HomeMy WebLinkAboutPOUDRE VALLEY HEALTH SYSTEM HARMONY CAMPUS, FREESTANDING EMERGENCY DEPARTMENT - PDP/FDP - FDP140029 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTn•
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APPENDIX A
VICINITY MAP
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APPENDIX
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D. Erosion Control Concept
Proposed erosion control concepts have been provided for and adequately provide for
the control of wind and rainfall erosion from the proposed development. Through the
construction of the proposed erosion control concepts, the City of Fort Collins
performance standards will be met. The proposed erosion control concepts presented
in this report and shown on the erosion control plan are in compliance with the City
of Fort Collins Erosion Control Criteria.
Erosion Control Escrow Estimate
The Erosion Control Escrow Estimate for the subject property is approximately
$16,588.00. Please refer to Appendix E for this calculation.
REFERENCES
1. Storm Drainage Design Criteria and Construction Standards by the City of Fort
Collins, Colorado, May 1984, Revised January 1997.
2. Erosion Control Reference Manual for Construction Sites by the City of Fort
Collins, Colorado, January 1991, Revised January 1997.
3. East Harmony Portion of McClellands Basin 100-Year Master Plan, by Icon
Inc., Fort Collins, Colorado, August 1999.
4. Final Drainage and Erosion Control Study for the PVHS Harmony Campus, by
the Sear -Brown Group, dated March,1999.
5. Final Drainage and Erosion Control Study for the PVHS Master Infrastructure
Plan, by Stantec, dated April 14, 2004.
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be implemented for the private stormwater improvements' operations/ maintenance
procedures for the project on an annual or bi-annual basis:
1) Storm Sewer Inlets, pipes and flared -end -sections, curb cuts and concrete
sidewalk culverts/chases, structures, manholes, and the water quality/ outlet
control structures shall be cleaned through the removal of debris and
sediment from the associated items to allow for adequate drainage through
the site to the proposed detention facility
2) Sedimentation/ silting shall be removed to allow for adequate drainage along
the bottom of the swales and LID pre -sedimentation basins. Grass scrubbing
along the bottom of the LID pre -sedimentation basins may be required to
remove sediment and promote grass growth.
3) Re -vegetation through the use of Natural Seeding/ Sod shall be provided for
disturbed areas and other permanent erosion controls shall be provided for
areas where erosion has taken place and requires remediation back to the
proposed condition shown in the plans
The Stormwater Operating/ Maintenance Procedures listed above are guidelines to
the minimum procedures that shall be implemented for the site, with these and
additional measures being utilized on an as -needed basis.
B. Drainage Conceut
The proposed drainage concepts presented in this study and shown on the utility
plans adequately provide for the transmission of developed on -site runoff to the
existing detention pond, located south of the subject site. The combination of the
existing and proposed storm conveyances will provide for the 100-year. developed
flows to reach the existing detention pond. The existing release rate of the existing
pond will be adhered to.
If groundwater is encountered at the time of construction, a Colorado Department of
Health Construction Dewatering Permit will be required.
C. Storm Water Ouality
The final design has addressed the water quality aspect of stormwater runoff. The
existing grass -lined detention pond and extended detention will provide an
opportunity for stormwater pollutants to filter out of the stormwater runoff before
flows are directed downstream. Furthermore, the LID items presented in this report
for the proposed site provide for additional water quality and treatment of runoff,
prior to flows being directed downstream.
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LID measures are provided for through the conveyance of 2.82 acres (of the 3.54 acre
total) over and through the porous paver areas and into the proposed LID pre -
sedimentation basin. The footprint of the LID basin is approximately 2,900 square
feet, with a depth of approximately 1.0'.
It's important to note that with 2.82 acres of the 3.54 acre site area (80% of site area)
being conveyed over and through the porous pavers and LID basin, and because
water quality is already provided for in the existing detention pond, the project
exceeds that normally required for water quality and LID treatment.
The LID basin, shown and called out in the civil utility plans, provides. for
approximately 1.0' of ponding depth, prior to the basin overflowing and spilling
south/ southeast and into the storm drainage swales and eventually into the existing
detention pond. Please refer to Appendices C and F, and sheets C-008 and C-010 of
the civil utility plans, for details on the porous paver areas and LID basins.
