HomeMy WebLinkAboutLONGVIEW MARKETPLACE @ SHENANDOAH - PDP - 47-95B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTui
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Final Drainage Report
Longview Marketplace
November 5, 2002
Plan.
Northern Engineering Services, Inc
The proposed site layout and construction schedule will leave little or no areas disturbed
without receiving an erosion control BMP. The measures proposed above will control
surface erosion during the construction process, and prevent sediment from leaving the
site. These structures are to remain in place until paving is completed and foundations
and landscaping have been established. The proposed erosion control plan after
construction will consist of permanent riprap, which will be provided at the locations
specified on the utility plans. All open space areas will be revegetated as specified on the
Landscape Plan.
An erosion control cost estimate for "during construction" sediment control along with
performance standard and effectiveness calculations have been provided for the site (See
Appendix G).
VII. CONCLUSIONS
7.1 Compliance with Standards
All drainage design considerations are in accordance with the City of Fort Collins Storm
Drainage Design Criteria Manual and the Urban Drainage and Flood Control District's
Drainage Criteria Manual.. Additionally, drainage stipulations outlined in previous
drainage studies and master plans for the area have been strictly followed. Off -site
stormwater will be safely routed through the site without being detained. Existing
stormwater facilities are being utilized to their maximum potential. Overall, the drainage
system proposed within this report and the supporting construction documents provide
adequate conveyance, detention and water quality enhancement for the developed
stormwater runoff from Longview Marketplace. Every attempt has been made to
minimize any negative impacts on the downstream receiving waters.
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Final Drainage Report
Longview Marketplace
November 5, 2002
Northern Engineering Services, Inc
A hydraulic analysis was performed on Storm Line OSSD using StormCAD software and
Record Drawing information obtained from the City of Fort Collins. The line was
originally designed to carry a total of 21.5 cfs, with 6.2 cfs coming from the southern
portion of Shenandoah P.U.D. It was determined that the line could handle an additional
flow of approximately 12.9 cfs, for a total of 34.4 cfs without flooding any downstream
inlets or manholes. The 0.27 cfs/acre established by Nolte was held for all off -site areas.
The total combined discharge (on -site release and off -site bypass) into the existing line is
approximately 13.8 cfs. This leaves around 5.3 cfs of remaining capacity in the line,
while providing 1.7 cfs of off -site conveyance through Longview Marketplace's
detention systems.
V. WATER QUALITY
5.1 Water Quality Measures and Criteria
The Developer of Longview Marketplace is very conscientious of the impacts of this
project, and as such, is proposing two separate water quality BMP's to treat the runoff
from the site. All areas, including the rooftops, will be routed through a water quality
mechanism before being released into the existing OSSD storm line. The primary water
quality method will be built into Detention Pond 1. This on -site water quality capture
volume (WQCV) is proposed to remove sediment and other pollutants from developed
runoff. Based on criteria for a 40-hour dry extended detention basin outlined in the
Urban Storm Drainage Criteria Manual, Volume 3 — Best Management Practices by the
Urban Drainage and Flood Control District (September 1999), the required water quality
capture volume for Pond 1 was determined to be approximately 0.853 acre-feet. This
required WQCV is achieved at an elevation of 5022.78 feet. A steel orifice plate with
vertical perforations will be built into the pond outlet structure to control the water
quality capture volume.
Additionally, a Stormceptor structure will be used to treat the runoff and separate the
hydrocarbons from the gas station area. "The Stormceptor System is a vertically -
orientated stormwater separator that removes oil, sediment and other pollutants from
urban run-off. Its built-in by-pass feature prevents trapped contents from flushing out
during intense rain storms.s5 A model STA-2400 is proposed for Storm Sewer Line SC.
This is a concrete unit with a sediment capacity of 217 cubic -feet and an oil capacity of
778 gallons.
VI. EROSION CONTROL PLAN
6.1 Erosion Control Criteria
The erosion control plan presented here is intended to control both wind and rainfall
erosion. The Erosion Control Reference Manual for Construction Sites (ECRM), City of
Fort Collins, has been referenced for this erosion control plan.
