HomeMy WebLinkAboutSupplemental information 2.16.23
BETA GROUP, INC.
89 Shrewsbury Street, Suite 300, Worcester, MA 01604
P: 508.756.1600 | W: www.BETA-Inc.com
February 16, 2023
Ms. Brittany DiRienzo, Conservation Administrator
Town of Yarmouth
Yarmouth Town Hall
1146 Route 28
South Yarmouth, MA 02664
Re: Yarmouth Riverwalk Park, Route 28
Notice of Intent Technical Stormwater Peer Review
DEP File Nos. SE 083-2372, SE 083-2373
Dear Ms. DiRienzo:
Attached for your review and approval is updated material reflecting revisions to the Stormwater
Management Design for the proposed development of the Yarmouth River Walk Park. The materials
include plan sheet updates and minor Stormwater Report updates made in response to the comments
received from Conservation Commission’s technical peer review engineers, TRC Companies, dated
February 15, 2023. In response to the comments furnished, BETA offers the following responses.
1. The Drainage Area plans are very difficult to compare to the HydroCAD report because they are
not labeled consistently. All the sub-catchments in the HydroCAD report should be shown and
labeled on the drainage area plan and the labels should match. Typically, the node ID is labeled
on the plans.
Response: The Existing and Proposed Watershed Area Plans have been revised to show the sub-
catchment areas and identify the node numbers to be more consistent with the HydroCAD
model. Refer to Sheets WS.1A, WS.1B, WS.2A and WS.2B.
a. POA 1 “infiltration system 1” is labeled 62,100 sf on the plans and listed as 46,860 sf in
HydroCAD (assuming POA 1 infiltration system 1 is node 1S: infiltration 1.)
Response: The Watershed Area Plans have been updated to reflect the subcatchment
areas 1S – Access Roadway Infiltration System (46,860 SF) and 2S – Area Drain in the
First Island (15,240 SF) and are now consistent with the HyrdoCAD model. Refer to Sheet
WS.2A – Rev 2.
b. IVW 2 is labeled 174,310 on the plans and listed as 160,788 in HydroCAD (node 30S).
Response: Watershed Area IVW 2 has been updated to 160,788 SF, which is now
consistent with the HydroCAD model. Refer to Sheet WS.2B – Rev 2.
Ms. Brittany DiRienzo, Conservation Administrator
February 16, 2023
Page 2 of 2
2. The outlet invert for Infiltration Basin 1 is entered as 4.65 in HydroCAD but shown as 4.75 on the
plans. Not likely to impact the results but should be corrected.
Response: The outlet invert for Infiltration Basin 1 is consistent between the plans and
HydroCAD. However, the outlet invert elevation for Infiltration Basin 3 has been corrected in
both the plan and detail to be consistent with the HydroCAD model. Refer to Sheets C.6.5 – Rev 2
and C.7.9 – Rev 2.
3. The detail for Infiltration System 2 is labeled “14 per row”. Should this be 6 per row according to
the HydroCAD calcs, plan view, and your response letter?
Response: The detail for Infiltration System 2 has been corrected to show “6 per row” consistent
with the plans and the HydroCAD model. See Sheet C.7.8 – Rev 2.
To respond to these comments, a revised copy of the Stormwater Management Report has been
included with the following parts being revised, noted as Rev. 2:
- Sheet C.6.5 – Grading & Drainage – Enlargement Plan 3
- Sheet C.7.8 – Drainage Detail – 1
- Sheet C.7.9 – Drainage Detail – 2
- Sheet WS.1A – Watershed Plan – Existing
- Sheet WS.1B – Watershed Plan – Existing
- Sheet WS.2A – Watershed Plan – Proposed
- Sheet WS.2B – Watershed Plan – Proposed
- Appendix F – Watershed Data
If you have any further questions or comments regarding this matter, please do not hesitate to contact us
at our office.
Very truly yours,
BETA Group, Inc.
Gary D. James, P.E.
Senior Project Manager
CC: K Williams, P.E. Town of Yarmouth
J Gold TRC Companies
A Galle BETA Group Inc.
