HomeMy WebLinkAboutJFK SENIOR APTS. - PDP - 61-98 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTli
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SHEET No. 25 OF 31
FORT COLLINS QUADRANGLE
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7. REFERENCES
City of Fort Collins, "Storm Drainage Design Criteria and Construction Standards",
(SDDCCS), dated May, 1984.
Soil Survey of Larimer County Area, Colorado". United States Department of
Agriculture Soil Conservation Service and Forest Service. December, 1980.
Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated March, 1969, and Volume 3 dated September,
1992.
"McClellands Basin Master Drainage Plan," by Greenhorn & O'Mara, Inc., 1986
"Hydrologic Update to the McClellands Master Drainage Plan (Lemay Avenue to Larimer
County Canal No. 2) and Harmony Centre Master Drainage Plan", by Lidstone &
Associates, Inc., 1997.
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0 contractor will be responsible for clearing mud tracked onto city streets on a daily basis.
6.JP Maintenance
All temporary and permanent erosion and sediment control practices must be maintained
and repaired as needed to assure continued performance of their intended function. Straw
bale dikes or silt fences will require periodic replacement. Sediment traps (behind hay
bale barriers) shall be cleaned when accumulated sediments equal about one-half of trap
storage capacity. Maintenance is the responsibility of the developer.
6.5 Permanent Stabilization
All soils exposed during land disturbing activity (stripping, grading, utility installations,
stockpiling, filling, etc.) shall be kept in a roughened condition by ripping or disking
along land contours until mulch, vegetation or other permanent erosion control is
installed. No soils in areas outside project street rights of way shall remain exposed by
land disturbing activity for more than thirty (30) days before required temporary or
permanent erosion control (e.g. seed/ mulch, landscaping, etc.) is installed, unless
otherwise approved by the Stormwater Utility. Vegetation shall not be considered
established until a ground cover is achieved which is demonstrated to be mature and
stable enough to control soil erosion as specified in paragraph 11.3.10 of the City of Fort
Collins Storm Drainage Construction Standards.
1 6. EROSION CONTROL
6.1 Erosion and Sediment Control Measures
Erosion and sedimentation will be controlled on -site by use of inlet filters, silt fences,
straw bale barriers, a sediment trap and gravel construction entrances. (See the Final
Drainage and Erosion Control Plan for details.) The measures are designed to limit the
overall sediment yield increase due to construction as required by the City of Fort Collins.
A construction schedule showing the overall period for construction activities is
contained in Appendix F and shown on the Final Drainage and Erosion Control Plan.
A sediment trap shall be constructed by over -excavating the permanent detention pond
located on the west side of the site. Silt fences or straw bale dikes will be utilized in
limited areas adjacent to any stripping stockpiles that are created during grading. They
will also be used to slow runoff around the perimeter of the site, along the south and east
property line.
6.2 Dust Abatement
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the
contractor shall furnish all labor, equipment, materials, and means required. The
Contractor shall carry out proper efficient measures wherever and as necessary to reduce
dust nuisance, and to prevent dust nuisance, which has originated from his operations
from damaging crops, orchards, cultivated fields, and dwellings, or causing nuisance to
persons. The Contractor will be held liable for any damage resulting from dust
originating from his operations under these specifications on right-of-way or elsewhere.
