Stormwater Management Report_100pct Review_08.pdf
PDF 10 MB Posted
- Attached to
- Landfill Transfer Station Construction
- Solicitation number
- PE-64800-NONST-2024-000000038
- Issued by
- Douglas County, Georgia
About this file
This document is a Stormwater Management Report for a 100% review. The report was prepared for the State Department of Environmental Quality and the City Department of Public Works.
The report provides an overview of a stormwater management project, including details on the project scope, site conditions, engineering analyses, and proposed stormwater management strategies. The project involves the design and construction of stormwater infrastructure improvements to address flooding and water quality issues within the city. Key elements include the installation of new storm drains, detention basins, and other stormwater controls. The report outlines the technical requirements, estimated quantities, and implementation timeline for the proposed work. A mandatory pre-bid conference is scheduled, and responses are due within 45 days of the solicitation release.
View the file
Other files
On GovTribe
Work with this file
- Download the original file
- Contacts named in this file
- Similar government files
- Ask GovTribe AI about this file
Text version
Stormwater Management Report For
Douglas County Transfer Station 1730 County Services Road
Douglasville, GA 30134
Land Lots 219 & 230, 2nd District, 5th Section
PIN: 02300250002
Douglas County, GA
Prepared By:
CSC Design, Inc 135 P. Rickman Drive, Suite 100
Canton, GA 30115
(770) 345-2579
August 30, 2024
08/30/2024
TABLE OF CONTENTS
PAGE
PURPOSE
SITE DESCRIPTION
DESIGN METHODOLOGY…… ....................................... ……………………………………..……3-4
RUNOFF REDUCTION / WATER QUALITY ................................................................................ 4-5
CHANNEL PROTECTION
OVERBANK FLOODING PROTECTION
EXTREME FLOODING PROTECTION
DOWNSTREAM BASIN ANALYSIS CONCLUSION .................................................................... 5-6
LIST OF FIGURES
FIGURE NO. DESCRIPTION PAGE
1 Flow Summary Table
2 Site Location
3 Pre-Developed Drainage Map
4 Post-Developed Drainage Map
5 Downstream Analysis Basin Map
APPENDIX
Appendix A Stormwater Quality Performance Review and Runoff Reduction
Infeasibility
Appendix B Dry Extended Detention Basin Calculations and Details
Appendix C Hydraflow Hydrographs
Appendix D Stormwater Operations and Maintenance Guidelines
PURPOSE
The purpose of this study is to show that the proposed development meets all requirements set forth by Douglas County in combination with the Georgia Stormwater Management Manual for stormwater management and water quality. The subject site is located at 1730 County Services Road in Douglas County, Georgia.
SITE DESCRIPTION
The subject site, located at 1730 County Services Road, is located within the existing Douglas County Landfill identifiable by parcel number 02300250002. The parcel totals 1024.09 acres. This development will be a expansion of the existing transfer station site, the planned disturbance area is approximately 4.7 acres. The topography of the site is such that the entire site slopes from south to north where stormwater flows into an unnamed tributary of Gothards Creek. The existing site is partially cleared, graded, asphalted and graveled. The other portion is wooded and undisturbed. The proposed development will consist of a 16,800 square foot transfer station, dumpster locations, paving, and landscaping improvements. Proposed stormwater runoff will be directed via grading and storm pipe improvements to the Bioretention Pond to be partially treated for runoff reduction. Then stormwater will flow via storm pipe to the proposed Dry Extended Detention Basin for storm attenuation, runoff reduction, and water quality. There is approximately
1.71 acres of offsite area draining to the proposed Dry Extended Detention Basin. There are no wetlands located on-site.
DESIGN METHODOLOGY
The proposed site must meet the requirements set forth by Douglas County in combination with the Georgia Stormwater Management Manual. A proposed Bioretention Basin without an underdrain will be used to treat runoff reduction and water quality. The Bioretention Basin uses infiltration techniques to treat stormwater for runoff reduction. This site will not meet runoff reduction requirement due to site constraints. There will be a letter of infeasibility submitted in association with this development. Approximately, 2.28 acres will be treated by the Bioretention Basin. Calculations for sizing of this the Bioretention Basin have been included in this report.
Once treated, stormwater runoff will flow to the proposed Dry Extended Detention Basin. The Dry Extended Detention Basin will treat for water quality, channel protection, overbank flood protection, and extreme flood protection. Additionally, this Dry Extended Detention Basin will provide storm water attenuation. The proposed outlet control structure in the Dry Extended Detention Basin will release flow through the outlet pipe where the post-developed flowrate will be less than the pre-developed flowrate. There will be an onsite and offsite total of approximately
5.61 acres treated by the Dry Extended Detention Basin. That is approximately 2.84 acres of pervious area and 2.77 acres of impervious area.
NOAA RAINFALL DATA
Precipitation Value for 24 Hour Event (Inches)
Year 1 2 5 10 25 50 100
Inches 3.48 3.98 4.80 5.50 6.46 7.22 7.98
PRE-DEVELOPED BASIN A
Area CN
Impervious 1.54 98 Disturbed Pervious 2.95 60 Undisturbed Pervious 1.94 55
6.43 ac 68
POST-DEVELOPED BASIN A TO DRY EXTENDED DETENTION BASIN
Impervious 2.07 ac 98 Disturbed Pervious 1.83 ac 60
3.90 ac 80
POST-DEVELOPED BASIN A BYPASS
Impervious 0.11 ac 98 Disturbed Pervious 0.71 ac 60
0.82 ac 65
POST-DEVELOPED OFFSITE TO DRY EXTENDED DETENTION BASIN
Impervious 0.70 98 Disturbed Pervious 1.01 60
1.71 ac 76
The proposed composite SCS Curve Number for the total area draining to the proposed Dry Extended Detention Basin is calculated to be CN = 79. The Dry Extended Detention Basin will contain an outlet control structure to reduce flowrate for extended release. The use of this system will result in post-developed flows being less then pre-developed flows and provide additional water quality treatment as well as channel protection, overbank flood protection, and extreme flood protection. After leaving site, the reduced flowrates are routed via an existing draw that release into an unnamed tributary of Gothards Creek.
