HomeMy WebLinkAboutSCOTT PLAZA - PDP - PDP130032 - REPORTS - DRAINAGE REPORTNovember 5, 2013
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT FOR
SCOTT PLAZA
Fort Collins, Colorado
Prepared for:
Taylor Fitzpatrick Capital, LLC
7825 E. Gelding St., Suite 102
Scottsdale, AZ 85260
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: 948-001
This 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.
November 5, 2013
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
SCOTT PLAZA
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report
for your review. This report accompanies the Project Development Plan submittal for the
proposed Scott Plaza development.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM),
and serves to document the stormwater impacts associated with the proposed 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.
Aaron Cvar, PE
Project Engineer
Scott Plaza
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain.......................................................................................................................................... 4
II. DRAINAGE BASINS AND SUB-BASINS ....................................................................... 5
A. Major Basin Description .................................................................................................................... 5
III. DRAINAGE DESIGN CRITERIA ................................................................................... 5
A. Regulations........................................................................................................................................ 5
B. Four Step Process .............................................................................................................................. 5
C. Development Criteria Reference and Constraints ............................................................................ 6
D. Hydrological Criteria ......................................................................................................................... 6
E. Hydraulic Criteria .............................................................................................................................. 6
G. Modifications of Criteria ................................................................................................................... 7
IV. DRAINAGE FACILITY DESIGN .................................................................................... 7
A. General Concept ............................................................................................................................... 7
B. Specific Details .................................................................................................................................. 8
V. CONCLUSIONS ........................................................................................................ 9
A. Compliance with Standards .............................................................................................................. 9
B. Drainage Concept .............................................................................................................................. 9
References ....................................................................................................................... 10
APPENDICES:
APPENDIX A–Hydrologic Computations
APPENDIX B–Detention Calculations
APPENDIX C–Water Quality/LID Supporting Documentation
APPENDIX D –Erosion Control Report
Scott Plaza
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2– Proposed Site Plan ................................................................................................ 3
Figure 3 – Existing Floodplains ............................................................................................. 4
MAP POCKET:
Proposed Drainage Exhibit
Scott Plaza
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in the northeast quarter of Section 15, Township 7 North,
Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado The project site is located on the south side of West Plum Street,
and just west of Shields Street.
The project site lies within the Old Town Master Drainage Basin. Per the Old Town
Master Drainage Plan, onsite detention is required. Onsite detention is required for the
runoff volume difference between the 100 year developed inflow rate and the 2 year
historic release rate. It is acknowledged that this is the standard requirement, but
since the existing outfall into Plum already floods a home the release rate could be
more restrictive. The proposed preliminary design addresses this with a reduced
release rate.
3. The proposed project is surrounded by existing and new development. Apartment
developments exist to the east and west of the proposed project. Commercial
development exists to the south of the proposed project. A new apartment
development is currently under construction to the north of the proposed project,
Scott Plaza
Preliminary Drainage Report 2
which was referred to as “The Retreat at 1200 Plum” (Ref. 6).
4. No offsite flows of significance enter the site.
B. Description of Property
1. The development area is roughly 1.2 net acres.
Figure 1 – Aerial Photograph
2. The subject property currently four multi-family buildings and a gravel drive/parking
area along the east side of the development site. Existing ground cover generally
consists of residential landscaping and gravel drive. Existing ground slopes are
generally mild (i.e., 1 to 5±%) through the interior of the property. A portion of the
site topography slopes south to north. The remainder of the existing site slopes to the
south, directing existing runoff into a concrete pan located along the south property
line.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey website:
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx,
the site consists of Nunn clay loam, which falls into Hydrologic Soil Group C.
Scott Plaza
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
Scott Plaza
Preliminary Drainage Report 4
4. The proposed project will consist of the construction of an apartment complex.
Parking areas and associated utilities will be constructed. A detention/water quality
facility will be incorporated into the architectural design of the structure. A vertical
chamber will be constructed to provide the required detention volume. This chamber
will also incorporate a sand filter in which water quality treatment will be provided.
