HomeMy WebLinkAboutBRINKMAN HEADQUARTERS - PDP/FDP - FDP130050 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTperformance standards will be met. The proposed erosion control concepts presented
in this report and shown on the erosion control plan are incompliance with the City
of Fort Collins Erosion Control Criteria.
' Erosion Control Escrow Estimate
The Erosion Control Escrow Estimate for the subject property is approximately
$13,298.00. Please refer to Appendix E for this calculation.
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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 Report, Harmony Technology Park 2nd
Filing, by JR Engineering, June 20, 2001.
5. 2004 High School Drainage and Erosion Control Study, Poudre School District
R-1, by Nolte Associates, Inc., June 24, 2002.
6. Final Drainage and Erosion Control Report, Harmony Technology Site Master
Plan, by Stantec Consulting, May 19, 2008.
7. Final Drainage and Erosion Control Study for Harmony Technology Park
Third Filing, by Stantec Consulting, May 19, 2008.
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C.
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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.
Drainage Concept
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 sewer systems 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.
Storm Water Quality
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.
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
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treatment, and because water quality is already provided for in the existing detention
pond, porous pavement may not be required for the project. Further analysis will
determine the need for'or removal of the porous pavement from the project.
The two LID basins, shown and called out in the civil utility plans, provide for
approximately 1' of ponding depth, prior to the basins overflowing and spilling south
in the storm sewer and into the existing detention pond. Please refer to Appendices C
and F, and sheets C-007 and C-012 of the civil utility plans, for details on the LID
basins. i
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 entrance/exit to the site. Gravel inlet filters will be placed at
proposed curb cuts and existing inlet, with straw wattles installed at the proposed
storm sewer and inlet outfail points from the site to mitigate the build-up of sediment
and transport of debris into existing Pond 110. Riprap and erosion control fabric will
also be utilized at concentration points (curb cuts) 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
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
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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 110) constructed with the
Harmony Technology Third Filing 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 soft pans, LID pre -
sedimentation basins, 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 have 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.
LID measures are provided for through the conveyance of 1.17 acres (of the 1.62 acre
total) through the two proposed LID pre -sedimentation basins, with the total footprint
of the two combined LID basins being approximately 1,564 square feet, with both
LID basins having a depth of approximately 1.0'. The 1.17 acres of area being
conveyed to the LID basins account for 72% of the total area, thereby, meeting City's
LID treatment of 50% of the site area. It's important to note that because the area
being routed to and through the LID basins exceeds the 50% requirement for LID
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City of Fort Collins. Please refer to the civil utility plans for details on the LID
Basin.
Basins 12
Basins 12 conveys runoff from the eastern portion of the building (roof) and green
area on the east side of the building overland to the east and out into the curb and
gutter on the west side of Lady Moon Drive. Three roof drains will be located within
basin 12 and will have lambs tongue outfall points to three, 2' wide x 3' long riprap
pads. During major storm events, runoff from basin 12 may discharge onto the riprap
pads and flow overland to the east and out to Lady Moon Drive. The 1.94 cfs (100-
year flow from basin 12) will flow south down Lady Moon Drive and combined with
that from Basin 13.
Basin 13
Basins 13 conveys runoff from the southwest portion of the building (roof) and green
areas on the south side of the building and along the southern property boundary area,
south and into the curb and gutter on the north side of Precision Drive. One roof
drain will be located within basin 13 and will have a lambs tongue outfall point to a
2' wide x 3' long riprap pad. During major storm events, runoff from basin 13 may
discharge onto the riprap pad and flow overland to the south and out to Precision
Drive. The 1.69 cfs (100-year flow from basin 13) will flow east down Precision
Drive and combine with that from Basin 12, where the flow will turn south. Runoff
from basins 12 and 13 will begin to combine with runoff from basin OS 1 of the HTP
Third Filing and will be conveyed south along the west side of Lady Moon Drive
towards existing design point OS1, where an existing inlet will capture the runoff
from basins OS1 and 12-13.
