HomeMy WebLinkAboutDRB090400Design Review Board
ACTION FORM
Department of Community Development
' 75 South Frontage Road, Vail, Colorado 81657
TOWArv
4% vir tel: 970.479.2139 fax: 970.479.2452
C'E'vCLOPHEV web: www.vailgov.com
Project Name: NEW TWO FAMILY DWELLING DRB Number: DRB090400
Project Description:
Participants:
CHANGE TO APPROVED PLANS. INCLUDED CHANGE FROM CASEMENT TO SINGLE HUNG
WINDOWS, LANDSCAPING, AND CIVIL DRAWINGS TO ADDRESS DEBRIS FLOW MITIGATION
NEEDS.
OWNER TOWN OF VAIL 09/09/2009
75 S FRONTAGE RD
VAIL
CO 81657
CONTRACTOR J.L. VIELE CONSTRUCTION
1000 S Frontage Road W, #202
Vail
CO 81657
License: 188-A
09/09/2009 Phone: 970-476-3082
APPLICANT TOWN OF VAIL 09/09/2009 Phone: 970-479-2100
75 S FRONTAGE RD
VAIL
CO 81657
License: 463-B
Project Address: 2657 AROSA DR VAIL Location:
Legal Description: Lot: 8 Block: C Subdivision: VAIL RIDGE
Parcel Number: 2103-142-0402-5
Comments: See conditions
BOARD/STAFF ACTION
Motion By: DuBois Action: APPROVED
Second By: Plante
Vote: 5-0-0 Date of Approval: 09/16/2009
Conditions:
Cond: 8
(PLAN): No changes to these plans may be made without the written consent of Town of
Vail staff and/or the appropriate review committee(s).
Cond: 0
(PLAN): DRB approval does not constitute a permit for building. Please consult with
Town of Vail Building personnel prior to construction activities.
Cond: 201
(PLAN): DRB approval shall not become valid for 20 days following the date of
approval, pursuant to the Vail Town Code, Chapter 12-3-3: APPEALS.
Cond: 202
(PLAN): Approval of this project shall lapse and become void one (1) year following
the date of final approval, unless a building permit is issued and construction is
commenced and is diligently pursued toward completion.
Planner: Warren Campbell DRB Fee Paid: $0.00
.
Departments of Community Development,
' 31 75 South Frontage Road ~
Vail, CpJorklokn
970
~r
W e 4 ` Deye~opin en~ e`
Application for Design Review
Changes to Approved Plans
General Information: This application is for all changes to approved plans prior to Certificate of Occupancy. An ap-
plication for Design Review cannot be accepted until all required information is received by the Community Development
Department. Design review approval expires one year from the date of approval, unless a building permit is issued and
construction commences.
Submittal Requirements:
1. Three (3) Copies of all pertinent approved plans will illustrated, labeled changes
2. Joint Property Owner Written Approval Letter, if applicable
Fee: $20
Single Family Duplex Multi-Family Commercial
Description of the Request: U~a b V 13
Physical Address: o~~s~OSG~
Parcel Number: PI031HPOYD25 (Contact Eagle Co. Assessor at 970-328-8640 for parcel no.)
Property Owner: oWn VOIi' ~~a .
Mailing Address: got. co 9 16 5 7
Phone: 17o" q- 1-
Owner's Signature:
eboa'
Primary Contact/ Owner Repre ntative: 5Av1ne AS G~bou2
Mailing Address:
Phone:
E-Mail: A-fi n^ ^@ vat 1 Ap✓. CDC Fax:
For Office Us nly: Cash CC: Visa/MC Last 4 CC #
Fee Paid: Received From:
Meeting Date: 9.147-01 DRB No.:
Planner: WC11 Project Nc
Zoning: P/s Land Use:
Location of the Proposal: Lot: Block: Subdivisic
Auth # Check #
.A,
~VAg, Inc.
Architects & Planners
Transmittal:
Project Name: TOV Arosa Drive Duplex
Date: September 14, 2009
RE: DRB Update
FROM: Stephanie Lord-Johnson
TO: Warren Campbell
CC:
VAg, Inc. Architects
TOV
We are sending via hand delivery the following:
Memo Letter X Drawings
Other
Description:
Project No: 2910
SEP 1 1 2009 II
TOWN OF VAIL——
Specifications
(1) Set of the new Civil Drawings - C0.0. C1.0, C2.1, C2.2, C2.3,C3.0, C4.0 C5.1, C5.2
(1) L 1.1 - Landscape Plan
(1) A3.1 - Elevations
(1) A3.2 - Elevations
for review & comment X as requested for your use & information
Other
Remarks:
Warren - We had dropped off a similar set of documents as per our discussion on September 91h. Hopefully these will still
get to you in adequate time for Wednesday's DRB meeting.
I have noted the changes as follow:
Civil Drawings - see Sheet C4.0 for the major changes in terms of the new boulder V to 6' tall boulder walls required by the
Geo Tech Report. Sheets C2.1 and C2.2 clarify theses boulder walls in more detail.
Landscape Plan - modifications only in response to the new Civil Engineering information - planting quantity and sizes did
notchange
Elevations - We are proposing to switch from Casement windows to Single Hung windows - these minorly effected the size
of the bedrooms windows and altered the mullion patterns. We tried to stay with the same concept that we had previously
pursued with the mullions in the casement windows.
Please call with any questions or comments.
Stephanie
Physical Address: (970) 949-7034 Mailing Address:
90 Benchmark Rd., Suite 202 fax: (970) 949-8134 P.O. Box 1734
Avon, CO 81620 email: generalCavagarchitects.com Vail, CO 81658-1734
970-476-8644 • FAX 970-476-8619 •1000 LIONS RIDGE LOOP • VAIL, CO 81657
DRAINAGE STUDY
OFF-SITE CONVEYANCE
for
AROSA DRIVE DUPLEX
2657 Arosa Drive
Vail, Colorado 81657
PLC Job No. 1695
September 1, 2009
Prepared For:
J.L. Viele Construction
Vail, CO 81657
Prepared By
Peak Land Consultants, Inc.
1000 Lions Ridge Loop
Vail, CO 81657
FSEP 0 3 21009
!i_ IL
~ ~
PURPOSE
The purpose of this study is to provide the drainage analysis for conveyance of the off-site
drainage through the property located at 2657 Arosa Drive in the Town of Vail, Eagle County,
Colorado.
Peak Civil Engineering completed the original drainage report in May of 1999, determining the
100-year storm event and 100-year snowmelt. In conjunction with the drainage report, Collins
and Lampiris Consulting Geologists completed a debris flow analysis also in 1999. Both of
these reports were completed for a preliminary site plan. The Town of Vail has moved forward
with Viele Construction to develop a duplex on the property and a detailed design has been
developed. Since the original drainage report was developed for a preliminary plan, this current
report will re-analyze only the conveyance through the site for the current design. HP Geotech
has also reanalyzed the debris flow and has provided recommendations for the current design.
The flows provided the Peak Land Consultants 1999 report will be utilized since the basin itself
has not had any significant change since its completion.
OFF-SITE HYDRAULICS
The 1999 Drainage report had determined the 100-year event to be 44.78 cfs and 100-year
snowmelt runoff as 54.12 cfs; the combined event would be 98.90 cfs. Based on these
calculations, HP Geotech has determined the bulk debris flow to be approximately 250 cfs.
DRAINAGE CONVEYANCE
The proposed site has many constraints for the desired development, including building height,
lot configuration, and roadway grade to name a few. The proposed site plan has been developed
which meets the all Town requirements and considered all the site constraints, as a result the
drainage will be conveyed in a storm culvert for the entire length of the development.
The general concept for conveyance is to design the storm culverts for the combined 100-year
storm and snowmelt events of 98.90 cfs. The assumption for the debris flow of 250 cfs is that
the storm culvert will plug with sediment and the flow will be conveyed over the culvert and
through the driveway section of the project. Debris will be directed away from the structure by a
deflection wall as shown on the current site plan. As the debris flow plugs the culvert, the water
level will rise above the culvert and overtop at that low point (Section D), which will have a
grouted overflow spillway. The flow will rise at the northwest corner of the building until it
overtops at the highpoint elevation of 7916.47' between Sections C and C2, which acts as a weir
for the small "pond" that has developed as a result of the culvert being plugged.
This report will analyze flow depths of the debris flow through the site at critical locations. HP
has specified 6" clearance from the debris flow elevation and top of foundation.
HYDRAULICS
Storm Pipe Design
The storm pipe has been designed to convey the combined 100-year storm and snowmelt events.
Hydraflow has been used to analyze the hydraulic grade line utilizing the data for slope, type of
pipe (HDPE), and considers the layout with losses for manholes and angle of deflection.
