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VICINITY MAP
POUDRE VALLEY HOSPITAL HARMONY CAMPUS
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VICINITY MAP
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. McClellands Basin 100-Year Master Plan Update, by RBD, Inc., Fort Collins,
Colorado, April 1, 1996.
4. McClellands Basin Master Drainage Plan, by Greenhorne & O'Mara, Inc., Fort
Collins, Colorado, June 20, 1986.
5. Final Drainage Report for Timberline Road, by Northern Engineering Services,
Inc., Fort Collins, Colorado, July 15, 1994.
6. SWMM Model for McClellands Basin, by Lidstone and Anderson, 1997.
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B. Drainage Concept
The proposed drainage concepts presented in this study and shown on the final
utility plans adequately provide for the transmission of developed on -site runoff to
the proposed detention ponds. The combination of on -site street capacities and the
on -site storm sewer system will provide for the developed flows to reach the
proposed detention ponds. The sizes, locations and release rates of these ponds will
allow the Poudre Valley Hospital site to develop in conformance with the
McClellands Basin Drainage Master Planning concepts accepted by the City of Fort
Collins.
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 sediment basin traps proposed within the on -site detention ponds are excellent
ways to allow storm water pollutants an opportunity to be filtered out of the storm
water as the storm water carries the pollutants across the site. Periodic
maintenance may be required to remove sediment deposits as they accumulate in
the on -site detention pond.
D. Erosion Control Concept
The proposed erosion control concepts adequately provide for the control of wind
and rainfall erosion from Poudre Valley Hospital. 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.
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All construction activities must comply with the State of Colorado permitting
process for Storm water Discharges Associated with Construction Activity. A
Colorado Department of Health NPDES Permit will be required before any
construction grading can begin.
VI. EROSION CONTROL
A. General Concept
The Poudre Valley Hospital 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, and after
construction until the disturbed ground is re -vegetated or paved. It is anticipated
that construction will begin March of 1999.
B. Specific Details
Erosion control for this site during construction includes the building of two
temporary detention ponds that will act as water quality ponds. Additional erosion
control measures include sediment/basin traps for the ponds, gravel mulch,
roughened soil, and silt fence to be installed along the downstream perimeter of the
site. All areas that remain disturbed for more than four weeks will require seeding
and mulching to prevent excessive erosion. During the four week period, disturbed
areas shall be roughened.
After construction, the loop road will have a paved surface and the foundation of
the office building will be constructed. The open areas will have sod grass
installed to reduce the erosion potential.
Calculations for erosion control performance standards have been completed per
the City of Fort Collins Erosion Control Reference Manual for Construction Sites
and can be found in the Appendix of this report.
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
Stormwater Utility will not maintain the on -site storm drainage facilities within the
Poudre Valley Hospital site. The owners of the Poudre Valley Hospital site will
maintain their on -site storm drainage facilities on a regular basis.
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conveyance element 39. Similarly, Basin 318 has an embedded conveyance that
leads to Detention Pond 393, which outlets into conveyance element 392, and also
ultimately merges with conveyance element 39. Conveyance element 39 turns at
the southeast corner of the site and merges with conveyance element 38, as it did
in the McClellands Basin SWMM model.
The SWMM Model data for this project takes into account the dual staged release
structures, and the 10 year and 100 year allowable release rates. The tailwater
used in the calculations was calculated using circular channel flow, which
represents the proposed future conditions as shown in the Overall Drainage Report
for this site. From running the model, it was found that Pond 393 requires 2.6 ac-
ft of storage in the 100-Year event and Pond 394 requires 2.4 ac-ft of storage in the
100-Year event. The amount of flow being released into Conveyance Element 39
from the proposed Poudre Valley Hospital site, as well as the undeveloped portion
of the site, at the 100-year release rate of 0.50 cfs/acre, is 62.7 cfs, which is the
flow that was originally being conveyed in element 39, 66.7 cfs. No downstream
off -site impact is anticipated by the construction of the on -site development and
detention ponds.
The SWMM models and data are located in the Appendix of this report.
V. STORM WATER QUALITY
A. General Concept
The State of Colorado requires Stormwater Management Plans as part of their
permit process. The Poudre Valley Hospital site development is anticipating
construction beginning in March of 1999. Therefore this study has sought to find
various Best Management Practices for the treatment of storm water runoff that
could be implemented in the construction phase of the project.
