HomeMy WebLinkAboutNORTHFIELD FILING 1 EXPANDED - FDP190012 - DOCUMENT MARKUPS - ROUND 3 - DRAINAGE RELATED DOCUMENTPage 7
drain to detention Pond A2. All of sub-basins A1 & A2 are treated by a LID infiltration
gallery in Pond A2.
Sub-basins A3 thru A4 consist of 2.41 acres of single-family attached and condominium
residential lots, public roadways and private drives. These basins include portions of
Schlagel Street and Pioneer Trail Road. Runoff from these basins (along with the upstream
flows from sub-basins A1 & A2) is conveyed along roadways and is captured by two 10’ Type
R sump curb inlets and directed to detention Pond A2. All of sub-basins A3 & A4 are treated
by a LID infiltration gallery in Pond A2.
Sub-basins A5 thru A6 consist of 1.49 acres of single-family attached and condominium
residential lots and private drives. Runoff from these basins is conveyed along private
drives and is captured by a double Type 13 valley sump inlet and directed to detention Pond
A2. All of sub-basins A5 & A6 are treated by a LID infiltration gallery in Pond A2.
Sub-basins A7 thru A9 consist of 1.99 acres of single-family attached and condominium
residential lots, a portion of the community clubhouse lot, and public roadways. These
basins include portions of Landmark Way, Collamer Drive, and Pioneer Trail Road. Runoff
from these basins is conveyed along roadways and discharged directly into detention Pond
A2 via a sump CoFC sidewalk culvert. All of sub-basins A7 thru A9 are treated by a LID
infiltration gallery in Pond A2.
Sub-basins A10 thru A11 consist of 1.82 acres of single-family attached and condominium
residential lots, and private drives. Runoff from these basins is conveyed along private
drives and is captured by a sump 10’ Type R curb inlet and directed to detention Pond A2.
All of sub-basins A10 & A11 are treated by a LID infiltration gallery in Pond A2.
Sub-basin A12 consists of 1.25 acres of condominium residential lots and the open space
encompassing detention Pond A2 and Infiltration Gallery A2. Flows within this basin are
conveyed via roof downspouts and concrete pans. Runoff is conveyed from Pond A2 via
storm pipes into Pond A1. All of sub-basin A12 is treated by the Infiltration Gallery A2.
Sub-basins A13 thru A14 consist of 1.08 acres of single-family attached and condominium
residential lots and private drives. Runoff from these basins is conveyed along private
drives and is captured by a double Type 13 valley sump inlet and directed to detention Pond
A1 via storm pipes. Conflicts with water & sewer utilities as well as grading constraints
prevent these basins from discharging to the surface of Pond A1. These basins are unable to
be treated in either a LID facility or standard water quality treatment. These basins
represent approximately 2% of the total onsite area of the Northfield project.
Sub-basin A15 consists of 2.48 acres of single-family attached and condominium residential
lots and public roadways. This basin includes the western half street section of N. Lemay
Avenue and a portion of Schlagel Street. Runoff from this basin is conveyed along roadways
Page 8
and is captured by a sump 5’ Type R curb inlet and directed to detention Pond A1 via storm
pipes. Grading constraints prevent these basins from discharging to the surface of Pond A1.
These basins are unable to be treated in either a LID facility or standard water quality
treatment. This basin represents approximately 3% of the total onsite area of the Northfield
project.
Sub-basin A16 consists of 0.80 acres of single-family attached residential lots and public
roadways. This basin includes the eastern half street section of N. Lemay Avenue and a
portion of Schlagel Street. Runoff from this basin is conveyed along roadways to a 4’ wide
curb cut on the east side of Lemay Avenue which directs runoff to a Type C area inlet. This
inlet is to be constructed as part of the A4 NECCO lateral. Due to this basin being on the
east side of Lemay, away from Northfield, runoff is unable to be directed to a water quality
enhancement facility.
Sub-basin A17 consists of 0.90 acres of landscaped open space to the north. Runoff from
this basin is conveyed over landscaping to a concrete pan near the north property line and
then into a Type 13 inlet to be constructed as part of the A4 NECCO lateral. This landscaped
basin is unable to be directed to a detention pond.
Sub-basin A18 consists of 3.02 acres of single-family attached residential lots and the open
space encompassing detention Pond A1. Flows within this basin are conveyed via roof
downspouts and concrete pans. Two outlet structures in Pond A1 have been designed to
limit discharge from the Northfield site into the NECCO storm system, along with providing
water quality capture volume to treat areas untreated by LID features.
