HomeMy WebLinkAboutBROOKVIEW APARTMENTS - PDP - PDP160003 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
January 6, 2016
BROOKVIEW APARTMENTS
Fort Collins, Colorado
Prepared for:
Old Town Square Properties
5 Old Town Square, Suite 216
Fort Collins, CO 80524
970-221-9332
Prepared by:
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
Phone: 970.221.4158
www.northernengineering.com
Project Number: 1109-001
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
RE: Preliminary Drainage and Erosion Control Report for
Brookview Apartments
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for
your review. This report accompanies Project Development Plan submittal for the proposed
Brookview Apartments development.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM),
and serves to document the stormwater impacts associated with the proposed project. We
understand that review by the City is to assure general compliance with standardized criteria
contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Stephanie Thomas, PE
Project Engineer
Brookview Apartments
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION ................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 1
C. Floodplain.......................................................................................................................................... 3
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 ............................................................................ 5
D. Hydrological Criteria ......................................................................................................................... 6
E. Hydraulic Criteria .............................................................................................................................. 6
F. Floodplain Regulations Compliance .................................................................................................. 6
G. Modifications of Criteria ................................................................................................................... 6
IV. DRAINAGE FACILITY DESIGN .................................................................................... 6
A. General Concept ............................................................................................................................... 6
B. Specific Details (to be provided with Final Design) ........................................................................... 7
V. CONCLUSIONS ........................................................................................................ 8
A. Compliance with Standards .............................................................................................................. 8
B. Drainage Concept .............................................................................................................................. 8
References ......................................................................................................................... 9
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations (to be provided with final design)
APPENDIX C – Erosion Control Report
Brookview Apartments
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph ................................................................................................ 2
Figure 2 – Proposed Site Plan ............................................................................................... 3
Figure 3 – Existing Floodplains ............................................................................................. 4
MAP POCKET:
DR1 - Drainage Exhibit
Brookview Apartments
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. Located in the Northwest ¼ of Section 19, Township 7 North, Range 68 West of the
6th Prime Meridian, City of Fort Collins, County of Larimer, State of Colorado. The site
is a part of Lot 1, Spring Creek Village 2nd.
3. Bounded to the north by existing apartment buildings. Bounded to the south by
Stuart Street. Bounded to the west by existing Stuart Professional Park Condos.
Bounded to the east by existing apartment buildings.
4. No offsite flows are directed into the site.
5. Brookview Apartments is an existing apartment complex. This project encompasses
the additional of a new apartment building to the existing complex.
B. Description of Property
1. The total disturbed site area is 0.81 acres. Total area of site is 1.19 acres.
Brookview Apartments
Preliminary Drainage Report 2
Figure 1 – Aerial Photograph
2. The existing site is comprised of an existing parking lot, curb and gutter, irrigated turf,
numerous conifer and deciduous trees, and berming.
3. Generally, the west half of the site slopes to the existing parking lot, the northeast
quarter of the site slopes to a low point leading to an existing concrete pan, and the
southeast quarter of the site slopes to Stuart Street.
4. A Web Soil Survey provided by the Natural Resources Conservation Service on
September 22, 2015 has identified the on-site soil as 68% Hydrologic Soil Group C and
32% Hydrologic Soil Group B. Hydrologic Soil Group B have a moderate infiltration
rate, and Hydrologic Soil Group C have a slow infiltration rate when thoroughly wet. For
conservative purposes, calculations have been done assuming a Hydrologic Soil Group C
for the site.
5. The proposed project site plan is composed of 2-Story Apartment Building and expanded
parking lot. This site will employ many water quality features and runoff reduction
facilities including porous pavers, and minimized directly connected impervious areas
(MDCIA).
Brookview Apartments
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
6. Existing irrigation facilities are expected on-site. Facilities will need to be relocated
during construction.
7. The project site is within the existing Brookview Apartments development. Additional
runoff from the site will be detained prior to being released and routed through the
existing development, as historic. The proposed project is not requesting a change in
the land use.
