29-Big Creek Greenway Bethelview Trailhead - Hydrology Report with Appendices.pdf

Drainage Report

Big Creek Greenway Design Services – On Call

Task 1 – Bethelview Trailhead Parking Lot Design

H&L # 1023020.02

For

Forsyth County Capital Projects

Prepared By

May 2024

Heath & Lineback Engineers, Inc.

2390 Canton Road Bldg. 200

Marietta, Georgia 30066

(770) 424-1668 * Fax: (770) 424-2907

1 Table of Contents

1.0 INTRODUCTION

a) Site Location, acreage, and current and proposed land use ………………………………………………

b) Offsite Drainage Areas ………………………………………………………………………………………………………

c) Project Methodology …………………………………………………………………………………………………………

2.0 SUMMAY TABLES

a) Storm event ……………………………………………………………………..………………………………………………..

b) Pre-developed flow rate ………..…………………………………………………………………………………………..

c) Developed flow rate ……………………………………………………………………………………………………………

d) Allowable flow rate ……………………………………………………………………………………………………………..

e) Peak elevation in the stormwater facility …………………………………………………………………………….

f) Developed velocity ………………………………………………………………………………………………………………

Appendix A - Pre-developed Drainage Map Appendix B - Pre-developed Weighted Curve Number Calculations Appendix C - Pre and Post Time of Concentration Calculations Appendix D - Developed Site Map Appendix E - Developed Weighted Curve Number Calculations Appendix F - Details of Water Quality facilities Appendix G - Water Quality Calculations Appendix H - Water Quality Performance Review Tool Appendix I - Pre-developed hydrographs and routings for the 1, 2, 10, 25 100 Year Storms Appendix J - Developed hydrographs and routings for the 1, 2, 10, 25 100 Year Storms Appendix K - Storage Calculations Appendix L - Control Structures Details

1.0 INTRODUCCION

a) Forsyth Bethelview Trail – Site Description

The jobsite, nestled in Cummings, Georgia, just east of Bethelview Road, spans approximately 3.08 acres and resides within a suburban landscape. Adjacent to the Bethelview Road Trailhead, with a gravel parking surface that currently serves the purpose of a parking lot, trees surrounding the area, and overlooking a pond.

The utilities on the jobsite include a 1.5” waterline, an existing culvert pipe structure that channels under the Big Greek Greenway trailhead, and a septic tank. Notably, upon entry, there's a 185-foot stretch of asphalt leading to the site, and electrical lines that run over Bethelview Road. Currently, three (3) designated ADA parking spots, restroom facilities and a warm-up area reside on the site.

Pre-Developed land use

Basin Name

Impervious

Area

(Ac.)

Pervious

Area

(Ac.)

Total

Area

(Ac.)

Area 1 (NW) 0.0000 0.4371 0.4371

Area 2 (NE) 0.0280 0.2631 0.2911

Area 3 (SE) 0.5413 0.0100 0.5513

Area 4 (S) 0.1703 0.0100 0.1803

Area 5 (SW) 0.4407 0.0100 0.4507

Total (Ac.) 1.1803 0.7302 1.9105

b) Offsite drainage areas

The Offsite Drainage Area of 0.44 Ac. has been identified in Drainage Maps as Basin 1, please refer to

Appendix A (Pre-developed) and Appendix D (Developed).

c) Project Methodology

The proposed drainage system has been divided into two main basins: Basin 1 and Basin 2. Basin 1 includes Area 1 (NW) with a total area of 0.44 Ac which runoff will be intercepted by Swale 1 (BMP 1), and

Area 2 (NE) with a total area of 0.73 Ac which runoff will be intercepted by Swale 2 (BMP 2). Basin 2 includes Area 3 (SE) with a total area of 0.55 Ac which runoff will be intercepted by Swale 3 (BMP 3); Area

4 (S) with a total area of 0.18 Ac which runoff will be intercepted by Swale 4 (BMP 4), and Area 5 (SW) with a total area of 0.45 Ac which runoff will be intercepted by Swale 5 (BMP 5).

a) BMP 1 & BMP 2

To eliminate contaminants through vegetative filtration, infiltration and biofiltration, Swale 1 (BMP 1) has been designed as an Enhanced Dry Swale that collects runoff from Area 1 (NW), which is considered an offsite area and therefore, it does not require treatment. However, it will be connected through an 18-inch pipe with Swale 2 (BMP 2), intended as a grass channel, part of the treatment from this Swale will be credited to Swale 1 (BMP 1).

Please refer to Appendix G for details and dimensions of the Enhanced Dry Swale (BMP 1). Calculations for this Enhanced Dry Swale are detailed in Appendix G.

b) Outlet Control Structure CS-1

The control structure CS-1 (please refer to Appendix L) is a square box of 3.5 ft x 3.5 ft and 6.17 ft high.

On its northeast face, there is a 6-inch high by 3.5 feet wide opening functioning as a vertical weir. The weir control elevation has been set at elevation 1056.55 ft (NAVD). The peak stage for 25 year and 24-hour storm is 1056.00 ft NAVD (refer to the Node Maximum Conditions Report, Swale 1 (NW), Appendix

J) and therefore, the maximum water level maintains a freeboard greater than 6 inches, 1057.55-1056.60=

0.95 ft > 0.5 ft.

Inside the box at the bottom, there is an underdrain covered for maximum infiltration. The discharge from the box is through a 36-ft 18-inch pipe, with an invert elevation of 1051.38 ft NAVD discharging into the lake at elevation of 1043.00 ft NADV, please refer to Appendix L for Control Structure details. Riprap has been placed at the outlet of the discharge for erosion control purposes.

c) BMP 3

The runoff coming from the 0.48 Ac impervious area of Area 3 (NE) will be treated in Swale 3. This treatment is planned as a Bioretention Area which reduces stormwater pollution through filtration, biological absorption, and activity microbial, using vegetation, an engineered soil mix and bottom drainage.

Please refer to Appendix G for details and dimensions of the Bioretention Area (BMP 3). Calculations for the Bioretention Area (BMP 3) are detailed in Appendix G.

d) Outlet Control Structure CS-3

The control structure CS-3 (please refer to Appendix L) is a square box of 3.5 ft x 3.5 ft and 5.58 ft high.

On its east face, there is a 6-inch high by 3.5 feet wide opening functioning as a vertical weir. The weir control elevation has been set at elevation 1051.03 ft (NAVD). The peak stage for 25 year and 24-hour storm is 1050.27 ft NAVD (refer to the Node Maximum Conditions Report, Swale 3 (SE) Appendix J) and therefore, the maximum water level maintains a freeboard greater than 6 inches, 1051.03-1050.27=0.76 ft > 0.5 ft.

Inside the box at the bottom, there is an underdrain covered for maximum infiltration. The discharge from the box is through a 79-ft 18-inch pipe, with an invert elevation of 1045.45 ft NAVD discharging into the

Bioretention Area BMP 3 at elevation of 1042.00 ft NADV, please refer to Appendix L for Control Structure details. Riprap has been placed at the outlet of the discharge for erosion control purposes.

e) BMP 4

The runoff coming from the 0.16 Ac impervious area of Area 4 (S) will be treated in Swale 4 (BMP 4). This treatment is intended to reduce stormwater pollution through filtration, biological absorption, and microbial activity, using vegetation, an engineered soil mix and underdrainage.

Please refer to Appendix G for details and dimensions of the Bioretention Area (BMP 4). Calculations for the Bioretention Area (BMP 4) are detailed in Appendix G.

f) Outlet Control Structure CS-4

The control structure CS-4 (please refer to Appendix L) is a square box of 3.5 ft x 3.5 ft and 5.58 ft high.

