HomeMy WebLinkAboutBDR FOUR-PLEX, 621 S. MELDRUM ST. - FDP - FDP130002 - REPORTS - DRAINAGE REPORTJune 18, 2013
FINAL DRAINAGE REPORT
Big Deal Four Plex
Fort Collins, Colorado
Prepared for:
Big Deal Real Estate Inc.
2519 Ridge Creek Road
Fort Collins, Colorado 80528
Prepared by:
200 South College Avenue, Suite 10
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 876-001
3This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
June 18, 2013
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage Report for
Big Deal Four Plex
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage Report for your review.
Comments from the Big Deal Four Plex PDP Round Number 2 review letter dated
01.04.13 have been addressed. Written responses can be found in the comprehensive
response to comments letter on file with Current Planning.
This report has been prepared in accordance with the Fort Collins Stormwater Criteria
Manual (FCSCM), and serves to document the stormwater impacts associated with the
proposed Big Deal Four Plex multi-family student housing project. We understand that
review by the City is to assure general compliance with standardized criteria contained in
the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Herman H. Feissner, PE
Project Engineer
Big Deal Four Plex
Final Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ......................................................... 1
II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 5
III. DRAINAGE DESIGN CRITERIA ......................................................................... 6
IV. DRAINAGE FACILITY DESIGN .......................................................................... 8
V. CONCLUSIONS............................................................................................. 10
References ............................................................................................................. 11
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers
B.2 – Swales
B.3 – Inlets
B.4 – Detention Facilities
APPENDIX C – Water Quality Design Computations
LIST OF TABLES AND FIGURES:
MAP POCKET:
EX1 – Existing Conditions Drainage Exhibit
C4.00 – Drainage Exhibit
NOTE: TABLE OF CONTENTS WILL BE UPDATED/CORRECTED WITH SUBSEQUENT
REPORT ISSUANCES.
Big Deal Four Plex
Final Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
Figure 1 – Vicinity Map
2. Big Deal Four Plex (project site) is located in Section 14, Township 7 North, Range
69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of
Colorado. More specifically, the project is located at 621 South Meldrum Street.
3. The project site is bordered to the north and south by existing single-family homes; to
the east by Meldrum Street (100' Right-of-Way); and to the west by an existing alley
(20' Right-of-Way).
4. There are no major drainageways within or adjacent to the site.
5. The existing Arthur Ditch bisects the east-west project axis. According to the ditch
company President, Mark Taylor, the existing ditch has a capacity of 60 to 70 cfs.
The ditch company generally runs flows of 50 - 55 cfs. The ditch receives existing
stormwater flows from two storm inlets in the alley.
The concrete ditch box is at grade (±5001.20) and visible across the project site. The
structural integrity of the ditch has yet to verified by a registered professional engineer.
At the time of writing, CTL Thompson was evaluating the existing concrete ditch box.
Big Deal Four Plex
Final Drainage Report 2
B. Description of Property
1. Big Deal Four Plex is comprised of ±0.22 acre.
2. The existing site improvements (See Figure 2 - Aerial Photograph) include: one single-
family home which fronts to Meldrum Street, a detached garage and a small shed.
Figure 2 – Aerial Photograph
3. The existing groundcover currently consists of several mature trees, grass, weeds and
bare soil.
4. The existing conditions runoff from sub-basin EX1 (see Existing Conditions Drainage
Exhibit) sheet flows from the west property line and the top of the Arthur Ditch across
flat grades (e.g., <2.00%) to a local low-point.
The excess surface runoff in sub-basin EX2 flows from the east edge of the Arthur
Ditch toward Meldrum Street.
5. A soils report (Soilogic Project # 12-1094) was completed by Soilogic, Inc. on
November 28, 2012. The report contains the results of a complete geotechnical
subsurface exploration as well as pertinent geotechnical recommendations. According
to the summary of findings presented in the aforementioned report, "Approximately 3
inches of vegetation and topsoil or wood chips was encountered at the surface at the
boring locations. The vegetative soil/wood chip layer was underlain by brown/rusty
brown/beige lean clay with varying amounts of sand, which varied to clayey sand with
depth in boring B-1. The lean clay/clayey sand varied from medium stiff to stiff in
terms of consistency or loose to medium dense in terms of relative density and
generally showed low swell potential at current moisture and density conditions. The
lean clay/clayey sand extended to the full depth of exploration, approximately 15 feet
below present site grade."
The boring logs show that USCS soil group CL is predominant on-site. These soils are
inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays and
lean clays.
Project
Site
Big Deal Four Plex
Final Drainage Report 3
6. There are no major drainageways within or adjacent to the project site.
7. The proposed Big Deal Four Plex project will include a single multi-family building
with four units and a plan area of approximately 2570 sq. ft. The completed structure
will be two stories. Other proposed improvements include: a new asphalt parking area
and updated landscaping.