The storm sewer profile included in the appendix shows a 30" HDP pipe can accommodate the
combined flow. The pipe is running nearly full and does not force discharge from the manhole.
Overland Debris Flow
In order to analyze the overland debris flow across the driveway, we have analyzed several
critical cross-section shown on Sheet XS-1 included in this report. The cross sections have been
analyzed in Hydraflow for irregular sections. Sheet XS-1 shows the approximate height of the
debris flow (250 cfs) at each of the critical cross sections. We have been directed by HP that
rising levels above the garage elevation is not of concern; although foundation heights should be
raised within the garages if flow is expected.
Section A - Debris flow elevation is 12.39', the FF 13.50'. Debris flow elevation is 1.1' lower
than FF. Flow may creep into the garage at elevation 12.5' at the 250 cfs flow.
Section B - Debris flow elevation is 15.20', FG at the building is 14.73'. Flow rises against the
building 0.47', foundation will need to be raised 1' above FG for this area.
Section C- Debris flow elevation is 17.35', garage elevation is 17.33'. Since flow is at the
garage elevation it is recommended the garage interior be protected from flow.
Section C2 -Debris flow elevation is 17.56', FF elevation is 18.33, elevation for flow to clear
below deck is 17.56'. At the debris flow of 250 cfs, flow will clear under the deck
and since debris flow elevation is more than 6" below FF, top of foundation will not
be required to be raised above FF.
Section D- Debris flow elevation is 17.15', FF elevation is 18.33, elevation for flow to clear
below deck is 17.56'. At the debris flow of 250 cfs, flow will clear under the deck
and since debris flow elevation is more than 6" below FF, top of foundation will not
be required to be raised above FF.
CONCLUSION
This drainage study has analyzed both the combined 100-year storm and snowmelt flows and the
debris flow conditions. It has been shown that the combined flows 100-year flows can be
conveyed through a 30" HDPE pipe with no pressurization, although the pipe is running full.
The analysis of the debris flow has shown critical sections for the 250 cfs elevation. It is
recommended that both garages expect debris flow of only a few inches. It is recommended that
the foundation walls through Section B and the wall as it wraps to the garage to the west, be
raised to accommodate per HP Geotech's recommendation. Expect 0.5' of flow against the
foundations. Sections C2 and D show that the debris flow will not be higher than the FF
elevation of 18.33'.
oa`.o.ca~°`°
;yti, a 'GIs t f .
L. Mark Luna°faZSSION~'~,~`
APPENDIX
HYDROLOGIC CALCULATIONS
E
J
a
ai
w
'o
a`.
W
W-
O
L-
a.
L
G1
3
co
E
L
O
cn
00
°o
°o o
°
o
°
o
m
m
C)
m
m
co
r~
n
r~ ti
r
~
}np 90'Z66L'I3'nul
CD
051661 '13'puJJ
Z :u
Nrl
0
M
O
N
O
O
O
0
rn
o
CO
U
(0
O
ul E8'906L'13 'nul
3n0 £9'9061 'D 'nul
0
6 :u
o
to
0
v
0
M
0
N
C7
0
ul
0
Ile;}n
0
oo
°o
°o" o
°o
00
a
ti i
r
C
i
D
Lo
o
f
W
~ - b6'Sb+6 EIS
O
O
f
8' 6 661 13
~ - t76179+0 EIS
PI
O
~7I
05'£061 '13 'nul
'8061'I~ TWO
O - 00'00+0 e~S
0
0
m
a
t
^O
W
m
E
E
c n
L
3
cn
E
L
O
C
co
3
o
a
U d
C Q
N N
O 2
F
w n
o
.
O
°
N
N
CN C O
O
CD
O
0 _ z
UJ
W
J -U-
7 ~
~
C9
61 v
h h
O N
C N
CO Cl)
CO CO
ui (6
u
04
= C
C)
y
O O
n n
~
~
C
3
O N
O
M
O
a
(7
o n
E
^ m
z
m
a) CL
c oe
CD n
.J N "
LO Lr)
p,
Cl) to
f0 O
7 J^.
O N
Cw
n
~o
° m
C~
i
^
c W
f"
(D
rn rn
n n
mw.
I, O
C C
J d
~n rn
d
Fr
U U
J N
CD d.
C N C
O O
Cl) Cl)
J N
(1) w
O
O O
LL
O m
m m
N
O O
0 0
ci
11
o
C
Q? C?
0
a a
n
d
E
a~ m
a a
ai
~
'a CL
U
CD
LL
01
O
`
O
~ o
J z
N
Q
z
0
0
c
A
w
N
0
3
a
m
a
S
~p N
U) O
a) N
v;
O
Uf m
m CL
3
0
LL
O
O C
D) C
~ Co
~ .O
NU
L (a
a) O
t:y)
J N
~ O
Q
c
O N
U N
>O
N
X
O
Co
X
N
N
W
E
3
O
T
O am
rn
O m
f0
.c C9
lt~) Co
N ~
C
J O
M CU LL
O U to N
Q L cm Q
O C M C
co CD E
O O) C U
i ~ N f0 ~
L1 Cn ~ ~ 0
c
N O
f~0
LL d
L"
U N W
fp
0
N ` N
o
0 0
W o
m
3:
c
a
a
LL
U)
N
0 0 0 0 0
C N M N M N
C) 0 0 0 0
0) C7 0 6 0 0
7
O
w
c
, (D N (D CO O
6 CD M O (q O
Cl) f; 0) O I-t
N N M t() to
a
c
W
C
O O CD N O co
N o (D M CA (D
'
O
•
O Cl) fl- O
N N CO to
ca
O U)
rn M
U
O ~
O N
N
N (D N V f`
O N N r 0
O LO
M
It
CD O O CO ti M N CA N 0) o LO O o o
V' V O) M C'M N Ln 0 0 0 Ln CO
0 L
V
N
N
O
C) C
6 O Lo M M M N N N N N N O N M M
r - r r r r r r r r r r r r r r
N
C
C W
N
O U)
CA
co
d)
rv
W
0
C) CD
dj
a)
N
rn
E
p o o u) u) (D co a) co N (D Lo M ao o
r f- r h f- (o M co CA N (D CD
C E
O
c
'
`
r
C
C
N l9
7 C o 0 0 0 CM M y '-t M f` CA M C)
N N M V' 't (n U)
fn o
C
Co o)
a) Q-
N
-
C m
w
Q U
Co N
t
to
(o >
U~w
j
rn
d 0 3 a
L~IO
N
0
a1
N
n
0
0
N
co
0
n
O
0
H
U
a
`m
m
v
0
Of
ar
Y
O
O
m
n
m
d
C
ai
0
d
m
rt
2
CL
O N
o to
o M
c~
am N
0
r CV
f0
f6
C~
am
3
0
J
QS
Q
C
U
C
C
fa
U
c`a
rn
m
O
N
Y
ctf w
4? ~n a=a✓
M
co
if )
r-
w O O h 0 m N
I- M O t0 Uf N N
M O cV cV u'i M
T T T
L (D L
a s CU c E (D
m-° xw = =3
z U)
15 m mw a)
3
0
w LL LL
LO O
> N
N N
01
N N
~a
3
0
LL
co
co
co
n
Cl)
0
N
co
O
n
O
0
F
U
.n
3
'0
m
0
m
a
.N
0
O
O
co
r -
P)
U
C
N
'0
O
L
C1
d
m
2
2
a
(3) 10
o ~
o r~
0 fV
~
0
O
O
tr)
O
In
IT
0
O
N
C
c
N fiS
~U
m ~
U -
3 m
o
J `
O
Q c
O
O U
U (n
m cn
~ N
O
U
N
X
O
.0
X
a)
;
to
E
3
0
T
o am
O m
t C7
~ N fD
O
co
C
J
O L P
LL
O U N m
Q m
o c m c
O O m
7 C L
C 0
o. inC~o
c
N 0
m E
LL a) (D
'i c=n W 'D ILL
o
s
V ?5 (D 0
2U)
itt (n
i2 =t'
O
O
O
N 0) c7 CO
Cl O ti N
O O N co
N
U
0 0
w
O CL U
C
.G O
c ~ 0
m a~ U)
~ c
fC
c
0
N
N
C N
CO
o
III
LO O
N fp
tp a
t 3
0
LL
U
b
h
O
U
0
0
M
co
0
h
0
O
0
U
M $
0
3
o
ui U
N
y
v
N
s
0
0
O
m
Ch,~
O
N
C
N
t
o
r
V
m
m
N
2
O
O
r
O
O
q q U~ O U~ O U~ O lp0
LO M M N N r- O
T" rl
(4) U014en913
2
a
rn co
o
o r~
0 N
O -
~ N
N O
O1 O
O
N (p
~a
3
0
LL
O
m
0
h
O
O C
m C
N M
L- r
m U
C~
co
a) ~
3 rn
J t
f0 ~
m ~
C
O Q)
U
N
>O
N
E
X
O
L
O
x
a`)
f6
0
T
O a)
rn
O N
m
t
0) IC
N O
(D
O
E
C
J
M CO LL
-
(mU N a)
o c `m c
C) O 3 C L
N
C
~ d c
a
dtn=~o
C
a)
a)
N E
O
11 a) N O
i N W o l~
+
ca
3 A
L
U
L
)
N
Un O O O
N m N ce)
L O O O O
0 6 O O O
7
O
C
0 owcoo
a - v v M
O Cl q N
a
C
W
c
O O o co co
q a-- 14' V
O O
42
N
CO
C)
O
O
O
~ N
O Ln
r
p O M cA N N O C) 0
O C O I~ c0 It 't 0 0 0
cp .2 (D 7 V v co v Lo c0
-t6 r
d
c*:! W
o N
Z6 `r
> Cl)
a) r
W Q
m
Q
V
- O O co co co o m O
rt of co m
O - V
W C
: V
C .O O O N 'q cD r- ~-q
cn o r- t- N N
C w (n
7
-C
U ~ w
0
CC)
N M O) O) r M I- O lh lh i-
O M N M f- O O 0 h o
O cn 6 M N 6 O 6 M 6
In - N N e- r
(N
cr)
O
N
0
h
co
0
U
d
.o
3
a
Y
O
O
m
h
CO
U
c
0
v
LO
N
I
C
m
U
N
O
U a`)
N T
07 L Q7
C O. O. co N
C a) rL O O a) C
c0
m (p
a N 0 p O O
Du ~:I-°2UU>>U) a
rn
0 0
cf
o r)
0 N
0
~
~2 N
O
~ C
O) M
CU
c`u U
C7
C13
a)
o a)
J ~
m
O
C
o a)
U (1)
O Y
O
0
N
M
E
:3 n
z N
N (D
_0
~ 3
o a
U- LL
0 O
> N
N O
N m
O
~a
3
0
U
O
(D
(D
N
n
ri
0
N
co
O
n
cc
0
U
z
3
O
0
D_
d
N
Y
O
O
co
r
Cl)
C
Vi
0
O
L
W
l0
N
N
N
2
CL
M
0 0
rri
O M
0 N
O ~
O
C
C
O (6
0) C
cis U
cu L
L
C~ co
L
N
O L~-
J L
cca ~O
m C
O
C Lp
O U
U (n
N to
L
U
N
r..