Existing Basin 180 (portion of SWMM Basin 100)
Existing Basin 180 of the HTP Third Filing is contained within the Masterplan
SWMM basin 100. Runoff from Basin 180 will continue to follow its historic flow
pattern from the northwest to the southeast. The proposed Brinkman site will provide
for an extension of the existing 36" RCP to the north, while also adding a second,
24" RCP extension to the west. The purpose of the 24" RCP extension is to provide
an outfall point for future development to the west of the Brinkman site, as the
proposed Brinkman site creates two specific natural low point areas: one at the
northeast corner of the Brinkman site; and, one at the southwest corner of the
Brinkman site. Therefore, the 24" RCP and 36" RCP extensions will provide an
outfall for future development, in accordance with the Masterplan for the HTP
Campus.
Offsite grading will be necessary to provide conveyance of runoff from basin 180 to
the outfall points at the proposed 24" RCP and 36" RCP. Please refer to the utility
plans for grading details.
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B. Specific Details
Basins 1
Basins 1 conveys its flow overland to the north, then west/ southwest in the proposed
soft pan/swale, which consists of a 50150 mix of sand and topsoil and is 2' wide x 1'
deep. The soft pan/swale will direct runoff towards a 2' curb cut at design point 1,
where runoff from basin 1 will pass through the curb cut and begin to combine with
that from Basin 2.
Basins 2-6
Basins 2 conveys runoff from a small portion of the roof and plaza area (northwest
corner of the building) overland to the west and across the parking lot towards design
point 2, where a 2' curb cut conveys runoff into the LID/pre-sedimentation basin.
Likewise, basins 3-5 (northwest quadrant of site) convey their runoff overland across
the parking lot area towards their respective design points, where 2' curb cuts pass
runoff through and into the LID/ pre -sedimentation basin (Basin 6), which is
designed to provide a ponding depth of approximately 0.70' to 1.00' and allow
pollutants and sediment to settle out of the runoff, prior to spilling south in the
proposed storm sewer and into Existing Pond 110. The runoff from basins 1-6
combines in basin 6 (LID Basin) and is directed to a proposed 15" nyloplast drain
basin riser with 24" standard H2O grate. A 15" ADS (N-12) pipe will convey runoff
southwest and into the proposed 36" RCP storm sewer, which carries flows south and
eventually into existing Pond 110.
It's important to note that Basin 6 contains the interior portion of the median area and
will have special media installed to provide LID treatment, as required by the City of
Fort Collins. Please refer to the civil utility plans for details on the LID Basin.
Basins 7-11
Basins 7 conveys runoff from a small portion of the plaza area (west -central area of
the building) overland to the west and across the parking lot towards design point 7,
where a 2' curb cut conveys runoff into the LID/pre-sedimentation basin. Likewise,
basins 8-10 (southwest quadrant of site) convey their runoff overland across the
parking lot area towards their respective design points, where 2' curb cuts pass runoff
through and into the LID/ pre -sedimentation basin (Basin 11), which is designed to
provide a ponding depth of approximately 0.70' to 1.00' and allow pollutants and
sediment to settle out of the runoff, prior to spilling south in the proposed storm
sewer and into Existing Pond 110. The runoff from basins 7-11 combines in basin 11
(LID Basin) and is directed to a proposed 15" nyloplast drain basin riser with 24"
standard H2O grate. A 15" ADS (N-12) pipe will convey runoff southwest and into
the proposed 36" RCP storm sewer, which carries flows south and eventually into
existing Pond 110.
It's important to note that Basin 11 contains the interior portion of the median area
and will have special media installed to provide LID treatment, as required by the
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existing detention pond via swales, curb and gutter, and storm sewer inlets and pipe
both upstream and downstream of the proposed pre-sedimentation/LID basins.
Existing detention Pond 110 provides approximately 7.98 acre-feet of storage for the
combination of detention and water quality, while having an allowed 100-year release
rate of 15 cfs, in accordance with the Harmony Technology Park Third Filing
Drainage Report, by Stantec Consulting, Inc, dated May 19, 2008, and the HTP Site
Masterplan Report, by Stantec Consulting, Inc., dated May 19, 2008. It's important to
note that existing Pond 110 has been sized to receive the 100-year developed flow
from the Brinkman Office Building site (developed imperviousness ratio of 72%),
with an allotted overall imperviousness ratio of 80% (from the HTP Site Masterplan
Report). The calculated composite 'C' value for Brinkman Office Building is 0.72,
which meets the requirements set forth in the previous Masterplan study.