VI. EROSION CONTROL
A. General Concept
The subject site lies within the Moderate Rainfall Erodibility Zone and the Moderate
Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists
for erosion problems during construction, but should be minimal after completion of
proposed development. Silt fence will be installed along the north, east, south, and
west sides of the site to prevent sediment from leaving the site. A tracking pad will
also be placed at center entrance/exit to the site. Gravel inlet filters will be placed at
proposed curb cuts, with straw wattles installed at the proposed pipe and drain inlets
and wattle check dams to mitigate the build-up of sediment and transport of debris
into existing Pond 593. Riprap and erosion control fabric will also be utilized at
concentration points (curb cuts) and sloped areas, as shown in the plans, to minimize
erosion and increase soil stabilization.
VII. 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.
The City of Fort Collins Storm water Utility will not maintain the on -site storm
drainage facilities within the subject site. The owners of the subject site will
maintain their on -site storm drainage facilities on a regular basis. The following shall
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OS1
Offsite Basin OS 1 contains 1.37 acres, and is the remaining balance of the basin area
from existing basin 105, from the PVHS Drainage Masterplan. Runoff from west
side of Basin OS 1 will flow east along the south side of the private drive and into the
existing swale, directly east of the private drive. Runoff from the east side and
majority portion of OS 1, will be conveyed overland to the east/ southeast through the
existing grass and into existing swale, which conveys runoff south and into existing
Pond 593.
C. Detention Ponds
No detention pond(s) are required for the subject site, as detention and water quality
are provided for in the existing detention pond (Pond 593), which was constructed
with the PVHS Harmony Campus Infrastructure.
D. Street Capacities
The street capacity calculations are not required for the subject site, as no new public
street construction will be built with this project. However, curb cut capacities have
been analyzed and calculations provided in Appendix D of this report.
V. STORM WATER QUALITY
A. General Concept
The water quality of stormwater runoff must be addressed on all final design utility
plans. Therefore, Best Management Practices for the treatment of stormwater runoff
for the subject site will include grass -lined swales with a soft pan, porous pavers, LID
pre -sedimentation basin, and the utilization of the existing grass -lined detention and
water quality pond south of the site. These water quality features will provide a
mechanism for pollutants to settle out of the stormwater runoff before flows are
directed to the McClellands Drainage Basin.
B. Specific Details
Best Management Practices (BMP) for the treatment of storm water runoff has been
incorporated into the final design for this project. This will include continued
utilization of extended detention in the existing, offsite detention pond, in which the
grass -lined pond will trap sediment, prior to releasing controlled flows downstream.
The existing detention facility has adequate capacity and will continue to provide
water quality and detention for the developed condition of the subject site, prior to
releasing flows downstream.
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Basin 4
Basins 4 conveys runoff from the north half of the private drive and drains east in
existing and proposed curb and gutter which discharges to a riprap pad, before
draining northeast and into the LID basin in basin 8.
Basin 5
Basins 5 conveys runoff from the building roof to roof drains and is piped east to a
12" HDPE storm pipe, which discharges to the soft pan swale in basin 8. Three roof
drains will be located within basin 5 and will overflow scuppers, in the event of
clogging or an overflow situation.
Basins 6- 7
Basins 6 and 7 convey runoff from the eastern side of the parking lot overland to the
east across the parking lot and through porous pavers to design points 6 and 7, where
3' curb cuts, in each basin, convey runoff into the soft pan in basin 8. Flow is then
conveyed south and into the LID/pre-sedimentation basin.
Basin 8
Basin 8 conveys runoff from the landscaped area north of the building and east ofthe
parking lot to the LID Basin. A drainage swale conveys runoff from the north side of
the building to the east, which combines with flow basin 5, before flowing south in
the soft pan swale. Runoff from basin 6 and 7 combines in the soft pan swale before
entering the LID basin. The proposed soft pan swale will consist of a 50/50 mix of
sand and topsoil and will be 2' wide x l' deep.
Runoff from basins 1, 2 and 3 will combine at design point 3, where a proposed
double 12" RCP storm pipes will convey runoff east and into the LID basin.
The runoff from basins 1-8 combines in the LID Basin and is directed to a proposed
24" perforated HDPE drain basin riser with 24" Nyloplast Standard H-20 grate. The
LID basin is designed to provide a ponding depth of approximately 1.00' and allow
pollutants and sediment to settle out of the runoff, prior to spilling southeast into the
offsite drainage channel and into existing Pond 593.