LID features will be provided throughout the project site, with permeable pavers being
proposed as the main LID feature. The locations of LID features will be determined at
Final design, and will conform to City of Fort Collins standard requirements. It is
acknowledged that the current City draft standards require that 50% of the new
impervious area be treated by an LID method and 25% of new parking lots must be
pervious.
5. No major irrigation ditches or related facilities are in the vicinity of the project site.
6. The proposed land use is an apartment complex.
C. Floodplain
1. The project site is not encroached by any City or FEMA floodplain.
Figure 3 –Area Floodplain Mapping
PROJECT
SITE
Scott Plaza
Preliminary Drainage Report 5
2. No offsite improvements are proposed with the project.
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
3. The project site is located within the Old Town Master Drainage Basin. Onsite
detention is required for the runoff volume difference between the 100 year developed
inflow rate and the 2 year historic release rate. It is acknowledged that this is the
standard requirement, but since the existing outfall into Plum already floods a home
the release rate could be more restrictive. The proposed preliminary design addresses
this with a reduced release rate.
B. Sub-Basin Description
4. A portion of the subject property historically drains overland north into the adjacent
Plum Street. The remainder of the site historically drains overland south into an
existing concrete pan located along the south property line. A more detailed
description of the project drainage patterns follows in Section IV.A.4., below.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the proposed
project.
B. Four Step Process
The overall stormwater management strategy employed with the proposed project 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
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low Impact Development (LID) strategies including:
Conserving existing amenities in the site including the existing vegetated areas.
Providing vegetated open areas throughout the site to reduce the overall impervious
area and to minimize directly connected impervious areas (MDCIA).
Routing flows, to the extent feasible, through vegetated swales to increase time of
concentration, promote infiltration and provide initial water quality.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, urban
development of this intensity will still generate stormwater runoff that will require
additional BMPs and water quality. The majority of stormwater runoff from the site will
ultimately be intercepted and treated using extended detention methods prior to exiting the
site.
Scott Plaza
Preliminary Drainage Report 6
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property. While this step may not
seem applicable to proposed development, the project indirectly helps achieve stabilized
drainageways nonetheless. By providing water quality where none previously existed,
sediment with erosion potential is removed from the downstream drainageway systems.
Furthermore, this project will pay one-time stormwater development fees, as well as
ongoing monthly stormwater utility fees, both of which help achieve City-wide drainageway
stability.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
Trash, waste products, etc. that were previously left exposed with the historic trailer
park will no longer be allowed to exposure to runoff and transport to receiving
drainageways. The proposed development will eliminate these sources of potential
pollution.
C. Development Criteria Reference and Constraints
The subject property is tied currently developed properties adjacent to the site. Thus,
several constraints have been identified during the course of this analysis that will
impact the proposed drainage system including:
Existing elevations along the property lines will generally be maintained.
As previously mentioned, overall drainage patterns of the existing site will be
maintained.
Elevations of existing downstream facilities that the subject property will release to
will be maintained.
D. Hydrological Criteria
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 proposed 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. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 80th percentile rain event, which has been
employed to design the project’s water quality features. The second event analyzed is
the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third
event considered is the “Major Storm,” which has a 100-year recurrence interval.
The fourth storm computed, for comparison purposes only, is the 10-year event.
4. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
1. As previously noted, the subject property maintains historic drainage patterns.
2. All drainage facilities proposed with the project are designed in accordance with
Scott Plaza
Preliminary Drainage Report 7
criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District
(UDFCD) Urban Storm Drainage Criteria Manual.
3. As stated above, no part of the subject property is located in a City or FEMA
regulatory floodplain.
4. The proposed project does not propose to modify any natural drainageways.
F. Modifications of Criteria
1. The proposed development is not requesting any modifications to criteria at this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the project drainage design are to maintain existing drainage
patterns, and to ensure no adverse impacts to any adjacent properties.
