HomeMy WebLinkAboutELIZABETH SUBDIVISION - PDP - PDP160046 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTCOLORADO CIVIL GROUP, INC.
DRAINAGE REPORT
FOR THE
ELIZABETH SUBDIVISION
CITY OF FORT COLLINS
JULY 2017
COLORADO CIVIL GROUP, INC. 5110 Granite St, Unit D Loveland, Colorado 80538 970-278-0029
July 26, 2017
Ms. Heather McDowell, PE
Water Utilities Engineering
City of Fort Collins
281 N College Avenue
Fort Collins, CO 80524
Re: Elizabeth Subdivision
Project No. 0036.0002.00
Dear Ms. McDowell,
We are pleased to submit this Final Drainage Report for the Elizabeth Subdivision. This report
was prepared based on current City of Fort Collins and UDFCD storm drainage criteria. In
addition, Chris Messersmith met with Wes Lamarque at the project site on February 14, 2017 to
discuss the project and the associated drainage design. Changes to the drainage design were
made based on that field meeting.
Please let me know if you have any questions or comments.
Sincerely,
COLORADO CIVIL GROUP, INC.
Jamie K. Galyon, PE
Elizabeth Subdivision Final Drainage Report July 2017
i
Table of Contents
1 Project Summary ...................................................................................................................................................... 1
1.1 Site Location ..................................................................................................................................................... 1
1.2 Project Description ........................................................................................................................................... 2
2 Project Imperviousness ............................................................................................................................................ 2
3 Proposed Drainage Facility Design ........................................................................................................................... 4
3.1 Four‐Step Process ............................................................................................................................................. 4
3.1.1 Step 1: Runoff Reduction .......................................................................................................................... 4
3.1.2 Step 2: Treat and Slowly Release Runoff .................................................................................................. 4
3.1.3 Step 3: Stabilize Drainageways ................................................................................................................. 5
3.1.4 Step 4: Implementation of Source Controls ............................................................................................. 5
3.2 BMP Selection Considerations .......................................................................................................................... 5
3.2.1 Soils ........................................................................................................................................................... 5
3.2.2 Watershed Size ......................................................................................................................................... 5
3.2.3 Base Flows ................................................................................................................................................ 6
3.3 BMP Design ....................................................................................................................................................... 6
3.3.1 Grass Swale ............................................................................................................................................... 6
3.3.2 Dry Well Detention Area .......................................................................................................................... 6
4 Hydrologic Analysis ................................................................................................................................................... 8
5 Conclusions ............................................................................................................................................................... 9
Appendix A: Existing Soil Properties ................................................................................................................................. A
Appendix B: BMP Sizing and Hydrology Calculations ...................................................................................................... B
Appendix C: Erosion Control Plan and Drainage Plan ..................................................................................................... C
Index of Figures and Tables
Figure 1‐1: Vicinity Map ................................................................................................................................................... 1
Table 2‐1: UDFCD Percent Impervious Recommendations .............................................................................................. 2
Table 2‐2: Existing Condition Imperviousness .................................................................................................................. 3
Table 2‐3: Proposed Condition Imperviousness ............................................................................................................... 3
Table 3‐1: LID Treatment .................................................................................................................................................. 8
Elizabeth Subdivision Final Drainage Report July 2017
1
1 Project Summary
1.1 Site Location
The Elizabeth Subdivision site is located in the Southeast Quarter of Section 13,
Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins,
County of Larimer, Colorado. The site is bounded on the north by East Elizabeth
Street and on the west, south, and east by neighboring single-family residential lots. A
vicinity map is presented in Figure 1-1. The project area is generally located at
Latitude 40° 34’27” and Longitude -105° 3’47”. The site is part of the Spring Creek
drainage basin and is included as part of the Spring Creek Master Drainage Plan.
Figure 1-1: Vicinity Map
PROJECT
AREA
S LEMAY AVE
MORGAN ST
S STOVER ST
E ELIZABETH ST
GARFIELD ST
LAUREL
ELEMENTARY
SCHOOL
E LAUREL ST
E PITKIN ST
Elizabeth Subdivision Final Drainage Report July 2017
2
1.2 Project Description
The Elizabeth Subdivision project includes the replatting of two parcels (parcels
9713400012 and 9713400006). The northwest lot will be increased from 5,000 square
feet to 7,840 square feet. A new single-family home will be built on the southeast lot.
The construction of the single-family home will include a driveway from Elizabeth Street
and off-street parking. The parking lot for the commercial building will be modified to
meet City of Fort Collins setback requirements and to accommodate the driveway for
the single-family home.
The project site is located within Zone‘X’ of Community-Panel Number 08069C0979H,
revised May 2, 2012. Zone‘X’is defined as“Areas determined to be outside the
0.2% annual chance floodplain.” A portion of the referenced map can be found in
Appendix A of this report.
