HomeMy WebLinkAboutLAKEVIEW SUBDIVISION - FDP - FDP130047 - REPORTS - DRAINAGE REPORTFINAL DRAINAGE AND
EROSION CONTROL REPORT
LAKEVIEW SUBDIVISION
Fort Collins, Colorado
November 21, 2013
Prepared for:
Century Communities, LLC
8390 E. Crescent Parkway, Suite 650
Greenwood Village, CO 80111
Prepared by:
200 South College Avenue, Suite 100
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 665-002
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.
ADDRESS:
200 S. College Ave. Suite 10
Fort Collins, CO 80524
PHONE: 970.221.4158
FAX: 970.221.4159
WEBSITE:
www.northernengineering.com
November 21, 2012
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Final Drainage and Erosion Control Report for
Lakeview Subdivision
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage and Erosion Control Report for your
review. This report accompanies the 11.21.13 Final Development Plan submittal for the proposed
Lakeview Subdivision Single-family development. Comments from the Preliminary Development
Plan Review Letter dated 09.20.13 have been addressed. Written responses thereto can be found
in the comprehensive response to comments letter on file with Current Planning.
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 Lakeview Subdivision
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.
Ryan O. Banning, PE
Project Engineer
Lakeview Subdivision
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 ........................................................................ 4
A. Major Basin Description ............................................................................................... 4
B. Sub-Basin Description ................................................................................................. 4
III. DRAINAGE DESIGN CRITERIA .................................................................................... 5
A. Regulations ................................................................................................................ 5
B. Four Step Process ....................................................................................................... 5
C. Development Criteria Reference and Constraints ............................................................. 6
D. Hydrological Criteria .................................................................................................... 7
E. Hydraulic Criteria ........................................................................................................ 7
F. Floodplain Regulations Compliance ............................................................................... 8
G. Modifications of Criteria ............................................................................................... 8
IV. DRAINAGE FACILITY DESIGN ..................................................................................... 8
A. General Concept ......................................................................................................... 8
B. Specific Details ......................................................................................................... 10
V. CONCLUSIONS ........................................................................................................ 12
A. Compliance with Standards ........................................................................................ 12
B. Drainage Concept ...................................................................................................... 12
References ......................................................................................................................... 13
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers
B.2 – Street Flow
B.3 – Inlets
B.4 – Detention Facilities
APPENDIX C – Water Quality Design Computations
APPENDIX D – Operations and Maintenance Guidelines for permanent BMPs
APPENDIX E – Erosion Control Report
Lakeview Subdivision
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph .................................................................................................. 2
Figure 2 – Proposed Site Plan ................................................................................................. 3
Figure 3 – Existing Floodplains ............................................................................................... 4
Table 1 – Detention Storage Summary ................................................................................... 11
MAP POCKET:
C500 - Drainage Exhibit
Lakeview Subdivision
Final Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The Lakeview Subdivision project site is located in the northwest quarter of Section
30, Township 6 North, Range 68 West of the 6th Principal Meridian, City of Fort
Collins, County of Larimer, State of Colorado.
3. The project site is located on the south side of Drake Road, east of Christ Center
Community Church (Church), and is bordered by single family residences on the south
and east. The existing right-of-way (ROW) along Drake Road adjacent to the property
is 90-feet.
4. The project site has an existing regional detention pond within the property located on
the southern property boundary. Said pond provides detention for the existing Church
property and will be upgraded with the proposed development to meet current City
criteria and standards for the existing Church property and proposed development. A
City of Fort Collins detention facility is located south of the subject property, and for
reference, Williams Lake is located northwest of the subject property. Per the ALTA
Land Title Survey prepared for the subject property by Northern Engineering
(Northern) and dated July 26, 2011, no existing drainage easements are within the
property. No public storm sewer is located immediately adjacent to the property.
5. Single family subdivisions are adjacent to the subject property including Silverwood
Lakeview Subdivision
Final Drainage Report 2
2nd Subdivision and Eldorado Springs 2nd Subdivision, which are both located east of
the project site, and Eastborough Subdivision, which is located south of the project
site. As previously noted, Drake Road borders the north property boundary, and the
entire remainder of the site to the west is bounded by Christ Center Community
Church property.
B. Description of Property
1. The Lakeview Subdivision property is approximately 11.23 net acres.
Figure 1 – Aerial Photograph
2. The subject property currently consists of athletic facilities including several soccer
fields, a baseball diamond, and a single small maintenance building. As such, the
ground cover generally consists of sod and some native seeding with numerous trees
and shrubs located mainly at the perimeter of the property. Due to the current use,
slopes are rather gentle throughout (i.e., 2±%). General topography slopes from
north to the south towards the detention area at the south end of the property.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey, the site consists of Stoneham loam and
Nunn clay loam, which fall into Hydrologic Soil Groups B and C respectively. More
site-specific exploration found varying materials including sandy clay with occasional
sand layers and sandy gravel. See the Geotechnical Engineering Report by CTL
Thompson (CTL Thompson Project No. FC05622-115) for additional information.
Lakeview Subdivision
Final Drainage Report 3
4. The proposed Lakeview Subdivision development project will develop the majority of
the existing site, removing the existing athletic facilities and small maintenance
building and sub-divide for 42 single-family residential lots. Existing landscaping north
of the project will be maintained and common landscaping tracts will be provided.
Figure 2– Proposed Site Plan
5. There are no irrigation ditches or related facilities in the project’s vicinity.
6. The proposed land use is residential, single-family dwellings. This is a permitted use
Lakeview Subdivision
Final Drainage Report 4
in the current Low Density Residential (R-L) Zoning.
C. Floodplain
1. The subject property is not located in either a FEMA regulatory or City of Fort Collins
designated floodplain. The nearest City designated floodplain is more than one-half
mile from the subject property.
2. FEMA places the subject property within the Zone X Flood Hazard Area, which
constitutes an area determined to be outside the 0.2% annual chance floodplain.
Figure 3 – Existing Floodplains
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The Lakeview Subdivision project is located within the City of Fort Collins’ Foothills
Drainage Basin, which is within central Fort Collins and is to a large degree
dominated by residential development.
2. A portion of the subdivided property is located within the City of Fort Collins’ Spring
Creek Drainage Basin. The project is not modifying this portion of the property.
B. Sub-Basin Description
1. The subject property historically drains overland towards the south and into the
Lakeview Subdivision
Final Drainage Report 5
existing detention facility located at the southern boundary of the property. The
detention area outlets into a City of Fort Collins detention facility immediately south of
the subject property. The Lakeview Subdivision development aims to preserve the
existing drainage patterns as much as possible, and will maintain the same outfall
location. A more detailed description of the project’s drainage patterns follows in
Section IV.A.4., below.
2. The existing Church property to the west of the subject site drains via overland flows
and channelized gutter flows to the existing drainage facility on the property. These
off-site drainage flows and patterns will be maintained and accounted for with the
proposed development. The project site does not drain across any off-site private
land.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the Lakeview
Subdivision project.
B. Four Step Process
The overall stormwater management strategy employed with the Lakeview Subdivision
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 as athletic facilities by implementing multiple Low Impact Development (LID)
strategies including:
Conserving existing amenities in the site including the existing vegetated areas and
large trees around the perimeter of the site, particularly the north edge of the site
adjacent to East Drake Road.
Utilize minimum allowable grades across lots to reduce the rate of runoff from the
properties and promote infiltration.
Minimize the use of storm sewer as a conveyance to increase travel times and promote
evaporation.
Implement a network of drywells prior to pond outfall to promote infiltration.
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 water quality measures to be implemented. All stormwater runoff from the site
will ultimately be routed to the south where it is intercepted and treated in the main water
quality and detention pond prior to leaving the site. A 40-hour release will be implemented
for the WQCV to allow sedimentation and runoff treatment.
Lakeview Subdivision
Final Drainage Report 6
Step 3 – Stabilize Drainageways
As stated in Section I.C, above, there are no major drainageways in or near the subject
property. While this step may not seem applicable to The Lakeview Subdivision
development, the proposed project indirectly helps achieve stabilized drainageways
nonetheless. Currently, the existing site includes an undersized detention pond located
where the proposed water quality and detention pond is being proposed. By providing
additional detention volume, downstream drainageways are further protected during flood
events. By providing water quality where none previously existed, sediment is removed
prior to 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.
Within the pond and the storm system, several BMPs will be utilized as site specific
permanent BMPS including:
A Snout devise on inflow pipes to reduce oil loads from the existing parking area.
A pre-forebay settling sump within the new inlet.
A sediment forebay at each of the inlet to the pond to allow sediment to settle from
the incoming stormwater runoff before being delivered to the main pond facility
An interconnected network of drywells with surrounding bioretention media
Natural bottom swales instead of pans to promote infiltration at the request of the City
A micro pool with initial surcharge volume included in the outlet structure design.
