detention ponds existing within this
basin. For the SWMM modeling herein, a conveyance element was
derived which modeled the maximum release rate of 6 cfs
occurring from this basin, and caused water over and above this
release rate to be detained at the upstream end of the conveyance
element. This way of modeling the existing facilities enables the
model to realize the intended release rate at this location so the
downstream system analysis can be completed utilizing the full
upstream impact. Per the SWMM Model output, the water
detained at conveyance element 307 is 5.3 ac.ft.. The actual
detention volume available within basin 203 based on field
verification is 8.0 ac.-ft.. Because the existing available volume
is greater than the required volume per the SWMM Model, this
method of modeling Basin 203 is adequate.
Element 303 - Church Site (Basin 205)
No SWMM model rating curves are available for the detention pond
existing within this basin. For the SWMM modeling herein, .a
conveyance element was derived which modeled the maximum
release rate of 0.5 cfs/acre occurring from this basin per the
criteria within the McClellands Basin, and caused water over and
above this release rate to be detained at the upstream end of the
conveyance element. This way of modeling the existing facilities
enables the model to realize the intended release rate at this
location so the downstream system analysis can be completed
utilizing the full upstream impact. The actual detention volume
available within basin 205 by a field verification is outside the
scope of this project.
Element 311 - Collinswood Treatment Complex (Basin 207)
No SWMM model rating curves are available for the detention pond
existing within this basin. For the SWMM modeling herein, a
conveyance element was derived which modeled the maximum
7
release rate of 0.5 cfs/acre occurring from this basin per the
criteria within the McClellands Basin, and caused water over and
above this release rate to be detained at the upstream end of the
conveyance element. This way of modeling the existing facilities
enables the model to realize the intended release rate at this
location so the downstream system analysis can be completed
utilizing the full upstream impact. The actual detention volume
available within basin 207 by a field verification is outside the
scope of this project.
A network of storm sewers and channels exist along the west side of
' Lemay Avenue, and along the westerly property line of the Hospital and
Church, and these systems transports stormwater runoff from the Pace
Membership Warehouse, Builders Square, Steele's Market, Church, and
' Collinswood Treatment Complex to the existing 36" pipes under Lemay
Avenue. As the Tennis center project is final designed, those existing
conveyance elements, particularly those associated with the easterly
' property line of the Tennis center should be examined to determine the
effects of development. This system will need to be extended across a
' portion of the Oak/Cottonwood Farm site to the existing 36" pipes. For
master planning purposes, the outlet to detention pond number 313 is
proposed to be connected into the existing storm sewer system on the
west side of Lemay Avenue and routed directly into the existing 36"
' culvert under Lemay Avenue.
' The original Overall Drainage Plan showed Detention pond being located
over towards the southwesterly corner of the existing Hospital site.
During construction of The Upper Meadow at Miramont first Filing, it was
' determined that pond 313 would be located adjacent to Boardwalk Drive.
This shift caused the contributory area to Pond 313 to decrease, and the
contributory area for Pond 340 to increase. The future Park site will now
' have detention provided within Detention pond 340. The shift in the
location of the pond was discussed with the Parks and Recreation
Department. Detention pond 313 will also have a permanent water
surface to store irrigation water forthe adjacent residential developments.
The SWMM model and the overall drainage plan reflect the shift in pond
313.
With the development of the first residential community within the
Oak/Cottonwood Farm Development, titled The Upper Meadow at
Miramont First Filing, the construction of Boardwalk Drive from Oakridge
Drive to Lemay Avenue was required. With the development of
Boardwalk Drive, and the need for the developable land lying west and
southwest of Boardwalk Drive to drain under Boardwalk Drive and to the
existing 36" culverts under Lemay Avenue, a second drainage system
was master planned along Boardwalk. A series of storm sewers and
open channels was constructed along Boardwalk from the existing 36"
storm sewers under Lemay Avenue, upstream to Oakridge Drive. A
detention pond was planned and partially constructed for the property in
the northwest corner of the Oak/Cottonwood Farm site with an 18"
storm sewer outlet to release runoff at the required 0.5 cfs per acre. On
the Overall Drainage Plan a storm sewer system has been shown in
Boardwalk Drive to transport the northwestern detention pond outlet
flows to the downstream storm sewer and open channel system. This
system was built according to this overall plan. At the time of this
update, Detention pond 322 will outlet onto Boardwalk Drive and be
conveyed by curb and gutter to the storm sewer system (a combination
of pipes and open channels). An agreement between GT Land and Front
Range Baptist Church exists that limits the release from basin 202 to
5.57 cfs for the 10 year storm event and 11.45 cfs for the 100 year
storm event (Based on the capacity of Boardwalk Drive Curb and Gutter).
