HomeMy WebLinkAboutDrainage Reports - 12/14/1993STORMWATER REVIEW COPY
Pinal Aporoved Report�
Final'Stldrm ainage Report
for
FLAGSTONE PATIO HOMES P.U.D.
FROPERTY OF
STEWART&ASSOCIATES
Consulting Engineers ar d Surveyors
103 South ilePdwm SLwet
loaf Cot", Cotolrodo 80521
y 3031482-9331
5'bAm
TABLE OF CONTENTS
TOPICS
Executive Summary
Storm Drainage Report
- Erosion Report
COVER / LOCATION
Erosion Control Design/Estimate PINK
- Times of Concentration YELLOW
Rational Runoff Computation
Hydraulic Design GREEN
Streets, Pans, Piping...
Referenced Attachments RED
EXECUTIVE SUMMARY
- The drainage basin master plan for the McClelland Drainageway
along Mail Creek would best describe the area for this
completion to a previously approved development.
Improvements in the surrounding area adjacent to the project
are not pertinent to this improvement. All adjacent properties
have been improved. This is a "fill-in" of a previously
approved, yet not completed PUD.
- Storm water release rates are addressed in our utilizing the
developed and sized detention facility for Larkborough
Subdivision. Previous work has included our acreage in sizing
and release computation.
There is no upstream concerns for this 3.63 ac of the
Rangeview PUD completion., No upstream flow applies to this
filing.
All adjacent property has been developed.
- No stormwater flows will be detained on site.
The affects of this project finalization will be to improve
current conditions in the existing Larkborough Subdivision.
Larkborough abuts this project on the west where our newly
constructed 2-ft concrete drainage pan will cut off offsite
flows in that direction. Thus improving that drainage pattern.
- No areas will be left with a grade of less than one percent,
without pans or underdrains.
All flows from this site are being released into Mail Creek,
either by the current Rangeview drainage system or in a
controlled release through Larkboroughs' existing detention
facility.
- No basin improvements are being proposed as part of this
project.
Property damage will not be expected as a result of this
3.6 ac development.
NOTE•
Please refer to the excerpt from previous work, to detail
inclusion of this project, in all of the aforementioned
existing improvements. These are included in the Storm
Drainage Report for Rangeview PUD.
Storm Drainage Report for the Flagstone Patio Homes P.U.D.
a Replat of a Portion of
Rangeview P.U.D.
The Flagstone Patio Homes P.U.D. is a Replat of a part of
Rangeview P.U.D. (circa 1982) that was originally a Replat of the
Mail Creek P.U.D.,(circa 1980) reference attachments. The
3.62-ac of this Replat are located in Larimer County Colorado, City
Of Fort Collins, specifically in Southeast Corner 1/4 of Section
35, Township 7 North, Range 69 West. This acreage is within the
original Rangeview boundary, though to date has not seen any
construction activity. Existing along the east boundary of the site
with the New Mercer Canal, is a 6-ft. easement that will replace
the 10-ft that was originally platted. Additionally, new storm
water/utility easements will be dedicated. What is being proposed
are 26 dwelling units consisting of 13 duplex buildings.
The site is in the Mail Creek basin, and been shown as fully
developed in all previously approved storm drainage reports. The
modifications in this Replat pertain to an increase in density
(dwellings/acre) while not substantially changing the amount of
impermeable area. These two factors should enhance the
acceptability of this project.
Storm Drainage Report.
Flagstone Patio Homes P.U.D.
Page 2
SITE HYDROLOGY
Total hard surfaced area in the 1982 proposal for the
20 duplex units were, 10 building times 115-ft x 50-ft or
57,500 sq.ft. of impermeable roof area. The current proposal in
26 units times 54-ft x 34-ft for a total impervious of 47,736
sq.ft., a net decrease in usage. No significant change in storm
drainage computations can be realized from this minor modification.
Times of concentration (TOC) were established by use of the
City of Fort Collins "Storm Drainage Design Criteria and
Construction Standards" (SDDCCS). A weighted "C" was established
for the entire site and used to determine the basin TOC's. These
TOC values were the basis for establishing intensities for design
storms, again from SDDCCS Table 3-1. Design storms of 2, 10, and
100-yr frequency has been evaluated. A spreadsheet was developed to
compute TOC's and direct runoff volumes. The Rational Method was
chosen because of the limited area of this project. The SDDCCS
suggests using a runoff coefficient of C=.50 for this type of
development, however because of this particular usage it was
decided to compute a basin coefficient for each sub -basin
independently (see attached).
The 3.62 acres in this project breakdown into six distinct
areas of runoff. Two of which total .97 acres, and have not changed
from the previous approval in design concept.
Storm Drainage Report
Flagstone Patio Homes P.U.D.
Page 3
Discharge from this area will release into Mail Creek through
either the existing storm drainage collection system (.92-ac) or
undetained offsite discharge (.05-ac). Runoff volumes for the .92-
ac are 2.0 and 5.4 cfs respectively for the minor and major storms.
While the 0.05-ac of undetained area generates 0.1 and 0.3-cfs in
minor and major events respectively. Both areas are discharging by
a method, and in a volume previously anticipated (see attachment).
The remaining 2.65 acres again falls into the realm of work
previously designed. While the aforementioned .97-ac area were not
included in any detention calculations, this acreage 2.65-ac is
being directed to an area intended, and designed for that purpose,
the existing Larkborough Detention facility. In the report for the
Mail Creek, the Larkborough Detention area, it is shown that the
"fully developed... upstream" condition is included with the design
criteria for said detention. Flagstone Patio Homes is upstream of
this facility, and included in the sizing. Thus, no further
consideration to sizing or capacities have been addressed for this
previously conceptualized improvement. Rather attention will focus
on newly constructed facilities as part of this replat.
