HomeMy WebLinkAboutPROMONTORY - PDP - 32-99 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI
report. The flow from the right-of-way of Boardwalk to the northeast of the Post Office site
is directed across the parking lot of the site and finally to the detention basin. For the
purposes of this report, adjacent Boardwalk Drive right-of-way is considered onsite flow.
3.3 Onsite Flows
Flows within this site will take the form of overlot, swale and gutter flow. The existing
drainage patterns have been maintained where possible. All grading has been designed to
carry flows away from structures to the proposed detention basin.
3.4 General Flow Routing
The final drainage pattern for this area has been developed to provide a drainage system that
is compatible with the surrounding area and in accordance with the Heart SID flow
allocation. This has been accomplished by utilizing existing drainage patterns to the fullest
extent possible and routing flows to limit the amount of required drainage facilities.
The proposed drainage facilities for this site consist of the swale on the west side of the
property, sidewalk culverts, an area inlet, and concrete pans to route as much runoff as
possible through parking areas to the proposed detention basin on the southwest side of the
site adjacent to Latimer Ditch No. 2. (See below for further discussion.)
The proposed drainage system meets the requirements for providing drainage relief by
reducing the impact of the flows generated by the development of this site on downstream
areas (restricting release rates to allocated levels) and meets the criteria in the SDDCCS. See
attached "Preliminary Drainage and Erosion Control Plan" for the location of all drainage
facilities.
3.5 Proposed Drainage Plan
A qualitative summarization of the drainage patterns within each sub -basin and at each
design point is provided in the following discussion paragraphs. Discussions of the detailed
design of drainage facilities identified in this section are included in the Appendices of this
report.
Runoff from Sub -basin 101 will be conveyed via overland flow to a swale that will
transport the water to the detention basin.
Runoff from Sub -basin 102 will be conveyed via overlot and gutter flow across the
parking area to design point 2 and then into the detention pond.
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7.
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2.
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4.
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Q
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, 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.
"Final Drainage Report for the Heart Special Improvement District", prepared by
Engineering Professionals, Inc., dated December 1984.
"Final Drainage Report for the Landings Office Park P.U.D.", prepared by Northern
Engineering Services, Inc., dated October 1995.
"Final Drainage Report for Aspen Station Post Office", prepared by Merrick &
Company Engineers & Architects, dated September 1991.
6.
5.5 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.
MISCELLANEOUS
6.1 Variances
There are no variances requested with the development of the Park Place P.U.D..
6.2 Irrigation Ditches
The development of Park Place P.U.D. will be in conformance with the flow allotted in the
Heart SID Drainage Report. Normal depth calculations for the canal under 100-year flow
conditions are in Appendix B. The detention basin will not be surcharged during the 100-
year event.
_ 6.3 Ditch Company Approval
Ditch company approval will be included in the Final Utility Plans for this development for
the Larimer Canal No. 2.
6.4 Maintenance Agreements
The developer will be responsible for the maintenance of all temporary drainage structures.
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erosion control plan has an effectiveness of 81.2%, which is greater than the required rainfall
performance standard of 77.7%.
A sediment trap shall be constructed by over -excavating the detention pond. 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 west property line.
5.2 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.
5.3 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 contractor will be
responsible for clearing mud tracked onto city streets on a daily basis.
5.4 Maintenance
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.
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4. DETENTION POND DESIGN
There is one detention pond proposed with the development of the Park Place P.U.D. This
pond is designed to reduce the developed 100-year runoff from this site to the flow allotted
for this area in the Heart SID drainage report (0.87cfs/acre). The allotted release from the
detention pond is as follows:
+4.89 Ac. * 0.87 cfs/Ac. (Heart SID Allotment)
+100 Year Offsite Flow (Basin 102a)
-Undetained Site Flow (Basins 105b and
PERMITTED RELEASE FROM BASIN =
+4.25cfs
+0.40cfs
-3.9 cfs
0.75 cfs
In addition to the allowable release from the Park Place site, offsite flow from the Landings
Office Park that enters the site to the north and east will be routed through the detention
pond. The allowable release rate was increased by 3.67 cfs that enters the site as discussed
in Section 2. The required pond size was calculated using the FAA Method. The required
size to detain the area from the Park Place site and release at 0.75 cfs is 0.86 ac-ft. The
orifice on the pond outlet was sized to release 4.42 cfs (0.75cfs allowed from Park Place +
3.67 from offsite flows). Design calculations for the detention basin are included in the
Appendices of this report.