O
X
N
N
L6
E
O
T
O N
O
O`
1
(6
r
O
N
O
N O
N
C
O M
CD r N
0) cc 0
O N LL
O O In LO
- LLB
CD m a)
N
C
m '
C -
O
W
Ti N N N
N C
Q (n
(D
m
U
w
_
~
av
a) E
ca o m
Q 'C U j
U- a) a) 0
W
LL
U
E
1
C - cc
L
A
0
0 0 0 6
Q L
N m U)
a`~: M2w
Cl) U3t o
0
N
O
O
N
O
r
~U
O
O
r
O
L6
O
Ln O Ln O to 00
c0 LO LO d co M
r r r r r ~ r
(4) UOIJeAGII~]
C
O
> O
N
oa
3
0
LL
co
cD
n
M
O
N
0
n
O
U
r
a~
m
v
0
0
m
v
N
O
0
m
n
M
U
N
N
v
m
w
2
2
CL
rnrn
o
Sri
O M
07 N
0-
~p N
in O
v N
01
N m
~a
3
0
LL
O
O C
~ C
m f6
L_ -C
co U
U
M
m ~
Q 0)
Q. N
~ L
(6
U 1
Q~
O O
V N
O Y
>O
N
JE
X
O
.n
N
co
E
O
O (D
O Q)
N
'D N
L 7 ~ t0
rn
to a :3
O_ c
m cco O
m ~p L LL
m U w a)
U m Q
o c m c
co .0 7 c t
N N Lcp YA
a(n~~0
c
a~
LL aa) (U 0
U N W Q LL
N ` ~ N
0 0 0 0 ' Cl.
a` l n
0
Cn O O O
c M N Cl)
L O O O
Q) O O O
O
Of
c
O Lo M I-
N r co O
O co M
a
c
W
c
O LO Co
O T co
O O co
C)
O
N LO
O Cl)
O h
T
O O M I- T N M O O
O c O N CO N M LO 0 0
c6 ,O w r-- co w w m 0 m
,
T T T T T T T T
~
~
O N
c ~ W
O co
Lo
> Ln
N T
w ai
a) a)
a 0 r O M T 'fit M M N h
C -
O
rn co co co cm Cl
c
7
:3 c 0 0 O 't co co O LO ai
N C/) O T N N M M M
U)
>
75
L <0 N
U W
it
H N
$ 4?
M
N
M ti
N LO m m N I- h 0 0 m 't
O LO LO N I- h LO O m O '[t
O Ln O OD r` T ti O w T 6
LO Cl) M M r r
N
m
so
0
N
N
n
M
O
N
co
0
n
m
0
H
U
t
V
m
0
m
Y
O
O
L21
n
m
U
c
N
00
m
v
m
m
m
2
C
O
U
N
O
U
c E L M a
C N M N -r- (D 2 2 a) c
W
o)ma o XU
t0 D + w
Ma 0 a) a) *C:
a
FL M:UU>>U) a
a
o~
a) N
O
r N
(D C
L) C
m m
C
~U
C7
M
m 5
a~
D
M
010
C
O
L) cn
(1) `
o
~C
C
n
Z
~ M
0 0
LL LL
U) O
> N
O N
N p
cca
3
0
LL
O
~D
O
N
N
n
M
O
N
W
O
n
m
0
H
U
Z
3
0
a~
a
.y
Y
O
O
m
co
U
C
N
b
O
t
N
O
N
N
l0
2
CL
O
0
o a~
O) N
O r
~a
~
o
m
0
N (p
~a
3
0
LL
O
LO
Cl)
O
O
M
O
C
C
N (6
rn s
cu
U
m
U ~
L
CL
a~
~ o
U c
O
C :a+
O U
U U)
O N
~ N
O
L
U
N
19
x
O
.O
fn
(0
3
O
p~
O N
rn
O N
m
L
to ~ (0
Q1 j
a c
O
rn s LL
co C) U N U
c " rn Lc
o c
ca c 0
C) 0 U N u
nu) fig[
c
O 0
LL 0 E i
v wLLl-0 u
y 0 g
d i~ LL u
9=
O
O
M N
O O M Lf)
O O h
r
a
N c
U O
N j
0
w
O1 a ~
o
O N (n
C
co c
o
U
in n in n
C6 (6
(g) U01;eAG13
cD
0
0
to
n
M
O FIC
LO
N co
0
n
O
0
F-
U
v
O d
N C
O
m a
m
-a
N
0
0
O co
In n
M
r
U
C
N
0
r
m
O
~
m
O
r
_
O
L6
J o
In o
L6
a
min
O N
~ N
O (7
Of N
r
0
~ N
N O
N N
O1
N N
~a
3
0
LL
O
c
-Z C
U CO
U
L
CD
Q
N
c L
N .
N
U
C ~
O QJ
U C
O N
U) Y
>O
N
N LO
N N
C O
L
O O
I
0
C
.O O
5 U)
O
N
i~5
M
X
W
O
X
'a
`
a
)
N
m
C
c)
E
o
°
3
65
O
C
m
U)
Cl
0 Y U
O
io a)
❑
N
cq (D
T
O V)
In Q _ m
~
0)
O r
(D Q ~ C
+J
0) m t LL.
O $ O O CD O CD O O
Co N V O N
i- U ` CD
O C O M UU) N N O O
Cj O CV t0 r CO (D (o c0 CV
O C (0 C
N m N r N
O O j C L
O>
CY)
0) (CO N
E- ~o
C = cu-
°O
(13 r
> (D
(U
C
W 6
CU N m
O
(D
N
- U C - O Lo O (O CD m r,- O
m
O O
ti t` ti N LO
m
E
LL a
0
r
C
m U) 'C
= C O 0 0 0 6 M- N O
)
i U) W o W
CO 0
❑
t0 N (N CO
a) -15 0 0 O ~
cu >
N
W a
a. :Y- mw
m a)
a=
c U~: W
a
i
N N N N co
co U)
co
m
N N M e- 'ct CD (D O In N W
O O 7 N O V' O O UP) V' OA
O O M M N r h O m r- O
N
co
LO
N
n
Cl)
0
N
co
0
r -
co
0
U
v
v
m
O
Y
O
0
m
n
cn
ci
c
a
0
m
D
f0
N
G1
(0
C
N
U
N
O
0 a`)
(n T
m (D
C1 a N C
c a) m m .C 2 W
2r (d Q a' 4=
t0
U y C2;++U O O m
OW2UU»Cn a
mn
o v
Oi
O N
O7 N
O ~
N
Lll O
~ N
N O
N N
~a
3
0
LL
C
C
(0
.C
U
L
fD
m
N
L
_L
L
O
a~
a~
N
Y
L
Y
U
O
0
L
O
Q
Q
t4
N
U
c
0
U
O
Cl)
O
IQ
r
1.