Drainage System B:
Drainage System B consists of 19.48 acres of improvements in the central portion of the
project site. Runoff from basins in System B drain to three interconnected extended
detention basins, Ponds B1, B2, & B3.
Sub-basin B1 consists of 2.13 acres of condominium and multifamily residential lots and
open space. Runoff is conveyed via roof downspouts and a concrete pan and is captured by
a Type 13 inlet. All of basin B1 will be treated by LID Infiltration Gallery B3 in Pond B3.
Sub-basins B2 thru B3 consist of 2.37 acres of single-family attached, condominium, and
multifamily residential lots, public roadways and private drives. This basin includes portions
of Schlagel Street. Runoff from these basins is conveyed along roadways and is captured by
two 10’ Type R sump curb inlets. All of sub-basins B2 & B3 will be treated by LID Infiltration
Gallery B3 in Pond B3.
Sub-basin B4 consists of 1.32 acres of single-family attached residential lots and private
drives. Runoff from this basin is conveyed along private drives and is captured by a double
Page 11
Sub-basins D1 thru D4 consist of 2.70 acres of multifamily residential lots, private drives,
and open space. Runoff is conveyed via roof downspouts, roadways, and concrete pans,
and is captured by Type 13 and area inlets, ultimately discharged to the surface of Pond D
and treated for standard water quality.
Sub-basin D5 consists of 0.43 acres of multifamily residential lots and open space. Runoff is
conveyed via roof downspouts and concrete pans and is captured by a single Type 13 inlet,
ultimately discharged to the surface of Pond D and treated for standard water quality.
Sub-basins D6 thru D7 consist of 0.19 acres of multifamily residential lots, and public
roadways. This basin includes portions of Steeley Drive. Runoff from these basins is
conveyed along roadways and is captured by two on-grade 5’ Type R curb inlets, ultimately
discharging to the surface of Pond D and treated for standard water quality.
Sub-basins D8 thru D13 consist of 3.40 acres of multifamily residential lots, private drives,
and open space. Runoff from these basins is conveyed via roof downspouts, roadways,
concrete pans and storm pipes, ultimately discharging to LID facility, Rain Garden D1.
Sub-basin D14 consists of 2.50 acres of open space encompassing detention Pond D. This
basin’s detention requirements allows a release rate equal to the current/historic runoff
rates and is accounted for in the Pond D detention volume calculations. An outlet structure
in Pond D has been designed to limit discharge into the NECCO storm system as well as treat
for standard water quality enhancement.
Sub-basin D15 consists of 0.44 acres of public roadway along the western half of N. Lemay
Avenue. Runoff is conveyed along Lemay Ave and collected by a sump 5’ Type R curb inlet.
Runoff is then conveyed by storm drain pipe into the existing 3’x10’ RCBC NECCO storm
drain. Due to grade constraints, this sub-basin cannot be routed to Pond D; the difference
in 100-yr runoff rate for the developed condition is reduced from the allowable release rate.
Refer to the tabulated release rate summary on page 15.
Drainage System E:
Drainage System E consists of 8.23 acres of public roadway improvements along Suniga
Road. Runoff from basins within the System E are conveyed to the existing NECCO storm
drain system. Detention for these basins is not required and water quality enhancement is
provided by Snout hoods within the curb inlets, per the NECCO report. Refer to Exhibit 4.2
of the NECCO report, included in the Appendix.
Sub-basins E1 thru E2 consist of 1.14 acres of public roadway along Suniga Rd. Runoff is
conveyed along Suniga Rd and collected by two sump quad Combo curb inlets. The north
Page 13
DRAINAGE FACILITY DESIGN
DRAINAGE CONVEYANCE DESIGN
Storm infrastructure to convey runoff will include concrete trickle pans, inlets, storm sewer and
culverts. Stormwater detention and water quality enhancement will be achieved through the
use of multiple interconnected extended detention basins, rain gardens, and infiltration
galleries. Storm inlets, storm sewers and the roadway culverts have been appropriately sized to
convey the minor and major storms.
