Appendix E Stormwater Analysis Phase I Existing and ... · 6/23/2016 · Existing and Proposed Conditions . Stormwater Management Calculations ... from the stormwater management

Appendix E

Stormwater Analysis – Phase I

Existing and Proposed Conditions

Stormwater Management Calculations

Former Route 44 Sand and Gravel Property Route 44

Carver, MA

Prepared For:

Langdon Environmental LLC.

Prepared By:

William M. Anderson, PE Anderson Engineering, LLC

190 Cedar Avenue Eats Greenwich, RI 02818

(401) 265-6169

May 2015

Stormwater Management Plan

The stormwater management plan to follow, has been designed for the subject property to mitigate post development conditions, and is organized as follows:

Introduction Methodology Soils Pre-developed Conditions Post-developed Conditions Stormwater Quality Downstream Drainage Area Analysis Conclusion Attachments

o Attachment 1 - General Location Map (USGS) o Attachment 2 - Soils Information o Attachment 3 - Pre-developed and Post-developed Drainage Area Maps o Attachment 4 - Pre-developed Conditions Stormwater Calculations o Attachment 5 - Post-developed Conditions Stormwater Management Calculations o Attachment 6 – Water Quality and Recharge Calculations o Attachment 7 – Infiltration Area Mounding Calculations o Attachment 8 – Permit Drawings

INTRODUCTION The Developer, Route 44 Development, LLC, has authorized Langdon Environmental, LLC to design the stormwater management facilities for the initial filling phase at the subject property. The purpose of this report is to summarize pre and post-developed conditions including the stormwater quantity and quality measures to be provided. The subject site is located predominately on the northerly side of Route 44 in the Town of Carver, Massachusetts and consists of 187+ acres. The site location is shown on the General Location Map (Attachment 1). The site is a former sand and gravel pit METHODOLOGY The HydroCAD Stormwater Modeling System Software which utilizes the United States Department of Agriculture (USDA) Soil Conservation Service (SCS) Technical Release No. 55 (SCS TR-55) and TR-20 (SCS TR-20) methodologies was utilized to determine pre and post-developed stormwater runoff rates and to design the stormwater management facilities. The Rational Method was utilized to calculate the stormwater runoff rates for design of the swales and culverts within the proposed development. Proposed culverts and swales were designed to convey a 10-year storm and flood routes will be designed to convey a 100-year frequency in accordance with the Massachusetts Stormwater Handbook.

SOILS The NRCS Soil Survey of Massachusetts identifies the soils at the subject site as predominately “700A – Udipsamments” and “657A – Aquepts”. Udipsamments soils are typically loamy fine sand to a depth of 24 inches followed by fine sand to depths of 72”+ and are considered moderately well drained with hydraulic conductivity in the range of 1.42 to 14.17 in/hr, typically. Aquepts soils are typically very fine sandy loams to a depth of 42” and typically have a 5” layer of muck below followed by loamy sand extending to depths of 65”+. Aquepts soils are considered poorly drained with hydraulic conductivity in the range of 0 to 0.01 in/hr. The soil ratings in the project area are classified as hydrologic soil group A. Group A soils typically have a moderate to rapid infiltration rates when thoroughly wet. See Attachment 2 for more information on the soils located in the project area. Soil test pits were conducted as part of a subsurface assessment by McArdle Gannon Associates, Inc. in August 2014. Test pits conducted in the vicinity of the proposed infiltration basins were identified as #2, #3, #34, #35, and #38. The soils were typically identified as a fine to moderate/coarse sand. Peat material was identified on the property; however the approximate extents are located outside of the proposed infiltration areas. Copies of the test pit logs are included in Attachment 2. PRE-DEVELOPED CONDITIONS The proposed initial development area encompasses a drainage area of approximately 20.2 acres. The site is sparsely vegetated with brush and some grasses. There are existing gravel and paved roadways that are included in the drainage analysis. The site has been divided into two (2) sub-drainage areas under pre-developed conditions. Drainage Area “1” is tributary to the northern portion of the proposed development and consists of 10.55 acres of drainage area. Drainage Area “2” is tributary to the southern portion of the proposed development and consists of 9.65 acres. The drainage areas are shown on Attachment 3 - Pre-developed and Post-developed Drainage Area Maps. The following is a summary of the pre-developed peak stormwater runoff rates for various design storms. The information and models used to estimate these rates can be found in Attachment 4 - Pre-Developed Conditions Stormwater Calculations. Summary of Pre-Developed Peak Stormwater Rates (cfs) for 1 to 100-year frequency storms Drainage Sub-Area