C. Floodplain
1. The subject property is not located in a FEMA or City regulatory floodplain.
Brookview Apartments
Preliminary Drainage Report 4
Figure 3 – Existing Floodplains
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The Brookview Apartments project is located within the Spring Creek Drainage Basin,
which is located between the foothills and Timberline Road from east to west and
approximately between Horsetooth Road and Prospect Road from north to south.
B. Sub-Basin Description
1. The historic drainage sub-basin H-A encompasses the western half of the site. This
basin drains north through the existing parking lot to an inlet near the northeast corner
of the parking lot. This inlet releases to Spring Creek. Basin H-A has an existing total
impervious area of 0.28 acres and 100-yr runoff of 3.64 cfs.
2. The historic drainage sub-basin H-B encompasses the northeast quarter of the site.
This basin drains to a small sump surrounded by berming. This sump when filled
overflows to the north. Stormwater runoff is directed to a concrete pan that traverses
the site to an inlet. This inlet releases to Spring Creek. Basin H-B has an existing
total impervious area of 0.0 acres and 100-yr runoff of 0.63 cfs.
3. The historic drainage sub-basin H-C encompasses the southeast quarter of the site.
This basin drains to Stuart Street and is conveyed via curb and gutter east along Stuart
Brookview Apartments
Preliminary Drainage Report 5
Street to a downstream inlet. Basin H-C has an existing total impervious area of 0.01
acres and 100-yr runoff of 0.69 cfs.
4. The total existing runoff from the site during a 100-yr event is 4.96 cfs.
5. The proposed plan will generally maintain these release points. The total proposed
runoff from the site will mimic the total existing runoff from the site.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the Brookview
Apartments project.
B. Four Step Process
The overall stormwater management strategy employed with Brookview Apartments
project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on
receiving waters. The following is a description of how the proposed development has
incorporated each step.
Step 1 – Employ Runoff Reduction Practices
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low Impact Development (LID) strategies including:
Providing large vegetated open areas throughout the site to reduce the overall
impervious area and to minimize directly connected impervious areas (MDCIA).
Providing permeable paver areas to increase time of concentration promote infiltration
and provide water quality.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
Additional water quality has not been provided within the detention pond, with guidance
from the City. It was determined that water quality treatment within the detention pond
would mostly be treating rooftop stormwater runoff. Since rooftops generally do not
produce the same amount of contamination as parking lots, it was determined that water
quality treatment would be unnecessary.
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property. This project discharges to
existing an existing parking lot and concrete pan.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
A portion of the existing parking lot will be treated for water quality via permeable
pavers. This will improve the runoff from the existing condition.
C. Development Criteria Reference and Constraints
1. All drainage facilities proposed with the Brookview Apartments 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.
Brookview Apartments
Preliminary Drainage Report 6
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 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. As of this report,
pervious pavers have not been added to Table RO-11. A coefficient of runoff of 0.40
was assumed for the pervious pavers. This is a value published by Advanced
Pavement Technology.
3. The Rational Formula-based Modified 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. The first event analyzed is the “Minor,” or “Initial” Storm, which has a 2-
year recurrence interval. The second event considered is the “Major Storm,” which
has a 100-year recurrence interval. The third 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, generally, the west half of the site slopes to the existing parking
lot, the northeast quarter of the site slopes to a low point leading to an existing
concrete pan, and the southeast quarter of the site slopes to Stuart Street..
2. All drainage facilities proposed with the Brookview Apartments 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 previously, the subject property is not located within a FEMA regulatory
floodplain.
4. The Brookview Apartments project does not propose to modify any natural
drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, all structures are located outside of any FEMA 100-year
floodplain, and thus are not subject to any floodplain regulations.
G. Modifications of Criteria
1. The proposed development is not requesting any modifications to criteria at this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the Brookview Apartments drainage design are to maintain the
allowable storm runoffs as outlined by the FCSCM.
2. A list of tables and figures used within this report can be found in the Table of
Brookview Apartments
Preliminary Drainage Report 7
Contents at the front of the document. The tables and figures are located within the
sections to which the content best applies.