2 Project Imperviousness
In order to determine the type of stormwater detention and treatment necessary for the
project site, the existing and proposed imperviousness were calculated and compared. The
Urban Drainage and Flood Control District (UDFCD) recommendations for percent impervious
were used to determine the overall imperviousness and are presented in Table 2-1.
Table 2-1: UDFCD Percent Impervious Recommendations
Land Use of Surface
Characteristics
Percentage
Imperviousness
Paved Streets 100%
Drives and Walks 90%
Roofs 90%
Landscaped Areas 2%
The imperviousness of the site was calculated for existing and proposed conditions. The
existing condition represents the current project site with no improvements or changes. The
proposed condition represents the project site with the proposed improvements. The
resulting areas and the associated imperviousness are presented in Table 2-2 and Table 2-3.
Elizabeth Subdivision Final Drainage Report July 2017
3
Table 2-2: Existing Condition Imperviousness
Area Identification
Basin Categories and Areas (SF)
Percent
Impervious
Landscaped
Areas Streets
Drives,
Walks, &
Roofs
2% 100% 90%
Commercial Building 1,231 90%
Accessory Structure 514 90%
Concrete Walks 682 90%
Asphalt Parking 5,003 100%
Elizabeth Street 1,889 175 99%
Landscaped Area 23,855 2%
TOTAL 23,855 6,892 2,603 29%
Table 2-3: Proposed Condition Imperviousness
Area Identification
Basin Categories and Areas (SF)
Percent
Impervious
Landscaped
Areas Streets
Drives,
Walks, &
Roofs
2% 100% 90%
Existing
Commercial Building 1,231 90%
Shed 514 90%
Concrete Walks 682 90%
Parking Lot 2,753 100%
Elizabeth Street 1,889 175 99%
Proposed Commercial
Proposed Concrete 667 90%
Proposed Asphalt 1,253 100%
Proposed Residential
Proposed Residence 3,807 90%
Future Garage Addition 83 90%
Proposed Concrete 150 90%
Proposed Asphalt 2,589 100%
Landscaped Area 17,558 2%
TOTAL 17,558 8,483 7,309 46%
Elizabeth Subdivision Final Drainage Report July 2017
4
The assumed imperviousness of Spring Creek drainage basin according to the Spring Creek
Master Drainage Plan is 53%. Since the project site remains under 53% impervious,
quantity detention is not required. Standard water quality treatment is required and
described in the following sections.
3 Proposed Drainage Facility Design
This section of the report presents the design of drainage facilities related to Elizabeth
Subdivision. The drainage design has been explained as it pertains to the “Four-Step
Process for Stormwater Quality Management” as outlined by UDFCD and adopted by the
City of Fort Collins.
3.1 Four‐Step Process
3.1.1 Step 1: Runoff Reduction
The first step in stormwater quality management is to reduce runoff peaks,
volumes, and pollutant loads from urbanizing areas by implementing Low Impact
Development (LID) strategies. LID practices include reducing unnecessary
impervious areas and routing runoff from impervious surfaces over permeable
areas to slow runoff and promote infiltration.
The Elizabeth Subdivision project does include an increase in impervious area
with the construction of the single family home and driveway. Runoff from the
new impervious areas is routed through the grass swale or landscaped area to
promote infiltration.
3.1.2 Step 2: Treat and Slowly Release Runoff
After reducing the runoff from a site, the second step in stormwater quality
management is to capture and slowly release a Water Quality Capture Volume
(WQCV). WQCV facilities may include bioretention, extended detention basins,
sand filters, constructed wetland ponds, and retention ponds.
Although there is no detention pond proposed as part of the Elizabeth
Subdivision project, the majority of the stormwater runoff is routed to the dry
well detention area. The dry well detention area allows for infiltration and slow
runoff.
Elizabeth Subdivision Final Drainage Report July 2017
5
3.1.3 Step 3: Stabilize Drainageways
Although steps 1 and 2 help to minimize the effects of runoff on downstream
drainageways, natural drainageways are often subject to bed and bank erosion
due to increases in the frequency, rate, duration, and volume of runoff. Step 3
includes measures to prevent drainageway erosion.
There are no drainageways on the Elizabeth Subdivision site. By implementing
steps 1 and 2, the project site does its part to reduce drainageway erosion
downstream.
3.1.4 Step 4: Implementation of Source Controls
The final step in stormwater quality management is source control. Site specific
needs such as material storage or other site operations require consideration of
targeted source control Best Management Practices (BMPs). These BMPs are
shown on the Erosion Control Plan (Appendix C) and explained in the Erosion
Control Report (ECR) for the project site.