6.157.107.107.507.506.806.807.207.277.357.457.25PROP. OUTLET CONTROL STRUCTURE 2RIM 7.00INV. EL. 4.65 12" OUT36" SPILLWAY INLETCREST ELEV - 6.20PROP INFILTRATION BASIN 3PROP. CURB INLETBC 6.70TC 7.107.207.307.407.507.407.307.507.757.207.107.006.907.007.106.906.807.007.757.507.506.807.287.28AREA DRAIN 6RIM 7.20INV 5.50TC 7.50TC 7.60TC 7.63INV OUT 5.25TC 7.90FFE7.504" PERF.4" PERF.66765
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612" FLARED END WITH RIP RAPINV. ELEV - 4.002 CHECK DAM IN SERIES,CREST ELEV. 6.004" PERF.4" PERF.
7
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776" HDPEPROP. EDGE INFILTRATIONTRENCH (TYP.)UNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review Only20020SCALE IN FEET: 1"=20'40GJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23C.6.5GRADING & DRAINAGE- ENLARGEMENT PLAN- 3MATCHLINE - MATCH TO SHEET C.6.4
PEER REVIEW RESPONSE #2 2/15/232
SCALE:AREA DRAIN1" = 1'-0"12"x12" NDS AREA DRAIN,SEE PLAN FOR LOCATION ANDRIM ELEVATIONSDRAIN PIPE,SEE PLAN FOR PIPESIZE AND INVERTELEVATIONS6"6"MIN.LOAM & SEEDCOMPACTEDCRUSHEDSTONE BASECLASS I OR II MATERIALPER ASTM D2321, LATEST EDITION,COMPACTED IN MAX. 8" LOOSE LIFTSTO 95% MIN. OF MAX. SPD* H , H = 12" FOR UP TO AND INCLUDING 36" N-12 = 24" FOR 42"-48" N-12FILTER FABRIC(AASHTO M-288)** SEE TABLE 112UNDISTURBEDEARTHH (RIGID PVMT.)*1BEDDING (CLASS I OR II MATERIAL)= 4" MIN. FOR 12"-24" N-12, 42"-48" HC= 6" MIN. FOR 30"-48" N-12HDPE PIPE2H (FLEX. PVMT.)*TABLE 1NOMINAL DIAMETER,IN (MM)FT (M)X (MIN.),0.69 (0.21)12 (300)0.68 (0.21)15 (375)0.74 (0.23)18 (450)0.84 (0.26)24 (600)1.5 (0.46)30 (750)1.5 (0.46)36 (900)1.5 (0.46)42 (1050)1.5 (0.46)48 (1200)TYPICAL SUB-SURFACE TRENCH DETAILHOT MIX ASPHALTSECTION A-APLANSECTION B-BSTONE AT PIPE ENDSDRAINAGEDETAILS - 1INFILTRATION SYSTEM NO. 2 - RESTROOM FACILITYUNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review OnlyAS SHOWNGJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23INFILTRATION BASIN NO. 3TEMPORARY SEDIMENT BASINC.7.8PEER REVIEW RESPONSE #2 2/15/232
INFILTRATION SYSTEM NO. 1 - ACCESS DRIVEWAY TREATMENT SYSTEMINSPECTION MANHOLEOUTLET CONTROL STRUCTURE AT INFILTRATION BASIN (1 & 3)PLANFRONT ELEVATIONSECTIONCHECK DAM CROSS SECTIONDRAINAGEDETAILS - 2UNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review OnlyAS SHOWNGJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23C.7.9PEER REVIEW RESPONSE #2 2/15/232
EXISTING WATERSHED LIMITS EXISTING WATERSHED FLOW PATHPaved Entrance Drive98LAND USE TYPECNHATCHDrive in Grass49Gravel Roadways96Exposed Gravel (Abutter)96Dirt Road to Upweller72Wooded30Brush, Fair35Brush, Good30Wetlands77Upweller Area Inside Fence98Grass Shoulder Along Access Drive49Lawn39Roadway Pavement (Courtland)98EXISTING WATERSHED PLAN LEGEND/KEYWS.1AWATERSHED PLAN -EXISTING - 1POA 4: 6S -DEPRESSION ATTHE END OFCOURTLAND WAYAREA = 24,293 SFPOA 1: 1S -DRIVE-IN AREA ATUPWELLER SITEAREA = 377,282 SFPOA 1: 2S -AREA OUTSIDE THEFORMER DRIVE-INDISCHARGE POINTAREA = 125,340 SFPOA 2: 4S -ISOLATED WETLANDS (IVW 1)AREA = 37,105 SFUNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review Only80SCALE IN FEET: 1"=40'40040GJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23PARKERS RIVERMA -
