HomeMy WebLinkAbout2590 MIDPOINT DRIVE - FDP - FDP160031 - REPORTS - DRAINAGE REPORTDrainage Report
for
Hess Land, LLC
2590 Midpoint Drive
Fort Collins, CO 80525
Prepared by: Mike Beach, P.E.
Date: September 26, 2016
5255 Ronald Reagan Blvd, Suite 210 Johnstown, CO 80534
(303) 322-6480 EMAIL: mbeach@ridgetopeng.com
Project # 16‐015‐002 Page 2
Section Page
1. Project Engineer’s Certification ........................................................................................ 3
2. Project Location & Overview ............................................................................................ 4
3. Drainage Design Criteria ................................................................................................... 4
4. Hydraulic Calculations ....................................................................................................... 5
5. Facility Design .................................................................................................................... 6
6. Conclusion ......................................................................................................................... 8
7. References ......................................................................................................................... 8
Appendix A – Site Vicinity Map
Appendix B – Flood Insurance Rate Map
Appendix C – NRCS Soils Map
Appendix D – Hydrologic Criteria
Fort Collins Rainfall Intensity Curve
Fort Collins Rainfall Intensity Table
Table RO‐3 – Recommended Percentage Imperviousness Values
Appendix E – Hydraulic Calculations
Runoff Coefficients & Imperviousness
Time of Concentration ‐ SF‐2
Rational Method Runoff Flows – SF‐3 (2‐Year Event)
Rational Method Runoff Flows – SF‐3 (100‐Year Event)
Detention Volume by Modified FAA Method (Subbasins 1 & 2)
Orifice Calculations
Detention Basin Stage‐Discharge Table (Subbasins 1 & 2)
Rain Garden Calculations (Subbasins 1 & 2)
Historic Runoff Flow Calculations (Coefficients, TOC, 2‐Yr event)
LID Table
Appendix F – Maps
Subbasin Map
Holsinger Drywall Stormwater Plan
Table of Contents
Project # 16‐015‐002 Page 3
Section 1: PROJECT ENGINEER’S CERTIFICATION
I hereby attest that this Final Drainage Report for the design of stormwater management
facilities for Lot 18 (2590 Midpoint Drive) was prepared by me, or under my direct supervision,
in accordance with the provisions of the City of Fort Collins Storm Drainage Design Criteria and
Construction Standards for the responsible parties thereof.
__________________________
Mike Beach, P.E.
Registered Professional Engineer
State of Colorado No. 45088
Project # 16‐015‐002 Page 4
Section 2: Project Location & Overview
Location
The sites address is 2590 Midpoint Drive, Fort Collins, CO; which is in the SE 1/4, of the NW 1/4,
of Section 20, TWP 7 N, R 68 W of the 6th PM in Larimer County, CO.
Located along the north side of Midpoint Drive and east of South Timberline Road, the site is
described as Lot 18 of the Prospect Industrial Park and contains 0.86 acres of undeveloped
vacant land. (See Appendix A – Site Vicinity Map)
Existing Condition
The existing site is covered by native vegetation and slopes predominately towards Midpoint
Drive at approximately 0.5% slope. Stormwater runoff collected into Midpoint Drive is
conveyed via gutter towards Sharp Point Drive where it is deposited into an inlet that conveys
the water to Poudre River.
Proposed Condition
The intent of the development is to construct a new single story pre‐engineered metal building,
approximately 9,047 SF, asphalt concrete parking, crushed asphalt overflow parking,
landscaping and a stormwater detention and conveyance system for Hess Land, LLC.
Floodplain
FEMA Floodplain mapping in this neighborhood is located on map‐panel 08069C0992G, revised
May 2, 2012, which indicates the subject property is located in Zone X, which is outside the
100‐year floodplain. (Appendix B – Flood Insurance Rate Map)
Existing Soils
The Natural Resource Conservation Service mapped the historic soils on the site as part of the
Caruso clay loam. The Hydrologic Class is Type ‘D’ Soils. (Appendix C – NRCS Soils Map)
Section 3: Drainage Design Criteria
Reference Manuals
Storm drainage design criteria is defined in the City of Fort Collins “Storm Drainage Design
Criteria and Construction Standards Manual (FCSDCM) and Amendments, which references to
the “Urban Drainage and Flood Control District” (UDFCD) and the “Urban Storm Drainage
Criteria Manual” (USDCM), Volumes 1, 2, and 3, dated 2008 with revisions (the Manual), are
used and referenced in this report.
Four Step Process
The City of Fort Collins has adopted the “Four Step Process” that is recommended in Volume 3
of the USDCM for selecting BMP’s in urban redevelopment areas. The goal of this process is to
minimize adverse impacts on receiving waters. The following describe how each step of the
process are incorporated in the proposed development:
Project # 16‐015‐002 Page 5
Step 1 – Employ Runoff Reduction Practices
By selecting a site that is undeveloped that currently does not have detention or water quality
treatment, the impacts of the proposed development will be less due to the addition of the
detention pond with the water quality capture volume included. The project proposes to install
rain gardens with underdrains and dry wells to aid in conveyance and infiltration opportunities
and reduce the effects of the added impervious areas.