3.2 BMP Selection Considerations
The following sections discuss the considerations for determining the best BMP or LID
solution to implement for the project.
3.2.1 Soils
The existing soil condition on the project site must be considered when
designing BMPs. Soils with good permeability provide opportunities for
infiltration of runoff and are well-suited for infiltration-based BMPs such as dry
wells, permeable pavement, and grass swales. The soil on the Elizabeth
Subdivision project site are in Hydrologic Soil Group B, which is defined as
soils having a moderate infiltration when thoroughly wet. For this reason,
infiltration based BMPs were considered a good option for the project site. Soil
information for the site may be found in Appendix A.
3.2.2 Watershed Size
The contributing drainage area is an important consideration for the design of
BMPs. For a small site, such as Elizabeth Subdivision, it is not feasible to
Elizabeth Subdivision Final Drainage Report July 2017
6
design a detention pond that releases the WQCV over a 40-hour drain time due
to the small orifices that would be required. Instead, it is recommended that
small watersheds use filtering BMPs, such as dry well detention.
3.2.3 Base Flows
BMPs such as constructed wetlands ponds, retention ponds, and wetland
channels require a base flow to prevent the BMPs from becoming dry and
unable to support wetland vegetation. No base flow exists for the Elizabeth
Subdivision project site, so no BMPs that require a base flow were considered
for the site.
3.3 BMP Design
3.3.1 Grass Swale
Grass swales are vegetated channels with low longitudinal slopes and broad
cross-sections that convey flow in a slow and shallow manner to facilitate
sedimentation.
For the Elizabeth Subdivision, the runoff from a portion of Basin D is conveyed
to the dry well detention area by a grass swale. The UDFCD provides
guidelines and tools for the design of grass swales, which have been used for
the Elizabeth Subdivision project. The sizing calculations have been included in
Appendix B.
3.3.2 Dry Well Detention Area
Dry well detention utilizes bioretention to reduce the transportation of pollutants
to downstream receiving waters through sedimentation, filtering, adsorption,
evapotranspiration, and biological uptake of constituents. In addition, a dry well
is provided to aid in the infiltration of storm water runoff. The UDFCD
equations for the calculation of Water Quality Capture Volume (WQCV) have
been used for the Elizabeth Subdivision project and are presented below. The
basin sizing calculations have been included in Appendix B.
The WQCV is calculated based on the imperviousness of the project site and
the drain time. The Elizabeth Subdivision detention area will drain through the
Elizabeth Subdivision Final Drainage Report July 2017
7
dry well and by overtopping the driveway to flow to Elizabeth Street. The drain
time for these methods of drainage is unknown. The most conservative drain
time presented by UDFCD, 40 hours, has been used in the sizing calculations
for the Elizabeth Subdivision.
WQCV = a(0.91I 3-1.19I 2+0.78I)
Where: WQCV = Water Quality Capture Volume (watershed inches)
a = Drain Time Coefficient (1.0 for a drain time of 40 hours)
I = Imperviousness, %/100 (0.46 for the Elizabeth Subdivision)
For the Elizabeth Subdivision, the resulting WQCV is 0.20 watershed inches.
With a total area of 33,530 square feet, the total WQCV required is 543 cubic
feet or 0.01 acre-feet. The proposed detention area has a volume of 0.015
acre-feet. At that volume, ponding will occur in the southeastern corner of the
commercial parking lot. The depth of ponding will be approximately 2 inches.
Runoff above that volume will overtop the residential lot driveway and flow to
Elizabeth Street through the proposed sidewalk chase.
The City of Fort Collins LID ordinance requires that for 75% of all newly added
or modified impervious areas be treated by LID techniques. Based on
conversations with the City of Fort Collins Engineering Department, no LID
systems are required for the single family residence lot because the ongoing
maintenance and inspections by erosion control inspectors can be difficult on a
private lot. For that reason, only the new or modified impervious area on the
commercial lot has been considered for the requirement of 75% treatment by
LID, although a portion of the residential lot, including all the impervious area,
is also treated by the dry well detention area. A small portion of the new or
modified impervious area on the commercial lot flows directly to Elizabeth Street
and is therefore not treated by the dry well detention area. Table 3-1 shows
how the LID requirements have been met for this project.
Elizabeth Subdivision Final Drainage Report July 2017
8
Table 3-1: LID Treatment
75% ON‐SITE TREATMENT BY LID FOR COMMERCIAL LOT
PROJECT AREA
TOTAL COMMERCIAL AREA (INCLUDING ROW) 10,162 SF
NEW COMMERCIAL IMPERVIOUS AREA 1,920 SF
REQUIRED MINIMUM AREA TO BE TREATED BY LID
(75% OF NEW COMMERCIAL IMPERVIOUS AREA) 1,440 SF
NEW IMPERVIOUS AREA TREATED BY LID 1,735 SF
PERCENT OF NEW IMPERVIOUS AREA TREATED BY LID 90 %
4 Hydrologic Analysis
Per City of Fort Collins criteria, the Rational Formula Method was used for the hydrologic
analysis of the Elizabeth Subdivision project site. The rainfall intensities from the Fort
Collins Amendments to the UDFCD manual Table RA-7 were used for the calculation of
runoff for a 100-year storm event.
