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FINAL DRAINAGE AND
EROSION CONTROL STUDY FOR
SUMMERHILL P.U.D.
FORT COLLINS, COLORADO
u
FINAL DRAINAGE AND
EROSION CONTROL STUDY FOR
SUMMERHILL P.U.D.
FORT COLLINS, COLORADO
I�
March 31, 1994
1
Prepared for:
Mel Price
2400 Vajobi Court
Fort Collins, Colorado 80526
' Prepared by:
RBD, Inc. Engineering Consultants
209 S. Meldrum
Fort Collins, Colorado 80521
(303) 482-5922
1 RBD Job No. 560-001
I
MSMINC.
Engineering Consultants
209 S. Meldrum
Fort Collins, Colorado 80521
303/482-5922
FAX: 303/482-6368
' March 31, 1994
' Mr. Glen Schleuter
City of Fort Collins
Utility Services Stormwater
.' 235 Mathews
Fort Collins, Colorado 80522
RE: Final Drainage and Erosion Control Study
for Summerhill P.U.D.
' Dear Glen:
We are pleased to submit to you, for your review and approval, this Final Drainage and
' Erosion Control Study for Summerhill P.U.D.. All computations within this report have
been completed in compliance with the City of Fort Collins Storm Drainage Design
Criteria.
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We appreciate your time and consideration in reviewing this submittal. Please call if you
have any questions.
Respectfully,
RBD Inc. Engineering Consultants
�r st`
Tim J. Bailey
Design Engineer
Roger A. Curtiss, P.E.
Project Engineer
' Other Offices: Denver 303/458-5526 • Vail 3031476-6340
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TABLE OF CONTENTS
DESCRIPTION
PAGE
I.
GENERAL LOCATION AND DESCRIPTION
1
A. LOCATION
1
B. DESCRIPTION OF PROPERTY
1
II.
DRAINAGE BASINS
1
A. MAJOR BASIN DESCRIPTION
1
B. SUB -BASIN DESCRIPTION
2
III.
DRAINAGE DESIGN CRITERIA
2
A. REGULATIONS q2
B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS
2
C. HYDROLOGICAL CRITERIA
2
D. HYDRAULIC CRITERIA
2
E. VARIANCES FROM CRITERIA
3'
IV.
DRAINAGE FACILITY DESIGN
3
A. GENERAL CONCEPT
3
B. SPECIFIC DETAILS
3
V.
STORM WATER QUALITY
4-
A. GENERAL CONCEPT
4
B. SPECIFIC DETAILS
4
VI.
EROSION CONTROL
5
A. GENERAL CONCEPT
5
B. SPECIFIC DETAILS
5
VII.
CONCLUSIONS
6
A. COMPLIANCE WITH STANDARDS
6
B. DRAINAGE CONCEPT
6
C. STORM WATER QUALITY
6
D. EROSION CONTROL CONCEPT
6
REFERENCES 7
APPENDIX
VICINITY MAP 1
HYDROLOGY 2
RETENTION 7
DESIGN OF SWALES AND SIDEWALK CULVERTS 11
EROSION CONTROL 17
EXCERPTS FROM THE WEST PROSPECT ROAD DRAINAGE REPORT 24
CHARTS, FIGURES AND TABLES 35
FINAL DRAINAGE AND
' EROSION CONTROL STUDY FOR
SUMMERHILL P.U.D.
FORT COLLINS, COLORADO
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The Summerhill P.U.D. development is located in the southwest part of Fort
Collins, on the south side of Prospect Road, between Taft Hill Road and
' Shields Street. A vicinity map of the proposed site is included in the
appendix. More particularly, the site is situated in the east half of the
northwest quarter of Section 22, Township 7 North, Range 69 West of the
6th P.M., City of Fort Collins, Larimer County, Colorado.
B. Description of Property
The Summerhill P.U.D. contains 5.28 acres more or less. The area is
currently undeveloped and is being proposed for multi -family residential
construction with 62 units. The site currently consists of pasture. The New
.' -Mercer Canal flows in the west to east direction immediately south of the
site. Topography for the site has the northeast two thirds of the site sloping
from the southwest to the northeast towards Prospect Road at
' approximately 1.7%, while the remainder of the site slopes from the
northeast to the southwest towards the New Mercer Canal at approximately
4.0%.
' II. DRAINAGE BASINS
' A. Major Basin Description
The Summerhill P.U.D. lies within the Canal Importation Storm Drainage
Basin. No major drainageway exists within the site.
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B. Sub -Basin Description
Historic, drainage patterns of the subject site are two thirds of the site
drainingnortheasterly across the site onto Prospect Road. The remaining
third of the site currently drains southwesterly into the New Mercer Canal.
DRAINAGE DESIGN CRITERIA
A. Regulations
The City of Fort Collins Storm Drainage Design Criteria is being used for the
subject site.
' B. Development: Criteria Reference and Constraints
1 The report entitled "Hydrologic Analysis and Final Hydraulic Design, West
Prospect Road Drainage" criteria and constraints are being utilized in this
Final Drainage Study. Drainage criteria not specified in the report will be in
' accordance with the City of Fort Collins Storm Drainage Design Criteria and
Construction Manual.
C. Hydrological Criteria
' The Rational method is being used to determine runoff peak flows from the
site and surrounding off -site tributary areas. The 2 and 100 year rainfall
' criteria, which was obtained from the City of Fort Collins, is the criteria
which was utilized. The criteria is included in the appendix.
D. Hydraulic Criteria
' All calculations within this study have been prepared in accordance with the
City of Fort Collins Drainage Criteria.
2
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' E. Variances from Criteria
' A variance is being sought for this project to allow for continued storm drain
retention in the pond south of the channel. This is to be a temporary pond
until the City completes planned drainage improvements in this area.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
' The Summerhill P.U.D. is planned as a multi -family residential housing
development. The site will consist of 62 units. Storm water flows for the
' northeasterly portion of the site will be routed to Westbridge Drive and then
onto Prospect Road. Flows from the southwesterly portion of the site will be
routed onto Underhill Drive, and then across the New Mercer Canal in a
grass -lined swale to be constucted in the existing bridge surface into an
existing retention pond on the south side of the canal. Included in the back
pocket of this report is the drainage plan for the Summerhill P.U.D..