A water quality outlet with 40-hour release to allow for settling.
C. Development Criteria Reference and Constraints
1. The subject property is part of the First Christian Planned Unit Development (PUD)
dated 8/26/80, which provided the drainage study for the subject property. Within
said study, drainage patterns and impervious areas (C-values) have been master
planned for the ultimate developed condition of the subject property. It was with the
First Christian PUD that the existing regional detention pond for the property was
designed and installed. Note that from a recent topographic survey of the pond, it
appears that the existing pond was not built per the original plans, and is currently
undersized as the actual spill elevation of the pond is approximately 2.2-feet below
the designed elevation.
This study will conform, to the extent possible, to the concepts within the original
drainage study performed with the First Christian PUD, including:
Drainage patterns and detention pond location.
Drainage basin designations.
Detention pond release rate in order to limit the impact to downstream facilities.
This study will also be updating several items within the original study including:
Hydrology calculations utilizing the current City of Fort Collins Rainfall Intensity
Data.
Detention storage volume calculations based upon current City of Fort Collins
criteria.
The addition of water quality treatment for the entire First Christian PUD property.
Lakeview Subdivision
Final Drainage Report 7
2. There are no known drainage studies for any adjacent properties that will have any
effect on the Lakeview Subdivision project.
3. The subject property is essentially an "in-fill" development project as the property is
surrounded by currently developed properties. As such, several constraints have been
identified during the course of this analysis that will impact the proposed drainage
system including:
Existing elevations along the east and south property lines adjacent to existing
residential properties will be maintained.
Existing elevations and vegetation on the north side of the subject property will be
preserved.
Except where prohibited, grades along the existing private drive on the west side of
the subject property will 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 Lakeview Subdivision 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 initial detention storage calculations. EPA SWMM has been utilized
for final detention storage calculations.
4. 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.
5. 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 historically drains to a separate detention
facility located south of the property, which is owned and maintained by the City of
Fort Collins. In order to maintain the current capacity of the downstream City of Fort
Collins detention facility and associated storm sewers, the release rate from the
proposed detention pond on the subject property will not increase from the rate
originally designed with the First Christian PUD.
2. All drainage facilities proposed with the Lakeview Subdivision 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.
Lakeview Subdivision
Final Drainage Report 8
3. As stated in Section I.C.1, above, the subject property is not located in either a FEMA
regulatory or a City of Fort Collins designated floodplain.
4. The Lakeview Subdivision project does not propose to modify any natural
drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, this project is not subject to any floodplain regulations.
However, extra care has been taken to ensure that neither existing nor proposed
structures will suffer damage during the 100-year storm as a result of the Lakeview
Subdivision development.
G. Modifications of Criteria
1. The proposed Lakeview Subdivision development is not requesting any modifications
to criteria at this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the Lakeview Subdivision drainage design are to maintain
existing drainage patterns, ensure no adverse impacts to any adjacent properties, and
to maintain the drainage concepts as outlined in the First Christian PUD design
documents.
2. The existing site does not have any off-site runoff that flows directly through the
project site. However, with the development of the site, the stormwater runoff from
the existing Church site west of the subject property will continue to flow through the
subject property to the proposed regional detention and water quality pond to be
located on the south end of the subject property. All detention and water quality
calculations within this Drainage Report account for runoff from the entirety of the site
as delineated within the First Christian PUD documents.
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 First Christian PUD documents divided the site into two (2) major drainage
basins, designated as Basins A and B. The subject property is located within Basin
B. Said documents further subdivided Basin B in to three (3) sub-basins, designated
as Basins B1, B2, and B3. This project has further divided Basin B3 into three (3)
additional basins in order to better calculate hydraulic capacities of streets and better
approximate overall times of concentration. The drainage patterns anticipated for
each sub-basin within Basin B are further described below.
Basin B1
Basin B1 consists of a portion of the existing Church property located south of the
existing Church building and west of the street-like private drive from Drake Road that
bisects the property. This basin is comprised of roof top area, drive lanes, and a large
area of landscaping. The basin drains towards the east and south where it is
conveyed to the proposed water quality and detention pond via street gutters through
basin B3-1.
Lakeview Subdivision
Final Drainage Report 9
Basin B2
Basin B2 consists of a portion of the existing Church property south of the existing
Church building and west of the street-like private drive from Drake Road that bisects
the property. The vast majority of this basin is comprised of existing parking lot and
drive lane. The basin drains towards south and east to a point directly west of the
proposed detention pond where the runoff will be intercepted and delivered to the
pond through inlets and storm sewer. Major storm runoff will overtop the curb and
gutter adjacent the pond and will be conveyed into the pond.
Basin B3-1
Basin B3-1 consists of 2.85-acres of single family along the west side of the existing
Church athletic facilities east of the private drive. Basin B3-1 is one of the basins
where the proposed development will occur. In the proposed condition, the basin will
consist of residential streets, single family residential lots and landscaped open area.
The entirety of the basin will be directed to the south via gutter flows and storm sewer
to the proposed detention and water quality pond.
Basin B3-2
Basin B3-2 consists of 6.18-acres of single family along the north and east sides of
the existing Church athletic facilities east of the private drive, along with a small
portion of the existing Church building and parking area to the west. Basin B3-2 is
the second basin where the proposed development will occur. In the proposed
condition, the basin will consist of residential streets, single family residential lots and
landscaped open area. The entirety of the basin will be directed to the south via gutter
flows and storm sewer to the proposed detention and water quality pond.
Basin B3-3
Basin B3-3 consists of 1.96-acres of open area and detention pond along the south
side of the existing Church athletic facilities east of the private drive. Basin B3-3 is the
third basin where the proposed development will occur. In the proposed condition,
the basin will consist of the back of residential lots and a large detention pond area.
The basin will be the collection point for runoff from all other basins and will discharge
into the existing detention pond on City property.
In addition to the above basins included within the First Christian PUD documents,
there are two (2) off-site basins that currently exist on the subject property. These
basins are further described below.
Basin OS1
Basin OS1 consists of a small area at the north edge of the subject property that
drains directly to East Drake Road via overland and gutter flows. The vast majority of
this basin is comprised of landscaped area; however a small portion of parking area
and drive lane is also included. The proposed development reroutes a portion of the
impervious parking area to the east for water quality treatment and extended release.
However, the majority of the off-site runoff from this basin will continue to drain to
East Drake Road.
Basin OS2
Basin OS2 consists of a small area at the south edge of the subject property that
drains towards the south into the existing City of Fort Collins detention facility. The
vast majority of this basin is comprised of landscaped area. Due to existing physical
Lakeview Subdivision
Final Drainage Report 10
constraints, the proposed development will continue to allow this basin to drain off-
site.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details
1. The main drainage problem associated with this project site is the deficiency of the
existing detention pond located at the south side of the subject property. Specifically,
as determined from a recent topographic survey of the pond, it appears that the
existing pond was not built per the original plans and is currently undersized, as the
actual spill elevation of the pond is approximately 2.2-feet below the designed
elevation. In order to accommodate the required detention and water quality
volumes, the proposed top of pond elevation must be raised. Due to the proximity of
existing residential properties adjacent to the detention area, special attention has
been given to this issue in order to minimize any aesthetic impacts the new pond
elevations may have. The development team has attempted to accomplish this by:
Providing retaining walls rather than large berms to adjust the top of pond
elevations, reduce the aerial extent of the pond and to provide and aesthetic
quality to the pond.
Maintain existing mature trees on the east edge of the existing pond.
Provide additional landscaping around the detention pond to "soften" the
appearance of the pond and associated walls.
Provide flat areas at the bottom of the pond as passive open space.
2. As previously stated, detention will be provided at the southern portion of the subject
property with an outlet connecting to the existing City of Fort Collins detention facility.
A SWMM model has been utilized to determine the detention storage volume to be
provided within the pond.
Water quality is also being provided for the proposed development, as well as for the
existing drainage basins as described in Section IV.A.4 of this report. To achieve this
objective, water quality is being accomplished through a multi-tiered, comprehensive
approach by providing the following BMPs:
Water quality Snouts upstream of each discharge location into the proposed pond.
Sedimentation pre-forebay settling basing within the inlets.
Sediment forebays at the inlets to the pond to allow sediment to settle from the
incoming stormwater runoff before being delivered to the main pond facility.
Drywells and bioretention media used to promote infiltration.
Micro pool utilized within the outlet structure of from the pond for final treatment.
40-hour release water quality outlet to promote further sedimentation.
The proposed water quality approach through the treatment BMPs, as noted
above, is comprehensive in nature. Further documentation of treatment
volumes and removal rates of each BMP will be documented with the Final
Drainage Report prepared during the City FDP process.