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8 COURTLAND WAYWOODED(TYP.)DRIVE-INGRASS (TYP.)DRIVE-INGRASS (TYP.)WOODED(TYP.)WOODED(TYP.)BRUSH,GOOD (TYP.)WETLAND(TYP.)WETLAND(TYP.)WOODED(TYP.)BRUSH,GOOD (TYP.)BRUSH,GOOD (TYP.)WOODED(TYP.)WOODED(TYP.)BRUSH,GOOD (TYP.)PEER REVIEW RESPONSE #2 2/15/232
EXISTING WATERSHED LIMITS EXISTING WATERSHED FLOW PATHPaved Entrance Drive98LAND USE TYPECNHATCHDrive in Grass49Gravel Roadways96Exposed Gravel (Abutter)96Dirt Road to Upweller72Wooded30Brush, Fair35Brush, Good30Wetlands77Upweller Area Inside Fence98Grass Shoulder Along Access Drive49Lawn39Roadway Pavement (Courtland)98EXISTING WATERSHED PLAN LEGEND/KEYWS.1BWATERSHED PLAN -EXISTING - 2UNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review Only80SCALE IN FEET: 1"=40'40040GJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23PARKERS RIVERPARKERS RIVERPOA 1: 3S -WOODLAND AREAOUTSIDE THE FORMERDRIVE-IN DEVELOPMENTAREA = 166,861 SFPOA 3: 5S -ISOLATED WETLANDS (IVW 2) AREA = 174,310 SFWETLAND(TYP.)WOODED(TYP.)WOODED(TYP.)WOODED(TYP.)WOODED(TYP.)DRIVE-INLAWN (TYP.)BRUSH,GOOD (TYP.)LEGEND EXISTING WATERSHED LIMIT EXISTING WATERSHED FLOW PATHBRUSH,GOOD (TYP.)PEER REVIEW RESPONSE #2 2/15/232
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888789877776889811674 Paved98PROPOSEDSidewalkReinforced TurfBasinRoof AreaLandscaped / LawnStabilized Aggregate Path986892989839Brush, Good30Wetlands77Upweller Area Inside Fence98Grass Shoulder Along Access Drive49Exposed Gravel (Abutter)96Roadway Pavement (Courtland)30LAND USE TYPECNHATCHEXISTINGPROPOSED WATERSHED PLAN LEGEND/KEY PROPOSED WATERSHED LIMITS PROPOSED WATERSHED FLOW PATHWooded30WS.2AWATERSHED PLAN -PROPOSEDUNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review Only80SCALE IN FEET: 1"=40'40040GJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23POA 1: 17S -INFIELD DEPRESSION 1AREA = 113,450 SFPOA 1: 5S - WEST SIDE OFACCESS DRIVEWAYTHROUGH CULVERTAREA = 30,300 SFPOA 1: 1S - ACCESSROADWAY INFILTRATIONSYSTEMAREA = 46,860 SFPOA 2: 20S - ISOLATEDWETLANDS 1 (IVW 1)AREA = 26,100 SFPOA 1: 7S -UNCONTROLLED TOPARKERS RIVER ALONGEAST SIDE OF PARKAREA = 130,164 SFPOA 1: 12S -BUILDING AREAAREA = 3,560 SFPOA 1: 13S - AD1AREA = 1,633 SFPOA 1: 15S -POROUS PAVEMENTAREA = 31,070 SFPOA 1: 14S - AREA DRAINSALONG PARKING AREAAREA = 10,420 SFPOA 4: 40S -DEPRESSION ATTHE END OFCOURTLAND WAYAREA = 21,713 SFPARKERS RIVERMA -
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8 COURTLAND WAYWOODED(TYP.)WOODED(TYP.)WOODED(TYP.)BRUSH,GOOD (TYP.)WETLAND(TYP.)WETLAND AREA 1 (IVW 1)WOODED(TYP.)BRUSH,GOOD (TYP.)BRUSH,GOOD (TYP.)WOODED(TYP.)WOODED(TYP.)EXPOSEDGRAVEL(ABUTTERS)BRUSH,GOOD (TYP.)POA 5: 50S - TOWARDSRTE 28 PAVEMENTAREA = 1,800 SFPARKERS RIVERARTISTS SHANTIES (TYP.)POA 1: 2S -AREA DRAIN IN THEFIRST ISLANDAREA = 15,240 SFPOA 1: 11S -ARTIST SHANTIESAREA = 1,080 SFPEER REVIEW RESPONSE #2 2/15/232