B. Specific Details
' Basins 1 and 2 consist of the front half of the northeast lots and the
adjacent private roadway. Flow is directed along the private road in a
' concrete in the driveover curb and gutter. The basins join together at the
low point in the northeast corner of the private road, concentration points
1 and 2. Flow is to be directed across the street by a cross pan, and then
' into a grass lined swale. The curb section is to be depressed to allow for
the cross pan to outlet into the swale. The grass lined swale is to outlet into
' a metal sidewalk culvert and onto Westbridge Drive. The culvert will not
handle flows from a large storm, but is to be installed to keep low flows
from flowing over the sidewalk. Flows above the capacity of the culvert will
' overtop the walk and sheetflow onto the street.
Basin 3 consists of the rear portion of the lots of Basins 1 and 2, and all of
' Westbridge Drive. Flow from the rear of the lots is to sheetflow over the
sidewalk onto Westbridge Drive or onto Prospect Road. The flow on
Westbridge Drive is then directed along the gutter onto Prospect Road,
' along with the runoff from Basins 1 and 2. This concept is consistent with
what was planned for in the Prospect Road Improvement Storm Drainage
Study. See Appendix.
3
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' Basins 4 and 5 consist of the southwest portion of the site. Flows are
directed along the pans or along the rear of the lots onto Underhill Drive.
' Flow is then to be directed along Underhill to the end of the cul-de-sac.
Here it enters an existing drainage swale through a concrete sidewalk
culvert to transport it across the bridge over the New Mercer Canal and into
the existing retention pond south of the canal. Runoff from basin 7 enters
the swale along the back property before flow crosses the canal.
' Basin 6 consists of the offsite drainage area which flows onto Underhill
Drive from the west and is routed across the bridge along with flows from
basins 4,5 and 7 in an existing grass lined swale over the New Mercer
' Canal and into the retention pond. The swale was built with the Underhill
P.U.D. Amendment. Basin 8 consists of the area on the south side of the
canal tributary to, and including, the retention pond.
' The runoff flows from basins 4 through 8 are to be retained in the existing
pond south of the canal. This pond is temporary until improvements are
built to accept the runoff. The retention pond was built with the Phase I
construction of Underhill P.U.D., criteria for the sizing of the pond is
included in the appendix. Flows entering the pond are essentially the same
' as they were with the. Phase I Underhill design. Previous 100 year
developed flows crossing the canal were calculated to be 27.4 cfs using a
"c" value of 0.65, compared to flows calculated to be 25.0 using a "c" value
' of 0.70 for the Summerhill P.U.D.. The swale continues for approximately 80'
past the canal until it can be directed in natural flow patterns to the retention
area.
V. STORM WATER QUALITY
' A. General Concept
Beginning in October of 1991, the water quality of storm water runoff was
required to be addressed on all final design utility plans. The Summerhill
' P.U.D. has an anticipated construction date beginning in Spring of 1994.
Therefore, water quality issues are being addressed in this report.
' B. Specific Details
The north portion of the site drains onto Westbridge Drive and then onto
Prospect Road. The drainage swale transporting the flow from the private
streets is set at a relatively flat grade, which is ideal for water quality. The
low velocities allow the storm water to filter out pollutants into the grass
lined swale. Because of the importance of water quality, we are not
' 4
' proposing to construct concrete trickle pans along the swale.
' Flows from the southwest portion of the site and from the area west of the
site are directed to the retention basin south of the canal. The retention
basin will be able to filter out any pollutants as water seeps away into the
soil.
' V. EROSION CONTROL
A. General Concept
The Summerhill P.U.D. is in the High Rainfall and Moderate Wind Erodibility
' Zones per the City of Fort Collins zone maps. The potential exists for
erosion problems during construction, and after construction until the
disturbed ground is again vegetated. It is anticipated that construction will
begin in the Spring of 1994.
Per the City of Fort Collins Erosion Control Reference Manual for
Construction Sites and related calculations in the appendix, the erosion
control performance standard for this site is 78.6%. From the calculations
in the appendix, the effectiveness of the proposed erosion control plan is
' 79.1% during the construction portion of this development. Therefore the
erosion control plan as specifically detailed below, will meet the City of Fort
Collins requirements.
B. Specific Details
' After the overlot grading has been completed, all disturbed areas, not in a
roadway, shall have a temporary vegetation seed applied per the City of
' Fort Collins specification. After seeding, a hay or straw mulch shall be
applied over the seed at a rate of 2 tons/acre, minimum, and the mulch
shall be adequately anchored, tacked or crimped into the soil per the
' methods shown on the Drainage and Erosion Control plan. After the utilities
have been installed, the roadway surfaces should receive the pavement
structure. The straw bale barriers should be installed prior to beginning the
overlot grading process.
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CONCLUSIONS
A.
B.
C.
Al
Compliance with Standards
All computations within this report have been completed in compliance with
the City of Fort Collins Storm Drainage Design Criteria.'
Drainage Concept
The proposed drainage concepts adequately provide for the transmission
of developed on -site runoff to the retention pond south of the New Mercer
Canal.The remainder of the site is adequately routed onto Prospect Drive
per the concept Prospect Road Improvement Storm Drainage Study.
STORM WATER QUALITY
Storm water quality aspects have been considered in the design of
Summerhill P.U.D.. The retention pond south of the New Mercer Canal
provides for the filtering of pollutants from a large portion of the site, while
a low velocity drainage swale provides for filtering for the remainder of the
site.
Erosion Control Concept
The proposed erosion control concepts adequately provide for the control
of wind and rainfall erosion from the Summerhill P.U.D.. Through the
construction of the proposed erosion control concepts, the City of Fort
Collins performance standards will be met. The proposed erosion control
concepts presented in this report and shown on the erosion control plan
are in compliance with the City of Fort Collins erosion control criteria.
0
REFERENCES
1. Storm Drainage Design Criteria and Construction Standards by the City of Fort
Collins, Colorado, May 1984, Revised January 1992.
2. Erosion. Control Reference Manual for Construction Sites by the City of Fort Collins,
Colorado, January 1991.
