Attachment 07 CRWC 22419 Hydrologic Calculations.pdf

STORMWATER MANAGEMENT REPORT FOR

CHATTOOGA RIVER WORK CENTER

9975 HIGHWAY 441S

LAKEMONT, GA. 30552

OWNER:

USDA FOREST SERVICE

REGION 8

1720 PEACHTREE STREET NW

STE 876S

ATLANTA, GA. 30309-2449

PREPARED BY:

CROFT & ASSOCIATES

3380 BLUE SPRINGS ROAD

KENNESAW, GA 30144

NOVEMBER 16, 2023

12/18/2023

12/18/2023

This Page Intentionally Left Blank

Table of Contents

Introduction

Executive Summary

Hydrologic Analysis

Existing Conditions

Proposed Conditions

Conclusion

Appendix A: Maps

Appendix B: Hydrographs

Appendix C: Calculations

Appendix D: Stormwater Maintenance Agreement and Checklist

This Page Intentionally Left Blank

Introduction The project site is located at 9975 Highway 441S in Lakemont, Georgia. The total property area for the

Chattooga River Ranger District Office is 9.00 acres with a project area for the Chattooga River Work

Center of 0.96 acres. The property is currently developed with a ranger’s office, vehicle laydown area, support buildings such as well pump house, and associated parking. The proposed project includes a new 4,335 square-foot work center building, sidewalks, and resurfacing the existing vehicle laydown area with gravel, the existing vehicle laydown area. There is an existing stormwater detention facility that will be modified as a result of the increased impervious area from this project. A vicinity map of the property is shown below in Figure 1.

Figure 1 – Vicinity Map

According to FIRM Panel 13241C0270D dated September 17, 2010, no portion of the property is located inside of a flood hazard zone. The FIRM panel is located in Appendix A.

Executive Summary The project area has been delineated into a single drainage basin in the existing condition and remains a single drainage basin in the developed condition. The basin in the existing condition has been designated as Existing Basin A and is approximately 1.01 acres. Existing Basin A includes a gravel vehicle laydown area, support sheds for the main work center building, and an existing sedimentation pond with a sand filter bed. Runoff from Existing Basin A drains from east to west as sheet flow and shallow concentrated flow until it reaches the existing stormwater detention pond. The existing stormwater detention pond was developed during the previous development of the property’s ranger office. For that design, the stormwater detention pond was labeled as Pond B1, and will be referred to as such in this report. Pond B1 was designed to hold runoff and infiltrate it into the ground. An overflow Outlet

Control Structure (OCS) was installed to accommodate runoff more than a 100-year storm event. Each

Point of Analysis (POA), where stormwater flows in this report are analyzed, and is shown in Appendix A.

Existing Basin A will be modified during the developed condition and is referred to as Proposed Basin A, in this report. Proposed Basin A is approximately 1.06 acres. In general, Proposed Basin A follows the same flow path as the existing condition. There is a slight increase in peak flow due to the added area, but the Curve Number (CN) and Time of Concentration (Tc) remained the same in the proposed condition. Pond B1 will be modified to accommodate the additional area and increased runoff while also being brought up to current requirements by installing an infiltration trench at the bottom of the pond to reduce runoff. The existing OCS will be adjusted to accommodate storm events over the 100-year storm event.

The tables below summarize the flow rates of the existing and proposed conditions. The proposed modifications to Pond B1 have been calculated to continue to infiltrate and manage flows up to the 100-year design storm for the proposed improvements. The OCS will be reinstalled at an elevation below the top of the pond to provide emergency overflow protection.