Basin 9
Basin 9 conveys runoff from the narrow, landscaped area along the west side of the
building and parking lot. Runoff will overland flow west to Snow Mesa Drive and
enter existing curb and gutter. It is not possible to drain this area into the lot due to
grading constraints of the site. The basin area disturbance will be limited to grading
near the lot and building as it is currently landscaped with sod trees and small walls.
Runoff will drain to the street inlet in Snow Mesa Drive and discharge to the existing
Pond 593 via storm sewer.
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the area being routed to and through the porous pavers and LID basin exceeds the
50% requirement for LID treatment, and because water quality is already provided for
in the existing detention pond, the project exceeds that normally required for water
quality and LID treatment.
The LID basin, shown and called out in the plans, provides for a minimum of 1' of
ponding depth, prior to the basin overflowing and spilling south and into the existing
drainage swale and ultimately entering the existing detention pond. It's important to
note that 1.47 acres of the site runoff will filter through a 2' wide soft pan before
entering the LID basin. Additionally, 0.45 acres will drain to porous pavers and drain
through the underlying porous paver media enhancing water quality. The LID basin
will contain a 24" Nyloplast Standard H-20 grate with perforated riser to enhance
infiltration, prior to flow overtopping the basin and entering the drainage swale and
existing detention pond. Please refer to Appendix C and sheets C-008 and C-010 of
the civil utility plans for details on the porous paver areas and LID basin.
B. Specific Details
Basin 1
Basin 1 conveys runoff from a small portion of the roof overhang and the parking lot
southeast across the parking lot and porous paver area towards design point 1, where
a 5' curb cut conveys runoff into a drainage Swale in basin 3.
Basin 2
Basin 2 conveys runoff from a small portion of the roof overhang and parking lot
overland to the southeast and across the parking lot towards design point 2, where a
6' curb cut conveys runoff through a riprap channel and 6' sidewalk culvert and into
a grass -lined swale in basin 3. The upper portion of basin 2 (approximately half the
basin area) will overland flow to a 3' curb cut and pass through a 3' sidewalk culvert
and concrete chase before reaching design point 2.
Basin 3
Basin 3 consists of a grass -lined drainage swale which conveys runoff from basin 2
and basin 3, east to design point 3. Combined runoff from basins 1, 2 and 3 enter 2-
12" RCP storm pipes and discharge to the LID basin to the east in basin 8. It's
important to note that during major storm events, calculations show that the swale
within basin 3 may pond to an elevation of approximately 4959, in which runoff will
spill south out of the swale and onto the private drive the outlet pipe before reaching
this elevation, due to grading constraints. The runoff will flow east, then northeast
and into the LID basin.
The City of Fort Collins intensity duration frequency curves were used to obtain
rainfall data for each storm specified. Detention pond sizing is not required, as
detention and water quality are provided for the subject site in the existing detention
pond (Pond 593) from the previous infrastructure improvements of the PVHS Master
Infrastructure Plan. However, BMP's and LID measures are being incorporated into
the proposed drainage development plan, with specific details and calculations shown
in Appendices C and F of this report.
D. Hydraulic Criteria
All hydraulic calculations, including final calculations and sizing for curb cuts,
drainage channels, swales, and erosion control and riprap measures have been
provided in accordance with the City of Fort Collins Drainage Criteria and can be
found in the Appendix.
E. Variance
No variances are being requested for this project.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
Nine drainage basins will provide conveyance of drainage for the 3.17 acres of the
3.549 acre site. The drainage will be routed to the existing detention pond via
1 swales, curb and gutter, and storm sewer pipe upstream of the proposed pre-
sedimentation/LID basin. The remaining 0.379 acres will continue to drain north and
1 east, as historically occurs.
1 Existing detention Pond 593 provides storage for the combination of detention and
1 water quality and was been sized to receive the 100-year developed flow from the
1 Emergency Department building site (developed imperviousness ratio of 65%), with
1 an allotted overall imperviousness ratio of 80% (from the PVHS Master
Infrastructure Plan). The calculated composite'C' value for Emergency Department
building is 0.65. Please refer to the rational calculations in Appendix B, and the
Drainage Basin Exhibit and PVHS Campus Master Infrastructure Plan, Drainage
Exhibit in Appendix F for additional information.