Step 2 – Water Quality Capture Volume (WQCV)
In order to reduce the sediment load and other pollutants leaving the site, it is important to
provide WQCV to minimize the downstream impacts. This project proposes to provide rain
garden/detention ponds located on the site. These ponds are sized to capture the WQCV and
allow infiltration & release to the proposed drywells.
Step 3 – Stabilize Drainageways
Since this site is in close proximity to Poudre River it is important to take this Step into
consideration. By providing stormwater detention and water quality and lowering the historic
runoff and providing a metered outflow the project impacts to the drainageway are essentially
reduced. The majority of the drainageway leaving the site is already stabilized.
Step 4 – Implement Site Specific and Other Source Control BMP’s
The proposed project will contain the following BMP’s:
Rain Garden/Dry Wells: All runoff from the site will be directed into and through the
proposed BMP facilities prior to leaving the site. As in the adjacent site (2600 Midpoint
Dr., Lot 19), we are proposing to install Dry Wells as necessary to connect the Rain
Garden Underdrains and aid in infiltration into the existing soil stratum.
Maintenance: In order for BMP’s to remain effective proper maintenance needs are
required. Scheduled visual inspections and routine repair after larger storm events are
critical in the maintenance and effectiveness of the installed BMP’s. The sites owner will
be advised of these practices during installation in order to maximize the efficiency of
the installed BMP’s. Maintenance Standard Operating Procedures are also included in
the Development Agreement with the City.
Section 4: Hydraulic Calculations
Criteria
Runoff criteria for the proposed sites was analyzed for the 2‐YR and 100‐YR storm events. The
Rational Method is being used for the design of the proposed improvements.
Rainfall Intensities used in the proposed design were determined as a function of the Time of
Concertation for each subbasin. The values used were determined by the City of Fort Collins
Rainfall Intensity/Duration/Frequency curve (Figure 3‐1 and Table 3‐1a (see Appendix D).
Project # 16‐015‐002 Page 6
Imperviousness
Values from Table RO‐3 (USDCM) were used in determining the sites imperviousness. The
overall proposed site improvements and landscaping equate to a total onsite proposed
Imperviousness of 58%.
Level 1 Watershed‐Level Volume Reduction Method is applied to the extent possible on the
site. Grass areas are strategically located in order to provide surface flow where allowed, prior
to the stormwater leaving the site.
Time of Concentration & Runoff Coefficient
The onsite area was separated into two (2) subbasins with slopes varying between 0.5% to 4%.
The calculated Time of Concentration (TC) for each basin are listed in Appendix E. See Basin
Map in Appendix F for more information.
WQCV
The UD‐BMP_v3.03 (UDFCD) spreadsheet was used to calculate the required Rain Garden water
quality capture volume for each of the two subbasins. See Appendix E for design information.
Detention
A “Modified FAA” Detention Spreadsheet for each of the subbasins was used to analyze the
100‐year storm event with the allowable predeveloped 2‐year release. See Appendix E for
design information.
Section 5: Facility Design
The proposed improvements will increase the amount of impervious area; however, measures
have been included in the design to minimize the amount of stormwater release from the site.
Detention is sized for the 100‐year rainfall event for each of the proposed ponds. The outlet
structures are designed to release at the historic predeveloped 2‐year event at a release of
0.142 cfs per for Subbasin 1.0 and 0.201 cfs per for Subbasin 2.0 (see Appendix E for historic
calcs). The runoff will sheet flow until a concentrated point and then be conveyed via trickle
channel or gutters and then deposited into the respective pond.
The site was broken into three developed subbasins; Subbasin 1.0 (0.331 acres), Subbasin 2.0
(0.470 acres), and Subbasin 3.0 (0.053 acres). See Appendix E for breakdown of the different
area types for each subbasin and Appendix F for the Subbasin Map.
Subbasin 1.0 contains the proposed building and minor areas adjacent to the building. The
runoff will be conveyed to the back of the building and outlet into proposed drainage pan
behind the building, which will convey the water to the new pond located between the new
building and Midpoint Drive.
Project # 16‐015‐002 Page 7
Subbasin 2.0 is primarily the parking and paved areas which drains to the west to a shared
detention/water quality pond with Lot 19. This pond is being reworked to include sufficient
volume as necessary for the newly added Subbasin 2 from Lot 18 (this project), as well as
maintaining the required volume from the adjacent site as determined in the Holsinger Drywall
(Lot 19) approved plans dated (4‐12‐2007). See Appendix F for that original design included.
Lot 19 pond as constructed today includes an approximate total volume of 9,291 CF (which
includes water quality and detention). Two existing “drywells” exist on Lot 19 as well to aid in
infiltration and water quality and will be kept at full build out of Lot 18. Care was taken in the
design to maintain the same 100‐Yr WSEL for the shared pond with both contributing lots,
which confirms the existing outlet structure will not need structural modifications.