On its North face, there is a 6-inch high by 3.5 feet wide opening functioning as a vertical weir. The weir control elevation has been set at elevation 1048.05 ft (NAVD). The peak stage for 25 year and 24-hour storm is 1048.17 ft NAVD (refer to the Node Maximum Conditions Report, Swale 4 (S) Appendix J) and therefore, the maximum water level maintains a freeboard greater than 6 inches, 1049.05-1048.17=0.88 ft > 0.5 ft.

Inside the box at the bottom, there is an underdrain covered for maximum infiltration. The discharge from the box is through a 7-ft 24-inch pipe, with an invert elevation of 1043.47 ft NAVD discharging into the lake at elevation of 1042.00 ft NADV, please refer to Appendix L for Control Structure details. Riprap has

This structure is connected to the control structure CS-5 (invert elev. 1044.23 ft NADV).

g) BMP 5

Area 5 (NW) is located in the northwest section of the parking area, and it has an impervious area of 0.37

Ac. and the runoff coming from the impervious area will be treated in Swale 5 (BMP 5). This treatment is intended to reduce stormwater pollution through filtration, biological absorption, and microbial activity, using vegetation, an engineered soil mix and underdrainage.

Please refer to Appendix G for details and dimensions of the Bioretention Area (BMP 5). Calculations for the Bioretention Area (BMP 5) are detailed in Appendix G.

h) Outlet Control Structure CS-5

The control structure CS-5 (please refer to Appendix L) is a square box of 3.5 ft x 3.5 ft and 5.58 ft high.

On its North face, there is a 6-inch high by 3.5 feet wide opening functioning as a vertical weir. The weir control elevation has been set at elevation 1049.01 ft (NAVD). The peak stage for 25 year and 24-hour storm is 1049.22 ft NAVD (refer to the Node Maximum Conditions Report, Swale 5 (NW) Appendix J) and therefore, the maximum water level maintains a freeboard greater than 6 inches, 1050.01-1049.22=0.79 ft > 0.5 ft.

Inside the box at the bottom, there is an underdrain covered for maximum infiltration. The discharge from the box is through a 21-ft 18-inch pipe, with an invert elevation of 1044.43 ft NAVD discharging into the lake at elevation of 1044.23 ft NADV, please refer to Appendix L for Control Structure details. Riprap has

2.0 SUMMARY TABLES

Summary table for LAKE (SWALE 1) discharge point

Storm

Event

Pre-Developed

Flow rate

Developed

Flow rate

Allowable

Flow Rate

Peak Elev.

SWALE 1

(NW)

Peak Elev.

SWALE 2

(NE)

Developed

Velocity cfs cfs cfs ft, (NAVD) ft, (NAVD) ft/seg

01Y24H 0.81 0.51 46.58 1053.02 1061.62 8.70

02Y24H 0.96 0.76 46.58 1054.04 1061.64 9.81

25Y24H 1.86 1.34 46.58 1054.22 1061.75 11.64

100Y24H 0.71 0.58 46.58 1054.25 1061.68 9.05

Summary table for LAKE (SWALE 4) discharge point

Storm

Event

Pre-Developed

Flow rate

Developed

Flow rate

Allowable

Flow Rate

Peak Elev.

SWALE 4

(S)

Peak Elev.

SWALE 5

(SW)

Developed

Velocity cfs cfs cfs ft, (NAVD) ft, (NAVD) ft/seg

01Y24H 0.81 0.51 48.26 1047.45 1049.20 5.02

02Y24H 0.96 0.76 48.26 1047.47 1049.23 5.66

25Y24H 1.86 1.34 48.26 1047.51 1049.30 6.71

100Y24H 0.71 0.58 48.26 1047.45 1049.19 5.22

Summary table for BIG CREEK (SWALE 3) discharge point

Storm

Event

Pre-Developed

Flow rate

Developed

Flow rate

Allowable

Flow Rate

Peak Elev.

SWALE 3

(SE)

Developed

Velocity cfs cfs cfs ft, (NAVD) ft/seg

01Y24H 0.69 0.57 47.05 1048.77 9.06

02Y24H 0.79 0.70 47.05 1048.79 9.64

25Y24H 1.26 1.18 47.05 1048.86 11.29

100Y24H 0.41 0.40 47.05 1048.74 8.14

Appendix A

Pre-developed Drainage Map

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Scale:

05/03/2024

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DESIGN TICKET NO. 230831-005347

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Georgia License No.

To the best of my knowledge these plans and specifications comply with the applicable minimum building codes.

VICTOR H. HERRERA

047786

Certificate of Authorization No.

2390 Canton Road, Building 200

Marietta, Georgia 30066 Tel : 770.424.1668 Fax :

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CTOR H. HERRERA

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CTOR H. HERRERA

BASIN 1

(OFFSITE)

BASIN 2

BASIN 3

BASIN 4

BASIN 5

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A P dtorres Area Measurement

0.28 ac dtorres Area Measurement

0.41 ac dtorres Area Measurement

0.32 ac dtorres Area Measurement

0.3 ac dtorres Image dtorres Area Measurement

0.64 ac dtorres Polylength Measurement 1,199.87 ft

Appendix B

Pre-Developed Conditions

Weighted Curve Number Calculations

Pre-Development Runoff Curve Number (CN)

Basin Cover Description

Soil

Hydrologic

Group

CN Area (Ac) CN x A Composite

CN

Woods - (good) B 55 0.4271 23.49

Open Space (poor) - grass < 50% B 79 0.0100 0.79

0.4371 24.28

Woods - (good) B 55 0.1248 6.86

Open Space (poor) - grass < 50% B 79 0.1383 10.92

Imperv. - paved parking lots,roofs,drives B 98 0.0280 2.75

0.2911 20.54

Imperv. - paved parking lots,roofs,drives B 98 0.5413 53.05

Open Space (poor) - grass < 50% B 79 0.0100 0.79

0.5513 53.84

Imperv. - paved parking lots,roofs,drives B 98 0.1703 16.69

Open Space (poor) - grass < 50% B 79 0.0100 0.79

0.1803 17.48

Imperv. - paved parking lots,roofs,drives B 98 0.4407 43.19

Open Space (poor) - grass < 50% B 79 0.0100 0.79

0.4507 43.98

Totals = 1.9105 160.11 83.80

Note: * Considered Off Site Area, so it does not need treatment

Area 5 (SW)

Total Area 5 (SW)

Area 3 (SE)

Total Area 3 (SE)

Area 4 (S)

Total Area 4 (S)

Area 1 (NW)*

Total Area 1 (NW)*

Area 2 (NE)

Total Area 2 (NE)

Appendix C

Pre and Post Time of Concentration Calculations

Date:

Designed By:

Approved By:

1- Sheet Flow (50 ft)

Sheet flow can be calculated using the following formula:

Where:

Tt = travel time (hr) n = Manning roughness coefficient (see Table 2.1.5-2)

0.800

L = flow length (ft), L= 50 ft

P2 = 2-year, 24-hour rainfall

P2 = 3.82 in

S = land slope (ft/ft)

S= 0.22 ft/ft

0.42 * (0.8*50)^0.8

60 * (3.82)^0.5* (0.22)^0.4

Tt = 0.12553 hr = 7.53 min

2- Shallow Concentrated Flow

Average veloci0es for es0ma0ng travel 0me for shallow concentrated flow can be computed from using Figure 2.1.5-5, or the following equations.

Unpaved V = 16.13(S)^ 0.5

Paved V = 20.33(S)^ 0.5

Where:

V = average velocity (ft/s)

S = slope of hydraulic grade line (watercourse slope, ft/ft)

S= 0.40 ft/ft

TIME OF CONCENTRATION

AREA 1 (NW)

March 6, 2024

J.R.

L.F.