Detention pond 321 will outlet on the west side of Boardwalk and be
conveyed downstream to Lemay Avenue by the same series of pipes and
open channels. A copy of this agreement has been included in the
appendix of this report.
The storm sewer system in Boardwalk Drive was sized to carry the 25
year storm runoff event due to the location of the proposed high and low
points in Boardwalk Drive. As storm events occur greater than the 25
year storm event, minor ponding is planned to occur at the low points.
In the event the storm sewer systems become plugged, overflow swales
have been provided to redirect storm water runoff to the proposed open
channel system to safely convey storm water runoff to the proposed
detention pond number 340 and the existing 36" culverts under Lemay
Avenue.
In order to achieve the required 0.5 cfs per acre release at the existing
36" culverts under Lemay Avenue, detention pond number 340 is
planned immediately upstream of the 36" culverts. During final design
of this detention pond, the hydraulics of the connection from the
detention pond to the existing 36" culverts will need to be worked out
to ensure the 0.5 cfs per acre release rate is not exceeded. A preliminary
rating curve based on the proposed ultimate design of this pond has been
included in the model, and the calculations are included in the appendix
of this report. The rating curve included is based on the existing 36"
pipes under Lemay being built according to plan, and that rating curve is
a preliminary design only. As pond 340 is finalized, these existing 36"
culverts will need to be reevaluated and the new rating curves based on
E
actual field conditions. The pond 340 size will need to be reexamined &
downstream flows to Oakridge will need to be decreased to 119 cfs (the
model currently shows a release to Oakridge of 129 cfs). Pond 340 will
need to be permanently designed when the area of the Overall plan
known as the Hamlet is developed, (the Hamlet was defined as a part of
the Miramont Phase 3 Preliminary Plan), or basin 213 is developed.
V. EROSION CONTROL
A. General Concept
The Oak/Cottonwood Farm site lies within the Moderate and High Rainfall
Erodibility Zone and within the Low to Moderate Wind Erodibility Zone
per the City of Fort Collins zone maps. Per the City of Fort Collins
Erosion Control Reference Manual for Construction Sites, at the time of
final design of the site, the erosion control performance standard will
need to be calculated and appropriate measures taken to control erosion
from the site.
VI. CONCLUSIONS
A. Compliance with Standards
All computations within this report have been completed in compliance
with the City of Fort Collins Storm Drainage Design Criteria.
B. Drainage Conceit
The proposed drainage concepts adequately provide for the transmission
of developed on -site runoff to the proposed detention facilities. The
sizes and locations of each detention pond within the study area will
enable the Oak/Cottonwood Farm site to develop in conformance with
the McClellands, Mail Creek and Fossil Creek Basin requirements. The
street systems will need to convey storm water runoff to the
downstream outlets without exceeding the capacities of the street
conveyance systems. If the street capacities are exceed, storm sewer
systems may be required to transport storm water runoff to the
downstream outlets. Per the City criteria, only the initial storm event is
required to be transported to the downstream outlets by storm sewer
systems once the street systems become overloaded. City requirements
for the transportation of the 100 year developed flows must also be
observed and complied with. Each of the on -site detention ponds in the
McClellands Basin will be required to provide one foot of freeboard and
10
an emergency overflow outlet in the event the outlet structure and pipe
become plugged. All on -site drainage facilities will be maintained by a
homeowners association, or other entity created by the developer. The
City of Fort Collins will maintain the storm sewer systems located within —
dedicated right-of-ways.
1
i
REFERENCES
1 . Storm Drainage Design Criteria and Construction Standards by the City of Fort
Collins, Colorado, May 1984.
2. Erosion Control Reference Manual for Construction Sites by the City of Fort
Collins, Colorado, January 1991.
3. Master Drainage Study for the Oakridge Business Park in Fort Collins, Colorado,
by RBD Inc., September 1990.