The combined Lot 18 and 19 WQCV and Detention modeling was completed to determine the
new outlet orifice size and 100‐Yr WSEL. The existing water quality/detention outlet structure
on Lot 19 will only need modifications to the steel orifice plate, which currently has three ½”
diameter perforations. The new plate as detailed in the construction drawings will require one
orifice with a 2‐3/4” orifice. See Appendix E for calculations. No other modifications are
required to the existing outlet structure.
Subbasin 3.0 contains a small portion of the access driveway, sidewalk, and landscape area that
due to the existing grades on the site being substantially higher than the adjacent roadway
cannot be directed to one of the detention ponds. The contributing area for this Subbasin is
approximately 0.053 acres. This runoff would sheet flow to Midpoint Drive and continue along
the curb and gutter to the next available catch basin.
See Basin Map in Appendix F for a reiteration of the existing and proposed volumes. The 100‐
Year water surface elevation with runoff from both site into this shared pond is shown on the
Subbasin Map.
For Water Quality, the project proposes to include the WQCV as Rain Gardens below the
Detention Pond with Underdrains tied directly to Drywells to aid in the infiltration and natural
discharge of the runoff. Both of the ponds include sized Rain Gardens for the appropriate
events in accordance with the City of Fort Collins criteria.
Below is a summary of each of subbasins design with supporting calculations within the
Appendix of this report.
Dev. 2‐
Year Flow
(cfs)
Dev. 100‐Year
Flow (cfs)
WQCV
(ac‐ft)
100‐Year
Vol. (ac‐ft)
Tot. Volume
Req'd (ac‐ft)
Tot. Volume
Provided (ac‐ft)
Release
Rate
(cfs)
Orifice (in)
Sub
1.0
0.6 2.98 0.005 0.084 0.089 0.100 0.142 1‐1/2"
Sub
2.0
0.62 3.07 0.008 0.114 0.122 0.142 0.201 2‐3/4"
Project # 16‐015‐002 Page 8
Dev. 2‐
Year
Flow
(cfs)
Dev. 100‐
Year Flow
(cfs)
WQC
V (ac‐
ft)
100‐
Year
Vol.
(ac‐ft)
Tot.
Volume
Req'd
(ac‐ft)
Tot.
Volume
Provided
(ac‐ft)
2‐Yr Hist.
Release
Rate (cfs)
Orifice
(in)
Sub
1.0
0.6 2.98 0.005 0.076 0.081 0.100 0.142 1‐1/2”"
Sub
2.0
0.62 3.07 0.008 0.087 0.095 0.142 0.201 2‐3/4"
Sub
3.0
0.12 0.54 N/A N/A N/A N/A N/A N/A
Section 6: Conclusions
All computations that have been reviewed or completed within this report are in compliance
with the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual
and the Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual
Volumes 1 &2.
The proposed drainage concepts presented in this report and on the construction plans
adequately provide for stormwater detention and water quality treatment of impervious areas
by releasing the 100‐Year storm event at the Predeveloped 2‐Year runoff rates. The Water
Quality design will benefit the site by reducing the initial discharge from the site and removal of
any sediments or other pollutants generated by the developed site.
Section 7: References
The Natural Resource Conservation Service Soil Survey for Larimer County and the WSS
website.
FEMA FIRM map‐panel 08069C0992G Effective 05/02/2012.
“City of Fort Collins Stormwater Criteria Manual” dated December 2011
Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual
(UDFCD), Volumes 1, 2, and 3, dated 2008 with revisions (the Manual).
w Appendix A
Site Vicinity Map
Appendix B
Flood Insurance Rate Map
Appendix C
NRCS Soils Map
Soil Map—Larimer County Area, Colorado
(Lot 18 - Midpoint Dr)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/29/2016
Page 1 of 3
4489990 4490010 4490030 4490050 4490070 4490090 4490110 4490130 4490150 4490170
4489990 4490010 4490030 4490050 4490070 4490090 4490110 4490130 4490150 4490170
497390 497410 497430 497450 497470 497490 497510 497530
497390 497410 497430 497450 497470 497490 497510 497530
40° 33' 44'' N
105° 1' 51'' W
40° 33' 44'' N
105° 1' 45'' W
40° 33' 38'' N
105° 1' 51'' W
40° 33' 38'' N
105° 1' 45'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 45 90 180 270
Feet
0 10 20 40 60
Meters
Map Scale: 1:944 if printed on A portrait (8.5" x 11") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at 1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil line
placement. The maps do not show the small areas of contrasting
soils that could have been shown at a more detailed scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more accurate
calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as of
Map Unit Legend
Larimer County Area, Colorado (CO644)
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
22 Caruso clay loam, 0 to 1 percent
slope
1.9 100.0%
Totals for Area of Interest 1.9 100.0%
Soil Map—Larimer County Area, Colorado Lot 18 - Midpoint Dr
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/29/2016
Page 3 of 3
Appendix D
Hydrologic Criteria
RAINFALL INTENSITY-DURATION-FREQUENCY CURVE
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00
STORM DURATION (minutes)
RAINFALL INTENSITY (inches/hour)
2-Year Storm 10-Year Storm 100-Year Storm
Figure RA-16 City of Fort Collins Rainfall Intensity-Duration-Frequency Curves
(13) Section 5.0 is deleted in its entirety.