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77Paved98PROPOSEDSidewalkReinforced TurfBasinRoof AreaLandscaped / LawnStabilized Aggregate Path986892989839Brush, Good30Wetlands77Upweller Area Inside Fence98Grass Shoulder Along Access Drive49Exposed Gravel (Abutter)96Roadway Pavement (Courtland)30LAND USE TYPECNHATCHEXISTINGPROPOSED WATERSHED PLAN LEGEND/KEY PROPOSED WATERSHED LIMITS PROPOSED WATERSHED FLOW PATHWooded30WS.2BWATERSHED PLAN -PROPOSEDUNLESS OTHERWISE NOTED OR CHANGED BY REPRODUCTIONSHEET NO.SCALEDATEDESIGNED BY:10056CHECKED BY:BETA JOB NO.:ISSUE DATE:DRAWN BY:REVISIONSNO.TITLEPROJECTPREPARED BYWest Yarmouth, MAYARMOUTHRIVERWALKPARKAKPFor Review Only80SCALE IN FEET: 1"=40'40040GJGJREGISTERED PROFESSIONALSTORMWATER APPLICATIONPERMIT - PLAN SETREGISTERED PROFESSIONAL11/18/221PEER REVIEW RESPONSE 2/2/23POA 1: 18S -INFIELD DEPRESSION 2 -DIRECT AREAAREA = 132,180 SFPOA 1: 4S -CUL-DE-SAC AREAAREA = 13,791SFPARKERS RIVERWETLAND(TYP.)WOODED(TYP.)WOODED(TYP.)WOODED(TYP.)WOODED(TYP.)POA 1: 6S WOODLANDAREA OUTSIDE THEFORMER DRIVE-INDEVELOPMENT TO THEBOARDWALKAREA = 164,861 SFPOA 3: 30S - ISOLATEDWETLANDS 2 (IVW 2)AREA = 160,788 SFWOODED(TYP.)PROP. KAYAK KIOSKSTAGE AREAPEER REVIEW RESPONSE #2 2/15/232
BETA GROUP, INC.
89 Shrewsbury Street, Suite 300, Worcester, MA 01604
P:508.756.1600 | W:www.BETA-Inc.com
Watershed Data –Existing Conditions
669 Route 28
Yarmouth, Massachusetts
September 2022
Rev2:February 2023
POA 1 Parkers River
1S-Drive-in area at Upweller Site
This area flows from the access drive down past the Upweller Site and includes all the gravel and
dirt pathways.
Area = 377,282 sq. ft.
= 8.661 acres
Land Use
Use Area CN
Paved entrance drive 38,578 98
Drive in grass 244,074 49
Gravel roadways 6,874 96
Exposed gravel (abutter)11,442 96
Dirt road to Upweller 2,328 72
Wooded 46,293 30
Brush, fair 20,368 35
Wetlands 6,125 77
Upweller area inside fence 1,200 98
Tc Calculation
Sheet Flow 50’-2.0% slope, woodland light underbrush
Shallow Concentrated flow 50’-0.5% slope, wooded
Shallow Concentrated flow 850’-0.5% slope across drive in field
2S-Area outside the former drive-in discharge point
This area sheet flows directly into the River and includes a portion of the existing drive-in area.
Drainage Area = 125,340 sq. ft.
= 2.877 acres
Land Use
Use Area CN
Drive in grass 107,144 49
Brush,good 18,196 30
Tc Calculation
Sheet Flow 50’-1.3% slope, short grass
Shallow Concentrated flow 420’-0.8% slope, nearly bare
February 2023
Page 2 of 3
3S-Woodland Area outside the former drive-in development
This area sheet flows directly into the Salt Marsh adjacent to the River. It is completely wooded
currently but will be traversed by reinforced earth walking paths to access the proposed
boardwalk
Area = 166,861 sq. ft.