N
~ L
E
~ n
Z U)
0 o
LL LL
O
O
O
U(
U)
n
0
0
f
O
O
n
co
0
H
U
a
d
N
O
L
G7
A
N
d
f0
a
rn n
Q a
0)
O N
0 N
r
0
C
C
Y ~
U L
N
ca
a)
Q
Q
L
~ L
N 0-
U c
c O
O U
U N
N U)
U) m
N
O
L
U
Y
~O
O
Q (L)
C
N L tL
U U c
c `co 0_)
g c
m
U) t i
N W
W
W o
t
O a
it FL 2
O
O
~NOJ
O O V) O
O O h O
r In
N
c
N c
V O
N >
0 a)
U
W
m
f0
c
O
~ U N
O C2 U
C
O
c ~
cm a~ W
W
U
U
m
N
O
M
O
O
M
O
N
O
O
N
v
c
O
ui
r
O
O
O
Lo
O
U O UC O to O 47 O UA O Un O O
cV c- O O 07 0 00 M r- r- 0 O
N N N N N r- c- r• T- r r• ~ T--
(:4) U0Il@A81A
w
tn o
rn
z, (p
~a
3
0
LL
(O
to
m
t6
U)
M
0
N
co
O
r -
co
0
U
?N
a
0
v
N
0
0
m
n
M
G
N
a
0
w
a
m
a
S
2
IL
rn r
O N
r O
O C7
0> fV
O r
N
N O
N ~
« Cl)
N m
ma
00
LL
N
C
C
f~
t
U
L
m
a~
L
O
N
m
t
N
Y
L
N
x
O
CD
x
M
3
O
O
O
o E
>
p
L
t
o N N
~ ~ c E
c
O) N N 0
co 0 U U) N
O C N C
C) 0 t6
.
co
U O C U
tp to
~
nfn=
~
C
N
LL 0 N O
n W 0
U ti W
m
N ` 3 L >
75
>
cl
`~E:m
a (n
U)
N
O N
C O
.C
m O
7
O
w
c
O p
aO
04
N
'D
C
W
C
O p
O
O
U)
Cl (n
O
0
N to
O r
O t~
r
p 0 0 to O O O LO O
O C O In 0 In to to N O
~ ~ d' I11 to to OO r Cr
'
N r r r r N N
N
O
O
~ W
C
O
O
to
> un
N r
W
n V
0 0 tt n O Cl O O
C C O r' to W I- O N O
3 0 0 0 0 to r I- r CO 0
N fn O" - N N N
C cu
w
N >
t'n
U W
N ~ N
LO
co
N
N O r r O to LO O N 0-
1-: fA mot' N M (O CO O M tD 00
O 6 w r ti O O r 00
U') N r r r r
N
3
m
to
Lo
n
M
O
N
co
co
co
0
H
U
a
a~
~o
-o
m
0
w
v_
N
0
0
m
n
M
E3
Vi
0
m
m
m
m
S
C
O
U
EFE
aa)
O
U (D
Ch a)
aI L
c n to
a a~
N C
C a~~ m mw
to d d a 0U)
Z, 2, U
tp Q O !11
o o
N o~ a CD
0 LL F- = U U » U) a
n
0)
O N
r CO
O N
Of N
O ~
~ N
O
J
LL
co
m
W
0
Z
O
U
W
O
.J
LL
w
w
O
J
>J
Q
W
C
C
N
c
U
L`a
0)
m
O
..Y
03
Lq
r
L
N
n `
C
~ n
z
y
0 Q
LL LL
h w
O
N
N O
0)
N
caa
3
0
LL
co
co
N
r
M
O
N
co
O
n
O
0
U
d
0
O
0
m
v
y
Y
O
O
QI
h
M
(J
c
N
cO
L
N
c0
N
d
N
a
O n
O N
~ C]
O N
~ N
O ~
v-
C
O
U C
O C
U
t
(n U
0 L
L
U ~
O t
J `
LL O
4-
O
0'0
N
J
>Q N
Cl)
0 O
Q U
w
N
E
X
0
.0
co
M
E
3
O
cm 3 o 0 m~
0
a >
TO
LO M ca
C
O) O L O
CD 0 Uf a
0) 0
O C lD C
O O 7 C t
~J C C
N u
aw. C
c
m
ii 00) E
U N w 0 l
0
s
a) je
.O 0 3
CL ~ E m i
0
0
LO N
N N LO Cr)
O O V7 CA
O CO I- ~
LO
N
C
c
V O
cu
0 a)
w
N 0
a U
0
0
c CO
0
cc ri)
C a`)
a m
U
cu
m
0
C
0
I~
0
0
co
q
to
N
O
0
N
w.i
0
c
0
41
O
0
O
L6
0
0 O O O O O O O O 00
~t 6 N r O of 06 r-: 0 to
N N N N N T- T- r- r-
UOIJEASIB
to 0
N (gyp
~a
3
0
LL
co
co
0
N
N
n
M
0
o)
0
n
CO
0
U
z
'E
3
v
0
0
a
0
0
m
n
Cl)
U
0
v
v
T
v
x
2
0-
a) co
o v
co
O N
0) N
0 -
CONSULTANT REPORTS
FROM 1999
PEAK LAND SURVEMG, INC. 970-476-6644 • FAX 970-476-8616 • 10DO LION'S RIDGE LOOP • VAIL, CO 81657
PEAK CIVIL ENGINEERING, INC.
OFFSITE DRAINAGE STUDY
A-FRAME SITE
TOWN OF VAIL, EAGLE COUNTY, COLORADO
MAY 17, 1999
Prepared For:
Town of Vail Community Development
Prepared By:
Peak Civil Engineering, Inc.
1000 Lion's Ridge Loop
Vail, CO 81657
PLC Job #500
PEAK LAND CONSULTANTS, INC.
I. INTRODUCTION
The A-Frame duplex is located at 2657 Arosa Drive in the Town of Vail, Eagle County,
Colorado. The existing site is located at the outlet of a large drainage basin which
extends north approximately 13,000 feet. The drainage basin consists of aspen forest,
evergreen forest, and a small amount of residential development.
The A-Frame site is scheduled to be re-developed as Town of Vail employee housing.
This drainage study estimates the runoff from a 100-year storm event and 100-year
snowmelt. Additionally, the ability of proposed drainage structures to convey the ninoff
through the site is illustrated.
II. HYDROLOGY
The drainage basin for the site was defined using the USGS Vail West and Mintum
Quadrangle maps. The basin slopes from north to south and was determined to be
approximately 676 acres(1.06 square miles). The off-site drainage basin plan is included
in the appendix.
The TR-55 Tabular Hydrograph Method found in the Softdesk Hydrology Module was
used to compute a peak flowrate for the 100-year event. A runoff curve number of 64
was used based on the basins soil type and cover conditions. A chart showing the
percentage of cover conditions and soil types is found in the appendix. Additionally, a
soils map is found in the appendix. Rainfall intensity was estimated from "Procedures
for Determining Peak Flows in Colorado", published by USDA-SCS.
Time of concentration for the basin was determined to be 0.8166 hours. This value was
based on 300 feet of sheet flow, 2300 feet of shallow concentrated flow, and 10400 feet
of open channel flow. The data used for time of concentration calculations is shown in
the appendix.
The runoff flowrate for the 100-year event was determined to be 44.78 cfs. A snowmelt
coefficient of 0.08 cfs/acre was also used in the analysis, leading to a snowmelt runoff of
54.12 cfs. Estimated flowrates over a 24-hour period are shown in the appendix.
111. HYDRA ICS
Flow from the drainage basin enters the existing site at the southwestern boundary and
continues along the northern boundary of the site. The drainage channel conveys flow
through the site passing under the driveway through an existing 24-inch culvert. The
channel discharges at the southeast comer of the lot towards a culvert under I-70 and
ultimately into the Gore Creek. The current grading allows water to flow away from the
existing building.
The culvert analysis was performed using the 100-year snowmelt runoff of 54.12 cfs
since it is the larger of the two 100-year runoff values. In the event that the 100-year
rainfall runoff and 100-year snowmelt runoff occur simultaneously, it is assumed that the
snowmelt runoff will flow through the culvert and excess rainfall runoff will overtop the
driveway. Therefore, it is recommended that a dip be placed across the driveway to
facilitate flow to the drainage channel on the opposite side. The driveway and
surrounding ground slopes away from the building, so a dip in the driveway should
adequately convey flow away from the duplex.