SITE HYDRAULICS
This 2.65-acres newly developed basin breaks down into
substantially three areas for hydraulic consideration. First is
basin A-1 from the Grading Plan (GP), which abuts the existing
Larkborough Subdivision on the west.
Storm Drainage Report
Flagstone Patio Homes P.U.D.
Page 4
The basin includes 0.80-ac and develops runoff volumes of 0.8 and
2.9-cfs for the minor and major events. These flows will be
directed into a grass swale that will flow to the existing
detention, North. No flow will be directed from the existing
Larkborough Subdivision into this swale as indicated by the
topography. Capacity will allow the 100-yr storm to be conveyed,
without overtopping (see GP). Additionally, the swale will function
as a cutoff for historic flows moving toward that portion of
Larkborough. Grades will match the existing grades in Larkborough.
The second basin A-2 carries the bulk of the storm water to
the aforementioned detention. A total area of 1.17-ac develops
1.9 and 6.2-cfs for the 2 and 100-yr storms. This flow will be
directed to the center line of the newly constructed private road
with an inverted crown. Near the center of this cul-de-sac, an
asphalt swale will direct these flows easterly. A grass swale will
then be built to carry these flows into the Larkborough detention
pond. Slope stabilization will be incorporated at all points of
grade and/or channel material transitions. Capacity will be capable
of handling the 100-yr event.
Sub -basin A-3 will release directly into the pond. The area of
.13 ac will generate minimal direct runoffs of 0.2 cfs and 0.6 cfs
and release through the landscaped areas behind lots 6 and 7.
Storm Drainage Report
Flagstone Patio Homes P.U.D.
Page 5
The final drainage, basin A-4 encompasses .55-ac and develops
flows of 0.6 and 2.1-cfs for the design storms. Here an earthen
swale will flow to the North nearly parallel to the New Mercer
canal on the East side of the property. This swale will merge with
the swale leaving the cul-de-sac approximately 90-ft South of the
North boundary line. Here again the combined flow will be directed
North through a swale that terminates in the existing detention
facility. Sizing is such that the entire 100-yr event from basin A-
2 and A-4 will be carried by this 90-ft section of surface channel.
Flows being directed to existing storm drainage facilities
fall within the design capacities constructed. All swale side
slopes will conform with SDDCCS requirements, and be capable of
carrying at least 133% of design flow. The swale adjacent to the
New Mercer Canal will for a stretch, of approximately 300-1f,
maintain a grade of 0.8 %. Pans will be constructed in all areas
where grades are less than 2.0%. Capacity will still meet standards
though grading will be slightly less.
Storm Drainage Report
Flagstone Patio Homes P.U.D.
Page 6
CONCLUSIONS
In the final analysis no risk to property or human health
would result from allowing the Flagstone Patio Homes P.U.D., with
the aforementioned minor modifications, to move forward. This
project has been designed to the standards of the City of Fort
Collins. Noteworthy, is that much of the required design has
already been reviewed, thus finalizing the development has no
unforeseen effects to adjacent property owners. Consideration has
been given to hydrology as it relates to use of the Larkborough
detention facility, and hydraulics have been planned into the
existing storm drainage collection system. Except for the site
specific considerations of hydraulic and hydrology the project had
substantially been completed in prior approved submissions.
Should questions arise on any topics relating to this project
please feel free to contact Alex Evonitz or myself at our office.
Respectfully,
Richard A. Rutherford, P.E. & L.S. *: 5028
/rangrept
Erosion Control Report for Flagstone Patio Homes P.U.D.
a Replat of a Portion of
Rangeview P.U.D.
The Flagstone Patio Homes P.U.D. is located on a portion of
the original Rangeview P.U.D. that to date has not been
constructed. This site located in southwest Fort Collins (described
earlier) falls into an area of moderate erosion for both wind and
rain. Currently, the site is in native weeds and grasses.
Additionally, drainage patterns are such that the Larkborough
Detention facility is the point of collection for runoff. The site
orientation is generally north and south, approximately 600-ft long
and 300-ft wide.
It is proposed that overlot grading be utilized for this
2.65-ac project. Noteworthy, is the fact that the .97-ac portion of
the site that abuts the existing development on the south will
quickly go from construction to landscaping in a manner similar to
any residential construction within an established development. The
fact that the 2.65-ac remaining is such a restricted area for
storage, and flatter slopes favor the concept of overlot grading.
The proposed storm drainage design integrates well into the
overlot grading concept being examined. We have identified two
specific release points for storm water into Larkboroughs
detention, these would serve as points for sediment filters in the
form of straw bail barriers.
n
Additionally, the entire North boundary of the site will be
surrounded by a straw barrier and silt fence. Results of the traps
fall within the performance standards for the period of
construction 79.7% proposed vs. 79.5% required. The 79.5%
represents the highest standard for the 4 basins of interest.
Actually, these numbers are conservative for the site because as we
break down specific basins, we increase for the requirements entire
site. Thus by utilizing the standard for the .80-ac subbasin for
the site we meet a more restrictive standard than that necessary
for the 2.65-ac..
Potential slope erosion into the existing detention pond will
be addressed with a product produced by North American Green. This
flexible channel liner will be utilized to stabilize the 4:1 slope
that is currently in native grass and weeds. Both during the
construction, and after completion of the project, this
non -degradable nylon geotechnical matrix will remain in place.
Vegetation will grow through the matrix providing a natural
appearance with easy maintenance. The nylon will provide the
necessary slope stability following development of the storm
drainage collection apparatus.
If the construction sequence that we have proposed is
implemented, there should be no significant impact as a result of
this development project. Computational sheets are included as part
of this submission. Should questions arise regarding this or any
aspect of this project certainly feel free to contact Alex Evonitz
or myself so we may clarify any misunderstanding.