1 5. EROSION CONTROL
5.1 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 entrance. (See the Overall Grading and
Drainage 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 shown on the Overall Grading and
Drainage Plan. Erosion control effectiveness calculations and cost estimates are included in
Appendix C. The required erosion control security deposit is $5,630.25. The proposed
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Table 3.1 DRAINAGE SUMMARY TABLE
Design
Point
Tributary
Sub -basin
Area
(ac)
C (10)
C (100)
tc (10)
(min)
tc (100)
(min)
Q(10)tot
(cfs)
Q(100)tot
(cfs)
1
101
0.56
0.38
0.48
7.6
6.9
0.91
2.40
102
2.54
0.82
1.00
10.1
9.2
7.86
20.40
102a
0.04
0.78
0.98
5.0
5.0
0.15
0.40
2
102+102a
2.58
0.82
1.00
10.6
9.6
7.71
20.30
3
103
0.51
0.39
0.49
10.2
9.5
1.49
3.30
4
104
0.09
0.90
1.00
5.0
5.0
0.41
0.90
5a
105a
0.17
0.67
0.84
5.0
5.0
0.66
1.80
5b
105b
0.27
0.57
0.71
7.3
6.1
0.88
2.80
106
0.36
0.10
0.13
10.8
10.8
0.13
0.30
6
101 - 104 +
106+Pipe
4.10
0.62
0.80
15.2
15.2 1
�ML24_90
107
0.39
0.29
0.36
9.5
8.7
0.44
1.20
3.7 Allowable Street Flow Capacities
Park Place P.U.D. increases flows on existing streets very slightly. The calculations for
allowable street capacities for surrounding, existing streets are shown on the output sheets
for the program UDINLET and don't exceed the maximum depths set forth in the SDDCCS.
3.8 Inlet Design
There is one inlet proposed with the Park Place P.U.D. development. This inlet is an area
inlet and designed per SDDCCS specifications and the calculations are shown in Appendix
B. The orifice plate at the detention basin outlet is designed in Appendix D.
3.9 Storm Sewer Design
There are three storm sewer pipe systems proposed with the development of Park Place
P.U.D. There is a 15" RCP pipe system from design point 3 to the detention basin, a 15"
RCP extension for the pipe entering the site from the Landings Office Park, and an 15" RCP
outlet pipe from the detention basin. Storm pipes were preliminarily sized using FlowMaster
and StormCAD computer programs. The output of these programs is shown in Appendix
B.
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As stated above, the Rational Method was used for all hydrologic analyses for the project
site. The Rational Method utilizes the SDDCCS equation:
Q = CrCIA (1)
where Q is the flow in 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, Cr, is 1.0 for the initial 10-year storm and 1.25 for the
major 100-year storm.
The appropriate rainfall intensity information was developed based on the new rainfall
intensity duration curves released by the City of Fort Collins in April of 1999.
In order to utilize the rainfall intensity curves, the time of concentration is required. The
following equation was used to determine the time of concentration:
t�= 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 ditch, channel, or gutter in minutes. The initial or
overland flow time is calculated with the SDDCCS Manual equation:
1 h = [1.87(1.1 - CCr)LOs]/(S)a33 (3)
where L is the length of overland flow in feet (limited to a maximum of 300 feet for
developed areas), S is the average slope of the basin in percent, and C and Cr are as defined
previously.
All hydrologic calculations associated with the subbasins and design points are attached in
the Appendices of this report. Table 3.1 provides a summary of the design flows for all
Subbasins and Design Points associated with this site.
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Runoff from Sub -basin 102a will be conveyed via overlot and gutter flow to join
runoff in Sub -basin 102 to be delivered to the detention basin.
Runoff from Sub -basin 103 will be conveyed via overland and swale flow to an area
inlet at design point 3. At this point the runoff will be routed to the detention basin
by a 15" concrete pipe.
The runoff from Sub -basin 104 will be routed via gutter flow. From here the storm
water will flow to a curb cut and sidewalk chase at design point 4 to join runoff from
Sub -basin 103 and be piped to the detention basin. That runoff not intercepted by
the curb cut and sidewalk chase will drain to Sub -basin 105a.
The runoff from Sub -basin 105a will be conveyed via overland and gutter flow to
Boardwalk Drive and then south to a curb cut and sidewalk chase that leads to Sub -
basin 103. The runoff not intercepted by the curb cut and sidewalk chase is directed
to Sub -basin 105b.