DETENTION/WATER QUALITY POND DESIGN
EPA SWMM 5.0 has been utilized for the final drainage design. UDFCD is referenced for the
standard water quality capture volume (WQCV) with a 40-hr drain time and the LID rain
gardens and infiltration galleries WQCV with a 12-hr drain time. Due to the limited grades on
the site, multiple ponds are proposed throughout the site. These ponds are interconnected via
storm pipes and control structures that are designed with orifice plates to restrict flow and
maximize pond volume while providing adequate freeboard. Overflow paths from each of the
ponds have been provided in the event that the outlet structures clog and overtop. Below is a
brief summary of the proposed design for each pond:
Pond A1:
Furthest downstream extended detention basin for all areas north of Suniga Road, with
standard water quality treatment provided via two outlet structures at the east and west ends,
which each discharge directly into the existing NECCO system via 7” and 13 ½” 100-yr orifice
plates to maximize volume and restrict release rates. Maximum depth of the pond is 3.20 feet,
with 1.0 feet of freeboard. Overtopping will occur simultaneously at two locations, near the
NECCO A7 lateral in Suniga Road and near design point A15 in Lemay Ave, spilling over sidewalk
and into the public ROW.
Pond A2:
Extended detention basin with LID Infiltration Gallery A2 for water quality treatment. A
Modified Type D outlet structure with a baffle wall separating the inlet and outlet
compartments will direct incoming flows into the gallery. Flows will then spread throughout
the gallery chambers, settling out sediments and infiltrating through the gravel sub-base, where
an 8” perforated underdrain set 12” below the bottom of the gallery will collect treated runoff
and convey it to the outlet side of the modified Type D structure. A 20” 100-yr orifice plate
maximizes volume in the pond and restricts flow to downstream Pond A1. During the major
storm event, pipe flow will surcharge into the pond and be detained. Maximum pond depth is
Page 14
3.44 feet, with 1.06 feet of freeboard. Overtopping will occur at the southeast corner of the
pond, spilling over the sidewalk and down toward design point A10/A11, where it will continue
flowing south and then east in the private drive (water surface will not inundate garages),
overtopping the sidewalk again into Pond A1.
Pond B1:
Extended detention basin with LID rain garden and standard water quality treatment via the
outlet structure located at the east end of the pond. A 12 ½” 100-yr orifice plate maximizes
volume in the pond and restricts flow to downstream Pond A1. The rain garden includes a
concrete forebay sized for 1% of the surface area for the WQCV with a rock embankment to
dissipate flows before entering the media material bed. Large storm events in excess of the
rain garden capacity will spill over a turf mat reinforced berm and down into Pond B1.
Maximum pond depth is 3.40 feet, with 1.60 feet of freeboard. Overtopping will occur at the
southeast corner at the intersection of Landmark Way and Suniga Road, spilling over the
sidewalk and into public ROW.
Pond B2:
Extended detention basin with LID infiltration gallery for water quality treatment. Modified
Type D outlet structure with a baffle wall separating the inlet and outlet compartments will
direct incoming flows into the gallery. Flows will then spread throughout the gallery chambers,
settling out sediments and infiltrating through the gravel sub-base, where an 8” perforated
underdrain set 12” below the bottom of the galleries will collect treated runoff and convey it to
the outlet side of the modified Type D structure. A 17” 100-yr orifice plate maximizes volume in
the pond and restricts flow to downstream Pond B1. During the major storm event, pipe flow
will surcharge into the pond and be detained. Maximum pond depth is 1.88 feet, with 1.62 feet
of freeboard. Overtopping will occur at the east corner near design point B11, spilling over the
sidewalk into Collamer Drive ROW, then over the street high point to the east (approximately
6” depth) and continuing down Landmark Way toward Suniga Road.
Pond B3:
Extended detention basin with LID infiltration gallery for water quality treatment. Modified
Type D outlet structure with a baffle wall separating the inlet and outlet compartments will
direct incoming flows into the gallery. Flows will then spread throughout the gallery chambers,
settling out sediments and infiltrating through the gravel sub-base, where an 8” perforated
underdrain set 12” below the bottom of the galleries will collect treated runoff and convey itto
the outlet side of the modified Type D structure. An 8” 100-yr orifice plate maximizes volume
in the pond and restricts flow to downstream Pond B2. During the major storm event, pipe
flow will surcharge into the pond and be detained. Maximum pond depth is 3.63 feet, with 1.0
Page 17
LOW IMPACT DEVELOPMENT
The City of Fort Collins updated the Low Impact Development ordinance in 2016 (Ordinance No.
007, 2016) to require:
• Treat at least 75% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques, or
• Treat at least 50% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques when 25% of private driveable surfaces are permeable.