2. 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.
3. The drainage patterns anticipated for proposed drainage basins are described below.
Basin 1
Basin 1 consists of the apartment building; the basin area is composed primarily of
rooftop. This basin will generally drain via parking and drive curb and gutter and an
internal downspout collection system into a detention/water quality facility which will
be incorporated into the architectural design of the structure. It is noted that the at-
grade parking level is covered and will not be routed through the architectural storm
tower.
The water quality facility incorporated into the architectural design is currently
proposed as a sand filter to be designed per USDCM Volume 3 (Reference 5)
methodology. This methodology yields a required volume of 1078 cubic feet. Please
see Appendix C for preliminary calculations.
Basin 2
Basin 2 consists of a small area (0.03 Ac.) of frontage along Plum Street which will
be partially surfaced with permeable pavers. This basin will sheet flow into Plum
Street.
Basin 3
Basin 3 consists of a small area (0.12 Ac.) of drive area which will be partially
surfaced with permeable pavers. This basin will sheet flow into Plum Street. The
permeable paver system is to be designed per USDCM Volume 3 (Reference 5)
methodology. This methodology yields a required volume of 140 cubic feet within the
paver sub-base material. Please see Appendix C for preliminary calculations.
Scott Plaza
Preliminary Drainage Report 8
Basin 4
Basin 4 consists of a small area (0.02 Ac.) of landscaped area along the back and
side of the proposed building. This basin will sheet flow into existing offsite
development.
Basin 5
Basin 5 consists of drive, parking, and landscaped area. This basin will sheet flow
into into an existing concrete pan located along the south property line. Historically,
0.55 Acres of existing development drained to design point 5. Historic development
consisted of rooftop and gravel. With the proposed 0.35 Acres now draining to this
design point, consisting of permeable pavers and landscaping, there will be a
reduction in runoff. The locations of LID features will be determined at Final design,
and will conform to City of Fort Collins standard requirements. At Final design, a
comparison of historic versus proposed runoff rates at design point 5 will be
determined.
The permeable paver system is to be designed per USDCM Volume 3 (Reference 5)
methodology. This methodology yields a required volume of 408 cubic feet within the
paver sub-base material. Please see Appendix C for preliminary calculations.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details
Water quality treatment will be provided in the detention/water quality sand filter
facility which will be incorporated into the architectural design of the structure. A
vertical chamber will be constructed to provide the required detention volume. This
chamber will also incorporate a sand filter in which water quality treatment will be
provided. The detention facility will outfall into the existing Plum Street storm system
via a proposed storm line connection within Plum Street.
A preliminary estimate of required detention volume of 0.11 acre-feet has been
calculated. Please see detention calculations provided in Appendix B. The release
rate determined for the proposed detention facility has been preliminarily set at 0.60
cfs. This release rate has been determined based on the methodology utilized for the
approved Final Drainage Report for “The Retreat at 1200 Plum” (Ref. 6). The
methodology accounts for impervious area that is allowed to be “grandfathered”.
There is 0.24 acres of impervious area within the development site which drains to
Plum Street. A 100-year discharge from this impervious area of 2.27 cfs has been
calculated. There is 0.37 acres of pervious area within the development site which
also drains to Plum Street. A 2-year discharge of 0.74 cfs has been calculated. The
sum of “grandfathered” impervious area discharge into Plum Street combined with 2-
year pervious area discharge is 3.01, which is considered as the allowable peak
release rate for the site. We have subtracted the 100-year discharge computed from
Basins 2, 3, and 4 (1.74 cfs total) for an allowable release rate of 1.2 cfs. We then
took half of this release rate, to take into consideration the downstream flooding
issues that have been identified in the March 2013 City Conceptual Review for this
project.