_ CONSTRUCTION SEQUENCE
PROJECT: ic,�T".i* �U i�ZjV nn STANDARD FORM C
.QUENCE. FOR 19 91 ONLY COMPLETED BY: `!5GSL*2T i �IiiOC. DATE:
Indicate by use of a bar line or symbols when erosion control measures will be installed.
Major modifications to an approved schedule may
require submitting a
new
schedule for
approval by the City Engineer.
3
YEAR
MONTH I I
_
�? f 1 14\I I
Z
1 I l--il I
OVERLOT GRADING
WIND EROSION CONTROL
Soil Roughing
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 L7ofUl FRAINa(tE)
VEGETATIVE:
Permanent Seed Planting)
Mulching/Sealant
Temporary Seed Planting
Sod Installation
Nettings/Mats/Blankets
Other I
4-4
----------------------------------------------------------------------------------------
STRUCTURES: INSTALLED BY U -)1-,?Prr5 MAINTAINED BY *_
VEGETATION/MULCHING CONTRACTOR
DATE SUBMITTED 1�- q
iI/SF-C:1989
APPROVED BY CITY OF FORT COLLINS ON
--------------------------------------------------
RAINFALL
PERFORMANCE STANDARD
EVALUATION
PROJECT:
iLayS�
2�, 1� .
1c,53
2----STANDARD
FORM A
COMPLETED
--------------------------------------------------------------
BY: S1��lJ�2S
'Ayac. IFve
l DATE: I I
-I- 3
DEVELOPEDIERODIBILITY1
Asb I Lsb
I Ssb
Lb Sb
I PS
SUBBASIN
---------
ZONE
-----------
I (ac)
(ft)
M
(feet)
M
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---------------------------------------------------------------------
DI/SF-A:1939
- -EFFECTIVENESS-CALCULATIONS------------- - -
--------- - - - - -
PROJECT �qis-vpcz < eQ O. STANDARD FORM B
COMPLETED BY: C �-)6(1'r � 45oc . Au-Q, DATE: I
I
Erosion Control
C-Factor
P-Factor
Method
Value
Value Comment
----------------------------------------------------------
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,go -
Sr�T Y'Clacz ..
1.0
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------------------
MAJORI PS I SUB
BASINI (%) 1BASIN
P 3,0�--2-
•---------------------------------------------------
AREA
(Ac) CALCULATIONS
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------------------------
)I/SF-8:1989
/z
EFFECTIVENESS CALCULATIONS
----------------------------------------------------------------------
PROJECT: STANDARD FORM B
COMPLETED BY: DATE:
Erosion Control
C-Factor
Method
Value
--------------------------------
Sra
4S
P T� CTnczt N
1, o
--------------------------------------
MAJORI
PS
SUB
AREA
BASIN
(%)
BASIN
(Ac)
-----
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------
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P-Factor
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--------------------------------
CALCULATIONS
---------------------------
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---------------------------------------------------------------------
I/SF-8:1989
STEWART$,LSSOCIATES 103 S. PH. 482-93 1 F X FORT
82 938OLLINS, CO 80521
Consulting Engineers and Surveyors
By:� Date:9'Z> Client: ' FM-FRSD*� Sheet No. of
Project: -p ���� ? �?u.lb.
Subject:IE�1 l U-, A F
Dc9e
I
y34/ six c) 41 ���� - } 1� 1I m
M�o x t,f 0�;-Fpo— 2E7P.
JD �nz kJ eAIa.S
Z l Do C1S� j 5O
JAN-11-93 MON 13:09 1 NORTH AMERICAN GREEN FAX NO. 8670247
P. 05
0
NORTH AMERICAN GREEN
FLEYJBLE CHANNEL LINERS
Developed for extreme slopes, high -discharge channels, and applica-
tions requiring semi -permanent to permanent protection and vegetal
reinforcement. The coconut and nylon flexible channel liners consist of
heavy duty, UV stabilized netting and a uniformly consolidated coconut
or nylon fiber matrix for superior erosion control performance.
C125
The 0125 flexible channel liner features a 100% coconut fiber
matrix sewn between two heavy duty, UV stabilized nets. The
heavy duty construction and high performance coconut fiber
matrix of the C125 provides increased durability, longevity,
and effectiveness required for protecting high -discharge chan-
nels and other difficult -to -stabilize sites.
A composite channel lining consisting of C125/vegetation sideslopes
and a concrete low -flow bottom provides a cost-effective, aesthetic
alternative to njorap. The North American Green Erosion Control Plan
Software System was used in designing the composite lining for opti-
mum channel scour protection.
XI,C
The P300 flexible channel liner features a 1000% recycled
nylon fiber matrix sewn between an extra heavy duty, UV sta-
bilized top net and a heavy duty UV stabilized bottom net. The
P300 is a non -degradable blanket designed to provide tempo-
rary protection of high -discharge channel surfaces until vege-
tation establishment, and permanent reinforcement of vegeta-
tion after maturity,
The P300 was used to establish and reinfeme the grass stands pro-
tecting the banks Of this permanent stream. High -velocity discharges
will damage established grasses without supplemental root protection
and reinforcement provided by the P300.
SureLock' Staple Gun
Use of the SureLock staple gun
makes staple placement quick
and simple. The patented,
spring -operated design and
extended handle of the Sure.
Lock staple gun eliminate con-
stant bending and stooping
involved in staple placement by
hand. The SureLock is the most
cost-effective method for
installing North American Green
blankets, as well as other materk
als and geotextiles that must be
anchored to the ground.
' 1
The North American Green Erosion Control Plan Software System pro1 Distributed By:
-
vides computer -assisted design of materials for slope erosion protec-
tion and channel scour resistance. The computer programs are based
on laboratory and field research involving erosion control blankets,
vegetation, and aprap, uhli>Ing a channel lining selection prOCedure
developed by the Federal Highway Administration. The North American
Green 50ftware System comas COmplete with a Comprehensive design
manual and aASlb programs on a5.25 or 3.5 inch floppYdisk,__
JAN-11-93 NOW 13:08 NORTH ANERICAN GREEN FAX NO, 8670247 P,03
Effective 2/20/69
NORTH
AMERICAN
GREEN
MATERIAL SPECIFICATIONS CATEGORY I
P300 Permanent Channel and shore lining shall be a machine -produced mat of 100Q/o
recycled nylon fiber.
