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Williams, Kenneth

From: Williams, KennethSent: Monday, February 27, 2017 3:15 PMTo: 'Sebastian Sandoval'Cc: Sauder, RyanSubject: RE: Wellers Corner-STPL 2016-0049

Yes, please forward a PDF of the revised response letter. Thanks  

From: Sebastian Sandoval [mailto:ssandoval@j2engineers.com]  Sent: Monday, February 27, 2017 2:39 PM To: Williams, Kenneth <Kenneth.Williams@loudoun.gov> Cc: Sauder, Ryan <Ryan.Sauder@loudoun.gov> Subject: RE: Wellers Corner‐STPL 2016‐0049  Ken,         We left a hard copy of the response letter with Ryan, there only 2 responses that needed to be updated. Ryan, let me know if you need a PDF of the response letter.  Thanks SS   Sebastian Sandoval P.E.

J2 Engineers, Inc. Office: 703-361-1550 ext. 326  

From: Williams, Kenneth [mailto:Kenneth.Williams@loudoun.gov] Sent: Monday, February 27, 2017 2:04 PM To: Sebastian Sandoval Cc: Sauder, Ryan Subject: RE: Wellers Corner-STPL 2016-0049  Hi Sebastian,  I was expecting a revised response letter but unless Ryan needs that for his review the email below will suffice.  Thanks for the PDF of the updated sheets.  Ken  

From: Sebastian Sandoval [mailto:ssandoval@j2engineers.com]  Sent: Monday, February 27, 2017 1:06 PM To: Williams, Kenneth <Kenneth.Williams@loudoun.gov> Cc: Sauder, Ryan <Ryan.Sauder@loudoun.gov> Subject: Wellers Corner‐STPL 2016‐0049  Ken, 

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        I hope you are well….as discussed this morning and as a follow up to a meeting with had with Ryan and Jimmy, we went ahead and added routing calculations to the plan set, and while the sheets affected simply had calculations and details added there was a storm manhole structured (#11) that was added at the end of Village View Terrace‐see sheet 4. Attached is PDF of the sheets inserted to Ryan’s set. Please let me know if anything else is needed.  Thanks SS   Sebastian Sandoval, P.E. | Senior Project Manager

J2 Engineers, Inc. 4080 Lafayette Center Drive, Suite 330 Chantilly, Virginia 20151 Office: 703-361-1550 ext. 326 Fax: 703-956-6845 Mobile: 703-862-0400 ssandoval@j2engineers.com | www.j2engineers.com    The information and files in this transfer is the property of J2 Engineers, Inc. (J2E), and has been prepared by J2E for exclusive use by its staff. It is provided herewith for information only and is not to be relied upon by any parties other than J2E staff and employees.  Any reliance thereupon by any party other than J2E staff and employees shall be at that user's sole risk; and said user choosing to rely upon this information agrees, that by relying on it, he/she/they accepts full responsibility for all work related thereto and agrees to indemnify and hold J2E harmless from any and all liability arising from or relating to the use of or reliance upon said information.  The information and files are and shall remain the property of J2E; however J2E exclusively permits the recipient to use the documents/files for information and reference in connection with the project. The party receiving this information is responsible for requesting any future updated and/or current copy of the information hereon prior to considering this information final. No update notification will be sent. Any comments or questions are to be directed in writing to the principals of J2E.  BY USING THE PROVIDED PLANS, PLATS, COMPUTATIONS AND/OR CAD FILES, THE RECIPIENT AGREES TO THESE TERMS AND CONDITIONS. 

