HomeMy WebLinkAboutLAKEVIEW - PDP - PDP130026 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
LAKEVIEW SUBDIVISION
Fort Collins, Colorado
August 21, 2012
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
August 21, 2012
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
Lakeview Subdivision
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies the 08.21.13 Project Development Plan submittal for the
proposed Lakeview Subdivision Single-family development. Comments from the Conceptual Review
Letter dated 02.14.13 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 ........................................................................................................ 11
A. Compliance with Standards ........................................................................................ 11
B. Drainage Concept ...................................................................................................... 12
References ......................................................................................................................... 13
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (reserved for future use)
B.2 – Street Flow (reserved for future use)
B.3 – Inlets (reserved for future use)
B.4 – Detention Facilities
APPENDIX C – Water Quality Design Computations (reserved for future use)
APPENDIX D – Operations and Maintenance Guidelines for Bioretention Planters
(reserved for future use)
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
Preliminary 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
Preliminary 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
Preliminary 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
Preliminary 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
Preliminary 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.
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.
Step 3 – Stabilize Drainageways
Lakeview Subdivision
Preliminary Drainage Report 6
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 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.
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 sediment forebay at the inlet to the pond to allow sediment to settle from the
incoming stormwater runoff before being delivered to the main pond facility
A micro pool will be included in the outlet structure design.
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.
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
Lakeview Subdivision
Preliminary Drainage Report 7
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 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.
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.
Lakeview Subdivision
Preliminary Drainage Report 8
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.
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
Lakeview Subdivision
Preliminary Drainage Report 9
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 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 B3-3
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
second basins 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 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
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.
Lakeview Subdivision
Preliminary Drainage Report 10
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 for open play area.
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.
An FAA method computation has been performed for the entirety of Basin B 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.
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.
Micro pool components will be utilized within the outlet structure of from the pond
for final treatment.
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
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.).
Lakeview Subdivision
Preliminary Drainage Report 11
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 4.34 4.35 3.7(a) 4967.55 4967.70 4968.70 1.15
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 E will contain with future FCP submittals 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 E will contain, with future
FDP submittals, 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.
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
Lakeview Subdivision
Preliminary Drainage Report 12
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
Preliminary 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 SURFACE
1
:
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
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite Runoff
Coefficient
Composite
% Imperv.
B1 2.838 0.671 0.288 0.034 0.367 1.478 0.53 0.53 0.66 45%
B2 4.704 3.799 0.023 0.000 0.000 0.882 0.80 0.80 1.00 81%
B3-1 2.85 0.65 0.33 0.02 0.73 1.115 0.63 0.63 0.79 57%
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 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 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 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 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
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Notes
RUNOFF COMPUTATIONS
R. Banning
August 20, 2013
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Design
Point
Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Flow,
Q100
(cfs)
C2 C
10 C100
Q C f C i A
8/20/2013 8:45 AM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Runoff
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers (reserved for future use)
B.2 – Street Flow
B.3 – Inlets (reserved for future use)
B.4 – Detention Facilities
APPENDIX B.1
STORM SEWERS (reserved for future use)
APPENDIX B.2
STREET FLOW (limit calculations only at this time)
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 (reserved for future use)
APPENDIX B.4
DETENTION FACILITIES
Lakeview Subdivision
Detention Pond Calculation | FAA Method
Project Number: 665-665 002
Fort Collins Colorado
Project Number:
Project Location Location: Fort Collins, Colorado
Calculations By: R. Banning Date: 8/20/2013
Pond No Basin B
Calculations By:
Pond No.: Basin B
Input Variables Results
Design Point B3-3
100 yr
g
Design Storm 100-yr Required Detention Volume
3
Design Storm Required Detention Volume
078 WQCV 16772 ft
Developed "C" = 0.78 WQCV 16772 ft 3
3
Developed C
Area (A)= 19.25 acres Quantity Detention 172279 ft
() y 3
Max Release Rate 370 cfs Total Volume 189051 ft
3
Max Release Rate = 3.70 cfs Total Volume 189051 ft
Total Volume 4.34 3 ac-ft
Ft.Collins Inflow
Of
Storage
Ti Ti
Ft.Collins
100 Q
Inflow
(R ff)
Outflow
Storage
Time Time 100-yr Q100 (Runoff) Dt ti
(Release) Volume
Detention
Intensity Volume
(Release) Volume
Intensity Volume Volume
(mins) (secs) (in/hr) (cfs) (ft
3
) (ft
3
) (ft
3
(mins) (secs) (in/hr) (cfs) (ft ) (ft ) (ft )
5 300 9.95 149.4 44820 1110 43710
10 600 772 7.72 115 115.9 69549 2220 67329
15 900 652 6.52 97 97.9 88108 3330 84778
20 1200 560 5.60 84 84.1 100901 4440 96461
25 1500 498 4.98 74 74.8 112162 5550 106612
30 1800 452 4.52 67 67.9 122162 6660 115502
35 2100 4.08 61.3 128649 7770 120879
40 2400 374 3.74 56 56.2 134775 8880 125895
45 2700 3.46 52.0 140270 9990 130280
50 3000 323 3.23 48 48.5 145495 11100 134395
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: 8/20/2013
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= 434 4.34 acft 4967 4967.55 ft ft.
Require Volume=
Design Storm WQCV
Ri Required d V Volume= l 16772 ft3 4962 4962.53 ft ft.
