HomeMy WebLinkAboutSPRING CANYON COMMUNITY PARK - PDP - 20-05 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTTable 4. Storm Sewer Inlet Summary for Spring Canyon Community Park.
Basin No.
Inlet Type
No. of
Inlets
On -Grade
or Sump?
Q100
cfs
1
Type R
3
Sump
9.8
2 and 6
Type 13
2
Sump
6.4
3
Type R
3
Sump
8.2
4
TVpe 13-combo
4
Sump
20.6
5
Type 13
2
Sump
11.6
7
Type R
3
Sump
9.6
8
Type 13-combo
3
Sump
13.7
9 and 10
Type 13
1
Sump
21.5
11
Type 13
1
Sump
22.4
12
Type 13
2
Sump
35.6
131
Type 13
1
On -Grade
0.0
13
Type 13
2
Sump
19.2
15
Type 13
1
Sump
7.1
18.
Type 13-combo
2
On -Grade
4.5
Pond A outlet
Type C
1
Sump
33.5
Pond B outlet
Type C
1
Sump
15.1
'Area inlet for pervious area in Basin 13 is for incidental runoff on a perched
area of the softball complex. All flow for this inlet is accounted for at the
downstream sump with 19.2 cfs.
4. EROSION CONTROL
Construction of the Spring Canyon Park will require implementation of erosion control BMPs
to minimize the amount of sediment carried offsite by wind and water. Drainage from the
park property flows into Spring Creek and erosion control practices must be implemented to
minimize the impacts.
The erosion control methods to be implemented during the construction of the Spring
Canyon Park is located on the Erosion Control Sheet C10. The City of Fort Collins erosion
and sediment control construction notes are included on this sheet. Erosion control BMPs
for construction of the Spring Canyon Park will include wattle dikes and straw bale dikes set
across all flowpaths determined by the general grading plan. The wattle dikes are placed in
the flow paths for each 2 feet of vertical drop to slow the conveyance of water and prevent
significant erosion before vegetation is installed. The straw bales dikes are to be used in the
constructed portion of the Spring Creek channel. Silt fencing is to be added around the
construction site to prevent sediment form leaving the site during construction. Drop inlet
protection will be installed around each inlet, grated manhole lid, and pond outlet structure to
prevent sediment from leaving the project site and entering Spring Creek or downstream
stormwater facilities. Straw mulch will be applied after seeding to prevent erosion from
runoff and help establish plant cover. A vehicle tracking pad is to be installed at the south
entrance of the project site to prevent mud from being carried off site on vehicle tires.
Vehicle tracking pads must also be provided at any other access locations to the worksite.
Erosion control performance standards will be calculated for the site prior in the final erosion
control plan.
6 Ayres Associates
Basins 16 and 17 are almost entirely overland and gutter flow to a low point at the west
central edge of the park. The low point will become Pond B, and will be located north of the
inline hockey rink and east of the parking lot roundabout. Pond B flow will ultimately be
carried to Spring Creek through an inlet and storm sewer pipe configuration that will be
determined at a later date. The 100-year WSEL at Pond B is 5,126.30 ft, and the total 100-
year detention volume is 0.15 ac-ft.
A summary of the pond storage characteristics is included in Table 3.
Table 3.
Detention Summary for Water Quality Ponds.
Design Storm
Pond
10-Year
100-Year
WSEL ft
Pond A
5,123.45
5,124.74
Volume ac-ft
Pond A
0.531
0.705
WSEL ft
Pond B
5,125.58
5,126.30
Volume(ac-ft
Pond B
0.038
0.146
Pond A begins to spill over the weir to the north at 5,124.00 ft elevation.
No additional detention volume assumed after weir flow occurs.
3.4 Hydraulic Analysis
Each of the storm sewer trunklines and the associated laterals were analyzed with the HEC-
22, energy gradeline method. This provided the basis for all pipe sizing, taking into account
the tailwater conditions and headloss associated with the different hydraulic structures. The
HEC-22 worksheet is included as part of the Appendix. Inlets for the storm sewer system
were sized using UD-Inlet v1.04(CASFM).xls; a spreadsheet developed by UDFCD applying
methods outlined in the USDCM.