3. The Brookview Apartments project is divided the site into three (3) drainage sub-
basins, designated as Basins A, B, and C. These basins correspond to the historic
sub-basins H-A, H-B, and H-C. Though the areas of the proposed basins may have
changed from the historic, the outfall location was maintained. The drainage patterns
anticipated for each basin and sub-basin are further described below.
Basin A
Basin A consists of a proposed parking lot, permeable pavers, sidewalks, and existing
vegetation. Runoff from this basin drains to the proposed parking lot. During a 2-year
event, approximately 30% of the runoff is expected to be captured in the permeable
pavers. During a 100-yr event, runoff will continue north through the existing parking
lot to an existing inlet that outfalls to Spring Creek. Basin A has a proposed total
impervious area of 0.32 acres (0.04 acres more than the existing condition) and 100-
yr runoff of 4.74 cfs (1.1 cfs more than the existing condition).
Basin B
Basin B consists of the proposed building, detention pond, and existing vegetation.
Runoff from the west and south side of the rooftops will be conveyed via roofdrain to
the detention pond. Runoff from the east and north side of the rooftops will be
released at grade and overland flow to the ponds. Basin B has a proposed total
impervious area of 0.18 acres (0.18 acres more than the existing condition) and 100-
yr runoff of 3.13 cfs (2.50 cfs more than the existing condition). Developed runoff
will be detained in the detention pond and released at the historic 2-yr rate of 0.14
cfs.
Basin C
Basin C consists of the proposed parking lot, sidewalk, and existing vegetation.
Runoff from this basin is captured and conveyed via curb and gutter east along Stuart
Street. Basin C has a proposed total impervious area of 0.03 acres (0.02 acres more
than the existing condition) and 100-yr runoff of 0.66 cfs (0.03 cfs less than the
existing condition).
The total runoff, including detention release, for the proposed site during a 100-yr
event is 5.54 cfs. The proposed runoff total 0.58 cfs more than the existing condition.
Due to the proximity of the site to Spring Creek, the effect of this additional runoff is
considered negligible. Downstream facilities are not expected to be impacted by this
project.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details (to be provided with Final Design)
1. All storm sewers were modeling using Hydraflow Storm Sewers Extension for
Autodesk AutoCAD.
2. Detention pond orifice plate were completed with an Excel spreadsheet.
Brookview Apartments
Preliminary Drainage Report 8
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the Brookview Apartments project complies with
the City of Fort Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with the Brookview Apartments project complies with
the City of Fort Collins’ Master Drainage Plan for the Spring Creek Drainage Basin.
3. There are no regulatory floodplains associated with the development.
4. The drainage plan and stormwater management measures proposed with the
development are compliant with all applicable State and Federal regulations governing
stormwater discharge.
5. The site achieves the requirements set forth by the City of Fort Collins for Low Impact
Development (LID) by providing 32% of proposed paved areas as permeable pavers
and providing 53% of total impervious areas as being treated through an LID
treatment and/or grass buffers.
B. Drainage Concept
1. The drainage design proposed with this project will effectively comply with City, State,
and Federal regulations. Proposed stormwater facilities will limit any potential
damage or erosion associated with its stormwater runoff. All existing downstream
drainage facilities are expected to not be impacted negatively by this development
2. The drainage design is anticipated to be fairly conservative. We have omitted any
runoff reduction that will manifest due to infiltration from pervious pavement. This is
currently unable to be calculated with available soils data.
Brookview Apartments
Preliminary Drainage Report 9
References
1. 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.
2. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
4. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
APPENDIX A
HYDROLOGIC COMPUTATIONS
Brookview Apartments
CHARACTER OF SURFACE
1
:
Runoff
Coefficient
Percentage
Impervious Project: Brookview Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: S. Thomas
Asphalt ……....……………...……….....…...……………….………………………………………………………….. 0.95 100% Date: December 30, 2015
Concrete …….......……………….….……….………………..….…………………………………………………….. 0.95 90%
Gravel (packed) ……….…………………….….…………………………..………………………………………….. 0.50 40%
Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90%
Pavers…………………………...………………..……………………………………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….. 0.15 0%
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….. 0.25 0%
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Sub-Basin ID
Sub-
BasinBasin
Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Roofs
(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
Brookview Apartments
Overland Flow, Time of Concentration:
Brookview Apartments
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)
1 H-A No 0.52 0.52 0.65 178 1.69% 12.2 12.2 9.5 126 3.17% 3.56 0.6 12.8 12.8 10.1
2 H-B No 0.25 0.25 0.31 85 2.71% 10.5 10.5 9.7 0 N/A N/A N/A 10.5 10.5 9.7
3 H-C No 0.28 0.28 0.34 48 9.17% 5.1 5.1 4.7 162 0.93% 1.92 1.4 6.5 6.5 6.1
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
Brookview Apartments
Rational Method Equation: Project: Brookview Apartments
Calculations By:
Date:
Rainfall Intensity:
1 H-A 0.73 13 13 10 0.52 0.52 0.65 2.02 3.45 7.72 0.76 1.30 3.64
2 H-B 0.25 11 11 10 0.25 0.25 0.31 2.17 3.71 7.88 0.14 0.24 0.63
3 H-C 0.21 7 7 6 0.28 0.28 0.34 2.60 4.44 9.31 0.15 0.26 0.69
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
HISTORIC RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Sub-Basin(s)
S. Thomas
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
December 30, 2015
Intensity,
i10
(in/hr)
C10
Q = C f ( C )( i )( A )
12/30/2015 9:05 AM D:\Projects\1109-001\Drainage\Hydrology\1109-001_Historic Rational Calcs.xlsx\Runoff
Brookview Apartments
CHARACTER OF SURFACE1:
Runoff
Coefficient
Percentage
Impervious Project: Brookview Apartments
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: S. Thomas
Asphalt ……....……………...……….....…...……………….………………………………………………………….. 0.95 100% Date: 12/30/15
Concrete …….......……………….….……….………………..….…………………………………………………….. 0.95 90%
Gravel (packed) ……….…………………….….…………………………..………………………………………….. 0.50 40%
Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90%
Pavers…………………………...………………..……………………………………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil
Flat <2% ……………………………………………………………………………………………………………… 0.10 0%
Average 2% to 7% ………………………………………………………………………………………………….. 0.15 0%
Steep >7% …………………………………………………………………………………………………………… 0.20 0%
Clayey Soil
Flat <2% ……………………………………………………………………………………………………………… 0.20 0%
Average 2% to 7% ………………………………………………………………………………………………….. 0.25 0%
Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf
= 1.00 10-year Cf = 1.00 100-year C
f = 1.25
Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11
Sub-Basin ID
Sub-
BasinBasin
Area
(ac)
Area of
Existing
Asphalt
(ac)
Area of
Proposed
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Pavers
(ac)
Area of
Roofs
(ac)
Soil Type and Average
Slope
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
Brookview Apartments
Overland Flow, Time of Concentration:
Brookview Apartments
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)
1 A No 0.60 0.60 0.75 77 2.34% 6.2 6.2 4.3 194 3.51% 3.74 0.9 7.0 7.0 5.2
2 B No 0.58 0.58 0.73 121 4.55% 6.4 6.4 4.6 0 N/A N/A N/A 6.4 6.4 5.0
3 C No 0.41 0.41 0.51 46 9.57% 4.1 4.1 3.5 170 1.00% 2.00 1.4 5.6 5.6 5.0
* Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins.