Scott Plaza
Preliminary Drainage Report 9
LID features include the aforementioned sand filter, and permeable pavement systems
within Basins 3 and 5. The total area draining to all LID features combined is 1.13
acres, which comprises 97.8% of the site. This exceeds the requirement stating that
50% of the site must pass through an LID feature. The site also exceeds the
requirement that 25% of parking and drive area must be composed of permeable
pavement, with the majority of parking and drive area outside of the parking structure
proposed as a permeable pavement.
In summary, a total detention volume of 0.11 acre-feet (4792 cubic feet) will be
provided within the parking structure detention vault, along with 1078 cubic feet of
water quality capture volume within the sand filter component of the detention vault.
The parking and drive areas outside of the parking structure will provide a total water
quality capture volume of 548 cubic feet
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the proposed project complies with the City of Fort
Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with this project complies with all applicable City of
Fort Collins Master Drainage Plans.
3. The drainage plan and stormwater management measures proposed with the
proposed development 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 any potential
damage associated with its stormwater runoff as all runoff is being captured and
routed to offsite drainage facilities which have either been previously approved by the
City of Fort Collins or are in the review and approval process with the City of Fort
Collins.
2. The drainage concept for the proposed development is consistent with all applicable
City of Fort Collins Master Drainage Plans.
Scott Plaza
Preliminary Drainage Report 10
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. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
6. Final Drainage and Erosion Control Report for The Retreat at 1200 Plum, Northern
Engineering, April 22, 2009.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: 948-001
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: ATC
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 ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year C
f
= 1.00 100-year C
f
= 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
1 28892 0.66 Note: For preliminary calculations, Composite Runoff Coefficients are 0.95 0.95 1.00 90%
2 1389 0.03 based on Table RO-10. 0.95 0.95 1.00 90%
3 5347 0.12 Composite % Imperviousness has been estimated based 0.95 0.95 1.00 90%
4 897 0.02 on UDFCD USDCM, Vol. I, Figures RO-3 and RO-4. 0.95 0.95 1.00 90%
5 15093 0.35 0.95 0.95 1.00 90%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Overland Flow, Time of Concentration:
Project: 948-001
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
T
t
= L / 60V
T
c
= T
i
+ T
t
(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*C
f
(2-yr
C
f
=1.00)
C*C
f
(10-yr
C
f
=1.00)
C*C
f
(100-yr
C
f
=1.25)
Length,
L
(ft)
Slope,
S
(%)
T
i
2-yr
(min)
T
i
10-yr
(min)
T
i
100-yr
(min)
Length,
L
Rational Method Equation: Project: 948-001
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
1 1 0.66 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 1.8 3.1 6.6
2 2 0.03 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.1 0.1 0.3
3 3 0.12 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.3 0.6 1.2
4 4 0.02 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.1 0.1 0.2
5 5 0.35 5 5 5 0.95 0.95 1.00 2.85 4.87 9.95 0.9 1.6 3.4
Area, A
(acres)
Intensity,
i
2
(in/hr)
100-yr
T
c
(min)
DEVELOPED RUNOFF COMPUTATIONS
C
100
Design
Point
Flow,
Q
100
(cfs)
Flow,
Q
2
(cfs)
10-yr
T
c
(min)
2-yr
T
c
(min)
C
2
Flow,
Q
10
(cfs)
Intensity,
i
100
(in/hr)
Basin(s)
ATC
September 10, 2013
Intensity,
i
10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C
APPENDIX B
D DETENTION CALCULATIONS
ETED
ATC
Pond No : 1
1
100-yr
1.00
Area (A)= 0.66 acres 4666 ft3
Max Release Rate = 0.60 cfs 0.11 ac-ft
Time Time
100-yr
Intensity
Q100
Inflow
(Runoff)
Volume
Outflow
(Release)
Volume
Storage
Detention
Volume
(mins) (secs) (in/hr) (cfs) (ft3) (ft3) (ft3)
5 300 9.950 6.57 1970 180.0 1790.1
