HomeMy WebLinkAboutDrainage Report345 Saddleback Road
Carbondale, CO 81623
Drainage Report
December 17, 2025
Existing Conditions
The property described as 345 Saddleback Road is located in Garfield County, Colorado limits
within the Aspen Glen subdivision, also known as Garfield County parcel number 239513406025.
The legal description of the site, as shown on Garfield County GIS, is "Section: 13 Township: 7
Range: 89 Subdivision: ASPEN GLEN FLG #7 Lot: H25 .585 ACRES". The ± 0.585-acre parcel
is currently undeveloped, with only one other single-family residence in the area located to the
southeast. The other surrounding parcels are currently undeveloped. Saddleback Road Right -Of -
Way is located to the east of the site under evaluation.
w
Shown above is an image of the Garfield County GIS Map
displaying the location of 345 Saddleback Road
The general topography on the site slopes from the southwest to the north, towards the Aspen
Glen Golf Course, with approximately four feet of elevation drop. Grades on the property appear
to be relatively consistent with an average slope of around five percent. The northern area of the
site steepens up as it approaches the Aspen Glen Golf Course property. Slopes begin to approach
4:1 in this area and steepen more within the Aspen Glen Golf Course property. Vegetation of the
site consists of native grasses. There are little to no mature trees located on the parcel. It is
assumed the area was cleared when the Aspen Glen subdivision was developed.
Crystal River Civil LLC 970.51fl.D312 Page 1 of 7
F�M
Proposed Conditions
The proposed scope of the project includes the construction of a single-family residence located
within the defined building area of the site. The development includes an attached garage,
concrete driveway and autocourt, hardscaped patios, and extensive landscaping surrounding the
residence. Drainage swales, inlets, and a trench drain are proposed surrounding the residence to
provide positive drainage away from the residence. All tie-in grades to existing topography do not
exceed 4:1 to meet Aspen Glen HOA development requirements. Three -foot -high berms are
proposed to the south and east of the residence to provide privacy from Saddleback Road.
Driveway centerline slopes do not exceed five percent, including the autocourt area. The
autocourt also functions as a turnaround area for all vehicles.
The stormwater runoff created by proposed conditions will be collected by drains, downspouts,
and drainage swales, which all convey the stormwater to a single drywell located just northeast
of the residence near the northeastern property corner. All roof areas are collected by
downspouts, which will tie into the proposed pipe network to be conveyed to the drywell. All patios
sheet flow towards drainage swales or drains, which tie into the pipe network and terminate at the
drywell for detention.
Drainage Analysis
Multiple inlets, downspouts, swales, and a trench drain collect runoff from the proposed
impervious and pervious areas, as well as areas that slope towards the structure from the south
and west. The entirety of the proposed residence will be conveyed to the proposed drywell via a
pipe network and overland swales. All impervious areas are collected by this system. The drywell
will overflow from the grated rim if a storm event exceeding the 100-year, 1-hour storm event
occurs because it is located at the natural low point of the site. A controlled outlet pipe is proposed
at the drywell to release runoff at the predeveloped flow rate of the captured drainage basin. The
runoff is routed towards the Aspen Glen Golf Course pond located to the north of the property.
This drainage analysis uses procedures that have been standardized by the Mile High Flood
District's Urban Storm Drainage Criteria Manual, or the USDCM. Peak flows of the site have been
calculated using the Rational Method to determine the impacts the proposed project has on the
existing conditions and to verify the capacity of the proposed infrastructure. This method uses the
analyzed basin's area, soil type (assumed soil type B), percentage of imperviousness, time of
concentration, and the historic storm data from NOAA Atlas 14 to determine the maximum flow
rate from a specified storm event. The Rational Method uses the equation below to determine the
Maximum Flow Rate:
Q=CIA
Where,
- Q is the peak stormwater runoff rate, in cubic feet per second
- C is a runoff coefficient of the drainage area
- I is the storm intensity, in inches per hour
Crystal River Civil LLC 970,510.5312 Page 2 of 7
2
- A is the area of the drainage basin, in acres
The Runoff Coefficient, C, is determined using table 6-5 from the USDCM. To determine the storm
intensity, I, equations for each storm event were derived from AutoCAD Civil 3D Hydraflow
analysis software using NOAA Atlas 14 data. For smaller basins with a time of concentration of
less than five minutes, a time of concentration of five minutes is assumed — when smaller times
of concentration are used in the Rational Method, the results tend to be inaccurate, as per the
USDCM. The rainfall event used for this analysis is for a 10-year, 1-hour and 100-year, 1-hour
storm events. Below are tables summarizing the calculations to determine the predeveloped and
developed conditions for the onsite basins.