PROPOSED TIME OF CONCENTRATION COMPUTATIONS
Brookview Apartments
Rational Method Equation: Project: Brookview Apartments
Calculations By:
Date:
Rainfall Intensity:
1 A 0.63 7 7 5 0.60 0.60 0.75 2.52 4.31 9.95 0.96 1.64 4.74
2 B 0.43 6 6 5 0.58 0.58 0.73 2.67 4.56 9.95 0.67 1.15 3.13
3 C 0.13 6 6 5 0.41 0.41 0.51 2.76 4.72 9.95 0.15 0.25 0.66
December 30, 2015
Intensity,
i10
(in/hr)
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
PROPOSED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Sub-Basin(s)
S. Thomas
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Q = C f ( C )( i )( A )
12/30/2015 9:04 AM D:\Projects\1109-001\Drainage\Hydrology\1109-001_Rational Calcs.xlsx\Runoff
Hydrologic Soil Group—Larimer County Area, Colorado
(Brookview Apartments)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/22/2015
Page 1 of 4
4490300 4490310 4490320 4490330 4490340 4490350 4490360 4490370 4490380 4490390
4490300 4490310 4490320 4490330 4490340 4490350 4490360 4490370 4490380 4490390
495220 495230 495240 495250 495260 495270 495280 495290 495300 495310 495320 495330 495340 495350 495360
495220 495230 495240 495250 495260 495270 495280 495290 495300 495310 495320 495330 495340 495350 495360
40° 33' 51'' N
105° 3' 23'' W
40° 33' 51'' N
105° 3' 17'' W
40° 33' 48'' N
105° 3' 23'' W
40° 33' 48'' N
105° 3' 17'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 30 60 120 180
Feet
0 5 10 20 30
Meters
Map Scale: 1:667 if printed on A landscape (11" x 8.5") 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
73 Nunn clay loam, 0 to 1
percent slopes
C 0.9 67.9%
101 Stoneham loam, 1 to 3
percent slopes
B 0.4 32.1%
Totals for Area of Interest 1.3 100.0%
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
Hydrologic Soil Group—Larimer County Area, Colorado Brookview Apartments
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/22/2015
Page 3 of 4
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Brookview Apartments
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/22/2015
Page 4 of 4
APPENDIX B
HYDRAULIC COMPUTATIONS (TO BE PROVIDED WITH FINAL REPORT)
APPENDIX C
EROSION CONTROL REPORT
Brookview Apartments
Preliminary 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 CS2 of the Utility Plans. The Utility
Plans at final design will also contain a full-size Erosion Control Plan 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 any existing
Development Agreement(s) of record, as well as the Development Agreement, to be recorded prior
to issuance of the Development Construction Permit. 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,
before commencing any earth disturbing 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
DR1 – OVERALL DRAINAGE EXHIBIT
T T T T
T
T
T T T
T T T
T
EAST STUART STREET
T T T
T T
T T
T T
G
BANK OF 21
GAS METERS
G
G
H-A H-B
H-C
1
EAST STUART STREET
EXISTING
BUILDING
EXISTING
BUILDING
EXISTING
BUILDING
STUART
PROFESSIONAL
PARK CONDOS
3RD
These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
200 South College Avenue, Suite 010
Fort Collins, Colorado 80524
N O R T H E RN
PHONE: 970.221.4158 FAX: 970.221.4159
www.northernengineering.com
DR2
NORTH
CityDate Engineer
Date
Date
Date
Date
Stormwater Utility
Parks & Recreation
Traffic Engineer
Date
Water & Wastewater Utility
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
X
X
X
X
X
X
X X
X
X
X
X
G
BANK OF 21
GAS METERS
G
G
1
2
B
A
C
1
EAST STUART STREET
EXISTING
BUILDING
EXISTING
BUILDING
EXISTING
BUILDING
STUART
PROFESSIONAL
PARK CONDOS
3RD
PROPOSED
BUILDING
PROPOSED
BUILDING
RETAINING WALL
PROPOSED
STORM DRAIN
PROPOSED SMALL
AREA INLET
PROPOSED SMALL
AREA INLET
PROPOSED
UNDERDRAIN
PROPOSED
STORM DRAIN
These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
200 South College Avenue, Suite 010
Fort Collins, Colorado 80524
N O R T H E RN
PHONE: 970.221.4158 FAX: 970.221.4159
www.northernengineering.com
DR1
NORTH
CityDate Engineer
Date
Date
Date
Date
Stormwater Utility
Parks & Recreation
Traffic Engineer
Date
Water & Wastewater Utility
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
Environmental Planner
LEGEND:
5013
PROPOSED CONTOUR 93
EXISTING CONTOUR
PROPERTY BOUNDARY
EXISTING STORM SEWER
NOTES:
FLOW PATH
DRAINAGE BASIN BUBBLE
A
DESIGN POINT A
BASIN BOUNDARY
PROPOSED STORM SEWER
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100 2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
1 A 0.63 0.60 0.75 7.0 5.2 0.96 4.74
2 B 0.43 0.58 0.73 6.4 5.0 0.67 3.13
3 C 0.13 0.41 0.51 5.6 5.0 0.15 0.66
Environmental Planner
LEGEND:
5013
PROPOSED CONTOUR 93
EXISTING CONTOUR
PROPERTY BOUNDARY
EXISTING STORM SEWER
NOTES:
FLOW PATH
DRAINAGE BASIN BUBBLE
A
DESIGN POINT A
BASIN BOUNDARY
PROPOSED STORM SEWER
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
Survey Area Data: Version 9, Sep 22, 2014
Soil map units are labeled (as space allows) for map scales 1:50,000
or larger.