1-yr storm event

2-yr storm event

10-yr storm event

25-yr storm event

100-yr storm event

Area “1” 0.77 2.14 9.23 15.75 31.63 Area “2” 0.43 1.45 7.27 12.93 26.98

POST-DEVELOPED CONDITIONS It is proposed to re-develop the site with future manufacturing/industrial, however this initial phase includes cleanup of the subject site and the initial filling for a level pad with approximately 50,000 cy of material and an ABC Materials processing pad at a size of 2.5 acres... Under post-developed conditions the site will consist of two (2) total sub-drainage areas. The sites post-development will predominately discharge to two (2) proposed stormwater infiltration basins each with a sediment forebay to be installed on the western end of the site redevelopment. The post development Area 1 predominately discharges to the west and encompasses the northern portion of the site. Impervious areas are assumed to be the 2.5 acre ABC Materials processing pad. A CN value of 85 was used for this area. Post development Area 2 will discharge to the western portion of the site as well and encompasses the southern area. This area is proposed to be filled leveling the area to approximate elevation of 88. Both drainage areas are designed to provide mitigation for stormwater quality and quantity requirements in accordance with the Massachusetts Stormwater Manual. Structural BMPs include two (2) infiltration basins with sediment forebays. The basins have been designed to accommodate the required water quality volume, recharge volume, and mitigate through the 100-yr storm event. Mitigation of post-developed stormwater runoff rates will be required to be less than or equal to pre-developed rates for all storms from the 2-to 100-year frequency. The post-developed drainage area map is provided in Attachment 3 (Pre-Developed and Post-Developed Drainage Area Maps). Design Calculations (Attachments 4, 5, and 6) and details of the stormwater management areas are included in Attachment 8 (Permit Drawings). The following is a summary of the post-developed stormwater rates discharging to the design points for the 2-to 100-year storm events. The table shows that post-developed runoff rates are less than or equal to pre-developed runoff rates. Summary of Post-Developed Peak Stormwater Rates (cfs) for 1 to l00-year frequency storms. Drainage Sub-Area

1-yr storm event

2-yr storm event

10-yr storm event

25-yr storm event

100-yr storm event

Area 1 2.85 5.88 17.27 26.62 47.97 Area 2 9.90 14.14 26.95 36.28 55.83 Emergency Spillway discharge from Infiltration Basin#1

0 0 0 0 24.67

Emergency Spillway discharge from Infiltration Basin#2

0 0 0 0 26.39

Basin #1 Elev. 74.16 74.60 76.42 77.87 78.59

Basin #2 Elev. 71.09 71.73 73.60 74.89 75.61 Total Storage provided by infiltration #1 (cf)

1,426 5,287 24,255 42,168 52,300

Total Storage provided by infiltration #2 (cf)

11,707 19,404 45,336 66,444 79,557

Peak rates were taken from HydroCAD output. The peak rates include the effects of the mitigation from the stormwater management system. STORMWATER QUALITY Stormwater quality measures in accordance with the requirements of the Massachusetts Stormwater Manual are provided by the Infiltration Basins for both areas. The following is a summary of the water quality volumes required and the water quality volume provided for each post development area. Calculations of the stormwater quality volume for each SMA are provided in Attachment 6 (Post-Developed Conditions Stormwater Management and Water Quality Calculations). A detail of the design of the SMA is provided in the permit plans. Summary of Water Quality Volume Post Development Area 1 Post Development Area 2 WQV Required (cf) 9,075 33,389 WQV Provided (cf) 43,908 68,251 The following is a summary of the ground water recharge volumes required and the ground water recharge volume provided by the Infiltration Areas. Based on the calculations, additional recharge is provided in comparison to pre-development conditions. Calculations of the recharge volume for each Post Development Area provided in Attachment 6 (Water Quality Calculations). A detail of the design of the Infiltration Systems are provided in Attachment 9 (Permit Drawings). Summary of Recharge Volume Post Development Area 1 Post Development Area 2 Rv Required (cf) 5,445 20,033 Rv Provided (cf) 43,908 68,251