Final design details, construction documentation, and Standard Operating
Procedures (SOP) Manual shall be provided to the City of Fort Collins for
review prior to Final Development Plan approval. A final copy of the approved
Lakeview Subdivision
Final Drainage Report 11
SOP manual shall be provided to City and is intended to be maintained on-site
by the entity responsible for the facility maintenance. Annual reports must
also be prepared and submitted to the City discussing the results of the
maintenance program (i.e. inspection dates, inspection frequency, volume loss
due to sedimentation, corrective actions taken, etc.).
3. Table 1, below, summarizes the detention storage and water quality information for
the main drainage facility.
Table 1 – Detention Storage Summary
Required Provided
B 4.39 4.69 3.7(a) 4967.43 4967.70 4968.70 1.27
b. See Section IV.B.2 for information regarding water quality treatment within the pond.
a. Peak Discharge rate as provided by the First Christian PUD drainage documents.
100-year
Water Surface
Elevation (ft)
100-year Detention
Basin ID Storage Volume (cu-ft)
100-year
Peak
Discharge
Pond Spillway
Elevation
Top of Pond
Elevation
Freeboard
Provided (ft)
4. Proper maintenance of the drainage facilities designed with the Lakeview Subdivision
development is a critical component of their ongoing performance and effectiveness.
The stormwater detention and water quality pond, as well as the BMP facilities
contained therein, may be accessed by maintenance staff via drive-over curb and
gutter and the 8’ access ramp/pan provided to the bottom of the pond from the north
side.
Operations and maintenance of the bioretention areas and sand filters shall follow the
recommendations for bioretention (rain garden) facilities, as outlined in the UDFCD
manual. Appendix D contains applicable excerpts to serve as guidance for the
professional maintenance staff and subcontractors responsible for maintenance of
these facilities at the Lakeview Subdivision development.
Maintenance of the stormwater water quality Snouts provided shall follow the
recommendations provided by the manufacturer. Appendix D will contains applicable
excerpts to serve as guidance for the professional maintenance staff and
subcontractors responsible for maintenance of these facilities at the Lakeview
Subdivision development.
5. The drainage features associated with the Lakeview Subdivision project are all private
facilities, located on private property. However, the new detention and water quality
facility and associated storm sewers serve publically accessed roads and multiple lots.
All storm facilities will be provided in a within drainage easements or tracts dedicated
as such.
6. As previously mentioned, the outfall for the entire Lakeview Subdivision project is the
existing COFC detention facility located south of the subject property. This facility
discharges flows near the southeast corner into an existing 21-inch storm sewer.
Stormwater conveyed by this City drainage system ultimately reaches Nelson
Reservoir east of the site. There are no additional facilities or upgrades needed off-
site in order to accommodate the developed runoff from the Lakeview Subdivision
development.
Lakeview Subdivision
Final Drainage Report 12
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Lakeview Subdivision project complies with
the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Lakeview Subdivision project complies with
the City of Fort Collins’ Master Drainage Plan for the Foothills Drainage Basin.
3. There are no regulatory floodplains associated with the Lakeview Subdivision
development.
4. The drainage plan and stormwater management measures proposed with the
Lakeview Subdivision 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 by providing a regional detention pond
that will serve the proposed Lakeview Subdivision development and existing Christ
Center Community Church facilities.
The proposed on-site stormwater facilities will also offer substantial water quality
treatment, in addition to peak volume attenuation, through a comprehensive water
quality treatment approach that includes multiple stormwater BMPs.
2. The proposed Lakeview Subdivision development will not have any impact on the
Master Drainage Plan recommendations for the Foothills Drainage Basin.
Lakeview Subdivision
Final Drainage Report 13
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. Geotechnical Investigation, Regency Multi-Family Residential, 2700 South Lemay Avenue,
Fort Collins, Colorado, August 24, 2011, CTL Thompson, Inc.(CTL Thompson Project No.
FC05622-115).
4. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
5. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
6. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
APPENDIX A
HYDROLOGIC COMPUTATIONS
Lakeview Subdivision
CHARACTER OF SURFACE1:
Runoff
Coefficient
Percentage
Impervious Project: Lakeview Subdivision
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: R. Banning
Asphalt ……....……………...……….....…...……………….…………… 0.95 100% Date:
Concrete …….......……………….….……….………………..….……… 0.95 90%
Gravel ……….…………………….….…………………………..………… 0.50 40%
Roofs …….…….………………..……………….………………………… 0.95 90%
General Single Family …………………………...………………..……… 0.60 50% Total Increase in Imperviousness Area
Lawns and Landscaping 4.48 Acres
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 C
f = 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
Single Family
(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
% Imperv.
Lakeview Subdivision
Overland Flow, Time of Concentration:
Lakeview Subdivision
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
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)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
B1 B1 No 0.53 0.53 0.66 210 1.90% 12.5 12.5 9.6 566 1.10% 2.10 4.5 17.0 17.0 14.1
B2 B2 No 0.80 0.80 1.00 205 1.20% 7.6 7.6 2.5 540 1.30% 2.28 3.9 11.5 11.5 6.5
B3-1 B3-1 No 0.63 0.63 0.79 165 3.60% 7.3 7.3 4.8 640 1.40% 2.37 4.5 11.8 11.8 9.3
B3-1 B3-2 No 0.58 0.58 0.73 65 3.10% 5.4 5.4 3.9 1150 1.00% 2.00 9.6 14.9 14.9 13.4
B3-3 B3-3 No 0.28 0.28 0.34 50 2.00% 8.7 8.7 7.9 400 0.50% 1.41 4.7 13.4 13.4 12.7
Lakeview Subdivision
Rational Method Equation: Project: Lakeview Subdivision
Calculations By:
Date:
Rainfall Intensity:
B1 B1 2.84 17.0 17.0 14.1 0.53 0.53 0.66 1.75 2.99 6.71 2.62 4.48 12.57
B2 B2 4.70 11.5 11.5 6.5 0.80 0.80 1.00 2.09 3.57 9.31 7.87 13.42 43.80
B3-1 B3-1 2.85 11.8 11.8 9.3 0.63 0.63 0.79 2.09 3.57 8.03 3.77 6.44 18.12
B3-1 B3-2 6.18 14.9 14.9 13.4 0.58 0.58 0.73 1.90 3.24 6.92 6.81 11.64 31.08
B3-3 B3-3 1.96 13.4 13.4 12.7 0.28 0.28 0.34 1.98 3.39 7.04 1.07 1.83 4.75
B3-1 B1&B3-1 5.69 18.3 18.3 15.2 0.58 0.58 0.73 1.70 2.90 6.52 5.62 9.58 26.93
B3-1 B1,B3-1 & B3-2 11.87 18.3 18.3 15.2 0.58 0.58 0.73 1.70 2.90 6.52 11.72 20.00 56.21
OS1 OS1 0.52 9.3 9.3 9.0 0.22 0.22 0.28 2.30 3.93 8.21 0.27 0.46 1.20
OS2 OS2 0.19 7.1 7.1 7.0 0.15 0.15 0.19 2.52 4.31 8.80 0.07 0.13 0.32
B Overall B Overall 18.54 18.7 18.7 15.4 0.60 0.60 0.76 1.68 2.86 6.52 18.76 32.03 91.28
Notes
RUNOFF COMPUTATIONS
R. Banning
November 19, 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
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Q C f C i A
11/19/2013 12:36 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Runoff
Hydrologic Soil Group—Larimer County Area, Colorado
(Lakeview Hydrologic Group)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/29/2013
Page 1 of 4
4488730 4488780 4488830 4488880 4488930 4488980 4489030 4489080 4489130
4488730 4488780 4488830 4488880 4488930 4488980 4489030 4489080 4489130
495240 495290 495340 495390 495440 495490 495540
495240 495290 495340 495390 495440 495490 495540
40° 33' 10'' N
105° 3' 22'' W
40° 33' 10'' N
105° 3' 9'' W
40° 32' 57'' N
105° 3' 22'' W
40° 32' 57'' N
105° 3' 9'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 50 100 200 300
Feet
0 30 60 120 180
Meters
Map Scale: 1:2,050 if printed on A portrait (8.5" x 11") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
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
the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Hydrologic Soil Group
Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
74 Nunn clay loam, 1 to 3
percent slopes
C 7.1 42.1%
75 Nunn clay loam, 3 to 5
percent slopes
C 0.0 0.0%
76 Nunn clay loam, wet, 1 to
3 percent slopes
C 1.5 9.0%
100 Stoneham loam, 0 to 1
percent slopes
B 3.3 19.9%
102 Stoneham loam, 3 to 5
percent slopes
B 4.8 28.9%
136 Water 0.0 0.1%
Totals for Area of Interest 16.8 100.0%
Hydrologic Soil Group—Larimer County Area, Colorado Lakeview Hydrologic Group
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/29/2013
Page 3 of 4
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive precipitation
from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly
wet. These consist mainly of deep, well drained to excessively drained sands or
gravelly sands. These soils have a high rate of water transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well drained
soils that have moderately fine texture to moderately coarse texture. These soils
have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of water
transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay layer
at or near the surface, and soils that are shallow over nearly impervious material.