6.2 Rainfall Erosion Control Plan
The proposed rainfall erosion control plan during construction will consist of several
temporary structural erosion control measures. A gravel bag sediment trap will be placed
at the outlet of the proposed detention pond. Vehicle tracking control pads and silt
fencing will be provided at the locations specified on the Grading and Erosion Control
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Final Drainage Report Northern Engineering Services, Inc
Longview Marketplace
November 5, 2002
TABLE 1
Sub -Surface Detention Storage Basin Summary
100-year Detention
Area Discharge Volume
Contributory Basins (acres) (cfs) Provided
On -Site All & Al2 2.848 1.4 Yes
Off -Site Al & A2 1.052 0.3 No
Totals All of Basin A 3.900 1.7----------
The second place of detention storage occurs in Detention Pond 1. This pond is located at
the southeast comer of the site near the intersection of Avondale Drive and South College
Avenue. Pond 1 will discharge into line OSSD via Storm Sewer Line B. Table 2
summarizes the areas draining to Detention Pond 1.
TABLE 2
Detention Pond 1 Basin Summary
100-year Detention
Area Discharge Volume
Contributory Basins (acres) (cfs) Provided
On -Site B, Cl_-C3, D, 17.067 8.4 Yes
E3, Ell, Ell, E21, E22, SC
Off -Site C4, E1, E2, E4 13.519 3.7 No
Totals — ------------------------------------ 30.586 12.1----------
Detention Pond 1 of Longview Marketplace is only designed to detain runoff from on -
site areas and adjacent roadways. Flows from off -site basins and roadways will be by-
passed through the pond undetained. The total amount of area receiving detention is
approximately 17.067 acres. This area is assumed to be 100% impervious. The Modified
FAA analysis resulted in a required stormwater detention volume of 4.245 acre-feet.
This detention volume will be provided in Pond 1 on top of any required water quality
capture volume. Additionally, one -foot minimum freeboard will be provided between the
100-year water surface elevation and the top of the pond. Table 3 summarizes the design
of both the Sub -Surface Detention System and Detention Pond 1.
TABLE 3
Detention Design Summary
_
Sub -Surface
Storage
Pond 1
"Pond Invert Elevation (ft)
5011.00
5012.67
Water Quality Capture Volume (ac-ft)
N/A
0.853
WQCV Water Surface Elevation (ft)
N/A
5022.78
Stormwater Detention Volume (ac-ft)
0.718
4.245
100-year Water Surface Elevation (ft)
5021.0
5031.89
Top of Pond Elevation (ft)
5023.0
5033.50
Maximum 100-year Release Rate (cfs)
1.7
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Final Drainage Report
Longview Marketplace
November 5, 2002
Northern Engineering Services, Inc
An inline Stormceptor model STA-2400 structure will be installed on Storm Line
SC before it discharges into Detention Pond 1.
4.6 Colorado Department of Transportation (CDOT) HWY 287
Longview Marketplace is being designed with two conditions of South College Avenue
(HWY 287) in mind. The first condition will be the "interim" state of College Avenue.
This will include approximately 22' of new asphalt along the west side of College, as
well as new vertical curb and gutter. The interim condition is expected to remain for
roughly 20 years.
This project's design also accommodates the "ultimate" section of HWY 287. The
ultimate roadway section of South College Avenue will further expand approximately 44'
west of the interim curb and gutter. To limit the amount the future reconstruction, both
Avondale Drive and the private entrance off College into the site have been designed to
the ultimate flowline of HWY 287. Concrete cross -pans will be built now in these streets
at the locations of the future intersections.
It is desired by CDOT to completely separate the stormwater runoff from Longview
Marketplace and South College. The proposed on -grade combination inlets will keep the
project's runoff from traveling into College Avenue for both the interim and ultimate
condition. Curb Inlets FS and FN will be installed at Avondale Drive and the private
entrance respectively to collect flows from College during the interim condition. A
temporary H.D.P.E. storm sewer will convey these flows to the relocated sump inlet in
HWY 287 adjacent to the site. This will allow the runoff from South College to continue
to follow its historic drainage pattern.