4. Final Drainage and Erosion Control Study for The Upper Meadow at Miramont
First Filing, Fort Collins, Colorado, by RBD, Inc., November 10, 1992.
5. Final Drainage and Erosion Control Study for The Upper Meadow at Miramont
Second Filing, Fort Collins, Colorado, by RBD, Inc.
6. Final Drainage and Erosion Control Study for Castleridge at Miramont First
Filing, Fort Collins, Colorado, by RBD, Inc., October 7, 1993.
7. Preliminary Design Report for Mail Creek Stability Study, by Lidstone and
Anderson & TST, Inc., January 28, 1994.
8. Preliminary Drainage and Erosion Control Study for Miramont 3rd Phase P.U.D.,
Fort Collins, Colorado, by RBD, Inc., February 4, 1994.
9. Final Drainage and Erosion Control Study for Miramont P.U.D. Third Filing, Fort
Collins, Colorado, by RBD, Inc., April 4, 1994.
10. Preliminary Drainage and Erosion Control Plan for the Oak Hill Apartments, Fort
Collins, Colorado, by RBD, Inc., February 4, 1994
11
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APPENDIX IV
Stuffer Envelope
Final Grading Plan
Drainage and Erosion Control Plan
Preliminary Drainage and Erosion Control Plan (Overall area; for reference)
Erosion Control Security Deposit Requirements
October 10, 1994
Project No: 1410-01-94
Re: EROSION CONTROL SECURITY DEPOSIT REQUIREMENTS:
The Courtyards at Miramont P.U.D. Second Filing; Fort Collins, Colorado
A. An erosion control security deposit is required in accordance with City of Fort Collins
policy (Chapter 7, Section C : SECURITY; page 7.23 of the City of Fort Collins
Development Manual). In no instance shall the amount of the security be less than
$1000.00.
1. According to current City of Fort Collins policy, the erosion control security deposit
is figured based on the larger amount of 1.5 times the estimated cost of installing
the approved erosion control measures or 1.5 times the cost to re -vegetate the
anticipated area to be disturbed by construction activity.
a The cost to install the proposed erosion control devices for the Courtyards at
Miramont P.U.D., Second Filing is $7,562.50. 1.5 times this estimate is
$11,343.75.
i. unit prices have been provided by Connell Resources.
b. Based on current data provided by the City of Fort Collins Storm Water Utility,
and based on an actual anticipated net affected disturbed area during
construction of the Courtyards at Miramont P.U.D., Second Filing
(approximately 8.66 acres) we estimate that the cost to re -vegetate the disturbed
area will be $5,629.00 ($650.00 per acre x 8.66 acres). 1.5 times the cost to re -
vegetate the disturbed area is $8,443.50.
i. The 8.66 acres is the actual area of the Courtyards at Miramont P.U.D.,
Second Filing housing project. The area of Tract B (the existing detention
pond; 1.974 acres) has been deducted from the overall platted area of 10.635
acres.
ii. The $650.00 per acre for re -seeding sites of less than 10 acres was quoted
to us by the City of Fort Collins Storm Water Utility staff.
CONCLUSION:
The erosion control security deposit amount required for this project will be $11,343.75.
Because of the anticipated construction phasing, separate erosion control deposit amounts
may be established for the phase to be constructed.
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226.5334
October 10, 1994
Project No. 1410-01-94
Basil Hamdan
City of Fort Collins Storm Water Utility
P.O. Box 580
Ft. Collins, Colorado 80522
Re: The Courtyards at Miramont P.U.D., Second Filing; Fort Collins, Colorado
Dear Basil,
Attached is the erosion control security deposit estimate for Courtyards at Miramont P.U.D.,
Second Filing.
ESTIMATE 1:
1,175 LF of silt fence at $3.50 per LF
15 Haybale dikes at $90.00 each
TOTAL ESTIMATED COST:
ESTIMATE 2:
re -vegetate the disturbed area of 8.66 acres at $650.00 per acre
TOTAL ESTIMATED COST:
$ 6,212.50
$ 1.350.00
S 7,562.50
x 1.50
$ 11,343.75
5 629.00
$ 5,629.00
x 1.50
S 8,443.50
The total required erosion control security deposit will be $ 11,343.75 if paid at one time.
Because of the projected phasing of the project, security deposits may be made based on
individual estimates for each phase, or phases, of construction.
If you have any,questions, please c9l] at 226-5334.