The existing 24" culvert under the driveway will not be adequate to handle the 100-year
snowmelt runoffs. Two 30" corrugated metal pipes with headwalls and end sections are
proposed, and will be capable of conveying the 100-year snowmelt. The corresponding
headwater depth for two 30" pipes is 2.9'. Therefore, it is recommended that 30' lorxg
pipes be placed at a4% slope with an invert entrance elevation of 7906.1' and exit
elevation of 7904.9'. This will prevent any damage to the duplex from headwater
backup. Calculations for the proposed culverts are included in the appendix. See the
Proposed Town of Vail Site Plan in the appendix for plan view of the culverts.
Channel analysis and rip rap calculations were performed using the total peak
flow(snowmelt runoff and 100-year event runoff) of 98.90 cfs. A trapezoidal channel 30
inches high with a bottom width of 24 inches and side slopes of 1.5:1 is proposed to
convey water through the site. Rip rap is recommended at the culvert entrance and exit.
Calculations for both the channel design and rip rap are included in the appendix. The
locations of channel calculations are shown on the Proposed Town of Vail Site Plan.
Appendix
Off-Site Drainage Map
ii) Rainfall Intensity Map
iii) Soil Survey Map
iv) TR-55 Output and Supporting Data
v) Hydraulic Calculations (Channel, Rip Rap, and Culvert)
vi) Proposed Town of Vail Site Plan
16,
'•?•:,~'I ? i ,i1 ~ ~l: ~j _ ' ~r' ~•\15'`', J;I,.',~ I I' _ ~\14,~i/ `••i~ ' •'l ~ ~
~~`--ter- 't 1''~„r.- ~ t~r /
` ~'\-r/-;.'/!' ..l i ~ , \ _ \ .\\-~i~~~ 511 _ '•'t 4 `~j,i~ _'~"<r:~~:::•.,5 , i r
mil{':, Jr' ii, I.~ - i'','r /'6`.~• i- - _.J ,J ,r lIl I},
i - 5~;;~.:i '',r' f' I ti~izz; ,l: 1,! ~ ~:i ~\~==~J,i!i`' I~;~j~~•
i I ;IS't~"•`;''' ~ _ \ •;~-ell ,:n,n,~=`--._'•'~
•1 ~ ,-j 'i t ' - ' t ..C(;~;"..,~.'~~~\'..~ ~ , ;ice ~~_r;~
-'_°-1~ ,.`r I`` ~5. ;.\\\ob. ~~c _I - ~~••'`f .1`'i, - :~-`.'(~Ury q' I
-es
00,
r " _ err , ~ 't_53 ~ • . ~ • '23 ~fi(~
~ - ,ik'--~ ! I:"EI ~ . ,/lei;/ _ _ ~_s : .:[~s; , j
of ;y~•.•(•1•. _ - ~ '1 , ~ 'r 5'I '-'/lrc.~.,,~~
i'
-1~' Ct`• - i ` r,•.'~,,, it?~`,•: 1(' -'`,z':;~/.rte ,Ft ,1:
• - ti n = r~r l 4: „ iS 6o l'r ~ - ` 1; 'i _-J`'.;~;•`.'\. '.1 I
•v-• _ _ .i~ili,, 1'11 4~,5 '~t ~51t ,``i, :,,;,/i~l.~%.,~/~. i •~,e.
1 `rte- ` s / \ \''1 'z•r 1 _ _ _ F
'i5;; ad, Facilet ~i1 5 ~•'°'\~`.-~_~-w' •~'e'-• ITV
r^1 _ R n; ap,
it
!!/r':
~ r.,,r'I,f 1.!i'I, lry` .;,,,'~:f'~:;~•"' ~-/,/ice/%~i •%,~~i-c_-J ;
1. / {~Y r-~~ mss' /
772
U16 -
' ; ~ x938:1
_~~E~ 'Z'{'-- ~a \ Lam`: , i. : \•.\V. --N
% r J j i
cot * tr01 Sol 901
Fox
!`:rte. u0111AW Euljvvu1bu3'43IAjvS uo(laAmvuoo IIOS
' - '.jn ;m jA o 1u97j jade jo Bjvd61
A3olojpAH;o volllO'v:)lAJaS wLIIRDM IauOlleN
cJ y¢j. J9 tt uohr,lclulwpgoljvydvowlgpwOluaeoplauopvN
yZ vojewwoo ;o }uvwpadv0 'SYl A4 pajadvid
bVjw::.~, Z l ~j_ t+ III ►wnIOA 'Z STUY ON
CS'' 5S 5Zt U it 0 14 t ii 91 6
L E -1 + Y~ :4a::::::: B 7
o13 ONixas : * 1 • ~ ' i s9WYlY 1
}3nE °I !n1 I u
YINnr
Nn -
0193nd s j zl
t- ]I~Ylf:il'~~.i:i,(.k .'4 • S%,' 4- 01 A C~
i
f K ==t - is}? $'JNI 5 5 t { ot`
113
,:v;,;;=:a.~._,~s_-mss. C~;') . ~ ►
s I 1 YH
rung.
t ''S• i=:~ ~ { iii S.• 1 - - - - r ~
I '~,iT.~~R.9' I rart / F,L y L~~t.". t,•': ~ 1 ~
1 A xU7~1' ;,•;k r1: ~NObxY' I 1
01
j - 1 t A3133 {
z
'G~~ ..c,... of v
I 8f tE Zt ~t 9f V~f OE 4 t
1 L. 7O, 1 - C . 1.bt tr Z~
Sol 901
Ol 60E ` S`Ol
"
kaw
r. ~aaaau v, a>nli
Solt- sv(ZJEy OP ASp1~10- GYFSO'k ~,\z-&A
EDW Alps QAA~RA~ 6tLV ~ SSE ra 4~-~~ CVS
QJNV?W~ Vf '
v sID N ~ s L -
A-FRAME OFF-SITE DRAINAGE BASIN CALCULATIONS
TR-55 Tabular Hvdrojzraph Method Input Summary
Description A-Frame - Off-Site Drainage
Rainfall Distribution Type II
Ia/P Interpolation Off
Total Area
1.0560 mil
Peak Time
13.0000 hrs
Peak Flow
44.7824 cfs
Peak Snowmelt Runoff..
54.12 cfs
Given Input Data:
Subarea D/S Subareas
Area CN
Tc
Tt
Rainfall
Description
(mil)
(hrs)
-
(hrs)
(in)
OFF-SITE
1.0560 64
0.8166
0.0000
2.4000
Sheet Flow
Manning's n 0.4000
Flow Length 300.0000 ft
Two Yr, 24 hr Rainfall 1.4000 in
Land Slope 0.1330 ft/ft
Computed Sheet flow time 0.6107 hrs
Shallow Concentrated Flow
-
Surface Unpaved
Flow Length 2300.0000 ft
Watercourse Slope 0.2960 ft/ft
Velocity 8.7781 fps
Computed Shallow flow time 0.0728 hrs
Channel Flow
Flow Area 6.0000 ft2
Wetted Perimeter 43.2666 in
Flow Length 10400.0000 ft
Channel Slope 0.1730 ft/ft
Manning's n 0.0400
Hydraulic radius 19.9692 in
Velocity 21.6988 fps
Computed Channel flow time 0.1331 hrs
Total Time of Concentration 0.8166 hrs
rrrrrwrwwwrrrrrrrrrrwrwwrrrrwrrrwr a rrwrrr a rrrwwwwwrrrrwwrwrrwrrrrrrrwr~
On-Site Channel Calculations
Channel Calculator - 6.67% Slope
Channel Section 1 -Northern Edge of Property
Given Input Data:
Shape
Trapezoidal
Solving for Depth of Flow
Flowrate 98.9000 cfs
Slope
0.0667 ft/ft
Manning's n
0.0400
Height
30.0000 in
Bottom width
24.0000 in
Left slope
. 1.5000 ft/ft
Right slope
1.5000 ft/ft
Computed Results:
Depth
23.7278 in
Velocity
10.0720 fps
Flow area
. 9.8193 ft2
Flow perimeter
109.5517 in
Hydraulic radius
12.9069 in
Top width
95.1833 in
Area
14.3750 ft2
Perimeter
. 132.1665 in
Percent full
. 79.0926%
. Critical Information
Critical depth
29.7982 in
Critical slope
0.0248 ft/ft
Critical velocity
6.9571 fps
Critical area
14.2156 ft2
Critical perimeter 131.43 88 in
Critical hydraulic radius 15.5742 in
Critical top width
113.3945 in
Specific energy 3.5538 ft
Minimum energy 3.7248 ft
Froude number 1.5959
Flow condition Supercritical.