10 600 7.720 5.10 3057 360.0 2697.1
15 900 6.520 4.30 3873 540.0 3332.9
20 1200 5.600 3.70 4435 720.0 3715.2
25 1500 4.980 3.29 4930 900.0 4030.2
30 1800 4.520 2.98 5370 1080.0 4289.8
35 2100 4.080 2.69 5655 1260.0 4394.9
40 2400 3.740 2.47 5924 1440.0 4484.2
45 2700 3.460 2.28 6166 1620.0 4545.7
50 3000 3.230 2.13 6395 1800.0 4595.4
55 3300 3.030 2.00 6599 1980.0 4619.3
60 3600 2.860 1.89 6795 2160.0 4635.4
65 3900 2.720 1.80 7001 2340.0 4661.3
70 4200 2.590 1.71 7179 2520.0 4659.5
75 4500 2.480 1.64 7366 2700.0 4665.6
80 4800 2.380 1.57 7540 2880.0 4659.8
85 5100 2.290 1.51 7708 3060.0 4648.1
90 5400 2.210 1.46 7876 3240.0 4636.4
95 5700 2.130 1.41 8013 3420.0 4593.1
100 6000 2.060 1.36 8158 3600.0 4557.6
105 6300 2.000 1.32 8316 3780.0 4536.0
110 6600 1.940 1.28 8451 3960.0 4490.6
115 6900 1.890 1.25 8607 4140.0 4467.1
120 7200 1.840 1.21 8744 4320.0 4423.7
Project Location : Fort Collins
Input Variables Results
Calculations By:
DETENTION POND CALCULATION; FAA METHOD
Project Number : 948-001
Date : 9/10/13
Design Point
Design Storm Required Detention Volume
Developed "C" =
D:\Projects\948-001\Drainage\Detention\948-001-DetentionVolume_FAA Method-8.14.13
9/11/2013
APPENDIX C
WATER QUALITY/LID SUPPORTING DOCUMENTATION
ETED
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of sand filter)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) Based on 24-hour Drain Time WQCV = 0.45 watershed inches
WQCV= 0.9 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including sand filter area) Area = 28,749 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 1,078 cu ft
VWQCV = WQCV / 12 * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 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 DWQCV = 4.50 ft
B) Sand Filter Side Slopes (Horizontal distance per unit vertical, Z = 0.00 ft / ft
4:1 or flatter preferred). Use "0" if sand filter has vertical walls.
948-001
Basin 1
Design Procedure Form: Sand Filter (SF)
A.Cvar
Northern Engineering
10/30/2013
C) Mimimum Filter Area (Flat Surface Area) AMin = 240 sq ft
D) Actual Filter Area AActual = 240 sq ft
E) Volume Provided VT = 1080 cu ft
3. Filter Material
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 = 1.1 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = 1,078 cu ft
iii) Orifice Diameter, 3/8" Minimum DO = 0.85 in
Choose One
Choose One
18" CDOT Class C Filter Material
Other (Explain):
YES
NO
948-001-UD-BMP_v3.02_SF, SF 10/30/2013, 2:14 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?
6-7. Inlet / Outlet Works
A) Describe the type of energy dissipation at inlet points and means of
conveying flows in excess of the WQCV through the outlet
Notes:
Design Procedure Form: Sand Filter (SF)
A.Cvar
Northern Engineering
10/30/2013
948-001
Basin 1
Choose One
YES NO
948-001-UD-BMP_v3.02_SF, SF 10/30/2013, 2:14 PM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia
Ia
= 90.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia
/ 100) i = 0.900
C) Tributary Watershed Area ATotal
= 5,227 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 2,733 sq ft
(Minimum recommended permeable pavement area = 1622 sq ft)
E) Impervious Tributary Ratio RT
= 0.8
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 140 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
948-001
Basin 3
Design Procedure Form: Permeable Pavement Systems (PPS)
A.Cvar
Northern Engineering
10/30/13
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 12.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.40
D) Slope of the Base Course/Subgrade Interface S = 0.005 ft / ft
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV
= 2.14 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= inches
(Use a minimum orifice diameter of 3/8 inches)
Basin 3
948-001
Design Procedure Form: Permeable Pavement Systems (PPS)
A.Cvar
Northern Engineering
10/30/13
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
(Use a minimum orifice diameter of 3/8-inches)
Notes:
948-001-UD-BMP_v3.02_MBP_basin3, PPS 10/30/2013, 2:38 PM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Type of Permeable Pavement Section
A) What type of section of permeable pavement is used?