=3.831 acres
Land Use
Use Area CN
Brush, good 166,861 30
Tc Calculation
Sheet Flow 50’-1.0% slope, woodlands
Shallow Concentrated flow 85’-1.0% slope, woodland
POA 2 4S-Isolated Wetlands (IVW 1)
Drainage Area = 37,105 sq. ft.
= 0.852 acres
Land Use
Use Area CN
Grass shoulder along access driveway 4,660 49
Brush, Good 28,958 30
Wetlands 3,487 77
Tc Calculation
Sheet Flow 50’-1.4% slope, wooded
Shallow Concentrated flow 29’-1.4% slope, wooded
POA 3 5S-Isolated Wetlands (IVW 2)
Drainage Area = 174,130 sq. ft.
= 3.997 acres
Land Use
Use Area CN
Woodlands 146,318 30
Wetlands 19,556 77
Lawn 8,256 39
Tc Calculation
Sheet Flow 50’-5.0% slope, dense grass
Shallow Concentrated flow 34’-2.80% slope, wooded
February 2023
Page 3 of 3
POA 4 6S-Depression at the end of Courtland Way
Drainage Area = 24,293 sq. ft.
= 0.558 acres
Land Use
Use Area CN
Roadway pavement 360 98
Brush, good 23,202 30
Lawn area 731 39
Tc Calculation
Sheet Flow 50’-5.8% slope, woods light underbrush
Shallow Concentrated flow 35’-6.80% slope, wooded
TOTAL WATERSHED AREA ANALYZED
POA 1 377,282
125,340
166,861 669,483
POA 2 37,105
POA 3 174,130
POA 4 24,293
TOTAL 905,011 sq. ft.
20.776 acres
BETA GROUP, INC.
89 Shrewsbury Street, Suite 300, Worcester, MA 01604
P:508.756.1600 | W:www.BETA-Inc.com
Watershed Data –Proposed Conditions
669 Route 28
Yarmouth, Massachusetts
September 2022
Rev2-February 2023
POA 1 Parkers River
Total Watershed Area to Infiltration System 1
Area = 62,100 Sq. Ft.(1S + 2S)
=1.426 acres
1S-Access Roadway Infiltration system
Area =46,860 sq. ft.
= 1.076 acres
Land Use
Use Area CN
Paved 14,261 98
Sidewalk 3,817 98
Reinforced turf 3,105 68
Basin 2,033 98
Landscaped/lawn 17,312 39
Pump Station
Paved 2,622 98
Roof area 2,250 98
Sidewalk 1,460 98
Tc Calculation
Use 6 minutes as a minimum
2S-Area drain in the first island
Area = 15,240 sq. ft.
=0.350 acres
Land Use
Use Area CN
Paved 7,230 98
Sidewalk 2,565 98
Reinforced turf 1,270 68
Landscaped/lawn 4,175 39
Tc Calculation
Use 6 minutes as a minimum
Pond 2P-Infiltration System 1
Water Quality Volume
Total Impervious area =39,980 sq. ft.
1” Rainfall =3,332 cu. ft.
February 2023
Page 2 of 11
Chamber System data
System will be 8 rows of Stormtech SC 301 chambers 14 per row.
Flow from forebay will enter Isolator Rows only through 2-12” diameter culverts at Inv. El. 5.50
that will be set flat with no slope. Inlets will be flared ends
Overall dimensions = 102.88’ x 28.17’ x 2.33’
Storage volume provided = 3,439.7 cu. ft. (from Hydro-CAD)
Infiltration rate =8.27 inches per hour
Bottom area = 102.88 x 28.17 = 2,898 sq. ft.
= 0.55 cfs
Dynamic sizing calculation
Sizing criteria =1” runoff in 2 hours
A(KT) +storage volume =Rv
Rv =3,123 cu. ft. minimum
A=2,898 sq. ft.