On-Site Channel Calculations
Channel Calculator - 12% Slope
Channel Section 2 - Above Culvert
Given Input Data:
Shape
Trapezoidal
Solving for Depth of Flow
Flowrate
. 98.9000 cfs
Slope
0.1200 ft/ft
Manning's n 0.0400
Height
30.0000 in
Bottom width
24.0000 in
Left slope
. 1.5000 ft/ft
Right slope 1.5000 ft/ft
Computed Results:
Depth
20.6608 in
Velocity
12.5348 fps
Flow area
. 7.8900 ft2
Flow perimeter
98.4937 in
Hydraulic radius
11.5354 in
Top width
85.9825 in
Area
14.3750 ft2
Perimeter
. 132.1665 in
Percent full
. 68.8695%
Critical Information
Critical depth
29.7982 in
Critical slope
0.0248 ft/ft
Critical velocity
6.9571 fps
Critical area
14.2156 ft2
Critical perimeter
131.4388 in
Critical hydraulic radius 15.5742 in
Critical top width
113.3945 in
Specific energy
4.1635 ft
Minimum energy
3.7248 R
Froude number 2.1059
Flow condition Supercritical
On-Site Channel Calculations
Channel Calculator- 16.67% Slope
Channel Section 3 - Below Culvert
Given Input Data:
Shape
Trapezoidal
Solving for
. Depth of Flow
Flowrate
98.9000 cfs
Slope
0.1667 fdft
Manning's n
0.0400
Height
30.0000 in
Bottom width
24.0000 in
Left slope
. 1.5000 ft/ft
Right slope
1.5000 ft/ft
Computed Results:
Depth
19.0987 in
Velocity
14.1636 fps
Flow area 6.9827 ft2
Flow perimeter
92.8613 in
Hydraulic radius
10.8281 in
Top width
81.2961 in
Area
14.3750 ft2
Perimeter
. 132.1665 in
Percent full
. 63.6623%
Critical Information
Critical depth
29.7982 in
Critical slope
0.0248 ft/ft
Critical velocity
. 6.9571 fps
Critical area
14.2156 ft2
Critical perimeter 131.4388 in
Critical hydraulic radius .
15.5742 in
Critical top width 113.3945 in
Specific energy 4.7091 ft
Minimum energy 3.7248 ft
Froude number
2.4595
Flow condition
Supercritical
'A
PAR
~ S
S-o (S5 - lY = Lv~ rlTU~ln~t}t C'~fAN,v~G SLVP (c7/F'f) .
ss = SP c~FIc G-feAJITl(
= 'ock Sr~~ rN F-cr
~Sa .S-07,p OF P I P p,4-P
15 SMA•LGe~P,
D~ 1NxC~~ Cji, A NNE I- t)F 041VFI,J!'ryt-V,--eT- .
(12.53 (c?,121 ~ o r
y, S
do = 1,32 ~f = 15,8 r~
r
J YP E So C MEAX Rq.- Tl« ~ 5ex)
D~e~r JA F C"NM F~ gFj LLj- Diej yr-um+ f Cvi y5 p-T
1q, /6
sP~ y S
05 1)0,
G 50
- _ [-YpG I~ ---Lf5D C.l~'I SAN _Pf~RT_.~4C~ S/~-E)_= IS
- i
i
i
OF 1?00e = 2.8
Foe WHIc"t
CLASSIFICATION AND GRADATION OF ORDINARY RIPRAP
Riprap
Smaller Than
Intermediate Rock
*
dso-
Designation
Given Size
Dimension
By Weight
(Inches)
(Inches)
Type VL
70-100
12
50-70
9
35-50
6
6**
2-10
2
Type L
70-100
15
50-70
12
35-50
9
9**
2-10
3
Type M
70-100
21
50-70
18
35-50
12
12
2-10
4
Type H
100
30
50-70
24
35-50
18
18
2-10
6
Type VH
100
42
50-70
33
35-50
24
24
2-10
9
*d50 = Mean particle size
Take, warn 4
U r b an. S-6v- V 1 -1>r. v q P- Ct• VeXi q MA M% Al
.~enuer Rt3 Bona Cunt{ 1 a~ Cdve-rn mm4s)
by WH.S5i+- YY)cLausl~~i~1 Ehgi~eerS~
mare,k l9 CA.
s
4J
3
in
cr
w
z
ti
F-
z
W
U
CC
W
r-
n
GRADATION OF ORDINARY RIPRAP
Tnkeh ~rrowt: nn ((1,y~
Ur'bQn S~orvn 1Jrr~inage l.Y 17~ri a rr~~NLta l
Deylve,+rRt,ovW ~otthci~ o~ oVerl1YffeAt~~
±y Wri9,+- IMCLau W yi Ev3,%"cer's,
W1arCk 19109.
INTERMEDIATE ROCK DIMENSION- INCHES
Manning Pipe Calculator- 2 X 30" Culverts
Given Input Data:
Shape
Circular
Diameter
. 30.0000 in
Flowrate
27.0600 cfs
Slope
0.0400 ft/ft
Manning's n
0.0240
Computed Results:
Depth
16.9045 in
Area
4.9087 ft2
Wetted Area
2.8501 R2
Wetted Perimeter
50.9432 in
Perimeter 94.2478 in
Velocity
. 9.4945 fps
Hydraulic Radius 8.0562 in
Percent Full
56.3484%
Full flow Flowrate 44.4352 cfs
Full flow velocity
9.0523 fps
Critical Information
Critical depth
21.6807 in
Critical slope
0.0185 ftfft
Critical velocity 7.0355 fps
Critical area
3.8462 ft2
Critical perimeter
60.4853 in
Critical hydraulic radius
9.1568 in
Critical top width...:
30.0000 in
Specific energy
2.8095 ft
Minimum energy
2.7101 ft
Froude number 1.5682
Flow condition Supercritical
chart 12
180 10,000
168 8,000
EXAMPLE (I,
156 6,000 D•361nch.s(3.0 [..1)
5,000 0/N. 66 cfs
144 4,000 (3)
Hf H,( 5. 6.
132 3,000 D (1.4 t) 6.
ti ll) 120 1.8 5.4 5.
'
H 2,000 I2) 2.1 6.3 5.
108 6.6 4'
■ ) 3. 4.
J
a
D n tse!
96
H
1,000
3
a:
800
9W
B4
y
600
500
2
400
H w 2
.
2
z
7
300
-
o
LL
U
/
=
1.5
fi0
?
200
Z
°
54
Z
W
W
M
W
100
/
UJ
48
80~
o
J
U
Q
z'
U
O
Z
LL
42
/
tn
s
°
50
=
~
l.0
1.0
a
~
40
w
W
FW-
36
Ht SCALE ENTRANCE
°
cr
33
C TYPE
W
Q
20
(1) Headrall
Q
8
8
30
(2) Mitered to conform
W
ci
to slope
=
p
27
10
(31' Projecting
_
5.
e
.7
.7
<
24
e
ai
6
21
5
To use scale (Z) or (3) project
4
horizontally to scale (1). then
6
use straight inclined line through
.6
3
D and 0 scales, or reverse as
18
Illustrated.
2
15
.5
2.
1.5
1_O
.9
.8
7
6
1.0 L- .5
12 HEADWATER DEPTH FOR
C. M. PIPE CULVERTS
FEDERAL HIGHWAY ADMINISTRATION 13-76 WITH INLET CONTROL
MAY 1973
W
cn Q-
a w
0
z
=ROM : Bruce A. Collins FAX NO. : 970 876 5397 Jun. 26 2007 11:45AM P2
COLLINS & LAwmis
CONSULTING GEOLOGISTS
P.O. BOX 23
SILT, CoLORADo 81652
PHONF•:JFAx (970) 876-5400 (24 Hotllts)
PIUNCIPArS
Bruce A. Collins, Ph.D.
Nicholas Lampiris. Ph.D.
April 19, 1999
Nina Timm
Community Development Dept.
Town of Vail
75 South Frontage Road
Vail, Colorado 81657
RE: 2657 A oSA D12wB-LoT 8,13raocv,C, V A>L R1DGE
Dear Ms. Timm:
I have completed myreview ofavailable informationregarding geologic hazards to whichthe subject
property is exposed, and have visited the site. In addition I have contacted representatives of Dames
& Moore, Inc.; Hydro-Triad, Ltd.; and Colorado Land Consultants, Inc., regarding the sections of
the T7tAPPERS RuNPRamNARX PLAN SuaMISSION AND ENVIRONMENTALIMPACTREPORT prepared
by these firms, in an unsuccessful effort to confirm the runoff calculations and culvert sizing based
thereon for crossing the unnamed drainage in which the subject lot is located.