 

GRAPHIC SCALE0

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Lic. No. 45207

PROP. SAN. SEW. ESM'T LABELESM'T WIDTH

PROP. WATER ESM'T LABELESM'T WIDTH

PROP. PUBLIC ACCESSESM'T LABEL

PROPOSED ROADWAY

5' PROP. SW (unless otherwise noted)

PERVIOUS PAVEMENT

PROPOSED CONTOUR

EXISTING CONTOUR

CLEARING & GRADINGPROPOSED LIMITS OF

EXISTING TREE LINE

OVERLAND RELIEF

PROPOSED 0.5' CONTOUR

PROPOSED 1' CONTOUR

OLR

EXISTING SANITARY SEWER

PROPOSED WATER LINE

EXISTING WATER LINE

PROPOSED SANITARY SEWER

PROPOSED 6" PVC UNDERDRAIN

EXISTING STORM DRAIN

PROPOSED FIRE HYDRANT

3/4" WATER METER CROCK

4" SANITARY LATERAL

PROPOSED CG-12 HC RAMPS(SEE SHEET 02)

CURB TRANSITION

VEHICLES PER DAY

DRY SWALE

WALL

TEST PIT

NOTES1. ALL ROADS ARE CATEGORY B1, UNLESS OTHERWISE

NOTED ON PLANS.2. MAX POSTED SPEED = 15 MPH3. ALL STREETS AND TRAVELWAYS ON SITE SHALL BE

PRIVATELY OWNED AND MAINTAINED4. CONTRACTOR SHALL VERIFY LOCATION OF ALL

EXISTING UTILITY CROSSINGS WITH PROPOSEDUTILITIES ON THIS PLAN WITH A TEST PIT.

5. ALL TRAVELWAYS ARE 25' WIDE (FOC TO FOC)UNLESS OTHERWISE NOTED.

6. HEAVY DUTY CLEANOUT COVER TO BE USED ONALL SANITARY CLEANOUTS IN THE TRAVELWAY.

7. NO DECKS OR OVER HANGS ALLOWED IN LOUDOUNWATER EASEMENTS

8. WATER METER BOXES LOCATED IN DRIVEWAYMUST BE TRAFFIC RATED PER APPROVEDMATERIALS

9. SEE SHEET 13 FOR PERVIOUS PAVEMENT ANDUNDER DRAIN DETAILS

PROP. LINE OF SIGHT ESM'T LABEL

Summary for Subcatchment 4S: OUTFALL A - POST-ENERGY

Runoff = 2.38 cfs @ 12.46 hrs, Volume= 0.288 af, Depth> 1.35"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 1-Year Rainfall=2.53"

Area (ac) CN Description* 2.550 89

2.550 100.00% Pervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

4.1 57 0.0600 0.23 Sheet Flow, S-1AGrass: Short n= 0.150 P2= 3.05"

0.1 10 0.0240 3.14 Shallow Concentrated Flow, S-2APaved Kv= 20.3 fps

43.2 519 0.20 Direct Entry, POROUS ASPHALT UNDERDRAIN47.5 586 Total

Summary for Subcatchment 7S: OUTFALL A - POST-FLOOD

Runoff = 8.38 cfs @ 12.46 hrs, Volume= 1.017 af, Depth> 2.77"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 10-Year Rainfall=4.61"

Area (ac) CN Description* 4.410 85

4.410 100.00% Pervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

4.1 57 0.0600 0.23 Sheet Flow, S-1AGrass: Short n= 0.150 P2= 3.05"

0.1 10 0.0240 3.14 Shallow Concentrated Flow, S-2APaved Kv= 20.3 fps

43.2 519 0.20 Direct Entry, POROUS ASPHALT UNDERDRAIN47.5 586 Total

Summary for Subcatchment 1S: OUTFALL B - POST-ENERGY

Runoff = 0.22 cfs @ 12.00 hrs, Volume= 0.010 af, Depth> 0.88"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 1-Year Rainfall=2.53"

Area (ac) CN Description* 0.140 81

0.140 100.00% Pervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

5.6 48 0.0200 0.14 Sheet Flow, SHEET FLOWGrass: Short n= 0.150 P2= 3.05"

0.4 53 0.0200 2.28 Shallow Concentrated Flow, SHALLOW CONCENTRATED FUnpaved Kv= 16.1 fps

1.8 331 0.0500 3.08 1.85 Channel Flow, Channel FlowArea= 0.6 sf Perim= 4.8' r= 0.13' n= 0.027

7.8 432 Total

FLOOD PROTECTION OUTFALL B 10 YEAR POST DEVELOPMENTSummary for Subcatchment 4S: OUTFALL B - POST-FLOOD