(Based on the land use and activities, proximity to adjacent
structures and soil characteristics.)
B) What type of wearing course?
2. Required Storage Volume
A) Effective Imperviousness of Area Tributary to Permeable Pavement, Ia
Ia
= 90.0 %
B) Tributary Area's Imperviousness Ratio (I = Ia
/ 100) i = 0.900
C) Tributary Watershed Area ATotal
= 15,246 sq ft
(including area of permeable pavement system)
D) Area of Permeable Pavement System APPS
= 8,395 sq ft
(Minimum recommended permeable pavement area = 4732 sq ft)
E) Impervious Tributary Ratio RT
= 0.7
(Contributing Imperviuos Area / Permeable Pavement Ratio)
F) Water Quality Capture Volume (WQCV) Based on 12-hour Drain Time WQCV = 408 cu ft
(WQCV = (0.8 * (0.91 * i
3
- 1.19 * i
2
+ 0.78 * i) / 12) * Area)
G) Is flood control volume being added?
H) Total Volume Needed VTotal
= cu ft
948-001
Basin 5
Design Procedure Form: Permeable Pavement Systems (PPS)
A.Cvar
Northern Engineering
10/30/13
Choose One
No Infiltration
Partial Infiltration Section
Full Infiltration Section
Choose One
YES
NO
Choose One
PICP
Concrete Grid Pavement
Pervious Concrete
Porous Gravel
3. Depth of Reservoir
A) Minimum Depth of Reservoir Dmin
= 12.0 inches
(Minimum recommended depth is 6 inches)
B) Is the slope of the reservoir/subgrade interface equal to 0%?
C) Porosity (Porous Gravel Pavement < 0.3, Others < 0.40) P = 0.40
D) Slope of the Base Course/Subgrade Interface S = 0.005 ft / ft
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
6. Filter Material and Underdrain System
A) Is the underdrain placed below a 6-inch thick layer of
CDOT Class C filter material?
B) Diameter of Slotted Pipe (slot dimensions per Table PPs-2)
C) Distance from the Lowest Elevation of the Storage Volume y = ft
(i.e. the bottom of the base course to the center of the orifice)
7. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is there a minimum 30 mil thick impermeable PVC geomembrane
liner on the bottom and sides of the basin, extending up to the top
of the base course?
B) CDOT Class B Separator Fabric
8. Outlet
(Assumes each cell has similar area, subgrade slope, and length
between lateral barriers (unless subgrade is flat). Calculate cells
individually where this varies.)
A) Depth of WQCV in the Reservoir DWQCV
= 2.06 inches
(Elevation of the Flood Control Outlet)
B) Diameter of Orifice for 12-hour Drain Time DOrifice
= inches
(Use a minimum orifice diameter of 3/8 inches)
Basin 5
948-001
Design Procedure Form: Permeable Pavement Systems (PPS)
A.Cvar
Northern Engineering
10/30/13
Choose One
YES
NO
Choose One
4-inch
6-inch
Choose One
Choose One
YES
NO
Placed above the liner
Placed above and below the liner
N/A
(Use a minimum orifice diameter of 3/8-inches)
Notes:
948-001-UD-BMP_v3.02_MBP_basin5, PPS 10/30/2013, 2:41 PM
APPENDIX D
EROSION CONTROL REPORT
Scott Plaza
Preliminary Erosion Control Report
EROSION CONTROL REPORT
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at existing and proposed storm inlets. Vehicle tracking control pads, spill
containment and clean-up procedures, designated concrete washout areas, dumpsters, and job site
restrooms shall also be provided by the Contractor.