Mounding Analysis As a requirement of the Stormwater Manual, a mounding analysis for the infiltration basin system was conducted for both the 1-yr storm event and the 10-yr storm events. Using the Hantush Equation (1967), the theoretical groundwater mounding was analyzed beneath the center of each infiltration basin. The Hantush analysis assumes only the bottom area of the basin is infiltrating. Based on the analysis, assuming a twenty-five (25) foot initial aquifer saturated thickness, the maximum mounding effect for the 1-yr storm event at the center of Basins 1 and 2 is 0.65 and 4.4’, respectively. Similarly, for the 10-yr storm event, the maximum mounding effect was estimated at10.0’ and 15.4’, respectively. However, for the 10yr event, the watertable did not exceed the surface elevation as movement was made away from the basin. Refer to Attachment 7 for further information. COMPLIANCE WITH MASSACHUSETTS STORMWATER STANDARDS Standard 1 – No untreated discharges or erosion to wetlands

Since the design storms are contained within the infiltration basins, no discharges are expected. For the 100 yr event, both emergency spillways have been adequately protected with riprap to prevent erosion.

Standard 2 – Peak Rate Attenuation

Refer to Attachments 4 and 5. All storm events are attenuated to below pre-development conditions.

Standard 3 – Stormwater Recharge

Refer to Attachment 6. Stormwater recharge requirements have been provided. Standard 4 – Water Quality

Refer to Attachment 6. Treatment volume for the first 1” of rainfall has been provided. Standard 5 – Land uses with higher potential pollutant loads

Refer to the Stormwater Pollution Prevention Plan. Standard 6 – Critical Areas

There are no stormwater discharges to Zone II, Interim Wetland Protection Areas or other Critical Areas.

Standard 7 – Redevelopment

Refer to the Stormwater Pollution Prevention Plan Standard 8 – Construction period controls

Refer to the erosion and sedimentation control plan. Standard 9 – Operation and Maintenance Plan

Refer to the Operation and Maintenance Plan. Standard 10 – Illicit discharges to drainage system

Refer to the Stormwater Pollution Prevention Plan CONCLUSION Through the use of the stormwater management systems the peak runoff rates under post-developed conditions will be mitigated for discharges from the site and relative to impacts to downstream drainage facilities. The stormwater management systems have been designed to provide stormwater quality measures in accordance with the Massachusetts Stormwater Manual.

ATTACHMENT 1

General Location Map

ATTACHMENT 3

Soils Information

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ATTACHMENT 3

Pre-developed and Post-developed Drainage Area Maps

ATTACHMENT 4

Pre-developed Conditions Stormwater Calculations

Drainage Diagram for CarverPrepared by {enter your company name here} 5/12/2015

HydroCAD® 7.00 s/n 002684 © 1986-2003 Applied Microcomputer Systems

Subcat Reach Pond Link

1S

Existing Area 1 - subcatchment

5S

Existing Area 2 -subcatchmnet

Type III 24-hr 1-yr-MA Rainfall=2.70"CarverPage 2Prepared by {enter your company name here}

5/12/2015HydroCAD® 7.00 s/n 002684 © 1986-2003 Applied Microcomputer Systems

Time span=5.00-20.00 hrs, dt=0.05 hrs, 301 pointsRunoff by SCS TR-20 method, UH=SCS

Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method

Runoff Area=10.555 ac Runoff Depth=0.17"Subcatchment 1S: Existing Area 1 - subcatchment Flow Length=1,262' Tc=18.6 min CN=59 Runoff=0.77 cfs 0.152 af

Runoff Area=421,067 sf Runoff Depth=0.13"Subcatchment 5S: Existing Area 2 -subcatchmnet Flow Length=1,172' Tc=18.5 min CN=57 Runoff=0.43 cfs 0.106 af