Woods: Dense underbrush…

Tt =

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

V = 16.13(S)^0.5

V = 16.13 * (0.4)^0.5

V = 10.20 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 66 ft

V = average velocity (ft/s)

3600 = conversion factor from seconds to hours

Tt = 0.0018 hr = 0.11 min

3- Open Channels

Manning's equation is :

Where:

V = average velocity (ft/s)

A = cross sectional flow area (ft2)

Depth of Water "y" = 1.50 ft

Bottom Width "b" = 4.00 ft

Left Side Slope "ZL" = 1:2

Right Side Slope "ZR" = 1:2

A = 10.50 ft

Pw = wetted perimeter (ft)

Pw = 10.71 ft

R = hydraulic radius (ft) and is equal to A/Pw

R= 0.98 ft

S = slope of the hydraulic grade line (ft/ft)

S= n = Manning's roughness coefficient for open channel flow

0.150

Unpaved

66.00

Grass: Short grass prairie…

3600 *10.2 Tt =

0.0400 ft/ft

1.49 * (0.98)^2/3*(0.04)^1/2

0.15

V = 1.96 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 153 ft

V = average velocity (cfs)

3600 = conversion factor from seconds to hours

Tt = 0.02168 hr = 1.30 min

Total Time of Concentration

TC = 7.53+ 0.11+1.3

TC =

If Tc < 10 min, them Tc = 10 min

8.94 min

V =

Tt = 153.00

3600 *1.96

Approved By:

1- Sheet Flow (50 ft)

Sheet flow can be calculated using the following formula:

Where:

Tt = travel time (hr) n = Manning roughness coefficient (see Table 2.1.5-2)

0.150

L = flow length (ft), L= 50 ft

P2 = 2-year, 24-hour rainfall

P2 = 3.82 in

S = land slope (ft/ft)

S= 0.10 ft/ft

0.42 * (0.15*50)^0.8

60 * (3.82)^0.5* (0.1)^0.4

Tt = 0.04509 hr = 2.71 min

2- Shallow Concentrated Flow

Average veloci0es for es0ma0ng travel 0me for shallow concentrated flow can be computed from using Figure 2.1.5-5, or the following equations.

Unpaved V = 16.13(S)^ 0.5

Paved V = 20.33(S)^ 0.5

Where:

V = average velocity (ft/s)

S = slope of hydraulic grade line (watercourse slope, ft/ft)

S= 0.10 ft/ft

March 6, 2024

J.R.

L.F.

TIME OF CONCENTRATION

AREA 2 (NE)

Grass: Short grass prairie…

Tt =

BETHELVIEW ROAD

V = 16.13(S)^0.5

V = 16.13 * (0.1)^0.5

V = 5.10 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 139 ft

V = average velocity (ft/s)

3600 = conversion factor from seconds to hours

Tt = 0.00757 hr = 0.45 min

3- Open Channels

Manning's equation is :

Where:

V = average velocity (ft/s)

A = cross sectional flow area (ft2)

Depth of Water "y" = 1.50 ft

Bottom Width "b" = 4.00 ft

Left Side Slope "ZL" = 1:2

Right Side Slope "ZR" = 1:2

A = 10.50 ft

Pw = wetted perimeter (ft)

Pw = 10.71 ft

R = hydraulic radius (ft) and is equal to A/Pw

R= 0.98 ft

S = slope of the hydraulic grade line (ft/ft)

S= n = Manning's roughness coefficient for open channel flow

0.150

0.0098 ft/ft

Unpaved

Tt = 139.00

3600 *5.1

Grass: Short grass prairie…

1.49 * (0.98)^2/3*(0.0098)^1/2

V = 0.97 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 100 ft

V = average velocity (cfs)

3600 = conversion factor from seconds to hours

Tt = 0.02864 hr = 1.72 min

Total Time of Concentration

TC = 2.71+ 0.45+1.72

TC = 4.88 min

If Tc < 10 min, them Tc = 10 min

V =

Tt = 100.00

3600 *0.97

Approved By:

1- Sheet Flow (100 ft)

Sheet flow can be calculated using the following formula:

Where:

Tt = travel time (hr) n = Manning roughness coefficient (see Table 2.1.5-2)

0.011

L = flow length (ft), L= 100 ft

P2 = 2-year, 24-hour rainfall

P2 = 3.82 in

S = land slope (ft/ft)

S= 0.10 ft/ft

0.42 * (0.011*100)^0.8

60 * (3.82)^0.5* (0.1)^0.4

Tt = 0.00971 hr = 0.58 min

2- Shallow Concentrated Flow

Average veloci0es for es0ma0ng travel 0me for shallow concentrated flow can be computed from using Figure 2.1.5-5, or the following equations.

Unpaved V = 16.13(S)^ 0.5

Paved V = 20.33(S)^ 0.5

Where:

V = average velocity (ft/s)

S = slope of hydraulic grade line (watercourse slope, ft/ft)

S= 0.10 ft/ft

March 6, 2024

J.R.

L.F.

TIME OF CONCENTRATION

AREA 3 (SE)

Smooth surfaces (concrete, asphalt, gravel, or bare soil)…

Tt =

BETHELVIEW ROAD

V = 20.33(S)^0.5

V = 20.33 * (0.1)^0.5

V = 6.43 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 0 ft

V = average velocity (ft/s)

3600 = conversion factor from seconds to hours

Tt = 0 hr = 0.00 min

3- Open Channels

Manning's equation is :

Where:

V = average velocity (ft/s)

A = cross sectional flow area (ft2)

Depth of Water "y" = 1.00 ft

Bottom Width "b" = 12.00 ft

Left Side Slope "ZL" = 1:2

Right Side Slope "ZR" = 1:2

A = 14.00 ft

Pw = wetted perimeter (ft)

Pw = 16.47 ft

R = hydraulic radius (ft) and is equal to A/Pw

R= 0.85 ft

S = slope of the hydraulic grade line (ft/ft)

S= n = Manning's roughness coefficient for open channel flow

0.150

0.0050 ft/ft

Paved

Tt = 0.00

3600 *6.43

Grass: Short grass prairie…

1.49 * (0.85)^2/3*(0.005)^1/2

V = 0.63 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 135 ft

V = average velocity (cfs)

3600 = conversion factor from seconds to hours

Tt = 0.05952 hr = 3.57 min

Total Time of Concentration

TC = 0.58+ 0+3.57

TC = 4.15 min

If Tc < 10 min, them Tc = 10 min

V =

Tt = 135.00

3600 *0.63

Approved By:

1- Sheet Flow (100 ft)

Sheet flow can be calculated using the following formula:

Where:

Tt = travel time (hr) n = Manning roughness coefficient (see Table 2.1.5-2)

0.011

L = flow length (ft), L= 100 ft

P2 = 2-year, 24-hour rainfall

P2 = 3.82 in

S = land slope (ft/ft)

S= 0.10 ft/ft

0.42 * (0.011*100)^0.8

60 * (3.82)^0.5* (0.1)^0.4

Tt = 0.00971 hr = 0.58 min

2- Shallow Concentrated Flow

Average veloci0es for es0ma0ng travel 0me for shallow concentrated flow can be computed from using Figure 2.1.5-5, or the following equations.

Unpaved V = 16.13(S)^ 0.5

Paved V = 20.33(S)^ 0.5

Where:

V = average velocity (ft/s)

S = slope of hydraulic grade line (watercourse slope, ft/ft)

S= 0.10 ft/ft

March 6, 2024

J.R.

L.F.