LID measures are provided for through the conveyance of approximately 80% (2.82
acres of the 3.54 acre site boundary) of the proposed building, parking lot, and green
areas of the site being routed through the porous paver areas and LID basin. Because
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imperviousness of 80% for the developed condition of the basin with all flow from
the basin being allowed to flow un-detained to the existing detention pond 593 (from
PVHS Second Filing), where all required water quality and detention needs are
provided for PVHS Harmony Campus site. Because the Emergency Department
building site has a combined imperviousness ratio of 65%, the 100-year developed
runoff from the site will be conveyed directly to existing pond 593, in accordance
with the drainage masterplan.
The balance of the onsite area, being 0.379 acres on the north edge of the site, is
within existing Basin 106 and will not be disturbed. This area will continue to drain
north, then east as occurs historically. Existing Basin 105 flow (which overlaps the
majority of the proposed development) is conveyed in an existing drainage channel to
the south and into existing detention pond (Pond 593). No offsite areas contribute
overland flow to or through the Emergency Department building project site.
Please refer to Appendix F of this report for the existing and proposed drainage basin
exhibits for the subject site.
M. DRAINAGE DESIGN CRITERIA
A. Regulations
Since the subject site has been previously modeled, the site is allowed to release un-
detained to existing detention pond 593, which has been sized to provide water
quality and detention for the developed 100-year runoff from the subject site.
However, LID improvements are required and have been provided for the project.
Please see the LID calculations in Appendix C.
B. Development Criteria Reference and Constraints
The criteria and constraints from the City of Fort Collins will be met. The calculated
65% impervious ratio for the proposed development is less than the allowed 80%
impervious ratio, from the PVHS Masterplan. The attenuated release in the existing
detention pond will remain in -tact and will not be altered.
C. Hydrologic Criteria
The Rational Method for determining surface runoff was used for the project site.
1 The 2-year and 100-year storm event intensities were used in calculating runoff
( values.
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of Snow Mesa Drive (along the site's west property boundary). To the south, a
private drive, constructed of concrete curb and gutter and asphalt pavement, drains to
the east and provides access to the property to the south.
Site drainage flows generally to the north and east. An existing open ditch, which
flows east through the center of the proposed site intercepts runoff from the south
half of the site and directs flow east to an existing swale, which then flows south to
an existing detention pond located in the southeast corner of the PVHS Harmony
Campus property. The existing pond was constructed with the PVHS Second Filing
and provides (and will provide) water quality and detention needs for the existing
conditions of undeveloped lots today, as well as the future full -build -out of the entire
PVHS Harmony Campus, in the fixture. Please refer to the PVHS Second Filing
Drainage report for details.
The majority of existing topography of the Emergency Department building site
generally slopes from the west to east/ northeast at approximately 0.50% to 2%.
U. DRAINAGE BASINS
A. Maior Basin Description
The site lies within the McClellands Drainage Basin, with site drainage previously
accounted for in the PVHS Harmony Campus Master Plan drainage study. The
approved grading and drainage master plan and SWMM Model for the PVHS
Campus (PVHS Second Filing) provided for the runoff from the entire PVHS
Campus being ultimately routed to the southeast comer of the PVHS Campus to the
existing detention/water quality pond, constructed with the PVHS Second Filing
project.
The proposed Emergency Department building site meets the intent of the "Final
Drainage and Erosion Control Study for the PVHS Harmony Campus", by the Sear -
Brown Group, dated March, 1999, and the "Final Drainage and Erosion Control
Study for the PVHS Master Infrastructure Plan", by Stantec, dated April 14, 2004.
The proposed improvements appear to have little effect on the existing drainage
system and facilities, and meet the intent of approved plans and drainage reports for
the PVHS Harmony Campus, with the site imperviousness being 65% versus the
allowable 80% from the SWMM Model.
B. Existing Sub -Basin Description
The existing Emergency Department building site is contained within existing sub -
basin 105 and basin 106 of the PVHS Second Filing. Existing basin 105 contains
approximately 4.54 acres (3.17 acres of the onsite area and 1.37 acres of offsite area).
Drainage basin 105 was modeled with the entire 4.54 acres having a percent
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FINAL DRAINAGE
AND EROSION CONTROL REPORT
FOR THE PVHS HARMONY CAMPUS, EMERGENCY DEPARTMENT FIFTH
FILING
FORT COLLINS, COLORADO
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The PVHS Harmony Campus, Emergency Department Fifth Filing (referred to as
"Emergency Department" here -forward) is bounded to the north by Harmony Road,
to the east by Wildwood Farms (Mountain Crest), to the south by a private drive, and
to the west by Snow Mesa Drive within the PVHS Harmony Campus.