Brian W. Shear, V�
Shear Engineering
BWS / be
cc: Albrecht Homes
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
THE UPPER MEADOW .
ttue P=1W
LEGEN
t4 T m 32 J� I ]BASIN DESIGNATION
"\ e / - J I SIIB BASIN BOUNDARI'
3B / )
B sF`.-; Y- Ia SWBASLN DESIGNATION
13 33 F re t" "1 1 + �, CONCENTRATION PONT
49 3t eEi j\"\..1"•"�,S I _ 1 ���all FLAW DIRECTION
ti 9 30 12 pcn
OAR -COTTONWOOD )ARMS DETENTION POND
10
U651GNATION
\ t1 pS 3 � N
'II If PAA#rNEp)Ts P .D. # ` EROSION CONTROL LEGEND
De
i GRAVEL INLET FILTER
Or OF
1
\ i 1
1 �1 1 \; A ♦l� �. SILT FENCE
n� \\, �'•� \ y2 _ 5 1 ' / { \` �r RIP RAP APRON
1 _ ` .. .. ..
AREA INLET FILTER
•^� N/,� XISTING TRO IC
PROM!
v 12 Be WFFI-6 AON
/*Oy b r ..'� /`orER'.,°' t �• T _1 STRAW BALE DIKE
a
i 3 93 am. Ni nr dtJ I ' '
IT/1 w _ 10 ,y 'II �v' GRAUArG. AND DRAINAGE GENERAL NOTES
A\I rmcvr ItF Collura I IJ II,T IT, ro,rdbl rFrr III 1 1\y
fnroey {y 61 su moral S fxllitw, rmL Mman near,
_
EC DRAINAGE e / 3 ^\ 1 lir - -y I�- /�`'� \ 11 d -a W ari.
/ Uilutt FAYMFxr� \ 1 \ 0 �. .��J ( /J� ^I III
nfro
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V 1
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ari ed wl h Cymt Yw AeAHIy F r f
f NWIh Water
NOTE
- r O l r ou wl P worn -PE az OW CbI c k
/ luIcn s \\ 3 \ _ 22 / ® MIRA MONT A P s 1 Pe c l m xozzz lew mention
ALL _ P dFnlmx Scc' r1 NIJ
UNLE99 OLXEIIW E W \ i e - r , 1 ( Fez 1�
PROPOSED PARK y / �J I TENNIS
/ uoreG ZONED rp �,\\ /3 \. — -� {� -� 23 I ( L CENTER �. \\yn B if s� eo s w 10 11 er LH m sm.
` PARCEL P \ \ \ ITAI
;\ 3 i
( 24 s fI. r fI UIdS
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U 11 I b III
��y gip p �ppppN V l l l l l l M W - FI f N
PIJflAHil ®R 1/d.,Ttl-FALLfeflfld.,d \ 0 1 \ Pra tl 1
1 e - 1 Sfo P h w Lpe. ed Y Jan.l rarnc .uheasaav A A.I AM' / / / y. ��8� _ _ ,�s:_U b. r
EXISTING I ,II
DETENTION Emwr m,
POND PHASEVII Crl \
- _ ZONED bP 1.o A.,
THE COTTAGES AT MIRAMONT P.U.D.
I� (PHASE W I 1 \ \
I
r�i N
I I� 11
,A-
I
FUTURE
EEFLOPMENT
I I O
III
I--
_ I o
,a :fir I 0 6
(BY OTHERS)
M�9RMN SEWER— - -
MR BY OTHERS
LEMAY AVENUE
I Li
MIRAMONT PHASE VI
REVISIONS Date _ MRaw 1ART or".n QUENT.. NnOF
SHEAR ENGINEERING CORPORATION """ PREAORARY MASTER DRAINAGE AND EROSION CONTROL PLAN RRP,m HG. $HIES He.
°" - - •YDescriptim Held Book Checked IUNS ALBRECHT HOMES FIRM SO. COLLEGE AVE, SUITE 12. PORT DOWNS. COLORADO COURTYARDS AT MIRAMONT P.U.D.
one-1 1
. — w o.Fhpm^ 1410-01-94
Ann—. Ernumerable
Scala 1' 1w Approved EMS PHONE: (303) 226-3334 (303) 428-4451 FORT COLLINS COIARADO
FOR REFERENCE ONLY