T 10•Year I-Hwr 0nsite Peak Disclrarge Calculations
RalnfalldoI
0_777e
SON Class ..
�1.
5?.42se
I�,P. +Te1°i•"
Dftchargn{ftrrSsCj
i::-•_;..
rvxe For basins with a flow length of less than 5001feet, a Time of Concentration is assumed at 5 minutes. These calculations are assuming a NRCS Hydrologic Soil Class B
Rainfall depth values derived from NOAA Atlas 14 data Intensity equation has been derived from the Aspen area NOAA Atlas 14 IDF Curve.
Predeveloped Conditions
.. sawn • . FP1tri _
C ValuC
ifmc of CancanvalSon
PeAk 016aharfle
tl3rrio• A.-r A. A'] I AJ r-.,l
1_'mir+
I{irNv;
fCrhoc
1 17587 0 0 00%
0.040
3 65
0.06
Developed Conditions
- $i11iq
tall Argo kip pWous Aram Pam
C Vallue
illne of Concantr4UM
enensay _
I ..PON Owdmm _
tt"� t Aye.
+9088
c :mr.��
IIrr:R+•
'R':si, y
1
17587 51.57%
0460
5
3,65
0.66
I00-Year I Haur 011site Peak Disc ha Cafe s
RainiawdeplhPl�tt
iMb[e7j 3
In:pnsltyStritt)
lzv.H16
!= [l1A s
tr Tr]
diRclWrgn�/$pC]
�=-1",
Mote For basins with a Flow length of less than 500 feet, a Time of Concentration is assumed at 5 minutes. These calculations are assuming a NRCS Hydrologic Soil Class B
j R;rrifa!I depth values derived from NOAA Atlas 14 data. Intensity equation has been derived from the Aspen area NOAA Atlas 14 OF Curve.
lPredeveloped Conditions
Hash Totai Afar MW&NIwit Area Percald iryrlkerviau■
CYspit:
111111105tlf 6oltt nlUon
Peak llkih tr .
;Namq. A, (rt"t
A.,n'• i n,-k--'
I
T.lra¢ll
1 17587
0 r 0 00-A
0 430
5
594
1.03
Developed Conditions
a,"
Area
Prruclnt ■
C V41utr Trine Of Corloe!'Rrati=
WHIR RY
Peak Elk
Man
A
m r
! VYn
'l,rt1
1 17587
9088
5167%
- 5
5-94
1.58
The onsite drainage conveyance structures proposed with this project have been designed to
have capacity for a 100-year, 1-hour storm event. The basins have been divided into sub -basins,
which were analyzed for each inlet and pipe. Spreadsheets showing these calculations are shown
below.
Crystal River Civil LLC 970.510.5312
Ba5tn Flow Rate Calculations •.�
. _. son Ci A l; intans#iy (rnlhr) I =(l12GafA �, Dischsrlpa ln' S6c} Q=Cl6,
1i+Fa7
pv-alues'.I.-n inthis table are analysing a 100-Year 1-Hour Storm Event. For basins with a flow length of less than 500 feet, a Time of Concentration of 5 minutes is assumed,
onditions
Srr6Oaa8t
alai Aroma
krCmYhxq Anet
is t iays
_ ... GVof„e
_
iinxlofCanrenVatlon
Inten
FIow.Rnle
Nanse}
A W
A, 11
NAt M)
G irrom Tablet
7 mir'�
t iM►
' j R'Isac
1.1
470
470
100 WV.
089
5
594
0.06
1.2
249
249
100.00°h
089
5
5.94
0.03
1.3
3.078
1,463
47.53%
064
5
5.94
0.27
1.4
537
537
100 00%
029
5
5.0-4
0.07
1.5
227
0
0.00%
043
5
594
0.01
1.6
414
414
10Q00 %
0.89
594
0.05
1.7
981
981
100.00Y
0.89
5
5.94
0.12
1.8
129
129
1fl0.00k
0.89
5
5.94
0.02
1.9
271
271
100 00%
0.60
5
594
0.03
1.10
159
159
100.00°/
0.89
5
594
0.02
1.11
388
388
100.00"4
0.89
5
5.94
0.05
1.12
191
0
0 00 %
043
5
5.94
0.01
1.13
434
434
10000 %
0.89
5
594
0.05
1.14
552
552
100.WG'
089
15
594
0.07
1.15
552
552
100,00%
0.89
5
5.94
0.07
1.16
2,856
257
8.015%
0.45
5
594
0.18
1.17
2,221
221
9.95%
0.45
5
594
0.14
1.18
350
350
100.00%
0.89
5
5 94
0."