8. The existing Arthur Ditch cuts diagonally across the project site. This general
alignment persists to the north and south of the project site (See Figure 3 – Existing
Drainage and Irrigation Infrastructure).
Figure 3 – Existing Drainage and Irrigation Infrastructure
9. The proposed land use is residential, multi-family dwellings. This is a permitted use in
the Neighborhood Community - Buffer District (NCB).
Project
Site
Big Deal Four Plex
Final Drainage Report 4
C. Floodplain
1. The subject property is not located in a FEMA regulatory or City of Fort Collins
designated floodplain. In particular, the project site is not located within a FEMA
designated 100-year floodplain per Map Number 08069C0979H (Effective date: May
2, 2012).
Figure 4 – FEMA Firmette (Map Number 08069C0979H)
Project
Site
Big Deal Four Plex
Final Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. Big Deal Four Plex is located within the City of Fort Collins Old Town major drainage
basin. This basin is located in north-central Fort Collins and has a drainage area of
approximately 2,120 acres, including approximately 400 acres of the Colorado State
University campus. The Old Town major drainage basin generally drains from west to
east. It receives some runoff from the Canal Importation Basin directly west of Old
Town. Most of the runoff from the Old Town major drainage basin drains into the
Poudre River.
Street flooding is a common occurrence in Old Town. Several capital projects such as
the Howes Street, Locust Street and Oak Street Outfall projects have addressed the
problem and improved drainage in the area.
2. As previously mentioned, the Arthur Ditch cuts diagonally across the project site. This
irrigation conveyance has not been directly influenced by stormwater flows from the
project site. However, with this design, we propose releasing attenuated developed
runoff into this existing conveyance as described below.
B. Sub-Basin Description
1. The existing site is defined with two sub-basins: EX1 and EX2. Sub-basin EX-1 is
situated between the west property line and the west edge of the Arthur Ditch. This
sub-basin drains to an existing low point with no defined outfall. Excess runoff could
fill this low-lying area and spill into sub-basin EX2.
Sub-basin EX2 is situated between the east edge of the Arthur Ditch and the east
property line. The existing runoff in sub-basin EX2 sheet flows from the west to east
and into Meldrum Street.
2. The Arthur Ditch does not currently receive stormwater flows from the subject site.
3. The project site does not receive any notable runoff from off-site properties.
Big Deal Four Plex
Final Drainage Report 6
III. DRAINAGE DESIGN CRITERIA
A. The overall stormwater management strategy employed with Big Deal Four Plex utilizes
the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters.
The following is a description of how the proposed development has incorporated each
step.
Step 1 – Employ Runoff Reduction Practices. The first consideration taken in trying to
reduce the stormwater impacts of this development is the site selection itself. By choosing
an already developed site with public storm sewer currently in place, the burden is
significantly less than developing a vacant parcel absent of any infrastructure.
Big Deal Four Plex aims to reduce runoff peaks, volumes and pollutant loads from
frequently occurring storm events such as the water quality (80th percentile) and the 2-
year storm event by implementing Low Impact Development (LID) strategies. Wherever
practical, runoff will be routed across landscaped areas or through grass- or cobble-lined
swales. This LID practice reduces the overall amount of impervious area, while Minimizing
Directly Connected Impervious Areas (MDCIA) at the same time. The combined
LID/MDCIA techniques will be implemented, where practical, throughout the
development, thereby slowing runoff and increasing opportunities for infiltration.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release.The efforts taken in Step 1 will help to minimize excess runoff from
frequently occurring storm events; however, urban development of this intensity will still
have stormwater runoff leaving the site. The primary water quality will occur in an
Extended Detention Basin (EDB) along the northwest property line (sub-basin A1). Water
Quality in sub-basin B will occur in the Udall Natural Area.
Step 3 – Stabilize Drainageways. As stated in Section I.B.6, above, there are no major
drainageways in or near the subject site.
Step 4 – Implement Site Specific and Other Source Control BMPs. This step typically
applies to industrial and commercial developments.
B. Development Criteria Reference and Constraints
1. The subject property is not part of an Overall Development Plan drainage study or
similar “development/project” drainage master plan.
2. There are no known drainage studies for any adjacent properties that will have an
affect on Big Deal Four Plex.
3. The site plan will be constrained on two sides by existing single-family development;
an alleyway; and Meldrum Street. The drainage outfall for sub-basin A1 is an existing
area inlet that ties into the existing 12” RCP storm sewer in the alleyway. The
proposed design releases at the calculated existing Q2 for sub-basin EX1 (i.e.,
0.072cfs).
C. Hydrological Criteria
Big Deal Four Plex
Final Drainage Report 7
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations
associated with the Big Deal Four Plex development. Tabulated data contained in
Table RA-7 has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. The Rational Formula-based Federal Aviation Administration (FAA) procedure has
been utilized for detention storage calculations.