Storage Volume 2,664 cu. ft.@ El. 6.60
K T=1.38 ft
Rv=2,898(1.38)+2,664 =3,999.2 +2,644=6,643.2 cu. ft.=1.99” ok
Outlet configuration
Outlet structure will be set east end of the forebay. Structure will be 4’ x 4’ precast
concrete
Top El. 7.2
Outlet will be 12” ADS culvert @ Inv. El. 4.75
Inlet –3’ wide spillway at crest El. 6.60
Gated emergency outlet 4” PVC @ Inv. El. 5.2+
Total Volume Stored at Elevation 6.60 = 2,664 + 4,323
= 6,987 cu. ft.
Time to Dewater = 6,987 / [2898 x 8.27/12)
= 6987/ 1,997
= 3.50 hours ok
Pond 1P-Collection Swale
Bottom El. 5.30
Sediment forebay Storage volume required = 0.1” =312.3 cu. ft.
Storage Volume provided
Elev.Area Average volume total
5.3 1,573 0
4,647 2,323.5 1,626.5
6.0 3,074 1626.5
8,139 4,069.5 4,069.5
7.0 5.065 5696.0
11,208 5,604 3,922.8
7.7 6,143 9618.8
February 2023
Page 3 of 11
Top of stone check dam will be set at Elevation 5.75
Forebay sizing =1045 cu. ft. = 0.32” ok
Bathroom System
Runoff from bathroom will be collected in stone trenches along the drip edge of the structure and
along the outside edge of the surrounding walkways. There will also be several area drains placed around
the perimeter of this area that will collect runoff and direct it into the infiltration system that will be
located east of the bathroom.Piping from these area drains will be either flat or have slopes less than
0.5%. Grading around the grates will be set to allow some ponding above the grates to allow some
elevation differential to develop and help flow to the leaching facility.
12S-Building area
Area =3,560 sq. ft.
= 0.082 acres
Land Use
Use Area CN
Roof 1,210 98
Walkways 2,165 98
Landscaped/lawn 185 39
Tc Calculation
Use 6 minutes as a minimum
13S-AD 1
Area =1,633 sq. ft.
= 0.037 acres
Land Use
Use Area CN
Walkways 462 98
Landscaped/lawn 1,171 39
Tc Calculation
Use 6 minutes as a minimum
14S-Area Drains along parking area
Area =10,420 sq. ft.
= 0.239 acres
Land Use
Use Area CN
Walkways 3,827 98
Landscaped/lawn 6,593 39
Tc Calculation
February 2023
Page 4 of 11
Use 6 minutes as a minimum
3P-Chamber System data
System will be 5 rows of Stormtech SC 301 chambers 6 per row.
Flow from all inlet piping will enter Isolator Row only
Overall dimensions = 18.17’ x 45.92’x 2.33’
Storage volume provided =959 cu. ft. (from Hydro-CAD)
Infiltration rate =8.27 inches per hour
= 0.08 cfs
Water Quality Volume
Total Impervious area =7,664 sq. ft.
1” Rainfall =639 cu. ft.
Dynamic sizing calculation
Sizing criteria = 1” runoff in 2 hours
A(KT) + storage volume =Rv
Rv =574 cu. ft. minimum
A=834 sq. ft.
K T=1.38 ft
Rv=834(1.38)+959 =1,150.9 +959=2,109.9 cu. ft.=3.30” ok
Outlets
The only outlet from this system will be through exfiltration. Inside the program, we have
assumed that overflow will be flow over the walkway from the area drain along the
parking lot. This would be at Elevation 7.20. It is entered as a broad crested weir, width
20’ breadth 8’.
Time to Dewater
100 Year flood level = El. 7.29 =940 cu. ft.
=940/(834 x 8.27/12)
=1.63 hours ok
15S-Porous Pavement
Porous pavement will receive runoff from the pavement above only. The center aisle will be solid
pavement but will flow across the porous section. The Reservoir will be sized for the entire area.
Watershed Area = 31,070 sq. ft.
Pavement area = 29,638 sq. ft.
Collection trench= 1,432 sq. ft.
Water Quality Volume
1” rainfall = 2,470 cu. ft.
Reservoir
Reservoir will be 6”t layer of 1-1/2” aggregate assume 35% voids
February 2023
Page 5 of 11
Volume = 29,638 (6”) 0.35
= 5,186.5 cu. ft. = 2.10” ok.
4S-Cul-de-Sac Area
This area is at the end of the roadway into the park. It includes the cul-de-sac pavement, the Kayak
rental kiosk area, and the walkways around the cul-de-sac.