The property lies in an unnamed drainage at the west end of the Town of Vail, immediately upstream
from the apex ofthe small alluvial fan that resulted from debris flows from the drainage over the pas
several thousand years. The fan itself has been largely obliterated by construction activities related
to Interstate Highway 70 and Arosa Drive, and the portion of the drainage of interest here has been
altered to at least some extent by the construction of Arosa Drive as well. The drainage has been
mapped in the "Moderate Hazard" debris flow zone, with this designation terminating at the edge
of 1-70 approximately 170 feet southeast of Lot 8. The existing structure on the lot, which is in
approximately the same location as the proposed duplex, and the existing and proposed driveways
are in the narrow flood plain of the drainage essentially at the transition between the channel and the
alluvial fan.
I agree with the "moderate" debris flow hazard assessment, although in my opinion the degree of
hazard is slight. There has been no known debris flow or even high-water damage to the existing
structure or the driveway leading to it in the 20 to 25 years they have been in place, including 1984
when significant debris flows occurred in several of the drainages north of I-70, or in the high-water
years of 1993 And 1995. There is no evidence for significant debris flow along the undisturbed south
side of the drainage in the vicinity of the lot, where coniferous vegetation appears to be in the 30 to
70-year age range- A single large angular rock, roughly four feet long, two feet wide, and two feet
high, rests on the east side of the channel of the present stream near the northwest corner existing
structure; whether this rock was moved to its present location by debris flow or was deliberately
FROM Bruce A. Collins FAX'NO- : 970 676 5397 Jun. 26 2007 11:46AM P3
2657 AROSA DR1VL - LOT 8, BI,OCK C, VAU. RIDGE Page 2
placed there is unknown.' Other rocks along the east bans, of the stream might have been deposited
by debris flow, but it must be remembered that this bank was altered to an unknown extent during
the construction of A.rosa Drive. Where exposed the soil profile on the lot consists almost entirely
of red to gray sand and silt, although pebbles and rocks up to two feet in maximum size are present
on the surface in parts of the area. This profile suggests that at least the more recent debris flows that
formed the fan immediately below the mouth of the drainage were dominated by mud rather than
rocks and probably had a higher water content than coarser flows that have occurred elsewhere
(Booth Creek, for example).
The origin and characteristics of debris flows in the Vail area are discussed in detail by Mears in his
report to the Town presented in November of 1984 and this discussion will not be repeated here.
There are several important points presented by Mears that must be kept in mind, however. Debris
flows in the Vail area in historic time have occurred in late spring almost entirely in response to rapid
snowmelt. Contributing factors are a low, above-normal snowpack; normal to below-normal
temperatures followed by sudden warming to above-normal values; and bank-full or flooding water
flows in the small, steep drainage basins typical of the area. Prolonged or intense rainfall during
periods of rapid snowmelt serves to decrease stability of both melting snow and underlying slopes,
increasing the possibility of, show- and landslides that contribute the debris to the flooding streams.
Debris flows resulting from intense summer thunderstorms, the more likely scenario in many other
parts of Colorado, have certainly occurred in the Vail valley and will occur again, although they have
not been a significant factor in the brief history of the Town.
The viscous nature of debris flow, together the tendency of the debris to choke off the existing
channel and spill over into another or create a new one, make modeling of such flows difficult and
accurate prediction of debris flow behavior virtually impossible. Data presented by Mears (1977)2
p. 22-25,1984, p. 16) suggest that the ability of a debris flow to sustain its movement as channel
slopes decreases rapidly below about 15% (8.5°); lager rocks begin to settle out and material
continuing downstream contains increasing water content_ Extrapolation from his Glenwood Springs
study indicates that the velocity of debris flows themselves in similar (although by no weans
identical) conditions to those found above Lot 8 decrease to :zero as the slope of the ground over
whichthey are moving decreases to 8% to 9% (4.6 ° to 5.1 The slope of the channel and therefore
essentially the entire valley floor of the drainage in question where it crosses the south lot line is
10.5%; It maintains this average slope for about 35 ft, to a point about 75 ft west of the west wall
of the proposed structure, where it decreases to an average of 8.5% over the next 23 ft and to a
weighted average of 5.5% from a point 54 ft west of the northwest comer of the proposed structure
past it to the projected west end of the driveway culvert (all as determined from the Peak Land
Surveying topographic map of Lot 8, showing existing and proposed structures, provided to nee by
the Town of Vail). It would thus appear that in the event of a debris flow in this drainage, it will be
slowing to a stop as it approaches Lot 8 and, other influencing factors aside, will come to a stop well
to the west of the proposed structure, Debris flows frequently occur in pulses, however, and as
subsequent pulses stop further up the now-reduced-gradient channel water released from the flows
t 1. should note that the south side of the lot was substantially snow covered at tho time of my examination. An old
photograph of the lot indicates thatthe chamnel ofthe existing stream was moved from just [forth of the large rock mentioned
here to Just south of it in connection with the construction of Arosa Drive,
2 Mears, ) 977, Debris-flow hazard analysis and mitigation - an example from Glenwood Springs, Colorado:
Colorado Geol. Survey tnf. Series 8, 51 p.).
FROM : Bruce A. Collins FAX N0. : 970 876 5397 Jun. 26 2007 11:47AM P4
2651 AROSn DRIvr, - LOT 8, BLOCK C, Van. RuX.Li Page 3
will cut down through them, resulting in a temporarily-steepened channel that could give rise to a
small flow down the face of the original flow. Such a flow would in turns stop quickly as the gradient
decreased.
Tf the studies published by Mears and the above scenario are correct it is unlikely that any but the
most catastrophic or otherwise unusual debris flow event will reach the proposed structure.
Nevertheless I would recommend the following precautions. The structure should be built as high
above the existing stream channel as grading and setback restrictions allow. Site grading and
foundation construction should combine so that the top of foundation walls on at lmst the west and
north sides extend at least six feet above the bottom of the stream channel as measured on a line
perpendicular to the channel through the northeast corner of the structure; at least three feet of this
wall should extend above final grade, should contain no doors, windows, or other significant
openings, and these walls should be designed in their entirety by a qualified engineer to withstand
impact pressures of at least 350 pounds per square foot _3 The site west of the structure should be
graded to guide water or debris flow away from it, and in particular should be graded to prevent
water from flowing behind it, along the south side- As an alternative to a six-foot-reinforced
foundationwall, a 6-foot berm constructed of large rock and compacted earth or equivalent materials
sufficient to withstand an impact load of 400 pounds per square foot notched into the south hillside
and angled from the southwest to the northeast west of the structure could be constructed in such a
manner as to channel a debris flow or flood to the east. Such a diversion structure might cause
significant erosion of the east bank below Arosa Drive, however, and would seriously complicate
drainage under the driveway (discussed further below). It would also require inspection and possible
maintenance after high-water events that might erode or otherwise weaken the berm.
High-water events which can still cant' significant amounts of mud and vegetation debris, occurring
in response to either rapid snowmelt or intense summer thunderstorms, are more likely to reach Lot
8 than full-fledged debris flows. The Trappers Run development plan proposed the construction of
a substantial fill from the Arosa Drive curve immediately northeast ofthe property upstream through
and Well past the lot. The existing drainage was to have been conveyed beneath the fill through a
culvert approximately 400 ft in length. A 100-year 24-hour peak flow of 184 cubic feet per second
(efs) was calculated, apparently by Dames & Moore, Inc., increasing to 195 efs as the result of the
proposed development, and a 54-inch culvert was subsequently designed to carry this flow. No
calculations substantiating these values accompany the planriing document, and although I have
contacted Dames & Moore as well as Hydro-Triad and Colorado Land Consultants, which used these
numbers for various purposes, I have been unable to locate any documentation of these calculations.
Utilizing the Office of Surface Mining's STORM program (v. 6.21) I have been able to
approximately recreate the peak flow rate, calculated at 151 efs. The assumptions used to make this
calculation assume essentially a "worst-worst" case, with 100% soil saturation (AMC-3) throughout
the drainage before the 100-year estimated rainfall of 3.0 inches. Other assumptions are shown on
the attached summary sheet (Vail 100-yr 24-hr Worst Case). Slight variations in these assumptions
3 The impact pressure of a debris flow can be approximated from the formula P ='/2(y/g)Ua, where P is the impact
pressure in poundslsquare foot, y is the density ofthe moving flow in pounds/cubic foot, g is the acceleration ofgravity (322
feet/second'), and 0 is the velocity ofthe flow in feet pet second (Mears, 1976, p. 64), Eixtrapolating from Mears' Glenwood
data for similar materials, a maximumvelocity of 6 ft/sec is estimated fnr a 10% slope, with a maximum flow density of 125
lbs/fl3, wbieh produces an estimated impact pressure of`70 ibs/fl~. Because of tho uncertainties involved, Y recommend a
safety factor of 5, producing the recommended strength of 3SO Ibs/ff'.