TIME OF CONCENTRATION

AREA 4 (S)

Smooth surfaces (concrete, asphalt, gravel, or bare soil)…

Tt =

BETHELVIEW ROAD

V = 6.43 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 0 ft

V = average velocity (ft/s)

3600 = conversion factor from seconds to hours

Tt = 0 hr = 0.00 min

3- Open Channels

Manning's equation is :

Where:

V = average velocity (ft/s)

A = cross sectional flow area (ft2)

Depth of Water "y" = 1.00 ft

Bottom Width "b" = 13.00 ft

Left Side Slope "ZL" = 1:2

Right Side Slope "ZR" = 1:2

A = 15.00 ft

Pw = wetted perimeter (ft)

Pw = 17.47 ft

R = hydraulic radius (ft) and is equal to A/Pw

R= 0.86 ft

S = slope of the hydraulic grade line (ft/ft)

S= n = Manning's roughness coefficient for open channel flow

0.150

0.0050 ft/ft

Paved

Tt = 0.00

Grass: Short grass prairie…

1.49 * (0.86)^2/3*(0.005)^1/2

V = 0.64 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 40 ft

V = average velocity (cfs)

3600 = conversion factor from seconds to hours

Tt = 0.01736 hr = 1.04 min

Total Time of Concentration

TC = 0.58+ 0+1.04

TC = 1.62 min

If Tc < 10 min, them Tc = 10 min

V =

Tt = 40.00

3600 *0.64

Approved By:

1- Sheet Flow (100 ft)

Sheet flow can be calculated using the following formula:

Where:

Tt = travel time (hr) n = Manning roughness coefficient (see Table 2.1.5-2)

0.011

L = flow length (ft), L= 100 ft

P2 = 2-year, 24-hour rainfall

P2 = 3.82 in

S = land slope (ft/ft)

S= 0.10 ft/ft

0.42 * (0.011*100)^0.8

60 * (3.82)^0.5* (0.1)^0.4

Tt = 0.00971 hr = 0.58 min

2- Shallow Concentrated Flow

Average veloci0es for es0ma0ng travel 0me for shallow concentrated flow can be computed from using Figure 2.1.5-5, or the following equations.

Unpaved V = 16.13(S)^ 0.5

Paved V = 20.33(S)^ 0.5

Where:

V = average velocity (ft/s)

S = slope of hydraulic grade line (watercourse slope, ft/ft)

S= 0.10 ft/ft

March 6, 2024

J.R.

L.F.

TIME OF CONCENTRATION

AREA 5 (SW)

Smooth surfaces (concrete, asphalt, gravel, or bare soil)…

Tt =

BETHELVIEW ROAD

V = 6.43 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 0 ft

V = average velocity (ft/s)

3600 = conversion factor from seconds to hours

Tt = 0 hr = 0.00 min

3- Open Channels

Manning's equation is :

Where:

V = average velocity (ft/s)

A = cross sectional flow area (ft2)

Depth of Water "y" = 1.00 ft

Bottom Width "b" = 11.00 ft

Left Side Slope "ZL" = 1:2

Right Side Slope "ZR" = 1:2

A = 13.00 ft

Pw = wetted perimeter (ft)

Pw = 15.47 ft

R = hydraulic radius (ft) and is equal to A/Pw

R= 0.84 ft

S = slope of the hydraulic grade line (ft/ft)

S= n = Manning's roughness coefficient for open channel flow

0.150

0.0050 ft/ft

Paved

Tt = 0.00

Grass: Short grass prairie…

1.49 * (0.84)^2/3*(0.005)^1/2

V = 0.63 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 122 ft

V = average velocity (cfs)

3600 = conversion factor from seconds to hours

Tt = 0.05379 hr = 3.23 min

Total Time of Concentration

TC = 0.58+ 0+3.23

TC = 3.81 min

If Tc < 10 min, them Tc = 10 min

V =

Tt = 122.00

Appendix D

Developed Site Map

B E

TH

E

LV

IE

W R

O A

D (V

A R

IA

B

LE

' R

/W

P/L

Revisions

Date:

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LE

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AT

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:\P R

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ED

B Y:

g la dy s an gu lo

PL

O T

D

AT

E:

Designed By:

Drawn By:

Checked By:

BCC Project No.:

SHEET NO:

Scale:

05/03/2024

J.R.

J.M.

R.L.

1023020.01

SH

EE

T

TI

TL

E:

DESIGN TICKET NO. 230831-005347

AS SHOWN

B E

T H

E

LV

IE

W

R O

A D

T R

A

IL

H E

A D

LA

N

D L

O T

8, N

D D

IS

TR

IC

T, S

T S

E C

TI

O

N

B E

TH

E

LV

IE

W R

D C

IT

Y

O F

C U

M M

IN

G

, G E

O R

G

IA

, 3

Georgia License No.

To the best of my knowledge these plans and specifications comply with the applicable minimum building codes.

VICTOR H. HERRERA

047786

Certificate of Authorization No.

2390 Canton Road, Building 200

Marietta, Georgia 30066 Tel : 770.424.1668 Fax :

w w w . h e a t h - l i n e b a c k . c o m

STATE OF

LICENSE

PROFESSIONAL ENGIN

EE

R

GEORGIA

No.047786V I

CTOR H. HERRERA

P O

S T-

D E

V E

LO

P

M E

N T

D R

A

IN

A G

E B

A S

IN

FIGURE-2

STATE OF

LICENSE

PROFESSIONAL ENGIN

EE

R

GEORGIA

No.047786V

IC

TOR H. HERRERA

STATE OF

LICENSE

PROFESSIONAL ENGIN

EE

R

GEORGIA

No.047786V I

CTOR H. HERRERA

BASIN 1

(OFFSITE)

BASIN 2

BASIN 3

BASIN 4

BASIN 5

D E

V E

LO

P

E D

S

IT

E M

A P dtorres Area Measurement

0.32 ac dtorres Polylength Measurement 1,199.87 ft dtorres Area Measurement Basin 1 (OFFSITE) dtorres Area Measurement Basin 2 dtorres Area Measurement

0.64 ac dtorres Image

Appendix E

Developed Weighted Curve Number Calculations

Post-Development Runoff Curve Number (CN)

Basin Cover Description

Soil

Hydrologic

Group

CN Area (Ac) CN x A Composite

CN

Woods - (good) B 55 0.3776 20.77

Open Space (good) - grass >75% B 61 0.0595 3.63

0.4371 24.40

Woods - (good) B 55 0.0906 4.98

Open Space (good) - grass >75% B 61 0.1725 10.52

Imperv. - paved parking lots,roofs,drives B 98 0.0280 2.75

0.2911 18.25

Imperv. - paved parking lots,roofs,drives B 98 0.4782 46.86

Open Space (good) - grass >75% B 61 0.0731 4.46

0.5513 51.32

Imperv. - paved parking lots,roofs,drives B 98 0.1583 15.51

Open Space (good) - grass >75% B 61 0.0220 1.34

0.1803 16.86

Imperv. - paved parking lots,roofs,drives B 98 0.3724 36.50

Open Space (good) - grass >75% B 61 0.0783 4.77

0.4507 41.27

Totals = 1.9105 152.10 80

Note: * Considered Off Site Area, so it does not need treatment

Total Area 4 (S)

Total Area 5 (SW)

Area 3 (SE)

Area 4 (S)

Area 5 (SW)

Total Area 3 (SE)

Total Area 1 (NW)*

Total Area 2 (NE)

Area 1 (NW)*

Area 2 (NE)

Appendix F

Details of Water Quality Facilities

FOREST Match to existing ground

Match to existing ground

1055.05 i = 4% i = 4% i = 4% 1061.17

1057.55

71.10 1064.59

153.00

PARKING

Match to existing ground Match to existing ground

.0

1063.97 i = 2.93% 1061.04

1066.97 PARKING 1064.04

100.00

.0

SWALE 1 (NW)

ENHANCED DRAY SWALE (W/ UNDERDRAIN)

GRASS CHANNEL (A HYDROLOGIC SOIL)

.8

.0

.8

.0

.0

.6

71.50 4.00

.0

SWALE 2 (NE)

.0

.0

.0

.0

.0

El. 1059.81

El. 1057.89 El. 1058.31

PARKING 1056.84

1051.03

1049.03 i = 0.50% 1049.705

1051.03 1051.03

BIG CREEK

135.00

1049.05 PARKING

1048.87

1047.05 i = 0.50% 1047.25

1048.87 1048.87

LAKE

40.00

SWALE 3 (SE)

.2

.0

.2

.0

.6

.0

SWALE 4 (S)

.2

.6

.0

.4

.6

BIORETENTION BASIN (W/ UNDERDRAIN)

.0

.0

.9

BIORETENTION BASIN (W/ UNDERDRAIN)

LAKE

1050.01 1050.01

1048.01 i = 0.50% 1048.62

1050.01

PARKING 1056.91

122.00

.3

SWALE 5 (NW)

.0

.5

.0

.0

.0

.7

BIORETENTION BASIN (W/ UNDERDRAIN)

Appendix G

Water Quality Calculations

Approved By:

Project Data

Basin Name:

Total Area: 19040 ft2 = 0.44 Ac.