The runoff from Sub -basin 105b will be conveyed via overland and gutter flow
south along Boardwalk Drive to Troutman Parkway and east to an existing inlet that
empties into an Larimer Ditch No. 2.
Sub -basin 106 is the area in and directly draining to the detention pond. From here,
the runoff is discharged into Larimer Ditch No. 2 on the southern side of the
property.
The runoff from Sub -basin 107 is conveyed via overland flow to the Larimer Ditch
No. 2 on the south side of the property.
3.6 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 Sub -basin. Runoff coefficients were assigned utilizing Table 3-2 of the SDDCCS
Manual.
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swale carries discharge from a detention pond on the southeast side of Landings Office Park
P.U.D. and a curb inlet on the NW comer of the intersection of Boardwalk Drive and
Landings Drive. This outfall design was done by Northern Engineering Services, Inc. in
October 1995 and approved in the "Final Drainage Report for the Landings Office Park
P.U.D." The 100-year release to this swale is 3.67 cfs, 3.3 cfs from the curb inlet and 0.37
cfs from the detention basin. For modeling purposes, the drainage information for this area
was duplicated directly from the Final Drainage Report for the Landings Office Park.
Anotheroffsite drainage source is the right-of-way of Boardwalk Drive adjacent to the site
and that not included in the Post Office drainage detention. These flows are split at the
northern entrance to the site. The drainage from that portion south-east of the entrance is
conveyed south to Troutman Parkway and then west on Troutman to a storm inlet that drains
to Larimer Canal No. 2. Since this area ultimately reaches the irrigation ditch, it has been
included in the existing and allocated release rate for the site. That drainage originating in
the portion of the Boardwalk right -of —way north of the entrance is directed onsite and to the
onsite detention pond. There are no other offsite considerations with this property.
The developed flows will be limited by release rate allotted to Larimer Canal No. 2. Because
storm release flows are allocated in the Heart SID, existing onsite drainage calculations are
not required for detention pond sizing and analysis.
3. DEVELOPED FLOWS
3.1 Method
The Rational Method was used to determine both the 10-year and 100-year flows for the sub -
basins indicated in this drainage report. A detailed description of the hydrologic analysis is
provided in Section 3.6 of this report.
3.2 Exterior Flows
Exterior flows enter this site in the drainage swale on the west side of the property and from
the right-of-way of Boardwalk on the northeast side of the Post Office site. The flow from
the drainage swale is contained within a 10' drainage easement across the property and
discharged into Larimer Canal No. 2. This drainage structure was approved in the "Final
Drainage Report for the Landings Office Park P.U.D." and the flows will not be modified
with this development. Information for this offsite flow is taken from the above drainage
3
1.4 Purpose and Scope of Report
This report defines the proposed preliminary drainage and erosion control plan for Park Place
P.U.D., including consideration of all onsite and tributary offsite runoff.
1.5 Design Criteria
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 January 1997. Runoff computations were prepared for the 10-year minor and 100-year
major storm frequency utilizing the rational method.
Where applicable, the criteria established in the "Urban Storm Drainage Criteria Manual",
1984, developed by the Denver Regional Council of Governments, has been utilized.
1.6 Master Drainage Basin
This site falls within the McClellands-Mail Creek Major Drainage Basin and the Heart
Special Improvement District. The report entitled "Final Drainage Report for Heart Special
Improvement District" (Heart SID) prepared by Engineering Professionals, Inc. and dated
December, 1984 provides storm drainage planning for the 43.5 acre district, as well as
analysis of the allowable developed release into Larimer Canal No. 2.
The Heart SID report sizes the Larimer Canal No. 2 through the district for a total discharge
of 240 cfs which includes 155 cfs from irrigation flows and 85 cfs from storm water flows.
Only areas specified in that report are allowed to discharge storm water to the canal and the
allowable release rate for this area is 0.87 cfs per tributary acre. This release rate allows only
the 85 cfs specified above to be discharged into the canal during the 100-year event.
2. HISTORIC (EXISTING) DRAINAGE
In general, the existing drainage pattern for this site consists of the routing of flows to
Larimer Canal No. 2 on the south side of the property. All of the flow is overland and there
are no indications of channelization on the site.