4. Two separate design storms have been utilized to address distinct drainage scenarios.
The first event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year
recurrence interval. The second event considered is the “Major Storm,” which has a
100-year recurrence interval.
D. Hydraulic Criteria
1. The drainage facilities proposed with the Big Deal Four Plex project are
designed in accordance with criteria outlined in the FCSCM and/or the Urban
Drainage and Flood Control District’s (UDFCD) Urban Storm Drainage Criteria
Manual.
2. As stated in Section I.C.1, above, the subject property is not located in a
FEMA regulatory or a City of Fort Collins designated floodplain.
F. Floodplain Regulations Compliance
1. As previously mentioned, this project is not subject to any floodplain
regulations.
G. Modifications of Criteria
1. The design contained herein changes the direction that existing conditions
stormwater runoff travels. We are proposing to release attenuated developed
runoff (Qout=0.072cfs) into the existing storm drain system in the alley. This
inlet discharges to the Arthur Ditch. The concept was discussed with and
approved by Mark Taylor on November 13, 2012. Considering the proposed
release rate and the existing ditch flows, he felt that it was okay to release into
the existing infrastructure and, ultimately, the Arthur Ditch.
Big Deal Four Plex
Final Drainage Report 8
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objective of the Big Deal Four Plex drainage design is, to the maximum
extent practicable, maintain existing drainage patterns, while not adversely impacting
adjacent properties.
2. No notable off-site runoff flows directly through the project site.
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within the
sections to which the content best applies.
4. The project site has been divided into three drainage areas, designated as sub-basins
A1, B1, B2, B3, C1 and C2. The drainage patterns anticipated for each basin are
further described below.
Sub-Basin A1
Sub-basin A1 encompasses nearly one-half of the total project site area. It is
comprised of landscaping, concrete walks and asphalt parking. A large part of the
parking area in this basin will comprise the on-site detention pond (Pond A). D.P. A1
is situated at the proposed outfall. A short section of pipe will connect to an existing
area inlet in the alleyway. This basin releases at a rate of 0.072 cfs during the 100-
year storm event.
Sub-Basins B1 through B3
Sub-basins B1 through B3 encompass the eastern portion of the project site. These
sub-basins are comprised of roof area, concrete walks and landscaping. The
downspouts on the north and south sides of the proposed structure will direct
developed runoff from the roof to finished grade or into a 6" PVC storm drain system.
Surface stormwater flows will collect in swales that run parallel to the north and south
property lines. These swales will drain into the existing curbline in Meldrum Street.
During the 2-year and 100-year storm events, the proposed condition will increase
(no) runoff into Meldrum Street by ±0.10 cfs and ±0.40cfs, respectively.
Overall, the project site will increase flows by ±0.11 cfs during the 2-year storm event
and ±0.22 cfs during the 100-year storm event.
Sub-Basins C1 through C2
Sub-basins C1 and C2 are located along the south and north property lines,
respectively. Each basin is comprised of landscaped area. These sub-basins drain to
the respective neighboring properties. In both cases, the developed runoff is negligible.
A full-size copy of the Drainage Exhibit (sheet C4.00) can be found in the Map Pocket
at the end of this report.
B. Specific Details
1. The proposed development will add ±0.072 acre of impervious area. This
includes the entire site and not just the increase in sub-basin A1.
Big Deal Four Plex
Final Drainage Report 9
2. The required storage volume was estimated with the FAA method.
To estimate the required storage volume, we calculated the existing 2-year
release rate (0.072 cfs) for sub-basin EX1. Refer to Appendix B.4 for the
calculation.
3. Water quality is provided for sub-basin A1 in an Extended Detention Basin
(EDB). The calculated Water Quality Capture Volume (WQCV), 105 cu. ft.,
can be provided with less than one foot of depth because of the proposed
detention pond configuration (i.e., long and narrow) and grading. The WQCV
depth was set to one foot. At this depth we provide 238 cu. ft . of storage.
This volume was added to the required 100-year storage volume, 649 cu. ft,
to reach the total required volume, 887 cu. ft.
4. The 100-year water surface elevation is 5001.39. An emergency spillway is
provided at the entrance to the parking lot. Water will begin spilling from the
parking area at elevation 5001.51.
5. Sub-basins B1 through B3 drain, without attenuation, into Meldrum Street.
Water quality for these basins is provided in the Udall Natural Area.
6. The drainage features associated with Big Deal Four Plex project are private
facilities and located on private property.
7. There are no additional facilities or upgrades needed off-site in order to accommodate
the developed runoff from Big Deal Four Plex.
Big Deal Four Plex
Final Drainage Report 10
V. CONCLUSIONS
A. Compliance with Standards
1. The design elements comply without variation except as noted above with respect to
the request to release attenuated developed runoff into the Arthurs Ditch.
2. The drainage design proposed with Big Deal Four Plex complies with the City of Fort
Collins Master Drainage Plan for the Old Town Basin.