The project site can also be described as situated in the northwest quarter of Section
5, Township 6 North, Range 68 West of the & P.M., of the City of Fort Collins,
Larimer County, Colorado. The Emergency Department building site is comprised of
approximately 3.549 acres. The drainage analysis includes 3.17 acres of the onsite
area and 1.37 acres of offsite area for a total area of 4.54 acres which matches the
existing drainage basin 105 area established with the PVH Master Infrastructure Plan.
The balance of the onsite area 0.379 acres is within existing drainage basin 106 and
will continue to drain north then east as occurs historically. Please refer to the
vicinity map in Appendix A for the site location.
B. Description of Property
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The site is comprised of an approximate 18,024 +/-square foot building footprint
1 along with associated parking lot, emergency entrance, drive -up entrance, private
drive improvements and utility improvements. Previously, the Emergency
Department building site was fallow agricultural land. Enhanced landscaping is
established within the northwest comer of the lot and along the Snow Mesa Drive
frontage. Existing landscaping and site features include sod grass, trees, shrubs, and
short retaining walls. Along the north side of the property, an existing concrete -lined
open -channel, irrigation ditch flows east along the south frontage of Harmony Road.
' An existing concrete sidewalk is also constructed adjacent to the south side of
Harmony Road, and is contained within the property. An existing 30" water main an
electrical duct bank also exist along the south side of Harmony Road and are
contained within existing easements, which parallel Harmony Road. An existing
concrete sidewalk is also constructed within the right-of-way and along the east side
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VICINITY MAP
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RATIONAL METHOD HYDROLOGY
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LID BASIN SIZING CALCULATIONS
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CURB CUT, INLET, & SWALE SIZING
D
EROSION CONTROL & RIPRAP SIZING ; EROSION ESCROW
E
PROPOSED DRAINAGE EXHIBIT & EXISING BASIN EXHIBIT
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TABLE OF CONTENTS
PAGE
I.
GENERAL LOCATION AND DESCRIPTION
5
A. LOCATION
5
B. DESCRIPTION OF PROPERTY
5
II.
DRAINAGE BASINS
6
A. MAJOR BASIN DESCRIPTION
6
B. EXISTING SUB -BASIN DESCRIPTION
6
III.
DRAINAGE DESIGN CRITERIA
7
A. REGULATIONS
7
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
7
C. HYDROLOGIC CRITERIA
7
D. HYDRAULIC CRITERIA
8
E. VARIANCE
8
IV.
DRAINAGE FACILITY DESIGN
8
A. GENERAL CONCEPT
8
B. SPECIFIC DETAILS
9
C. DETENTION PONDS
11
D. STREET CAPACITIES
11
V.
STORM WATER QUALITY
I 1
A. GENERAL CONCEPT
11
B. SPECIFIC DETAILS
I 1
VI.
EROSION CONTROL
12
A. GENERAL CONCEPT
12
VII.
CONCLUSIONS
12
A. COMPLIANCE WITH STANDARDS
12
B. DRAINAGE CONCEPT
13
C. STORM WATER QUALITY
13
D. EROSION CONTROL CONCEPT
13
E. EROSION CONTROL ESCROW ESTIMATE
14
REFERENCES
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November 26, 2014
Mr. Glen Schleuter
City of Fort Collins
Storm Water Dept.
700 Wood Street
Fort Collins, Colorado 80521
i RE: Final Drainage and Erosion Control Report for PVHS Harmony Campus, Emergency
i Department Fifth Filing
Dear Glen:
We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion
Control Report for the PVHS Harmony Campus, Emergency Department Fifth Filing. All
computations within this report have been completed in compliance with the City of Fort Collins
Storm Drainage Design Criteria.
We appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Respectfully,
Aspen Engineering
Prepared by: Reviewed by:
Tony Willkomm, P.E. John Gooch, P.E.
Senior Project Engineer Principal
� W A- = I N7,
Final Drainage and Erosion Control
Report for
PVHS Harmony Campus
Emergency Department Fifth
Filing
Fort Collins, Colorado
November 26, 2014