Runoff = 2.62 cfs @ 11.99 hrs, Volume= 0.126 af, Depth> 2.80"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 10-Year Rainfall=4.61"

Area (ac) CN Description* 0.540 85

0.540 100.00% Pervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

5.6 48 0.0200 0.14 Sheet Flow, SHEET FLOWGrass: Short n= 0.150 P2= 3.05"

0.4 53 0.0200 2.28 Shallow Concentrated Flow, SHALLOW CONCENTRATED FUnpaved Kv= 16.1 fps

1.8 331 0.0500 3.08 1.85 Channel Flow, Channel FlowArea= 0.6 sf Perim= 4.8' r= 0.13' n= 0.027

7.8 432 Total

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LAND COVER LEGEND

MANAGED TURF

IMPERVIOUS COVER

DRAINAGE DIVIDE

POST DEVELOPMENT WATER QUALITY LAND COVER MAP

POST DEVELOPMENT TIME OF CONCENTRATIONENERGY BALANCE OUTFALL A 1 YEAR POST DEVELOPMENT

FLOOD PROTECTION OUTFALL A 10 YEAR POST DEVELOPMENT

ENERGY BALANCE OUTFALL B 1 YEAR POST DEVELOPMENT

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Summary for Subcatchment 5S: OUTFALL A - PRE - ENERGY

Runoff = 10.80 cfs @ 11.99 hrs, Volume= 0.517 af, Depth> 2.71"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 10-Year Rainfall=4.61"

Area (ac) CN Description* 2.290 84

2.290 100.00% Pervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

5.6 84 0.0610 0.25 Sheet Flow, S-1AGrass: Short n= 0.150 P2= 3.05"

0.5 51 0.0463 1.64 Sheet Flow, S-2ASmooth surfaces n= 0.011 P2= 3.05"

1.6 348 0.0302 3.53 Shallow Concentrated Flow, S-3APaved Kv= 20.3 fps

0.1 66 0.0391 7.83 24.29 Channel Flow, S-4AArea= 3.1 sf Perim= 6.9' r= 0.45'n= 0.022 Earth, clean & straight

7.8 549 Total

A Soils B Soils C Soils D Soils Total Area (acres): 2.29Area (acres) 0.00 0.00 0.00 0.00

CN 30 55 70 77 0Area (acres) 0.00 0.00 1.30 0.00

CN 39 61 74 80

Area (acres) 0.00 0.00 0.99 0.00

CN 98 98 98 98

CN(D.A. A)

84

1‐year storm 2‐year storm 10‐year storm

1.14 1.56 2.92

1.14 1.56 2.92

Adjusted CN* 84 84 84

Runoff Reduction 

Volume (ft3):

RVDeveloped (watershed‐inch)  with Runoff Reduction*

Impervious Cover 

Drainage Area A

RVDeveloped  (watershed‐inch)  with no Runoff Reduction*

Managed Turf ‐‐ disturbed, graded for yards or other 

turf to be mowed/managed

Forest/Open Space ‐‐ undisturbed, protected 

forest/open space or reforested land

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Drainage Area A ‐ Pre

Drainage Area A ‐ Post

OUTFALL A

PRE-DEVELOPMENT CALCULATIONS

POST-DEVELOPMENT CALCULATIONS

TC CALCULATIONS

SEE ROUTING CACULATIONS

1 YEAR ROUTING

A Soils B Soils C Soils D Soils Total Area (acres): 2.55Area (acres) 0.00 0.00 0.00 0.00

CN 30 55 70 77 2,825Area (acres) 0.00 0.00 0.51 0.01

CN 39 61 74 80

Area (acres) 0.00 0.00 2.03 0.00

CN 98 98 98 98

CN(D.A. A)

93

1‐year storm 2‐year storm 10‐year storm

1.81 2.30 3.82

1.50 2.00 3.51

Adjusted CN* 89 90 90

Runoff Reduction 

Volume (ft3):