Total Runoff Area = 20.221 ac Runoff Volume = 0.258 af Average Runoff Depth = 0.15"



Subcatchment 1S: Existing Area 1 - subcatchment

Runoff = 0.77 cfs @ 12.53 hrs, Volume= 0.152 af, Depth= 0.17"

Runoff by SCS TR-20 method, UH=SCS, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsType III 24-hr 1-yr-MA Rainfall=2.70"

Area (ac) CN Description9.642 56 Brush, Fair, HSG B0.696 85 Gravel roads, HSG B0.217 98 Paved parking & roofs

10.555 59 Weighted Average

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

7.4 178 0.0926 0.4 Sheet Flow, Sheet flow off pileRange n= 0.130 P2= 3.30"

1.8 343 0.0379 3.1 Shallow Concentrated Flow, Gravel RoadUnpaved Kv= 16.1 fps

0.8 80 0.0063 1.6 Shallow Concentrated Flow, Paved RoadPaved Kv= 20.3 fps

8.6 661 0.0166 1.3 Shallow Concentrated Flow, Open areaNearly Bare & Untilled Kv= 10.0 fps

18.6 1,262 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

0.85

0.8

0.75

0.7

0.65

0.6

0.55

0.5

0.45

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.05

0

Type III 24-hr 1-yr-MARainfall=2.70"Runoff Area=10.555 acRunoff Volume=0.152 afRunoff Depth=0.17"Flow Length=1,262'Tc=18.6 minCN=59

0.77 cfs



Subcatchment 5S: Existing Area 2 -subcatchmnet



Area (sf) CN Description400,678 56 Brush, Fair, HSG B

20,389 85 Gravel roads, HSG B421,067 57 Weighted Average


0.7 50 0.0200 1.2 Sheet Flow, gravel roadSmooth surfaces n= 0.011 P2= 3.30"

17.8 1,122 0.0110 1.0 Shallow Concentrated Flow, Shallow FlowNearly Bare & Untilled Kv= 10.0 fps

18.5 1,172 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

0.480.460.440.42

0.40.380.360.340.32

0.30.280.260.240.22

0.20.180.160.140.12

0.10.080.060.040.02

0

Type III 24-hr 1-yr-MARainfall=2.70"Runoff Area=421,067 sfRunoff Volume=0.106 afRunoff Depth=0.13"Flow Length=1,172'Tc=18.5 minCN=57

0.43 cfs




















18.6 1,262 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

2

1

0

Type III 24-hr 2-yr-MARainfall=3.30"

Runoff Area=10.555 acRunoff Volume=0.312 af

Runoff Depth=0.35"Flow Length=1,262'

Tc=18.6 minCN=59

2.14 cfs











18.5 1,172 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

1

0


Runoff Area=421,067 sfRunoff Volume=0.235 af


Tc=18.5 minCN=57

1.45 cfs




















18.6 1,262 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

10

9

8

7

6

5

4

3

2

1

0




Tc=18.6 minCN=59

9.23 cfs











18.5 1,172 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

8

7

6

5

4

3

2

1

0




Tc=18.5 minCN=57

7.27 cfs




















18.6 1,262 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0




Tc=18.6 minCN=59

15.75 cfs











18.5 1,172 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0




Tc=18.5 minCN=57

12.93 cfs




















18.6 1,262 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

34

32

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0




Tc=18.6 minCN=59

31.63 cfs











18.5 1,172 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0




Tc=18.5 minCN=57

26.98 cfs

ATTACHMENT 5

Post-developed Conditions Stormwater Management Calculations

Drainage Diagram for CarverPrepared by {enter your company name here} 5/12/2015

HydroCAD® 7.00 s/n 002684 © 1986-2003 Applied Microcomputer Systems

Subcat Reach Pond Link

2S

Proposed Area 1

6S

Proposed Area 2

3P

Infiltration Basin #1

7P

Infiltration Basin #2





Runoff Area=10.555 ac Runoff Depth=0.36"Subcatchment 2S: Proposed Area 1 Flow Length=1,218' Tc=10.8 min CN=66 Runoff=2.85 cfs 0.315 af