(14) Section 6.0 is deleted in its entirety.
(15) Section 7.0 is deleted in its entirety.
(16) Section 7.1 is deleted in its entirety.
(17) Section 7.2 is deleted in its entirety.
(18) Section 7.3 is deleted in its entirety.
(19) Section 8.0 is deleted in its entirety.
(20) Table RA-1 is deleted in its entirety.
(11) Section 4.0 is amended to read as follows:
4.0 Intensity-Duration-Frequency Curves for Rational Method:
The one-hour rainfall Intensity-Duration-Frequency tables for use the Rational Method
of runoff analysis are provided in Table RA-7 and in Table RA-8.
Table RA-7 -- City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
for Use with the Rational Method
(5 minutes to 30 minutes)
2-Year 10-Year 100-Year
Duration
(min)
Intensity
(in/hr)
Intensity
(in/hr)
Intensity
(in/hr)
5 2.85 4.87 9.95
6 2.67 4.56 9.31
7 2.52 4.31 8.8
8 2.4 4.1 8.38
9 2.3 3.93 8.03
10 2.21 3.78 7.72
11 2.13 3.63 7.42
12 2.05 3.5 7.16
13 1.98 3.39 6.92
14 1.92 3.29 6.71
15 1.87 3.19 6.52
16 1.81 3.08 6.3
17 1.75 2.99 6.1
18 1.7 2.9 5.92
19 1.65 2.82 5.75
20 1.61 2.74 5.6
21 1.56 2.67 5.46
22 1.53 2.61 5.32
23 1.49 2.55 5.2
24 1.46 2.49 5.09
25 1.43 2.44 4.98
26 1.4 2.39 4.87
27 1.37 2.34 4.78
28 1.34 2.29 4.69
29 1.32 2.25 4.6
30 1.3 2.21 4.52
DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF
Table RO-3—Recommended Percentage Imperviousness Values
Land Use or
Surface Characteristics
Percentage
Imperviousness
Business:
Commercial areas 95
Neighborhood areas 85
Residential:
Single-family *
Multi-unit (detached) 60
Multi-unit (attached) 75
Half-acre lot or larger *
Apartments 80
Industrial:
Light areas 80
Heavy areas 90
Parks, cemeteries 5
Playgrounds 10
Schools 50
Railroad yard areas 15
Undeveloped Areas:
Historic flow analysis 2
Greenbelts, agricultural 2
Off-site flow analysis
(when land use not defined)
45
Streets:
Paved 100
Gravel (packed) 40
Drive and walks 90
Roofs 90
Lawns, sandy soil 0
Lawns, clayey soil 0
* See Figures RO-3 through RO-5 for percentage imperviousness.
C A = K A + ( 1 . 31 i 3 − 1 . 44 i 2 + 1 . 135 i − 0 . 12 ) for CA ≥ 0, otherwise CA = 0 (RO-6)
C CD = K CD + ( 0 . 858 i 3 − 0 . 786 i 2 + 0 . 774 i + 0 . 04 ) (RO-7)
C B = (CA + C CD ) 2
2007-01 RO-9
Urban Drainage and Flood Control District
Appendix E
Hydraulic Calculations
Historic Runoff Coefficients & Percent Impervious Calculated By: RSB
Project - Lot 18 - Midpoint Dr Checked By: MRB
Job Number: 16-015-002 Date: 7/28/2016
IMP% Soil Types: Caruso Clay loam, 0-1 %
Table RO-11 (COFC) Roof 0.95 90 Hydrologic Soil Group: D
Table RO-3 (UDSDCM Asphalt 0.95 100
Concrete 0.95 96
Landscaping (flat) 0.20 0
Landscaping (steep) 0.35 0
Gravel & Pavers 0.50 40
Multi-family (attached) 0.65 70
Commercial 0.95 95
Undeveloped Historical 0.20 2
Basin Total Area Roof Paved Gravel Sidewalk Landscape Runoff % Comments
Description (ac) Area (sf) Area (sf) Area (sf) Area (sf) Area (sf) Coeff C Imperv
EX-1 0.331 14418 0 0 0 0 4980 0.20 0
EX-2 0.470 20473 0 0 0 0 7077 0.20 0
EX-3 0.053 2309 0 0 0 0 2309 0.20 0
Total Basin 0.85 37200 0 0 0 0 14366 0.08 0
Equations:
Calculated C coefficeints & Percent Impervious are Weighted
C = Summation (Ci*Ai) / At
Ci = Runoff Coefficient for Specific Area (Ai)
Ai = Area of Surface with Runoff Coefficient of Ci
n - Number of different surfaces to be considered
Runoff
Coeff C
Total Area
(sq. ft.)