RVDeveloped (watershed‐inch)  with Runoff Reduction*

Impervious Cover 

Drainage Area A

RVDeveloped  (watershed‐inch)  with no Runoff Reduction*

Managed Turf ‐‐ disturbed, graded for yards or other 

turf to be mowed/managed

Forest/Open Space ‐‐ undisturbed, protected 

forest/open space or reforested land

Channel Protection - 1 Year Storm EventI.F. (Improvement Factor) equals 0.8 for sites > 1 acre or 0.9 for sites ≤ 1acre. 0.80

QDeveloped = 2.33 CFS (From Hydrocad)

RVDeveloped = (1.48 in) x (2.55 ac) x (1 ft/12 in) 0.31 AC-FT

QPre-Developed = 4.31 CFS (From Hydrocad)

RVPre-Developed = (1.14 in) x (2.29 ac) x (1 ft/12 in) 0.22 AC-FT

Criteria

QDeveloped ≤ I.F.*(QPre-developed* RVPre-Developed)/RVDeveloped 2.33 CFS < 2.38 CFS OK

Under no condition shall QDeveloped be greater than QPre-Developed 2.33 CFS < 4.31 CFS OK

nor shall QDeveloped be required to be less than that calculated in the equation

(QForest * RVForest)/RVDeveloped 2.33 CFS<

N/A CFS OK

Flood Protection - 10 Year Storm EventQDeveloped = The allowable peak flow rate of runoff from the developed site. 15.87 CFS

QPre-Developed = The peak flow rate of runoff from the site in the pre-developed

condition. 19.38 CFS

Criteria

QDeveloped ≤ QPre-developed 15.87 CFS < 19.38 CFS OK

PROVIDED ALLOWABLE

PROVIDED ALLOWABLE

ENERGY BALANCE COMPUTATIONS - OUTFALL A

SEE SHEETS 08

Summary for Subcatchment 4S: PERVIOUS PAVEMENT

Runoff = 11.93 cfs @ 11.99 hrs, Volume= 0.591 af, Depth> 3.09"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 10-Year Rainfall=4.61"

Area (ac) CN Description* 1.230 98

0.480 74 >75% Grass cover, Good, HSG C0.590 80 >75% Grass cover, Good, HSG D2.300 88 Weighted Average1.070 46.52% Pervious Area1.230 53.48% Impervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

4.4 62 0.0605 0.23 Sheet Flow, S-1AGrass: Short n= 0.150 P2= 3.05"

0.4 86 0.0547 3.77 Shallow Concentrated Flow, S-2AUnpaved Kv= 16.1 fps

3.2 Direct Entry, S-2A8.0 148 Total

Summary for Subcatchment 4S: PERVIOUS PAVEMENT

Runoff = 5.27 cfs @ 11.99 hrs, Volume= 0.249 af, Depth> 1.30"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 1-Year Rainfall=2.53"

Area (ac) CN Description* 1.230 98

0.480 74 >75% Grass cover, Good, HSG C0.590 80 >75% Grass cover, Good, HSG D2.300 88 Weighted Average1.070 46.52% Pervious Area1.230 53.48% Impervious Area

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

4.4 62 0.0605 0.23 Sheet Flow, S-1AGrass: Short n= 0.150 P2= 3.05"

0.4 86 0.0547 3.77 Shallow Concentrated Flow, S-2AUnpaved Kv= 16.1 fps

3.2 Direct Entry, S-2A8.0 148 Total

Summary for Pond 5P: OUTLET

Inflow Area = 2.300 ac, 53.48% Impervious, Inflow Depth > 1.30" for 1-Year eventInflow = 5.27 cfs @ 11.99 hrs, Volume= 0.249 afOutflow = 2.10 cfs @ 12.13 hrs, Volume= 0.244 af, Atten= 60%, Lag= 7.9 minPrimary = 1.76 cfs @ 12.13 hrs, Volume= 0.240 afSecondary= 0.33 cfs @ 12.13 hrs, Volume= 0.003 af

Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsPeak Elev= 292.07' @ 12.13 hrs Surf.Area= 0 sf Storage= 3,136 cf