Drainage Area = 13,791 sq. ft.
= 0.317 acres
Land Use
Use Area CN
Paved 5,958 98
Kiosk Area 175 98
Sidewalk 145 98
Stabilized Aggregate 620 92
Basin 1,903 98
Landscaped/lawn 4,990 39
Tc Calculation
Use 6 minutes as a minimum
Water quality Volume
Total impervious =6,898 sq. ft.
1” volume =574.8 cu. ft.
4P-Infiltration basin 3
All impervious surfaces from this area will be collected and directed into the basin. most will
come directly into the basin from a small trench from the edge of the pavement. Area drains will
be provided in the Kiosk area to collect the runoff from the storage area.The check dams that
form the forebay will be set at crest elevation 6.0,
5.0 850
2,150 1,075.0 1,075.0
6.0 1,300 1075.0
3,040 1,520 15.2
6.01 1,740 1090.0
4,075 2,37.5 2,037.5
7.0 2,335 3,127.5
4,977 2,488.5 829.5
7.33 2,642 3,957.0
Infiltration Rate = 8.27” / hour
= 0.16 cfs
Static storage provided =1,432 cu. ft. at Elev. 6.20
= 2.49” ok
Sediment forebay sizing
Volume required = 0.1” =58 cu. ft.
Volume provided =
February 2023
Page 6 of 11
1st bay 149 cu. ft.
2nd bay 134 cu. ft.
17S-Infield depression 1
Area = 113,450 sq. ft.
= 2.604 acres
Land Use
Use Area CN
Sidewalk 6,650 98
Reinforced turf 11,650 68
Woods 13,020 30
Infield grass 65,720 49
Landscaped/lawn 16,410 39
Tc Calculation
Sheet Flow 50’-0.8% slope, woods light underbrush
Shallow Concentrated flow 172’-1.10% slope, grass
Water quality volume
Total impervious area = 24,880 sq. ft.
Volume = 1” = 2,073 cu. ft.
Basin area
Elev.Area Average volume total
6.15 200 0
59,600 29,800 20,860
6.85 59,400 20,860
Outlets
Exfiltration will be the only outlet from this basin area. To assist with infiltration, a
stone filed trench 24” w x 8” deep x 100’ long will be provided. Area drains will be
provided at each end of the trench to allow surface runoff to enter the trench.
Time to Dewater
Based on Hydro-CAD printout, basin will be dry in 26 hours.
February 2023
Page 7 of 11
18S-Infield depression 2
Direct area
Area = 132,180 sq. ft.
=3.034 acres
Land Use
Use Area CN
Sidewalk 8,020 98
Stage area 1,950 98
Reinforced turf 10,710 68
Infield grass 104,435 49
Landscaped 6,345 39
Earth path 720 92
Tc Calculation
Sheet Flow 50’-1.0% slope, grass dense
Shallow Concentrated flow 50’-1.0% slope, grass
Water quality volume
Total impervious 16,896 sq. ft.
Volume = 1408 cu. ft.
11P-Basin Data
Trench 2 Basin area
Elev.Area Average volume total
6.15 240 0
58,140 29,070 20,349
6.85 57,900 20,349
Total water quality volume =1,720 cu. ft.
Outlets
Exfiltration will be the only outlet from this basin area. To assist with infiltration, a
stone filed trench 48” w x 8” deep x 60’ long will be provided. Area drains will be
provided at each end of the trench to allow surface runoff to enter the trench.
Dewater time
Based on Hydro-CAD printout, basin will be dry at 25 hours
February 2023
Page 8 of 11
7S-Uncontrolled to Parkers River along East side of park
This area sheet flows directly into the Parkers River and includes the access driveway to the
Upweller site, and the developed areas east of the parking. All the walkways in this area will be
reinforced earth paths. The artist shanties will have a drip edge around them to collect the roof
runoff and will be analyzed separately.
Area = 130,164 sq. ft.