Date(s) aerial images were photographed: Apr 22, 2011—Apr 28,
2011
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor shifting
of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(Brookview Apartments)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/22/2015
Page 2 of 4
S. Thomas
December 30, 2015
Design
Point
Sub-Basin
Overland Flow Gutter/Pipe Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
12/30/2015 9:04 AM D:\Projects\1109-001\Drainage\Hydrology\1109-001_Rational Calcs.xlsx\Tc
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Impervious
Area (ac)
Basin Treated
thru LID?
Percent of
Basin Treated
with LID
Impervious
Area Treated
with LID (ac)
LID Treated
Impervious
Area (ac)
A 0.63 0.15 0.07 0.08 0.04 0.01 Clayey | Average 2% to 7% 0.29 0.60 0.60 0.75 50% 0.32 YES 30% 0.09 0.09
B 0.43 0.00 0.00 0.02 0.00 0.19 Clayey | Average 2% to 7% 0.23 0.58 0.58 0.73 43% 0.18 YES 100% 0.18 0.18
C 0.13 0.00 0.01 0.02 0.00 0.00 Clayey | Average 2% to 7% 0.10 0.41 0.41 0.51 21% 0.03 NO 0% 0.00 0.00
TOTAL 1.20 0.15 0.08 0.12 0.04 0.19 Clayey | Average 2% to 7% 0.62 0.57 0.57 0.72 44% 0.53 NO 0.28
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
Permeable Pavement LID Treatment
Total Pavement, including Existing (ac)= 0.27 Total Impermeable Area(ac)= 0.53
Total Proposed Pavement (ac)= 0.11 Total Impermeable Area Treated with LID(ac)= 0.28
Total Permeable Pavement (ac)= 0.04 Percent Treated with LID= 53%
LID Requirements
Composite Runoff Coefficient with Adjustment
PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
LID Treatment
12/30/2015 9:03 AM D:\Projects\1109-001\Drainage\Hydrology\1109-001_Rational Calcs.xlsx\Composite C
S. Thomas
December 30, 2015
Design
Point
Sub-Basin
Overland Flow Gutter/Pipe Flow Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
-
=
12/30/2015 9:05 AM D:\Projects\1109-001\Drainage\Hydrology\1109-001_Historic Rational Calcs.xlsx\Tc
% Imperv.
Impervious
Area (ac)
Basin
Treated thru
LID?
LID Treated
Impervious Area
(ac)
H-A 0.73 0.21 0.04 0.07 0.00 0.00 Clayey | Average 2% to 7% 0.40 0.52 0.52 0.65 38% 0.28 NO 0.00
H-B 0.25 0.00 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.25 0.25 0.25 0.31 0% 0.00 NO 0.00
H-C 0.21 0.01 0.00 0.00 0.00 0.00 Clayey | Average 2% to 7% 0.21 0.28 0.28 0.34 4% 0.01 NO 0.00
TOTAL 1.20 0.22 0.04 0.07 0.00 0.00 Clayey | Average 2% to 7% 0.86 0.42 0.42 0.52 24% 0.28 NO 0.00
1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis
Composite Runoff Coefficient with Adjustment LID Treatment
EXISTING COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
12/30/2015 9:05 AM D:\Projects\1109-001\Drainage\Hydrology\1109-001_Historic Rational Calcs.xlsx\Composite C