Table A – Flow Summary at Basin A POA

Storm Frequency

(year)

Existing Flow to Existing Pond

B1 (cfs)

Existing Condition Flow

Rate at POA (cfs)

Proposed Flow to Proposed Pond B1 (cfs)

Proposed Condition Flow

Rate at POA (cfs)

Change in Flow Rate at

POA (cfs)

1 3.05 0.00 3.20 0.00 0.00

2 3.77 0.00 3.96 0.00 0.00

5 5.08 0.00 5.33 0.00 0.00

10 6.26 0.00 6.57 0.00 0.00

25 8.00 0.00 8.40 0.00 0.00

50 9.45 0.00 9.92 0.00 0.00

100 11.00 0.00 11.54 0.00 0.00

Hydrologic Analysis The hydrologic portion of this study was performed with the SCS TR-20 method. SCS 24 hour, Type II rainfall data from NOAA were multiplied for the 1, 2, 5, 10, 25, 50, and 100 year storm events and combined with the SCS Unit Hydrograph (shape factor 484) with area, curve number, and time of concentration parameters to produce direct hydrographs.

According to a soils report for Rabun County, Georgia obtained from the Natural Resources

Conservation Service (NRSC), the soils on the project site are sandy clay loam (MU) and classified as

Hydrologic Soil Group “D”. The soils map is located in Appendix A. However, geotechnical exploration was performed by Geohydro Engineers and the soil was found to be Type “B”.

The stormwater models for existing and proposed conditions were created using Hydraflow

Hydrographs Extension for Autodesk Civil 3D 2024. The analysis of the existing conditions was performed using the original design drawings for the main work center. It is worth noting that the elevation datum used for the original design is different from the new development. Therefore, the elevations used for the existing Pond B1 will be different than in the proposed condition.

Existing Conditions One drainage basin has been delineated in the existing condition, Existing Basin A. Existing Basin A is approximately 1.01 acres and consists of a gravel vehicle laydown area. Stormwater runoff from this basin flows west towards an existing stormwater detention pond, Pond B1, located near the western side of the property.

Pond B1 consists of two components: a Sand Filter Bed and a Sedimentation Chamber. The two components utilize a Sedimentation Chamber Outlet Pipe to transfer runoff stormwater between each other. A 12-inch high berm was designed to provide separation between the two components and serve as an emergency overflow for the Sand Filter Bed. The intent of the previous design for Pond B1 was for stormwater runoff to flow across the project site and directly into Pond B1. Stormwater runoff would then infiltrate into the ground via the Sand Filter Bed. In case of a large storm event that would exceed the capacity of Pond B1, an Outlet Control Structure was installed to capture the emergency overflow stormwater and discharge the stormwater to the North. Based on the Construction Documents for the

Chattooga River Ranger Office and the survey provided for the design of the Chattooga River Work

Center, Pond B1 was not built as designed. Facility management has stated that, despite the design and construction discrepancies, they have not seen the pond overtop.

Pond B1 was designed to have a maximum available storage of approximately 29,998 cubic feet. Its current maximum available storage is approximately 9,545 cubic feet. The designed 12-inch high berm separating the Sand Filter Bed from the Sedimentation Chamber has been compromised and there appears to be no separation berm. The Outlet Control Structure that is to serve as emergency overflow protection was installed with a weir elevation approximately 1.4 feet above the top of the pond.

Therefore, stormwater runoff that exceeds the capacity of Pond B1 will flow over the top of the Pond and not through the Outlet Control Structure to the POA.

Existing Basin A has a curve number (CN) of 82 and a time of concentration (Tc) of 11.2 minutes.

Calculations for this drainage basin are shown in the tables below.

Table C – Existing Basin A to Pond B1 CN Calculations

Curve Number

CN

value Area (Ac.)

Woods 55 0.10

Open Space, good condition 61 0.08

Gravel 85 0.71

Impervious 98 0.12

Total Area (Ac.) 1.01

Weighted CN 82

Table D – Existing Basin A to Pond B1 Tc Calculations

Proposed Conditions The drainage basin in the developed condition is Proposed Basin A. Proposed Basin A is approximately

1.06 acres. The Basin includes the gravel vehicle laydown area, work center building, concrete sidewalk, and Pond B1. All of the runoff from this basin surface flows west into Pond B1. The proposed building will have roof drains that will drain through underground pipe and discharge directly into the pond.