Runoff Area=421,067 sf Runoff Depth=1.05"Subcatchment 6S: Proposed Area 2 Flow Length=1,076' Tc=13.9 min CN=82 Runoff=9.90 cfs 0.850 af

Peak Elev=74.16' Storage=1,426 cf Inflow=2.85 cfs 0.315 afPond 3P: Infiltration Basin #1 Discarded=1.66 cfs 0.314 af Primary=0.00 cfs 0.000 af Outflow=1.66 cfs 0.314 af





Subcatchment 2S: Proposed Area 1



Area (ac) CN Description7.142 56 Brush, Fair, HSG B2.500 85 Gravel Processing Area0.696 85 Gravel roads, HSG B0.217 98 Paved Roads



2.9 178 0.9260 1.0 Sheet Flow, PileRange n= 0.130 P2= 3.30"



3.5 478 0.0200 2.3 Shallow Concentrated Flow, Gravel Processing AreaUnpaved Kv= 16.1 fps

1.8 139 0.0165 1.3 Shallow Concentrated Flow, RangeNearly Bare & Untilled Kv= 10.0 fps

10.8 1,218 Total




Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

3

2

1

0




Tc=10.8 minCN=66

2.85 cfs






Area (sf) CN Description400,678 82 Proposed Fill Area



0.7 50 0.0200 1.2 Sheet Flow, sheet flowSmooth surfaces n= 0.011 P2= 3.30"

11.6 500 0.0020 0.7 Shallow Concentrated Flow, top of Fill AreaUnpaved Kv= 16.1 fps

0.8 172 0.0465 3.5 Shallow Concentrated Flow, Fill SlopeUnpaved Kv= 16.1 fps

0.8 354 0.0150 7.2 172.26 Trap/Vee/Rect Channel Flow, SwaleBot.W=6.00' D=2.00' Z= 3.0 '/' n= 0.030

13.9 1,076 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

11

10

9

8

7

6

5

4

3

2

1

0




Tc=13.9 minCN=82

9.90 cfs



Pond 3P: Infiltration Basin #1

Inflow Area = 10.555 ac, Inflow Depth = 0.36" for 1-yr-MA eventInflow = 2.85 cfs @ 12.21 hrs, Volume= 0.315 afOutflow = 1.66 cfs @ 12.53 hrs, Volume= 0.314 af, Atten= 42%, Lag= 19.6 minDiscarded = 1.66 cfs @ 12.53 hrs, Volume= 0.314 afPrimary = 0.00 cfs @ 5.00 hrs, Volume= 0.000 af

Routing by Stor-Ind method, Time Span= 5.00-20.00 hrs, dt= 0.05 hrsPeak Elev= 74.16' @ 12.53 hrs Surf.Area= 8,683 sf Storage= 1,426 cfPlug-Flow detention time= 6.7 min calculated for 0.313 af (99% of inflow)Center-of-Mass det. time= 5.6 min ( 861.7 - 856.1 )

# Invert Avail.Storage Storage Description1 74.00' 58,224 cf Custom Stage Data (Irregular) Listed below

Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area(feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft)74.00 8,496 388.6 0 0 8,49675.00 9,690 409.1 9,086 9,086 9,85776.00 10,941 425.8 10,309 19,396 11,04377.00 12,248 444.6 11,588 30,984 12,41678.00 13,612 463.3 12,924 43,908 13,84179.00 15,032 482.1 14,316 58,224 15,332

# Routing Invert Outlet Devices1 Primary 78.00' 20.0' long x 1.0' breadth Broad-Crested Rectangular Weir

Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 Coef. (English) 2.69 2.72 2.75 2.85 2.98 3.08 3.20 3.28 3.31 3.30 3.31 3.32

2 Discarded 0.00' 0.011500 fpm Exfiltration over entire Surface area

Discarded OutFlow Max=1.66 cfs @ 12.53 hrs HW=74.16' (Free Discharge)2=Exfiltration (Exfiltration Controls 1.66 cfs)