3. "Supplemental Drainage Report for Underhill P.U.D., Phase I" by Engineering
Professionals, Inc., March 1982.
4. "Hydrologic Analysis and Final Hydraulic Design, West Prospect Road Drainage,
Fort Collins, Colorado" by Lidstone & Anderson, Inc., February 1993
5. "Amendment to Final Drainage Study for Underhill P.U.D.,. Fort Collins, Colorado"
by RBD Inc., November 1993
7
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March 31, 1994
Mr. Glen Schlueter
1
City of Fort Collins
Utility Services Stormwater
235 Mathews
1
Fort Collins, Colorado 80522
Re: Summerhill P.U.D.
1 Erosion Control Cost Estimate
1 Dear Glen:
This letter is intended to satisfy the City of Fort Collins requirements for an erosion control
1 security deposit for Summerhill P.U.D.. The City of Fort Collins current cost factors will be
used for this estimate.
1 There will be approximately 5.02 acres disturbed within this project. Using the City criteria
of $650.00 per acre for construction sites between 1 and 10 acres, and using a 150%
contingency, the total obligation for a security deposit would be:
1 (5.02 acres) * ($650.00 per acre) * (150% contingency) = $4,895
1 An estimate was prepared using all improvements shown on the construction plans using
cuurent bid prices. The amount estimated was $1,836 (see attached cost breakdown).
Using the City criteria of 150% of estimated costs, the total obligation would be $2,754.
1 Therefore, the total obligation required will be $4,895
1 Please call if you have any questions regarding this estimate.
Respectfully,
1 RBD Inc. Engineering Consultants
1 Tim J. Bailey
1
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SUMNERHILL P.U.D.
EROSION CONTROL
COST ESTIMATE
EROSION CONTROL ITEM
QUANTITY
UNIT
COST
TOTAL
COST
Hay or Straw Mulch w/
Temporary Seed
4.09 Acres
$400
$1,636
Straw Bale Check Dams
2 Each
$100
$200
TOT -al = :?.LIdSb
+ 150% Contingency = $2,754
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APPENDIX
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EUUeETH STREET
PROJECT SITE
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SUPPLEMENTAL DRAINAGE REPORTL,o
i for
UNDERHILL P.U.D. , PHASE I
i
iPrepared for:
Cit,•: of Fort Collins
1
i, :larch, 1982
1
iPrepared by:
i Engineering Professionals, Inc.
2020 Airway Avenue
i Fort Collins, Colorado
80524
i(303) 221-3700
1 j,=
' III. MAJOR DRAINAGE SYSTEM:
The Underhill P.U.D. is located within the canal importation.
' drainage basin. Accordingly, the major drainaqe basin study
titled "Diversion of Storm -Plater Runoff Through Irrigation
Canals from Mulberry Street to Spring Creek Fort Collins,
Colorado", Volumes I and II, and. prepared by Resource Consul-
tants, Inc., is included herein by reference. The existing
1 100 year floodplain is not specifically delineated in the
canal importation study. However, although the exact limits
' are not known, it will occur below the New Mercer Canal.
Therefore, no construction of units will occur in the third
' phase pf Underhill until either the canal importation improvements
are constructed or a detailed hydraulic investigation of the
floodplain characteristics is made to assure that proposed
structures meet minimum elevation requirements above the flood
plain.
As indicated on the preliminary drainage plan submitted with the
Underhill master plan, the final drainage system will be desicned
to discharge into the canal importation improvements. Three
detention ponds will be used to discharge into the major impor-
tation canal at the 2 year historic release rate.
IV. HYDROLOGIC and HYDRAULIC ANALYSIS:
11
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The hydrologic analysis for the first phase was accomplished
using the Rational Method as delineated in the City's Storm
Drainage Criteria Manual. The results of the Rational Method
analysis are summarized as follows:
Rational Method Parameters
Allowable
Design Storm
C
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Gutter
Capacity
(min)
(in/hr)
(acres)
I (cfs)
(cfs)
2-Year
Developed
0.65
11.0
2.52
.4.8
7.9
9.5
100-Year
Developed
0.65
11.0
7.02
4.8
27.4
28.7*
* Curb full at New Mercer Ditch Crossing
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Pam,`
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The analysis indicates that no storm sewer is -needed for
the first phase. Detailed calculations can be reviewed in
Appendix "A" included herein.
Neither the New Mercer or the Larimer County No. 2 Canals are
willing to accept storm runoff. As a result of this requirement,
a meeting was held with Mr. Mauri Rupel and Mr. Bob Smith of
the City's engineering staff, and interim drainage improvements
were delineated to retain storm runoff until the canal importa-
tion improvements are.constructed. The retention criteria sugaested
by Mr. Smith was that the retention
runoff created b Pond be capable of storing
y one and one half 100 year, 3 hour design storms
from the developed first phase. Due to the nature of the soils
south of the New Mercer Canal (sandy silty clay with distinct
sand and gravel layers) it is our opinion that stored runoff will
seep away rapidly.'The following table summarizes the calculations
for required retention volume:
Description Volume (Acre -Feet)
100 year, 3 hour Precipitation
Infiltration Loss 1.24
(0.31)
Detention and Depression Loss
(0.12)
Net Volume
0.81
Volume Required = 0.81 Ac./Ft. x 1.5 = 1.22 Ac./Ft.
V. RECOMMENDATIONS:
Based on the results of the drainage study summarized herein,
the following recommendations are made:
A. Do not include storm sewer in the first phase of the
Underhill P.U.D.
B. Slope Westbridge Drive.to Prospect Street for a short
distance to assure that storm runoff on Prospect remains
on Prospect.
C. Construct an interim retention pond below the New Mercer
Canal in the approximate location proposed for the detention
pond in Phase III as delineated on the master plan. The
capacity for said pond shall be 1.2 acre/feet.
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DESIGN OF SWALES AND SIDEWALK CULVERTS
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CHANNEL RATING INFORMATION
TYPICAL FORT COLLINS SIDEWALK CULVERT
STA ELEV
0.00
100.20
0.00
99.76
1.00
99.74
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0.81
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0.86
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CHANNEL RATING INFORMATION
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(feet) (sq ft) (fps) (cfs) NO.
