HomeMy WebLinkAbout1.05 Drainage ReportPNIYON MESA
DRAINAGE REPORT
FOR
PRELIMINARY PLAN fl]BNISSION
Garlield CountY, Colorado
Prepared for
JOIIN ELMORE II
Aspen, Colorado
Prepared by
Schmueser Gordon Meyer
Glenwood Springs' Colorado
't:,l
t,.
May 2ffi6
PINYON MESA
DRAINAGE REPORT
Garfield CountY, Colorado
CONTENTS
1. INTRODUCTION & OVERVIEW
2. STORMWATER RUNOFF
ON-SITE DRAINAGE CONSI DERATIONS
HYDROLOGIC ANALYSIS
1. Designation of Drainage Easrns
2. MethodologY
3. Basin Area
4. Rainfall
5. Time of Concentration
6. TravelTime
7. Runoff Curve Number
8. Resu/fs
TABLES
I GARFIELD COUNTY RAINFALL
2 PRE.DEVELOPMENT BASINS. PEAK DISCHARGE AT POINTS OF CONCENTRATION
3 POST.DEVELOPMENT BASINS. PEAK DISCHARGE AT POINTS OF CONCENTRATION
APPEND!X
1) REACH FLOWPATH
2) PRE AND POST DEVOPLMENT CALCULATIONS
3
4
5
5
5
6
6
6
6
7
7
{. INTRODUCTION
The pinyon Mesa Drainage Report has been prepared to satisfy the requirements of the Garfield
county code and conditions. The following are the objectives of the report
I ldentify existing and proposed drainage basins, and quantify expected runoff rates,
volumes and frequencies.
Z Describe the features of the drainage design ne@ssary to ensure adequate protection
from flooding for the development, both on-site and downstream.
3 Review the existing drainage study and the associated pond
4 Provide design calculations for proposed drainage structures.
S Demonstrate that the Historical runoff is maintained in a post development condition
though the use of detention.
PROJEGT OVERVIEW
This development is located 1.25 miles east of the intersection of Highway 82 along County Road
114. proposed devetopment of this subdivision is to include eighty one4uarter and one-third acre
lots for residential development of single family homes.
pinyon Mesa is a resubmission of Filing 10 of Los Amigos Ranch PUD and al! calculations will
conform with the assumptions made in the drainage report submitted within the Los Amigos
Ranch PUD application.
The design reports containing the results from the 2,25,50 and 100 year storms are included for
both historic and developed conditions. Since this development was originally submitted as Filing
10 of Los Amigos Ranch pUD, historic conditions contain no development in Los Amigos Ranch-
2.1 ON€ITE DRAINAGE CONSIDERATIONS
The drainage design for Pinyon Mesa utilizes severaldrainage goals, including, 1) taintain
historical flows 2) preventing flood damage. This report will show that the increase in
historicalflows created by a developed Pinyon Mesa Property will be mitigated thought the use
of a pond that was built for this purpose in Basin 4.1'
Major drainage paths are evaluated to ensure capacity to safely convey a 1O0-year storm event:
individual structures will be designed to collect a25-year storm event, with any bypass flow
safely conveyed within the downstream drainage route'
2.2 HYDROLOGIC ANALYSIS
2.2.1. Designation of Drainage Bastns
The off-site basin delineation was completed to assess existing runoff pattems, quantify existing
runoff flows and provide a baseline for the drainage design. The designation of off-site drainage
basins and basin boundaries are found on Sheet DR1. The on-site postdeveloped drainage
structures are on sheet DR2.
2.2.2 MethdologY
Hydrologic procedures outlined in the SoilConservation Service (SCS) Technica! Release 55
,Urban Hydrology for Small Watersheds" OR-55) were utilized to determine peak flonra and
volumes of runoff generated by the basins 4.1, 4.2,.1.0, and 2.0. The model is a simplified
procedure based on the TR-20 computer program and uses a set of more readily available input
parameters to define watershed characteristics and estimate runoff. A uniformly distributed time
varying rainfall is imposed over the basin area. The rainfall is then converted to runoff by using
a runoff curve number based on soils, plant cover, impervious area, interception and surface
storage. The runoff is then transformed into a hydrograph (flow rate versus time), using unit
hydrograph theory and routing methods based on the traveltime through drainage segments,
The Pinyon Mesa Basins are attached in Appendix 1-
2.2.3. Basin Area
Basin areas were delineated from a USGS quad map map of the area. sheet DR1 shows the
location of these Basins
2.2.4. Rainfall
TR-55 uses a 24-hour rainfalltotal and a synthetic time distribution to produce a centrally
peaked design storm. The SCS Type l! distribution is applicable to this region- Twenty-four
hour rainfall amounts for specific return periods were obtained from the NoAA Atlas 2 maps
contained in "procedures for Determining Peak Flows in Colorado', SCS, 1980 and are shown
in Table 1.