6.3 Tracking Mud on City Streets
It is unlawful to track or cause to be tracked mud or other debris onto city streets or
rights -of -way unless so ordered by the Director of Engineering in writing. Wherever
construction vehicles access routes or intersect paved public roads, provisions must be
made to minimize the transport of sediment (mud) by runoff or vehicles tracking onto the
paved surface. Stabilized construction entrances are required per the detail shown on the
Erosion Control Plan, with base material consisting of 6" coarse aggregate. The
1 10 1
�r TABLE 5.2 — DETENTION POND 305
AREA -CAPACITY RATING CURVE
Elevation
Area
Area
(ac)
Cumulative
Storage (ac-ft)
18.00
0
0
0
19.00
1946
0.0447
0.015
20.00
6094
0.1399
0.103
21.00
8248
0.1893
0.267
22.00 1
11293 1
0.2592 1
0.490
TABLE 5.3 — DETENTION POND 305
CAPACITY -DISCHARGE_ RATING CURVE
Remarks
Elevation
(ft)
Storage
(ac-ft)
Outlet Q
(cfs)
18.00
0.000
0.00
19.00
0.015
0.40
10-yr WSEL-
19.80
0.080
0.56
20.00
0.103
0.60
21.00
0.267
0.74
100-yr WSEL-
21.80
0.440
0.84
spill elev -
22.00
0.490
0.86
top of berm -
22.00
0.490
0.86
Stora e: See Table 5.2 Area -Capacity Rating Curve
10 yr Outlet: 15" pipe w/ 4" dia. Orifice plate
100 yr Outlet: 15" pi2e w/ 4" dia. Orifice plate
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pond outlet structure is included in the Final Utility Plans for the site. Orifice plate sizing
and the stage -discharge curve was calculated using the orifice equation which states,
Qo = CoAo [2g(h-Eo)]1/2 (4)
where Qo =orifice outflow (cfs)
Co = orifice discharge coefficient
g = gravitational acceleration
Ao = effective area of the orifice (ft)
E. = geometeric center elevation of the orifice (ft)
h = water surface elevation (ft)
n
The pond outlet structure will be connected to the proposed storm sewer adjacent to JFK
tParkway.
The volume available for detention storage was calculated using the following formula,
V = 1/3 d [A+B+sgrt(AB)] (5)
Where V = Volume between contours under questions, cu. Ft.
d = depth between contours, ft
�. A = surface area of contour, ft2
B = surface area of contour line at a depth relevant to d, ft2
The 100-year and 10-year maximum water surface elevations (WSEL) were found by
iterating on the outlet orifice size, the resulting pond storage -discharge rating curves and
the SWMM analysis detention storage requirements. The required storage volume for the
10-year event is 0.08 acre-feet, and the required storage volume for the 100-year event is
0.44 acre-feet. The final WSEL for the 10-year and 100-year event respectively is 4919.8
feet msl and 4921.8 feet msl. Tables 5.2 and 5.3 summarize the operating parameters for
r the proposed detention pond.
�. 8
5.
AA and BB are subcritical. Sizing for the swales are included in Appendix B and cross
sections are shown on the Drainage and Erosion Control Plan.
REGIONAL HYDROLOGIC ANALYSIS
5.1 SWMM Analysis
The regional hydrologic analysis was performed using MODSWMM. The JFK
Apartments site is subcatchment 391 of the LA Report SWM Model. The resistance
factors, surface retention storage, and infiltration rates are equal to the recommended
values in the Fort Collins SDDCCS Manual and as detailed in said report.
TABLE 5.1 SWMM SUBCATCHMENT PARAMETERS
Subbasin
Basin
Width (ft)
Area
(ac.)
%
Impervious
Slope (ft/ft)
391
600
2.8
70
0.02
Pond 491 from the LA Report SWM Model is included in this model. A SWMM
schematic is included in Appendix D.
5.2 Detention Pond Design
The proposed pond (491) for JFK Apartments is located on the west side of the site.
In accordance with the LA Report criteria, the maximum release rate from the site is 1.0
cfs. This is based upon a development agreement that is part of the LA report. The
actual developed 2-year release rate from the site is 0.6 cfs and the 100-year release is 0.8
cfs
To meet the allowable release rates, an orifice plate is required for the 100-year outlet
pipe and the 10-year outlet pipe for the proposed Type III pond outlet_ A detail of the
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4. STORM WATER FACILITY DESIGN
4.1 Curb Inlets & Chases
Curb inlets, curb cuts or sidewalk culverts are proposed where sump conditions exist or
where street runoff carrying capacity is exceeded or where JFK Parkway is collected and
discharged into our detention pond. Inlet capacity reduction factors were used to account
for inlet clogging. Inlets were sized using the computer program UDMUT that was
developed by James C. Y. Guo of the University of Colorado at Denver. Results of
UDMUT sizing is equivalent to using Figures 5-2 to 5-6 of the Fort Collins SDDCCS
Manual. Computer output files for the inlet sizing are provided in Appendix B of this
report. All inlet locations and sizes are shown on the Final Drainage and Erosion Control
Plan for the construction of this project.