4.7 Detention
While stormwater detention is not mandated by the Fossil Creek Drainage Basin Master
Drainageway Plan, detention is necessary due to site release rate constraints. Runoff
from Longview Marketplace site will be detained in two locations. The first location is
the Sub -Surface Detention Storage. This system will be used to detain developed runoff
from Basin A. Basin A contains both on -site and off -site areas; however, detention
storage will be provided for the on -site areas only. The total amount of area receiving
detention is approximately 2.848 acres. This area is assumed to be 100% impervious.
The resulting Modified FAA analysis requires a stormwater detention volume of 31,273
cu-ft. The Sub -Surface Detention Storage System will drain into Storm Line B, and
subsequently travel through line OSSD. The system is located directly underneath
Detention Pond 1. Table 1 summarizes the areas draining to the underground storage
pipes.
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Final Drainage Report
Longview Marketplace
November 5, 2002
Northern Engineering Services, Inc
adjacent ridgeline, and eventually travel into HWY 287.
4.5.4 Basin D (0.960 acre)
Basin D has been divided into two (2) sub -basins labeled D1 and D2. This basin
is located along the private drive entrance into the site along South College
Avenue. Runoff from this basin will travel to the east via the private drive
vertical curb and gutter. A series of on -grade combination inlets will intercept
flows from Basin D before they reach South College Avenue. Storm Sewer Line
D will carry flows from the combination inlets to Storm Line C, where runoff will
continue to travel into Detention Pond 1. Emergency overflow from Basin D will
by-pass the on -grade inlets and travel into College Avenue.
4.5.5 Basin E (15.494 acres)
Basin E has been divided into eight (8) sub -basins labeled El — E4, El 1, E12,
E21, and E22. Basin E is located towards the north end of the site. Basins E1 and
E2 are undeveloped off -site areas adjacent to Longview Drive that drain back into
the roadway. Basins EI I and E12 are the Longview Drive street section itself.
Runoff from these basins will travel to the east via the Longview Drive vertical
curb and gutter to Inlet E1 located in the west flowline of Strasburg Avenue.
Basin E3 consists of parking areas and building rooftops. This basin drains to the
west towards Inlet E2 located in the east flowline of Strasburg Avenue. Basin E4
is an undeveloped off -site area located west of Strasburg Avenue that drains back
into the roadway. Basins E21 and E22 are the Strasburg street section itself.
Runoff from these basins will travel to the south via the Strasburg Avenue vertical
curb and gutter to sump inlets located at the low -point of the roadway.
Storm Sewer Line E collects runoff from Inlets E1 and E2 and conveys flow into
Storm Line C, where it continues to travel into Detention Pond 1. Emergency
overflow from Basin E will overtop to the east and travel into College Avenue.
The design of existing Storm Line OSSD did not account for runoff from off -site
Basins E1, E2, and E4. Therefore, Storm Line E is only designed to carry the 10-
year flows from these basins. The 100-year runoff from Basins El, E2, and E4
will overtop Strasburg Avenue, and travel to the historic drainage outfall in HWY
287.
4.5.6 Basins 17-A & 17-B (0.694 acre)
Basin 17 was defined in the Final Drainage Report for Shenandoah P.U.D. First
Filing. This basin travels undetained into Benson Lake through an existing 48"
RCP under College Avenue. A license agreement was recorded in September of
1996 to allow this drainage. A copy of this agreement is included in the appendix
of this report.
4.5.7 Basin SC (0.307 acre)
Basin SC is an isolated area contained within Basin B2. This basin contains a gas
station, and thus, its runoff has been separated from the surrounding areas.
t Runoff from this basin will drain through an area inlet into Storm Sewer Line SC.
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Final Drainage Report
Longview Marketplace
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4.4 Hydraulic Criteria
The City of Fort Collins SDDCM has been referenced for all hydraulic calculations. The
modified FAA Method as outlined in Volume I of the USDCM was used to size the
detention ponds. In addition, the following computer programs have been utilized:
• The computer program "CONTECH Underground Stormwater Detention System
Design Program vl.1.1" by Contech has been used to determine underground
storage volumes
• The computer program "StormCAD v4.1.1 [4.2014a]" by Haestad Methods has
been used to design and analyze the storm sewer lines and outlet pipes
• The computer program "F1owMaster v6.1 [614o]" by Haestad Methods has been
used to design and analyze curb inlets, weirs, and street capacities
4.5 Drainage Patterns
4.5.1 Basin A (3.900 acres)
Basin A has been divided into four (4) sub -basins labeled Al, A2, Al l and Al2.