STANDARD FORM SF-2
Event: 2-Year Historic TIME OF CONCENTRATION
Cf = 1.00 SUBDIVISION: Lot 18
CALCULATED BY: MRB DATE: 7/28/2016 REV:
SUB-BASIN INITIAL/OVERLAND TRAVEL TIME t c CHECK FINAL REMARKS
DATA TIME (ti) (t t) (URBANIZED BASINS) tc
DESIG: C AREA LENGTH SLOPE ti LENGTH SLOPE Mannings VEL. tt COMP. TOT. LENGTH tc=(L/180)+10
Ac Ft % Min Ft % n FPS Min tc Ft Min Min
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
EX-1 0.20 0.33 60 1.5 11.4 175 0.5 0.025 2.1 1.4 12.8 235 11.3 11.3
EX-2 0.20 0.47 75 1.0 14.6 155 0.5 0.025 2.1 1.2 15.8 230 11.3 11.3
EX-3 0.20 0.05 45 1.0 11.3 0 0.5 0.025 2.1 0.0 11.3 45 10.3 10.3
Total Basin 0.08 0.85 50 2.0 10.7 200 0.5 0.025 1.3 2.6 13.3 250 11.4 11.4
References/Equations:
Table RO-12 COFC
tc = ti + tt
ti = {1.87(1.1 - C*Cf)*L}/S^0.33
tt = L/Vel
Velocity from Manning's Equation with R=0.1 (per COFC Figure 3-3)
Final tc = Min of ti + tt and/or Urbanized Check
Location: Lot 18 RATIONAL METHOD PEAK RUNOOF
Calculated By: RSB Event: 2-Year
Date: 7/28/2016 Historic Flow Rate
Cf = 1.00
SUB-BASIN Direct Runoff Comments
DATA
DESIG: C AREA C*Cf tc i Q
Ac min (in/hr) (cfs)
EX-1 0.20 0.33 0.20 11.3 2.14 0.142
EX-2 0.20 0.47 0.20 11.3 2.14 0.201
EX-3 0.20 0.05 0.20 10.3 2.25 0.024
Total Basin 0.20 0.85 0.20 11.4 2.15 0.367
Q = Cf*C*i*A
Q = Peak Discharge (cfs)
C = Runoff Coefficient
Cf = Frequency Adjustment Factor
I = Rainfall Intensity (in/hr) from COFC IDF Curve (I = 24.221 / (10+tc)^0.7968
A = Drainage Area (ac)
Runoff Coefficients & Percent Impervious Calculated By: RSB
Project - Lot 18 - Midpoint Dr Checked By: MRB
Job Number: 16-015-002 Date: 7/28/2016
IMP% Soil Types: Caruso Clay loam, 0-1 %
Table RO-11 (COFC) Roof 0.95 90 Hydrologic Soil Group: D
Table RO-3 (UDSDCM Asphalt 0.95 100
Concrete 0.95 96
Landscaping (flat) 0.20 0
Landscaping (steep) 0.35 0
Gravel & Pavers 0.50 40
Multi-family (attached) 0.65 70
Commercial 0.95 95
Undeveloped Historical 0.20 2
Basin Total Area Roof Paved Gravel Sidewalk Landscape Runoff % Comments
Description (ac) Area (sf) Area (sf) Area (sf) Area (sf) Area (sf) Coeff C Imperv
1.0 0.331 14418 9047 0 0 874 4980 0.72 62
2.0 0.470 20473 0 8097 5037 720 6662 0.60 53
3.0 0.053 2309 0 1505 0 389 415 0.82 81
Total Basin 0.85 37200 9047 9602 5037 1983 12057 0.66 58
Equations:
Calculated C coefficeints & Percent Impervious are Weighted
C = Summation (Ci*Ai) / At
Ci = Runoff Coefficient for Specific Area (Ai)
Ai = Area of Surface with Runoff Coefficient of Ci
n - Number of different surfaces to be considered
Runoff
Coeff C
Total Area
(sq. ft.)