4.2 Storm Sewer Pipe
Storm sewer outlet pipes from inlets are sized based on the theoretical capacity of the
inlets. All other culverts are sized to convey the peak flows from Rational Method
calculations. The computer program StormCAD, developed by Haestad Methods, Inc.,
was used for the storm pipe design. StormCAD considers whether a culvert is under inlet
or outlet control and if the flow is uniform, varied, or pressurized and applies the
appropriate equations (Manning's, Kutter's, Hazen -Williams etc).
A flared end section and riprap is required at all storm sewer outfalls. Riprap is sized
according to the pipe size and the flow conditions at the outlet. Guidelines from the
"Urban Storm Drainage Criteria Manual" (UDFCD) were used to design the riprap
outfalls. Calculations for riprap sizing can be found in Appendix E.
4.3 Open Channels
�I There are two swales (AA and BB) proposed for the JFK Senior Apartments site. Swale
�J AA is designed to, hydraulically connect the parking lot drainage to the culvert entering
the north detention area. This swale is inundated by and part of the 100 year storage
volume. All of the swales were designed to carry 133% of the major storm runoff (100-
year recurrence interval). The maximum channel side slope is 4:1 and flows in swales
6
The appropriate rainfall intensity information was developed based on rainfall intensity
duration curves in the SDDCCS Manual. The time of concentration used in the rainfall
intensity curves was calculated using the following equation,
tc = ti + tt (2)
where t, is the time of concentration in minutes, ti is the initial or overland flow time in
minutes, and tt is the travel time in the channel, pipe, or gutter in minutes. The initial or
overland flow time is calculated with the equation:
ti = [1.87(1.1 - CCf)Lo"]/(S)0.33 (3)
where L is the length of overland flow in feet (limited to a maximum of 500 feet), S is the
average slope of the basin in percent, and C and Cf are as defined previously.
All hydrologic calculations associated with the subbasins are attached in the Appendix of
this report. Table 3.1 provides a summary of design flows for all subbasins and design
points for this site.
TABLE 3.1 DRAINAGE SUMMARY TABLE
DESIGN
POINT
SUBBASIN (S)
AREA
(ac)
C
10-YR
tc
10-YR
(min)
Q
10-YR
(cfs)
C
100-YR
tc
100-YR
(min)
Q
100-YR
(cfs)
1
100
0.18
0.46
9.40
0.38
0.58
10.00
0.92
2
100 & 101
0.99
0.79
12.56
3.19
0.99
11.44
8.24
3
100 - 102
1.15
0.76
12.88
3.54
0.96
12.09
9.08
4
103
0.28
0.39
11.11
0.47
0.49
11.11
1.16
5
100-104 & 106
2.78
0.63
12.88
7.06
0.79
12.88
17.60
6
106
0.33
0.84
6.52
1.46
1.00
10.00
2.97
1W
l� I The outflow from design point 1 and the runoff from subbasin 101 flow east
along a gutter to design point 2. This is located at a sidewalk culvert discharging
IF to swale AA.
The outflow from design point 2 and the runoff from subbasin 102 are conveyed
through swale AA to design point 3. This is located at a culvert under a
sidewalk. The culvert directly discharges into the detention area.
Runoff. from subbasin 103 is conveyed via overland flow to a sidewalk culvert
This is design point 4.
The outflow from design point 4 and the runoff from subbasin 104 are conveyed
through Swale BB into the detention pond.
Runoff from subbasin 105 is free -discharge to JFK Parkway.
Runoff from subbasin 106 is collected runoff from JFK Parkway that is conveyed
17 into the detention pond by two — four foot sidewalk culverts into the detention
-i pond. This is design point 6. This is the non -tributary area that is collected and
detained to compensate for the free -discharge above.