3. There are no regulatory floodplains associated with the Big Deal Four Plex
development.
4. The drainage plan and stormwater management plan measures proposed with the Big
Deal Four Plex student housing project are compliant with all applicable State and
Federal regulations governing stormwater discharge.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit potential damage
associated with its stormwater runoff. The Big Deal Four Plex will detain for the sub-
basin A1 developed condition and release at 0.072 cfs during the 100-year storm.
2. The proposed Big Deal Four Plex development will not impact the Master Drainage
Plan recommendations for the Old Town Basin.
Big Deal Four Plex
Final Drainage Report 11
References
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
4. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX A
HYDROLOGIC COMPUTATIONS
Big Deal Four Plex
Project: Big Deal Four Plex
Project Site Area 9513 Calculations By:
EX1 3794 Date:
EX2 5719
A1 4292
B1 1043
B2 1523
B3 1818
C1 447
C2 391
Basin Area, sq. ft. Surface Description % Impervious Area, sq. ft. Notes
EX1 253 Roofs 90% 227
EX1 42 Roofs 90% 38
EX1 479 Concrete (e.g., walks & parking) 90% 431 Arthur Ditch
Impervious Area 696
% Impervious 18%
EX2 840 Roofs 90% 756
EX2 479 Concrete (e.g., walks & parking) 90% 431 Arthur Ditch
EX2 26 Concrete (e.g., walks & parking) 90% 24
EX2 185 Roofs 90% 166
EX2 148 Pavers (e.g., flagstone or wood deck) 22% 32
Impervious Area 1410
% Impervious 25%
Total Impervious Area 2106
% Impervious 22%
Basin Area, sq. ft. Surface Description % Impervious Area, sq. ft. Notes
A1 1817 Asphalt 100% 1817
A1 541 Concrete (e.g., walks & parking) 90% 487
A1 305 Roofs 90% 275
A1 298 Pavers (e.g., flagstone or wood deck) 22% 66
SUMMARY OF EXISTING AND PROPOSED IMPERVIOUS AREA
H. Feissner
February 14, 2013
EXISTING CONDITION
PROPOSED CONDITION
Areas, sq. ft.
2/14/2013 3:29 PM
A1 298 Pavers (e.g., flagstone or wood deck) 22% 66
Impervious Area 2644
% Impervious 62%
B1 179 Concrete (e.g., walks & parking) 90% 161
B1 373 Roofs 90% 336
Impervious Area 497
% Impervious 48%
B2 332 Concrete (e.g., walks & parking) 90% 299
B2 946 Roofs 90% 851
Impervious Area 1150
% Impervious 76%
B3 131 Concrete (e.g., walks & parking) 90% 118
B3 914 Roofs 90% 823
Impervious Area 941
% Impervious 52%
C1 21 Concrete (e.g., walks & parking) 90% 19
Impervious Area 19
% Impervious 4%
Total Impervious Area 5250
% Impervious 55%
Area, sq. ft. Area, acre
Total Impervious Area Increase 3144 0.072
Big Deal Four Plex
CHARACTER OF SURFACE1:
Runoff
Coefficient
Percentage
Impervious Project: Big Deal Four Plex
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: H. Feissner
Asphalt ……....……………...……….....…...……………….………………………………………………………….0.95 100% . Date:
Concrete …….......……………….….……….………………..….…………………………………………………….0.95 90% .
Gravel ……….…………………….….…………………………..……………………………………………………… 0.50 40%
Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90%
Pavers …………………………...………………..……………………………………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….0.15 0% .
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….0.25 0% .