Pond B1 will be dug out where the existing trailers are located to provide more storage, and have an infiltration trench installed at the bottom of the expanded pond area. In addition, the OCS will be modified to an elevation 6 inches below the top of pond. Pond B1 has been designed to meet Runoff

Reduction requirements. Excess stormwater will be routed through the outlet control structure to the

POA.

Based on the Site Development Review Tool V2.2, the target Runoff Reduction Volume is 1,401 cubic feet. The calculated amount of Runoff Reduction Volume provided by the Pond B1’s infiltration trench is

2,444 cubic feet. The infiltration trench is approximately 46 feet long, 68 feet wide, and 2 feet deep located at the bottom of Pond B1. Approximately 0.03 acres of impervious and gravel area from the development of this project is untreated due to site constraints. However, these areas are routed to another existing stormwater detention pond on-site. Runoff from storm events that exceeds the capacity of the Pond B1 will overflow through the outlet control structure that discharges to the northern portion of the property. This basin has a CN of 82 and a Tc of 11.2 minutes. Calculations for this drainage basin are shown in the tables below. Details of the proposed pond and outlet control structure are included in Appendix C.

Table G – Proposed Basin A to Pond B1 CN Calculations

Curve Number

CN

value Area (Ac.)

Woods 55 0.11

Open Space, fair condition 61 0.20

Gravel 85 0.38

Impervious 98 0.37

Total Area (Ac.) 1.06

Weighted CN 82

Table H – Proposed Basin A to Pond B1 Tc Calculations

Table I – Proposed Pond B1 Flow Rates

Storm Frequency (year)

Flow Rate Entering Pond (cfs)

Flow Rate Leaving Pond (cfs)

1 3.203 0.00

2 3.961 0.00

5 5.332 0.00

10 6.568 0.00

25 8.400 0.00

50 9.921 0.00

100 11.54 0.00

Table J – Proposed Pond B1 Stage Storage

Stage (ft) Elevation (ft) Cumulative Volume (cuft)

0 1685 0

1 1686 3,696

2 1687 8,466

3 1688 14,041

4 1689 20,459

5 1690 27,754

Conclusion The results of this hydrology analysis show that the modifications to Pond B1 will provide adequate volume to manage runoff reduction and the increased runoff flows for the work center development at the point of analysis in the 1-, 5-, 10-, 25-, 50-, and 100- year storm events.

APPENDIX A

MAPS

Hydrologic Soil Group—Rabun and Towns Counties, Georgia

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

8/1/2023

280520 280560 280600 280640 280680 280720 280760 280800 280840 280880 280920

280520 280560 280600 280640 280680 280720 280760 280800 280840 280880 280920

34° 45' 16'' N

3'

2' ' W

34° 45' 16'' N

3'

5' ' W

34° 45' 6'' N

3'

2' ' W

34° 45' 6'' N

3'

5' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 17N WGS84 0 50 100 200 300

Feet 0 25 50 100 150

Meters Map Scale: 1:1,980 if printed on A landscape (11" x 8.5") sheet.

Soil Map may not be valid at this scale.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Area of Interest (AOI)

Soils Soil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Lines A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Points A

A/D

B

B/D

C

C/D

D

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:20,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Rabun and Towns Counties, Georgia Survey Area Data: Version 14, Sep 14, 2022

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Mar 19, 2022—Apr 20, 2022

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Hydrologic Soil Group—Rabun and Towns Counties, Georgia

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

8/1/2023

Hydrologic Soil Group

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

LhE Lily fine sandy loam, 10 to 25 percent slopes

B 5.7 51.3%

RLF Ramsey-Lily association, stony, steep

D 5.4 48.7%

Totals for Area of Interest 11.1 100.0%

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.

These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Hydrologic Soil Group—Rabun and Towns Counties, Georgia

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

1.01 ac

Existing Conditions Basin A Total Area: 1.01 Ac

CN: 80

Tc: 11.2 min.