--------- --------------- --------- ------
0.20 0.2 0.7 0.15 0.42
0.40 0.8 1.2 0.95 0.47 Q
0.80 3.2 1.9 6.03 0.52 Qp.= 7. (q dS ek= L�. O
1 1.00 5.0 2.2 10.92 0.5 "
1.40 9.8 2.7 26.79 0.58 Qt9e = Z.7..Zc sd �' 4
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1.80 16.2 3.2 52.35 0.60 Q ieB+33%a= 3�� 7-
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EROSION CONTROL
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RAINFALL PERFORMANCE STANDARD EVALUATION
PROJECT: STANDARD FORM A
COMPLETED BY: DATE:
DEVELOPED
SUBBAgIN
ERODIBILITY
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z�
CONSTRUCTION SEQUENCE /
PROJECT: SLI.VAMe-rk1 II STANDARD FORK C
' SEQUENCE FOR 19'I�4, :ONLY COMPLETED BY: TSB DATE:
Indicate by use of a bar line or symbols w;:en erosion control measures Will be installed.
Major modifications to an approved schedule may require submitting a new schedule for
' approval by the City Engineer.
YEAR
' MONTH IMITI�I�ISIDINI I I I
ovr nT.or GRAnTi:r.
' WIND EROSION CONTROL
Soil Roughening
Perimeter Barrier
' Additional Barriers
Vegetative Methods
Soil Sealant
' other
RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers
Sand Bags
' Bare Soil Preparation
Contour Furrows
Terracing
Asphalt/Concrete Paving
' Other
VEGETATIVE:
' Permanent Seed Planting
Y.ulching/Sealant
' Te.-,,porary Seed Planting
Sod Installation
Nettings/Mats/Blankets
' Other
' STRUCTURES: INSTALLED BY MAINTAINED BY
VEGETATION/MULCHING CONTRACTOR
DATE SUBMITTED APPROVED BY CITY OF FORT COLLINS ON
' MARCH 1931 B-16 p DESIGN CRITERIA
EXCERPTS FROM WEST PROSPECT ROAD
DRAINAGE REPORT
I1. EXISTING CONDITION HYDROLOGIC ANALYSIS
2.1 Descriution of General Drainage Patterns
S t1MtAE1=HILL, POD l5 1N T+iE-5E aL5 DDr-AQ_1_
As described in Section 1.1, the Prospect Road drainage basin between Shields Street
and Taft Hill Road is generally separated into four quadrants. These quadrants are
separated by two divides; the east -west divide is located approximately 800 feet east of Taft
Hill road, while the north -south divide is defined by the crown of Prospect Road.
drainage pattern at the Shields Street -Prospect Road intersection was examined
in detail. A description of the runoff pattern for each of the four comers of this
intersection, defined by the crowns of Shields Street and Prospect Road, follows: (a) runoff
in the northwest comer flows along the north side of Prospect Road to the sump inlet
located approximately 400 feet west of the intersection; (b) runoff from the southwest
portion of the intersection (this area is bounded on the south by the curb along the south
side of Prospect Road extended to the crown of Shields Street) flows along the south side
of Prospect Road to the sump identified above; (c) runoff in the southeast comer is carried
south on Shields Street; and (d) since there are no existing facilities to handle the runoff
which originates in the northeast area, this runoff concentrates at the northeast corner of
the intersection and ponds until it reaches a level at which it flows south over the crown of
Prospect Road and south on Shields Street. It was assumed that flow does not cross from
east to west over the Shields Street crown. Although the northeast comer of this
intersection does not contribute runoff to the current study area, the lack of inlets in this
basin dictated that this area be examined in conjunction with this study. .
The drainage pattern at the Taft Hill Road -Prospect Road intersection was also
examined in detail. The examination was supplemented by information provided in the
report Final Drainage Report for Prospect Road S.I .", [The Engineering Company,
1988]. This report indicates that all drainage from the area immediately northwest of the
intersection will be conveyed by a future inlet into the storm drain system; it will not flow
into the Prospect Road study reach. The drainage from the area southwest of the
intersection will be contained by the detention pond located at the southwest corner of the
intersection. At the intersection, the ground slopes away from Prospect Road to the south;
3
1 therefore, storm runoff occurring south of Prospect Road will not flow onto Prospect Road,
1 but will be directed south along Taft Hill Road. In the southeast area, between the
intersection and the drainage divide located approximately 800 feet east of the intersection,
1 the ground slopes away from Prospect Road to the south. Any water not falling on the
street or sidewalk will flow away from the street to the south and will not contribute to the
1 runoff on Prospect Road. Storm runoff originating in the area northeast of the intersection
will be concentrated along the north side of Prospect Road 200 feet east of the intersection.
An existing grated drop inlet is located in this sump on the north side of the road.
1 .
1 2.2 Model Parameters and Results
This analysis models existing conditions to the -extent that all runoff to Prospect Road
,q,,Y,was assumed to be conveyed to the respective sumps at the east and west end of the study
• area. Due to their limited size, the three existing on-line inlets within the study area were
1 assumed to be ineffective. The Storm Water Management Model (SWMM) was used to
compute runoff values for both the 10- and 100-year events for the areas tributary to
1 Prospect Road. Discharges were computed at various locations along Prospect Road.
Determination of the basin geometry, infiltration parameters, land use characteristics, and
1 conveyance facility configurations will be discussed in detail. in the following sections.
In general, the drainage basins contributing runoff to Prospect Road were delineated
1 using 1" =100' topographic mapping/aerial photography with a two -foot contour interval
provided by the City of Fort Collins. The following supplemental mapping was used to
1 more accurately define specific areas of interest. The design grading and drainage plans for
The Bridges P.U.D., at a scale of 1" = 50' and 2-foot contour interval, was used to identify
1 flow characteristics in The Bridges development. Strip mapping provided by the City of Fort
Collins, at a scale of 1" = 40' and a 1-foot contour interval, was used to more accurately
1 define slopes and elevations specifically along Prospect Road.