TABLE 1
GART'IELD COUNTY
RAINFALL
RETURN PERIOD (Years)
24-Hour
Stonn Total
2 25 100
1.3"2.0"2.4"
2.2.5 Time of Concentration
Time of concentration Oc) is defined as the time it would take for a drop of water falling on
the most hydrologically remote point in a watershed to reach the outfall- TR-55 uses a
segmented approach consisting of sheetflow; shallow concentrated flow and channel flow to
estimate Tc. The T6 is affected by surface roughness; overland slope and channe! slope
and flow pattems. Ts influences the shape and peak of the runoff hydrograph with shorter
times producing higher and sharper peaks. Tc directly affects the rainfall intensity used in
RationalMethod.
2.2.6 Travel Time
Travel Time (tt) is the time it takes for outflow from individual subareas to travel through
downstream sub-areas and reach the watershed outfall. lt may consist of shallow
concentrated or channel flow and is used only when more than one sub-area is used to
model a watershed.
2.2.7. Runoff Curue Number
The Runoff Curve Number (CN) determines the amount of rainfallthat becomes runoff and
the amount that infiltrates or is abstracted. Major faclors that determine CN are hydrologic
soil group (HSG) cover type and hydrologic condition'
Soils are classified into one of four hydrologic soil groups based on their minimum infiltration
rate, with Type "A'soils having the highest infiltration capabilities. SoilgrouPs were
determined from the SCS soil survey. Soil groups for the area were mostly B with small area
of C type. The soil group for the entire project was @nservatively modeled using a Type C
soil. The existing on-site soils within the overalldrainage basin are predominantly
hydrologic soilgroup Type B soils. To take a more conservative approach, the runoff curve
numbers selected from the appropriate land use were an average of the Type B and Type C
curve numbers.
Pinyon Mesa
Drainage Report
Cover type considers whether the surface is bare soil, vegetated' or impervious to some
extent. Hydrologic condition is usually estimated from density of plant and residue @ver
with'Tair,,to'good' conditions having lower runoff potential. cover on this proiecl consists
of junipers, sagebrush, weeds, grasses and landscaping with a majority of the cover
attributed to pavements and gravel parking. off site basins consist of residential
development (1/3 to 2 acre lots) and a mixture of juniper, sagebrush and pasture'
2.2.8.Resulfs
The results of the Rational and TR-55 analysis for the pre-developed basins are
summarized in Table 2. Flows are routed through the site shown in sheet DR2' The results
for the post-developed basins are summarized in Table 3. See Sheet DRI for tocations of
each off-site Reach. Based on the results from win TR-55, the Pinyon Mesa development
does not increase the 100 year storm flow at the outlet because of storm water runoff
mitigation above our devetopment. The historic rate prior to construction of the pond was
283cfs for a 100 year event. The post developed number of 275cfs for a 100 year event
includes both the pond and a built out condition at the Los Amigos property.