Tc

FIGURE 1

SD

SD

SD

SD

SD

SD

SD

ST

ST

ST

ST

ST

ST

ST

ST

ST

SD

SD

SDSD

SD

SD

SD

SDSD

SD

2022-419

United States Department of Agriculture Forest Service

USDA FOREST SERVICE

REGION 8

CHATTOOGA

RIVER WORK

CENTER

9975 Highway 441S Lakemont, GA

30552

PROJECT NO.

CHECKED

DRAWN

DESIGNER

ARCHIVE NO.

DATE SIGNED

DRAWING TITLE

PROJECT NAME

SHEET

DWG SHEET NO.

CROFT & Associates 3380 Blue Springs Road Kennesaw, Georgia 30144

770.529.7714 (p) 770.529.7716 (f) www.croftandassociates.com

LMC

CKJ

CKJ

N O

R

TH

1" = 20'

0 10 40 FT20

FIGURE 2

PROPOSED CONDITIONS

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Rabun and Towns Counties, Georgia

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

APPENDIX B

HYDROGRAPHS

Hydraflow Table of Contents Chattooga River Walk Center Hydrology Calculations.gpw

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hydrograph Return Period Recap

1 - Year Summary Report Hydrograph Reports

Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 TR-55 Tc Worksheet

Hydrograph No. 2, Reservoir, Ex. Pond B1 Pond Report - Existing Pond B1

Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 TR-55 Tc Worksheet

Hydrograph No. 4, Reservoir, Prop Pond B1 Pond Report - Proposed Pond B1

2 - Year Summary Report Hydrograph Reports

Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 Hydrograph No. 2, Reservoir, Ex. Pond B1 Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 Hydrograph No. 4, Reservoir, Prop Pond B1

5 - Year Summary Report Hydrograph Reports

Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 Hydrograph No. 2, Reservoir, Ex. Pond B1 Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 Hydrograph No. 4, Reservoir, Prop Pond B1

10 - Year Summary Report Hydrograph Reports

Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 Hydrograph No. 2, Reservoir, Ex. Pond B1 Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 Hydrograph No. 4, Reservoir, Prop Pond B1

25 - Year Summary Report Hydrograph Reports

Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 Hydrograph No. 2, Reservoir, Ex. Pond B1 Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 Hydrograph No. 4, Reservoir, Prop Pond B1

50 - Year Summary Report

Hydrograph Return Period Recap

Hyd. Hydrograph Inflow Peak Outflow (cfs) Hydrograph

No. type hyd(s) Description

(origin) 1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr

1 SCS Runoff ------ 3.052 3.774 ------- 5.080 6.258 8.004 9.453 11.00 Existing Basin A to Pond B1

2 Reservoir 1 0.000 0.000 ------- 0.000 0.000 0.000 0.000 0.000 Ex. Pond B1

3 SCS Runoff ------ 3.203 3.961 ------- 5.332 6.568 8.400 9.921 11.54 Proposed Basin A to Pond B1

4 Reservoir 3 0.000 0.000 ------- 0.000 0.000 0.000 0.000 0.000 Prop Pond B1

Proj. file: Chattooga River Walk Center Hydrology Calculations.gpw Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024

Hydrograph Summary Report

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 3.052 2 720 7,911 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 766 0 1 131.66 5,348 Ex. Pond B1

3 SCS Runoff 3.203 2 720 8,302 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 1744 0 3 1686.31 5,156 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 1 Year Monday, 11 / 13 / 2023

Hydrograph Report

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 3.052 cfs Storm frequency = 1 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 7,911 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 3.87 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 1 Year

Hyd No. 1

TR55 Tc Worksheet

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024

Hyd. No. 1

Existing Basin A to Pond B1

Description A B C Totals

Sheet Flow Manning's n-value = 0.800 0.011 0.011 Flow length (ft) = 98.9 0.0 0.0 Two-year 24-hr precip. (in) = 4.45 0.00 0.00 Land slope (%) = 32.00 0.00 0.00