Basins Al and A2 are undeveloped off -site areas adjacent to Avondale Drive that
drain back into the roadway. Basins Al I and Al2 are the Avondale street section
itself. Runoff from this basin will travel to the southeast via the Avondale vertical
curb and gutter. A series of on -grade combination inlets will intercept flows from
Basin A before they reach South College Avenue. Storm Sewer Line A will carry
flows from the combination inlets into the sub -surface detention storage system.
Emergency overflow from this basin will by-pass the on -grade inlets and travel
into College Avenue.
4.5.2 Basin B (4.895 acres)
Basin B has been divided into three (3) sub -basins labeled B1 - B3. This basin is
located at the southeast corner of the site, and excludes the solitary Basin SC.
Basin B 1 contains Detention Pond 1. Basins B2 and B3 consist of parking areas
and building rooftops. Runoff from Basins B2 and B3 will sheet flow into pans
and vertical curb and gutter. Curb cuts will allow flow to travel directly into
Detention Pond 1. Storm Sewer Line B will convey the discharge from
Detention Pond 1 into the Storm Line OSSD Re -alignment. This line connects
into the existing 24" RCP storm sewer line at intersection of HWY 287 and
Avondale Drive. Emergency overflow from Detention Pond 1 will safely spill to
the south into College Avenue.
4.5.3 Basin C (8.930 acres)
Basin C has been divided into four (4) sub -basins labeled C1 — C4. This basin is
located at the center of the site. Basins C 1 — C3 consist of parking areas and
building rooftops. Basin C4 is an undeveloped off -site area that drains into the
loading drive along the western property boundary. Basins C1 & C3 each drains
to its own sump inlet. Basin C2 drains to three sump inlets each designed to
intercept approximately one-third of the total basin area. All inlets collect runoff
and convey it into Storm Sewer Line C. Storm Sewer Line C drains into
Detention Pond 1. Emergency overflow from each sump area will overtop the
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Final Drainage Report
Longview Marketplace
November 5, 2002
Northern Engineering Services, Inc
In order to shift the historic drainage from Longview Marketplace from one basin to
another, the release rate into the OSSD storm sewer will have to be increased.
Fortunately, the pipeline was installed with rubber gaskets. Therefore, the storm sewer
can become pressurized in order to accommodate the increased discharge from Longview
Marketplace. Most of the 23.0 acres accounted for in the original design of the OSSD
storm sewer lie west of the Longview Marketplace boundary. As such, the original
assumptions made for this area will remain unchanged.
Off -site runoff from future filings of Shenandoah P.U.D. enters the site in multiple
locations. Most of the runoff is conveyed to the site via off -site streets. All off -site
runoff will be bypassed through Longview Marketplace's detention pond. Adequate
conveyance for historic off -site flows will be provided, but water quality treatment and
detention storage will not.
IV, POST -DEVELOPMENT CONDITIONS
4.1 Post -development Conditions
The Longview Marketplace development will include the following:
• King Soopers Supermarket;
• (7) seven commercial/office/retail buildings;
• (1) one bank;
• (1) one gas station;
• new curb, gutter, walk, and asphalt along the west side of HWY 287;
• on -site street improvements;
• drainage improvements and utility services.
Off -site street, grading, and drainage design will be done with Longview Marketplace;
however, the construction of these improvements will be done with future filings.
4.2 Design Criteria and References
Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria
Manual, (SDDCM) and the Urban Storm Drainage Criteria Manual (USDCM) by the
Urban Drainage and Flood Control District have been referenced for this study. The
"Final Drainage Report for Shenandoah P.U.D. First Filing" prepared by Northern
Engineering Services, Inc. and the "Final Drainage and Erosion Control Study for
Ridgewood Hills P.U.D. Third Filing" prepared by Nolte Associates have also been
referenced.
4.3 Hydrologic Criteria
The Rational Method has been used to estimate peak stormwater runoff within the
developed site. The minor 10-year and major 100-year design storms have been used in
the design of the proposed drainage system, which includes curb inlets, combination
inlets, storm sewer, a detention pond, and a Stormceptor® structure. Rainfall intensity
data for the Rational Method has been taken from Figure 3-1 a updated by the City of Fort
Collins in 1999.