Plug-Flow detention time= 25.7 min calculated for 0.243 af (97% of inflow)Center-of-Mass det. time= 17.1 min ( 800.2 - 783.1 )

Volume Invert Avail.Storage Storage Description#1 288.00' 7,822 cf Custom Stage Data Listed below

19,556 cf Overall x 40.0% Voids

Elevation Inc.Store Cum.Store(feet) (cubic-feet) (cubic-feet)

288.00 0 0289.00 28 28290.00 738 766291.00 2,479 3,245292.00 4,227 7,472293.00 5,598 13,070294.00 6,486 19,556

Device Routing Invert Outlet Devices#1 Primary 289.67' 6.0" W x 6.0" H Vert. Orifice/Grate C= 0.600 #2 Secondary 291.90' 1.5' long Sharp-Crested Rectangular Weir 2 End Contraction(s)

1.0' Crest Height

Primary OutFlow Max=1.76 cfs @ 12.13 hrs HW=292.06' (Free Discharge)1=Orifice/Grate (Orifice Controls 1.76 cfs @ 7.04 fps)

Secondary OutFlow Max=0.31 cfs @ 12.13 hrs HW=292.06' (Free Discharge)2=Sharp-Crested Rectangular Weir (Weir Controls 0.31 cfs @ 1.33 fps)

Summary for Pond 5P: OUTLET

Inflow Area = 2.300 ac, 53.48% Impervious, Inflow Depth > 3.09" for 10-Year eventInflow = 11.93 cfs @ 11.99 hrs, Volume= 0.591 afOutflow = 8.92 cfs @ 12.06 hrs, Volume= 0.585 af, Atten= 25%, Lag= 4.2 minPrimary = 2.17 cfs @ 12.06 hrs, Volume= 0.444 afSecondary= 6.75 cfs @ 12.06 hrs, Volume= 0.141 af

Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsPeak Elev= 293.17' @ 12.06 hrs Surf.Area= 0 sf Storage= 5,673 cf

Plug-Flow detention time= 18.9 min calculated for 0.583 af (99% of inflow)Center-of-Mass det. time= 14.5 min ( 777.9 - 763.5 )

Volume Invert Avail.Storage Storage Description#1 288.00' 7,822 cf Custom Stage Data Listed below

19,556 cf Overall x 40.0% Voids

Elevation Inc.Store Cum.Store(feet) (cubic-feet) (cubic-feet)

288.00 0 0289.00 28 28290.00 738 766291.00 2,479 3,245292.00 4,227 7,472293.00 5,598 13,070294.00 6,486 19,556

Device Routing Invert Outlet Devices#1 Primary 289.67' 6.0" W x 6.0" H Vert. Orifice/Grate C= 0.600 #2 Secondary 291.90' 1.5' long Sharp-Crested Rectangular Weir 2 End Contraction(s)

1.0' Crest Height

Primary OutFlow Max=2.16 cfs @ 12.06 hrs HW=293.15' (Free Discharge)1=Orifice/Grate (Orifice Controls 2.16 cfs @ 8.65 fps)

Secondary OutFlow Max=6.61 cfs @ 12.06 hrs HW=293.15' (Free Discharge)2=Sharp-Crested Rectangular Weir (Weir Controls 6.61 cfs @ 4.22 fps)

Summary for Subcatchment 10S: 10YR - FLOOD - UNCONTROLLED

Runoff = 2.60 cfs @ 12.10 hrs, Volume= 0.163 af, Depth> 0.93"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 1-Year Rainfall=2.53"

Area (ac) CN Description0.670 98 Unconnected pavement, HSG A0.230 80 >75% Grass cover, Good, HSG D1.210 74 >75% Grass cover, Good, HSG C2.110 82 Weighted Average1.440 68.25% Pervious Area0.670 31.75% Impervious Area0.670 100.00% Unconnected

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)10.8 109 0.0200 0.17 Sheet Flow, S-1A2

Grass: Short n= 0.150 P2= 3.05"1.5 147 0.0110 1.69 Shallow Concentrated Flow, S-2A2