B. Specific Details
Best Management Practices (BMP) for the treatment of storm water runoff have
been incorporated into the design for this project. The first BMP will be in place
prior to overlot grading of Phase I. This will be the construction of the detentions
ponds, which will also function as water quality features during the construction
phase of this project. Pond 394 have a sedimentary basin trap for pollutants to
settle out of the storm water runoff prior to being released into McClellands Basin
Drainageway. The BMP's for this site also include the installation of silt fence
during construction.
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In future phases, there will be another entrance into the site off of Harmony Road
and the Main Private Road will be completed. The developed flows from these
areas, Basins 19, 19A, 21, 23, will also be detained in Detention Pond 393. The
developed runoff off of these roads will enter the pond through Type "R" Inlets
and storm drainpipes. Detention Pond 393 was designed for" future conditions and
has the capacity to detain the developed runoff from these areas. The pipes and
inlets are shown on the Drainage and Erosion Control Plan in the back pocket of
this report and they are drawn with a lighter line type to represent future
conditions.
Undeveloped runoff from the southern portion of the site, Basins 25-29 and 31,
flows south towards the existing grass -lined drainage ditch (Conveyance Element
39) at the south boundary of the site, as it has historically. Due to the proposed
detention ponds and the staged release structures, the Swale will not receive flows
greater than the 100 year historic flows previously entering it. Please refer to the
SWMM models in the appendix and the Drainage and Erosion Control Plan in the
back pocket of this report for the historic and proposed flows in the swale.
SWMM Model
In order to analyze the detention ponds within the Poudre Valley Hospital Phase I
development, the Urban Drainage Districts SWMM routing computer model was
used. As part of the McClellands Basin Master Plan, a SWMM model was
developed for this basin, however, the City of Fort Collins is currently updating
the McClellands Basin SWMM Model and it was not available to use at the time
this report was written. The City of Fort Collins recommended using the SWMM
Model that was last updated by Lidstone and Anderson in 1997 and the City will
later include the PVH Model into their updated model when it is ready. The
SWMM Model by Lidstone and Anderson that was used to analyze the site can be
found in the appendix of this report. Included in the back pocket of this report is
a new SWMM Model Exhibit drawing for the area directly north of the Stetson
Creek and Timber Creek Developments, east of the Harmony Crossing
Development, and west of the Wildwood Farms Development.
With this project, Basin 316 of the McClellands Basin SWMM model was
modified. The area of basin 316 has been increased from 99 acres to 103.81 acres
due to the addition of a portion of Harmony Road, which was not originally
included in this basin. For this project, basin 316 was subdivided into three basins,
316, 317, and 318, which now have 67.0 acres, 17.3 acres, and 19.5 acres
respectively. See the Detention Pond Design by SWMM section in the appendix
for a schematic. Conveyance element 39 was subdivided into conveyance elements
391 and 39. Basin 317 has an embedded conveyance that leads to Detention Pond
394, which outlets into conveyance element 391, and ultimately merges with
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Basins 3 contains the portion of Timberline Road that will be detained in Pond 394.
The developed flow from this portion of Timberline, east of the crown of the road
and north of the unnamed public road, will be routed onto the project site via
curb/gutter where it is intercepted by a Type R Inlet and conveyed to detention
pond 394 through the storm drain pipes. The south portion of Timberline, Basin
4, is conveyed south to the existing inlet and drains into detention pond 394 via a
proposed storm drainpipe (Profile E). The majority of Basins 5-11 consists of
parking lots and a portion of the parking access. The developed flow off of this
area is conveyed via curb and gutter to a series of Type "R" inlets and storm
drainpipes (Profile A) which outlet into the detention pond 394. Approximately
one third of the building drains into roof drains, Basin 13, that combine with the
storm drain line (Profile A) at a manhole located in the parking area.
Detention Pond 393 is a detention pond as well as an irrigation pond and has a total
storage capacity of approximately 7 acre-feet, where 2.6 acre-feet of this storage
has been allocated for the 100 year detention storage. The 100 year water surface
elevation of Pond 393 is 4955.10'. The pond is comprised of two ponds, located
in Basins 20 and 22, with an equalizing pipe connecting them. In order to maintain
water in the pond for irrigation purposes, the outlet structure will be placed above
the irrigation high water surface. As with the outlet structure for Pond 394, there
is a 10 year and 100 year staged release rate which outlets into a temporary
trapezoidal swale that conveys the flows to the existing grass -lined drainage
(SWMM model Conveyance Element 39) ditch at the south boundary of the site.