These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in their
natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Lakeview Hydrologic Group
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/29/2013
Page 4 of 4
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers
B.2 – Street Flow
B.3 – Inlets
B.4 – Detention Facilities
APPENDIX B.1
STORM SEWERS
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2013
ST-1 Church Parking Lot
Circular
Diameter (ft) = 2.00
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.015
Calculations
Compute by: Known Q
Known Q (cfs) = 7.87
Highlighted
Depth (ft) = 1.08
Q (cfs) = 7.870
Area (sqft) = 1.74
Velocity (ft/s) = 4.53
Wetted Perim (ft) = 3.31
Crit Depth, Yc (ft) = 1.00
Top Width (ft) = 1.99
EGL (ft) = 1.40
0 1 2 3 4
Elev (ft) Section Depth (ft)
99.50 -0.50
100.00 0.00
100.50 0.50
101.00 1.00
101.50 1.50
102.00 2.00
102.50 2.50
103.00 3.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2013
Pond Outfall Pipe Design Flow
Circular
Diameter (ft) = 1.50
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.015
Calculations
Compute by: Known Q
Known Q (cfs) = 3.70
Highlighted
Depth (ft) = 0.82
Q (cfs) = 3.700
Area (sqft) = 0.99
Velocity (ft/s) = 3.74
Wetted Perim (ft) = 2.50
Crit Depth, Yc (ft) = 0.74
Top Width (ft) = 1.49
EGL (ft) = 1.04
0 1 2 3
Elev (ft) Section
99.50
100.00
100.50
101.00
101.50
102.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2013
Pond Outfall Pipe Emergency Overflow Capacity
Circular
Diameter (ft) = 1.50
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.015
Calculations
Compute by: Known Depth
Known Depth (ft) = 1.50
Highlighted
Depth (ft) = 1.50
Q (cfs) = 6.435
Area (sqft) = 1.77
Velocity (ft/s) = 3.64
Wetted Perim (ft) = 4.71
Crit Depth, Yc (ft) = 0.98
Top Width (ft) = 0.00
EGL (ft) = 1.71
0 1 2 3
Elev (ft) Section
99.50
100.00
100.50
101.00
101.50
102.00
Reach (ft)
APPENDIX B.2
STREET FLOW
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK = 11.0 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft
Manning's Roughness Behind Curb nBACK = 0.015
Height of Curb at Gutter Flow Line HCURB = 4.38 inches
Distance from Curb Face to Street Crown TCROWN = 15.0 ft
Gutter Width W = 1.17 ft
Street Transverse Slope SX = 0.020 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.098 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO = 0.025 ft/ft
Manning's Roughness for Street Section nSTREET = 0.015
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX = 15.0 15.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 4.4 12.0 inches
Allow Flow Depth at Street Crown (leave blank for no) check = yes
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow = 10.0 146.7 cfs
Major storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak'
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
Lakeview Subdivision
Maximum Grade 2.5% Street Capacity
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Minor storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak'
Street Cap Max Grade.xlsm, Q-Allow 8/20/2013, 8:55 AM
Project:
Inlet ID:
Gutter Geometry (Enter data in the blue cells)
Maximum Allowable Width for Spread Behind Curb TBACK = 11.0 ft
Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft
Manning's Roughness Behind Curb nBACK = 0.015
Height of Curb at Gutter Flow Line HCURB = 4.38 inches
Distance from Curb Face to Street Crown TCROWN = 15.0 ft
Gutter Width W = 1.17 ft
Street Transverse Slope SX = 0.020 ft/ft
Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.098 ft/ft
Street Longitudinal Slope - Enter 0 for sump condition SO = 0.005 ft/ft
Manning's Roughness for Street Section nSTREET = 0.015
Minor Storm Major Storm
Max. Allowable Spread for Minor & Major Storm TMAX = 15.0 15.0 ft
Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 4.4 12.0 inches
Allow Flow Depth at Street Crown (leave blank for no) check = yes
MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm
MAJOR STORM Allowable Capacity is based on Depth Criterion Qallow = 4.4 94.5 cfs
Major storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak'
ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm)
Lakeview Subdivision
Min Grade 0.5% Street Capacity
(Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)
Minor storm max. allowable capacity GOOD - greater than flow given on sheet 'Q-Peak'
Street Cap Min Grade.xlsm, Q-Allow 8/20/2013, 8:55 AM
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Aug 12 2013
Basin B Street Discharge
Triangular
Side Slopes (z:1) = 12.00, 12.00
Total Depth (ft) = 1.50
Invert Elev (ft) = 67.62
Slope (%) = 0.50
N-Value = 0.015
Calculations
Compute by: Known Q
Known Q (cfs) = 11.30
Highlighted
Depth (ft) = 0.57
Q (cfs) = 11.30
Area (sqft) = 3.90
Velocity (ft/s) = 2.90
Wetted Perim (ft) = 13.73
Crit Depth, Yc (ft) = 0.57
Top Width (ft) = 13.68
EGL (ft) = 0.70
0 5 10 15 20 25 30 35 40 45 50
Elev (ft) Section Depth (ft)
67.00 -0.62
67.50 -0.12
68.00 0.38
68.50 0.88
69.00 1.38
69.50 1.88
70.00 2.38
Reach (ft)
APPENDIX B.3
INLETS
Project =
Inlet ID =
Design Information (Input) MINOR MAJOR
Type of Inlet Inlet Type =
Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') alocal
= 3.00 3.00 inches
Number of Unit Inlets (Grate or Curb Opening) No = 1 1
Water Depth at Flowline (outside of local depression) Flow Depth = 6.0 7.3 inches
Grate Information MINOR MAJOR
Length of a Unit Grate Lo
(G) = N/A N/A feet
Width of a Unit Grate Wo
= N/A N/A feet
Area Opening Ratio for a Grate (typical values 0.15-0.90) Aratio
= N/A N/A
Clogging Factor for a Single Grate (typical value 0.50 - 0.70) Cf
(G) = N/A N/A
Grate Weir Coefficient (typical value 2.15 - 3.60) Cw
(G) = N/A N/A
Grate Orifice Coefficient (typical value 0.60 - 0.80) Co
(G) = N/A N/A
Curb Opening Information MINOR MAJOR
Length of a Unit Curb Opening Lo
(C) = 10.00 10.00 feet
Height of Vertical Curb Opening in Inches Hvert
= 6.00 6.00 inches
Height of Curb Orifice Throat in Inches Hthroat
= 6.00 6.00 inches
Angle of Throat (see USDCM Figure ST-5) Theta = 63.40 63.40 degrees
Side Width for Depression Pan (typically the gutter width of 2 feet) Wp
= 2.00 2.00 feet
Clogging Factor for a Single Curb Opening (typical value 0.10) Cf
(C) = 0.10 0.10
Curb Opening Weir Coefficient (typical value 2.3-3.6) Cw
(C) = 3.60 3.60
Curb Opening Orifice Coefficient (typical value 0.60 - 0.70) Co
(C) = 0.67 0.67
MINOR MAJOR
Total Inlet Interception Capacity (assumes clogged condition) Qa
= 8.3 13.4 cfs
WARNING: Inlet Capacity less than Q Peak for MAJOR Storm Q PEAK REQUIRED
= 7.9 43.8 cfs
INLET IN A SUMP OR SAG LOCATION
Lakeview Subdivision
Church Parking Lot Inlet B2 Capacity
CDOT Type R Curb Opening
H-Vert
H-Curb
W
Lo (C)
Lo (G)
Wo
WP
Inlet Capacity Parking Lot.xlsm, Inlet In Sump 11/19/2013, 9:24 AM
APPENDIX B.4
DETENTION FACILITIES
Lakeview Subdivision
SWMM Exhibit
Project: Lakeview
Date: 11/19/2013
11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\SWMM Exhibit
Lakeview Subdivision
St Stage - Storage St Calculation C l l ti
665 002
gg
Project Number: 665-002
F t C lli C l d
Project Number:
Pjt Project Location: L ti Fort Collins, Colorado
Calculations By: R. Banning Date: 11/19/2013
Pond No : N/A
Calculations By:
Pond No.: N/A
Required Volume Water Surface Elevation (WSE)
Design Point B3 3
q
B3-3
100
Design Point
Di Design Storm S 100-yr
Require Volume= 439 4.39 acft 4967 4967.43 ft ft.