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf
= 1.00 10-year Cf
= 1.00 100-year Cf
= 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Basin ID
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Gravel
(ac)
Area of
Roofs
(ac)
Area of
Pavers
(ac)
Soil Type and Average
Slope
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite Runoff
Coefficient
Composite
Big Deal Four Plex
Overland Flow, Time of Concentration:
Project: Big Deal Four Plex
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = T
i + Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
Big Deal Four Plex
Rational Method Equation: Project: Big Deal Four Plex
Calculations By:
Date:
Rainfall Intensity:
Existing Conditons
EX1 EX1 0.09 8.75 8.75 8.11 0.35 0.35 0.44 2.35 4.02 8.38 0.072 0.12 0.32
EX2 EX2 0.13 13.97 13.97 12.95 0.41 0.41 0.51 1.95 3.34 7.04 0.10 0.18 0.47
Proposed Condition
A1 A1 0.10 5.00 5.00 5.00 0.69 0.69 0.87 2.85 4.87 9.95 0.20 0.33 0.85 Q
100 release=0.072 cfs
B1 B1 0.02 5.00 5.00 5.00 0.62 0.62 0.78 2.85 4.87 9.95 0.04 0.07 0.18 Sized Nyloplast 12" Standard Grate for 2x Q
100
B2 B2 0.03 5.00 5.00 5.00 0.84 0.84 1.00 2.85 4.87 9.95 0.08 0.14 0.35
N/A B2 (Roof Area) 0.02 5.00 5.00 5.00 0.95 0.95 1.00 2.85 4.87 9.95 0.06 0.10 0.22 Q
100 flow in 6" ADS = 0.18 + 0.22 = 0.40 cfs
N/A B2 (Finished Grade) 0.01 5.00 5.00 5.00 0.69 0.69 0.86 2.85 4.87 9.95 0.02 0.04 0.09
B3 B3 0.04 5.00 5.00 5.00 0.65 0.65 0.82 2.85 4.87 9.95 0.08 0.13 0.34
C1 C1 0.01 5.00 5.00 5.00 0.28 0.28 0.35 2.85 4.87 9.95 0.008 0.014 0.036
C2 C2 0.01 5.00 5.00 5.00 0.25 0.25 0.31 2.85 4.87 9.95 0.006 0.011 0.028
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
RUNOFF COMPUTATIONS
H. Feissner
June 18, 2013
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C
10 C100
Q C f C i A
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers
B.2 – Swales
B.3 – Inlets
B.4 – Detention Facilities
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX B.1
STORM SEWERS
Channel Report
Hydraflow Express Extension for AutoCAD® Civil 3D® 2012 by Autodesk, Inc. Thursday, Feb 14 2013
<Name>
Circular
Diameter (ft) = 0.50
Invert Elev (ft) = 5000.00
Slope (%) = 0.50
N-Value = 0.012
Calculations
Compute by: Known Q
Known Q (cfs) = 0.40
Highlighted
Depth (ft) = 0.39
Q (cfs) = 0.400
Area (sqft) = 0.16
Velocity (ft/s) = 2.43
Wetted Perim (ft) = 1.09
Crit Depth, Yc (ft) = 0.33
Top Width (ft) = 0.41
EGL (ft) = 0.48
0 1
Elev (ft) Section
4999.75
5000.00
5000.25
5000.50
5000.75
5001.00
Reach (ft)
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX B.2
SWALES
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Jun 19 2013
Sub-Basin B2 | Proposde Swale
Triangular
Side Slopes (z:1) = 4.00, 4.00
Total Depth (ft) = 0.20
Invert Elev (ft) = 5000.84
Slope (%) = 1.35
N-Value = 0.035
Calculations
Compute by: Known Depth
Known Depth (ft) = 0.20
Highlighted
Depth (ft) = 0.20
Q (cfs) = 0.167
Area (sqft) = 0.16
Velocity (ft/s) = 1.04
Wetted Perim (ft) = 1.65
Crit Depth, Yc (ft) = 0.17
Top Width (ft) = 1.60
EGL (ft) = 0.22
0 .5 1 1.5 2 2.5 3
Elev (ft) Section Depth (ft)
5000.00 -0.84
5000.50 -0.34
5001.00 0.16
5001.50 0.66
5002.00 1.16
Reach (ft)
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX B.3
INLETS
3130 Verona Avenue • Buford, Georgia 30518 • (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490
Nyloplast Grate Inlet Capacity Charts • March 20010
Nyloplast 12" Standard Grate Inlet Capacity Chart
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10
Head (ft)
Capacity (cfs)
Orifice Flow
Weir Flow
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX B.4
DETENTION FACILITIES
Big Deal Four Plex
876-001
Detention Pond Calculation | FAA Method
Project Number: 876-001
Fort Collins, Colorado
H. Feissner Date: 2/15/2013
Project Number:
Project Location:
Calculations By: H. Feissner Date: 2/15/2013
Pond No.: Pond A
Calculations By:
A1
Input Variables Results
Design Point A1
100-yr
0.87 WQCV 238 ft3
Design Point
Design Storm Required Detention Volume
Developed "C" = 0.87 WQCV 238 ft3
Area (A)= 0.10 acres Quantity Detention 649 ft3
Developed "C" =
Area (A)= 0.10 acres Quantity Detention 649 ft
Max Release Rate = 0.072 cfs Total Volume 887 ft3
Total Volume 0.020 ac-ft
Ft.Collins Inflow Storage
Time Time
Ft.Collins
100-yr
Intensity
Q100
Inflow
(Runoff)
Volume
Outflow
(Release) Volume
Storage
Detention
Intensity Volume Volume
(Release) Volume
Volume
(mins) (secs) (in/hr) (cfs) (ft3) ft ) (ft3) ft ) (ft3) ft )
5 300 9.95 0.9 260 22 238
10 600 7.72 0.7 403 43 360
15 900 6.52 0.6 511 65 446
20 1200 5.60 0.5 585 86 498
25 1500 4.98 0.4 650 108 542
30 1800 4.52 0.4 708 130 578
35 2100 4.08 0.4 745 151 594
40 2400 3.74 0.3 781 173 608
45 2700 3.46 0.3 813 194 618
50 3000 3.23 0.3 843 216 627
55 3300 3.03 0.3 870 238 632
60 3600 2.86 0.2 896 259 637
65 3900 2.72 0.2 923 281 642
70 4200 2.59 0.2 946 302 644
75 4500 2.48 0.2 971 324 647
80 4800 2.38 0.2 994 346 648
85 5100 2.29 0.2 1016 367 649
90 5400 2.21 0.2 1038 389 649
95 5700 2.13 0.2 1056 410 646
Big Deal Four Plex
876-001
Stage - Storage Calculation
Project Number: 876-001
Fort Collins, Colorado
H. Feissner Date: 2/15/2013
Project Number:
Project Location:
Calculations By: H. Feissner Date: 2/15/2013
Pond No.: Pond A
Calculations By:
Design Point A
Required Volume Water Surface Elevation (WSE)
A
WQCV
238 ft3 5000.00 ft.