subsequently, while no detention is necessary to reduce 100 yearflow levels, water quality
inlets will be installed to minimize the impact from the development'
The actual calculations and computed printouts that contain Ts, T1, CN and runofr results
can be found in the Calculations Appendix 1
Pinyon Mese
Drainage Report
TABLE 2
TABLE 4
Runoff 1AreaRunoffAmountRunoffAmountBasin89.4145.150.0570.678DA4.1 1y.91zil.630.0460.553DA4.2 93.5199.960.060o.724DA1 73.0390.510.0490.593DA2 283.33600.25o.2122.548Outlet
cfs
109.66
147.52
96.90
Runoff 1
145.15
264.63
99.96
AreaRunoffAmount
0.057
0.053
0.068
Runoff Amount
0.635
0.678
Basin
DA4.2
DA4.1
73.03
275.30
90.51
600.25o.221-
0.049
0.820
2.726
0.593
DA1
Outlet
DA2
R4 (Length = 4876 ft)
Rli (Structure = Pond)
DA4.1 (Area = 145.15 ac, CN = 77rTc=O'357)
D.A4.2 (Area = 264.63 ac, CN = 76tTc =O.419)
RI Lengtt = 694 ft)
DAI (Area =99.71ac, CN = 8Or Tc= 0.179)
R2 (Length = 2645 ft)t_
DA2 (Area = 9O.51 ac, CN = 75,Tc = O.124)
R3 (Length = 776ft)
REACH FLOW PATH Project O15O2F
Outlet
DAI (Area = 99.96
R1 Length = 694 ft)
R2 (Length = 2645 ft)t_
DA2 (Area = 9O.51 ac, CN = 75,Tc = O.124)
R3.(Length =776ft)
R4 (Length = 4876 ft)
DA4.1 (Area = f45.15 ac' CN = 77tTc =O.357)
DA4.2 (Area = 264.63 ac, CN = 75rTc =O.419)
CN = 78r Tc= O.179)
REACH FLOW PATH Project O15O2F
Outlet
111981u1 so2\F-Lorver Bench\Reach Flor Path.ts
NEK 015 02 F
Pinyon uesa (Historic)
Garfield CounEY, Colorado
Storm DaEa
Rainfall Depth by RainfalI Reeurn Period
2-Yr
(in)
5 -Yr
( in)
10-Yr
( in)
25-Yr
( in)
50-Yr
(in)
100 -Yr
(in)
1 -Yr(in)
1.3 1.5 1.8
SEorm Data Source:
Rainfall Distribution I:,Pe :
Dimensionleee Unit HYdrograPh:
2.O 2.2
User-provided custom Etorm daEa
Type II
<standard>
2.4 1.0
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Pinyon Mesa (Historic)
Garfield counEy, Colorado
waterBhed Peak Tab1e
Peak FIow by Rainfall Return Periodsub-Areaor Reach
Identifier
2-Yt
(cfs)
25-Yr
(cfs)
100-Yr
(cfs)
SUBAREAS
DA4 .1
DA4 .2
DA1
DA2
REACHES
R1
Down
Down
Down
Down
10.05
10.24
14 .35
7 .17
17 .72
1,1 .72
54.78
18.12
61.59
44 .75
142.96
t42.86
89 .44
134 . 91
oc E1
73.03
19
89
89
44 .75
44.45
29
29
116
115
78
43
54
54
13
!2
t1
o2
05
98
20
20
10
9
241.46
241.2L
1
7
R2
R3
R4
73.03
72.84
199.64
r99 .54
OUTI,ET 23 .26 164 .19 283.33
WinTR-55, Version l'.00.08 Page 1 5/3L/20o6 8:05:40 AM
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sub-Area
or Reach
Ident i f ier
2-Yr
(cfs )
(hr)
25-Yr
(cfs)
(hr)
100-Yr
(cfe)
(hr)
01502F
Pinyon Mesa (Historic)
Garfield County, Colorado
HydrograPh Peak/Peak Time Tab1e
Peak Flow and Peak Time (hr) by Rainfall Return Period
SUBAREAS
DA4 .1
DA4 .2
DA1
DA2
REACHES
Down
R2
Down
R3
Dowrr
R4
Dovrn
OUTI,ET
10.05 54.18 89 .44
r2.2L ]-2.L6 L2.76
lo .24 78.12
12.26 12.t9
134 .91
L2,L7
RT
14 .35 61 .59 95 .51
12.06 1,2.03 12.02
1 .r7 44.15 73 .03
12.02 12.0012.04
20.13 L42.96 247 .46
L2.52 L2.L9 L2.!8
20 .L2 142.86 241 .2t
12.56 12.22 t2.20
t2.04
L2.21
!7 ,72 Ll6 .29 199.64
12.41 72.27 12.23
:.7.12 116.29 199.64
L2.52 ].2.29 12.26
10 .05 s4 .78 89 .44
12.2L 12.76 ].2.16
9 .98 54.43 89.19
12.49 ]-2.34 12.34
23 .25 164 .19 283 .33
1 ,r1
1 .02
44.75 73.03
t2.02 12.00
44.45 12.88
!2.L6 L2.l2
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Sub-Area
IdenEif ier
Drainage Time of
Concentration
(hr)
Receiving
Reach
Sub-Area
DeecripEion
01502F