FROM : Bruce A. Collins FRX NO. : 970 876 5397 Jun. 26 2007 11:47RM P5
2657 AROSA DRIVE-LOT 8, Bt.OCK C;, VAM RilxiF page 4
would easily increase the calculated discharge to the 184 cfs given in the Dames & Moore report.
A similar calculation for a 25 year 24-hour storm with 100% saturation produces a discharge at the
evaluation point (essentially the intake to the driveway culvert) of 83 cfs (Vail 25-yr 24-hr Worst
Case). Assuming a "normal" storm situation, that is all Soil Conservation Service (SCS) default
values except time of concentration, the 100-year 24-hour peak discharge is 63 cfs and the 25-year
peak is 27 efs (Vail 100-yr and 25-yr 24-hr Non-saturated, respectively). Time of concentration for
all cases was calculated independently of upland-curve values to more accurately reflect the nature
of the drainage and the intensity of mountain thunderstorms; using the SCS values decreases the
calculated discharge in all cases substantially a It should be noted that adjustment of the SCS curve
number to account for total saturation was the only change between the "worst case" and "non-
saturated" runs, all other assumptiorui remaining the same.
A, rough back-calculation with average dimensions from the existing channel suggests its capacity
is approximately 50 cfs at a flow speed of 8.7 feet per second (attacbed, "Existing Channel). Thus
the existing channel should be able to handle the calculated `5normal" 25-yr 24-hr storm with little
difficulty, so long as it does not become obstructed with debris, and neither the calculated "normal"
100-yr 24-hr or "worst case" 25-yr 24 hr peak flows of 63 cfs and 83 cfs should threaten the
structure. The suggested mitigation measures £or debris flow above should minimize any hazard
from. the calculated 100-yr 24 hr discharge of 151 cfs.
Based on the above calculations my calculations suggest that at the "worst case" 100-yr peak flow
rate of 151 cfs, multiplied by a safety factor of 1.2 (considering that other safety factors have already
been incorporated in the flow calculations) to produce a design flow of 182 cfs, a round concrete-
pipe culvert 48 inches in diameter or its equivalent would be necessary to pass the flow without
unacceptable damming of water on the upstream side, although the velocity ratio is virtually 100%.
Even at 54 inches as recommended in the Trappers Run plan my preliminary calculations suggest
a headwater depth of 7 feet. The larger diameter was probably selected to facilitate eleanout in the
culvert, which was to have been about 400 ft long. On the other hand the "normal" adjusted 100-yr
peak flow of 75 cfs can be handled with a 36-inch culvert, with a headwater depth of slightly less
than 5.5 feet. Use of corrugated metal pipe will increase both the diameters necessary to pass the
flows and the headwater depths slightly. A qualified civil engineer should be consulted to formulate
actual design requirements for whatever drainage option is chosen for the site.
Considering both the limited area and the limited elevation difference between Arosa Drive and the
proposed structure available for the reconstructed driveway, I would suggest twin 24-inch culverts
together with the "sculpting" of a dip crossing above the culverts sufficient to provide a channel to
pass excess water. Even this may require moving the access point either further upstream or down
in order to create the necessary elevation difference. Alternatively a combination of the reinforced
stream-side foundation for the structure recommended above and site grading might suffice to
incorporate the driveway into an overflow channel, although with no significant elevation difference
between the driveway and Arosa Drive at least some flooding of the latter would probably also
occur.
4 The formula used to calculate time of concentration, is t = 0.928(nL)0.6/(i. - )S"), where u is ,Mannings n, here
calontatcd as a wojoted average of o.030; 7. is the length of the drainage In feet, L is tllb rainfall excess intensity in inches
(rainfall intensity less infiltration; for these calculations infiltration was assumed to be 0, and intensity the entire 24-hr storm
total in one hour); and S is the slope in feet per tbot.
FROM : Bruce A. Collins
FAX N0. : 970 876 5397 Jun. 26 2007 11:48AM P6
2657 AROSA DiuvE - LoT 8, BI.O(:K C, VAIL R )GE
Page S
Drainage below the site consists of a half-buried culvert- that appears to be no more than 30 inches
in diameter extending from a small depression beneath an embankment into a larger basin that drains
under I-70 into Gore Creek; the culvert under I-70 appears to be at least 48 inches in diameter with
a headwater of close to 10 feet. A 36-inch culvert is required to pass the "normal" 100-year
discharge without damming that would probably result in overtopping oftbe embankment below the
driveway. This culvert and the embankment through which it passes appears to be on the right-of-
way of Interstate 70.
In summary, the structure proposed for construction on Lot 8, 2657 Arosa Drive, is exposed to a
moderate debris flow hazard as indicated on the Town of Vail geologic hazard maps, but the actual
risk of a damaging debris flow is slight. There have been no such events in the 20 to 25 years the
current structure has been located on the property. The exposed soil profile and outer evidence
present at the site suggest that flows of predominantly mud with only a few larger rocks were
responsible for at least the upper portion of the small fan at the mouth of the drainage, now largely
obliterated by the construction of Interstate 70. The gradient of the stream as it enters the property
is at or near the minimum required for debris flow movement. The gradient from well upstream of
the proposed structure to the east property line is below this minimum. The present channel appears
to be adequate to contain both nonnal 25-year and 100-year 24-hour storm events that do not contain
significant debris. The proposed structure could be exposed to worst-case 25 year and 100 year
events depending on placement on the lot, and while the actual hazard appears minimal it could be
exposed to debris flow as well. Mitigation steps include locating the structure as high as possible
on the lot, extending reinforced foundation walls so that the combination of grade and foundation
totals at least six feet above the bottom of the stream channel at its closest point northwest of the
structure, extending at least two feet of the reinforced foundation walls above final grade regardless
ofheight above the stream, and final grading around the structure to provide positive drainage away
from it. A partial alternative to siting and foundation mitigation is a competent berm from the
hillside southwest of the structure northeasterly, parallel to the stream, although this alternative has
consequences that may be unacceptable.
Minimal elevation differences and space limitations complicate design for a culvert under the
driveway that will pass even the normal 100-year 24-hour water flood event (it should be kept in
mind that the "worst case" 100-year precipitation event probably has an actual recurrence frequency
ofconsiderably more than 100 years because of the assumption ofcoineident 100% soil saturation).
Based on preliminary calculations a 36-inch round concrete culvert with a bell end at the headwall
would adequately pass the 75 cfs adjusted peak flow, but would require a headwater of nearly 5.5
feet. I suggest the consideration of side-by-side 24-inch culverts beneath a dip crossing sufficient
to provide a channel for excess drainage over the driveway. Both upstream and downstream faces
of such a structure should be rip-rapped or otherwise armored to prevent erosion, and the driveway
area graded so as to prevent backup of water toward the structure- The access point for the driveway
might have to be moved to provide adequate elevation differences regardless of which approach is
chosen- Another option would be deepening of the existing channel from approximately due north
ofthe northwest comer ofthe proposed structure to the property line, which might provide sufficient
elevation for the necessary headwater without relocating the driveway; I do not have sufficiently-
detailed topographic maps to determine the feasibility of this option. Drainage off the property to
the east does not appear adequate for a normal 100-year event regardless ofthe choice of design and
mitigation choices trade on the site. Since culvert design is not my area of expertise, regardless of
the drainage option selected a qualified civil engineer should be employed to confirm these capacity
calculations and provide final designs.
FROM Bruce A. Collins FAX NO. : 970 876 5397 Jun. 26 2007 11:48RM P7
2657 AROSA Dlttve -LOT 13lfX:K C, VAII. RiDG1 Page 6
'Me property is not included in mapped snow avalanche or rockfall hazard zones. Alluvial fan and
channel f111 deposits derived from Minturn (Pennsylvanian) and Maroon (Pennsylvanian - Permian)
Formation rocks are frequently hydrocompactive, and soil testing for foundation design should be
sufficient to account for this possibility. The property is in a geologically sensitive area but so long
as final grading and drainage facilities are properly designed and constructed neither the proposed
structure not the recommended mitigations will increase the hazard to other property or structures,
or to public rights-of-way, buildings, roads, streets, easements, utilities, or facilities or other
properties of any kind. This report is intended to comply with appropriate portions of Town of Vail
Regulations Chapter 12-21-15, and nothing contained herein should be interpreted as suggesting that
the subject properties are not exposed to the mapped hazards, or'that mitigations recommended
herein will eliminate such hazards in their entirety. if you have any questions, or if T can be of
further service, please do not hesitate to contact me.
Enc.