STANDARD FORM SF-2
Event: 2-Year TIME OF CONCENTRATION
Cf = 1.00 SUBDIVISION: Lot 18
CALCULATED BY: MRB DATE: 7/28/2016 REV:
SUB-BASIN INITIAL/OVERLAND TRAVEL TIME t c CHECK FINAL REMARKS
DATA TIME (ti) (t t) (URBANIZED BASINS) tc
DESIG: C AREA LENGTH SLOPE ti LENGTH SLOPE Mannings VEL. tt COMP. TOT. LENGTH tc=(L/180)+10
Ac Ft % Min Ft % n FPS Min tc Ft Min Min
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
1.0 0.72 0.33 60 1.5 4.8 175 0.5 0.016 1.3 2.2 7.0 235 11.3 7.0
2.0 0.60 0.47 75 1.0 8.1 155 0.5 0.016 1.4 1.8 10.0 230 11.3 10.0
3.0 0.82 0.05 25 2.0 2.1 25 1.9 0.016 1.4 0.3 2.4 50 10.3 5.0
Total Basin 0.66 0.85 50 2.0 4.6 200 0.5 0.016 1.3 2.6 7.2 250 11.4 7.2
References/Equations:
Table RO-12 COFC
tc = ti + tt
ti = {1.87(1.1 - C*Cf)*L}/S^0.33
tt = L/Vel
Velocity from Manning's Equation with R=0.1 (per COFC Figure 3-3)
Final tc = Min of ti + tt and/or Urbanized Check
STANDARD FORM SF-2
Event: 100-Year TIME OF CONCENTRATION
Cf = 1.25 SUBDIVISION: Lot 18
CALCULATED BY: MRB DATE: 7/28/2016 REV:
SUB-BASIN INITIAL/OVERLAND TRAVEL TIME tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASINS) tc
DESIG: C AREA C*Cf LENGTH SLOPE ti LENGTH SLOPE Mannings VEL. tt COMP. TOT. LENGTH tc=(L/180)+10
Ac Ft % Min Ft % n FPS Min tc Ft Min Min
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
1.0 0.72 0.33 0.90 60 1.5 2.5 175 0.5 0.016 1.3 2.2 4.7 235 11.3 5.0
2.0 0.60 0.47 0.75 75 1.0 5.7 155 0.5 0.016 1.4 1.8 7.6 230 11.3 7.6
3.0 0.82 0.05 1.02 25 2.0 0.6 25 1.9 0.016 1.4 0.3 0.9 50 10.3 5.0
Total Basin 0.66 0.85 0.82 50 2.0 2.9 200 0.5 0.016 1.3 2.6 5.5 250 11.4 5.5
References/Equations:
Table RO-12 COFC
tc = ti + tt
ti = {1.87(1.1 - C*Cf)*L}/S^0.33
tt = L/Vel
Velocity from Manning's Equation with R=0.1 (per COFC Figure 3-3)
Final tc = Min of ti + tt and/or Urbanized Check
Location: Lot 18 RATIONAL METHOD PEAK RUNOOF
Calculated By: RSB Event: 2-Year
Date: 7/28/2016
Cf = 1.00
SUB-BASIN Direct Runoff Comments
DATA
DESIG: C AREA C*Cf tc i Q
Ac min (in/hr) (cfs)
1.0 0.72 0.33 0.72 7.0 2.52 0.60
2.0 0.60 0.47 0.60 10.0 2.21 0.62
3.0 0.82 0.05 0.82 5.0 2.85 0.12
Total Basin 0.66 0.85 0.66 7.2 2.50 1.41
Q = Cf*C*i*A
Q = Peak Discharge (cfs)
C = Runoff Coefficient
Cf = Frequency Adjustment Factor
I = Rainfall Intensity (in/hr) from COFC IDF Curve (I = 24.221 / (10+tc)^0.7968
A = Drainage Area (ac)
Location: Lot 18 RATIONAL METHOD PEAK RUNOOF
Calculated By: RSB Event: 100-Year
Date: 7/28/2016
Cf = 1.25
SUB-BASIN Direct Runoff Comments
DATA
DESIG: C AREA C*Cf tc i Q
Ac min (in/hr) (cfs)
1.0 0.72 0.33 0.90 5.0 9.95 2.98
2.0 0.60 0.47 0.75 7.6 8.76 3.07
3.0 0.82 0.05 1.02 5.0 9.95 0.54
Total Basin 0.66 0.85 0.82 5.5 9.54 6.71
Q = Cf*C*i*A
Q = Peak Discharge (cfs)
C = Runoff Coefficient
Cf = Frequency Adjustment Factor
i = Rainfall Intensity (in/hr) from COFC IDF Curve (i = 84.682 / (10+tc)^0.7975
A = Drainage Area (ac)
DETENTION VOLUME CALCULATIONS
RATIONAL VOLUMETRIC (FAA) METHOD
LOCATION: Lot 18 - Midpoint Dr
CALCULATED BY: MRB
PROJECT NUMBER: 16-015-002
DATE: 7/26/2016
BASIN: 1.0