Design Point
Design Storm
Require Volume= 238 ft 5000.00 ft.
Design Storm 100-yr
Required Volume= 887 ft3 5001.39 ft.
Require Volume=
Required Volume= 887 ft 5001.39 ft.
Contour
Contour Incremental Area Cumulative Volume Incremental Volume
Contour Cummulative
Elevation (Y-
values)
Contour
Area
Depth
Incremental Area
Avg. End
Cumulative Volume
Avg. End
Incremental Volume
Conic
Cummulative
Volume Conic (X-
values) values)
ft3 ft. ft3 ft3 ft3 ft3
4,999.00 27 0.00 0 0 0 0
4,999.20 184 0.20 21 21 19 19
4,999.40 284 0.20 47 68 46 65
4,999.60 287 0.20 57 125 57 122
4,999.80 290 0.20 58 183 58 180
5,000.00 293 0.20 58 241 58 238
5,000.20 296 0.20 59 300 59 297
5,000.40 300 0.20 60 360 60 357
5,000.60 304 0.20 60 420 60 417
5,000.80 317 0.20 62 482 62 479
5,001.00 418 0.20 73 555 73 553
5,001.20 796 0.20 121 677 119 672
5,001.40 1473 0.20 227 904 224 895
5,002.00
5,001.50
5,001.00
Contour Elevation
5,000.50
Contour Elevation
Big Deal Four Plex
Developed Condition Orifice Plate Sizing Calculations
100-Year Developed Condition Attenuated to 2-Year Historic Rate
Design Point Sub-Basin A1 Orifice Calculation:
Qo = CA(2gH)
0.5
Tailwater Elevation 5000.03
100-year WSEL 5001.39
Invert Out 4998.93
Allowable Release Rate 0.072 cfs
H 1.30 ft
C 0.65
g 32.2 ft/s
Qo 0.072 cfs
Diameter 0.1242 ft
A 0.01 ft
2
A 1.74 in
2
Diameter of Orifice: 1 1/2 in
2/20/2013 12:01 PM
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Sheet 1 of 4
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia
Ia = 62.0 %
B) Tributary Area's Imperviousness Ratio (i = Ia / 100 ) i = 0.620
C) Contributing Watershed Area Area = 0.100 ac
D) For Watersheds Outside of the Denver Region, Depth of Average d6 = in
Runoff Producing Storm
E) Design Concept
(Select EURV when also designing for flood control)
F) Design Volume (1.2 WQCV) Based on 40-hour Drain Time VDESIGN
= 0.0024 ac-ft
(VDESIGN = (1.0 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12 * Area * 1.2)
G) For Watersheds Outside of the Denver Region, VDESIGN OTHER
= ac-ft
Water Quality Capture Volume (WQCV) Design Volume
(VWQCV OTHER = (d
6*(VDESIGN
/0.43))
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VDESIGN USER
= ac-ft
(Only if a different WQCV Design Volume is desired)
I) Predominant Watershed NRCS Soil Group
J) Excess Urban Runoff Volume (EURV) Design Volume
For HSG A: EURVA = (0.1878i - 0.0104)*Area EURV = ac-f t
For HSG B: EURVB = (0.1178i - 0.0042)*Area
For HSG C/D: EURVC/D = (0.1043i - 0.0031)*Area
Design Procedure Form: Extended Detention Basin (EDB)
Big Deal Four Plex
Northern Engineering
February 20, 2013
Fort Collins, Colorado | Pond A
H. Feissner
Choose One
Excess Urban Runoff Volume (EURV)
Choose One
A
B
C / D
Water Quality Capture Volume (WQCV)
2. Basin Shape: Length to Width Ratio L : W = 7.5 : 1
(A basin length to width ratio of at least 2:1 will improve TSS reduction.)