Developed drainage basins were delineated based on existing and proposed improvements.
The proposed drainage patterns match the existing drainage patterns. The Final Drainage
Plan is located in Appendix C. Descriptions of the delineated basins are listed below. The
physical parameters and hydraulic calculations for the basins can be found in Appendix B.
Basin A consists of Elizabeth Street and sidewalk. Although an ADA bypass sidewalk will
be constructed within this basin, the area of the new sidewalk is currently asphalt parking
lot, so there are no changes in imperviousness or drainage pattern proposed for this basin.
Runoff from Basin A remains in Elizabeth Street and exits the site at Design Point A.
Basin B consists of a portion of the existing commercial building and landscaped area. The
basin drains directly to Elizabeth Street at Design Point B, which is consistent with the
existing drainage pattern.
Basin C consists of the landscaped area east of the proposed residential driveway. The
basin drains to a grass swale and then to Elizabeth Street through a proposed sidewalk
chase at Design Point C. From the existing condition to the proposed condition, the
Elizabeth Subdivision Final Drainage Report July 2017
9
imperviousness for the basin is reduced by removal of existing parking lot pavement and
replacement with landscaped area. The sizing calculations for the swale and sidewalk chase
can be found in Appendix B.
Basin D includes a portion of the commercial building, single family residence, existing
accessory structure including future addition, commercial parking lot, and residential driveway.
The entire basin drains to the dry well detention area between the residential driveway and
the commercial parking lot. As the detention area fills, overflow will fill the grass swale
between the commercial parking lot and the residential driveway, and ultimately over the
residential driveway at Design Point D to Basin C and the sidewalk chase into Elizabeth
Street. The depth of flow over the residential driveway will be less than 2 inches, as shown
in the weir capacity calculations presented in Appendix B.
Basin D1 is a sub-basin of Basin D which was delineated for the purpose of sizing the
swale that runs behind the accessory structure. The swale sizing is presented in Appendix
B.
Basin E includes the landscaped area surrounding the single family residence on the east
side. The basin flows to the east to Design Point E, which mirrors the existing drainage
pattern.
Basin F includes the landscaped area south of the single family residence. The basin flows
to the southeast to Design Point F, which mirrors the existing drainage pattern.
Basin G includes the single family residence. Flow from the roof drains will be directed to
the culvert under the residential driveway at Design Point G, where it will enter the dry well
detention area. The capacity of the culvert has been analyzed and is presented in Appendix
B.
5 Conclusions
The final drainage design for the Elizabeth Subdivision project, as outlined in this Drainage
Report, meets or exceeds the drainage criteria set forth by the City of Fort Collins and the
UDFCD. The design safely and effectively collects and conveys runoff per the applicable
criteria and mimics existing drainage patterns where possible.
Elizabeth Subdivision Final Drainage Report July 2017
A
Appendix A: Existing Soil Properties
Drainage Class—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 1 of 3
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
494640 494650 494660 494670 494680 494690 494700 494710 494720
494640 494650 494660 494670 494680 494690 494700 494710 494720
40° 34' 27'' N
105° 3' 48'' W
40° 34' 27'' N
105° 3' 44'' W
40° 34' 23'' N
105° 3' 48'' W
40° 34' 23'' N
105° 3' 44'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 25 50 100 150
Feet
0 5 10 20 30
Meters
Map Scale: 1:613 if printed on A portrait (8.5" x 11") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
Excessively drained
Somewhat excessively
drained
Well drained
Moderately well drained
Somewhat poorly drained
Poorly drained
Very poorly drained
Subaqueous
Not rated or not available
Soil Rating Lines
Excessively drained
Somewhat excessively
drained
Well drained
Moderately well drained
Somewhat poorly drained
Poorly drained
Very poorly drained
Subaqueous
Not rated or not available
Soil Rating Points
Excessively drained
Somewhat excessively
drained
Well drained
Moderately well drained
Somewhat poorly drained
Poorly drained
Very poorly drained
Subaqueous
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
Drainage Class
Drainage Class— Summary by Map Unit — Larimer County Area, Colorado (CO644)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
94 Satanta loam, 0 to 1
percent slopes
Well drained 0.4 53.0%
95 Satanta loam, 1 to 3
percent slopes
Well drained 0.4 47.0%
Totals for Area of Interest 0.8 100.0%
Description
"Drainage class (natural)" refers to the frequency and duration of wet periods under
conditions similar to those under which the soil formed. Alterations of the water
regime by human activities, either through drainage or irrigation, are not a
consideration unless they have significantly changed the morphology of the soil.