The subcatchments and conveyance elements used in the SWMM model to perform
1 the hydrologic analysis are identified on Plates 1 and 2. Due to the divided drainage
configuration in the basin, as described in Section 2.1, four SWMM models were used to
1
i4
z 7�
analyze the study reach. Schematics showing the linkages of the subcatchments and
' conveyance elements for the four models are shown in Figures 2.1 through 2.4.
The subcatchment areas, slopes and widths were determined based on the 1" =100'
' topographic mapping. In general, the amount of impervious area in each subcatchment was
measured directly from the 1" =100' aerial photographs. This step was taken because many
of the subcatchments are narrow and include a large percentage of street or other
impervious area. At the other end of the spectrum; a few subcatchments are sparsely
' developed and nearly devoid of impervious area. For the exceptions, where subcatchments
appear to be accurately represented by the low density residential land use designation
' indicated on City zoning maps, the 45 percent imperviousness value, as defined in the SDC
Manual, was adopted.
' Infiltration rates for the subcatchments were taken from the Spring Creek Master
Drainageway Plan [EPI, 1988] which encompasses the current study area, The maximum
' and m;mmum infiltration rates are 0. m15 /hr and 0.50 in/hr, respective The decay rate
' of 0.0018 sec" was also obtained from the Spring Creek Master Plan. The Manning's n
coefficients and surface retention storage values for impervious and pervious areas were
taken from the SDC Manual. The subcatchment input parameters for each of the
subcatchments are summarized in Table 2.1.
Streets were generally modeled as conveyance elements, thus storm flows were routed
' along the street. Along Prospect Road, conveyance elements consisted of one-half of a
' typical street cross section. Although this is considered an existing condition analysis,�he_
proposed street cross section for Prospect Road was used_jn. th_e..�odej; __ cross seGlion-
is shown in Figure 2.5. The configuration for the section shown in the figure was provided
by the City of Fort Collins Engineering Department. V gitudinal slope and length of
the conveyance elements was determined using the 50' 'p mapping described above.
Per the SDC Manual, Manning's n roughness values of 0.016 were used for the conveyance
' elements along streets. The conveyance element parameters used in the SWMM model are
summarized in Table 2.2.
Rainfall hyetographs for both the _lo-_and..100-year. storm.events..were-taken from.the
Spring Creek Master Plan; these hyetographs are given in Table 2.3. The total rainfall
' depths for the 10- and 100-year storm events are 1.83 and 2.88 inches,. respectively.. It is
' 5
�spect Road Drainage between Shields Street and Taft Hill Rd. 02/26/92
posed conditions, with on-line inlets -- 100-year event Lidstone 8 Anderson
AREA
GUTTER
WIDTH
AREA
PERCENT
SLOPE
RESISTANCE
FACTOR
SURFACE STORAGE(IN)
INFILTRATION RATE(IN/HR)
GAGE
N BER
OR MANHOLE
'(FT)
(AC)
IMPERV.
(FT/FT)
IMPERV.
PERV.
IMPERV.
PERV.
MAXIMUM
MINIMUM
DECAY RATE
NO
' -2
0
0.
.0
.0
.0300
.016
.250
.100
.500
.51
.50
.00180
2
101
890.
1.2
55.1
.0035
.016
.250
.100
.500
.51
.50
.00180
1
1 3
103
800.
2.1
47.1
.0143
.016
.250
.100
.500
.51
.50
.00180
1
15
105
400.
.3
53.3
.0036
.016
.250
.100
.500
.51
.50
.00180
1
4
104
1100,
3.9
40.0
.0082
.016
.250
.100
.5011
.51
.50
.001110
1
5
201
640.
1.2
40.0
.0038
.016
.250
.100
.500
.51
.50
.00180
1
6
202
640.
1.0
65.4
.0085
.016
,250
.100
.500
.51
.50
.00180
1
16
117
450.
3.4
40.0
.0412
.016
.250
.100
.500
.51
.50
.00180
1
17
115
360.
1.2
40.0
.0239
.016
.250
.100
.500
.51
.50
.00180•
1
7
203
475.
5.5
40.0
.0174
.016
.250
.100
.500
.51
.50
.00180
1
3
203
430.
3.1
47.2
.0130
.016
.250
.100
.500
.51
.50
.00180
1
I
I 22
123
200.
2.2
40.0
.0412
.016
.250
.100
.500
.51
.50
.00180
1
108
200.
2.0
40.0
.0279
.016
.250
.100
.500
.51
.50
.00180
1
1
JL9
109
390.
1.0
45.0
.0198
.016
.250
.100
.500
51
.50
.00180
1
11
112
335.
4.0
13.1
.0047
.016
.250
.100
.500
.51
.50
.00180 1
206
855.
.8
99.9
.0066
.016
.250
.100
.500
.51.
.50
.00180 1
112
119
740.
.7
99.9
.0085
.016
.250
.100
.500
.51
.50
.00180 1
I18
:. 19
206
385.
.4
99.9
.0135
.016
.250
.100
.500
.51
.50
.00180 1
1
204
220.
1.3
28.1
.0257
.016
.250
.100 .
.500
.51
.50
.00180 1
114
550.
.8
65.2
.0375
.016
.250
.100
.500
.51
.50
.00180 1
�.113
14
113
1620.
3.0
55.7
.0229
.016
.250
.100
.500
.51
.50
.00180 1
8
205
560.
.6
99.9
.0101
.016
.250
.100
.560
.51
.50
.00180 1
20
205
200.
.2
99.9
.0034
.016
.250
.100
.500
.51
.50
.00180 1
TAL
NUMBER OF
SUBCATCHMENTS, 23
TAL
TRIBUTARY
AREA (ACRES),
44.37
NYDROGRAPHS WILL BE SAVED
FOR THE
FOLLOWING
23 SUBCATCHMENTS
FOR SUBSEQUENT
USE WITH
UDSWM2-PC
2
3
4
5
6
7
23
15
16
17
'
22
9
21
10
11
12
18
19
1
13
14
8
20
1
1
1
.
ii
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1
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1
1
1.
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1
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m
Note: Diversions Apply,
the With -Project
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2�
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25JAN93 16:21:42 Ill 2 J 103 I O°IJ II O PAGE
1
THIS RUN EXECUTED 25JAN93 16:21:42
:ff+fiaaaaaaaaaafraffa»aaaaaafir -. �. .