3. Basin Side Slopes
A) Basin Maximum Side Slopes Z = 0.00 ft / ft
(Horizontal distance per unit vertical, 4:1 or flatter preferred)
4. Inlet
A) Describe means of providing energy dissipation at concentrated
inflow locations:
876-001_UD-BMP_v3.02, EDB 2/20/2013, 10:32 AM
Sheet 2 of 4
Designer:
Company:
Date:
Project:
Location:
5. Forebay
A) Minimum Forebay Volume VFMIN
= 0.000 ac-ft A FOREBAY MAY NOT BE
(VFMIN = 0% of the WQCV) NECESSARY FOR THIS SIZE SITE
B) Actual Forebay Volume VF
= ac-ft
C) Forebay Depth DF
= in
(DF = 12 inch maximum)
D) Forebay Discharge
i) Undetained 100-year Peak Discharge Q100
= cfs
ii) Forebay Discharge Design Flow QF
= cfs
(QF = 0.02 * Q
100)
E) Forebay Discharge Design
F) Discharge Pipe Size (minimum 8-inches) Calculated DP = in
G) Rectangular Notch Width Calculated WN
= in
PROVIDE A CONSISTENT LONGITUDINAL
6. Trickle Channel SLOPE FROM FOREBAY TO MICROPOOL
WITH NO MEANDERING. RIPRAP AND
A) Type of Trickle Channel SOIL RIPRAP LINED CHANNELS ARE
NOT RECOMMENDED.
MINIMUM DEPTH OF 1.5 FEET
F) Slope of Trickle Channel S = 0.0100 ft / ft
H. Feissner
(flow too small for berm w/ pipe)
Fort Collins, Colorado | Pond A
Big Deal Four Plex
February 20, 2013
Northern Engineering
Design Procedure Form: Extended Detention Basin (EDB)
Choose One
Wall with Rect. Notch
Berm With Pipe
Choose One
Concrete
Soft Bottom
Wall with V-Notch Weir
7. Micropool and Outlet Structure
A) Depth of Micropool (2.5-feet minimum) DM
= ft
B) Surface Area of Micropool (10 ft
2
minimum) A
M = sq ft
C) Outlet Type
D) Depth of Design Volume (EURV or 1.2 WQCV) Based on the Design H = 1.00 feet
Concept Chosen Under 1.E.
E) Volume to Drain Over Prescribed Time WQCV = 0.0020 ac-ft
F) Drain Time TD
= 3 hours DRAIN TIME < 40 HOURS
Sheet 3 of 4
Designer:
Company:
Date:
Project:
Location:
8. Initial Surcharge Volume
A) Depth of Initial Surcharge Volume DIS
= in
(Minimum recommended depth is 4 inches)
B) Minimum Initial Surcharge Volume VIS = cu ft
(Minimum volume of 0.3% of the WQCV)
C) Initial Surcharge Provided Above Micropool Vs= cu ft
9. Trash Rack
A) Type of Water Quality Orifice Used
B) Water Quality Screen Open Area: At = 38.5*(e
-0.095D
)*Aot
At = 12 square inches
C) For 2", or Smaller, Circular Opening (See Fact Sheet T-12):
i) Width of Water Quality Screen and Concrete Opening (Wopening) W
opening = inches
ii) Height of Water Quality Screen (HTR) H
TR = inches
iii) Type of Screen, Describe if "Other"
D) For 2" High Rectangular Opening:
i) Width of Rectangular Opening (Worifice) W = inches
Northern Engineering
H. Feissner
Design Procedure Form: Extended Detention Basin (EDB)
February 20, 2013
Big Deal Four Plex
Fort Collins, Colorado | Pond A
Choose One
Circular (up to 2" diameter)
Rectangular (2" high)
Choose One
S.S. Well Screen with 60% Open Area*
Other (Describe):
i) Width of Rectangular Opening (Worifice) W = inches
ii) Width of Water Quality Screen Opening (Wopening) W
opening = ft
iii) Height of Water Quality Screen (HTR) H
TR = ft
iv) Type of Screen, Describe if "Other"
v) Cross-bar Spacing inches
vi) Minimum Bearing Bar Size
Choose One
Aluminum Amico-Klemp SR Series (or equal)
Other (Describe):
876-001_UD-BMP_v3.02, EDB 2/20/2013, 10:32 AM
Sheet 4 of 4
Designer:
Company:
Date:
Project:
Location:
10. Overflow Embankment
A) Describe embankment protection for 100-year and greater overtopping:
B) Slope of Overflow Embankment ZE
= ft / ft
(Horizontal distance per unit vertical, 4:1 or flatter preferred)
11. Vegetation
12. Access
A) Describe Sediment Removal Procedures
Notes:
Fort Collins, Colorado | Pond A
Design Procedure Form: Extended Detention Basin (EDB)
February 20, 2013
Northern Engineering
H. Feissner
Big Deal Four Plex
Choose One