Similar to Detention Pond 394, a 25'. emergency overflow spillway was designed
for this pond with its elevation equal to the 100 year WSEL.
Runoff from the northeastern portion of the site will be routed to and detained in
Detention Pond 393, located near the northern boundary of the site. Developed
flow from a portion of Harmony Road, Basin 1, and the eastern parking areas,
Basins 15-18, is conveyed via a swale and curb and gutter toward the center of the
large parking lot where the flow is intercepted by two, large Type "R" inlets
(Profile B). Also combining at this point are the developed flows off of two-thirds
of the building, Basin 12 and 14. The roof flows are conveyed to the inlets via a
network of reinforced concrete pipes. The flows are then conveyed via a large
elliptical pipe to Detention Pond 393. The storm drainpipes are sized to be able to
convey the 100-year developed flow off of the buildings, however, the roof drains
within the building will not have such a large capacity and there will be overflow
into the parking lot during the 100-year storm event. In order to account for this,
the inlets in the parking lot were designed to be able to accept the 100-year
developed flows from the contributing basins plus the extra flow off of the building
that is over the 10-year developed flow.
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swales. There are two proposed ponds, ##393 and ##394, that will be constructed
with Phase I of this project and they will discharge into the McClellands Basin
Drainageway at the 10-year and 100-year allowable staged release rates. The
release rates are based on the requirements of the Master Plan for the
McClellands Basin, which requires on -site detention using a staged release rate
of 0.20 cfs/acre for a 10-year design storm and 0.50 cfs/acre for a 100 year
design storm
B. Specific Details
Overall Drainage Plan
Please refer to the Overall Drainage Report completed by The Sear -Brown Group
for information on the Overall Drainage Plan.
Phase I Development
The entire Poudre Valley Hospital property contains approximately 104 acres of
which approximately 35 acres are being developed with the first phase. The site
has been broken into thirty-three on -site drainage basins. Please refer to the
Drainage and Erosion Control Plan in the back pocket of this report.
Basins 1, 2 and 24 contain portions of Harmony Road, which develop runoff that
will sheet flow into the Spring Canyon Lateral, located between the project site and
Harmony road, as it has historically done.
Runoff from the western portion of the site will be routed to and detained in
Detention Pond 394, located at the southwest corner of the site.. The area
contributing to Detention Pond 394 is approximately 17.27 acres and consists of
Basins 3-11, 13, 30 and 32. Detention Pond 394 has a 100-year storage capacity
of 2.4 acre-feet. The bottom of the pond has a minimum grade of 0.50% and has
concrete trickle pans that facilitate the flow southeast towards the outlet structure
box. The outlet structure allows for a 10 year and 100 year staged release rate,
which releases the detained flows into the existing grass -lined drainage ditch
(SWMM model Conveyance Element 39) at the south boundary of the site. In the
event this outlet structure box becomes clogged, a 30' wide emergency overflow
spillway was designed. The elevation of the spillway is equal to the 100-year water
surface elevation (WSEL). The allowable release rates were determined using the
requirements from Master Plan for the McClellands Basin: 0.20 cfs/acre for a 10-
year design storm and 0.50 cfs/acre for a 100 year design storm. The detention
ponds for this site were analyzed using SWMM Modeling and are discussed in a
later section of this report.
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B. Development Criteria Reference and Constraints
The criteria and constraints from The McClellands Basin 100-Year Master Plan and
the subsequent update dated April 1, 1996 are being utilized in this Final Drainage
Study. The Poudre Valley Hospital site is currently being utilized as agricultural
land, and the McClellands Basin Master Plan for the site does not include on -site
detention facilities for the future development. With this phase of development for
the Poudre Valley Hospital Site, on -site detention is required and detention ponds
will be provided.
C. Hydrologic Criteria
The Poudre Valley Hospital PDP Drainage Report will utilize the SWMM Model
that was last updated by Lidstone and Anderson in 1997 and simply expand on it.
The City of Fort Collins is currently updating the McClellands Basin SWMM
Model and is not available for this project. The City will later include the PVH
Model into their updated model when it is ready. SWMM hydrologic models will
be run for the Project Development Plan.