The blanket shall be of consistent thickness with the nylon fiber evenly
distributed over the entire area of the mat. The blanket shall be covered on the
top with black polypropylene netting having ultraviolet additives to reduce
breakdown, approximate 112 inch x 1/2 inch mesh size. The bottom net shall also
be UV stabilized polypropylene, with a 5/8 inch x 5/8 inch mesh size. The
blanket shall be sewn together with polyester thread.
Nylon fiber channel and shore lining shall be P300 as manufactured by
North American Green, or equivalent. Nylon fiber channel and shore lining shall
have the following properties:
Material Content
Recycled Nylon Fiber
Netting
Thread
Physical Specifications (Roll)
Width
Length
Weight
Area
100%
(.80 Ib/y2) (.436 kg/m2)
One side heavyweight UV stabilized
(5.0 Ibs/1,000 sq ft approx wt)
One side heavyweight UV stabilized
(3.0 Ibs/1,000 sq ft approx wt)
100% Polyester Black
6.5 feet (2m)
83.5 feet (25.4rn)
48 Ibs ± 10% (21.8 kg)
60 sq yd (50m2)
JU LY 1993
COMPOSITE RUNOFF CALCULATIONS
FOR EACH SUB -BASIN
By: Stewart and Associates
BASIN
A-/
BASIN
A-2
Surface Character
Runoff'
Area
S Ft
Runof'C"
Area
.FL
Street, Oriym
Perkin lots
Aa harc
o.9s
o.9s
7551
Concrete
0.95
1792
0.95
5760
Gravel
0.50
0.50
Roof
0.951 9100
0.951 1/688
Lawn, Sandy Soil
Flat< 2%
0.10
Q10
Assnagi,2W7%
0.15
0.15
Stea>7%
0.201
0.20
Lawn, Heavy Soil
Flat < 2%
0.20
238711
0.20
22966
Avers 2 to 7%
0.25
0.25
Steep >7%
K 0.35
0.35
BASIN
A-4
Runoff"C"
Arm
S .FC
0.95
2016
0.95
0.50
0.95 8282
0.10
0.15
0.20
0.201
13680
0.25
SUMMARY OF BASINS
CA123%rngcompo.wk3
BASIN
A-5
RunoM"C"
Arm
S .Ft
0.95
0.95
224
0.50
0.95 918
0.10
0.15
0.20
0.20
1038
0.25
0.35
BASIN
A-6
RunoC" "C'
Arm
S FC
0.95
9804
0.95
WE
0.50
0.951 11934
0.10
0.15
0.20
0.20
14737
0.25
0.35
5 houses with 1/2 roof area of 1500 sf.(eg 1/2 roof = 750s1)
BASIN 5096500 3119225 0.61 5 houses with 112 roof arm of 1500 at.
A-2
BASIN:
5663.00 284560
1 1 0.50 5 houses with 1/2 roof arm of 1500 sf.
A-3
0.52 Shouses with 1/2 roof arm of 1500 sf.
BASIN
2395&00 1250G10
A-4
0.59 k 9 houses with 1/2 roof arm of 1500 sf.
BASIN
2176.00 1 F-129210
A 5
BASIN 4007500 2701&50 0.67 4 houses with 112 roof arm of 1500 sf.
A 6
3.62 = Tat. Arm For Composithiii
NOTE: - All composites are based on the equatim in 3.1.6 SDDCCS Manual
- These basins are of interest because of there Largely grass arm without streets
- These composite'C" values are used in the spmdshests with the appropriate bruins
STEWART&ASSOCIATES
Consulting Engineers and Surveyors
By: Date: Client:
Project:
Subject:
, N&I V.J
103 S. MELDRUM, FORT COLLINS, CO 80521
PH. 482-9331 FAX 482-9382
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STEWART&ASSOCIATES 103 S. PH 482-93 DRF X FORT
COLLINS, CO 80521
C nsultingEngineersandSurveyors
By: Date: ZS Clierd: Sheet No. of I
Project: A� hd AC.STIIr 9�
Subject:
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`RAI`4GE-VfEVV-SUMMARY TABLE OF STORM DRAINAGE
COMPUTATIONS
***NOTE: See Individual Basin Calculations
Attached
Total Runoff From
5.61
Basins
Project Area
_._...:.-.:59.1
10 yr. runoff
A-1...A-6
`17.6
100 yr. runoff
Total Runoff To
S 3.5
2 yr. rurwfF
Basins
Existing Stonn Drainage P -.. ' 6.0
10 yr. runoff
A-1...A-4
Facilities
F 11.91.
100 yr. runoff
Total Runoff To
0.1
2 yr. runoff
Basins
Existing New Mercer
0.1
10 r. runoff
A-5, A-6
Ditch East Boundy
0.31
100 yr. runoff
NOTES : — TOC's were for the 100 yr event in all cases
— In basins previously approved (A-5,6) confirmation of direct mnoff was undertaken
113 RANGVIW
Rangeview continued B:\range\mngviw.wk3 Disk #1
JULY 1993
BASIN RUNOFF COMPUTATIONS FOR THE 2 / 10 / 100 YR. STORM EVENT
ru r
Rangeviear P.U.D.
b:\rancviw.wk3 yy�>
HISTORIC TIME OF CONCENTRATION CALCULATION FOR RATIONALMETH00
0.20=Runoff C 1.00-Cf2,10 1'.25=Cf 100
D. Pnt.
Slope
%
C' Cf
Length
feet
I Overt Tc
min.