Seven classes of natural soil drainage are recognized-excessively drained,
somewhat excessively drained, well drained, moderately well drained, somewhat
poorly drained, poorly drained, and very poorly drained. These classes are defined
in the "Soil Survey Manual."
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Drainage Class—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 3 of 3
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 1 of 4
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
494640 494650 494660 494670 494680 494690 494700 494710 494720
494640 494650 494660 494670 494680 494690 494700 494710 494720
40° 34' 27'' N
105° 3' 48'' W
40° 34' 27'' N
105° 3' 44'' W
40° 34' 23'' N
105° 3' 48'' W
40° 34' 23'' N
105° 3' 44'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 25 50 100 150
Feet
0 5 10 20 30
Meters
Map Scale: 1:613 if printed on A portrait (8.5" x 11") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at 1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil line
placement. The maps do not show the small areas of contrasting
soils that could have been shown at a more detailed scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more accurate
calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as of
the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Hydrologic Soil Group
Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
94 Satanta loam, 0 to 1
percent slopes
B 0.4 53.0%
95 Satanta loam, 1 to 3
percent slopes
B 0.4 47.0%
Totals for Area of Interest 0.8 100.0%
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
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 3 of 4
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 4 of 4
Wind Erodibility Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 1 of 3
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
494640 494650 494660 494670 494680 494690 494700 494710 494720
494640 494650 494660 494670 494680 494690 494700 494710 494720
40° 34' 27'' N
105° 3' 48'' W
40° 34' 27'' N
105° 3' 44'' W
40° 34' 23'' N
105° 3' 48'' W
40° 34' 23'' N
105° 3' 44'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 25 50 100 150
Feet
0 5 10 20 30
Meters
Map Scale: 1:613 if printed on A portrait (8.5" x 11") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
1
2
3
4
4L
5
6
7
8
Not rated or not available
Soil Rating Lines
1
2
3
4
4L
5
6
7
8
Not rated or not available
Soil Rating Points
1
2
3
4
4L
5
6
7
8
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
Wind Erodibility Group
Wind Erodibility Group— Summary by Map Unit — Larimer County Area, Colorado (CO644)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
94 Satanta loam, 0 to 1
percent slopes
5 0.4 53.0%
95 Satanta loam, 1 to 3
percent slopes
5 0.4 47.0%
Totals for Area of Interest 0.8 100.0%
Description
A wind erodibility group (WEG) consists of soils that have similar properties
affecting their susceptibility to wind erosion in cultivated areas. The soils assigned
to group 1 are the most susceptible to wind erosion, and those assigned to group
8 are the least susceptible.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Lower
Wind Erodibility Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 3 of 3
Wind Erodibility Index—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 1 of 3
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
4491390 4491400 4491410 4491420 4491430 4491440 4491450 4491460 4491470 4491480 4491490 4491500
494640 494650 494660 494670 494680 494690 494700 494710 494720
494640 494650 494660 494670 494680 494690 494700 494710 494720
40° 34' 27'' N
105° 3' 48'' W
40° 34' 27'' N
105° 3' 44'' W
40° 34' 23'' N
105° 3' 48'' W
40° 34' 23'' N
105° 3' 44'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 25 50 100 150
Feet
0 5 10 20 30
Meters
Map Scale: 1:613 if printed on A portrait (8.5" x 11") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
0
38
48
56
86
134
160
180
220
250
310
Not rated or not available
Soil Rating Lines
0
38
48
56
86
134
160
180
220
250
310
Not rated or not available
Soil Rating Points
0
38
48
56
86
134
160
180
220
250
310
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
Wind Erodibility Index
Wind Erodibility Index— Summary by Map Unit — Larimer County Area, Colorado (CO644)
Map unit symbol Map unit name Rating (tons per acre
per year)
Acres in AOI Percent of AOI
94 Satanta loam, 0 to 1
percent slopes
56 0.4 53.0%
95 Satanta loam, 1 to 3
percent slopes
56 0.4 47.0%
Totals for Area of Interest 0.8 100.0%
Description
The wind erodibility index is a numerical value indicating the susceptibility of soil to
wind erosion, or the tons per acre per year that can be expected to be lost to wind
erosion. There is a close correlation between wind erosion and the texture of the
surface layer, the size and durability of surface clods, rock fragments, organic
matter, and a calcareous reaction. Soil moisture and frozen soil layers also
influence wind erosion.