=2.988 acres
Land Use
Use Area CN
Stabilized aggregate walkway 4,837 92
Access driveway to upweller 2,497 96
Gravel Path 929 96
Wetlands 6,125 77
Upweller area inside fence 1,200 98
landscaped 31,301 39
Brush, good 71,833 30
Exposed gravel (abutter)11,442 96
Tc Calculation
Sheet Flow 50’-0.5% slope, woodland
Shallow Concentrated flow 180’-1.0%slope, woodland
11S-Artist Shanties
Buildings are each 10’ x 12’–9 buildings
Total area = 1,080 sq. ft.
Each building will have drip edge that is 18” deep x 18” wide x 12’ long
Volume =27.0 cu. ft. (35% voids) =9.5 cu ft. per trench
Total volume = 18(9.5) =171 cu. ft.
Water Quality Volume=90 cu. ft.
Infiltration rate = 8.27” / hour
Total = 0.09 cfs
February 2023
Page 9 of 11
6S-Woodland Area outside the former Drive-in development to the Boardwalk
This area sheet flows directly into the salt marsh adjacent to the river. It is completely wooded
currently but will be traversed by reinforced earth walking paths to access the proposed
boardwalk
Area = 164,861 sq. ft.
= 3.784 acres
Land Use
Use Area CN
Stabilized Aggregate walkway 3,180 92
Grass shoulder 7,980 39
Brush, good 153,701 30
Tc Calculation
Sheet Flow 50’-1.0% slope, woodlands
Shallow Concentrated flow 85’-1.0% slope, woodland
5S-West side of access driveway through culvert
This area is along the west side of the access driveway which will be trapped by raising the
driveway and parking area. It will be connected by a 12” culvert 180’ long, across the circle prior
to the parking. There are no impervious surfaces proposed in this area. Nor will there be any
impervious surfaces tributary to this area from the development. A portion of this area is within
the former drive-in area which will be landscaped.
Area =30,300 sq. ft.
= 0.696 acres
Land Use
Use Area CN
Grass shoulder & landscaped 18,741 39
Brush, good 11,559 30
Tc Calculation
Sheet Flow 50’-2.0% slope, woodlands
Shallow Concentrated flow 80’-0.6% slope, woodland
February 2023
Page 10 of 11
Outlet will be 8” culvert 180’ long @ slope = 0.50%
POA 2 -20S Isolated Wetlands 1 (IVW 1)
Drainage Area = 26,100 sq. ft.
= 0.599 acres
Land Use
Use Area CN
Landscaped 6,990 39
Brush, good 15,623 30
Wetlands 3,487 77
Tc Calculation
Sheet Flow 50’-1.28% slope, wooded
Shallow Concentrated flow 29’-1.28% slope, wooded
POA 3 –30S-Isolated Wetlands 2 (IVW 2)
Drainage Area = 160,788 sq. ft.
= 3.691 acres
Land Use
Use Area CN
Stabilized aggregate walkway 1,560 92
Landscaped shoulder 3,450 39
Wooded 127,966 30
Wetlands 19,556 77
Lawn 8,256 39
Tc Calculation
Sheet Flow 50’-5.0% slope, dense grass
Shallow Concentrated flow 34’-2.80% slope, wooded
February 2023
Page 11 of 11
POA 4 –40S-Depression at the end of Courtland Way
Drainage Area = 21,713 sq. ft.
= 0.498 acres
Land Use
Use Area CN
Roadway pavement 360 98
Reinforced turf 1640 68
Landscaped 3225 39
Brush 15,757 30
Lawn area 731 39
Tc Calculation
Sheet Flow 50’-5.8% slope, woods light underbrush
Shallow Concentrated flow 35’-6.80% slope, wooded
POA 5 –50S-Towards Rte 28 pavement
Drainage Area = 1,800 sq. ft.
= 0.04 acres
Land Use
Use Area CN
Lawn area 1,800 39
Tc Calculation
Use 6 minutes as a minimum
TOTAL WATERSHED AREA ANALYZED
POA 1 Infiltration System 1 62,100
Infiltration System 2 15,613
Cul de sac 13,791
Porous pavement 31,070
Infield Area 1 113,450
Infield Area 2 132,180
Artist shanties 1,080
Uncontrolled east side 130,164
West side of access road 30,300
Woodland area to boardwalk 164,861
694,609
POA 2 26,100
POA 3 160,788
POA 4 21,713
POA 5 1,800
TOTAL 905,010 sq. ft. ok 1.0’
20.776 acres