HEC-2 WATER SURFACE PROFILES
sion 4.6.0; February 1991
affrrfrffffefffffffffffffraffaraf
Prospect Road drainage analysis street capacity comps. 1/25/93
2 Normal depth comps for a range of 00s in order to find street capacity
1/2-typical street cross section; vertical face at curb
Road section corresponding to SWMM conveyance element 102
1 ICHECK INO NINV IDIR STRT METRIC HVINS 0 WSEL FQ
' 2 1 0.0046 1.0
�NPROF IPLOT PRFVS XSECV XSECH FN ALLDC IBW CHNIM ITRACE
1 -1
>' 2 7.0 153.
C 0.016 0.016 0.016 0.1 0.3
1 4 100 133.5 /
0.5 100 0.0 100.01. 0.067 101.01 0.72 133.50
i
1
1
25JAN93 16:21:42
SECHO DEPTH CWSEL CRIWS WSELK EG
'0 OLOS OCH OROS ALOE ACH
TIME VLOB VCH VROB XNL XNCH
SLOPE XLOSL XLCH XLOBR ITRIAL IDC
IF 1
100 CEHV= .300
1N0 1.000
'20 CRITICAL DEPTH ASSUMED
'1.000 .39 39 .39 1.00 .48
7.0 .0 .0 .0 2.9
.00 .00 2.60 .00 .000 .016
007171 0. 0. 0. 0 22
25JAN93 16:21:42
SECNO DEPTH CWSEL CRIWS WSELK EG
0 OLOS OCH OROS ALOE ACH
IME VLO8 VCH VROB XNL XNCH
LOPE XLOSL XLCH XLOBR ITRIAL IDC
2
100 CEHV= '.300
0 1.000
CROSS SECTION 1.00 EXTENDED .72 FEET
'1.000 1.22 1 2 1.24 1.00 1.68
153.0 .0 •153.0 .0 .0 28.2
.00 .00 5.42 .00 .000 .016
04584 0. 0. 0. 0 11
PAGE 2
HV
HL
OLOSS
L-BANK ELEV
ARDS
VOL
TWA
R-BANK ELEV
XNR
WTN
ELMIN
SSTA
ICONT
CORAR
TOPWID
ENDST
.09
.00
.00
.50
.0
.0
.0
.72
000
.000
.00
100.00
8
.00
16.98
116.99
HV
HL
OLOSS
L-BANK ELEV
ARDS
VOL
TWA
R-BANK ELEV
XNR
WTN
ELMIN
SSTA
ICONT
CORAR
TOPWID
ENDST
.46
.00
.00
.50
.0 .
.0
.0
.72
000
.000
.00
100.00
5
.00
33.50
133.50
PAGE 4
CHARTS, FIGURES, AND TABLES
1
1
1
1
1
No Text
DRAINAGE CRITERIA MANUAL
RUNOFF
50
30
�- 20
z
w
U
cc
w
a 10
z
W
a.
0 5
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cc 3
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■■�
IIII,III■III►,■■►I
IIIIIIIIIIIIIIII I
2 .3 .5 1 2 3 5 10 20
VELOCITY IN FEET PER SECOND
FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR
USE WITH THE RATIONAL FORMULA.
*MOST FREQUENTLY OCCURRING `UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFERENCE: "Urban Hydrology For Small Watersheds' Technical
Release No. 55, USDA, SCS Jan. 1975.
5-1-84
URBAN DRAINAGE & FLOOD CONTROL DISTRICT
DRCOG
'
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N N M M M M M M M M M M c1 M M M M M M M M r r r r r
co0 q q q q coq q coc o coc0 coq co co cocD co co co CD co coq
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r♦ N N M M M M M C^1 P'l f"'f C') P1 !'1 M M M M M M M M M M M M
g q q q q q q q q q q q q q q q q q q q q q q q q q
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g 0 q q q q 0 0 q q q q q co g q q 0 q q q q- q q q*
NN GINMrN vo r� =m0M0010 M ,M000000
CT O. O r44 rr44 4r44 r44H4 4ri 4 NN NNNN
f, g q q 0 q 0 q q q q q q q q q q q q q q q q q q q
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a
I.!AFiCH 1991 E-4 DESIGN CRITERIA
Table 8B C-Factors and P-Factors for Evaluating EFF Values.
Treatment C-Factor
P-Factor
'
BARE SOIL
..............................
Packed and smooth ..... :............. ............... 1.00
1.00
Freshlydisked........................................................................ 1.00
0.90
Roughirregular surface........................................................... 1.00
0.90
'
SEDIMENT BASIN/TRAP................................................................. 1.00
0.50111
STRAW BALE BARRIER, GRAVEL FILTER, SAND BAG ........................ 1.00
0.80
'
SILT FENCE BARRIER..................................................................... 1.00
0.50
ASPHALT/CONCRETE PAVEMENT ................................................... 0.01
1.00
GRASS See Fig. 8-A
1.00
ESTABLISHED DRY LAND (NATIVE) ..........................
'
SODGRASS................................................................................ 0.01
1.00
TEMPORARY VEGETATION/COVER CROPS .................................... 0.451:1.
1.00
'
HYDRAULIC MULCH @ 2 TONS/ACRE........................................... 0.10,31
1.00
SOILSEALANT ..................................................... ............... 0.01-0.60
1.00
'
EROSION CONTROL MATS/BLANKETS............................................ 0.10
1.00
GRAVEL MULCH
Mulch shall consist of gravel having a diameter of approximately
'
114" to 1 1/2" and applied at a rate of at least 135 tons/acre.............. 0.05
1.00
HAY OR STRAIN DRY MULCH
After Planting grass seed, apply mulch at a rase of 2 tons/acre (minimum) and adequately anchor,
'
tack or crimp material into the soil.
Slope (010
'
1 to 05.............................................................................0.06
6 to 10. 0.06
1.00
1.00
11 to 15 ................ 0.07
1.00
16 to 20............................................................................. 0.11
1.00
'
21 to 25.............................................................................0.14
25 to 33
1.00
1.00
.............................................................................0.17
>33.......................................................................... 0.20
1.00
'
NOTE: Use of otiYr C-Factor or P-Factor values repored in ulis table must be substantiated by documentation.