To satisfy the required implementation of Low Impact Development (LID) techniques,
Northfield will utilize below grade infiltration galleries (such as ADS StormTech chamber
system) and bioretention ponds/rain gardens. Details and specifications for these facilities are
provided in the Appendix. Other LID techniques were explored, but due to the limited grade
available and the amount of detention volume required, shallow infiltration galleries assisted in
maintaining storm drain grades and detention volumes. Pavers within the private drives did not
treat enough contributing area to justify their use. Infiltration galleries promote infiltration
while capturing fine sediment that drains off the impervious areas. The proposed galleries are
configured entirely as ‘Isolator rows’ which are surrounded by filter fabric and include an inlet
manifold for access, removal of sediment and maintenance, along with an inspection port on
each row. Standard water quality treatment is also provided within the detention ponds and
has been sized for those tributary basins not already treated by the LID facilities. A Standard
Operations Procedure will be included as part of the Development Agreement to assist in
ensuring that these BMPs will adequately perform over time.
Impervious calculations for the tributary areas to each of the LID infiltration galleries, rain
gardens, and standard water quality facilities along with a colored coded exhibit showing all
areas treated are provided in the Appendix. LID treatment requirements have been exceeded,
achieving approximately 107% of the required impervious area treatment in the rain gardens
and infiltration galleries. As previously noted in the drainage basin descriptions, grading
constraints and tight/shallow utility conflicts prevented a fraction of the site from being routed
through a water quality treatment facility before being discharged into the storm system. Two
interior basins A13 & A14, along with the adjacent western half street of Lemay Ave (Basins A15
and D15), the small portion of basin A16 lying on the Northfield site (not including the eastern
half street section of Lemay), and the northeastern-most landscape basin A17 together
represent approximately 8% of the total site area not able to be treated for water quality.
Consideration is being requested that the overtreatment provided within the LID facilities be a
compromise for the areas being unable to be directed to a water quality or LID facility. We
Page 18
believe this meets the intent of the water quality treatment criteria to the maximum extent
possible.
Below is a description of the 4-step process for selecting structural BMPs:
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for
receiving water protection that focuses on reducing runoff volumes, treating the water quality
capture volume (WQCV), stabilizing drainageways and implementing long-term source controls.
The Four Step Process applies to the management of smaller, frequently occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low
Impact Development (LID) strategies, including Minimizing Directly Connected Impervious
Areas (MDCIA).
Captured runoff from strategic areas are routed through below grade infiltration galleries and
bioretention pond/rain gardens. Infiltration galleries and rain gardens will slow runoff, promote
infiltration, and filter runoff prior to being released into the adjacent storm drain system.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release
The infiltration galleries and rain gardens are designed to provide water quality capture volume
per Urban Drainage’s recommendations and calculations. The captured runoff is designed for a
12-hr drain time.
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate and volume of runoff during and following development. Because the site will
drain to an existing storm system, bank stabilization is unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
The proposed project will improve upon site specific source controls compared to historic
conditions by providing localized trash enclosures within the development for disposal of solid
waste; Snouts, infiltration galleries, and rain gardens for water treatment prior to flows
entering storm systems; and additional water quality measures to protect and prolong the
design life of BMPS delineated in Step 1.
