HomeMy WebLinkAboutWPO201500015 Plan - As-built WPO VSMP 2017-08-11 PROJECT MANAGEMENT
SHIA/IP CIVIL ENGINEERING
LAND PLANNING
ENGINEERING
August 11, 2017
Mr. Bobby Jocz
Albemarle County
Department of Community Development
Regarding: Free State Run—Stormwater Detention System As-Built
Dear Mr. Jocz,
Please find enclosed, two as-built plans and Hydrocad calculations for the stormwater detention system at
Free State Run. Please note that this is only regarding the detention system and does not include biofilters
as they are not yet completed.
It was previously determined that the runoff outflow post-development should not exceed 1.80 cfs. Using
Hydrocad, the as-built 1-year outflow was determined to be 1.79 cfs and therefore meets the required post-
development rate of 1.83 cfs as shown in the table below. The as-built 10-year outflow was determined to
be 17.35 cfs and therefore exceeds the required post-development rate of 17.18 cfs. We have determined
this to be due to the 10-year orifice as-built diameter of 12.8 inches being larger than the design value of
12.6 inches. The contractor will be informed of this matter and modifications to the standpipe will be made.
The necessary changes to remedy this issue will not require any changes to the 96"cmp detention pipe
and therefore we believe that at this time the bond can be reduced to reflect the value of the pipe.
Summary Table for project outflows:
Pre-Development Post-Development As-Built
1-Yr Flow 4.06 cfs 1.83 cfs 1.79 cfs
10-Yr Flow 17.18 cfs <17.18 cfs 17.35 cfs
Should have any questions please feel free to contact me by email at Justin@shimp-engineering.com or by
telephone at 434-227-5140 ext. 3.
tin Shimp, P.E.
himp Engineering, P.C.
Free State Run (As-Built)
Prepared by Shimp Engineering P.C. Printed 8/11/2017
HydroCAD?9.10 s/n 07054 ?2011 HydroCAD Software Solutions LLC Page 1
Summary for Pond 4P: Detention Pipe
1-Year Storm
Inflow Area= 2.600 ac, 56.54% Impervious, Inflow Depth > 1.49", for 1 year storm event
Inflow = 6.11 cfs @ 11.95 hrs, Volume= 0.322 of
Outflow = 0.49 cfs @ 12.72 hrs, Volume= 0.322 af, Atten= Lag=46.1 min
Primary = 0.49 cfs @ 12.72 hrs, Volume= 0.322 af
Routing by Stor-Ind method;Time Span= 0.00-24.00 hrs, dt=0.05 hrs
Peak Elev=417.41'@ 12.72 hrs Surf.Area= 1,739 sf Storage=5,637 cf
Plug-Flow detention time= 114.9 min calculated for 0.321 af(100% of inflow)
Center-of-Mass det. time= 114.0 min (940.1 - 826.0 )
Volume Invert .wail.Storage Storage Q nv)4'
#1 413.05' 10,938 cf 96.0"1 x 217.61 rpe Storage S=0.0024'i„
Device Routing Invert Outlet Devices
#1 Primary 413.05' 15.0" Round Culvert L=93.0' Ke=0.400
Inlet 1 Outlet Invert=413.05'i 409.50' S= 0.0382 Cc= 0.900
n= 0.013
#2 Device 1 413.05' 3.0"Vert.1 yr orifice C=0.600
#3 Device 1 417.72' 12.8"Vert. 10 year orifice C=0.600
#4 Device 1 420.98' 24.0" Horiz.Overflow Standpipe C=0.600
Limited to weir flow at low heads
Primary Outflow flax=0.49 cfs @ 12.72 his HOV=417.41' (Free Discharge)
t_1=Culvert (Passes 0.49 cfs of 12.23 cfs potential flow)
-2=1 yr orifice (Orifice Controls 0.49 cfs @ 9.91 fps)
-3=1 0 year orifice (Controls 0.00 cfs)
-4=Overflow Standpipe (Controls 0.00 cfs)
Inflow Area = 6.920 ac, 43.21% Impervious. Inflow Depth > 1.14" for 1 year storm event
Inflow = 1.79 cfs @ 12.05 hrs, Volume= 0.658 af
Primary = 1.79 cfs @ 12.05 hrs, Volume= 0.658 af, Atten= 0%, Lag= 0.0 min
Primary outflow= Inflow,Time Span= 0.00-24.00 hrs. dt= 0.05 hrs
Free State Run (As-Built)
Prepared by Shimp Engineering P.C. Printed 8/11/2017
HydroCAD?9.10 s/n 07054? 2011 HydroCAD Software Solutions LLC Page 2
Summary for Pond 4P: Detention Pipe
10-Year Storm
Inflow Area= 2.600 ac, 56.54% Impervious, Inflow Depth > 3.72" for 10 year storm event
Inflow = 15.29 cfs @ 11.96 hrs, Volume= 0.807 of
Outflow = 7.95 cfs @ 12.07 hrs, Volume= 0.791 af, Atten= 48%, Lag= 6.2 min
Primary = 7.95 cfs @ 12.07 hrs, Volume= 0.791 of
Routing by Stor-Ind method,Time Span=0.00-24.00 hrs, dt=0.05 hrs