Impervious Area: 0 ft2 = 0.00 Ac. 0%

Length of Swale: 153 ft

Swale Slope: 0.04 ft/ft k = Hydraulic conductivity: 22.2 in/hr (Test I-1)

Runoff Reduction Volume (RRv)

𝑅𝑣 = Volumetricrunoffcoefficient = 0.05+0.009(I)

𝑅𝑣 = 0.0500

RRv = 79 ft3

Storage Volume

14.00 '

1057.55

10.00 '

1056.55

1055.05

2 2

Engineered Soil Media

(30 in)

1052.55

Gravel

(6 in) 1051.55

2.00 '

4.00 '

Volume Provided is: 𝑉𝑃 = 𝑃𝑉+ 𝑉𝐸𝑆(𝑁𝐸𝑆) + 𝑉𝐴(𝑁𝐴)

May 9, 2024

J.R.

L.F.

Area 1 (NW)

'' 1 1

ENHANCED SWALE

BMP 1

BETHELVIEW ROAD

Where:

VP = Volume Provided (temporary storage)

PV = Ponding Volume….................................................. 1589 ft3

VES = Volume of Engineered Soils…..................................... 1470 ft3

NES = Porosity of Engineered Soil…............................. (use 0.25) 0.25

VA = Volume of Aggregate….............................................. 441 ft3

NA = Porosity of Aggregate….................................. 0.4

VP = 1589+1470(0.25) + 441(0.4)

VP = 2133 ft3

IF RRv < VP, them is OK

Verify that the Enhanced Dry Swale will drain in the specified timeframes.

a) Ponded volume should drain within 24 hours

Where:

Af = Top surface area of filter media…..................................... 588 ft2

PV = Ponding volume…........................................................... 1589 ft3 df = Filter media depth…................…..................................... 2.5 ft k = Hydraulic conductivity…...................…..................................... 44.4 ft/day hf = Average water depth…............…..................................... 0.75 ft tf = Drain time (days)

44.4 * (0.75 + 2.5) * 588 t f = 0.05 days = 1.12 hr

IF tf < 24 hr, them is OK, Ponded Volume drain within 24 hours

b) Enhanced Dry Swale will drain should drain within 72 hours

Where:

VP = total volume provided ….................…................................ 2133 ft3 kdesign = hydraulic conductivity…............................................ 22.2 in/hr (Test I-1)

Safety factor of 2 …..............….........................................22.2 ft/day

Aa= bottom surface area of aggregate….............................................306 ft2 tf = Drain time (days)

22.2 * 306 t f = 0.31 days = 7.54 hr t f = 1589*2.5 t f =

IF tf < 72 hr, them is OK, Enhanced Dry Swale drain within 72 hours

Calculate the number of check dams, height, and spacing needed for the minimum swale length.

a) Segment Length (L1) = Check Dam Height / swale slope

L1 = 1.50 / 0.04

L1 = 37.5 ft

b) Segment Volume (WQ1) = V1+V2

V1 = ((0 + (((10+4)/2) * 1.5))/2)*37.5

V1 = 197.00 ft3

V2 = (0+ (10* ((18/12)*2)))/2)*1.5

V2 = 22.50 ft3

WQ1 = 197+ 22.5

WQ1 = 219.50 ft3

b) Number of Segments Required (N) = WQV/WQ1

N = 268 / 219.5

N = 1.22 (Round up)

N = 2

c) Number of Check Dams (ND) = Number of Segments Required (N) -1

ND = 2 - 1

ND = 1

V1 V2

Approved By:

Project Data

Basin Name:

Total Area: 24014 ft2 = 0.55 Ac.

Impervious Area: 20829 ft

= 0.48 Ac. 87%

Length of Swale: 135 ft k = Hydraulic conductivity: 2.5 in/hr (Test I-3)

Runoff Reduction Volume (RRv)

𝑅𝑣 = Volumetric runoff coefficient = 0.05+0.009(I)

𝑅𝑣 = 0.8306

RRv = 1662 ft3

Forebay storage (FS)

VFB = Impervious Area x 0.1 in

VFB = 0.48 Ac. X 0.1 in

VFB = 0.048 Ac.-in

VFB = 174 ft

Storage Volume

18.00 '

1051.03

14.00 '

1050.03

2 2

Hardwood Mulch (3 to 4 in) 3

Engineered Soil Media

(24 to 48 in)

No. 8 or 89 Aggregate 2

(2 to 3 in)

No. 57 Aggregate

(12 in)

2.67 '

5.00 '

10.00 '

May 9, 2024

J.R.

L.F.

Area 3 (SE)

'' 1 1

BIORETENTION AREA

BMP 3

BETHELVIEW ROAD

Volume Provided is: 𝑉𝑃 = 𝑃𝑉+ 𝑉𝐸𝑆(𝑁𝐸𝑆) + 𝑉𝐴(𝑁𝐴)

VP = Volume Provided (temporary storage)

PV = Ponding Volume….................................................. 1600 ft

VES = Volume of Engineered Soils…..................................... 1800 ft

NES = Porosity of Engineered Soil…............................. (use 0.25) 0.25

VA = Volume of Aggregate….............................................. 560 ft3

NA = Porosity of Aggregate….................................. 0.4

VP = 1600+1800(0.25) + 560(0.4)

VP = 2274 ft3

IF RRv < VP, them is OK

Verify that the bioretention basin will drain in the specified timeframes.

a) Ponded volume should drain within 24 hours

Where:

Af = Top surface area of filter media…..................................... 1170 ft2

PV = Ponding volume…........................................................... 1600 ft3 df = Filter media depth…................…..................................... 2 ft k = Hydraulic conductivity…...................…..................................... 5 ft/day hf = Average water depth…............…..................................... 0.5 ft tf = Drain time (days)

5 * (0.5 + 2) * 1170 t f = 0.22 days = 5.25 hr

IF tf < 24 hr, them is OK, Ponded Volume drain within 24 hours

b) Bioretention basin should drain within 72 hours

Where:

VP = total volume provided ….................…................................ 2274 ft3 kdesign = hydraulic conductivity…............................................ 2.5 in/hr

Safety factor of 2…..............….........................................2.5 ft/day

Aa= bottom surface area of aggregate …............................................330 ft2 tf = Drain time (days)

2.5 * 330 t f = 2.76 days = 66.15 hr

IF tf < 72 hr, them is OK, Bioretention basin drain within 72 hours t f = 1600*2

Approved By:

Project Data

Basin Name:

Total Area: 7855 ft2 = 0.18 Ac.