Furthermore, the calculated 100-year runoff from the developed site 14.65, compared
to the allowable 100-year flow of approximately 14.84 cfs, as calculated using the
HTP Masterplan SWMM model of 32.9 acres with a combined flow of 297.7 cfs,
providing for 9.05 cfs/acre. Please refer to the rational calculations in Appendix B,
and the Drainage Basin Exhibit and HTP Third Filing and HTP Site Masterplan
Report excerpts in Appendix F for additional information.
It's important to note that an additional 24" RCP has been added and stubbed to the
west of the Brinkman site to provide an outfali for future development to the west of
' the Brinkman site. Likewise, the existing 36" RCP, stubbed north of Precision Drive
' today, will be extended north of the Brinkman site to continue to provide an outfall
1 for the historic runoff from existing basin 180 (of the HTP Third Filing Report) and
also as an outfall for future development to the north, in accordance with the HTP
Site Masterplan Report and SWMM Model.
LID measures are provided for through the conveyance of approximately 72% (1.17
acres of the 1.62 acre site boundary) of the proposed building, parking lot, and green
areas of the site being routed through the LID basins. Because the area being routed
to and through the LID basins exceeds the 50% requirement for LID treatment, and
because water quality is already provided for in the existing detention pond, porous
pavement may not be required for the project. Further analysis will determine the
need for or removal of the porous pavement from the project.
The LID basins, shown and called out in the plans, provide for 1' of ponding depth,
prior to the basins overflowing and spilling south and into the existing detention
' pond. Please refer to Appendix C and sheet C-012 of the civil utility plans for details
on the LID basins.
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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.
C. Hydrologic Criteria
The Rational Method for determining surface runoff was used for the project site.
The 2-year and 100-year storm event intensities were used in calculating runoff
values.
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 110) from the previous infrastructure improvements of the Harmony
Technology Park Third Filing and HTP Masterplan. 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,
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
Thirteen drainage basins will provide conveyance of drainage for the 1.62 acre (1.64
acres including ROW that will be dedicated to City FC) site to the existing detention
pond (Pond 110), located south of the site. The drainage will be routed to the
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II. DRAINAGE BASINS
A. Maior Basin Description
The site lies within the McClellands Basin. The site drainage has been previously
accounted for in the Harmony Technology Third Filing drainage study, and the
Harmony Technology Park Site Master Plan (HTPMMP). The project drainage will
be in conformance to these two studies, as well as the original study completed for
the majority HTP site, which can be found in the East Harmony Portion of the
McClellands Creek Master Drainage Plan (August 1999).
B. Existing Sub -Basin Description
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1 The existing Brinkman Office Building site is contained within existing sub -basin
180 of the HTP Third Filing, and SWMM basin 100 of the HTP Masterplan report
(EX7 of the existing Rational Calculations). Existing basin 180 contains
approximately 12.04 acres, and was modeled with the entire 12.04 acres having a'c'
value of 0.32, with a 100-year runoff rate of approximately17.37 cfs for the historic
condition of the basin. However, the HTP Masterplan Report specifies the Brinkman
site being contained within SWMM Basin 100 (32.9 acres) being allowed a
1 developed impervious value up to 80%, with all flow from the Brinkman site being
allowed to flow un-detained to the existing detention pond 110, where water quality
( and detention needs are provided for the proposed Brinkman site. Because the
Brinkman Office Building site has a combined imperviousness ratio of 72%, the 100-
year developed runoff from the site will be conveyed directly to existing pond 110.
Please refer to the Third Filing Drainage Report and HTPMSP report for further
' details (excerpts can be found in Appendix F of this report). Please also see the
drainage exhibit in Appendix F of this report for the existing basin and the
overlapping proposed drainage basins for the subject site.