Primary OutFlow Max=0.00 cfs @ 5.00 hrs HW=74.00' (Free Discharge)1=Broad-Crested Rectangular Weir ( Controls 0.00 cfs)




InflowOutflowDiscardedPrimary

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

3

2

1

0

Inflow Area=10.555 acPeak Elev=74.16'Storage=1,426 cf

2.85 cfs

1.66 cfs1.66 cfs

0.00 cfs







Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area(feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft)70.00 9,898 469.5 0 0 9,89871.00 11,332 488.5 10,607 10,607 11,42472.00 12,825 507.4 12,071 22,678 13,00273.00 14,376 526.3 13,593 36,271 14,64074.00 15,983 545.1 15,172 51,443 16,33075.00 17,647 563.9 16,808 68,251 18,08076.00 19,367 582.8 18,500 86,752 19,897










Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

11

10

9

8

7

6

5

4

3

2

1

0

Inflow Area=9.666 acPeak Elev=71.09'

Storage=11,708 cf

9.90 cfs

2.20 cfs2.20 cfs

0.00 cfs























10.8 1,218 Total




Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

6

5

4

3

2

1

0




Tc=10.8 minCN=66

5.88 cfs













13.9 1,076 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0




Tc=13.9 minCN=82

14.14 cfs

















Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

6

5

4

3

2

1

0

Inflow Area=10.555 acPeak Elev=74.60'Storage=5,437 cf

5.88 cfs

1.77 cfs1.77 cfs

0.00 cfs

















Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

15

1413

12

11

10

9

8

7

6

54

3

2

1

0


Storage=19,405 cf

14.14 cfs

2.38 cfs2.38 cfs

0.00 cfs























10.8 1,218 Total




Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

19181716151413121110

9876543210




Tc=10.8 minCN=66

17.27 cfs













13.9 1,076 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0




Tc=13.9 minCN=82

26.95 cfs

















Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

19181716151413121110

9876543210


Storage=24,225 cf

17.27 cfs

2.20 cfs2.20 cfs

0.00 cfs

















Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

30

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0


Storage=45,338 cf

26.95 cfs

2.94 cfs2.94 cfs

0.00 cfs























10.8 1,218 Total




Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0




Tc=10.8 minCN=66

26.62 cfs













13.9 1,076 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

40383634323028262422201816141210

86420




Tc=13.9 minCN=82

36.28 cfs

















Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0


Storage=42,168 cf

26.62 cfs

2.57 cfs2.57 cfs

0.00 cfs

















Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

40383634323028262422201816141210

86420


Storage=66,448 cf

36.28 cfs

3.35 cfs3.35 cfs

0.00 cfs























10.8 1,218 Total




Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

50

45

40

35

30

25

20

15

10

5

0




Tc=10.8 minCN=66

47.97 cfs













13.9 1,076 Total


Runoff

Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

60

55

50

45

40

35

30

25

20

15

10

5

0




Tc=13.9 minCN=82

55.84 cfs












Primary OutFlow Max=24.22 cfs @ 12.37 hrs HW=78.58' (Free Discharge)1=Broad-Crested Rectangular Weir (Weir Controls 24.22 cfs @ 2.1 fps)





Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

50

45

40

35

30

25

20

15

10

5

0


Storage=52,300 cf

47.97 cfs

27.44 cfs

2.77 cfs

24.67 cfs












Primary OutFlow Max=26.16 cfs @ 12.44 hrs HW=75.61' (Free Discharge)1=Broad-Crested Rectangular Weir (Weir Controls 26.16 cfs @ 2.1 fps)





Hydrograph

Time (hours)201918171615141312111098765

Flo

w (

cfs)

60

55

50

45

40

35

30

25

20

15

10

5

0


Storage=79,558 cf

55.84 cfs

29.98 cfs

3.58 cfs

26.40 cfs

ATTACHMENT 6

Water Quality and Recharge Calculations

ATTACHMENT 7

Infiltration Basin Mounding Analysis

use consistent units (e.g. feet & days or inches & hours) Conversion TableInput Values inch/hour feet/day