D. Hydraulic Criteria
All calculations within this study have been prepared in accordance with the City
of Fort Collins Storm Drainage Criteria and are included in the appendix.
E. Variances from Criteria
A variance from the City of Fort Collins Storm Drainage Criteria is being sought
for the increase in runoff into the Spring. Canyon Lateral from the additional 12'
wide pavement surface on Harmony Road. This area has historically been pervious
and while stormwater was directed toward the ditch, runoff generally seeped into
the ground prior to entering the ditch. With the addition of the 12' wide pavement
surface, stormwater will still be directed toward the ditch but some added runoff
will enter the ditch due to the increased imperviousness.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
As development occurs within the Poudre Valley Hospital site, the drainage
concepts shown on the Drainage and Erosion Control Plan in the back pocket of
this report should be followed. Generally, the 10 year and 100 year developed
on -site stormwater flows will be conveyed to the two on -site detention ponds via
curb and gutter, cross -pans, sidewalk chases, inlets, storm drainpipes, and
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site is located in Basin 316. Applicable portions of these studies are included in the
Appendix.
Historic drainage patterns on the subject site are in a southeasterly direction per the
McClellands Basin 100-Year Master Plan Update. The site historically discharges
into Conveyance Element 39 (see the Detention Pond Design by SWMM section
in the appendix). Conveyance Element 39 is currently 2160 feet long and is an
open channel that runs along the southern property line of the PVH site. At the
southeast corner of the site, Conveyance Element 39 turns the corner and flows
south along the east property line of the Timber Creek PUD and the Stetson Creek
PUD. Excerpts from the McClellands Basin 100-Year Master Plan Update can be
found in the appendix of this report. The flow ultimately discharges into the
McClellands Basin Drainageway.
A portion of Timberline Road and Harmony Road will be detained on the Poudre
Valley Hospital Site. Sections of the Final Drainage Report for Timberline Road,
done on July 15, 1994, by Northern Engineering Services, Inc., which show this
area of roadway has been included in the Appendix. These sections specify the
area of Timberline to be detained as well as storm flows.
No off -site runoff from properties surrounding the Poudre Valley Hospital site pass
through the site. With the construction of the site, no additional flows are
anticipated.
Poudre Valley Hospital will have Detention Ponds #393 and #394 on site. The
total area draining to these two ponds is equal to approximately 35 acres. This area
is included in Phase I of the Poudre Valley Hospitaf Site.
B. Sub -Basin Description
Historic drainage patterns on the subject site are in a southeasterly direction per
Appendix B, page 56 of the McClellands Basin 100-Year Master Plan Update.
Excerpts from the McClellands Basin 100-Year Master Plan Update can be found
in the appendix of this report. No off -site runoff from properties surrounding the
Poudre Valley Hospital site traverse through the site. With the construction of
Phase I of the site, no additional flows are anticipated.
III. DRAINAGE BASIN CRITERIA
A. Regulations
The City of Fort Collins Storm Drainage Design Criteria is being used for the
subject site.
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FINAL DRAINAGE AND EROSION CONTROL REPORT
FOR THE POUDRE VALLEY HOSPITAL HARMONY CAMPUS
FORT COLLINS, COLORADO
I. GENERAL LOCATION AND DESCP-JPTION
A. Location
The Poudre Valley Hospital Harmony Campus site is located south of Harmony
Road and east of Timberline Road in southeastern Fort Collins, Colorado. The site
is shown on the Vicinity Map in the Appendix. More particularly, the site is
situated in the northwesterly portion of Section 5, Township 6 North, Range 68
West of the Sixth P.M., City of.Fort Collins, Larimer County, Colorado.
B. Description of Property
The overall Poudre Valley Hospital site contains approximately 104 acres of land,
all of which is currently undeveloped and being proposed for the Harmony Campus
of Poudre Valley Hospital. The majority of the property currently consists of
cultivated farmland. The site generally slopes in a southeasterly direction at
approximately 2.0%.
Only Phase I of this project, located in the northwest corner of the property,
containing approximately 36 acres, is being covered in this report. The remainder
of the property will mostly remain undisturbed until future phases of development.