�r
The detention pond discharges into a release pipe, design point 5, along JFK
j Parkway. This connects to an existing storm sewer 350 feet south of our property.
t
3.3 Hydrologic Analysis of the Proposed Drainage Conditions
The Rational Method was used to determine both 10-year and 100-year peak runoff
values for each subbasin. The Rational Method is based on the Rational Formula,
Q = CfCIA
(1)
where Q is the maximum rate of runoff in cubic feet per second (cfs), A is the total area
of the basin in acres, Cf is the storm frequency adjustment factor, C is the runoff
coefficient, and I is the rainfall intensity in inches per hour. The frequency adjustment
factor (Cf) is 1.0 for the initial 10-year storm and 1.25 for the major 100-year storm.
4
r
I
I flow.
An area at the south west corner of our site freely discharges to JFK Parkway. Our access
point to JFK Parkway controls our grading to the extent that this area cannot be collected
and discharged into the detention area.
1
This free discharge area is counter -balanced by collection and detention of a portion of
JFK Parkway's runoff. This is hydraulically connected to the detention pond by sidewalk
culvert's. This connection limits the effective use of freeboard in the detention area.
Detention is required and will be provided using a detention pond located on the west
portion of the site. Total release rate is in accordance with the aforementioned LA
Report.
The detention pond will released storm water into a proposed storm sewer along the east
side of JFK Parkway. This storm sewer will connect into the existing inlet at the low
point on the east side of JFK Parkway south of our site.
This existing storm sewer system is designed to carry the detained release from our site.
The developed impervious percentage of our site is 56% which is below the assumed
70% shown in the LA Report.
Street capacity will not be exceeded in JFK Parkway during the minor or major storm
events. Street capacity calculations are included in Appendix A.
3.2 Proposed Subbasin Descriptions
A summary of the drainage patterns within each subbasin and at each design point is
provided in the following discussion. Details of the drainage facility design are included
�1 in Section 4.
Runoff from subbasin 100 is conveyed via overland flow to a sidewalk culvert.
This is design point L_
3
Storm Drainage Criteria Manual" (UDFCD), 1984, developed by the Denver Regional
Council of Governments, was used.
The Rational Method was used to calculate peak 10-year minor and 100-yr major runoff
values. Local drainage facilities such as curb chases and storm pipes were designed to
convey peak flows. Regional hydrologic calculations were made using the runoff block
of UDSWM2-PC Rainfall/Runoff Prediction and Watershed Simulation Program
(SWMM) endorsed by the Urban Drainage and Flood Control District.
1.5 Master Drainage Basin & Other Drainage Reports
This site is included in the McClellands Drainage Basin. The master study for this
property is the "McClellands Basin Master Drainage Plan" by Greenhorn and O'Mara,
Inc., 1986. This study has been revised by "Hydrologic Update to the McClellands Master
Drainage Plan (Lemay Avenue to Larimer County Canal No. 2) and Harmony Centre
Master Drainage Plan" by Lidstone and Anderson, Inc., 1997 (LA Report). The LA
Report showed and impervious area of 70 percent and a release rate of 1.0 cfs
2. HISTORIC DRAINAGE
Historically the JFK Senior Apartments site drains from the north to the south at a slope
�) of 1 to 6 percent. Runoff then overflows the south and west property lines. This
�J continues south and east across Martin West Properties. This historic system was
augmented by the construction of JFK Parkway, inlets, and a piped system to discharge
into the Harmony Centre Detention Pond.
�J
�l 3. DEVELOPED DRAINAGE
�J
�) 3.1 General Flow Routing
The final drainage pattern for JFK Senior Apartments uses the existing drainage patterns
as much as possible and routes flows to limit the number of drainage structures required.
The site is graded to carry flows away from structures and into the streets and proposed
detention ponds. Flows within the site take the form of overlot, swale, street, or conduit
`� 2
1. INTRODUCTION
1.1 Project Description
The JFK Senior Apartments is a proposed development that consists of apartment
buildings, a clubhouse, a parking lot and drive area, and landscape area, including a
detention pond. JFK Senior Apartments is located in the Southwest One -Quarter of
Section 36, Township 7 North, Range 69 West of the Sixth Principal Meridian, in the
City of Ft. Collins, Larimer County, Colorado. The site is bounded by JFK Parkway on
the west, Troutman Parkway on the north, by an existing apartment complex within
Somerset P.U.D. on the east, and undeveloped land owned by Martin West Property lies
to the south. A vicinity map is included after the Table of Contents of this report.