Impervious Area: 6895 ft

= 0.16 Ac. 88%

Length of Swale: 40 ft k = Hydraulic conductivity: 6.7 in/hr (Test I-2)

Runoff Reduction Volume (RRv)

𝑅𝑣 = Volumetric runoff coefficient = 0.05+0.009(I)

𝑅𝑣 = 0.8400

RRv = 550 ft3

Forebay storage (FS)

VFB = Impervious Area x 0.1 in

VFB = 0.16 Ac. X 0.1 in

VFB = 0.016 Ac.-in

VFB = 58 ft

Storage Volume

18.00 '

1049.05

14.00 '

1048.05

2 2

Hardwood Mulch (3 to 4 in) 3

Engineered Soil Media

(24 to 48 in)

No. 8 or 89 Aggregate 2

(2 to 3 in)

No. 57 Aggregate

(12 in)

2.67 '

5.00 '

10.00 '

May 10, 2024

J.R.

L.F.

Area 4 (S)

'' 1 1

BIORETENTION AREA

BMP 4

BETHELVIEW ROAD

Volume Provided is: 𝑉𝑃 = 𝑃𝑉+ 𝑉𝐸𝑆(𝑁𝐸𝑆) + 𝑉𝐴(𝑁𝐴)

VP = Volume Provided (temporary storage)

PV = Ponding Volume….................................................. 460 ft

VES = Volume of Engineered Soils…..................................... 470 ft

NES = Porosity of Engineered Soil…............................. (use 0.25) 0.25

VA = Volume of Aggregate….............................................. 135 ft

NA = Porosity of Aggregate….................................. 0.4

VP = 460+470(0.25) + 135(0.4)

VP = 632 ft

IF RRv < VP, them is OK

Verify that the bioretention basin will drain in the specified timeframes.

a) Ponded volume should drain within 24 hours

Where:

Af = Top surface area of filter media…..................................... 315 ft2

PV = Ponding volume…........................................................... 460 ft3 df = Filter media depth…................…..................................... 2 ft k = Hydraulic conductivity…...................….....................................13.4 ft/day hf = Average water depth…............…..................................... 0.5 ft tf = Drain time (days)

13.4 * (0.5 + 2) * 315 t f = 0.09 days = 2.09 hr

IF tf < 24 hr, them is OK, Ponded Volume drain within 24 hours

b) Bioretention basin should drain within 72 hours

Where:

VP = total volume provided ….................…................................ 632 ft3 kdesign = hydraulic conductivity…............................................ 6.7 in/hr

Safety factor of 2…..............….........................................6.7 ft/day

Aa= bottom surface area of aggregate …..................................... 76 ft2 tf = Drain time (days)

6.7 * 76 t f = 1.24 days = 29.79 hr

IF tf < 72 hr, them is OK, Bioretention basin drain within 72 hours t f = 460*2

Approved By:

1- Sheet Flow (100 ft)

Sheet flow can be calculated using the following formula:

Where:

Tt = travel time (hr) n = Manning roughness coefficient (see Table 2.1.5-2)

0.011

L = flow length (ft), L= 100 ft

P2 = 2-year, 24-hour rainfall

P2 = 3.82 in

S = land slope (ft/ft)

S= 0.10 ft/ft

0.42 * (0.011*100)^0.8

60 * (3.82)^0.5* (0.1)^0.4

Tt = 0.00971 hr = 0.58 min

2- Shallow Concentrated Flow

Average veloci0es for es0ma0ng travel 0me for shallow concentrated flow can be computed from using Figure 2.1.5-5, or the following equations.

Unpaved V = 16.13(S)^ 0.5

Paved V = 20.33(S)^ 0.5

Where:

V = average velocity (ft/s)

S = slope of hydraulic grade line (watercourse slope, ft/ft)

S= 0.10 ft/ft

March 6, 2024

J.R.

L.F.

TIME OF CONCENTRATION

AREA 5 (SW)

Smooth surfaces (concrete, asphalt, gravel, or bare soil)…

Tt =

BETHELVIEW ROAD

V = 6.43 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 0 ft

V = average velocity (ft/s)

3600 = conversion factor from seconds to hours

Tt = 0 hr = 0.00 min

3- Open Channels

Manning's equation is :

Where:

V = average velocity (ft/s)

A = cross sectional flow area (ft2)

Depth of Water "y" = 1.00 ft

Bottom Width "b" = 11.00 ft

Left Side Slope "ZL" = 1:2

Right Side Slope "ZR" = 1:2

A = 13.00 ft

Pw = wetted perimeter (ft)

Pw = 15.47 ft

R = hydraulic radius (ft) and is equal to A/Pw

R= 0.84 ft

S = slope of the hydraulic grade line (ft/ft)

S= n = Manning's roughness coefficient for open channel flow

0.150

0.0050 ft/ft

Paved

Tt = 0.00

Grass: Short grass prairie…

1.49 * (0.84)^2/3*(0.005)^1/2

V = 0.63 cfs

Travel time: ratio of flow length to flow velocity:

Where:

Tt = travel time (hr)

L = flow length (ft)

L= 122 ft

V = average velocity (cfs)

3600 = conversion factor from seconds to hours

Tt = 0.05379 hr = 3.23 min

Total Time of Concentration

TC = 0.58+ 0+3.23

TC = 3.81 min

If Tc < 10 min, them Tc = 10 min

V =

Tt = 122.00

Prepared by: J.R. Date: 4/4/2024

Check by: A.R. Date: 4/4/2024

Approved by: A.V. Date: 4/4/2024

STA.

Grate

(BK)

STA.

Grate

(AH)

01+78.52 1050.20 02+52.76 1050.94 82.00 0.1142 0.95 0.56 0.0090 0.0923 5.73 Ok, Effective Length > Lt

Frequency = 10 (Years)

TC= 10 (min) Time of Concentration

I = 5.19 ( In/hr) NOAA Intensity for storm 10yr-24hr n = 0.016

El. 1050.20

El. 1049.27

El. 1049.87

El. 1047.62

Stucture

No.

TD Parking Lot

Analysis of data from the Federal Highway Administration tests of slotted inlets with slot widths 1.75 in indicates that the length of slotted inlet required for total interception can be computed by equation 4-22. Chart 7, is therefore applicable for both curb-opening inlets and slotted inlets.

Slotted Drain opening length required to intercept 100 percent of the gutter flow.

Lt

(ft)

General design work that involves replacement of a roadside ditch with a pipe system by extending side drain pipes. (Drainage Manual, Chapter 3)

(Urban Drainage Design Manual, Cap. 4.4.4.3. Slotted Inlets)

TRENCH DRAIN CALCULATION

TD_Parking Lot

From To Effective

Length

Area

(Ac)

Runoff

Coefficient

(C)

Q

Segment

(ft /sec)

SL

(ft/ft)

SX

(ft/ft)

Trench Drain

Remark

Sta. 001+78.52 Sta. 002+52.76

82.00

Slope 0.72%

El. 1050.94

El. 1047.82

BETHELVIEW ROAD

Appendix H

Water Quality Performance Review Tool

Name of Developer: Date Submitted:

Development Name: Permit Number:

Site Location / Address: Developer Contact:

Phone Number:

Name of Engineer(s):

Development Type: Maintenance Responsibility:

1.47

1.47

1.47

0.00

I (ac) P (ac) CA (ac)

BIG CREEK DB 1 1.04 0.44 0.00

BASIN 2 DB 2 0.00 0.00 0.00

Drainage Basin 3 DB 3 0.00 0.00 0.00

Drainage Basin 4 DB 4 0.00 0.00 0.00

Drainage Basin 5 DB 5 0.00 0.00 0.00

Drainage Basin 6 DB 6 0.00 0.00 0.00

Drainage Basin 7 DB 7 0.00 0.00 0.00

Drainage Basin 8 DB 8 0.00 0.00 0.00

Drainage Basin 9 DB 9 0.00 0.00 0.00

Drainage Basin 10 DB 10 0.00 0.00 0.00

1.04 0.44 0.00

Yes

Yes

3,655

3,655

4,386

85%

Tracking #: Conditions of Approval:

Reviewed By:

Date Approved:

Jorge Rodriguez

BETHELVIEW ROAD TRAILHEAD

BCC Engineering

Total Pre-Development Area (ac):

I = Impervious Area, P = Pervious Area, CA = Conservation Area

Target Runoff Reduction Volume Achieved?