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Final Drainage Report Northern Engineering Services, Inc.
Longview Marketplace
November 5, 2002
easements of various types run along the eastern property boundary adjacent to HWY
287 and a 6' City of Fort Collins Electrical Easement runs along the southern property
line.
2.3 Irrigation Ditches and Reservoirs
The North Louden Irrigation ditch has historically meandered through the middle of the
site. Construction plans entitled "North Louden Ditch Re -Alignment" were submitted in
August of 2002. The re -alignment will divert the ditch completely away from Longview
Marketplace. This construction is expected to take place before Longview Marketplace
develops, thus, it is shown as an existing improvement on the utility plans. Robert
Benson Lake is located east of the site across College Avenue and currently receives
historic drainage from portions of Shenandoah P.U.D.
III. PRE -DEVELOPMENT CONDITIONS
3.1 Major Basin Description
The site is located in the Fossil Creek Drainage Basin. According to the "Fossil Creek
Drainage Basin Master Drainageway Plan," on -site detention is not required. However,
the release rate from Longview Marketplace is limited by the downstream storm sewer,
so on -site detention is necessary.
A portion of the overall Shenandoah P.U.D. site is located in a non-contributing area
which drains to Robert Benson Lake. This non-contributing area was delineated with the
Final Drainage Report for Shenandoah P.U.D., First Filing dated July 24, 1997 by
Northern Engineering Services, Inc..
Longview Marketplace is also a part of SWMM Subcatchment 55 included in the
SWMM modeling for the Fossil Creek Drainageway Planning Study. The model will be
updated separately from this drainage study.
3.2 Pre -development Drainage Patterns
The site drains generally from west to east, at slopes ranging from 3.5% to 15%, to a low
point in South College Avenue. An existing 14"x23" HERCP storm sewer conveys
stormwater under College Avenue to the east towards an existing drainageway.
A 24" RCP storm sewer (OSSD) was recently installed along the southern property
boundary as part of Ridgewood Hills P.U.D., Third Filing. This storm sewer was
designed to allow a total of 6.2 cfs from the southern portion of Shenandoah P.U.D.. An
area of approximately 23.0 acres from Shenandoah was assumed to historically drain to
this line, resulting in an allowable release rate of 0.27 cfs per contributory acre.
Unfortunately, the majority of Longview Marketplace lies outside of the area accounted
for in the design of the Ridgewood Hills off -site storm sewer. This is because Longview
Marketplace has historically drained to the sump inlets and storm sewer located in HWY
287. However, this existing drainage outfall has been deemed insufficient by the City of
Fort Collins' Stormwater Utility for the developed runoff from the site.
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Final Drainage Report
Longview Marketplace
November 5, 2002
Final Drainage Report
for
Longview Marketplace
Fort Collins, Colorado
November 5, 2002
Northern Engineering Services, Inc.
I. INTRODUCTION
1.1 Objective
This report summarizes the results of a comprehensive analysis of both pre- and post -
development hydrologic and hydraulic conditions for the Longview Marketplace site in
Fort Collins, Colorado. Specifically, this report will serve the following:
• Adhere to the hydrology and hydraulics of preceding drainage studies
• Account for off -site runoff from adjacent areas and accommodate possible future
development
• Attempt to utilize existing stormwater appurtenances to their maximum capacity
i Minimize any adverse effects downstream of the project due to developed
stormwater
1.2 Mapping and Surveying
Initial land surveys of the entire Shenandoah P.U.D. site were conducted in 1995 and
1996 by Landstar Surveying. However, since a lot of development has occurred in the
areas surrounding the project over the past six years, a more current and accurate survey
was desired for this design. As a result, a new site survey was conducted by Northern
Engineering Services, Inc. in September of 2002. The existing topography was given at a
one -foot contour interval.
1.3 Site Reconnaissance
Recent site visits have been conducted in 2002 by Northern Engineering Services, Inc..
Existing drainage patterns and land use were amongst the items confirmed during these
visits.