Pinyon MeEa (Historic)
Garfield County, Colorado
sub-Area Summary Table
Curve
NumberArea
(ac)
DA4 .1
DA4 .2
DA1
DA2
Totaf Area: 600.25 (ac)
145.15
264.63
99 .96
90.51
0 .410
0.419
0.179
0.124
17
15
18
15
R4
R3
OutsleE
R2
winTR-55, Version 1.00.08 Page 1 5/31/2ooi 8:05:40 AM
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Reach
IdenEifier
Receiving
Reach
ldentifier
Reach
Length(fr)
Routing
Metshod
015 02F
Pinyon MeEa (HisEoric)
Garfield county, Colorado
Reach summary Tab1e
R1
R2
R3
R4
outIeE
R1
R1
R3
694
2645
716
4876
CHANNEI,
CHANNET
CHANNEI,
CHANNEL
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Sub-Area
Identi fier/
Flow
Length(fr)
I{etted
Perimeter(fr)velocity
( ft, /sec )
Travel
Time
(hr)
01502F
Pinyon tr,teea (Historic)
Garfield County, Colorado
sub-Area Time of ConcenEraEion Det'ai1s
Manninga's End
Slope n Area
(ftlft) (sq ft)
DA4 .1
SI{EET
SIIAI,LOW
SHALI,OW
DAA.2
SHEET
SHALLOW
SHALI,OW
CHANNEI,
DA1
SHEET
SHALLOW
st{Ar,Low
CHANNEL
DA2
SHEET
CTIANNEL
CHANNEL
100
18s8
2331
30
50
50
100
2000
r532
2458
375
t47
30s
805
100
485
998
L652
0.3333
0.1649
0.0802
o.0726
30
25
50
45
0.0915
0.1073
0.0454
0.1
0.0
0.0
13
05
05
08
0
0
0
0
0
0.1
0.0
0.0
0.0
0
0
0
124
098
188
.41
0.087
0.010
0.o21
0.0
0.1
0.1
0.1
o.2
0.2
0.1
Time of concentration
0 30.00 t9 .9?10.387
Time of Concentrat,ion 0.419
0
0
0.178
0.102
0.073
0.066
o.o74
0 .016
0.061
0.02880. oo 32.62 16.389
Time of Concentration t19
100
786
1446
222
546
186
0.130
0.045
0.045
30.00
30.00
t9 .97
L9 .91
Time of Concentratsion
21.833
L4 .877
124
winTR-55, Version 1.00.08 Page 1 5/3t/2006 8:05:40 AM
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Sub-Area
Ident i f ier Land Use
01 502F
PinYon Mesa (HisEoric)
Garfietd counEy, colorado
Sub-Area Land Use and Curve Number Details
Hydrologic
SoiI
GrouP
Sub-Area
Area
(ac)
Curve
Number
DA4 .1
DAA.2
DA1
DA2
Pasture, grassland or range
Pasture, grassland or range
Pinyon - juniPer
saglbrush (w/ grass understory)
Sagebrush (w/ grass undereEory)
ToEal Area / vreighEed Curve NuElber
CN directlY entered bY user
ToEal Area / WeighEed Curve Number
(poor)
(poor)
(poor)
(poor)
(poor)
62.265
L2.71
52.23
16.955
.98
41
89
2l
87
1
1
B
C
B
B
c
B
c
B
c
B
c
B
19
85
75
67
80
145 .15
264.63
264.63
3r.256
5 .085
7.8r4
55.805
71
75
15
Pinyon - juniPer
Pinyon - juniPer
saglbrush (w/ grase understory)
salebrueh (w/ grasE underetory)
Totsal Area / weighced Curve Number
Pinyon - juniPer
Pinyon - juniPer
saglbrush (w/ grass underatory)
ToEaI Area / weighEed Curve Number
(poori
(poor
(poor
(poor
(poor
(poor
(poor
75
85
67
80
99.96 78
15
85
61
90. s1 75
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{
I
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Reach
Identsifier
Reach
IJength(fr)
Reach
Manning'B
n
Friction
Slope(frlfr )
BotEom
vridEh
(fE)
015 0 2F
Pinyon Mesa (HisEoric)
Garfield county, Colorado
Reach Channel Rating Details
Side
Slope
0.0561
0.0687
o .172
0 .1352
R1
R2
R3
R4
694
2645
776
4876
3 :13 :13 :13 :1
0.1
0.1
0.1
0.1
2
2
2
2
Reach
Ident if ier Stage(ft)
Flow
(cfs )
End
Area
(sq ft)
Top
widrh(ft)
Friction
Slope
lfE / tEl
R1
R2
R3
R4
0
0
1
2
5
10
20
0
0
1
5
10
20
0
0
1
5
10
20
0
0
1
2
5
10
20
0
5
0
0
0
0
0
0
5
0
0
0
0
0
0
5
0
0
0
0
0
0
5
0
0
0
0
0
0
2
r2
59
55s
3251
r97 82
000
995
s28
725
191
244
796
0
1.8
5
16
85
320
L240
5
I
14
32
62
122
0
1.8
5
16
85
320
1240
614 .