Equations: A trib. To pond = 0.331 acre
QD = CiA C100 = 0.90 (C*Cf)
Vi = T*CiA = T*QD Developed C*A = 0.30 acre
Vo =m*QPO*(60*T) QPO = 0.142 cfs
S = Vi - Vo tc = 5 min
Rainfall intensity from Larimer County Area 1 IDF Curve
Storm Rainfall QD Vol. In Outflow Vol. Out Storage Storage
Duration, T Intensity, i (cfs) Vi Adjustment Vo SS
(min) (in/hr) (ft3) Factor, m (ft3) (ft3) (ac-ft)
5 9.95 3.0 889 1.00 43 847 0.019
10 7.72 2.3 1380 0.75 64 1316 0.030
20 5.60 1.7 2002 0.63 107 1895 0.044
30 4.52 1.3 2424 0.58 149 2275 0.052
40 3.74 1.1 2674 0.56 192 2482 0.057
50 3.23 1.0 2887 0.55 234 2652 0.061
60 2.86 0.9 3067 0.54 277 2790 0.064
70 2.62 0.8 3278 0.54 320 2959 0.068
80 2.38 0.7 3403 0.53 362 3041 0.070
90 2.22 0.7 3571 0.53 405 3167 0.073
100 2.05 0.6 3664 0.53 447 3217 0.074
110 1.93 0.6 3795 0.52 490 3305 0.076
120 1.80 0.5 3861 0.52 533 3328 0.076
130 1.60 0.5 3718 0.52 575 3143 0.072
140 1.40 0.4 3503 0.52 618 2886 0.066
150 1.20 0.4 3217 0.52 660 2557 0.059
160 1.15 0.3 3289 0.52 703 2586 0.059
170 1.10 0.3 3342 0.51 746 2597 0.060
180 1.05 0.3 3378 0.51 788 2590 0.059
Required Storage Volume: 3328 ft3
0.076 acre-ft
DETENTION VOLUME CALCULATIONS
RATIONAL VOLUMETRIC (FAA) METHOD
LOCATION: Lot 18 - Midpoint Dr
CALCULATED BY: MRB
PROJECT NUMBER: 16-015-002
DATE: 7/26/2016
BASIN: 2.0
Equations: A trib. To pond = 0.470 acre
QD = CiA C100 = 0.75 (C*Cf)
Vi = T*CiA = T*QD Developed C*A = 0.35 acre
Vo =m*QPO*(60*T) QPO = 0.201 cfs
S = Vi - Vo tc = 7.6 min
Rainfall intensity from Larimer County Area 1 IDF Curve
Storm Rainfall QD Vol. In Outflow Vol. Out Storage Storage
Duration, T Intensity, i (cfs) Vi Adjustment Vo SS
(min) (in/hr) (ft3) Factor, m (ft3) (ft3) (ac-ft)
5 9.95 3.5 1052 1.00 60 992 0.023
10 7.72 2.7 1633 0.88 106 1527 0.035
20 5.60 2.0 2369 0.69 166 2202 0.051
30 4.52 1.6 2868 0.63 227 2641 0.061
40 3.74 1.3 3164 0.60 287 2877 0.066
50 3.23 1.1 3416 0.58 347 3068 0.070
60 2.86 1.0 3629 0.56 408 3222 0.074
70 2.62 0.9 3879 0.55 468 3411 0.078
80 2.38 0.8 4027 0.55 528 3499 0.080
90 2.22 0.8 4226 0.54 589 3637 0.083
100 2.05 0.7 4336 0.54 649 3687 0.085
110 1.93 0.7 4490 0.53 709 3781 0.087
120 1.80 0.6 4568 0.53 769 3799 0.087
130 1.60 0.6 4399 0.53 830 3569 0.082
140 1.40 0.5 4145 0.53 890 3255 0.075
150 1.20 0.4 3807 0.53 950 2857 0.066
160 1.15 0.4 3892 0.52 1011 2881 0.066
170 1.10 0.4 3955 0.52 1071 2884 0.066
180 1.05 0.4 3997 0.52 1131 2866 0.066
Required Storage Volume: 3799 ft3
0.087 acre-ft
Orifice Calculations
Lot 18 ‐ Midpoint Dr
d = diameter (inches)
Q = flow (cfs)
h = hydraulic head (ft)
d = sqrt((36.88*Q)/(sqrt(h)))
Subbasin 1.0
Diameter Standard Size
d = sqrt(36.88*0.049)/(sqrt(2.5) = 1.45‐inches 1‐1/2" Orifice
Subbasin 2.0
d = sqrt(36.88*0.070)/(sqrt(1.0) = 2.72‐inches 2‐3/4" Orifice
Spillway
Emergency Spillways for Both Subbasins are set at the same elevation as the 100‐Yr WSEL, which
is the same elevation of the top of the outlet structure. Any event above the 100‐Yr
event will fill the ponds and overtop the structure/spillway and be released into the
adjacent roadway.