The Type-C inlet at Pond A was designed to operate in conjunction with a weir north of the
pond. A range of inlet flows were developed from a range of depths based on incremental
variation in WSEL. The discharge exiting Pond A over the weir to the north was calculated
for the same range of WSELs, and the combined total discharge of weir flow and inlet flow
was incorporated into a rating curve of discharge versus WSEL. This rating curve is
included in the Appendix. It indicates a 100-year WSEL of 5,124.74 ft for a discharge of
207.9 cfs, calculated from the rational method analysis. This total discharge includes 33.5
cfs of inlet flow, and 174.4 cfs of weir flow. The inlet will be set at an elevation of 5,123.45 ft.
The same UDFCD software used for sizing the inlet at Pond A was used to size the
remaining inlet structures throughout the park. All inlets for the storm sewer system for the
Spring Canyon Community Park are summarized in Table 4.
The Type-C inlet at Pond B will be.set at an elevation of 5,125.58 ft, and the 100-year WSEL
will be 5,126.30. ft. The 100-year discharge from Pond B will be 15.1 cfs.
To prevent local scour at storm sewer outlets, it is necessary to include riprap revetment as
outlet protection. Riprap revetment design will be based on procedures outlined in the
UDFCD criteria manual. The two lines discharging into Pond A, and the outlets for Ponds A
and B will require riprap, especially in the Spring Creek channel, to prevent local scour and
erosion. The north weir overflow for Pond A will be protected on the upstream and
downstream face with Recyclex turf reinforcement mat (TRM), or an approved alternative, to
protect the weir from erosion and possible breach. The TRM will be seeded with a native
dryland grass mixture approved for the Front Range and irrigated for the first year after
installation.
Ayres Associates
Table 2. Rational Method Parameters and Results by
Basin Number.
Basin
No.
Drainage
Area
ac
Percent
Impervious
%
010
cfs
0100
cfs
1
0.96
95
4.8
9.8
2
0.31
34
0.6
1.7
3
1.54
68
3.5
8.2
4
4.98
36
7.4
20.6
5
2.49
52
4.7
11.6
6
0.88
26
1.6
4.7
7
2.09
49
3.7
9.6
8
2.72
37
4.3
13.7
9
2.93
74
7.3
16.3
10
0.84
58
1.7
5.2
11
5.29
31
7.9
22.4
12
8.60
27
12.1
35.6 .
13
4.54
31
6.8
19.2
14
3.94
41
6.6
17.7
15
1.72
29
2.4
7.1
16
1.86
72
5.9
13.3
17
0.41
25
0.6
1.8
18
0.44
1 95
1 2.2
4.5
The storm drainage system for the park includes two main storm sewer trunklines. The first,
and largest, is known as Line A. This line extends from its outlet point at Pond A back to the
southeast corner of the park, including Basins 9 through 12. Two laterals and one trunkline
branch from Line A. The second trunkline extends from Line A and carries runoff from the
southwestern and south-central portions of the park, including Basins 1 through 6, 13, and
18. Two laterals branch off of Line D. A lateral drains Basin 15 directly to the pond, but
does not connect to the trunklines. Basin 14 drains directly to Pond A by overland and gutter
flow. Basins 16 and 17 drain to.Pond B by overland and gutter flow.
Detention for the water quality Ponds A and B was determined using the UDFCD method.
This method incorporates the total impervious percentage of area upstream of the pond and
calculates the water quality capture volume in inches, the depth of the average runoff, and
the total upstream tributary area. The calculated required storage for the 10-year storm will
then be the total volume captured by the pond to contain the 10-year flow. Any flow
exceeding this volume will then enter a Type-C inlet that discharges through directly into
Spring Creek.
The total volume captured by detention Pond A is 0.53 ac-ft. Water will rise to an elevation
of 5,123.44 ft. All flows exceeding this WSEL will enter a Type C inlet that discharges
through a 30-inch RCP storm sewer pipe connected to Spring Creek. Weir flow to the north
occurs when the WSEL exceeds 5,124.00 ft. All weir flow will be conveyed by a swale to
Spring Creek near the northern border of the park. The anticipated 100-year WSEL for
Pond A is 5,124.74 ft.