Travel Time (min) = 10.37 + 0.00 + 0.00 = 10.37

Shallow Concentrated Flow Flow length (ft) = 232.90 0.00 0.00 Watercourse slope (%) = 7.73 0.00 0.00 Surface description = Unpaved Paved Paved Average velocity (ft/s) =4.49 0.00 0.00

Travel Time (min) = 0.87 + 0.00 + 0.00 = 0.87

Channel Flow X sectional flow area (sqft) = 0.00 0.00 0.00 Wetted perimeter (ft) = 0.00 0.00 0.00 Channel slope (%) = 0.00 0.00 0.00 Manning's n-value = 0.015 0.015 0.015 Velocity (ft/s) =0.00

0.00 0.00

Flow length (ft) ({0})0.0 0.0 0.0

Travel Time (min) = 0.00 + 0.00 + 0.00 = 0.00

Total Travel Time, Tc .............................................................................. 11.20 min

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 1 yrs Time to peak = 766 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 131.66 ft Reservoir name = Existing Pond B1 Max. Storage = 5,348 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600 3960

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 1 Year

Hyd No. 2 Hyd No. 1 Total storage used = 5,348 cuft

Pond Report 6

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Pond No. 2 - Existing Pond B1

Pond Data

Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 128.00 ft

Stage / Storage Table

Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)

0.00 128.00 33 0 0

2.00 130.00 1,625 1,260 1,260

4.00 132.00 3,398 4,915 6,174

6.00 134.00 5,033 8,377 14,551

8.00 136.00 10,775 15,447 29,998

Culvert / Orifice Structures Weir Structures

[A] [B] [C] [PrfRsr] [A] [B] [C] [D]

Rise (in) = 18.00 0.00 0.00 0.00

Span (in) = 18.00 0.00 0.00 0.00

No. Barrels = 1 0 0 0

Invert El. (ft) = 131.00 0.00 0.00 0.00

Length (ft) = 60.00 0.00 0.00 0.00

Slope (%) = 1.67 0.00 0.00 n/a

N-Value = .013 .013 .013 n/a

Orifice Coeff. = 0.60 0.60 0.60 0.60

Multi-Stage = n/a No No No

Crest Len (ft) = 16.00 0.00 0.00 0.00

Crest El. (ft) = 135.50 0.00 0.00 0.00

Weir Coeff. = 3.33 3.33 3.33 3.33

Weir Type = Rect --- --- ---

Multi-Stage = Yes No No No

Exfil.(in/hr) = 1.000 (by Contour)

TW Elev. (ft) = 0.00

Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

Stage (ft)

0.00 128.00

2.00 130.00

4.00 132.00

6.00 134.00

8.00 136.00

Elev (ft)

Discharge (cfs)

Stage / Discharge

Total Q

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 3.203 cfs Storm frequency = 1 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 8,302 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 3.87 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 1 Year

Hyd No. 3

TR55 Tc Worksheet

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024

Hyd. No. 3

Proposed Basin A to Pond B1

Description A B C Totals

Sheet Flow Manning's n-value = 0.800 0.011 0.011 Flow length (ft) = 98.9 0.0 0.0 Two-year 24-hr precip. (in) = 4.45 0.00 0.00 Land slope (%) = 32.00 0.00 0.00

Travel Time (min) = 10.37 + 0.00 + 0.00 = 10.37

Shallow Concentrated Flow Flow length (ft) = 341.64 0.00 0.00 Watercourse slope (%) = 18.28 0.00 0.00 Surface description = Unpaved Paved Paved Average velocity (ft/s) =6.90 0.00 0.00

Travel Time (min) = 0.83 + 0.00 + 0.00 = 0.83

Channel Flow X sectional flow area (sqft) = 0.00 0.00 0.00 Wetted perimeter (ft) = 0.00 0.00 0.00 Channel slope (%) = 0.00 0.00 0.00 Manning's n-value = 0.015 0.015 0.015 Velocity (ft/s) =0.00