Target TSS Removal Achieved?

Total Target Water Quality Volume (cf)

% TSS Removal Achieved

Total Target Runoff Reduction Volume (cf)

Runoff Reduction Volume Achieved (cf)

Total Treated Area (ac):

Total Untreated Area (ac):

TOTAL

Georgia Stormwater Management Manual

Stormwater Quality Site Development Review Tool

Version 2.2

General Information

Site Summary

Official Use Only

Total Post-Development Area (ac):

0%

20%

40%

60%

80%

100%

DB 1 DB 2 DB 3 DB 4 DB 5 DB 6 DB 7 DB 8 DB 9 DB 10

TS

S

R e d u ct io n

Total Suspended Solids (TSS) Removal

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

DB 1 DB 2 DB 3 DB 4 DB 5 DB 6 DB 7 DB 8 DB 9 DB 10

R

R T ar ge t M e t

Runoff Reduction (RR)

Development Name: data input cells

Drainage Basin Name: calculation cells constant values

Indicate Pre-Development Land Cover and Runoff Curve Numbers in the Site's Disturbed Area

HSG* A

(acres) CN HSG B (acres) CN

HSG C

(acres)

CN

HSG D

(acres) CN Total % Cover

98 1.18 98 98 98 1.18 80%

30 0.11 55 70 77 0.11 8%

68 0.18 79 86 89 0.18 12%

0 0 0 0 0.00 0%

0 0 0 0 0.00 0%

0.00 0%

0.00 0%

0.00 1.47 0.00 0.00 1.47 100%

1.18

0.83

Indicate Post-Development Land Cover and Runoff Curve Numbers in the Site's Disturbed Area

HSG A

(acres) CN HSG B (acres) CN

HSG C

(acres)

CN

HSG D

(acres) CN Total % Cover

98 1.04 98 98 98 1.04 70%

30 0.03 55 70 77 0.03 2%

39 0.41 61 74 80 0.41 28%

0 0 0 0 0.00 0%

0 0 0 0 0.00 0%

0.00 0%

0.00 0%

0.00 1.47 0.00 0.00 1.47 100%

1.04

0.68

1.51

Scenario 1: Natural Conservation Area *See the GSMM Volume 2, Section 2.3.3.3 for more information. Scenario 3: Soil Restoration *See the GSMM Volume 2, Section 4.23 for more information.

Scenario 2: Site Reforestation/Revegetation *See the GSMM Volume 2, Section 4.22 for more information. Scenario 4: Site Reforestation/Revegetation & Soil Restoration

Total Conservation Area Credit (acres) 0.00

Site Data

Georgia Stormwater Management Manual

Stormwater Quality Site Development Review Tool, v2.2

Area (ac) of development protected by a conservation easement or equivalent form of protection.

Check the box if a portion of the post-developed area is protected by a conservation easement or equivalent form of protection.

Jorge Rodriguez

BIG CREEK

Impervious (ac)

Weighted CN

Impervious (ac)

Rv

Weighted CN

Select a land cover type…

Local Jurisdiction Input

Total

Conservation Area Credits

Select a land cover type…

Check the box if a portion of the post-developed area employs site reforestation/revegetation and is protected by a conservation easement or equivalent form of protection.

Area (ac) of development reforested/revegetated and protected by a conservation easement or equivalent form of protection.

Check the box if a portion of the post-developed area employs soil restoration and is protected by a conservation easement or equivalent form of protection.

Area (ac) with restored soils in a reforested & revegetated area and protected by a conservation easement or equivalent form of protection.

Note: The green cell will unlock if the Scenario 1 box above is checked

Note: The green cell will unlock if the Scenario 2 box above is checked

Area (ac) of development with restored soils and protected by a conservation easement or equivalent form of protection.

Check the box if the same portion of the post-developed area employs site reforestation/revegetation and soil restoration, and is protected by a conservation easement or equivalent form of protection.

Note: The green cell will unlock if the Scenario

4 box above is checked

*See the GSMM Volume 2, Section 4.22 and 4.23 for more information.

Note: The green cell will unlock if the Scenario

3 box above is checked

Cover Type

Impervious

Woods - Good Condition

Open space - Poor condition (grass cover < 50%)

Select a land cover type…

Potential Max Soil Retention, Spre (in)

Potential Max Soil Retention, Spost (in)

Woods - Good Condition

Open space - Good condition (grass cover > 75%)

Other

Total

*HSG = hydrologic soil group

Cover Type

Impervious

Select a land cover type…

Local Jurisdiction Input

Other constant values

Site Data

Georgia Stormwater Management Manual

Stormwater Quality Site Development Review Tool, v2.2 Jorge Rodriguez

BIG CREEK

Target Runoff Reduction Storm (in) 1.00 Total Site Area for Water Quality Volume (acres) 1.47

Target Runoff Reduction Volume (cf) 3,655

Target Water Quality Volume (cf) 4,386

On-site

Pervious Area

(acres)

On-site

Impervious

Area

(acres)

Offsite Area

(acres)

RR Volume from Direct

Drainage (cf)

RR Volume from

Upstream

Practices (cf)

Total RR

Volume

Received by

BMP (cf)

Runoff

Reduction %

RR Achieved

(cf)

Remaining

RR Volume

(cf)

WQv from

Direct

Drainage (cf)

Effective

TSS

Removal %

BMP 1 Enhanced Dry Swale (w/ underdrain) 0.00 0.00 0.44 2,133 0 108 108 50% 108 0 0 80%

BMP 2 Grass Channel (A & B hydrologic soils) 0.26 0.03 144 BMP 1 144 0 144 25% 36 108 173 50%

BMP 3 Bioretention Basin (w/ upturned underdrain) 0.07 0.48 2,784 1,662 0 1,662 75% 1,662 0 1,995 85%

BMP 4 Bioretention Basin (w/ upturned underdrain) 0.02 0.16 837 550 0 550 75% 550 0 660 85%

BMP 5 Bioretention Basin (w/ upturned underdrain) 0.08 0.37 2,279 1,298 0 1,298 75% 1,298 0 1,558 85%

BMP 6 Select a BMP… 0 0 0 N/A 0 0 0 N/A

BMP 7 Select a BMP… 0 0 0 N/A 0 0 0 N/A

BMP 8 Select a BMP… 0 0 0 N/A 0 0 0 N/A

BMP 9 Select a BMP… 0 0 0 N/A 0 0 0 N/A

BMP 10 Select a BMP… 0 0 0 N/A 0 0 0 N/A

TOTAL 0.44 1.04 0.44 3,655 3,655 4,386

UNTREATED AREA (acres) 0.00 0.00

Target Runoff Reduction Volume (cf) 3,655

Target Achieved? Yes!

Remaining Runoff Reduction Volume (cf) 0

Target Water Quality Volume (cf) 4,386

% TSS Removal Achieved 85%

Target Achieved? Yes!

Remaining TSS Removal % 0%

Storage Volume

Provided by

BMP

(cf)

Area Draining to Each BMP RR Conveyance

Volume

Provided by

BMP

(cf)

WQ CalculationsRunoff Reduction Calculations

Down-stream

BMP

Select BMPs for Runoff Reduction and Water Quality

Water Quality Goals constant values

Site Data

Georgia Stormwater Management Manual

Stormwater Quality Site Development Review Tool, v2.2 Jorge Rodriguez

BIG CREEK

1-yr, 24-hr storm

2-yr, 24-hr storm

25-yr, 24-hr storm

100-yr, 24-hr storm

Target Rainfall Event (in) 3.36 3.82 6.06 7.44

1-yr, 24-hr storm

2-yr, 24-hr storm

25-yr, 24-hr storm

100-yr, 24-hr storm

2.54 2.98 5.17 6.53

2.05 2.46 4.57 5.90

1.37 1.78 3.88 5.21

Adjusted CN 78 78 80 81

*See Stormwater Management Standards to Determine Detention Requirements.