Vel.Chan.
ft/sec
Tc Chan.
min.
Tc Total
min.
COMMENTS
1 2 yri
1.3001
0.20
463.00
33.2
Overland T.O.C.
0.001
0.0
0.0
-: 33.2.
2 yr Total T.O.C.
1 100
1.3001
0.251
463.001
31.31
1
1
1 Overland T.O.C.
0.001
1 0.01
0.01
31.3
100 yrTotal T.O.C.
NOTE: Velocity in a Channel per FIGURE 3-2
If C' Cf >- 1 use C' Cf = 1 (thru out computations)
HISTORIC RUNOFF COMPUTATIONS FROM RATIONAL METHOD
0.20 - Runoff C 1.00 = Cf 2 10 1.25 = Cf 100
D. Pnt.
Area
acres
C' Cf
I (2yr.)
in/hr
I (10yc)
in/hr
1 (100yr.)
in/hr
O VOI.Bsn.
efs
Total 0
cfa
COMMENTS
1
2.85
0.20
1.40
0.80
0.8
2 Yr. runoff
0.20
2.50
1 1.431
1A
10 yr. runoff
0.25
4.001
2.1351
2.9
100 yr. runoff
DEVELOPED TIME OF CONCIETRATION CALCULATION FOR RATIONAL METHOD
0.67 s 'C' Value 1.25 - Cf 1 GO
O. Pnt.
Slope
%
C' Cf I Length
feat
Overt Tc
min.
Vel.Chan.
*340
To Chan.
min.
Te Total
min.
COMMENTS
1 100
2.01
0.711 55.01
4.31
1
Overand T.O.C.
0.71 461.01
1 1.001
7.71
11.9
100 yrTotal T.O.C.
2(IOOvd 0.711 70.01 4.8 1 1 1 Overland T.O.C.
0.711 467.01 1 1.731 4.51 9.3 100 yr Total T.O.C.
3 100 r 2.0 0.71 35.0 3.41 1 Overand T.O.C.
0.711 0.01 1 2.001 0.0 <' 3:41 100 r Total T.O.C.
6 100 r 2.51 0.711 40.01 3.41 i i i Overand T.O.C.
0.711 0.01 1 2.001 0.01 3.4 100 r Total T.O.C.
NOTE: Velocity m a Channel per FIGURE 3-2
If C' Cf > - 1 use C ' Cf = 1 (thru out computations)
2/3 rangviw
Ranaeview continued
'. DESIGN RUNOFF COMPUTATIONS FROM RATIONAL METHOD
1 X0 = Cf 100 ` 1.25 = Of 2,10 - NOTE: TOC 100 USED FROM ABOVE
D. Pnt.
Area
scree
C' Cf
I 1 (2yr.)
In/hri
I 1 (10yr.)
fin/hri
I (100yr.)
I 1In1hu
Q Vol. Ban.
fc&lcfs
Total 0
COMMENTS
A-1
0.80
0.44
2.35
0.83
0.8
2 r. runoff
0.44
4.10
1.44
1.4
/0 r. runoff
0.551
1 6.701
2.95
2.9
101 r. runoff
A-2
1 1.171
0.811
2.80
1
1 1.861
1.91
2 yr. runoff
0.611
4.501
1 3.211
3.21
10 yr. runoff
0.761
1 7.001
6.241
6.21
100 yr. runoff
A-3
0.13
0.501
3.28
1
1 0.21
0.2
2 r. runoffA-2 A-3
0.50
4.70
0.31
0.3
10 r. runoff A-2 A-3
0.631
1
1 7.001
0.571
0.61
100 r. runoff A-2 A-3
A-4
0.55
0.521
2.15
0.61
0.61
2 yr. runoff
0.521
3.751
1.071
1.11
10 yr. runoff
0.651
1
1 6.001
2.151
2.11
100 yr. runoff
2.65 = ACRES THAT WILL GO TO EXISTING DETENTION
A-5
0.051
0.591
3.28
0.10
0.1
2 r. runoff
0.59
4.70
0.14
0.1
10 yr. runoff
0.741
1
1 7.001
0.261
0.31
100 yr. runoff
NOTE: This area will release to the New Mercer Canal
A-6
0.921
0.671
3.281
1
1-2.021
2.0
2 yr. runoff
0.671
1 4.701
1 2.901
2.91
10 yr. runoff
0,841
1
1 7.001
5.391
5.41
100 yr. runoff
NOTE: This area will release to the existing Rangeview storm drainage facilities
0.97 = ACRES THAT WILL GO TO THE EXISTNG STORM DRAINAGE DESIGN
0
EQUATIONS USED:
OVERLAND TIME OF CONCENTRATION (TOC) - 1.87 (1.1 - C - CQ ^ .5 / S " .33
CHANNELIZED TIME OF CONCENTRATION (TOC) = CHANNEL LENGTH / VEL(fps) s 60
RATIONAL METHOD = Q= C s Cf s I a A-
313 ranow
July 1993
Manning's Equation for the Theoretical Capacity
of Non -Symetrical Triangular Section
0.020 = Side Slope 1 0.016 = Manning's (n)
0.020 = Side Slope 2 This Section
0.02 = Channel Slope
TYPICAL 2% S.S.
0.010 = Side Slope 1 0.016 = Manning's (n)
0.010 = Side Slope 2 1 This Section
0.01 = Channel Sloe TYPICAL EXIT
Flow Depth
ft/ft
0.
0.20
Intercept
ft from CL
Area 1
s /ft
025
1.00
Intercept
ft from CL
5.00
10.00
Area 2
s /ft
0.25
Total Discharge
This Section cfs
0.89
S.66
�
Intercept
ft from CL
10.00
20.00
Area 1
/ft
0.50
2.00
Intercept
ft from CL
10.00
20.00
Area 2
s /ft
0.50
-' 2.00
I V V VL-VC-JMIi
Total Discharge
This Section cfs
1.26
" 8.00'
10.00
0.30
1 .00
2.251
15.00
2.25
16 6
30.00
4.50
30.60
4.50
23.60
0.40
20.