Require Volume=
Design Storm WQCV
Ri Required d V Volume= l 16772 ft3 4962 4962.63 ft ft.
Contour
Contour
Elevation (Y-
Contour
Area
Depth SWMM Stage Incremental Volume Total Volume Total Volume
values)
Area
p g
values)
ft3 ft ft ft. ft ft3 ft ft3 ft acre-acre feet
4 4,960 960.70 0 000 0.00 0 0 0 0
4 4,961 961.00 113 030 0.30 -1.1 63 11 11 000 0.00
4 4,962 962.00 11385 100 1.00 -0.063 63 4207 4218 010 0.10
4,963.00 29970 1.00 0.37 19922 24140 0.55
4 4,964 964.00 32671 100 1.00 137 1.37 31279 55420 127 1.27
4 4,965 965.00 36597 100 1.00 237 2.37 34581 90000 207 2.07
4,, 966.00 40815 1.00 3.37 38648 128649 2.95
4 4,967 967.00 42827 100 1.00 437 4.37 41775 170424 391 3.91
4 4,967 967.70 54225 070 0.70 507 5.07 33856 204280 469 4.69
4 4,969 969.00
4,968.00
4,96 967.00
n
4 966 00
ion
4,966.00
El ev vat
4 965 00
ur
4,965.00
Co ont tou
4,, 964.00
4 4,963 963.00
4 4,962 962.00
-50000 0 50000 100000 150000 200000 250000
Cummulative Volume Volume, cu cu. ft ft.
Lakeview Subdivision
ORIFICE RATING CURVE
Pond Outlet
100-yr Orifice
Project: Lakeview Subdivision
Date: 11/19/2013
By: R. Banning
100-yr WSEL= 4967.43
Orifice Plate
Outflow Q 3.7 cfs
Orifice Coefficient Cd 0.65
Gravity Constant g 32.2 ft/s^2
100-year head H 6.73 ft
Orifice Area Ao 0.27 ft^2
Orifice Area Ao 39.37 in^2
Radius r 3.5 in
Diameter d 7.1 in
Orifice Curve
Stage (ft) H (ft) Q (cfs) SWMM Stage Note
4960.70 0 0.00 Pond Invert
4961.70 1 1.43
4962.63 1.93 1.98 0 WQ WSEL
4963.63 2.93 2.44 1.00
4964.63 3.93 2.83 2.00
4965.63 4.93 3.17 3.00
4966.63 5.93 3.47 4.00
4967.43 6.73 3.70 4.80 100-yr WSEL
4967.63 6.93 3.75 5.00
4967 70 3 0 Oi
11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Orifice Size
4967.70 7 3.77 5.07 Overtopping
11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Orifice Size
Weir Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Wednesday, Nov 20 2013
Lakeview Pond Overflow Weir
Trapezoidal Weir
Crest = Sharp
Bottom Length (ft) = 100.00
Total Depth (ft) = 1.00
Side Slope (z:1) = 4.00
Calculations
Weir Coeff. Cw = 3.10
Compute by: Known Q
Known Q (cfs) = 91.30
Highlighted
Depth (ft) = 0.44
Q (cfs) = 91.30
Area (sqft) = 44.77
Velocity (ft/s) = 2.04
Top Width (ft) = 103.52
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Depth (ft) Lakeview Pond Overflow Weir Depth (ft)
-0.50 -0.50
0.00 0.00
0.50 0.50
1.00 1.00
1.50 1.50
2.00 2.00
Weir W.S. Length (ft)
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS
Lakeview Subdivision
WQ Capture & Forebay Volumes
Project: Lakeview Subdivision
Date: 11/19/2013
By: R. Banning
B3-2 I= 50%
WQCV From Figure 3.2 USDCM
40-hour 0.24 watershed inches
Required Storage 0.124 Acre-ft
5385 ft^3
TOTAL AREA I= 53%
WQCV From Figure 3.2 USDCM
40-hour 0.24 watershed inches
Required Storage 0.385 Acre-ft
16772 ft^3
B2 I= 81%
Area 4.704 acres
WQCV From Figure 3.2 USDCM
40-hour 0.33 watershed inches
Required Storage 0.129 Acre-ft
5635 ft^3
Forbay Volume 113 ft^3
Depth 12 in
North Forebay I= 50%
Area 11.87 acres
WQCV From Figure 3.2 USDCM
40-hour 0.21 watershed inches
Required Storage 0.208 Acre-ft
9048 ft^3
Forbay Volume 181 ft^3
Depth 18 in
11/19/2013 12:37 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\WQ Capture
Lakeview Subdivision
FOREBAY NOTCH RATING CURVE
Forebay A
WQ V-notch
Project: Lakeview Subdivision
Date: 11/19/2013
By: R. Banning
Orifice Plate
Outflow Q0.88 cfs
Orifice Coefficient Cd 0.6
Gravity Constant g 32.2 ft/s^2
Notch Top Width W top 0.37 ft
Notch Top Width W top 4.4 in
Forebay Wall Height h1 ft
Notch Area Ao 0.18 ft^2
Notch Area Ao 26.32 in^2
Angle theta 0.18
Orifice Curve
Stage (ft) a w A (ft^2) Q (cfs)
0 0.00 0.00 0.00 0.00
0.1 0.02 0.04 0.00 0.00
0.2 0.04 0.07 0.01 0.02
0.3 0.05 0.11 0.02 0.04
04 007 015 003 009
a
h
0.4 0.07 0.15 0.03 0.09
0.5 0.09 0.18 0.05 0.16
0.6 0.11 0.22 0.07 0.25
0.7 0.13 0.26 0.09 0.36
0.8 0.15 0.29 0.12 0.50
0.9 0.16 0.33 0.15 0.68
1 0.18 0.37 0.18 0.88
11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Forebay A Notch
Lakeview Subdivision
FOREBAY NOTCH RATING CURVE
Forebay B
WQ V-notch
Project: Lakeview Subdivision
Date: 11/19/2013
By: R. Banning
Orifice Plate
Outflow Q1.12 cfs
Orifice Coefficient Cd 0.6
Gravity Constant g 32.2 ft/s^2
Notch Top Width W top 0.25 ft
Notch Top Width W top 3.0 in
Forebay Wall Height h1.5 ft
Notch Area Ao 0.19 ft^2
Notch Area Ao 27.35 in^2
Angle theta 0.08
Orifice Curve
Stage (ft) a w A (ft^2) Q (cfs)
0 0.00 0.00 0.00 0.00
0.1 0.01 0.02 0.00 0.00
0.2 0.02 0.03 0.00 0.01
0.3 0.03 0.05 0.01 0.02
04 003 007 001 004
a
h
0.4 0.03 0.07 0.01 0.04
0.5 0.04 0.08 0.02 0.07
0.6 0.05 0.10 0.03 0.11
0.7 0.06 0.12 0.04 0.17
0.8 0.07 0.14 0.05 0.23
0.9 0.08 0.15 0.07 0.31
1 0.08 0.17 0.08 0.41
1.1 0.09 0.19 0.10 0.52
1.2 0.10 0.20 0.12 0.64
1.3 0.11 0.22 0.14 0.78
1.4 0.12 0.24 0.17 0.94
1.5 0.13 0.25 0.19 1.12
11/19/2013 12:38 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Forebay B Notch
APPENDIX D
OPERATIONS AND MAINTENANCE GUIDELINES FOR PERMANENT BMPS
Lakeview Subdivision
Final Operation and Maintenance Guide
PERMANENT BMP OPERATION AND MAINTENANCE GUIDE
The Lakeview Subdivision private drainage facilities contain permanent BMPs that must be
maintained by the Homeowners. The following is the recommended maintenance measures and
schedule for each permanent BMP.
Pre-forebay/Sedimentation Sump
Description
The pre-forebay is a system of measures within the inlet located in the drive aisle between the
church parking facility and the Lakeview Subdivision detention pond. The system consists of
sedimentation sump and snout apparatus. The sedimentation sump is extra volume (2-3’ deep) at
the bottom of the inlet and below invert of the outlet pipe. The Snout apparatus is a hood shaped
devise that covers the outlet pipe from the inlets.
Function
The inlet will contain a perpetual pool of water within the sedimentation sump between the invert
(bottom) and the bottom of the snout apparatus. The pool is intended to allow for sedimentation by
pausing the motion of water prior to discharge from the inlet. The increased time runoff resides
within the inlet will allow for a minimal amount of sedimentation and allow for separation of
hydrocarbons from runoff. The snout apparatus is intended to separate hydrocarbons (ie. oil) from
impervious area runoff by skimming the top of the pool. Hydrocarbons will separate from runoff and
buildup within the top layer of the permanent pool. Runoff from below the hydrocarbons and the
bottom of the snout will outfall into the pond.