Northfield
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
REQUIRED WATER QUALITY CAPTURE VOLUME (WQCV):
Tributary Area, A* 3.020 acres
*sub-basin A18 (not treated by LID)
Imperviousness, I 12.5%
WQCV (watershed inches) 0.081 inches 40-Hour Drain Time (Fig SQ-2)
Required WQCV 0.024 acre-feet Including 20% for Sedimentation
Stage Storage
Volume (pond volume calculated using the prismoidal formula):
Pond A1
CONTOUR (FT) AREA (FT
2
) AREA (ACRE)
VOLUME
(ACRE-FT)
DEPTH (FT)
CUMULATIVE VOLUME
(ACRE-FT)
4948.00 0 0.00 0.00 0.00 0.00
4948.5 5679 0.13 0.02 0.50 0.02
4949.0 22767 0.52 0.15 1.00 0.17
4949.5 45079 1.03 0.38 1.50 0.56
4950.0 67209 1.54 0.64 2.00 1.20
4950.5 78292 1.80 0.83 2.50 2.03
4951.0 81175 1.86 0.92 3.00 2.95
4951.5 83146 1.91 0.94 3.50 3.89
4952.0 85329 1.96 0.97 4.00 4.86
0.02 4948.51 ft
Critical Pond Elevations - A1 Basin
J.Claeys
Highland Development
18-1000-00
August 28, 2019
Fort Collins Amendments to the Urban Drainage and Flood Control District Criteria Manual
Required Water Quality Capture Volume =
Acre-Ft Interpolates to an Elev. of
( )
3
AAAADepth 1 2 1 2
V
+ +
=
* * 1 . 2
12
Area
WQCV
Volume
=
18-1000-00 PondCalcs.xls Page 2 of 8 Highland Development Services
E. SUNIGA ROAD
REDWOOD STREET
DRY CREEK
LAKE CANAL DITCH
FUTURE LEMAY AVENUE
N. LEMAY AVENUE
COLLAMER DRIVE
PIONEER TRAIL ROAD
STEELEY DRIVE
LANDMARK WAY
N. LEMAY AVENUE
RAIN
GARDEN
D1
SCHLAGEL STREET
FUTURE
SUNIGA
ROAD
POND B3
POND A2
POND A1
POND B2
POND C
POND B1
POND D
RAIN GARDEN B1
SUNIGA ROAD AREA
DETENTION / LANDSCAPE AREA
PROPOSED SINGLE FAMILY AREA
PROPOSED MULTI-FAMILY AREA
AREA CONTRIBUTING TO LID TREATMENT
LEGEND
0
100'
100 50 100 200
SCALE: 1" =
NO. REVISION BY DATE
HIGHLAND
DEVELOPMENT SERVCIES
6355 FAIRGROUNDS AVENUE, SUITE 100 | WINDSOR, CO 80550
PHONE: 970.674.7550 | FAX: 970.674.7568 | www.Highland-DS.com
PREPARED BY OR UNDER THE
DIRECT SUPERVISION OF:
FOR AND ON BEHALF OF HIGHLAND
DEVELOPMENT SERVICES
REVIEW SET
NOT FOR
CONSTRUCTION
SHEET OF
DRAWN BY
CHECKED BY
DATE
SCALE (H)
HDS PROJECT #
SCALE (V)
NORTHFIELD
LID & WQ TREATMENT AREAS EXHIBIT
8/28/19
1" = 100'
N/A
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Low Impact Development Summary
Sq-Ft Acres
Impervious Area (sq-
ft)
% of Impervious
Area Requiring
Treatment
Impervious Area
Requiring
Treatment
537,816 12.35 330,931 50% 165,465
1,189,400 27.30 794,336 75% 595,752
40,986 0.94 20,720 75% 15,540
304,148 6.98 248,720 0% N/A
445,251 10.22 0 0% N/A
2,517,600 57.80 1,394,707 - 776,757
LID
Facility
Contributing
Basins
Area Drainage
to LID
(sq-ft)
% Impervious
Impervious
Area Treated
(sq-ft)
WQCV12-hr
(watershed inches)
WQCV12-hr
(cu-ft)
Treatment
Method
A2 A1+…+A12 427,599 66.5% 302,122 0.21 7,414 Infiltration Gallery
B1 B13+…B17 110,074 79.3% 93,219 0.26 2,378 Rain Garden
B2 B10+…+B12 146,450 55.7% 86,485 0.18 2,173 Infiltration Gallery
B3 B1+…+B9 426,521 54.7% 251,577 0.18 6,243 Infiltration Gallery
D1 D8+…+D13 148,227 61.5% 98,626 0.19 2,384 Rain Garden
776,757
832,029
107.1%
Northfield
Low Impact Development
Total % Treatment
Development Area Breakdown
City of Fort Collins - Ordinance No. 007, 2016
- Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or
- Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are
permeable.
Total Impervious Area Treated (sq-ft)
Total Impervious Area Required for Treatment (sq-ft)
Summary
Treatment Areas
Detention / Landscape Areas (no treatment)
J.Claeys
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
J.Claeys
HDS
August 27, 2019
Northfield
LID Facility B1 - Rain Garden
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
18-1000-00 UD-BMP_v3.07_Pond B1.xlsm, RG 8/27/2019, 4:27 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
NO SPRINKLER HEADS ON FLAT SURFACE
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
J.Claeys
HDS
August 27, 2019
Northfield
LID Facility D1 - Rain Garden
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
18-1000-00 UD-BMP_v3.07_Pond D.xlsm, RG 8/27/2019, 4:29 PM
Highland Development Services
18-1000-00
August 26, 2019
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016)
Totals
Description
Single Family Area
Multifamily Area
Commercial Area
Suniga Road (no treatment)
KRB
JTC
18-1000-00
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1 1
N
W E
S
PROPOSED COMMERCIAL AREA
AREA CONTRIBUTING TO STD WQ TREATMENT