3597 .
21891.9s8
000
314
864
093
384
819
0
3
13
65
2
5
8
14
32
62
0.0551
0.058?
o.172
0.1352
1
0.000
5.243
2!.936
104 .578
972.r33
s692.88s
34639.408
0
1.8
5
16
85
320
t240
2
5
I
14
32
62
t22
0
4
L9
92
861
5047
3 07 r.1
000
649
448
7tg
886
270
044
0
1.8
5
16
85
320
7240
2
5
I
t4
32
62
L22
vlinTR-55, Version 1.00. 08 Page 1 5/31/2ooG 8:05:40 AM
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Sub-Area
or Reach
Identifier
015 0 2F
PinYon Mesa (DeveloPed)
Garfield County, Colorado
HydrograPh Peak/Peak Time Table
Peak Ftow and Peak Time (hr) by Rainfall Ret'urn Period
2-Yr 25'Yt 100-Yr
(cfe) (cfs) (cfs)
(hr) (hr) (hr)
SI'BAREAS
DA4 .1
DA4.2
DA1
DA2
REJACHES
Down
Down
Down
R1
R2
11. 04 59.67 96.90
12 .18 12 .13 12 .12
13.85 81 .9A !47 .52
t2.24 r2,r7 !2.11
20 .97 73 .30 109.66
t2.o4 L2.02 L2.O2
1 .r7 44.75 73.03
12.o2 12.00L2.04
20.11 133.44 226.O0
L2.27 12 .L8 12.16
20.14 r33.29 225.67
r2.3r 12 .20 12 .18
44.75 73.03
t2.02 12.00
44.45 72.88
12.16 12.t2
31. ?3 52.59
12.36 L2.32
31.70 52. s8
t2.56 12.53
R4
Down
R5
Down
OI}TLET
12.04
L2.27
13.82 93.18 161.26
12.25 12.20 !2.r9
13 . 8o 93 .13 161'.20
12.29 72.22 L2.2r
1 .!1
1.02
R3
5.96
12.47
s.95
L2.AL
11..04
L2.L8
5 .96
12.47
59.61 96.90
r2.L3 L2.12
31.73 s2.59
L2.36 12.32
26.15 150.84 215.30
winTR-55, version 1.00.08 Page 1 5/31/2oo, 8:04:13 AM
User:
Project:
SubTitle:
State:
CounEy:
Filename:
WinTR-55 Current Data DeEcription
--- IdenEificaEion Data ---
NEK Date: 5/3t/2006
O15O2F Units: English
Pinyon Mesa (Historic) Areal Units: Acreg
Colorado
carfield
r : \ 1 9 I 1 \ o 1 5 02 \ F- Lower Bench\Drainage\ExDrainage . vrs 5
--- Sub-Area DaEa ---
Description Reach Area (ac)RCN TcName
DA4.1
DA4.2
DA1
DA2
ToEaI area: 600.25 (ac)
2-',{t(in)
5 -Yr
( in)
--- Storm Data
Rainfall Depth by Rainfall Return Period
R4
R3
OutleE
R2
25-Yr
( in)
145.15
264 ,63
99.96
90.51
.41
0.419
.119
.L24
77
75
18
15
1,0-Yr
( in)
50 -Yr
( in)
10 0 -Yr
( in)
1-Yr
( in)
1.3 1.5 1.8
Storm Dat,a Source:
RainfatL Dietribution T)4)e:
Dimeneionless Unit HYdrograPh:
2.O 2.2
User-provided cuatom sEorm data
Type II
<6Eandard>
2.4 1.0
winTR-55, Version I.00.08 Page 1 5/3|/2OOG 8:05:40 AItl