2.8500 R Recharge (infiltration) rate (feet/day) 0.67 1.330.150 Sy Specific yield, Sy (dimensionless, between 0 and 1)16.50 K Horizontal hydraulic conductivity, Kh (feet/day)* 2.00 4.00

77.500 x 1/2 length of basin (x direction, in feet)29.000 y 1/2 width of basin (y direction, in feet) hours days2.000 t duration of infiltration period (days) 36 1.50

25.000 hi(0) initial thickness of saturated zone (feet)

35.065 h(max) maximum thickness of saturated zone (beneath center of basin at end of infiltration period)10.065 Δh(max) maximum groundwater mounding (beneath center of basin at end of infiltration period)

Ground‐water Mounding, in feet

Distance from center of basin in x direction, in feet

10.065 09.875 209.269 408.776 508.117 607 248 70

This spreadsheet will calculate the height of a groundwater mound beneath a stormwater infiltration basin. More information can be found in the U.S. Geological Survey Scientific Investigations Report 2010‐5102 "Simulation of groundwater mounding beneath hypothetical stormwater infiltration basins".

The user must specify infiltration rate (R), specific yield (Sy), horizontal hydraulic conductivity (Kh), basin dimensions (x, y), duration of infiltration period (t), and the initial thickness of the saturated zone (hi(0), height of the water table if the bottom of the aquifer is the datum). For a square basin the half width equals the half length (x = y). For a rectangular basin, if the user wants the water‐table changes perpendicular to the long side, specify x as the short dimension and y as the long dimension. Conversely, if the user wants the values perpendicular to the short side, specify y as the short dimension, x as the long dimension. All distances are from the center of the basin. Users can change the distances from the center of the basin at which water‐table aquifer thickness are calculated.Cells highlighted in yellow are values that can be changed by the user. Cells highlighted in red are output values based on user‐specified inputs.The user MUST click the blue "Re‐Calculate Now" button each time ANY of the user‐specified inputs are changed otherwise necessary iterations to converge on the correct solution will not be done and values shown will be incorrect. Use consistent units for all input values (for example, feet and days)

In the report accompanying this spreadsheet (USGS SIR 2010‐5102), vertical soil permeability (ft/d) is assumed to be one‐tenth horizontal hydraulic conductivity (ft/d).

Re‐Calculate Now

12.000

Groundwater Mounding, in feet7.248 706.130 805.063 904.181 1002.840 120

Disclaimer

This spreadsheet solving the Hantush (1967) equation for ground-water mounding beneath an infiltration basin is made available to the general public as a convenience for those wishing to replicate values documented in the USGS Scientific Investigations Report 2010-5102 "Groundwater mounding beneath hypothetical stormwater infiltration basins" or to calculate values based on user-specified site conditions. Any changes made to the spreadsheet (other than values identified as user-specified) after transmission from the USGS could have unintended, undesirable consequences. These consequences could include, but may not be limited to: erroneous output, numerical instabilities, and violations of underlying assumptions that are inherent in results presented in the accompanying USGS published report. The USGS assumes no responsibility for the consequences of any changes made to the spreadsheet. If changes are made to the spreadsheet, the user is responsible for documenting the changes and justifying the results and conclusions.

0.000

2.000

4.000

6.000

8.000

10.000

12.000

0 20 40 60 80 100 120 140

Groundwater Mounding, in feet








0.658 00.644 200.600 400.564 500.517 600 456 70




Re‐Calculate Now

0.700


Disclaimer


0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0 20 40 60 80 100 120 140









15.469 015.295 2014.750 4014.314 5013.746 6013 015 70




Re‐Calculate Now

18.000


Disclaimer


0.0002.0004.0006.0008.000

10.00012.00014.00016.00018.000

0 20 40 60 80 100 120 140









4.454 04.399 204.227 404.089 503.910 603 681 70




Re‐Calculate Now

5.000


Disclaimer


0.0000.5001.0001.5002.0002.5003.0003.5004.0004.5005.000

0 20 40 60 80 100 120 140


Documents

Appendix E Stormwater Analysis Phase I Existing and ... · 6/23/2016 · Existing and Proposed Conditions . Stormwater Management Calculations ... from the stormwater management