There is an existing drainage swale that is the outfall from Landings Office Park P.U.D. and
runs to Larimer Canal No. 2 in a drainage easement on the west edge of the property. This
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1. INTRODUCTION
1.1 Project Location
Park Place P.U.D. is the proposed mixed -use development of the remaining land adjacent to
the Post Office and Somerset P.U.D. on the southwest side of Boardwalk Drive. The south
end consists of multi -family residential units and the north end is proposed commercial office
space. This project is located in the SE'/a of the NW'/a and the NE'/a of the SW'/a of Section
36, Township 7 North, Range 69 West of the Sixth Principal Meridian, in the City of Fort
Collins, Larimer County, Colorado. A vicinity map is located after the Table of Contents.
This project is bounded on the south by Larimer Canal No. 2 and Tract A of Somerset P.U.D.
The site is bounded on the west by the Post Office on J.F.K. Parkway, and on the north and
east by Boardwalk Drive.
1.2 Existing Site Characteristics
The site is currently undeveloped and consists primarily of poorly to very poorly covered
range type land. The entire site slopes at a grade of 1 to 5 percent to the south and drains to
Larimer Canal No. 2.
1.3 Soils
According to the "Soil Survey for Larimer County Area, Colorado' (USDA), the soils for
this site are comprised of Renohill clay loam (89), Heldt clay loam (48), and Tassel sandy
loam (106).
The Renohill clay loam complex consists of nearly level soils on uplands. Pertinent
characteristics of this soil include medium runoff and a slight to moderate hazard of wind
and water erosion. Renohill clay loam is categorized in Hydrologic Group C.
The Heldt clay loam complex consists of nearly level soils on fans and valley sides. Pertinent
characteristics of this soil include medium runoff, a slight hazard of wind erosion and a slight
to moderate hazard of water erosion. Heldt clay loam is categorized in Hydrologic Group C.
The Tassel sandy loam complex consists of gently sloping to moderately steep soils on
uplands. Pertinent characteristics of this soil include medium to rapid runoff and a severe
hazard of wind and water erosion. Tassel sandy loam is categorized in Hydrologic Group D.
I VICINITY MAP
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APPROXIMATE SCALE: 1 "=2000'
FIGURE 1
TABLE OF CONTENTS
PAGE
1.
INTRODUCTION
1.1
............................................................:.................................................. I
Project Location
1.2
......................................................................................................1
Existing Site Characteristics
1.3
....................................................................................1
Soils
1.4
.........................................................................................................................1
Purpose and Scope of Report
1.5
.................................................................................. 2
Design Criteria........................................................................................................
1.6
2
Master Drainage Basin
............................................................................................ 2
2.
HISTORIC (EXISTING) DRAINAGE
............................................................................... 2
3.
DEVELOPED FLOWS
3.1
....................................................................................................... 3
Method
3.2
.................................................................................................................... 3
Exterior Flows
3.3
......................................................................................................... 3
Onsite Flows
3.4
............................................................................................................ 4
General Flow Routing.............................................................................................
3.5
4
Proposed Drainage Plan
3.6
.......................................................................................... 4
Hydrologic Analysis of the Proposed Drainage Conditions
.................................... 5
3.7
Allowable Street Flow Capacities
3.8
.............................................. 7
.............................
Inlet Design.............................................................................................................
3.9
7
Storm Sewer Design...................................................................................
............. 7
4.
DETENTION POND DESIGN
........................................................................................... 8
5.
EROSION CONTROL
5.1
........................................................................................................ 8
Erosion and Sediment Control Measures
5.2
................................................................ 8
Dust Abatement
5.3
....................................................................................................... 9
Tracking Mud on City Streets
5.4
................................................................................. 9
Maintenance
5.5
............................................................................................................ 9
Permanent Stabilization
......................................................................................... 10
6.
MISCELLANEOUS
6.1
..........................................................................................................10
Variances
6.2
...............................................................................................................10
Irrigation Ditches
6.3
...................................................................................................10
Ditch Company Approval
6.4
......................................................................................10
Maintenance Agreements
......................................................................................10
7. REFERENCES..................................................................................................................11
APPENDIX A: HYDROLOGIC CALCULATIONS
APPENDIX B: HYDRAULIC CALCULATIONS
APPENDIX C: EROSION CONTROL CALCULATIONS
APPENDIX D: DETENTION CALCULATIONS
G o I o..r 'a d o C. a 1. i f o r n i a
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PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT FOR
PARK PLACE P.U.D.
Prepared for:
LAGUNITAS COMPANY
3307 S. COLLEGE AVENUE, SUITE 200
FORT COLLINS, CO 80525
Prepared by:
JR ENGINEERING
2620 East Prospect Road, Suite 190
Fort Collins, Colorado 80525
(970)491-9888
September 28, 1999
Job Number 9116.01