Maintenance
Hydrocarbons and sediment will need to be removed regularly from the inlet. Sediment should be
removed prior to the depth of the water reducing below 2’ from the top of the sediment buildup to
the snout bottom. The layer of hydrocarbons should be removed from the inlet prior to accumulation
beyond half of the height of the snout. A vacuum truck should be used to remove all sediment,
hydrocarbons and residual water from the inlet. Remaining sediment may be removed manually and
disposed of in a legal manner. The sump should then be filled with clean water.
The Snout apparatus should be replaced as age deterioration occurs and prior to failure. The seal
should be checked regularly to ensure hydrocarbons are not bypassing the device.
Schedule
Maintenance should occur as triggered by the conditions indicated above and at least bi-annually.
Lakeview Subdivision
Final Operation and Maintenance Guide
Sedimentation Forebay
Description
The sedimentation forebays are concrete lined pool made with concrete or earthen berm walls 1-2’
tall, located strategically throughout the drainage basin and at pond inlet. The forebays contain
small outlet pipes or notches and measures including concrete aprons or riprap to minimize erosion
when overtopping occurs. Energy dissipation including small walls or buried boulders may be
included in the forebay design just below the inlet to the forebay.
Function
The forebay will allow runoff to pool in a convenient place prior to entering the pond. There is an
extended outfall time designed for each basin. The increased residence time of runoff within the
forebay is intended to allow sedimentation from the runoff prior to entering the pond. The concrete
bottom is intended to allow for easy removal of sediment by shoveling or mechanical methods. The
forebay will normally be slightly wet unless evaporation of runoff within the forebay occurs between
runoff events.
Maintenance
Sediment should be regularly removed from the forebay and legally disposed of. Removal is
normally achieved by shoveling in some fashion. Maximum sediment accumulation should be 4” at
the outlet from the forebay. Sprinklers should be positioned to avoid spraying within the forebay to
minimize damp conditions and conditions favorable to mosquito breeding.
Schedule
Maintenance should occur as triggered by the conditions indicated above and at least bi-annually.
Lakeview Subdivision
Final Operation and Maintenance Guide
Drywell – See attached FAQ sheet for additional information
Description
The drywell is a method of promoting infiltration. The facility is a vertical well, either empty or filled
with gravel material to achieve filtering. Material surrounding the well consists of washed rock,
providing volume for runoff within the voids prior to recharging into groundwater. Drywells and
surrounding materials are usually wrapped with geotexile fabrics to prevent sediment deposition
within voids. Where implemented, gravel and geotextile fabrics should be used perpetually to
reduce the maintenance requirements.
Function
Runoff is designed to accumulate around and enter into the inlet to the drywells. Runoff will
percolate into the voids of the surrounding materials and ultimately recharge into groundwater.
Maintenance
Water quality and sedimentation facilities upstream of any drywell should be maintained properly to
extend the useful life of the drywell. Geotextile/Filter fabrics should be inspected regularly and
replaced when sediment load prevents runoff from free passing through the fabric. Gravels within
the drywell should be removed and replaced as sediment accumulates within the media.
Surrounding materials should be replaced along with an additional 4” of native material adjacent
the surrounding material if fabrics and gravels are replaced but function is not restored.
Schedule
Maintenance should occur as triggered by the conditions indicated above and at least bi-annually.
Lakeview Subdivision
Final Operation and Maintenance Guide
Bio-retention Materials
Description
Bio-retention materials allow vegetative growth and promote infiltration of runoff where used. The
material should be underlined by a porous media such as sand or pea gravels to increase the
infiltration potential. Geotextile fabric should be implemented between the bio-retention materials
and the porous media to minimize sediment migration into the porous material and to define the
limits of the bio-retention material. Bio-retention materials should be planted with wetland plants
and those with sparse root systems. Bio-retention materials should only be used were erosive
potential is extremely low.
Function
Bio-retention materials are places in areas where runoff is very slow or pooling of water will occur.
Wetland material growth will occur and promote degradation of pollutants and sedimentation
through natural processes and runoff impedance. Runoff will also infiltrate into the material
increasing the potential for groundwater recharge.
Maintenance
Growth of wetland materials should be allowed perpetually within bio-retention median and only be
cut or mowed when additional maintenance such as trash removal is required. Bi-annual Aeration
of bio-retention media is recommended to increase the infiltration potential. The material may need
to be replaced as sediment loading occurs to restore infiltration potential. When required the media
should be removed along with the underlying geotextile fabric. Underlying porous material should
be tested to insure infiltration capacity has not been compromised. The geotexile fabric and bio-
retention material should then be replaced and replanted.
Schedule
Maintenance should occur as triggered by the conditions indicated above and at least bi-annually.
Lakeview Subdivision
Final Operation and Maintenance Guide
Micro-pool and Initial Surcharge Volume
Description
The micro-pool is located adjacent the outlet from the pond. The pool is intended to promote
microbial growth that consumes organic materials in runoff. The pool contains a concrete bottom
and ramp to facilitate maintenance. The pool is surrounded with boulders or berms to increase the
depth of the pool above the outlet invert, creating the initial surcharge volume.
Function
Micro-pools promote microbial growth and are intended to be at sufficient depth to increase organic
consumption and minimize insect breeding habitat. The stagnant pool is necessary to achieve the
benefit of pollutant reduction.
The initial surcharge volume provides a place for minor storms to accumulate around the outlet
while minimizing the saturated soils at the bottom of the pond. This serves to increase the lower
level outfall through the water quality plate and minimize insect breeding areas.
Maintenance
The micro-pool should be allowed to accumulate water with minimal disturbance. The pool may
become anaerobic promoting consmption of organics. The sediment and water from the pool should
be removed when the accumulation has decreased the pool depth to 2’ or less to minimize insect
habitat. Removal should be by legal method only and may require a vacuum truck. Remaining
sediment should be manually removed and the pool should be refilled with clean water. The initial
surcharge volume should be restored to the plan elevations during sediment removal.
Schedule
Maintenance should occur as triggered by the conditions indicated above and at least bi-annually.
Lakeview Subdivision
Final Operation and Maintenance Guide
Water Quality Outlet Structure
Description
The water quality outlet structure is a multi-cell concrete structure that contains orifice plates for
regulating release from the pond. Trash racks are installed over the plates to minimize clogging. The
outfall from the structure is to a pipe or swale outside of the pond.
Function
The plates are installed to slow the release of water creating a 40-hour water quality release pool
and minimizing the 100-year release to allowable per downstream requirements. The pond will
accumulate volume as designed due to the restriction of outflow.
Maintenance
The orifice plates must be installed and properly maintained within the water quality outlet
structure. Failure to install the plates will overwhelm downstream storm conveyance. Failure to
properly maintain the plates may create unintended perpetual pools within the pond or an
overtopping condition during major storms. Upstream sedimentation facilities should be maintained
to increase the longevity and reduce the maintenance of the overall pond. Sediment should be
removed from the pond when these structure no longer function. Due to these structures sediment
should never accumulate at the water quality plate within the structure. Major pond maintenance
may be required if this condition takes place.
Trash racks should be cleaned of debris regularly and immediately if debris accumulates on the
racks. The orifice plates should be inspected for degradation and replaced if no longer functional as
designed. Sediment and debris should be cleaned at least bi-annually from the bottom of the
structure and the outlet pipe behind the orifice plates. Ensure that the integrity of the racks brackets
and the overall structures are not compromised and replace as needed.
Schedule
Maintenance should occur as triggered by the conditions indicated above and at least bi-annually.
Overview
Infiltration trenches and dry wells are standard stormwater
management structures that can play an important role in Low
Impact Development site design. Dispersed around the site,
these infiltration structures can recharge groundwater and help
to maintain or restore the site’s natural hydrology. This approach
contrasts with conventional stormwater management strategies,
which employ infiltration as a secondary strategy that occurs in
large basins at the end of a pipe.
Dry wells and infiltration trenches store water in the void space
between crushed stone or gravel; the water slowly percolates downward into the subsoil. An overflow
outlet is needed for runoff from large storms that cannot be fully infiltrated by the trench or dry well.
Bioretention, another important infiltration technique, is discussed in another fact sheet. Infiltration
trenches do not have the aesthetic or water quality benefits of bioretention areas, but they may be useful
techniques where bioretention cells are not feasible.
Applications and Design Principles
Infiltration structures are ideal for infiltrating runoff from small drainage areas (<5 acres), but they need to be
applied very carefully. Particular concerns include potential groundwater contamination, soil infiltration capacity,
clogging, and maintenance. Pretreatment is always necessary, except for uncontaminated roof runoff. Trenches
and dry wells are often used for stormwater retrofits, since they do not require large amounts of land; directing
roof runoff to drywells is a particularly cost-effective and beneficial practice.
