HomeMy WebLinkAboutWPO201700014 Study WPO VSMP 2017-09-15 (2) WOOLLEY ENGINEERING
APPROVED
May 5,2017 by the County
Community DevelopAlbemarlement Department
Date 9/4-
MEMORANDUM File '70i 000 of
To: Mr. Bobby Jocz, EIT
County of Albemarle,Virginia
From: Mr. Eric Woolley, PE
Woolley Engineering
Regarding: SDP 2016-051—UVA Research Park: Town Center 4
Major Site Plan Amendment
Adequate Channel Analysis
This memo shall address the conditions of the downstream storm water conveyance system that
currently supports Town Centers One, Three and Four of the UVA Research Park. The
approved Site Development Plan(SDP) for Town Centers Three and Four was engineered with
phasing of the development in mind. Town Center Three is substantially complete, and has been
in use for approximately 9 years. The vision for Town Center Four has changed since the
original site planning phase and is currently under review for a Major Site Plan amendment.
The first phase of the original plan implementation required that the storm drainage piping and
outfall for the two buildings would need to be installed with the Town Center Three project.
That storm drainage piping reach and outfall is currently in place. The current Major Site Plan
Amendment for Town Center Four proposes to utilize the existing outlet,the first leg of existing
storm piping and the next storm structure located just upstream from the existing outfall. A new
piping system is proposed to carry the overland surface flow through the existing outfall point.
The fully developed Town Center District improvements are incrementally brought on-line with
each successive building phase. The revised new storm drainage routing plan will introduce
more surface flow area than the previous site plan illustrated; however, the piping system was
overdesigned with the initial development in anticipation of the proposed future development
illustrated on the Park's Master Plan. Storm drainage calculations provided with the WPO
submission have shown that the existing pipe to be repurposed would be adequately sized.
Due to the fact that more flow volume is anticipated with this submission, we will illustrate on
the following pages that the downstream accepting channel can easily absorb the increased flows
of the 2-year storm without topping its banks. Attached to this memo are three cross-section
analyses of the downstream channel. The existing channel was designed and enhanced with the
first phase of construction for the Research Park. The channel is a direct contributing conveyor
of storm water to the Park's existing regional stormwater management facility.
WOOLLEY ENGINEERING 220 East High Street (434) 973-0045
Charlottesville, Virginia 22902
- / v TOWN CENTER 4, / a
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s Existing Parking \ ' � \/:7-", --77":7:"''' k'l'11:(111:11r.\‘f*:
Existing Piping \ \\ \ \0 \��,`�*
) Outfall (Beginning `\ I �' :\;-% ''' '%
j\ ', ' \ A
of ex. Channel) ; • �' '; '��\
I/
Top of Bank (From \\ \
topographic survey, O
dated August 2016) �\ \� r
Proposed new T\,\ \\ q �,
hand-placed \i \ \ Proposed Storm
class I rip-rap ; ' Drainage Piping
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/ Temporary
O / // /
Sediment Basin
Cross-section (typical)
li I
i
ri
i\/r
/.\\
O // Ex. Sanitary
i Sewer
Ex. Storm Piping —w • •
- - .
Existing SWM Pond #1 ` .,. •
W/E 452.49 I
• Edge of Water
(Observed
• June 2016)
. ( /1 f • \ _A
WOOLLEY ENGINEERING
Channel Cross-Section Location Exhibit
Consulting Civil Engineers
0 220 East High Street May 5,2017
Charlottesville •Virginia 22902 Scale: 1"=100'
(434)973.0045 www.woolley-eng.com
- � WOOLLEY ENGINEERING
Cross Section #1
M if•x`� { :i ...t. ^
g„ L
AJI - 1 t !.
a per_.
P
•, a��:4`'°�. -" - �y.. +�, View of Western Top of Bank
}c. ;4 e . ,�- • 1,7: ,.4 1• s
r ?j,0' .. , S- `/
•
'pp
.1-‘,. ',171,4';')'.'''':44fAt ,, :, .;:.'-' i-,-11.1,%-..,‹It.' .4'4.. Ls:- .el - ,. :
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4'�'�,4., �^ � `fid -S:•
'''�
-.0 t`: 4, . . ... . ._ ,..
..,
a-
. , . .... .
..._........, . . View of the Center of Channel
4 .