1.19
365
365
100.00%
0.89
5
594
0.04
1.20
509
509
100.00 o/I
0.$9
5
9•:
0.08
1.21
290
290
100 00%
0.89
5
5 94
0.04
1.22
2,364
497
21.02 %
1 a 52
5
594
0.17
Crystal River Civil LLC 970.510.5312 Page 4 of 7
Pipe Capacity Calcutations
I
ipe $6C-Nort ' . _ - �� .. . -
hi a11111ti9 CiSYOw.10at, n
G.01
A1annlnds Equ4tio,i Ift' 511 L'r = to < `, 81' tii
Hvt Pipe Flow Rate (Qp) is the summation of the flow rates from the the collected sub basins through each pipe, or os
Pipe
CoAt yad Sub Basins'
P7pa t fuw Race
Stope
Prop:Pipe DTerneter
Pipe Svewrlol Area
Pipe Max Flow Rate
Pei c8es! et Cap�ciy.
(Name)
#
0 ft'f9eC
S e°pl
O Irt
A- rt
Q W0 s'r
Al
1.S
0.D6
2.00%
4
0.087
0.351
0,16
A2
1A
0.06
200%
4
0.087
Sk351
0.16
A3
1.1-1.2
0.09
200%
4
0.087
0.351
0.25
A4
1,3
0,27
2.00%
4
M87
0.351
0.77
A5
1 A -1.3
036
2.00 %
6
0 196
1.034
O,3d
A6
1.1-1.3
0.36
200%
6
0196
1.034
0.34
A7
1.4
0,07
2,00%
4
0.087
0.351
0.13
A8
1.4-1.5
0.08
200%
4
OW
0.351
0.22
A9
1.6
0.05
2-00%
4
0 087
0.351
0.14
A10
1.4-1.6
0.13
2.00%-
4
0.087
0.351
0.37
All
1.4-1.7
025
2.00%
4
0.087
0.351
0.71
Al2
1.4-1.a
0.26
2.00% 1
4
0 087
0.351
0.75
A13
1.1-1.8
0.62
2.00 %
6
0.196
1.034
0.60
A14
1.1-1.9
0.65
200%
6
0,196
1.034
0.63
.A15
1.10
0.02
2.00%
4
0 087
0 351
0.06
A16
1.1-1.10
0.67
2.00%
6
0 196
1.034
0.65
B1
1.11
0.05
2.00%
4
0 087
0.351
0.13
B2
1.11-1.12
0.06
2.00%
4
0 067
0.351
0.17
B3
1,13
0.05
2,00%
1 4
0.087
CL351
0.15
B4
IA 1-1.13
0.11
2 00 %
4
0.087
0,351
0.32
85
1.14
0.07
200%
4
0.087
0,351
0.19
B6
114-1.15
0.13
2.00%
4
0.087
0.351
0.38
B7
1.11-1.16
D-42
200%
6
0.196
1.034
0.41
B8
1.11-1.17
q56
2.00%
6
0.196
1.034
0.54
B9
1.18
0.04
2.00%
4
0.087
0.351
0.12
Bic
1.11-1.18
aso
2.00%
6
0.196
1.034
0.58
811
1.11-1.18
0.60
1.00 %
6
0.196
0.731
0.82
B12
1.19
0.04
200%
4
0.087
0.351
0.13
813
1.19-220
011
200%
4
Q087
0,351
0.30
814
1.11-1.20
0,71
1.00 %
6
0,196
0 731
0.97
B15
1.21
0.04
2,00%
4
0.087
0.351
0.10
B16
1.11-1,21
0.74
2,00%
6
0.196
1.034
0.72
,y
Enatylve @7ki Wru1, A, iR 1 nr "i i -
tyilnrDrlt=l.4n.
Round Inlet CaPacltY Calculation
inYvk DrEre C.ap�c.ty. Q. { Q, : t;,.�,V :'p1. v4j➢ rr HaCa peony. Q. W-Owl
✓'i,. • �..};'
Crdt CJ*rOcWnt.C,
ass
Ct it FaCwr,C
0.5,
Ar-Opr- an CAPWft Ra 0,R
0.6
3
tntat.Y
015
"&:Wc IV" Li' UL P, 3
P,n I -C, P
imm
AS -inlet
1.5
-
0
F3rwzwWa-A a
Ot%.-Floc.Caluaty
" t71 fsi
MWr10 cap=ay
S3
3uhbaskt
t7:Rr
'1.01
1124nlet
1.12
8
- --
-
B74nlet
1,18
12
7 N
'-
0.10
815-Inlet
1,21
8
t 1'�__
_
0•�
Drywell ARim 1.22 24
L.C4
0.17
Crystal River Civil LLC 970.510.5312 Page 5 of 7
-- R octang ula r hies Capa c hy'Uk utation
fft t*w NWAm; kmt1
•' I1-y�'~ 71
LNIRara CN. 0,Wh1
CVr/k',a:.oiRKia1LC
0.65
L Fyr.(p,C
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E17:-'9.v 1.riY. AVM LhCKn FWx Cu;laAy the ik�Jir ".=�.