There is a concrete irrigation ditch along the northern property line of this site
called the Spring Canyon Lateral, owned by the Warren Lake Company. This
ditch is to be relocated approximately 23 feet south of the current location;
however, an engineer that will be designated by the ditch company will perform the
design and relocation.
II. DRAINAGE BASINS
A. Major Basin Description
The Poudre Valley Hospital site lies entirely within the McClellands Basin. The
McClellands Basin SWMM Model was last updated by Lidstone and Anderson in
1997 for areas north of Harmony Road. In the update, the Poudre Valley Hospital
1
APPENDIX
VICINITY MAP
HYDROLOGY
INLET SIZING AND CURB CUTS
STORM DRAIN SCHEMATICS AND PIPE SIZES
SWALE SIZING
SWALE ANALYSIS — CONVEYANCE ELEMENT 39
RIPRAP CALCULATIONS
DETENTION POND DESIGN BY SWMM MODEL
WEIR ANALYSIS
EROSION CONTROL CALCULATIONS
EXCERPTS FROM McCLELLANDS BASIN
MASTER DRAINAGE PLAN
EXCERPTS FROM McCLELLANDS BASIN
100-YR MASTER PLAN UPDATE
SWMM MODEL BY LIDSTONE AND ANDERSON, 1997
EXCERPTS FROM FINAL DRAINAGE PLAN
FOR TIMBERLINE ROAD
TABLES AND FIGURES
PAGE
1
3
9
22
58
62
65
72
181
184
193
197
200
232
244
TABLE OF CONTENTS
DESCRIPTION PAGE
I. GENERAL LOCATION AND DESCRIPTION
A. LOCATION 1
B. DESCRIPTION OF PROPERTY 1
II. DRAINAGE BASINS
A. MAJOR BASIN DESCRIPTION 1
B. SUB -BASIN DESCRIPTION 2
III. DRAINAGE DESIGN CRITERIA
A.
REGULATIONS 2
B.
DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 3
C.
HYDROLOGICAL CRITERIA 3
D.
HYDRAULIC CRITERIA 3
E.
VARIANCES FROM CRITERIA 3
IV. DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
3
B. SPECIFIC DETAILS
4
OVERALL DRAINAGE PLAN
4 .
PHASE I DEVELOPMENT
4
SWMM MODEL
6
V. STORM WATER QUALITY
A. GENERAL CONCEPT 7
B. SPECIFIC DETAILS 7
VI. EROSION CONTROL
A. GENERAL CONCEPT 8
B. SPECIFIC DETAILS 8
VII. CONCLUSIONS
A. COMPLIANCE WITH STANDARDS 8
B. DRAINAGE CONCEPT 9
C. STORM WATER QUALITY 9
D. EROSION CONTROL CONCEPT 9
REFERENCES 10
THE SEAR -BROWN GROUP
FULL,SERVICE DESIGN PROFESSIONALS
FORMERLY RBD, INC.
209 SOUTH MELDRUM
FORT COLLINS, COLORADO 80521-2603
970-482-5922 FAX:970-482-6368
January 29, 1999
Mr. Basil Harridan
City of Fort Collins
Water Utilities--Stormwater
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage and Erosion Control Report for the Poudre Valley Hospital -
Harmony Campus
Dear Basil:
We are pleased to resubmit to you, for your review and approval, this Final Drainage and Erosion
Control Report for the Poudre Valley Hospital - Harmony Campus. All computations within this
report have been completed in compliance with the City of Fort Collins Storm Drainage Design
Criteria. The Overall Drainage Report is being submitted simultaneously.
We appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
1 Respectfully,
The Sear -Brown Group
Prepared by:
Traci Downs, E.I.T.
Project Engineer -
��c,�
Storm Gewirtz, E.I.T.
Project Engineer
cc: File 823-001
Albert Kahn Associates
I-:\JOBS\523-001\DRAINAGE\PDPUNew FOldeADRAINRYEDOC
NEW YORK•PENNSYLVANIA
' COLORADO•UTAH
STANDARDS IN EXCELLENCE
Reviewed.by:
Not available - will sign when final
Kevin Gingery, P.E.
Engineering Manager
EQUAL OPPORTUNITY EMPLOYER
Final Drainage and Erosion
Control Report
Poudre Valley Hospital
Harmony Campus,
Fort Collins, Colorado
January 29, 1999
I
THE
SEAR -BROWN
GROUP
Standards in Excellence
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