1
iD' s i
.i
kt,
, 1
£
1:
:::::;
il'
^Q d 'S 4.Y eU
y r °Z
J t
' _ View of the Eastern Top of Bank
3 WA Research Park: Town Center Four
WOOLLEY ENGINEERING
Cross Section #1
490
485
M=Top of bank Infamo0on taken from
2-YEAS STORM EEVAIION tapogropfic field Army by 1st Hughes
480 / 8 Assodafec doped August,2016
f! Channel lbw depth far fhb CMOS mdlon
475 as observed m ApR 25 2017 row 1 S
i470
465
460
455
450
-40 -35 -30 -25 -23 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60
Channel WIdlh(feel
Cross Section Calculations:
Q = C * i *A
Drainage Area- 1
LAND USE AREA(ac.) C C x A Wei s hted Runoff Coefficient
Industrial 10.24 0.9 9.22 0.63
Woods 8.13 0.3 2.44 2-Year Rainfall Intensity
18.37 11.66 i= 3.24 in/hr
tc = 17.30 mins
Q1 = 37.73 ft3/s (drainage area peak discharge)
1.486
V /
= * R2/3 * S1/2
n /
Existing conditions:
n=0.035 (Manning's roughness coefficient)
R= 0.12 (hydraulic radius)
S=0.07 (channel slope)
V1 = 2.77 ft/s (cross-sectional average velocity)
Q = 2.13 ft3/s (cross-sectional flow rate)
Fr= 1.03 (Froude number)
2-Year Storm (Peak Discharge):
Q1 = 37.73 ft3/s
n= 0.035
R= 0.57
S = 0.07
V1(2_yr) = 7.85 ft/s
Maximum water elevation for 2-year storm: 8.28"
Cross Section Characteristics:
The channel bed contains large and medium cobble as well as fine gravel. There is some pooling in this area
with a depth of 6"that can be seen in the image view of the center of channel on the following page. The
channel flow depth observed on April 25, 2017 was 1.5" for this section. There are a few small trees located
along the side slopes near cross section 1 as well as one large tree.
4
Ira
WOOLLEY ENGINEERING
Cross Section #2
t k•' vim'• 1 >.' .
T .
G� f J`' h,'''''''''t.'.
d'F1•• x .1'
- View of the Center of Channel
, sI _,
`•.:. ..,
_.
'. . ., • .., ,.!, .t5:- ,-- . „:, ,,:0,:to:,.- '=, _ ,';
I *" st. .. fi W 4 w.:..
II ♦ b„^ t f M R y E
,o-4} M:= .
A
+F. . >.
1\:4:1 ' ,
View of Western Top of Bank View of the Eastern Top of Bank
5 UVA Research Park: Town Center Four
WOOLLEY ENGINEERING
Cross Section#2
490
485
18=Top of hank InformHon Iden from
$opopropNc field anew by 6k Hughes
480 &Associates dated August,7016
Channel flow depth for his crows section
1 475 ce observed on Apel 25.1017 was 10'
470
2-YEAR STORM ELEVATION
465
460
455
450
-40 35 -SO -25 20 -15 -10 -5 0 5 10 15 70 25 30 35 40 45 50 55 60
Charnel Width(feet)
Cross Section Calculations:
Q = C * i *A
Drainage Area-2
LAND USE AREA(ac.) C C x A Weighted Runoff Coefficient
Industrial 10.50 0.9 9.45 0.60
Woods 10.48 0.3 3.14 2-Year Rainfall Intensity
20.98 12.60 i= 3.24 in/hr
tc = 17.34 mins
Q2 = 40.77 ft3/s (peak flow)
H._1.486)
V = * R2/3 * S1/2
Existing conditions:
n=0.035 (Manning's roughness coefficient)
R=0.08 (hydraulic radius)
S= 0.07 (channel slope)
V2 = 2.11 ft/s (cross-sectional average velocity)
Q = 0.55 ft3/s (cross-sectional flow rate)
Fr= 1.32 (Froude number)
2-Year Storm (Peak Discharge):
Q2 = 40.77 ft3/s
n=0.035
R=0.71
S =0.07
V2(2_yr) = 9.04 ft/s
Maximum water elevation for 2-year storm: 13.08"
Cross Section Characteristics:
The channel bed contains medium cobble as well as medium and fine gravel. The channel flow depth observed
on April 25, 2017 was 1.0" for this section. Side slopes for this area contains ferns, grasses, and small
vegetation. There are a few small trees located on the banks along the channel on the East and West side.
6
rill
WOOLLEY ENGINEERING
Cross Section #3
Ill
, , 14911pit, - IMP- --',
,... ,...r , ' .---- ., --. ... ..
ti
tilik+�+�^ _ z �`` a •iy. !mai.'i
'£
-..,--w, ,, 4,,o
�*c}olt.,- a&�'tg a '' t�'tL t
.,� -- Jv ?' «'fie {'R` a ` ""(
. .. +
a '.-At. - yt -44' 'c 4, l it
View of the Center of Channel
Looking Downstream to the point of termination at an existing 54"RCP culvert
ate' `.,t - a -,t-A, '4y .g 'y ... .` r t.i A' ..
/ilk* `V Rye..