Unpaved Kv= 16.1 fps1.6 245 2.55 Direct Entry, S-3A20.1 48 0.0162 6.70 8.22 Pipe Channel, S-4A2

15.0" Round Area= 1.2 sf Perim= 3.9' r= 0.31'n= 0.013 Concrete pipe, bends & connections

1.2 203 2.82 Direct Entry, S-5A20.1 40 0.0060 4.57 8.24 Pipe Channel, S-6A2

21.0" x 15.0", R=22.0" Elliptical Area= 1.8 sf Perim= 4.9' r=n= 0.013 Concrete pipe, bends & connections

1.2 60 0.83 Direct Entry, S-7A216.5 852 Total

Summary for Subcatchment 18S: 1 YR - ENERGY - UNCONTROLLED

Runoff = 2.05 cfs @ 11.98 hrs, Volume= 0.092 af, Depth> 2.12"

Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType II 24-hr 10-Year Rainfall=4.61"

Area (ac) CN Adj Description0.130 98 Unconnected pavement, HSG A0.390 74 >75% Grass cover, Good, HSG C0.520 80 77 Weighted Average, UI Adjusted0.390 75.00% Pervious Area0.130 25.00% Impervious Area0.130 100.00% Unconnected

Tc Length Slope Velocity Capacity Description(min) (feet) (ft/ft) (ft/sec) (cfs)

4.5 66 0.0662 0.25 Sheet Flow, S-1A2Grass: Short n= 0.150 P2= 3.05"

2.0 273 0.0191 2.23 Shallow Concentrated Flow, S-2A2Unpaved Kv= 16.1 fps

6.5 339 Total

Summary for Link 19L: OUTFALL A

Inflow Area = 4.410 ac, 43.08% Impervious, Inflow Depth > 2.80" for 10-Year eventInflow = 15.87 cfs @ 12.07 hrs, Volume= 1.030 afPrimary = 15.87 cfs @ 12.07 hrs, Volume= 1.030 af, Atten= 0%, Lag= 0.0 min

Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs

Summary for Link 19L: OUTFALL A

Inflow Area = 2.820 ac, 48.23% Impervious, Inflow Depth > 1.16" for 1-Year eventInflow = 2.33 cfs @ 12.11 hrs, Volume= 0.273 afPrimary = 2.33 cfs @ 12.11 hrs, Volume= 0.273 af, Atten= 0%, Lag= 0.0 min

Primary outflow = Inflow, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs

10 YEAR ROUTING

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OUTFALL STRUCTURE 10Q10 =8.92 CFSPipe Diameter = Do = 15" HDPETW = 1.0 > 0.5 Do = 0.63'Max. Tailwater ConditionLa = 10'd50 =1.1' (Class I)d50 =1.6' (Class II)dmax = d50 x 1.5 = 1.65'Apron Thickness = dmax x 1.5 = 2.48'Minimum Thickness = 2.5' (Class I)Minimum Thickness = 3.6' (Class II)

W=7.75'

La=10'

3Do=3.75'

Do=15"

Project: 0From To Drainage C C x A Inlet Rain Runoff Invert Elev. Length Slope Dia. Capacity VEL. FlowPoint Point Area Factor Increment Cumm. Time Fall Q Upper Lower Q Time

Min. In/Hr C.F.S. End End FT. % IN. C.F.S. F.P.S. MIN.*

11 10 2.30 0.65 1.50 1.50 8.17 5.90 8.85 289.62 289.24 75.37 0.50% 15 4.58 3.73 0.34

STORM SEWER DESIGN COMPUTATIONS

Outlet JUNCTION LOSS InletINLET UPSTREAM Water Do Qo Lo Sfo Hf 1.3 0.5 FINAL Water RIM STATION INLET Surface Vo Ho Qi Vi QiVi 2 Hi Angle Hd Ht Ht Ht H Surface ELEV.