(1) Must be constructed as the first step in overlot grading.
(2) Assumes planting by dates identified in Table 11-4, thus dry or hydraulic mulches are not required.
(3) Hydraulic mulches shall be used only betv:een March 15 and May 15 unless irrigated.
(4) Value used must be substantiated by documentation.
' rr,ARCH 1991 8.6 DESIGN CRITERIA
'
Table 8-B C-Factors and P-Factors for Evaluating EFF Values (continued from
previous page).
Treatment C-Factor
P-Factor
'
CONTOUR,FURR0INED SURFACE
Must be maintained throughout the construction period, otherwise P-Factor = 1.00.
Mlaximum
length refers to the dov.n slope length.
'
Basin Maximum
Slope Length
M (feet)
1 to 2 00..........................................................................1.00
0.50
'
3 to 5 00. .1.00
3
0.0
6 to 8 200..........................................................................1.00
0.50.
9 to 12 120..............................................................:...........1.00
0.60
13 to 16 0..........................................................................1.00
0.80
'
6
17 to 20 0. .1.00�
0.0
> 20 50..........................................................................
1.00
0.80
TERRACING
'
Must contain 10-year runoff volumes, v:ithout overflowing, as determined by applicable
hydrologic
methods, otherwise P-Factor = 1.00.
'
Basin
Slope M
1 to 2 . ...........................................................................
1.00
0.12
'
9 to 8
9 to 12.
1.00
1 .00
0.12
0.12
...................................................................................
13 to 16.....................................................................................
1.00
0.14
17 to 20....................................................................................
1.00
0.16
'
> 20....................................................................................
1.00
0.18
NOTE: Use of oa`r_r C-Factor or P-Factor -%sl-jes reported in this tab:e must be substantiated by documentation.
1
' MARCH 1991 8.7 DESIGN CRITERIA
R-M-P Medium Density Planned Residential District — designation for medium density
'
areas planned as a unit (PUD) to provide a variation in use and building placements
with a minimum lot area of 6,000 square feet.
R-L-M Low Density Multiple Family District — areas containing low density multiple family
'
units or any other use in the R-L District with a minimum lot area of 6,000 square feet
for one -family or two-family dwellings and 9,000 square feet for multiple -family
dwellings.
M-L Low Density Mobile Home District — designation for areas for mobile home parks
containing independent mobile homes not exceeding 6 units per acre.
M-M Medium Density Mobile Home District — designation for areas of mobile home
parks containing independent mobile homes not exceeding 12 units per acre.
B-G General Business District — district designation for downtown business areas,
including a variety of permitted uses, with minimum lot areas equal to 1 /2 of the total
floor area of the building.
B-P Planned Business District — designates areas planned as unit developments to
provide business services while protecting the surrounding residential areas with
'
minumum lot areas the same as R-M.
H-B Highway Business District — designates an area of automobile -orientated busi-
nesses with a minimum lot area equal to 1/2 of the total floor area of the building.
B-L Limited Business District — designates areas for neighborhood convenience
'
centers, including a variety of community uses with minimum lot areas equal to two
times the total floor area of the building.
_•.
C Commercial District —designates areas of commercial, service and storage areas.
I-L Limited Industrial District= designates light industrial
areas of uses with a minimum
area of lot equal to two times the total floor area of the building not to be less than
20,000 square feet.
'
IT Industrial Park District —designates light industrial park areas containing controlled
industrial uses with minimum lot areas equal to two times the total floor area of the
building not to be less than 20,000 square feet.
'
I-G General Industrial District -designates areas of major industrial development.
T Transition District — designates areas which are in a transitional stage with regard
to ultimate development.
'
For current and more explicit definitions of land uses and zoning classifications, refer to the
Code of the City of Fort Collins, Chapters 99 and 118.
'
Table 3-3
RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE ANALYSIS
'
Character of Surface Runoff Coefficient
Streets, Parking Lots, Drives:
Asphalt................................................................................................ 0.95
Concrete............................................................................................. 0.95
Gravel................................................................................................. 0.50
Roofs.......................................................................................................... 0.95
Lawns, Sandy Soil: -
Flat<2%............................................................................................. 0.10
Average2 to 7%.................................................................................. 0.15
Steep>7%.......................................................................................... 0.20
Lawns, Heavy Soil:
'
Flat <2%................................................................. ............................ 0.20
Average2 to 7%.................................................................................. 0.25
1
Steep>7%.......................................................................................... 0.35
' MAY 1984 3-4 DESIGN CRITERIA
_ I
i
1
1
0.3`
1
1
0.,
1
1
O.R
i
I. U
4
k
1 U 0.1
1
1 0.11
1
1 0.0<
i
1 0.00
1
1 MARCH 1991
0
Figure 8-A
ESTABLISHED GRASS AND C-FACTORS
FORT COLLINS, COLORADO
20 40 60 80
ESTABLISHED GRASS GROUND COVER (%)
8-8
100
DESIGN CRITERIA
1
1
1
1
1
i
1
1
1
1
i
1
1
1
1
i
i
1
1
CLIENT` '�� nc �ZT l !mil l 1`G JOB NO.
INC PROJECT CALCULATIONS FOR(f'1iT=fl- QAJ
Engineering Consultants MADE BY_,=!�,' DATE Z•9Z CHECKEDBY DATE SHEET Z OF Z.
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X:;Zy3.iS + .:,3.75 .looao;-lo0,06 . r I/z ..39 1.4z .+ 1.42 1p7,Sp ?9.94�
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Engineering Consultants
I
I
CLIENT Q= ;=r1F7_ 0" 1, TUB JOB NO.
PROJECT CALCULATIONS. FOR(5UrT-=?_, R_L�tLI
MADE BY--aL'-- DATE CHECKED BY DATE -SHEET I OF
I
4Y.
Calculations for Curb Capacities and Velocities
Major and Minor Storms
per City of Fort Collins Storm Drainage Design Criteria
' RESIDENTIAL with drive over curb and gutter Prepared by: RBD, Inc.
0 is for one side of the road only February 28, 1992
V is based on theoretical capacities
o 2.63 sq.ft.
Area a 20.11 sq.ft.