` ..t X ., # .+! �
,,
i
t
—
`:r %" ` .It
s a ,.., s RL#' \ i ` ..a044
te {
,„„,
View of the Center of Channel
Looking Upstream
WA Research Park: Town Center Four
WOOLLEY ENGINEERING
Cross Section #3
490
405
lB=Top of bank kdormatlon taken from
topographic Reid suvey by Oct Hughes
4110 i AssodOMs doted August,7016
Channel flowdepth for Pis aver s.dton
475 as observed on AO 25.2017 was 1S
2-TEAR STORM ELEVATION465 I'
460
455
450
-40 -35 -00 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 40
Charnel Width(Met)
Cross Section Calculations:
Q = C * i *A
Drainage Area-3
LAND USE AREA(ac.) C C x A Wei_hted Runoff Coefficient
Industrial 10.68 0.9 9.62 0.58
Woods 12.58 0.3 3.78 2-Year Rainfall Intensity
23.27 13.39 i= 3.24 in/hr
t, = 17.36 mins
Q3 = 43.34 ft3/s (peak discharge)
/1.486
V = I 1 * R2/3 Si/z
\ n
Existing conditions:
n= 0.035 (Manning's roughness coefficient)
R= 0.12 (hydraulic radius)
S=0.06 (channel slope)
V3 = 2.56 ft/s (cross-sectional average velocity)
Q = 1.00 ft3/s (cross-sectional flow rate)
Fr= 1.36 (Froude number)
2-Year Storm (Peak Discharge):
Q3 = 43.34 ft3/s
n= 0.035
R= 0.76
S = 0.06
V3(2_yr) = 8.94 ft/s
Maximum water elevation for 2-year storm: 13.8"
Cross Section Characteristics:
The channel bed for cross section 3 contains medium to small cobble as well as fine gravel. The channel flow
depth observed on April 25, 2017 was 1.5" for this section. Side slopes for this area contains relatively dense
areas of ferns, grasses, and small vegetation. There are a few small trees located on both channel banks.
8
WOOLLEY ENGINEERING
Existing Outfall from Storm Drainage Piping at Town Center Four
„-/ is 1,,,,,7,, .
SI
,,,,,iiii
, .. 1
i 1< ♦11.
o!t'
,^4,
�- w - j� k ..if arm £ 7 �.
ti- _
k` `, View of the ex. Precast End-Wall
\ ( 1 ' , .1 '
/:
k \ '4-i'jt X
,.. t , .. ,',t;.-.
� `'� "�..... View of the ex. Outfall Condition
f View of existing channel at the
confluence of storm drainage
13.
piping outlet protection
Fy Additional Rip-rap outlet
protection is proposed on the
-H�.. _ ,, , current site plan to be hand placed
.' �_ + • in this location.
a .w , ,
#, $y ,R1
A
X. k; s'}t
47.: n
io
h , ,
9 UVA Research Park: Town Center Four
WOOLLEY ENGINEERING
On April 25, 2017, we walked along the drainage channel and observed the flow path and
existing conditions of the channel. We were joined by Vinny Pero (US Army Corps of
Engineers,) Frank Pohl (Albemarle County Engineer) and Bobby Jocz (Albemarle County
Engineering Department.) All photographs utilized in this memo were taken the day of this site
visit.
At the request of the property owners,the channel was inspected in April 2016 by Wetland
Studies and Solutions, Inc. (WSSI.) Their evaluation of the current conditions suggested that
the channel should be considered waters of the U.S. (WOTUS.) On August 9, 2016, the U.S.
Army Corps of Engineers accepted WSSI's Jurisdictional Determination of the channel's
condition. Upon meeting with Mr. Pero on-site, the Corps' position was that the channel is in
excellent condition and should not be disturbed by machinery. They also concurred that only
hand-placed riprap armament should be considered for channel enhancement. The Corps agreed
that the proposed new riprap would likely satisfy the restrictions of Nationwide Permit 18. As
directed by Mr. Pero, no other documentation shall be required by the Corps.
Based upon the data provided with each cross-section worksheet, and visual observation of the
channel, it is our opinion that the concentrated runoff from the improved site will be discharged
into an adequate channel. The additional proposed riprap outfall protection will reduce velocity
and protect the channel from erosion. The existing channel is well-defined and the banks are
capable of conveying the 2-year storm. Furthermore, the subject channel ultimately outfalls
directly into the Park's regional stormwater management facility. The facility was engineered
and constructed to contain the 2, 10 and 100-year storm with a fully developed condition for the
entire Research Park. Current build-out of the Research Park does not yet approach 25% of the
full potential of the allowable development.
It is acknowledged that the UVA Research Park has been Master Planned for additional future
development of the contributing drainage area of the subject channel. Thus, the applicant
reserves the right to further enhance the channel in the future in accord with the standards of
engineering practice and design. Please do not hesitate to call with any questions or concerns.
Thank you for your time and consideration.
Sincerely,
Eric Woolley, PE
Cc: Chris Schooley, UVA Foundation
Nat Perkins, UVA Foundation
10 UVA Research Park: Town Center Four