Existing SWMM Basin 100 and Existing basin 180 conveys the majority of its flow
overland to the southeast and into the existing 36" FES/storm drain system, which
conveys flow south and into the existing detention pond (Pond 110 of the Third
Filing report). No other offsite areas contribute overland flow to or through the
Brinkman Office Building project site.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
Since the subject site has been previously modeled, the site is allowed to release un-
detained to the existing detention pond 110, which has been sized to provide water
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FINAL DRAINAGE
AND EROSION CONTROL REPORT
FOR THE HARMONY TECHNOLOGY PARK FOURTH FILING
FORT COLLINS, COLORADO
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The Harmony Technology Park Fourth Filing (referred to as "Brinkman Office
Building" here -forward) is bounded to the north by vacant land within the HTP
Campus, to the east by Lady Moon Drive, to the south by Precision Drive, and to the
west by vacant land within the HTP Campus.
1 The project site can also be described as situated in the northwest quarter of Section
4, Township 6 North, Range 68 West of the 6"' P.M., of the City of Fort Collins,
Larimer County, Colorado. The Brinkman Office Building site is comprised of
approximately 1.62 acres. It is important to note that rational calculations within this
1 report provide for approximately 1.64 acres of basin area, to match previous
1 masterplan basin area modeling. However, upon platting of this project and the
1 dedication of 2'of additional right-of-way along the south property boundary, the site
1 boundary will be 1.62 acres. Please refer to the vicinity map in Appendix A for the
site location.
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B. Description of Property
1 The Brinkman Office Building site is comprised of an approximate 30,000 +/-square
foot building (contained within two stories) along with associated parking lot, entry
plaza and outdoor meeting area, and utility improvements. Previously, the Brinkman
Office Building site was fallow agricultural land, with a portion of the lot being
' overlot graded with the construction of the HTP Third Filing roadway and utility
' infrastructure, including a 36" RCP w/ FES storm drain extension for masterplan
storm drainage improvements.
' The majority of existing topography of the Brinkman Office site generally slopes
' from the northwest to southeast at approximately 0.90%, with a southwest portion of
the site sloping at approximately 3 :1 at the inlet to the masterplan storm drain system.
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APPENDIX
PAGE
VICINITY MAP A
RATIONAL METHOD HYDROLOGY B
LID BASIN SIZING CALCULATIONS C
CURB CUT, INLET, & SWALE SIZING D
EROSION CONTROL & RIPRAP SIZING ; EROSION ESCROW E
PREVIOUS REPORT EXCERPTS, PROPOSED DRAINAGE F
EXHIBIT w/ EXISTING BASINS SHOWN
TABLE OF CONTENTS
DESCRIPTION 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
6
A. REGULATIONS
6
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
6
C. HYDROLOGIC CRITERIA
7
D. HYDRAULIC CRITERIA
7
E. VARIANCE
7
IV.
DRAINAGE FACILITY DESIGN
7
A. GENERAL CONCEPT
7
B. SPECIFIC DETAILS
8
C. DETENTION PONDS
10
D. STREET CAPACITIES
10
V.
STORM WATER QUALITY
10
A. GENERAL CONCEPT
10
B. SPECIFIC DETAILS
10
VI.
EROSION CONTROL
11
A. GENERAL CONCEPT
11
VII.
CONCLUSIONS
11
A. COMPLIANCE WITH STANDARDS
11
B. DRAINAGE CONCEPT
12
C. STORM WATER QUALITY
12
D. EROSION CONTROL CONCEPT
12
E. EROSION CONTROL ESCROW ESTIMATE
13
REFERENCES
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December 10, 2013
Mr. Glen Schleuter
City of Fort Collins
Water Utilities --Storm water
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage and Erosion Control Report for the Harmony Technology Park Fourth
Filing
Dear Glen:
We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion
Control Report for the Harmony Technology Park Fourth 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
John Gooch, P.E.
Principal
Final Drainage and Erosion Control
Report for
Harmony Technology Park
Fourth Filing
Fort Collins, Colorado
December 10, 2013