5utaia�l+F7o1V
The Town of Carbondale requires stormwater runoff from a development site to not exceed more
than the historic runoff. For this design, CRC is proposing using historic data from a 100-year, 1-
hour storm event. Detention is necessary to offset the increased flows from proposed impervious
areas to be released at the historic rate. An analysis has been performed using the FAA Method
to determine this necessary detention volume. See the table below displaying the calculations for
the maximum difference between the stormwater volume entering the system and volume leaving
the system.
FAA Mothod Detention Volume Calculations
Sash Number
I
Swim Eve nISlza
1oaar 1-HW
Rain Sal] De pili, P, (Inj
19
Developed B.Wn C Valua
0.66
Basin Tlma of ConcentratJDm.Tz min
5
Basin Area.
17587
Pradevelo erd Flow Pale ek.
1,03
RAIntall Duration Swrt (rnln]
5
tntentiryUnlhh
s 01a
1 (11.44 Td)^" Developed Volume In (R�)
V,=iF,n-a7dA
PmdavaWW Vohtrns vt'
V. - NO s 7 "in Volume (t(')
V=V.Va
This AnaWs Uses the Federal Atialion Association Stormwater tvlanagement Whod. By Calculcl,m i the Difference in the Volumas, the
Capacity Required for Detention is Determined.
_• .ARWt+ADuMbim
hlwwfly
t).eve Ow
etadavoioped Vole
V SISI
Volume ❑ilferdIXC
V WIS
T,, min)
I(ttvlxl
V '1s
5
5.94
479.19
309.62
169.57
6
5.57
538.97
340.58
198.39
7
5.24
591.51
371.54
21997
8
4.95
637.99
402.51
235.48
9
4.68
679.34
433.47
245.87
10
4.44
716.32
464.43
251.89
11
4.23
749.55
495.39
254.16
12
4.03
779.54
526.35
253.18
13
3.85
806.71
557.32
249.39
14
3.68
831.41
588.28
243.14
- -
i1tAldnplfri i
254,16
To meet this required storage, the storm system will convey runoff to the drywell, with an outlet
that releases via a pipe with a designed orifice plate towards the Aspen Glen Golf Course pond
to the north. The proposed 270 cubic feet of storage meets the requirement of a 100-year, 1-hour
event for Basin 1. Sizing for the drywell is shown in the table below.
Crystal River Civil LLC 970.510.5312 Page 6 of 7
Stara p Calc ulaf Inn - DryvmMl
trnamJll Caparlry, V�} E>I:nmaitanac°Y.V. fll� - -- - .. 4amki�m7 GC �N. V {h'1
�'�11 Mnme R:ian.enlfSufs. i 6[.: dRs.lne±f� Siwua. f5.rkyf T Grarel Fsevfhe LfSe r-fal Cd�:o+X. j' �L![t�Li GNa[#Y i.Ol�1�MOd �..a�KY CN7CYuf1/3 Vukem. liA �.M :��
To utilize the FAA Rational Method of storage volume for detention, a controlled outlet pipe from
the drywell that releases stormwater at the predeveloped peak flow rate of the site for a 100-year
storm event is required. A three-inch orifice plate is called out on the design drawings for the
drywell included with this civil plan, utilizing the orifice calculation below.
Historic Release Orifice Calculation
Coefficient of Discharge (ca)
0.62
32.2
5053.20
5052
1.20
Sharp Edged
Ws
ft
ft
ft
i Gravitational Constant (g)
Rim Elevation
ormce Elevation
Etevation Differance (h)
Note- This calculation uses the Bernoulli Equation to determine the historic, pre-
deve Ioned flow rate throw h an orifce at drains e s tem outlet.
Historic Flow Rate (4)
Area of Orifice A)
Orifice Dlameter (De)
ft3is
Aa J c• f, -A ft
I Da — ,—_-, inches
1.03
0.21
3.07
For location, sizing, and all information regarding the stormwater design please see the civil
grading and drainage plan. If there are any comments regarding the stormwater analysis
performed for the site, feel free to contact me directly.
Vince Tomczak
Principal, P.E. O `p4 �
Crystal River Civil LLC V:� �• fi0; p
vince C stalRiverCivil.com
(970) 510 - 5312 ;.- �51'
Crystal liver Civil LLC 970.510.5312 Page 7 of 7