Grading and Erosion Control Notes can be found on the Utility Plans. The Final Plans will contain a
full-size Erosion Control sheet as well as a separate sheet dedicated to Erosion Control Details. In
addition to this report and the referenced plan sheets, the Contractor shall be aware of, and adhere
to, the applicable requirements outlined in the Development Agreement for the development. Also,
the Site Contractor for this project will be required to secure a Stormwater Construction General
Permit from the Colorado Department of Public Health and Environment (CDPHE), Water Quality
Control Division – Stormwater Program, prior to any earth disturbance activities. Prior to securing
said permit, the Site Contractor shall develop a comprehensive StormWater Management Plan
(SWMP) pursuant to CDPHE requirements and guidelines. The SWMP will further describe and
document the ongoing activities, inspections, and maintenance of construction BMPs.
MAP POCKET
DRAINAGE EXHIBITS
E) Length Between Lateral Flow Barriers (max = 48.61 ft.) L = 20.0 ft
F) Volume Provided Based on Depth of Base Course V = 2,910 cu ft
Flat or Stepped: V = P * ((Dmin-1
)/12) * Area
Sloped: V = P * [(Dmin -
(Dmin
- 6*SL-1)) / 12] * Area Volume assumes uniform slope & lateral flow barrier spacing.
Calculate the volume of each cell individually when this varies.
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells = TBD
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
TBD at Final Design
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
948-001-UD-BMP_v3.02_MBP_basin5, PPS 10/30/2013, 2:41 PM
E) Length Between Lateral Flow Barriers (max = 51.19 ft.) L = 20.0 ft
F) Volume Provided Based on Depth of Base Course V = 947 cu ft
Flat or Stepped: V = P * ((Dmin-1
)/12) * Area
Sloped: V = P * [(Dmin -
(Dmin
- 6*SL-1)) / 12] * Area Volume assumes uniform slope & lateral flow barrier spacing.
Calculate the volume of each cell individually when this varies.
4. Lateral Flow Barriers
A) Type of Lateral Flow Barriers
B) Number of Permeable Pavement Cells Cells = TBD
5. Perimeter Barrier
A) Is a perimeter barrier provided on all sides of the
pavement system?
(Recommeded for PICP, concrete grid pavement, or for any
no-infiltration section.)
TBD at Final Design
Choose One
YES- Flat or Stepped Installation
NO- Sloped Installation
Choose One
Concrete Walls
PVC geomembrane installed normal to flow
N/A- Flat installation
Other (Describe):
Choose One
YES
NO
948-001-UD-BMP_v3.02_MBP_basin3, PPS 10/30/2013, 2:38 PM
10
Q C f C i A
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
T
t
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
T
t
(min)
2-yr
T
c
(min)
10-yr
T
c
(min)
100-yr
T
c
(min)
1 1 No 0.95 0.95 1.00 40 2.00% 1.4 1.4 0.9 215 0.50% 1.41 2.5 N/A N/A 5 5 5
2 2 No 0.95 0.95 1.00 30 2.00% 1.2 1.2 0.8 50 0.50% 1.41 0.6 N/A N/A 5 5 5
3 3 No 0.95 0.95 1.00 40 2.00% 1.4 1.4 0.9 120 0.50% 1.41 1.4 N/A N/A 5 5 5
4 4 No 0.95 0.95 1.00 8 2.00% 0.6 0.6 0.4 50 0.50% 1.41 0.6 N/A N/A 5 5 5
5 5 No 0.95 0.95 1.00 40 2.00% 1.4 1.4 0.9 235 0.50% 1.41 2.8 N/A N/A 5 5 5
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
September 10, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
10-year C
f
= 1.00
September 10, 2013