Rating Options
Units of Measure: tons per acre per year
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Wind Erodibility Index—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 3 of 3
Elizabeth Subdivision Final Drainage Report July 2017
B
Appendix B: BMP Sizing
and Hydrology Calculations
ELIZABETH SUBDIVISION
TABLE B‐1: IMPERVIOUSNESS
Existing Condition
2% 100% 90%
Commercial Building 1,231 90%
Shed 514 90%
Concrete Walks 682 90%
Asphalt Parking 5,003 100%
Elizabeth Street 1,889 175 99%
Landscaped Area 23,855 2%
TOTAL 23,855 6,892 2,603 29%
Proposed Condition
2% 100% 90%
Existing
Commercial Building 1,231 90%
Shed 514 90%
Concrete Walks 682 90%
Parking Lot 2,753 100%
Elizabeth Street 1,889 175 99%
Proposed Commercial
Proposed Concrete 667 90%
Proposed Asphalt 1,253 100%
Proposed Residential
Proposed Residence 3,807 90%
Future Garage Addition 83 90%
Proposed Concrete 150 90%
Proposed Asphalt 2,589 100%
Landscaped Area 17,558 2%
TOTAL 17,558 8,483 7,309 46%
Area Identification
Basin Categories and Areas (SF)
Landscaped
Areas
Streets
Percent
Impervious
Drives, Walks,
& Roofs
Area Identification
Basin Categories and Areas (SF)
Landscaped
Areas
Streets
Percent
Impervious
Drives, Walks,
& Roofs
ELIZABETH SUBDIVISION
TABLE B‐2: BASIN PARAMETERS
Existing Condition
Drives, Walks
& Roofs
2% 100% 90% (%/100) (acres)
A 77 1,987 636 95% B 0.06
B 5,637 4,912 2,570 56% B 0.30
C 11,488 0 0 2% B 0.26
D 6,045 0 0 2% B 0.14
TOTAL (acres) 0.53 0.16 0.07 TOTAL 0.77
Proposed Condition
Drives, Walks
& Roofs
2% 0% 90% (%/100) SF (acres)
A 72 1,895 733 95% 104 B 0.06
B 1,177 0 834 38% 43 B 0.05
C 1,412 0 63 6% 38 B 0.03
D 5,450 6,594 3,112 63% 5,742 B 0.35
D1 3,149 903 1,608 43% 2,216 B 0.13
E 1,175 0 0 2% 0 B 0.03
F 7,850 0 0 2% 0 B 0.18
G 410 0 2,573 78% 2,573 B 0.07
TOTAL (acres) 0.47 0.22 0.15 8,143 TOTAL 0.83
Basin I.D.
Basin Categories and Areas (SF)
Percent Imp. Soil
Classification
Landscaped Basin Area
Areas
Streets
New/Modified
Impervious
Area
Landscaped
Areas
Streets
Basin Area
Basin I.D.
Basin Categories and Areas (SF)
Percent Imp. Soil
Classification
ELIZABETH SUBDIVISION
TABLE B‐3: BASIN HYDROLOGY
Existing Condition
100‐Year 2‐Year 100‐Year
I100 Q2 Q100
(acres) (minutes) (in./hour) (in./hour) (ft3/s) (ft3/s)
A 0.06 95% B 5.0 0.79 0.88 2.9 10.0 0.1 0.5
B 0.30 56% B 5.0 0.34 0.55 2.9 10.0 0.3 1.6
C 0.26 2% B 5.0 0.03 0.36 2.9 10.0 0.0 1.0
D 0.14 2% B 5.0 0.03 0.36 2.9 10.0 0.0 0.5
Proposed Condition
100‐Year 2‐Year 100‐Year
I100 Q2 Q100
(acres) (minutes) (in./hour) (in./hour) (ft3/s) (ft3/s)
A 0.06 95% B 5.0 0.79 0.87 2.9 10.0 0.1 0.5
B 0.05 38% B 5.0 0.22 0.49 2.9 10.0 0.0 0.2
C 0.03 6% B 5.0 0.04 0.38 2.9 10.0 0.0 0.1
D 0.35 63% B 5.0 0.39 0.58 2.9 10.0 0.4 2.0
D1 0.13 43% B 5.0 0.25 0.50 2.9 10.0 0.1 0.6
E 0.03 2% B 5.0 0.03 0.36 2.9 10.0 0.0 0.1
F 0.18 2% B 5.0 0.03 0.36 2.9 10.0 0.0 0.6
G 0.07 78% B 5.0 0.54 0.68 2.9 10.0 0.1 0.5
Runoff Coefficients Rainfall Intensity Runoff
2‐Year
C2
100‐Year
C100
2‐Year
I2
Basin I.D.
Basin Area
Percent
Impervious
Soil Class.