0.00 0.00

Flow length (ft) ({0})0.0 0.0 0.0

Travel Time (min) = 0.00 + 0.00 + 0.00 = 0.00

Total Travel Time, Tc .............................................................................. 11.20 min

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 1 yrs Time to peak = 1744 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1686.31 ft Reservoir name = Proposed Pond B1 Max. Storage = 5,156 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 1 Year

Hyd No. 4 Hyd No. 3 Total storage used = 5,156 cuft

Pond Report 10

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Pond No. 3 - Proposed Pond B1

Pond Data

Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 1685.00 ft

Stage / Storage Table

Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)

0.00 1685.00 3,056 0 0

1.00 1686.00 4,376 3,696 3,696

2.00 1687.00 5,176 4,770 8,466

3.00 1688.00 5,985 5,575 14,041

4.00 1689.00 6,863 6,418 20,459

5.00 1690.00 7,736 7,294 27,754

Culvert / Orifice Structures Weir Structures

[A] [B] [C] [PrfRsr] [A] [B] [C] [D]

Rise (in) = 18.00 0.00 0.00 0.00

Span (in) = 18.00 0.00 0.00 0.00

No. Barrels = 1 0 0 0

Invert El. (ft) = 1686.58 0.00 0.00 0.00

Length (ft) = 60.00 0.00 0.00 0.00

Slope (%) = 3.43 0.00 0.00 n/a

N-Value = .023 .013 .013 n/a

Orifice Coeff. = 0.60 0.60 0.60 0.60

Multi-Stage = n/a No No No

Crest Len (ft) = 16.00 0.00 0.00 0.00

Crest El. (ft) = 1689.50 0.00 0.00 0.00

Weir Coeff. = 3.33 3.33 3.33 3.33

Weir Type = Rect --- --- ---

Multi-Stage = Yes No No No

Exfil.(in/hr) = 1.000 (by Contour)

TW Elev. (ft) = 0.00

Note: Culvert/Orifice outflows are analyzed under inlet (ic) and outlet (oc) control. Weir risers checked for orifice conditions (ic) and submergence (s).

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00

Stage (ft)

0.00 1685.00

1.00 1686.00

2.00 1687.00

3.00 1688.00

4.00 1689.00

5.00 1690.00

Elev (ft)

Discharge (cfs)

Stage / Discharge

Total Q

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 3.774 2 720 9,801 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 986 0 1 132.15 6,784 Ex. Pond B1

3 SCS Runoff 3.961 2 720 10,286 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 2006 0 3 1686.63 6,679 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 2 Year Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 3.774 cfs Storm frequency = 2 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 9,801 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 4.45 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 2 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 2 yrs Time to peak = 986 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 132.15 ft Reservoir name = Existing Pond B1 Max. Storage = 6,784 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600 3960

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 2 Year

Hyd No. 2 Hyd No. 1 Total storage used = 6,784 cuft

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 3.961 cfs Storm frequency = 2 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 10,286 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 4.45 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 2 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 2 yrs Time to peak = 2006 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1686.63 ft Reservoir name = Proposed Pond B1 Max. Storage = 6,679 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880 3120

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 2 Year

Hyd No. 4 Hyd No. 3 Total storage used = 6,679 cuft

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 5.080 2 720 13,278 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 1808 0 1 132.81 9,563 Ex. Pond B1

3 SCS Runoff 5.332 2 720 13,935 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 766 0 3 1687.19 9,541 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 5 Year Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 5.080 cfs Storm frequency = 5 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 13,278 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 5.48 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 5 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 5 yrs Time to peak = 1808 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 132.81 ft Reservoir name = Existing Pond B1 Max. Storage = 9,563 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 5 Year

Hyd No. 2 Hyd No. 1 Total storage used = 9,563 cuft

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 5.332 cfs Storm frequency = 5 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 13,935 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 5.48 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 5 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 5 yrs Time to peak = 766 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1687.19 ft Reservoir name = Proposed Pond B1 Max. Storage = 9,541 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 5 Year