Irrigated
Not Irrigated
876-001_UD-BMP_v3.02, EDB 2/20/2013, 10:32 AM
Big Deal Four Plex
Preliminary Erosion Control Report
APPENDIX D
OPERATIONS AND MAINTENANCE GUIDELINES FOR EXTENDED DETENTION BASINS (EDBS)
Big Deal Four Plex
Preliminary Erosion Control Report
MAP POCKET
C4.00 – DRAINAGE EXHIBIT
(Min TD for WQCV= 40 hours; Max T
D for EURV= 72 hours)
G) Recommended Maximum Outlet Area per Row, (Ao) A
o = 0.12 square inches
H) Orifice Dimensions:
i) Circular Orifice Diameter or Dorifice
= 3 / 8 inches
ii) Width of 2" High Rectangular Orifice Worifice
= inches
I) Number of Columns nc
= 1 number
J) Actual Design Outlet Area per Row (Ao) A
o = 0.11 square inches
K) Number of Rows (nr) nr
= 3 number
L) Total Outlet Area (Aot) A
ot = 0.3 square inches
M) Depth of WQCV (HWQCV) H
WQCV = feet
(Estimate using actual stage-area-volume relationship and VWQCV)
N) Ensure Minimum 40 Hour Drain Time for WQCV TD WQCV
= hours
Choose One
Orifice Plate
Other (Describe):
876-001_UD-BMP_v3.02, EDB 2/20/2013, 10:32 AM
5,000.00
Contour Elevation
5,000.00
Contour Elevation
4,999.50
4,999.00
0 200 400 600 800 1000
Cummulative Volume, cu. ft.
2/15/20134:26 PM D:\Projects\876-001\Drainage\Detention\876-001__Detention Pond\Stage_Storage
100 6000 2.06 0.2 1075 432 643
105 6300 2.00 0.2 1096 454 643
110 6600 1.94 0.2 1114 475 639
115 6900 1.89 0.2 1135 497 638
120 7200 1.84 0.2 1153 518 634
2/15/2013 4:25 PM D:\Projects\876-001\Drainage\Detention\876-001__Detention Pond\FAA_CoFC idf
6/18/2013 3:39 PM
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Existing Conditons
EX1 EX1 No 0.25 0.25 0.31 34 1.20% 8.8 8.8 8.1 0 0.00% N/A N/A 0 0.00% N/A N/A 8.75 8.75 8.11
EX2 EX2 No 0.25 0.25 0.31 94 1.35% 14.0 14.0 12.9 0 0.00% N/A N/A 0 0.00% N/A N/A 13.97 13.97 12.95
Proposed Condition
A1 A1 No 0.95 0.95 1.00 45 2.00% 1.5 1.5 1.0 0 0.00% N/A N/A 12 1.00% 1.50 0.1 5.00 5.00 5.00
B1 B1 No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
B2 B2 No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
N/A B2 (Roof Area) No 0.95 0.95 1.00 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
N/A B2 (Finished Grade) No 0.95 0.95 1.00 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
B3 B3 No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
C1 C1 No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
C2 C2 No 0.25 0.25 0.31 0 0.00% N/A N/A N/A 0 0.00% N/A N/A 0 0.00% N/A N/A 5.00 5.00 5.00
TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
H. Feissner
June 18, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
6/18/2013 3:38 PM
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
6/18/2013 3:38 PM
% Imperv.
Existing Conditons
EX1 0.09 0.00 0.01 0.00 0.01 0.000 Clayey | Flat <2% 0.07 0.35 0.35 0.44 18%
EX2 0.13 0.00 0.02 0.00 0.02 0.003 Clayey | Flat <2% 0.09 0.41 0.41 0.51 25%
Proposed Condition
A1 0.10 0.04 0.01 0.00 0.01 0.01 Clayey | Average 2% to 7% 0.03 0.69 0.69 0.87 62%
B1 0.02 0.00 0.00 0.00 0.01 0.00 Clayey | Average 2% to 7% 0.01 0.62 0.62 0.78 48%
B2 0.03 0.00 0.01 0.00 0.02 0.00 Clayey | Average 2% to 7% 0.01 0.84 0.84 1.00 76%
B2 (Roof Area) 0.02 0.00 0.00 0.00 0.02 0.00 Clayey | Average 2% to 7% 0.00 0.95 0.95 1.00 90%
B2 (Finished Grade) 0.01 0.00 0.01 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.00 0.69 0.69 0.86 57%
B3 0.04 0.00 0.00 0.00 0.02 0.00 Clayey | Average 2% to 7% 0.02 0.65 0.65 0.82 52%
C1 0.01 0.00 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.01 0.28 0.28 0.35 4%
C2 0.01 0.00 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.01 0.25 0.25 0.31 0%
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
June 18, 2013
Composite Runoff Coefficient with Adjustment
6/18/2013 4:57 PM
SUMMARY
2/14/2013 3:29 PM