Comments

Post-Development Runoff Volume (in) with BMPs

Post Development Runoff Volume (in) with no BMPs

Pre-Development Runoff Volume (in)

Channel and Flood Protection Calculations

Appendix I

Pre-developed hydrographs and routings for the 1, 2, 10, 25 100 Year Storms

Date: 04/04/24

Designed By: J.R.

Approved By: L.F.

Basin Data: AREA 1 (NW)

Time of concentration (Tc) = 8.94 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.44 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*8.94

Tp = 6.864 min = 0.114 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.44/640))/0.114

300 qpu = 1.81 cfs

484 qpu = (484* (0.44/640))/0.114

484 qpu = 2.92 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

0.44 3 0.37 1.07 0.67 1.22

0.87 6 0.97 2.82 0.99 1.79

1.31 9 0.86 2.51 0.94 1.70

1.75 12 0.49 1.42 0.75 1.36

2.19 15 0.22 0.63 0.55 0.99

2.62 18 0.08 0.24 0.37 0.67

3.06 21 0.03 0.08 0.24 0.44

3.50 24 0.01 0.03 0.15 0.28

3.93 27 0.00 0.01 0.10 0.17

4.37 30 0.00 0.00 0.06 0.11

4.81 33 0.03 0.06

5.24 36 0.02 0.04

5.68 39 0.01 0.02

6.12 42 0.01 0.01

6.56 45 0.00 0.01

6.99 48 0.00 0.00

Time 484 300

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8 t/ T p q/qpu

Hydrograph Area 1 (NW)

Peaking Factor =484

Peaking Factor = 300

Approved By: L.F.

Basin Data: AREA 2 (NE)

Time of concentration (Tc) = 4.88 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.29 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*4.88

Tp = 4.428 min = 0.074 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.29/640))/0.074

300 qpu = 1.84 cfs

484 qpu = (484* (0.29/640))/0.074

484 qpu = 2.96 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

0.68 3 0.78 2.30 0.90 1.66

1.36 6 0.82 2.44 0.93 1.70

2.03 9 0.29 0.87 0.62 1.13

2.71 12 0.07 0.20 0.34 0.63

3.39 15 0.01 0.04 0.17 0.32

4.07 18 0.00 0.01 0.08 0.15

4.74 21 0.00 0.00 0.04 0.07

5.42 24 0.02 0.03

6.10 27 0.01 0.01

6.78 30 0.00 0.01

7.45 33 0.00 0.00

Time 484 300

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8 t/ T p q/qpu

Hydrograph Area 2 (NE)

Approved By: L.F.

Basin Data: AREA 3 (SE)

Time of concentration (Tc) = 4.15 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.55 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*4.15

Tp = 3.99 min = 0.067 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.55/640))/0.067

300 qpu = 3.85 cfs

484 qpu = (484* (0.55/640))/0.067

484 qpu = 6.21 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

0.75 3 0.87 5.39 0.95 3.64

1.50 6 0.70 4.32 0.87 3.33

2.26 9 0.19 1.16 0.52 1.98

3.01 12 0.03 0.20 0.26 0.99

3.76 15 0.00 0.03 0.12 0.45

4.51 18 0.00 0.00 0.05 0.19

5.26 21 0.02 0.08

6.02 24 0.01 0.03

6.77 27 0.00 0.01

7.52 30 0.00 0.00

Time 484 300

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8 t/ T p q/qpu

Hydrograph Area 3 (SE)

Approved By: L.F.

Basin Data: AREA 4 (S)

Time of concentration (Tc) = 1.62 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.18 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*1.62

Tp = 2.472 min = 0.041 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.18/640))/0.041

300 qpu = 2.06 cfs

484 qpu = (484* (0.18/640))/0.041

484 qpu = 3.32 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

1.21 3 0.93 3.08 0.97 2.00

2.43 6 0.13 0.43 0.44 0.91

3.64 9 0.01 0.02 0.13 0.27

4.85 12 0.00 0.00 0.03 0.07

6.07 15 0.01 0.02

7.28 18 0.00 0.00

Time 484 300

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8 t/ T p q/qpu

Hydrograph Area 4 (S)

Approved By: L.F.

Basin Data: AREA 4 (S)

Time of concentration (Tc) = 3.81 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.45 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*3.81

Tp = 3.786 min = 0.063 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.45/640))/0.063

300 qpu = 3.35 cfs

484 qpu = (484* (0.45/640))/0.063

484 qpu = 5.40 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

0.79 3 0.91 4.91 0.96 3.22

1.58 6 0.62 3.37 0.83 2.78

2.38 9 0.14 0.78 0.46 1.56

3.17 12 0.02 0.11 0.22 0.73

3.96 15 0.00 0.01 0.09 0.31

4.75 18 0.00 0.00 0.04 0.12

5.55 21 0.01 0.05

6.34 24 0.01 0.02

7.13 27 0.00 0.01

7.92 30 0.00 0.00

Time 484 300

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8 9 t/ T p q/qpu

Hydrograph Area 5 (SW)

Appendix K

Developed hydrographs and routings for the 1, 2, 10, 25

100 Year Storms

Approved By: L.F.

Basin Data: AREA 1 (NW)

Time of concentration (Tc) = 8.94 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.44 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*8.94

Tp = 6.864 min = 0.114 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.44/640))/0.114

300 qpu = 1.81 cfs

484 qpu = (484* (0.44/640))/0.114

484 qpu = 2.92 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

0.44 3 0.37 1.07 0.67 1.22

0.87 6 0.97 2.82 0.99 1.79

1.31 9 0.86 2.51 0.94 1.70

1.75 12 0.49 1.42 0.75 1.36

2.19 15 0.22 0.63 0.55 0.99

2.62 18 0.08 0.24 0.37 0.67

3.06 21 0.03 0.08 0.24 0.44

3.50 24 0.01 0.03 0.15 0.28

3.93 27 0.00 0.01 0.10 0.17

4.37 30 0.00 0.00 0.06 0.11

4.81 33 0.03 0.06

5.24 36 0.02 0.04

5.68 39 0.01 0.02

6.12 42 0.01 0.01

6.56 45 0.00 0.01

6.99 48 0.00 0.00

Time 484 300

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8 t/ T p q/qpu

Hydrograph Area 1 (NW)

Approved By: L.F.

Basin Data: AREA 2 (NE)

Time of concentration (Tc) = 4.88 min

Computer calculation time increment (d) = 3 min

Peaking Factor = 300

Peaking Factor = 484

Area = 0.29 Ac.

(1) Calculate Tp and time increment

Tp = d/2 + 0.6 Tc

Tp = 3/2 + 0.6*4.88

Tp = 4.428 min = 0.074 hrs

(2) Calculate qpu qpu = PF*A/Tp

300 qpu = (300* (0.29/640))/0.074

300 qpu = 1.84 cfs

484 qpu = (484* (0.29/640))/0.074

484 qpu = 2.96 cfs

BETHELVIEW ROAD

Approved By: L.F.

BETHELVIEW ROAD

TRAILHEAD

CITY OF CUMMING, GEORGIA

(3) Calculate unit hydrograph for both 484 and 300.

t/Tp Time q/qpu Q484 q/qpu Q300

0 0 0.00 0.00 0.00 0.00

0.68 3 0.78 2.30 0.90 1.66

1.36 6…