Hyd No. 4 Hyd No. 3 Total storage used = 9,541 cuft

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 6.258 2 720 16,472 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 988 0 1 133.42 12,142 Ex. Pond B1

3 SCS Runoff 6.568 2 720 17,287 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 766 0 3 1687.68 12,232 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 10 Year Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 6.258 cfs Storm frequency = 10 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 16,472 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 6.40 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

7.00 7.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 10 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 10 yrs Time to peak = 988 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 133.42 ft Reservoir name = Existing Pond B1 Max. Storage = 12,142 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880 3120

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

7.00 7.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 10 Year

Hyd No. 2 Hyd No. 1 Total storage used = 12,142 cuft

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 6.568 cfs Storm frequency = 10 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 17,287 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 6.40 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

7.00 7.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 10 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 10 yrs Time to peak = 766 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1687.68 ft Reservoir name = Proposed Pond B1 Max. Storage = 12,232 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600

Q (cfs)

0.00 0.00

1.00 1.00

2.00 2.00

3.00 3.00

4.00 4.00

5.00 5.00

6.00 6.00

7.00 7.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 10 Year

Hyd No. 4 Hyd No. 3 Total storage used = 12,232 cuft

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 8.004 2 720 21,295 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 1944 0 1 134.18 15,978 Ex. Pond B1

3 SCS Runoff 8.400 2 720 22,349 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 904 0 3 1688.36 16,363 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 25 Year Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 8.004 cfs Storm frequency = 25 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 21,295 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 7.76 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 25 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 25 yrs Time to peak = 1944 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 134.18 ft Reservoir name = Existing Pond B1 Max. Storage = 15,978 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 25 Year

Hyd No. 2 Hyd No. 1 Total storage used = 15,978 cuft

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 8.400 cfs Storm frequency = 25 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 22,349 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 7.76 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 25 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 25 yrs Time to peak = 904 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1688.36 ft Reservoir name = Proposed Pond B1 Max. Storage = 16,363 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 480 960 1440 1920 2400 2880 3360 3840 4320

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 25 Year

Hyd No. 4 Hyd No. 3 Total storage used = 16,363 cuft

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 9.453 2 720 25,364 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 1520 0 1 134.58 19,035 Ex. Pond B1

3 SCS Runoff 9.921 2 720 26,619 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 892 0 3 1688.91 19,884 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 50 Year Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 9.453 cfs Storm frequency = 50 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 25,364 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 8.89 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 50 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 50 yrs Time to peak = 1520 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 134.58 ft Reservoir name = Existing Pond B1 Max. Storage = 19,035 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240 3600 3960

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 50 Year

Hyd No. 2 Hyd No. 1 Total storage used = 19,035 cuft

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 9.921 cfs Storm frequency = 50 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 26,619 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 8.89 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 50 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 50 yrs Time to peak = 892 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1688.91 ft Reservoir name = Proposed Pond B1 Max. Storage = 19,884 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 50 Year

Hyd No. 4 Hyd No. 3 Total storage used = 19,884 cuft

Hyd. Hydrograph Peak Time Time to Hyd. Inflow Maximum Total Hydrograph

No. type flow interval Peak volume hyd(s) elevation strge used Description

(origin) (cfs) (min) (min) (cuft) (ft) (cuft)

1 SCS Runoff 11.00 2 720 29,764 ------ ------ ------ Existing Basin A to Pond B1

2 Reservoir 0.000 2 738 0 1 135.01 22,334 Ex. Pond B1

3 SCS Runoff 11.54 2 720 31,238 ------ ------ ------ Proposed Basin A to Pond B1

4 Reservoir 0.000 2 748 0 3 1689.45 23,732 Prop Pond B1

Chattooga River Walk Center Hydrology Calculations.gpwReturn Period: 100 Year Monday, 11 / 13 / 2023