Whether for retrofits or new construction, multiple infiltration structures will
be needed to treat large sites; they are often used in the upland areas of large
sites to reduce the overall amount of runoff that must be treated downstream.
Trenches and dry wells are tough to site in dense urban settings, due to the
required separation from foundations, and because urban soils often have
poor infiltration capacity due to many years of compaction. Infiltration
trenches and dry wells should not receive runoff from stormwater hotspots
Low Impact Development strategies use careful site design and decentralized stormwater management
to reduce the environmental footprint of new growth. This approach improves water quality, minimizes
the need for expensive pipe-and-pond stormwater systems, and creates more attractive developments.
F A C T S H E E T # 5
INFILTRATION TRENCHES
AND DRY WELLS
Management Objectives
Remove suspended solids, heavy
metals, trash, oil and grease.
Reduce peak discharge rate and
total runoff volume.
Provide modest infiltration and
recharge.
Provide snow storage areas.
Improve site landscaping.
M A S S A C H U S E T T S L OW I M PACT D E V E L O P M E N T T O O L K I T
(such as gas stations) unless the stormwater has already been fully treated by another
stormwater treatment practice to avoid potential groundwater contamination.
Infiltration structures must be constructed with adequate vertical separation from
the groundwater table, generally 2’ or more between the bottom of the trench or pit
and the seasonally high groundwater table. Soils must be sufficiently permeable (at
least 0.3”/hour) to ensure that trenches can infiltrate quickly.
Infiltration trenches and dry wells operate on similar principles, though trenches
are linear troughs and dry wells are round or square in plan view. In both cases, the
excavated hole or trench, 3’-12’ deep, is lined with filter fabric and backfilled with
washed, crushed stone 1.5”-3” in diameter. The bottom of infiltration trenches is
often filled with a 6”-12” filter layer of washed, compacted sand. A 4”-6” perforated
PVC observation well will permit monitoring of the structure and observation of
drainage time.
Trenches and dry wells should be designed to store the design volume and infiltrate
it into the ground through the bottom of the trench or well within 72 hours.
Because of their limited size, infiltration structures are best used to infiltrate the
first inch/half inch of runoff from frequent small storms; they are not effective for
infiltrating the runoff from large storms. Overflow from trenches and dry wells
should be directed to a swale or other conveyance, sized to prevent erosion.
Because dry wells and infiltration trenches can be prone to clogging, pretreatment
of stormwater runoff is a necessity. Where dry wells accept roof runoff through a
system of gutters and downspouts, screens at the top of downspouts should suffice.
For runoff from paved surfaces, designers should use grass swales, filter strips,
settling basins, sediment forebays, or a combination of two or more strategies to
pretreat stormwater before it is discharged to an infiltration trench or dry well. In
groundwater protection areas (Zone II and Interim Wellhead Protection Areas)
infiltration may only be used for uncontaminated rooftop runoff.
Above, top: A perforated pipe
delivers rooftop runoff to the full
length of this infiltration trench,
under construction. After comple-
tion the area will be covered with
sod and the trench will be invisible.
Photo: Cahill Associates, Inc. 2004
Above: A roadside infiltration
trench that receives runoff via
periodic curb cuts; this trench may
be prone to clogging because there
is no pretreatment. Photo: Lower
Columbia River Estuary Partnership
Right: A schematic section of an in-
filtration basin. Image: American
Groundwater Trust, Plainfield CT
Stormwater Manual
Benefits and Effectiveness
Dry wells and infiltration trenches reduce stormwater runoff volume, including
most of the runoff from small frequent storms. Consequently, downstream pipes
and basins are smaller, and the local hydrology benefits from increased base flow.
Dry wells and infiltration trenches also reduce peak discharge rates by retaining
the first flush of stormwater runoff and creating longer flow paths for runoff.
Infiltration structures are moderately expensive to construct and can help to
reduce the size of downstream stormwater management structures.
These techniques have an unobtrusive presence; they do not enhance the
landscape (like bioretention areas do), but they have a lower profile than large
infiltration basins.
Limitations
Infiltration trenches and dry wells cannot receive untreated stormwater
runoff, except rooftop runoff. Pretreatment is necessary to prevent premature
failure that results from clogging with fine sediment, and to prevent potential
groundwater contamination due to nutrients, salts, and hydrocarbons.
Infiltration structures cannot be used to treat runoff from portions of the site
that are not stabilized.
Rehabilitation of failed infiltration trenches and dry wells requires complete
reconstruction.
Infiltration structures are difficult to apply in slowly permeable soils or in fill
areas.
Where possible, the design should maintain a minimum separation from paved
areas (generally 10’, depending on site conditions) to prevent frost heave.
Unlike bioretention areas, infiltration trenches and dry wells do not help meet
site landscaping requirements.
Above, and Cover: The parking lot
runoff directed to this infiltration
basin is pretreated by a vegetated
filter strip. Note concrete level
spreader (at right) to facilitate
sheetflow across filter strip.
Photo:California Stormwater
Quality Association
Design Details
Determine infiltration rate of underlying soil through field
investigations; use a minimum of one boring at each dry
well, two borings at each infiltration trench, with at least
one additional boring every 50 feet for trenches over 100
feet. Base trench/drywell sizing on the slowest rate obtained
from soil infiltration tests. Determine the infiltrative
capacity of the soil through an infiltration test using a
double-ring infiltrometer. Do not use a standard septic
system percolation test to determine soil permeability.
Do not use trenches or dry wells where soils are >30% clay
or >40% silt clay.
Use of vertical piping for distribution or infiltration
enhancement may cause the trench or drywell to be
classified as an injection well which needs to be registered
with the state.
Trim tree roots flush with the trench sides in order to
prevent puncturing or tearing the filter fabric. Since tree
roots may regrow, it may be necessary to remove all trees
within 10 feet of the infiltration structure and replace them
with shallow-rooted shrubs and grasses.
If used, distribution pipes should have perforations of 0.5”
and should be capped at least 1 foot short of the wall of the
trench or well.
For infiltration trenches receiving runoff via surface flow, a
horizontal layer of filter fabric just below the surface of the
trench, covered with 2”-6” of gravel or crushed stone, will
help to retain sediment near the surface; this will prevent
clogging and allow for rehabilitation of the trench without
complete reconstruction.
Required set backs for surface water supply (Zone 1 and
Zone A): 400 feet setback from a source and 100 feet from
tributaries. Required setback from private wells: 100 feet
Required setback from septic systems: 100 feet. Required
setback from building foundations: 10 feet for drywells and
20 feet for infiltration trenches.
Because of clogging problems, infiltration trenches and
drywells should never be used to infiltrate runoff from
drainage areas that are not completely stabilized. For best
performance, contractors, should avoid compaction of soils
around trenches and dry wells during construction.
Additional information
Massachusetts Stormwater Management Policy: Volume Two:
Stormwater Technical Handbook; MA DEP & MA CZM;
1997
Maintenance
After construction, inspect after every major storm for
the first few months to ensure stabilization and proper
function.
On a monthly basis, remove sediment and oil/grease
from pretreatment devices, overflow structures, and the
surface of infiltration trenches.
Semi-annually, check observation wells 3 days after
a major storm. Failure to percolate within this time
period indicates clogging
Semi-annually, inspect pretreatment devices and
diversion structures for sediment build-up and
structural damage.