4 Ayres Associates
for the Spring Canyon Community Park. The proposed locations of two detention ponds and
the two outlets to Spring Creek are indicated on the proposed plan sheets. Also shown are
the locations of the minor storm drainage facilities that include curb inlets, grate inlets,
combined inlets, storm sewer pipes, and minor drainage swales. Section 3.3 of this report
presents a specific -description of the proposed drainage plan for the park.
The design of inlets was performed based on the methodologies outlined in the Urban Storm
Drainage Criteria Manual (USDCM) published by the Urban Drainage and Flood Control
District (UDFCD) in Denver, Colorado. Storm sewers were designed using methods
established in the Hydraulic Engineering Circular Number 22 Urban Drainage Design
Manual, also known as HEC-22. Hydrologic calculations for the design of the local drainage
facilities were performed using the rational method, as described in the Fort Collins manual.
A detailed description of the design of the local drainage facilities is provided in Section 3.3.
The detention ponds were sized in accordance with methods outlined in Volume 3 of the
USDCM. The rational method analysis was used to determine the 10- and 100-year runoff
for the subbasins that contribute to a pond. Details of the proposed conditions hydrology are
included in Section 3.2.
3.2 Proposed Conditions Hydrology
The tributary area for the Spring Canyon Community Park site includes a 46.5 acre portion
of the park and Horsetooth Road immediately south of the park. There is no development
planned around the park that might add runoff to the site.
The proposed Spring Canyon Community Park was subdivided into 18 individual sub -basins
with regard to topography and flow contribution. These basins are numbered 1 through 18,
and were incorporated into rational method calculations performed according to the City of
Fort Collins Storm Drainage Design Criteria and Construction Standards manual. Basins 1
through 15, and 18, will drain to the detention pond known as Pond A, on the north side of
the site. Pond A will maintain a constant water surface elevation (WSEL) of approximately
5122.0 ft. Basins 16 and 17 will drain to a smaller depression known as Pond B. This pond
will retain stormwater, and will be sized with an outlet pipe at a later time. Both ponds will
capture the entire 10-year runoff volume to meet water quality requirements for flows
emptying into Spring Creek. The Appendix contains storage discharge relationships for
Ponds A and B in the developed condition.
The rational method calculations contain four distinct impervious values describing land uses
within the park. These land uses consist of undeveloped areas (typically mowed grass),
gravel areas, ponds, and asphalt or concrete paving. The impervious values for these areas
are 20%, 50%, 95%, and 95%, respectively. The basin parameters and hydrologic
calculations are included in the Appendix for the 10- and 100-year storm events. This data is
summarized in Table 2.
3.3 Proposed Drainage Plan
A discussion of the detailed design of drainage facilities is included this section. Attached to
this report are the Drainage and Erosion Control Plan Sheets. Storm drainage on the Spring
Canyon Community Park will follow the flowpaths determined from the grading plan. Flow
tends to concentrate in a series of inlets that drain to a storm sewer network. Drainage will
eventually make its way to the Pond A (north central park site) and Pond B (west central
park site), where runoff discharged from the project site will be held to controlled release
rates.
Ayres Associates
In the western portion of the Park site, Spring Creek is a poorly -defined channel that also
appears to have been excavated to.convey nuisance stormwater flows to the north. Several
large deciduous trees have grown adjacent to the Spring Creek channel. On the far north
end of the Park site, the Spring Creek channel becomes more well-defined, and bends to the
northeast. At its confluence with the Pleasant Valley and Lake Canal (PV&L), Spring Creek
is conveyed in a 12-inch pipe under the canal, with any excess flows being conveyed over .
the ditch. It should be noted that at this location, the canal appears to have been dug
primarily from excavation, meaning the downstream bank does not appear to be a fill -slope,
but instead native soil. With the existing condition climate and irrigation practices, the Spring
Creek channel does not have a consistent base flow until downstream of the PV&L Canal.
On the southern boundary of the Park, Horsetooth Road has been extended west to
Horsetooth Court. Runoff from Horsetooth Road, Horsetooth Court and releases from the
Springfield Subdivision detention pond are all conveyed on the south side of Horsetooth
Road west to the valley low point.
In the southwest corner of the proposed Park site, there is an existing fenced -in dog park.
The vegetation in this park site has been predominantly removed in this area, resulting in a
more hard -packed earth, rather than grassed vegetation that characterizes the surrounding
Park site.