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 1

Existing Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 11.00 cfs Storm frequency = 100 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 29,764 cuft Drainage area = 1.010 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 10.10 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.120 x 98) + (0.710 x 85) + (0.080 x 61) + (0.100 x 55)] / 1.010

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

12.00 12.00

Q (cfs)

Time (min)

Existing Basin A to Pond B1

Hyd. No. 1 -- 100 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 2

Ex. Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 100 yrs Time to peak = 738 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 1 - Existing Basin A to Pond B1Max. Elevation = 135.01 ft Reservoir name = Existing Pond B1 Max. Storage = 22,334 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 480 960 1440 1920 2400 2880 3360 3840 4320

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

12.00 12.00

Q (cfs)

Time (min)

Ex. Pond B1

Hyd. No. 2 -- 100 Year

Hyd No. 2 Hyd No. 1 Total storage used = 22,334 cuft

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 3

Proposed Basin A to Pond B1

Hydrograph type = SCS Runoff Peak discharge = 11.54 cfs Storm frequency = 100 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 31,238 cuft Drainage area = 1.060 ac Curve number = 82* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 11.20 min Total precip. = 10.10 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484

* Composite (Area/CN) = [(0.370 x 98) + (0.380 x 85) + (0.200 x 61) + (0.110 x 55)] / 1.060

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

12.00 12.00

Q (cfs)

Time (min)

Proposed Basin A to Pond B1

Hyd. No. 3 -- 100 Year

Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2024 Monday, 11 / 13 / 2023

Hyd. No. 4

Prop Pond B1

Hydrograph type = Reservoir Peak discharge = 0.000 cfs Storm frequency = 100 yrs Time to peak = 748 min Time interval = 2 min Hyd. volume = 0 cuft Inflow hyd. No. = 3 - Proposed Basin A to Pond B1Max. Elevation = 1689.45 ft Reservoir name = Proposed Pond B1 Max. Storage = 23,732 cuft

Storage Indication method used. Exfiltration extracted from Outflow.

0 360 720 1080 1440 1800 2160 2520 2880 3240

Q (cfs)

0.00 0.00

2.00 2.00

4.00 4.00

6.00 6.00

8.00 8.00

10.00 10.00

12.00 12.00

Q (cfs)

Time (min)

Prop Pond B1

Hyd. No. 4 -- 100 Year

Hyd No. 4 Hyd No. 3 Total storage used = 23,732 cuft

Contents continued... Chattooga River Walk Center Hydrology Calculations.gpw

Hydrograph Reports Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 Hydrograph No. 2, Reservoir, Ex. Pond B1 Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 Hydrograph No. 4, Reservoir, Prop Pond B1

100 - Year Summary Report Hydrograph Reports

Hydrograph No. 1, SCS Runoff, Existing Basin A to Pond B1 Hydrograph No. 2, Reservoir, Ex. Pond B1 Hydrograph No. 3, SCS Runoff, Proposed Basin A to Pond B1 Hydrograph No. 4, Reservoir, Prop Pond B1

APPENDIX C

CALCULATIONS

Name of Developer: Date Submitted:

Development Name: Permit Number:

Site Location / Address: Developer Contact:

Phone Number:

Name of Engineer(s):

Development Type: Maintenance Responsibility:

1.01

1.06

1.06

0.00

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

Basin A DB 1 0.37 0.69 0.00

Drainage 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

0.37 0.69 0.00

Yes

Yes

1,401

1,401

1,681

100%

Tracking #: Conditions of Approval:

Reviewed By:

Date Approved:

Georgia Stormwater Management Manual

Stormwater Quality Site Development Review Tool

Version 2.2

General Information 11/16/2023

Travis Hemingway

803-508-0180

CROFT & Associates

USDA Forest Service

Site Summary

Official Use Only

Total Post-Development Area (ac):

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

Chattooga River Work Center

9975 Highway 441S

Commercial/Retail

USDA Forest Service

Lakemont, GA. 30552

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

T S

S R e d u ct io n

Total Suspended…