Contour
Contour
Elevation (Y-
Contour
Area
Depth Column Not Used Incremental Volume Total Volume Total Volume
values)
Area
p
values)
ft3 ft ft ft. ft3 ft ft3 ft ft3 ft acre-acre feet
4 4,960 960.75 0 000 0.00 0 0 0 0
4 4,961 961.00 1253 025 0.25 104 104 000 0.00
4 4,962 962.00 13074 100 1.00 6119 6223 014 0.14
4,963.00 27577 1.00 19860 26083 0.60
4 4,964 964.00 33565 100 1.00 30491 56574 130 1.30
4 4,965 965.00 34455 100 1.00 33975 90549 208 2.08
4,, 966.00 36675 1.00 35524 126073 2.89
4 4,967 967.00 41176 100 1.00 38865 164938 379 3.79
4 4,968 968.00 47189 100 1.00 44104 209042 480 4.80
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.
APPENDIX C
WATER QUALITY DESIGN COMPUTATIONS (reserved for future use)
APPENDIX D
OPERATIONS AND MAINTENANCE GUIDELINES FOR BIORETENTION PLANTERS (reserved for future use)
APPENDIX E
EROSION CONTROL REPORT
Lakeview Subdivision
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 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.
Lakeview Subdivision
Preliminary Erosion Control Report
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 21
LOT 23
LOT 22 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
TRACT B
TRACT A
LOT 42
B2
OS1
EXTENDED DETENTION BASIN/
DETENTION POND
100-YR VOLUME: 4.34 AC-FT
100-YR WSEL: 4967.55
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
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
100' SPILLWAY
CHRIST CENTER
COMMUNITY
CHURCH
N�. R��������:
B�: D���:
REVIEWED BY:
R. B������
DESIGNED BY:
DRAWN BY:
SCALE:
DATE:
AUGUST 2013
PROJECT:
665-002
S����
O�10S�����
LAKEVIEW SUBDIVISION
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E���������� S�������, I��.
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� P����������� E������� ��
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E���������� S�������, I��.
NOT FOR CONSTRUCTION
REVIEW SET
08/21/13
200 S���� C������ A�����, S���� 010
F��� C������, C������� 80524
E N G I N E E R I N G
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PHONE: 970.221.4158 FAX: 970.221.4159
���.�������������������.���
C600
DRAINAGE EXHIBIT
A. B����
A. B����
1"=50'
NORTH
( IN FEET )
1 ���� = ��.
50 0 50 F���
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 ��
D���
D���
D���
D���
D���
D���
APPROVED:
CHECKED BY:
CHECKED BY:
CHECKED BY:
CHECKED BY:
CHECKED BY:
C��� E�������
W���� & W��������� U������
S��������� U������
P���� & R���������
T������ E�������
E������������ P������
C��� �� F��� C������, C�������
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
K��� ����'������.
C��� ������ ��� ���.
R
BASIN B POND SUMMARY
VOLUME REQ'D (��-��) VOLUME PROVIDED (��-��) POND INVERT 100-YEAR WATER SURFACE
POND SPILL ELEV.
BASIN B 4.34 4.35 4960.75 4967.55 4967.70
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(�����)
C2 C100
2-��
T�
(���)
100-��
T�
(���)
Q10
(���)
Q100
(���)
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 B3-1 2.85 0.63 0.79 11.8 9.3 3.77 18.12
B3 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 18.76 91.28
8/20/20138:52 AM
D:\Projects\665-002\Drainage\Detention\
665-002__Detention Pond_Single-Family ROB.xlsm\Stage_Storage_North Wall ROB
55 3300 3.03 45.5 150135 12210 137925
60 3600 286 2.86 42 42.9 154594 13320 141274
65 3900 2.72 40.8 159279 14430 144849
70 4200 259 2.59 38 38.9 163333 15540 147793
75 4500 2.48 37.2 167567 16650 150917
80 4800 238 2.38 35 35.7 171531 17760 153771
85 5100 2.29 34.4 175360 18870 156490
90 5400 221 2.21 33 33.2 179189 19980 159209
95 5700 2.13 32.0 182297 21090 161207
100 6000 206 2.06 30 30.9 185585 22200 163385
105 6300 2.00 30.0 189189 23310 165879
110 6600 194 1.94 29 29.1 192252 24420 167832
115 6900 1.89 28.4 195811 25530 170281
120 7200 184 1.84 27 27.6 198919 26640 172279
8/20/2013 8:48 AM
D:\Projects\665-002\Drainage\Detention\
665-002__Detention Pond_Single-Family ROB.xlsm\FAA_with church
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
August 20, 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.
8/20/2013 8:44 AM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Tc
B3-2 6.18 0.90 0.72 0.06 1.68 2.813 0.58 0.58 0.73 50%
B3-3 1.96 0.00 0.03 0.01 0.27 1.650 0.28 0.28 0.34 14%
B1&B3-1 5.69 1.32 0.62 0.06 1.09 2.592 0.58 0.58 0.73 51%
B1,B3-1 & B3-2 11.87 2.23 1.34 0.12 2.77 5.406 0.58 0.58 0.73 50%
OS1 0.52 0.05 0.00 0.00 0.00 0.473 0.22 0.22 0.28 9%
OS2 0.19 0.00 0.00 0.00 0.00 0.195 0.15 0.15 0.19 0%
B Overall 18.54 6.03 1.39 0.13 3.05 7.938 0.60 0.60 0.76 54%
EXISTING TOTAL 19.25 4.70 0.34 0.19 0.62 13.396 0.39 0.39 0.49 29%
TOTAL AREA 19.25 6.08 1.39 0.13 3.05 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
August 20, 2013
Composite Runoff Coefficient with Adjustment
8/20/2013 8:44 AM D:\Projects\665-002\Drainage\Hydrology\665-002_Proposed_Rational_Calcs_Single-Family ROB.xlsx\Composite Runoff Coefficient