35.93
40.00
8.00
40.00
8.00
50.82
0.50
25.00
6.25
25.001
6.251
65 14
50.00
12.50
50.00
12.50
92.14
0.60
30.00
9.00
30.001
9.001
105.93
60.00
18.00
60.00
18.001
149.82
0.70
35.00
12.251
35.001
12.251
159.79
>
70.00
24.50
70.00
24.501
226.00
0.80
40.00
16.001
40.00
16.00
228.14
80.00
32.00
80.00
32.00
322.67
0.90
45.00
20.251
45.00
20.25
312.33x
90.001
40.50
90.00
40.50
441.74
1.00
50.00
25.00
50.00
` 25.001
413.65
100.00
50.00
100.00
50.001
585.04
11 ro mai mmy s krq vawe is Trom z�uucc,j Tor mis umng
These two section shown are examples of possible design concerns in street sections
G •Z ek
S1��GAD ASS T�'1 IZ•5-�T '� E
Q=va
FAT S.1 cfs V z Z.S�; %s v-vlelj
July 1993
Manning's Equation for the Theoretical Capacity
of Non-Symetrical Triangular Section
0.250 = Side Slope 1 0.035 = Manning's (n)
0.250 = Side Slope 2 This Section
0.250 = Side Slope 1 0.035 = Manning's (n)
0.250 = Side Slope 2 This Sedion
0.02 = Channel Slope TYPICAL 4:1 0.008 =Channel Sloe TYPICAL4:1
Flow Depth
ft/ft
Intercept
ft from CL
Area 1
s /ft
1 Intercept
ft from CL
Area 2
s /ft
Total Discharge
This Section cfs
Intercept
ft from CL
Area 1
s /ft
Intercept
ft from CL
Area 2
s /ft
Total Discharge
This Section cfs
0.10
0.40
021
0.40
0.02
0.03
'"s"
0.40
0.02
0.40
0.02
0.02
0.20
0.80
0.08
0.80
0.08
0.20
-0.80
0.08
0.80
0.08
0.13
0.30
1.20
0.18
1.20
0.18
0.60
.
1.20
0.18
1.20
0.18
0.38
0.40
1.60
0.321
1.60
0.32
1.29
1.60
0.32
1.60
0.32
0.
0.50
2.00
0.50
2.00
0.50
2 34
'
2.00
0.50
2.
0.5u1.48
0.60
2.40
0.721
2.40
0.72
3.80
2.40
.72
2.40
0.7
2.40
0.70
2.80
0.98
2.60
0.98
5.7
o':.
2.80
0.98
2.80
0.98
3.
80
3.20
1.28I
.20
1. 8
8.18
3.20
1:28
3.20
1.28
5.17
1.621
.6
62
11.20
.::i
3.60
1.62
3.60
1.62
7.08
1.D0
4.D0
2.
4.D0
2.00
.83
400
2.00
4.00
2.00
9.38'
NOTE: - The Manning's (n) Value is from SDDCCS forthis lining
EAST (0tj/tp' Sw RS - These two section shown are examples of possible design concerns in grass swales
�too = �¢� = S .3 c �s � �ATrm ass 3a�.�e"�l *�
�
kT WWK l7�TN C i �C tt� Qtoo Q¢� = 7�i C �/ oeA7
K� = 1 T)�d of ilea. v AT MPx a At tT-ti
O q%7 % f.
o of i�z_
([
' + , [ _ f � t.! n.�t' � .. a l y1.1•n'1t :., �,t` a ,, ,� T r , .,r.i'..
' { � {e s;.; i r, ! 1, - r a i! a aTj�}} }� f{c i '}t'i. � � 3}�t { j �a i[.:r tt {rti k w � 1
x A+r {, ' ! C ; � L..f+li' .•w,9"�f i! i iiNt¢[ a. .7��'.a �.li � � (!j we{ } � � _ f Iti °ftiih`t7 fly. (l.,j } �.
, ! .i ni lx i! � {�iieylt S ".S ~+ � /{ fi iil1 S{♦}( •� 1{'��,/I�f At f t�ji iw wn� 1 1�}�'S �1 j1 T' t tl ,i .ill w. �k =j �lQ �t; i
+ 7� "r+� ii fi i f'i t 1 ���� ..! ',! t i ! u �'[jNi� lt•. ii� fC._ �t!{ t _t'i + t1�5�. t'�1t{ ).i it i. + it i.
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{ , � IT tI�{<:�irl� `ify¢vr- r•M,}%rti} a at ��! }i Y(�. L tit ii y " .fin•. �{` \ {�2�
l r � Zt F Y.i r �a 1 a � w e.(I.fSif�: }��ii�l1; 3&� � �Ii� 1 lF` +' � i� str a }ri.ar:i:l:il i. i �n i �[i{..r. .x.
.._.-�" 1,'7 �� _ ne;�.�i, t4 .e!. J`-i +sa......,...-31.tt. >.u.s» su.. S _)ti{s:l:r`-� 1 E. _ j�. �' 11 -,
6. Evaluate potential flooding hazard areas and associated damages
within each of these floodplains.
7. Develop alternative improvement plans and preliminary designs
to accomodate the 100-year storm runoff.
8. Evaluate the economic consequences of the alternatives and develop
a cost -benefit analysis for use in selecting an improvement plan.
9. Prepare a final report documenting the results of the study.
Summary of Study Findings
There is no way of predicting when a flood will occur in the Mail Creek
and McClellands Drainageways. Should a flood of even minor magnitude occur under
existing channel conditions, considerable damage to homes, businesses, railroads
and streets could result. Implementation of the recommended improvement plan
would prevent potential damage caused by floods greater than a 2-year event.