If ponding occurs on the surface of an infiltration
trench, remove and replace the topsoil or first layer of
APPENDIX E
EROSION CONTROL REPORT
Lakeview Subdivision
Preliminary Erosion Control Report
EROSION CONTROL REPORT
A comprehensive (SWMP) 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 Sheet C001 of 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 Lakeview Subdivision 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
C500 – DRAINAGE EXHIBIT
ELEC
WV
WV
H Y
D
H Y
D
CABLE VAULT
CONTROL IRR
T
C
C
CT
C T
C
S
S
T T
T
T
F
E
S
B2
4.70 ��
EXISTING
CHURCH BUILDING
B1
2.84 ��
B3-2
6.18 ��
B3-1
2.85 ��
OS1
0.52 ��
B3-3
1.96 ��
LOT 22 LOT 21 LOT 20 LOT 19
LOT 18
LOT 17
LOT 16
LOT 15
LOT 14
LOT 13
LOT 12
LOT 11
LOT 10
LOT 9
LOT 8
LOT 7
LOT 2
LOT 1
LOT 24
LOT 25
LOT 26
LOT 27
LOT 28
LOT 29
LOT 30
LOT 31
LOT 32
LOT 33
LOT 34
LOT 35
LOT 36
LOT 37
LOT 38
LOT 39
LOT 40
LOT 41
TRACT C
U&AE
TRACT A
LOT 42
B2
OS1
EXTENDED DETENTION BASIN/
DETENTION POND
100-YR VOLUME: 4.39 AC-FT
100-YR WSEL: 4967.43
40-HOUR WQ RELEASE
OS2
0.19 ��
LOT 133
OWNER:
ROSCHKE FAMILY TRUST
LOT 132
OWNER:
KLINEDINST,
NICHOLAS J/TARA C
EASTBOROUGH
LOT 131
OWNER:
JORISSEN, DAVID W
WILBUR, WENDY P
TRACT A
OWNER: CITY OF FORT COLLINS
LOT 111
OWNER:
HOLMES, RICHARD L/
SHARON M
LOT 110
OWNER:
VANDER WILT,
DOUGLAS W/
LOIS K
LOT 109
OWNER:
DU CHATEAU,
PAUL C/SARA J
LOT 108
OWNER:
GRIDER, DAN A,
THE WILD ROSE
REVOCABLE
TRUST
LOT 106
OWNER:
LEWIS, ANDREW/
S JUANETTE
ELDORADO
SPRINGS
SECOND FILING
LOT 105
OWNER:
BACKES,
KARI K
LOT 104
OWNER:
RICHARDSON,
DONALD L/
MARILYN J
LOT 6
OWNER:
MT. VERNON
INVESTMENT
GROUP LLC
LOT 7
OWNER:
RAVENSCHLAG,
RALPH W/
CHERYL E
SILVERWOOD VILLAGE
SECOND FILING
LOT 8
OWNER:
KENNING, MARK R/
DIANE L
LOT 9
OWNER:
BEANER, ROGER W/
JOANN E
LOT 10
OWNER:
PELKEY, SCOTT
HOWE, CHARLES
B3-1
B1
B3-3
OS2
OS1
LOT 112
OWNER:
CALE, GARY S.
SILVERWOOD VILLAGE
FIRST FILING
ELDORADO
SPRINGS
SECOND FILING
LOT 5 LOT 6
LOT 4
LOT 3
CHRIST CENTER
COMMUNITY
CHURCH
TRACT B
UTILIY, ACCESS &
DRAINAGE EASEMENT
LOT 22
LOT 23
100'
OVERFLOW
N�. R��������:
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DESIGNED BY:
DRAWN BY:
SCALE:
DATE:
NOVEMBER 2013
PROJECT:
665-002
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50
100 150
LEGEND:
4953
PROPOSED CONTOUR 93
PROPOSED STORM SEWER
PROPOSED SWALE
EXISTING CONTOUR
PROPOSED CURB & GUTTER
NOTES:
PROPOSED INLET
A
DESIGN POINT
FLOW ARROW
DRAINAGE BASIN LABEL
BASIN
DESIGNATION
BASIN
AREA (AC)
DRAINAGE BASIN BOUNDARY
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
1.REFER TO THE "PRELIMINARY DRAINAGE REPORT FOR REGENCY LAKEVIEW' BY NORTHERN ENGINEERING, DATED AUGUST 21, 2013 FOR ADDITIONAL INFORMATION.
B2
1.45 ��
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CHECKED BY:
CHECKED BY:
CHECKED BY:
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UTILITY PLAN APPROVAL
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
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BASIN B POND SUMMARY
VOLUME REQ'D (��-��) VOLUME PROVIDED (��-��) POND INVERT 100-YEAR WATER SURFACE
POND SPILL ELEV.
BASIN B 4.39 4.69 4960.75 4967.43 4967.70
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
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B1 B1 2.84 0.53 0.66 17.0 14.1 2.62 12.57
B2 B2 4.70 0.80 1.00 11.5 6.5 7.87 43.80
B3-1 B3-1 2.85 0.63 0.79 11.8 9.3 3.77 18.12
B3-1 B3-2 6.18 0.58 0.73 14.9 13.4 6.81 31.08
B3-3 B3-3 1.96 0.28 0.34 13.4 12.7 1.07 4.75
OS1 OS1 0.52 0.22 0.28 9.3 9.0 0.27 1.2
OS2 OS2 0.19 0.15 0.19 7.1 7.0 0.13 0.32
stone and the top layer of filter fabric.
Upon failure, perform total rehabilitation of the trench
or dry well to maintain storage capacity within 2/3 of
the design treatment volume and 72-hour exfiltration
rate.
Cost
Infiltration trenches and dry wells are moderately
expensive to construct. Because trenches and dry
wells can infiltrate stormwater closer to the source,
conveyance structures such as swales and pipes can
be downsized. It is important that developers and
property owners provide a budget for maintenance
activities, since lack of maintenance is the primary
cause for premature failure of infiltration structures.
This publication is one component of the Massachusetts Low Impact Development Toolkit, a production of the Metropolitan Area
Planning Council, in coordination with the I-495 MetroWest Corridor Partnership, with financial support from US EPA.
The Massachusetts Low Impact Development Interagency Working Group also provided valuable input and feedback on the LID Toolkit.
FOR MORE INFORMATION, VISIT: WWW.MAPC.ORG/LID AND WWW.ARC-OF-INNOVATION.ORG.
Above: Precast concrete drywell inserts prior to installation.
Photo: Lower Columbia River Estuary Partnership
11/19/201312:40 PM
D:\Projects\665-002\Drainage\Detention\
665-002__Detention Pond_SWMM Final ROB.xlsm\Stage_Storage
Survey Area Data: Version 7, May 1, 2009
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—Nov 18,
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.
Hydrologic Soil Group—Larimer County Area, Colorado
(Lakeview Hydrologic Group)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
10/29/2013
Page 2 of 4
B3-1 B1&B3-1 No 0.58 0.58 0.73 205 2.00% 11.0 11.0 7.9 950 1.20% 2.19 7.2 18.3 18.3 15.2
B3-1 B1,B3-1 & B3-2 No 0.58 0.58 0.73 205 2.00% 11.0 11.0 7.9 950 1.20% 2.19 7.2 18.3 18.3 15.2
OS1 OS1 No 022 022 028 45 11 10% 49 49 46 368 0 50% 141 43 93 93 90
TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow 1
Design
Point
Basin
Overland Flow
R. Banning
November 19, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
OS1 OS1 No 0.22 0.22 0.28 45 11.10% 4.9 4.9 4.6 368 0.50% 1.41 4.3 9.3 9.3 9.0
OS2 OS2 No 0.15 0.15 0.19 20 23.50% 2.8 2.8 2.7 368 0.50% 1.41 4.3 7.1 7.1 7.0
B Overall B Overall No 0.60 0.60 0.76 210 1.90% 10.8 10.8 7.5 1150 1.50% 2.45 7.8 18.7 18.7 15.4
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
11/19/2013 12:36 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Tc
B1 2.838 0.671 0.288 0.034 0.367 0.000 Sandy | Average 2% to 7% 1.478 0.53 0.53 0.66 45%
B2 4.704 3.799 0.023 0.000 0.000 0.000 Sandy | Average 2% to 7% 0.882 0.80 0.80 1.00 81%
B3-1 2.85 0.65 0.33 0.02 0.73 0.00 Sandy | Average 2% to 7% 1.115 0.63 0.63 0.79 57%
B3-2 6.18 0.90 0.72 0.06 1.68 0.00 Sandy | Average 2% to 7% 2.813 0.58 0.58 0.73 50%
B3-3 1.96 0.00 0.03 0.01 0.27 0.00 Sandy | Average 2% to 7% 1.650 0.28 0.28 0.34 14%
B1&B3-1 5.69 1.32 0.62 0.06 1.09 0.00 Sandy | Average 2% to 7% 2.592 0.58 0.58 0.73 51%
B1,B3-1 & B3-2 11.87 2.23 1.34 0.12 2.77 0.00 Sandy | Average 2% to 7% 5.406 0.58 0.58 0.73 50%
B1,B3 13.83 2.23 1.37 0.13 3.05 0.00 Sandy | Average 2% to 7% 7.056 0.54 0.54 0.67 45%
OS1 0.52 0.05 0.00 0.00 0.00 0.00 Sandy | Average 2% to 7% 0.473 0.22 0.22 0.28 9%
OS2 0.19 0.00 0.00 0.00 0.00 0.00 Sandy | Average 2% to 7% 0.195 0.15 0.15 0.19 0%
B Overall 18.54 6.03 1.39 0.13 3.05 0.00 Sandy | Average 2% to 7% 7.938 0.60 0.60 0.76 54%
EXISTING TOTAL 19.25 4.70 0.34 0.19 0.62 0.00 Sandy | Average 2% to 7% 13.396 0.39 0.39 0.49 29%
TOTAL AREA 19.25 6.08 1.39 0.13 3.05 0.00 Sandy | Average 2% to 7% 8.605 0.59 0.59 0.74 53%
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
November 19, 2013
Composite Runoff Coefficient with Adjustment
11/19/2013 12:37 PM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Composite Runoff Coefficient