Time of
Concentration
Rainfall Intensity Runoff
2‐Year
I2
Runoff Coefficients
100‐Year
C100
Basin I.D.
Time of
Concentration 2‐Year
C2
Basin Area Soil Class.
Percent
Impervious
Project:
Channel ID:
Design Information (Input)
Channel Invert Slope So = 0.0100 ft/ft
Manning's n n = 0.040
Bottom Width B = 1.00 ft
Left Side Slope Z1 = 4.00 ft/ft
Right Side Slope Z2 = 4.00 ft/ft
Freeboard Height F = 0.00 ft
Design Water Depth Y = 0.30 ft
Normal Flow Condtion (Calculated)
Discharge Q = 0.81 cfs
Froude Number Fr = 0.49
Flow Velocity V = 1.23 fps
Flow Area A = 0.66 sq ft
Top Width T = 3.40 ft
Wetted Perimeter P = 3.47 ft
Hydraulic Radius R = 0.19 ft
Hydraulic Depth D = 0.19 ft
Specific Energy Es = 0.32 ft
Centroid of Flow Area Yo = 0.12 ft
Specific Force Fs = 0.01 kip
Normal Flow Analysis - Trapezoidal Channel
Elizabeth Subdivision
Basin D1-Grass Swale
UD-Channels-swale.xls, Basics 7/25/2017, 2:20 PM
Project:
Pipe ID:
Design Information (Input)
Pipe Invert Slope So = 0.0050 ft/ft
Pipe Manning's n-value n = 0.0130
Pipe Diameter D = 8.00 inches
Design discharge Q = 0.50 cfs
Full-flow Capacity (Calculated)
Full-flow area Af = 0.35 sq ft
Full-flow wetted perimeter Pf = 2.09 ft
Half Central Angle Theta = 3.14 radians
Full-flow capacity Qf = 0.86 cfs
Calculation of Normal Flow Condition
Half Central Angle (0<Theta<3.14) Theta = 1.67 radians
Flow area An = 0.20 sq ft
Top width Tn = 0.66 ft
Wetted perimeter Pn = 1.11 ft
Flow depth Yn = 0.37 ft
Flow velocity Vn = 2.55 fps
Discharge Qn = 0.50 cfs
Percent Full Flow Flow = 58.1% of full flow
Normal Depth Froude Number Frn = 0.83 subcritical
Calculation of Critical Flow Condition
Half Central Angle (0<Theta-c<3.14) Theta-c = 1.56 radians
Critical flow area Ac = 0.17 sq ft
Critical top width Tc = 0.67 ft
Critical flow depth Yc = 0.33 ft
Critical flow velocity Vc = 2.89 fps
Critical Depth Froude Number Frc = 1.00
CIRCULAR CONDUIT FLOW (Normal & Critical Depth Computation)
Elizabeth Subdivision
Culvert at Design Point G
Culvert-DP G.xlsm, Pipe 7/25/2017, 2:10 PM
Project:
Basin ID:
Design Information (Input):
Width of Basin Bottom, W = ft Right Triangle OR…
Length of Basin Bottom, L = ft Isosceles Triangle OR…
Dam Side-slope (H:V), Zd = ft/ft Rectangle OR…
Circle / Ellipse OR…
Irregular (Use Overide values in cells G32:G52)
MINOR MAJOR
Storage Requirement from Sheet 'Modified FAA': 0.00 acre-ft.
Stage-Storage Relationship: Storage Requirement from Sheet 'Hydrograph': acre-ft.
Storage Requirement from Sheet 'Full-Spectrum': acre-ft.
Labels Water Side Basin Basin Surface Surface Volume Surface Volume Target Volumes
for WQCV, Minor, Surface Slope Width at Length at Area at Area at Below Area at Below for WQCV, Minor,
& Major Storage Elevation (H:V) Stage Stage Stage Stage Stage Stage Stage & Major Storage
Stages ft ft/ft ft ft ft
2
ft
2
User ft
3
acres acre-ft Volumes
(input) (input) Below El. (output) (output) (output) Overide (output) (output) (output) (for goal seek)
4976.60 (input) 177 0.004 0.000
4976.80 0.00 0.00 241 42 0.006 0.001
4977.00 0.00 0.00 312 97 0.007 0.002
4977.20 0.00 0.00 402 169 0.009 0.004
4977.40 0.00 0.00 538 263 0.012 0.006
4977.60 0.00 0.00 850 401 0.020 0.009
4977.80 0.00 0.00 1,570 643 0.036 0.015
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Project:
Basin ID:
STAGE-STORAGE SIZING FOR DETENTION BASINS
4976.00
4976.20
4976.40
4976.60
4976.80
4977.00
4977.20
4977.40
4977.60
4977.80
4978.00
0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.02
Stage (ft. elev.)