II. SITE LOCATION AND DESCRIPTION
2.1 Site Location
The Longview Marketplace site is located in the southern half of the original Shenandoah
P.U.D.. More specifically, the site is located within the eastern half of the southeast
quarter of Section 14, Township 6 North, Range 69 West of the 61h Principal Meridian in
the City of Fort Collins, County of Larimer, State of Colorado. The project is bounded
by Triangle Drive of Shenandoah First Filing on the north, County Road 32 on the south,
South College Avenue (HWY 287) on the east, and Ridgewood Hills P.U.D. on the west.
(See Vicinity Map)
2.2 Site Description
The Longview Marketplace site is approximately 19.633 acres and has historically been
an undeveloped field. An existing Excel Energy natural gas sub -station exists near the
southwest property corner. A 50'easement runs along the southern property boundary
and contains Excel Energy's high-pressure gas main. Four existing recorded utility
NOVEMBER, 2002
VICINITY MAP
1 "=2000'
Table of Contents
VICINITY MAP
Page
I.
INTRODUCTION
1.1 Objective..........................................................................................
1
1.2 Mapping and Surveying...................................................................
1
1.3 Site Reconnaissance.........................................................................
1
II.
SITE LOCATION AND DESCRIPTION
2.1 Site Location....................................................................................
1
2.2 Site Description................................................................................
1
2.3 Imgation Ditches and Reservoirs.....................................................
2
III.
PRE -DEVELOPMENT CONDITIONS
3.1 Major Basin Description ...................... :............................................
2
3.2 Pre -development Drainage Patterns ................................................
2
IV.
POST -DEVELOPMENT CONDITIONS
4.1 Post -development Conditions..........................................................
3
4.2 Design Criteria and References.......................................................
3
4.3 Hydrologic Criteria ............................. :............................................
3
4.4 Hydraulic Criteria............................................................................
4
4.5 Drainage Patterns............................................................................
4
4.6 Colorado Department of Transportation (CDOT) HWY 287 ..........
6
4.7 Detention..........................................................................................
6
V.
WATER QUALITY
5.1 Water Quality Measures and Criteria ..............................................
8
VI.
EROSION CONTROL PLAN
6.1 Erosion Control Plan and Criteria ....................................................
8
6.2 Rainfall Erosion Control Plan ..........................................................
8
VII.
CONCLUSIONS
7.1 Compliance with Standards.............................................................
9
REFERENCES..........................................................................................
10
APPENDICES
APPENDIX A- Hydrology Calculations
APPENDIX B - Detention & Water Quality Calculations
APPENDIX C - Inlet Calculations
APPENDIX D- Storm Sewer Calculations
APPENDIX E - Street Capacity Calculations
APPENDIX F - Excerpts By Others
APPENDIX G- Erosion Control Calculations
NORTHERN
ENGINEERING
NESERVICES, INC.
November 5, 2002
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Longview Marketplace
Fort Collins, Colorado
Project Number: 02-044.03
Dear Staff'.
Northern Engineering Services, Inc. is pleased to submit this Final Drainage Report for the
Longview Marketplace site for your review. We understand that review by the City of Fort
Collins is to assure general compliance with standardized criteria contained in the Storm
Drainage Design Criteria and Construction Standards. This report was prepared in compliance
with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and
Construction Standards manual.
If you should have any questions or comments as you review this report, please feel free to
contact us at your convenience.
Sincerely,
' NORTHERN ENGINEERING SERVICES, INC.
W � I ry
AAJ 4J
IV-
Nicholas W. Haws, E.I.T.
Project Engineer
Koger A. 114UM
Vice President
27362
420 SOUTH HOWES, SUITE 202 / FORT COLLINS, COLORADO 80521 / 970.221.4158 / FAX 970.221.4159
Final Drainage Report
for
Longview Marketplace
Fort Collins, Colorado
November 5, 2002
Prepared For:
Dillon Companies, Inc. DB/A King Soopers, Inc.
P.O. Box 5567 T.A.
Denver, CO 80217
Quadrant Properties
8000 Maryland Avenue, Suite 640
Clayton, MO 63105
Prepared By:
NE
NORTHERN
ENGINEERING
SERVICES, INC.
420 S. Howes, Suite 202 Fort Collins, Colorado 80521
Phone: (970) 221-4158 Fax: (970) 221-4159
Project Number: SHN (02-044.03)
First Submittal