PROPOSED DETENTION POND - STAGE/STORAGE
Pond: 1.0
Location: Lot 18
Calculated By: MRB
Date: 7/28/2016
V = 1/3 d (A + B + sqrt(A*B))
V = Volume between Contours, ft^2
d = Depth between Contours, ft
A = Surface Area of Contour, ft^2
96 0
96.5 245 0.00 0.00
97 525 0.00 0.01
WQCV = 97.5 835 0.01 0.01 0.00
98 1125 0.01 0.02 0.01
99 1665 0.03 0.06 0.04
100‐Year WSEL = 100 2228 0.04 0.10 0.09
Required Detention Volume = 0.076 See "Detention Volume Calculations"
Provided Detention = 0.090
Required WQCV = 0.005 See "WQCV" RG Calc Sheet
Provided WQCV = 0.010
Total Required Volume = 0.081
Total Volume Provided = 0.100
Stage
(ft)
Surface
Area
(ft^2)
Incremental
Storage
(ac‐ft)
Total
Storage
(ac‐ft)
Detention
Storage (ac‐
ft)
PROPOSED DETENTION POND - STAGE/STORAGE
Pond: 2.0
Location: Lot 18
Calculated By: MRB
Date: 7/28/2016
V = 1/3 d (A + B + sqrt(A*B))
V = Volume between Contours, ft^2
d = Depth between Contours, ft
A = Surface Area of Contour, ft^2
97 0
97.8 501 0.003 0.003
WQCV = 98.8 2000 0.027 0.030
99 5175 0.016 0.046 0.016
100‐Year WSEL = 99.6 8937 0.096 0.142 0.112
Required Detention Volume = 0.087 See "Detention Volume Calculations"
Provided Detention = 0.112
Required WQCV = 0.008 See "WQCV" RG Calc Sheet
Provided WQCV = 0.030
Total Required Volume = 0.095
Total Volume Provided = 0.142
Stage
(ft)
Surface
Area
(ft^2)
Incremental
Storage
(ac‐ft)
Total
Storage
(ac‐ft)
Detention
Storage (ac‐
ft)
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 62.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.620
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.19 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 14,418 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 233.6 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 156 sq ft
D) Actual Flat Surface Area AActual = 245 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 835 sq ft
F) Rain Garden Total Volume VT= 540 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = N/A ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
MRB
Ridgetop Engineering
May 24, 2016
Lot 18 - Midpoint Drive
Basin 1
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.03_Basin 1, RG 5/24/2016, 4:39 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)
MRB
Ridgetop Engineering
May 24, 2016
Lot 18 - Midpoint Drive
Basin 1
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
UD-BMP_v3.03_Basin 1, RG 5/24/2016, 4:39 PM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 53.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.530
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.17 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 22,825 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 326.6 cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 218 sq ft
D) Actual Flat Surface Area AActual = 501 sq ft
E) Area at Design Depth (Top Surface Area) ATop = sq ft
F) Rain Garden Total Volume VT= cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = N/A ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
MRB
Ridgetop Engineering
September 25, 2016
Lot 18 - Midpoint Dr
Basin 2
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
UD-BMP_v3.03_Basin 2, RG 9/25/2016, 12:18 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)
MRB
Ridgetop Engineering
September 25, 2016
Lot 18 - Midpoint Dr
Basin 2
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
UD-BMP_v3.03_Basin 2, RG 9/25/2016, 12:18 PM
LID Table
75% On-Site Treatment by LID Requried
New Impervious Area 15,691 sq. ft.
Required Minimum Impervious Area to be Treated 11768 sq. ft.
Area tributary to Rain Gardens 13,751 sq. ft.
Run-on Area N/A sq. ft.
Impervious Area Treated by Rain Gardens 13751 sq. ft.
Actual % On-Site Treated by LID 88%
Project # 16‐015‐002 Page 14
Appendix F
Maps
MIDPOINT DRIVE
LOT 18
BUILDING
9,047 SF
FFE = 4901
LOT 19, HOLSINGER
DRYWALL
FFE: 4897.6
SUBBASIN 1.0
AREA = 0.331 AC
SUBBASIN 2.0
AREA = 0.470 AC
SUBBASIN 3.0
AREA = 0.053 AC
DRAINAGE
PLAN
C-2.1
6 Of
PROJECT TITLE
REVISIONS
SHEET TITLE
SHEET INFORMATION
DATE
SEAL
DATE
PREPARED FOR
ENGINEERING R IDGE & CONSULTING T OP
5255 Ronald Reagan Blvd.,
Ste. 210
Johnstown, CO 80534
T (303) 322-6480
W ridgetopeng.com
DRAWN BY:
CHECKED BY:
PROJECT NO.:
R4 ARCHITECTS
LOT 18 SPEC.
BUILDING
226 REMINGTON, UNIT 3
FORT COLLINS, CO
2590 MIDPOINT DR
FORT COLLINS, CO
16015002
MRB
BSA
10
SUBMITTAL
FINAL DEVELOPMENT
PLAN
7/27/2016
CITY COMMENTS 09/02/2016
WATER QUALITY TREATMENT LEGEND
Know what'sbelow.
Call before you dig.
R
Minimum 8" Thick Layer of
CDOT No. 4 Aggregate
Minimum 4" Perforated
PVC Pipe (Optional
Depending on Underlying
This unofficial copy was downloaded on Dec-23-2015 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
This unofficial copy was downloaded on Dec-23-2015 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
Soil Conditions)
12" Ponding Depth
Minimum 12" Thick Layer
of Bioretention Sand Media
(see Bioretention Sand
Media Specification below)
Minimum 6" Thick Layer of
Pea Gravel Diaphragm
Parking/Building
Water Surface
Minimum CDOT
No. 4 Aggregate
Above and Below
PVC Pipe
Undisturbed Soil
CONNECT UNDERDRAIN
TO DRY WELL
the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 10, Sep 22, 2015
Soil map units are labeled (as space allows) for map scales 1:50,000
or larger.
Date(s) aerial images were photographed: Apr 22, 2011—Apr 28,
2011
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor shifting
of map unit boundaries may be evident.
Soil Map—Larimer County Area, Colorado
(Lot 18 - Midpoint Dr)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/29/2016
Page 2 of 3