Elev. in cfs ft % ft Vi /2g Elev.(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)

10 290.2411 290.24 15.00 8.85 75.37 1.87 1.41 7.21 0.20 0.00 0.00 0.20 0.00 0.10 1.51 291.75 293.95

0 8.85 0.00 0.00 0.00 0.00

Starting Elevation

HYDRAULIC GRADE LINE COMPUTAIONS

Inf lowOutflowPrimarySecondary

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

5

4

3

2

1

0

Inflow Area=2.300 acPeak Elev=292.07'Storage=3,136 cf

5.27 cfs

2.10 cfs

1.76 cfs

0.33 cfs

InflowOutflowPrimarySecondary

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

12

10

8

6

4

2

0

Inflow Area=2.300 acPeak Elev=293.17'Storage=5,673 cf

11.93 cfs

8.92 cfs

2.17 cfs

6.75 cfs

1 YEAR ENERGY - POND OUTLET HYDROGRAPH 10 YEAR FLOOD - POND OUTLET HYDROGRAPH

2.17

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NOTE:

THE OWNER IS RESPONSIBLE FOR MAINTENANCE OF THE PERMEABLE PAVEMENT TO THE EXTENT NOT MAINTAINED BY LOUDOUN COUNTYPERSUANT TO SECTION 1096.02 OF THE CODIFIED ORDINANCE. FURTHERMORE, MAINTENANCE RESPONSIBILITIES SHALL BE ESTABLISHED INTHAT REQUIRED DEED OF EASEMNT AND RESERVATION

PERMEABLE PAVEMENT DESIGN (POROUS ASPHALT)

3"

2"

12" MINIMUM

8"

PERMEABLE PAVEMENTPermeable Pavement Information

Pervious Pavers Design Level LEVEL 1

Impervious Area (Ac) 1.62 ac

Tv (cf) (From VRRM spredsheet) (SEE SHEET 10) 5587 ft3

Drainage Area

Permeable Pavement Surface Area 25482 ft2

External Contributing Impervious Area 45085 ft2

Ratio 1.77 < 2

Depth of Stone Reservior Layer, dstone (ft) (Equation 7.1)

P=Rainfall Depth 0.083 ft

AI=Contributing impervious drainage area 70567 ft2

RvI=Volumetric runoff coefficient for impervious cover 0.95

Ap=Area of permeable pavement 25482 ft2

Nr=Porosity of reservoir layer 0.4

dstone =[(P X AI X RvI) + (P X AP)] / (Nr x AP) 0.75 ft

Maximum Reservior Depth, dstone‐max (Equation 7.2)

i=Field‐verified infiltration rate for the native soils 1 in/hr

td=Maximum allowable drain time 48 hours

Nr=Porosity of reservoir layer 0.4

dstone‐max=(0.5 X i X td) / (Nr X 12) 5.00 ft

Volume of Stone Reservior Layer, V

dstone =[(P X AI X RvI) + (P X AP)] / (Nr x AP) 0.75 ft

SA=Permeable Pavement Surface Area 25482.00 ft2

V = DSTONE X SA 19198.07 ft3

Volume of Stone Reservior Provided 19447.05 ft3

Trench Conversion

Lengh of Trench, L 846.26 ft

Width of Trench, W 6 ft

Min Depth of Trench = V / (L*W) 3.78 ft

Min Depth of Trench Provided 3.83 ft

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DRY SWALE DESIGNDRY SWALEDry Swale Information

Dry Swale Design Level LEVEL 1

Dry Swale Soil Media, Vr. 0.25

Gravel, Vr 0.4

Surface Storage behind check dams, Vr 1

Tv (cf) (From VRRM spredsheet) 778 ft3

Dry Swale Design Depths

Depth of Soil Media 2 ft

Depth of Gravel 1.75 ft

Surface Ponding Depth 0 ft

Equivalent Storage Depth

 = (Soil Depth x Vrs)+(Gravel Depth x Vrg)+ Ponding Depth 1.200 ft

Minimum Required Surface Area, SA

SA = Tv / Equivalent Storage Depth 648 ft2

Actual Surface Area, SA

Length 162 ft

Width 4 ft

SA = Length x Width 648 ft2

DRY SWALE CROSS SECTION - 2 YEAR

DRY SWALE CROSS SECTION - 10 YEAR