In selecting the recommended plan, a systems approach was used as well
as evaluating isolated improvements. We initially evaluated the cost (including
maintenance and operation) of a wide variety of improvements, and combinations
of these improvements, in order to find the most effective plan. We then added
to this, those major drainage improvements which are likely to be built when un-
improved ground is developed. Therefore, economically beneficial improvements
in conjunction with improvements likely to occur as a direct result of develop-
ment are part of the final plan. Continuity of the plan from reach -to -reach
was a major consideration, as were the environmental and aesthetic aspects of
the alternatives.
Flooding problems in Reach I occur only during intense storms because of
the well-defined channel. With peak flow reductions affected by detention in
Reach 2B, an improved spillway at Fairway Dam is all that is necessary to elimi-
nate flood damage. Reach 2A and 2B exhibit extensive flood damage potential due
to the lack of a well-defined channel for even the 2-year storm flows. Because
of the limited amount of development in this area, a grass -lined channel with
box culvert crossings of Harmony Road, Crest Road and Nordic access road will
effectively pass the 100-year storm event. The proposed upstream detention sys-
tem will allow a reduction in the size and construction costs of downstream im-
provements. Also, since the recommended detention is in an undeveloped area,
final location and configuration can be coordinated at the time ( if convenient)
of development and possibly be utilized as a multi -use facility. Grass -lined
channels between improvements are likely to occur at time of development with
final locations established in conjunction with the developer's plan. _
1� Reach 3, the New Mercer Canal, has the capacity to carry approximately the
25-year storm in addition to the ditch's irrigation flows. Peak flow reductions
due to detention in Reach 4 enables the canal to carry the 100-year storm event
within its existing banks. An improved overflow spillway section in the existing
Larkborough detention pond safely passes the 100-year storm flows.
I-2
Land Use
A percent impervious area was estimated for each subbasin for use in the
SWMM program by calculating a weighted average of the different types of land uses
within each subbasin. Types of land use for the City of Fort Collins were taken
from the aerial mapping, current City and County zoning maps and land use plans.
Typical percents of impervious area for each type of land use were taken from the
Fort Collins Drainage Criteria Manual (Reference #2) and verified against real mea-
surements taken from the 100-foot scale mapping. Percents impervious for existing
basin conditions includes all subdivision proposed and approved although not neces-
sarily constructed at the time of this analysis. Future basin values are derived
primarily from zoning maps and land use plans for the City and Larimer County, and
assume all development in the basin is complete according to the zoning.
Subareas were determined from USGS 7-1/2 minute quadrangle maps, 100-scale
orthophotographic mapping from the City of Fort Collins, the Fossil Creek Basin
study, and the location of major basin features such as railroads, arterial streets
and irrigation canals. Land uses and subareas are shown for historic, existing,
and future basin conditions on Figures II-1, II-2 and II-3, respectively (included
in the rear pocket).
I nSgp,
Losses due to infiltration were estimated from USDA Soil Conservation Ser-
vice Soils Survey. A variable infiltration rate using Horton's equation is avail-
able in the SWMM program, and this option was utilized in the derivation of hydro -
graphs. Initial and final infiltration rates were estimated by taking weighted
averages of the maximum and minimum permeabilities of the different types of soils
within each subbasin. Outliners were not included. A decay rate of 0.0018/sec.
was adopted from the Fossil Creek Study. Values of infiltration coefficients for
the subbasins range from 0.40 to 3.00.
Maximum depression storage values were obtained from the Urban Storm Drain-
age Criteria Manual. Uniform depression storage coefficients of 0.3 for pervious
and 0.1 for impervious areas were used in this study.
Flood Hydrographs
Selected flood hydrographs are illustrated in Figures III-2, III-3, III-4,
III-5, III-6, III-7, III-8 and III-9. Peak flood flows for the various design
frequencies have been plotted in Table III-2. Complete hydrologic data and,com-
puter output is contained in the Technical Addendum, available through the City
of Fort Collins.
Flood Histor
Information concerning the historic flooding occurrences in Mail Creek and
McClellands Basin is sparce. Because of the lack of development within the boun-
daries of the floodplain, few reports were filed that indicated (due to lack of)
significant flood damage
McCLELLANDS BASIN
Bordering the Mail Creek Basin on the north, the McClellands Basin shares
with Mail Creek similarities of land use, topography, soils and manmade features
which affect drainage. Upstream of Timberline Road, the basin is long and narrow
in shape. It is 2.37 miles in length and 6,400 feet wide at its broadest point.
It drains 1.75 square miles more or less. The basin originates at an elevation
of 5,025 feet above MSL and falls 89 feet to an elevation of 4,936 feet above MSL
at Timberline Road.
The historic McClellands Basin (see Figure II-1, in back pocket) drained
approximately 1,117 acres west of Timerline Road. Land uses were predominately
agricultural. West of College Avenue, there are few places where there is a dis-
tinct drainage channel. The basin is intersected by the Pleasant Valley and Lake
and the New Mercer Irrigation Canals, which were built in the late 1800's and
carry approximately 30 cfs and 80 cfs respectively in the vicinity of Harmony
Road. There are no wasteways or spill structures in McClellands, so it is highly
probable that most storm runoff originating upstream of these canals was diverted
to Mail Creek since the construction of the canals.
The McClellands Drainage Basin has been experiencing steady development in
recent years in the subbasins north of Harmony Road in the City of Fort Collins.
Most of the development has been done in accordance with the drainage criteria of
Fort Collins, and considerable on -site detention is being created. Development
is forthcoming in the section south of Harmony Road, portions of which have been
annexed into the City, however, existing land uses in the lower reaches are still
agricultural.