Peak Elev=421.05'I@ 12.07 hrs Surf.Area=574 sf Storage= 10,818 cf
Plug-Flow detention time= 92.5 min calculated for 0.790 of(98%of inflow)
Center-of-Mass det.time= 80.7 min (880.8 -800.2 )
Volume Invert Avail.Storage Storage Description
#1 413.05' 10,938 cf 96.0" D x 217.61 Pipe Storage S=0.0024'+"
Device Routing Invert Outlet Devices
#1 Primary 413.05 15.0" Round Culvert L= 93.0' Ke= 0.400
Inlet I Outlet Invert= 413.05 .+'409.50 S= 0.0382 Cc= 0.900
n= 0.013
#2 Device 1 413.05 3.0"Vert. 1 yr orifice 0= 0.600
#3 Device 1 417.72 12.8" Vert. 10 year orifice 0= 0.600
#4 Device 1 420.98 24.0" Horiz. Overflow Standpipe 0= 0.600
Limited to weir flow at low heads
Primary Outflow MM1ax=7.73 cfs @ 12.07 hrs HW=--420.96' (Free Discharge)
utvert (Passes 7.73 cfs of 16.65 cfs potential flow)
-2=1 yr orifice (Orifice Controls 0.66 cfs @ 13.43 fps)
-3=10 year orifice (Orifice Controls 7.07 cfs @ 7.92 fps)
-4=Overflow Standpipe (Controls 0.00 cfs)
Inflow Area = 6.920 ac, 43.21% Impervious, Inflow Depth > 3.17" for 10 year storm event
Inflow = 17.35 cfs @ 12.07 hrs, Volume= 1.826 of
Primary = 17.35 cfs @ 12.07 hrs, Volume= 1.826 af, Atten= 0%, Lag= 0.0 min
Primary outflow = Inflow. Time Span= 0.00-24.00 hrs, dt= 0.05 hrs
Free State Run (As-Built)
Prepared by Shimp Engineering P.C. Printed 8/11/2017
HydroCAD?9.10 s/n 07054? 2011 HydroCAD Software Solutions LLC Page 3
Hydrographs for Free State Run (As-Built)
1-Year Storm
Ilydrograph
1 nets
Inflow Area=6.92011
1
1 z 3 4 5 s i e 9 10 1.1 1.2 13 is 15 16 11 18 t9 20 21 22 23 24
Time Omura)
10-Year Storm
HYdroliraPh
h80w
■
19 ■Primary
a
Infl
18. ',TJS eb
uv Area=6- 20
16
1E
14
13
12 -
1/
70
6
3
1
} i
0
0 1 2 3 4 5 6 7 8 9 10 11 - 16 17 18 19 20 21 22 23 24 Time I hours]
Free State Run (As-Built)
Prepared by Shimp Engineering P.C. Printed 8/11/2017
HydroCAD?9.10 s/n 07054? 2011 HydroCAD Software Solutions LLC Page 4
Drainage Diagram for Free State Run (As-Built)
#4A�
#5 1 Det ration Pond
` ' D mage Area
Post-Offsite Drainage
Forebay Area
5P',
— Sediment Forebay
Detention Pond
/2P\ /3 \4 #3
Det ntion Pond BioFilter BioFilter Drainage Area
/4; \ (#2
Untreated Storm Pipe
Detention Pipe Area
Point Of Analysis
<#1>
Untreated Drainage
Area
V5MF AS -BUILT PLAN FOR
FLEE STATE RUN
TAX MAP 62, PARCEL 8
R10 DISTRICT, ALE3EMARLE COUNTY, VIRGINIA
VICINITY MAP SCALE: 1"_1,000'
mak.
IMAGE PROVIDED BY GOOGLE MAPS
SHEET INDEX
C I - COVED SN EET
C2 - UNDERGROUND DETENTION
AS -BUILT FLAN * I'KOFILE
OWNER / DEVELOPER
Owner:
Free State Partners, LLC.
P.O. Box 645
Charlottesville, VA 22902
Developer:
Red Dirt Development
P.O. Box 645
Charlottesville, VA 22902
ZONING
R4— Residential, Airport Impact Overlay Dlstrict
MAGISTERIAL DISTRICT
Rio
Existing sewer behind Lot 26.
Elevation: 429.11', NAVD88 Vertical Datum
SOURCE OF AS -BUILT SURVEY
Source of Survey:
Rc)ger W. Ray & Associates. Provided to Shimp Engineering: 03/20/17.
NOTE: AS -built only includes
underground detention system.
The, b ofi Ite rS are not yet
Completed.
IPPROVI'D
by the i dber,arle County
Community Cevf opment Department
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IMAGE PROVIDED BY GOOGLE MAPS
SHEET INDEX
C I - COVED SN EET
C2 - UNDERGROUND DETENTION
AS -BUILT FLAN * I'KOFILE
OWNER / DEVELOPER
Owner:
Free State Partners, LLC.
P.O. Box 645
Charlottesville, VA 22902
Developer:
Red Dirt Development
P.O. Box 645
Charlottesville, VA 22902
ZONING
R4— Residential, Airport Impact Overlay Dlstrict
MAGISTERIAL DISTRICT
Rio
Existing sewer behind Lot 26.
Elevation: 429.11', NAVD88 Vertical Datum
SOURCE OF AS -BUILT SURVEY
Source of Survey:
Rc)ger W. Ray & Associates. Provided to Shimp Engineering: 03/20/17.
NOTE: AS -built only includes
underground detention system.
The, b ofi Ite rS are not yet
Completed.
IPPROVI'D
by the i dber,arle County
Community Cevf opment Department
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INV IN=427.55
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