1.2 Existing Site Characteristics
The JFK Senior Apartments project site includes approximately 2.88 acres of land that is
covered with rangeland grasses and weeds. Soil on the site includes Fort Collins loam
(35) and Nunn clay loam (74) according to the "Soil Survey for Larimer County Area,
Colorado" (USDA). The Fort Collins and Nunn series consists of deep, well -drained
soils that formed in alluvium. The characteristics of the Fort Collins series include slow
runoff and slight erosion. The characteristics of the Nunn series include medium runoff,
moderate water erosion, and slight wind erosion. The site is within the moderate wind
erodibility zone according to the Wind Erodibility Map for the City of Fort Collins.
1.3 Purpose and Scope of Report
This report defines the proposed final drainage plan for JFK Senior Apartments,
including consideration of all on -site and tributary off -site runoff. The plan includes
design of all drainage facilities required for this development.
1.4 Design Criteria & Methods
�1
This report was prepared to meet or exceed the submittal requirements established in the
"City of Fort Collins Storm Drainage Design Criteria and Construction Standards"
(SDDCCS), dated May 1984. Where applicable, the criteria established in the "Urban
1 /
VICINITY MAP
N.T.S.
JFK SENIOR APARTMENTS
VICINITY MAP
w
TABLE OF CONTENTS
PAGE
ABLEOF CONTENTS...............................................................................................................iii
VICINITYMAP............................................................................................................................. iv
1. INTRODUCTION...............................................................................................................1
1.1 Project Description..................................................................................................1
1.2 Existing Site Characteristics....................................................................................1
1.3 Purpose and Scope of Report ..................................................................................1
1.4 Design Criteria & Methods.....................................................................................1
1.5 Master Drainage Basin & Other Drainage Reports ................................................. 2
2. HISTORIC DRAINAGE..................................................................................................... 2
3. DEVELOPED DRAINAGE................................................................................................ 2
3:1 General Flow Routing............................................................................................. 2
3.2 Proposed Subbasin Descriptions............................................................................. 3
3.3 Hydrologic Analysis of Proposed Conditions......................................................... 5
4. STORM WATER FACILITY DESIGN............................................................................ 6
4.1 Curb Inlets & Chases............................................................................................... 6
4.2 Storm Sewer Pipes.................................................................................................. 6
4.3 Open Channels........................................................................................................ 7
5. REGIONAL HYDROLOGIC ANALYSIS.........................................................................7
5.1 SWMM Analysis.....................................................................................................7
5.2 Detention Pond Design............................................................................................ 8
6. EROSION CONTROL...................................................................................................... 11
6.1 Erosion and Sediment Control Measures..............................................................11
6.2 Dust Abatement.....................................................................................................11
6.3 Tracking Mud on City Streets............................................................................... 11
6.4 Maintenance.......................................................................................................... 12
6.5 Permanent Stabilization.........................................................................................12
7. REFERENCES..................................................................................................................13
APPENDIX A - HYDROLOGIC & STREET CAPACITY CALCULATIONS
APPENDIX B - INLET, PIPE AND SWALE DESIGN
APPENDIX C - DETENTION POND DESIGN
APPENDIX D - SWMM ANALYSIS
APPENDIX E - RIPRAP DESIGN
APPENDIX F - EROSION CONTROL CALCULATIONS
APPENDIX G - EXCERPTS FROM OTHER REPORTS
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FINAL DRAINAGE AND
EROSION CONTROL STUDY
JFK SENIOR APARTMENTS
Prepared for:
KAUFMAN & BROAD MULTI -HOUSING GROUP, INC.
320 Golden Shore, Suite 200
Longbeach, California 90802
(562)256-2055
Prepared by:
JR ENGINEERING, LTD.
2620 E. Prospect Rd., Suite. 190
Fort Collins, Colorado 80525
(970)491-9888
November 23, 1998
Job Number 9212.00