Storage (acre-feet)
STAGE-STORAGE CURVE FOR THE POND
UD-Detention_v2.34.xls, Basin 7/25/2017, 2:21 PM
Project:
Channel ID:
Design Information (Input)
Channel Invert Slope So = 0.0050 ft/ft
Manning's n n = 0.040
Bottom Width B = 4.00 ft
Left Side Slope Z1 = 4.00 ft/ft
Right Side Slope Z2 = 4.00 ft/ft
Freeboard Height F = 0.00 ft
Design Water Depth Y = 0.50 ft
Normal Flow Condtion (Calculated)
Discharge Q = 4.07 cfs
Froude Number Fr = 0.39
Flow Velocity V = 1.36 fps
Flow Area A = 3.00 sq ft
Top Width T = 8.00 ft
Wetted Perimeter P = 8.12 ft
Hydraulic Radius R = 0.37 ft
Hydraulic Depth D = 0.38 ft
Specific Energy Es = 0.53 ft
Centroid of Flow Area Yo = 0.22 ft
Specific Force Fs = 0.05 kip
Normal Flow Analysis - Trapezoidal Channel
Elizabeth Subdivision
Basin C - Grass Swale
Swale-ElizabethSt.xls, Basics 7/25/2017, 2:12 PM
Project:
Channel ID:
Design Information (Input)
Channel Invert Slope So = 0.0050 ft/ft
Manning's n n = 0.013
Bottom Width B = 2.00 ft
Left Side Slope Z1 = 0.01 ft/ft
Right Side Slope Z2 = 0.01 ft/ft
Freeboard Height F = 0.00 ft
Design Water Depth Y = 0.50 ft
Normal Flow Condtion (Calculated)
Discharge Q = 3.91 cfs
Froude Number Fr = 0.97
Flow Velocity V = 3.90 fps
Flow Area A = 1.00 sq ft
Top Width T = 2.01 ft
Wetted Perimeter P = 3.00 ft
Hydraulic Radius R = 0.33 ft
Hydraulic Depth D = 0.50 ft
Specific Energy Es = 0.74 ft
Centroid of Flow Area Yo = 0.25 ft
Specific Force Fs = 0.05 kip
Normal Flow Analysis - Trapezoidal Channel
ELIZABETH SUBDIVISION
SIDEWALK CHASE
Sidewalk Chase-Channel.xls, Basics 7/25/2017, 2:11 PM
ELIZABETH SUBDIVISION
WEIR ANALYSIS
Lw dQ
(feet) (feet) (cfs)
Sidewalk Chase 0.5 2.6 2 0.50 2.12
Driveway Overtopping 0.5 2.5 15 0.14 2.46
Weir Coefficient (Cw) 3UDFCD Table ST‐7
Weir Capacity (Q) Q = CwLwd1.5 UDFCD Equation ST‐27
Allowable
Flow
Description
2‐Year Peak
Inflow
100‐Year
Peak Inflow
Weir Width
Weir Flow
Depth
Elizabeth Subdivision Final Drainage Report July 2017
C
Appendix C: Erosion Control Plan
and Drainage Plan
SF
X
A
B C
D
E
G
F
DATE REVISION DESCRIPTION
REVISIONS
FILENAME:
0036.0002.00_DRAINAGE
0036.0002.00
1" = 20'
JULY 26, 2017
OF
DESIGNED:
CHECKED:
JOB NO.:
SCALE:
DATE:
1" = 20' SHEET NO.:
0 20 40
scale feet
CALL THE UTILITY NOTIFICATION CENTER OF COLORADO
3 DAYS BEFORE YOU DIG
811 OR 1-800-922-1987
www.UNCC.org
CEM
CEM/JKG
5110 GRANITE STREET, UNIT D
LOVELAND, COLORADO 80538
(970) 278-0029
CCGCOLORADO
CIVIL
GROUP, INC.
ENGINEERING CONSULTANTS
0" 1" BAR IS ONE INCH ON ORIGINAL DRAWING
COLORADO CIVIL GROUP, INC.
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STAGE-STORAGE SIZING FOR DETENTION BASINS
ELIZABETH SUBDIVISION
Check Basin Shape
BASIN D
UD-Detention_v2.34.xls, Basin 7/25/2017, 2:21 PM
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
Survey Area Data: Version 10, Sep 22, 2015
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.
Wind Erodibility Index—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 2 of 3
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
Survey Area Data: Version 10, Sep 22, 2015
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.
Wind Erodibility Group—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 2 of 3
Survey Area Data: Version 10, Sep 22, 2015
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
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 2 of 4
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
Survey Area Data: Version 10, Sep 22, 2015
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.
Drainage Class—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
2/25/2016
Page 2 of 3