On the western boundary of the Park, the northern frontage of the Spring Creek channel is
bounded on the west by Cottonwood Glen Park, a neighborhood park constructed in 2000.
The drainage patterns on the Cottonwood Glen Park generally direct water from west to
east. A portion of the runoff is intercepted by a landscape/irrigation lake and released to
Spring Creek. The remainder of the runoff is discharged directly to Spring Creek.
The Spring Creek Master Drainage Plan provided a big -picture hydrologic analysis of the
Spring Creek Basin, including the Park site. The hydrologic modeling was done in the
MODSWMM model, to be representative of developed conditions with existing drainage
facilities. The discharge in Spring Creek at various design points in the vicinity of the Park
site are given in Table 1.
Table 1. 100-Year Discharge From Spring Creek Master Plan MODSW MM Model.
Location
Model Node
Discharge
Horsetooth Road
961
1,412
Mid -point of Spring Canyon Community Park
962
1,680
Pleasant Valley and Lake Canal
338
1,871
Model SCDEV100.OUT provided by City of Fort Collins, March 24, 2005
3. PRELIMINARY DRAINAGE PLAN FOR THE SPRING CANYON
COMMUNITY PARK
3.1 General
The preliminary drainage plan for the Spring Canyon Community Park has been developed
to provide a drainage system that meets the requirements established in the City of Fort
Collins Storm Drainage Design Criteria and Construction Standards manual. This has been
accomplished by designing a series of inlets, storm sewers, and detention ponds that will
collect, convey, and detain runoff. Sheets C6 and C9 show the grading and drainage plan
2 Ayres Associates
1. INTRODUCTION
The Spring Canyon Community Park (SCCP) project consists of approximately 136 acres
located on the north side of West Horsetooth Road (LCR-40) and east of the Pineridge
Natural Area in Fort Collins, Colorado. Figure 1 shows a vicinity map of the project site.
The proposed development would convert an agricultural use area (alfalfa hay) to a
recreational park with numerous athletic facilities, recreational opportunities, and maintained
multi -use open areas.
Figure 1. Vicinity map of the Spring Canyon Community Park.
2. EXISTING DRAINAGE CONDITIONS
The existing Spring Canyon Community Park development site is primarily undeveloped.
For decades, the property has been used as flood -irrigated grassland. The regularity of the
existing ground contours shows evidence of a historic reworking of the land, with a ground
slope of approximately 1.0% from south to north. Around the southern portion of the site,
the Taft lateral is a periodic irrigation channel that is fed from a pressurized pipe system, with
an outlet near the western terminus of Horsetooth Road. Through the middle of the site, a
small drainage collector channel has been excavated to convey excess irrigation and
stormwater flows north to Spring Creek.
Ayres Associates
TABLE OF CONTENTS
1. Introduction...................................................................................................................1
2. Existing Drainage Conditions.........................................................................................1
3. Preliminary Drainage Plan for the Spring Canyon Community Park ..............................2
3.1
General...........................:......................................................................................2
3.2
Proposed Conditions Hydrology.............................................................................3
3.3
Proposed Drainage Plan.............................................:..........................................3
3.4
Hydraulic Ahalysis...................................................................................................5
4. Erosion Control..............................................................................................................6
TECHNICAL APPENDIX................................................................................................... --
LIST OF FIGURES
Figure 1. Vicinity map of the Spring Canyon Community Park.............................................1
LIST OF TABLES
Table 1. 100-Year Discharge From Spring Creek Master Plan MODSWMM Model.............2
Table 2. Rational Method Parameters and Results..............................................................4
Table 3. Detention Summary for Water Quality Ponds........................................................5
Table 4. Storm Sewer Inlet Summary for Spring Canyon Community Park . ..................... :..6
Ayres Associates
DRAFT
PRELIMINARY DRAINAGE REPORT
FOR
SPRING CANYON COMMUNITY PARK
Prepared for
City of Fort Collins
Stormwater Utility
215 North Mason
Fort Collins, Colorado 80524
,3756?>/G
AMES �.::....
ASSOCIATES
P.O. Box 270460
Fort Collins, Colorado 80527
(970) 223-5556, FAX (970) 223-5578
Ayres Project No. 32-0890.00 (Task 5)
SP-CAN4T.DOC
April 2005