.
.Area
Minor
Storm :
Major
Storm
Slope :
Red. .
Minor
. C
V .
Major .
0
V
'
M :Factor :
X
: (cfs)
(fps) .
X :
(cfs)
(fps)
0.40 :
0.50 :
86.71
. 2.74
2.09 :
696.73 :
22.03
2.19
0.50 :
0.65 :
86.71
: 3.99
2.33 :
696.73 :
32.02 :
2.45
'
0.60 :
0.80 :
66.71
: 5.37 :
2.55 :
696.73 :
43.17 :
2.68
0.70 :
0.80 :
86.71
: 5.80 :
2.76 :
696.73
46.63
2.90
0.80 :
0.80 :
86.71
:• 6.20
2.95 :
696.73 :
49.85
3.10
0.90 :
0.80 :
86.71
6.58 :
3.13 :
696.73 :
52.68
3.29
'
1.00 :
0.80 :
66.71
6.94
3.30 :
696.73
55.74
3.46
1.25
0.80 :
86.71
7.76
3.69 :
696.73 :
62.32 :
3.87
'
1.50
1.75
0.80 :
0.80 :
$6.71
86.71
8.50
: 9.18 :
4.04 :
4.36 :
696.73
696.73
68.27 :
73.73 :
4.24
4.58
2.OD :
0.80 :
86.71
: 9.81
4.66 :
696.73 :
78.83
4.90
2.25 :
0.78 :
66.71
: 10.15
4.95 :
696.73 :
81.52
5.20
2.50 :
0.76 :
86.71
: 10.42 :
5.21 :
696.73 :
83.72
5.48
2.75 :
0.74 :
86.71
: 1D.64
5.47 :
696.73 :
85.50 :
5.75
3.00 :
0.72 :
86.71
: 10.81
5.71 :
696.73 :
66.89 :
6.00
3.25 :
0.69 :
86.71
: 10.79 :
5.94 :
696.73 :
66.67 :
6.25
'
3.!0 :
0.66 :
86.71
: 10.71
6.17 :
696.73 :
66.03
6.48
3.75 :
0.63 :
86.71
: 10.58 :
6.38 :
696.73 :
85.00 :
6.71
'
4.00 :
4.25 :
0.60 :
0.58 :
86.71
86.71
: 10.41 :
: 10.37 :
6.59 :
6.80 :
696.73 :
696.73 :
83.61 :
83.31 :
6.93
7.14
4.50 :
0.54 :
86.71
: 9.93 :
6.99 :
696.73 :
79.81 :
7.35
4.75 :
0.52 :
86.71
: 9.83 :
7.19 :
696.73 :
78.96 :
7.55
'
5.0D :
0.49 :
66.71
: 9.50 :
7.37 :
696.73 :
76.34 :
7.75
5.25 :
0.46 :
86.71
: 9.14 :
7.55 :
696.73 :
73.43 :
7.94
5.50 :
0.44 :
66.71
: 8.95 :
7.73 :
696.73 :
71.89 :
8.13
5.75 :
0.42 :
86.71
8.73 :
7.91 .
696.73 :
70.17 :
8.31 .
'
6.00 :
0.40 :
86.71
: 8.50 :
8.08 :
696.73 :
68.27 :
8.49
11
VA
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1 L I _, 14A. 11 I Th.
WEST PROSPECT ROAD
n Me MISS
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61 =_-60 58
BL B 1 BLDGC 0
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JBB TA
_. 'jLso IICSIDNED Charm
MARCH 94
APPROVED DAa - 11 —
NEW
MERCER
CANAL
Sew
AS seek
res
Engineering Consultants
PC
OVERLOT GRADING NOTES
f
All overlot drainage Shall be graded to a minimum slope or zx.
z
All tab anoll be Waded with a minimum tall or 05 in the Frst 10 away from
foundations
3
The minimum cover for Tznm gross to the lowest e.Vemty of the Iwneatlon Wall
1
shall be 36"
-
{ Y' METAL SOEWALK CUU£RL
J�
6
The finished grade tuns the deer end of mutes an sleep streetsmay per
a ion
dropped to d the slope down to me Protective sealed as long as 36'
l
`
Maintained
o t ined.
'
J'U
I
5.
The minimum f a tin Fractions above finished grade shall be B'.
N
�
s
Slopes of 4:1 ter shoe be sodded to mlmmze erosion.
w greater
)
accordance
All Iota with ovt gracing fills of 9' or greater shall be constructed in cwdanPe
W
>
I
79
dat19G (FHA).
WRn
p
B
minimum
Sanitary newer lines shall oInstalled 'm t-slope or sx to the
111 sewer MCI,
aan¢ory a
W
Il prl9k.mbsseeparc[eilde.alkyd
aa,ma dyrFray centerine Wade
t
4~1
10.
The mMinum distance from house finished floor elevation to the sanitary fewer
login invert shall be 12 vertacily.
i
—
11.
The Bnkhed Wade and rosined tap of foundation elevations ore eased on a scaled
bulling setback Shorn from property line. Any variation of setbocF or building
size enlargement may real me finished top of foundation elevations to change.
LEGEND
A or B
MA GRADING DESIGNATION
�JO
PROPOSED SPOT ELEVATION
r
`g 60)
EXISTING ELEVATION
—B3�
PROPOSED CONTOUR
EXISTING CONTOUR
iF
TOP OF CONCRETE FWNDATON WALL
GARDEN
DAYLIGHT GARDEN
LEVEL BASEMENTS
GAR
GARAGE LEVEL
SUMMERHILL P.U.D.
FORT COLLINS, COLORADO
Y
,e l
iI
SCALE 1=40'
GALL ralTIA OF MO ADO
1-800-922-1987
ck 534worker 4-6700 "�
City of Fort Collins, Colorado
UTILITY PLAN APPROVAL
APPROVED: abortion of of EOXlnewro" Date
CHECKED By. ester h Vw1 wAUr Utility Deter
CHECKED BY:
Stormwster UU6ly Deter
CHECKED BY
Psrte W Recrea0oa Dale
CHECKED BY: — Woe
CHECKED By
rats
+P= ' Sul
FHA GRADING PLAN Jp