Manmade features affecting drainage patterns in the McClellands Basin are
the Union Pacific and Colorado & Southern Railroads, College Avenue, Harmony
Road and the Larimer County No. 2 and New Mercer Canals. The existing and future
McClellands Basin are illustrated in Figures II-2 and II-3 (back pocket).
MAIL CREEK STUDY REACHES
Mail Creek reaches included in this study begin at the confluence with
Fossil Creek and extend approximately 3.3 miles upstream to the center of Sec-
tion 34. For analysis, study reaches (Figure II-4) were broken out into the
following homogeneous segments:
Reach
IA
- Mail Creek from confluence with Fossil Creek to Mail
Creek Lane.
Reach
1B
- Mail Creek Lane to Palmer Drive.
Reach
1C
- Palmer Drive to U.S. 287 (College Avenue).
Reach
1D
- U.S. 287 to C & S Railroad.
Reach
2A
- C & S Railroad to Shields Street.
Reach
2B
- Shields Street to upstream study limits.
�r Reach
3
- New Mercer Canal between Mail Creek and McClellands —
tributary.
Reach
4A
- McClellands tributary from New Mercer Canal to center
of Section 34.
Reach
4B
- McClellands tributary from center of Section 34 to Shields
Street.
Reach
5
- McClellands tributary from Shields Street to upstream
study limits.
i
50
EXIST(N'
AR �(OPLAINW B V
$'tY 'WAR
�. xiv
FF �y[Yp-}-� /K
r1,
•
I t
1
-
5050 'NOTE'AREA FROM ROAD 70
-
-HARMONY
MAIL CREEK WAS INCLUDED IN I
I DAMAGE ASSESMENT BUT WAS
NOT INCLUDED IN THE FLOOD—
5045 —PLAINL_P—LAd—fL—PBOFILE.-------i-- — IMPROVED—._ ----
�
— �---- — —
— _ -- —r ---�
� --�I-- ---
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. 100 YR. W.S. PROFILE
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i I
I I I i
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STING CHANNE
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i
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5025
0-too 540 10+00 15.00 20.0 0
—
. ORSET OTH ROAD
505
-�t-
t x 1 ' • �I1�T I p• I I •° • BM 503:
r: s'so I----� I'1'�I,. .��• J � .i e�lxl I la I '\'�� `
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It
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Gr ��• ° \ ��`�i '� ._ I •7 ~ � �_\ �.s, " !!'< :ALE
3 � •
r— ---- — -- ,< . �.
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or
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31
INDEX OF IMPROVEMENTS
GRASSLINED CHANNEL
RECOMMENDED
DETENTION POND
O STRUCTURAL IMPROVEMENTS
Lai "
W -
Iq C3
a�cf).cn
o(aLJJ
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FIGURE LI
SHEET
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j^\ .�...��� �;\ r �)i •n\ l � 1 M �- ... � ° �;�.IN.M �nU rr. rE NN
.. ��. I.
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n
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I
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..... ... /.....: �. n y : .I
.. ........ . ..
4 .: :::.: .'i: •:::�.. •'r ...'•:.L: ... ::.::.::^ � •I I '�4 I UNION I I I ��
.......
,. ,. TIMBFRLIN
V'
n
P
r
m 7
N
>'
n
c
=
s
r
1
d
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m
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m
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m
m
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0
m
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—
r
P
m
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0
cf) MCCLELLANDS' 4 MAIL sCREEK
m DRAINAGE STUDY' `' CORNEU CONSUlTINCj COMPANY
fT1 �, MAN A(if MtNI .� lNI;INII itINlj
— ,— ---- TONING MAP _ x'646 ,!y"r eollltie ". cofox4do 6UV.1 (wl
rr''Y
I• \ 1
James H. Stewart and Associates, Inc. 1 of 3
Consulting Engineers and Surveyors
Laboratory:
214 North Howes Street 301 Lincoln Court
P.O. Box 429 P.O. Box 429
Fort Collins, Colorado 80522 Fort Collins, Colorado 80522
(303) 482-9331 (303) 4S"309
DRAINAGE REPORT
RANGEVIEW P.U.D. (MAIL CREEK P.U.D.)
The Rangeview P.U.D. is a replat of Mail Creek P.U.D.. The Mail Creek
P.U.D. had 5.9 acres draining to the detention pond and 1.5 acres flowing
overlot to the south. The Rangeview P.U.D. design proposes to drain 3.5
acres to the detention pond and 3.9 acres to the south and into the New
Mercer Canal. This will require approval of the irrigation company.
Bill Bartran has talked with Louis Swift about putting the water into
the New Mercer Canal, and Mr. Swift is in favor of the idea.
Draining the 3.9 acres into the canal will slightly relieve the overloaded
dedention pond and will get the water away and into Mail Creek before the
upstream peaks arrive. It is proposed to carry the run-off into the New
Mercer Canal in a 15 inch pipe on a slope of 5 percent. The capacity will
be 12 cfs, which will handle the 100 year flow. The north 3.5 acres draining
to the detention pond will be carried on the surface, on pavement and
concrete pans. The volume flowing to the north pond will be 0.63 acre
feet, and the capacity of the pond is approximately 11.5 acre feet.
The following two pages of computations show mass diagrams for the two
drainage areas of Rangeview. On both the area flowing north and the
area flowing south, unrestricted flow will allow about 2/3 of the total
run-off to get into the New Mercer Canal and through the pipe to Mail
Creek within the first 30 minutes of the storm.
We believe that if approval is given by the irrigation company, draining
the south 3.9 acres directly into the ditch and into Mail Creek will
provide a better and more workable situation, and that this variation
from the detention requirement is warranted.
G E*
A
i
COMPUTATIONS
JameS ri..ZStewart a( Assoc. L Fort Collins, Colorado
By: P1 R Date Client: pQT e r 5 o n F ASS O c. Sheet No. z of
Chkd By: Date Project p��>��'�t ` "' V• �• Job No.
Subject
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