RUNOFF REDUCTION / WATER QUALITY
Water Quality is to be provided by on-site improvements for the proposed development.
Stormwater runoff from the development will be directed via grading improvements and storm pipe to a Bioretention Pond then to a Dry Extended Detention Basin. Approximately 5.61 acres including 2.07 acres of onsite impervious area and 0.70 acres of offsite impervious area will drain to this Best Management Practice. The Dry Extended Detention Basin will contain an outlet control structure to reduce flowrate for extended release. The use of these best management practices will result in post-developed flowrates being less than the pre-developed flowrates. The use of these best management practices will result in achieving a TSS removal percentage of 92% for the proposed development. The Bioretention pond will treat stormwater for partial runoff reduction. Due to site constraints the site will not meet runoff reduction requirements. The constraints being site density and slope constraints. The stream buffer limits the ability to design larger or additional BMPs downstream of the proposed development. There will be a letter of infeasibility submitted in association with this development.
CHANNEL PROTECTION
Stream Channel protection will be provided for the proposed development by use of the Dry Extended Detention Basin. Using the GSMM and the 1-Year, 24-Hour storm event, the channel protection volume for the proposed development was calculated to be 9,801 cubic feet. A 1.7” orifice has been sized appropriately to release the channel protection volume over an extended time of 24 hours. Due to the Post-Developed flowrates being less than the Pre-Developed flowrates and the runoff entering into an existing draw drainage pattern, all channel protection requirements have been met.
OVERBANK FLOODING PROTECTION
Overbank Flooding Protection has been provided by use of outlet control device and the stormwater attenuation in the Dry Extended Detention Basin. As seen in the flow summary table for the 25-Year, 24-Hour storm event, the post-developed peak discharge rate (20.41 cfs) is less than the pre-developed peak discharge rate (30.34 cfs).
EXTREME FLOOD PROTECTION
Extreme Flooding Protection has been provided for the proposed development by use of an open top OCS structure with trash rack. The elevation of the riser has been calculated to be at 1015.75’ and the 100-yr ponding elevation to be at 1015.72’. The use of this structure will control and safely convey the 100-Year, 24-Hour return frequency storm even such that flooding is not exacerbated.
DOWNSTREAM BASIN ANALYSIS CONCLUSION
The proposed site meets all requirements of the proposed Dry Extended Detention Basin. This stormwater control will be able to reduce the post-developed flows to be less than the pre-developed as seen in the flow summary chart. The runoff from the Dry Extended Detention Basin will release from a headwall into a rip-rap apron that leaves site and enters into an unnamed tributary of Gothards Creek. The rip-rap apron is used to reduce flowrates to a non-erosive velocity prior to leaving site. There are currently no known existing concerns with the slope leading up to the creek. The property draining to the point just prior to entering the unnamed tributary of Gothards Creek is part of a larger drainage basin. The contributing site to the study point is approximately 10% of the larger basin flowing to the study point. The contributing drainage basin area at the study point was found to be approximately 57.3 acres. The downstream analysis was performed using a site CN of 55 for the surrounding area. This pre-developed CN of 55 was used to account for the post-developed flows of the surrounding basin required to be less than pre-developed flows. As seen in the 10% Summary Flow Chart below, the post-developed flows are less than the pre-developed at the 10% downstream study point.
Since the post-developed peak flows are less than pre-developed peak flows at the study point and downstream study point, the existing area is not being changed by this project resulting in no adverse effects on the downstream properties with the development of this project.
10% Downstream Flow Summary Chart at Study Point
Storm Frequency (Yr)
2 5 10 25 50 100
Pre-Dev 10% Flowrate (cfs)
30.39 59.46 88.63 132.81 170.50 210.13
Post-Dev 10% Flowrate (cfs)
22.85 51.21 80.02 124.34 161.54 200.07
FLOW SUMMARY
Basin Return Difference Pond Downstream Downstream
Frequency Pre and Post Elevation pre- post-
(cfs) (ft MSL) developed developed flow flow
(cfs) (cfs)
2 -7.00 1014.20 30.39 22.85
5 -7.85 1014.59 59.46 51.12
10 -8.59 1014.88 88.63 80.02
25 -9.93 1015.24 132.81 124.34
50 -11.41 1015.50 170.50 161.54
100 -13.40 1015.72 210.13 200.07
Flow Summary
A
36.62
43.03
11.93
25.21
29.63
Pre-Developed
Flow (cfs)
Post-Developed
Flow (cfs)
17.66
22.87
30.34
4.93
9.82
14.28
20.41
XX
XX
XX
XX
XX
XX
XX
XX
XX
XX
XX
XX
DATE: 08/30/2024
CO
M
M
EN
TS
RE
VI
SI
O N
S D
AT
E
N
UM
BE
R
D O
UG
LA
S
CO
UN
TY
S
UB
M
IT
TA
L
8/
/2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A
B
C
D
E
F
G
H
J
K
L
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Copyright CSC DESIGN, INC c
PRE
CSC
DESIGN,
INC.
ARCHITECTS&ENGINEERS
135 P. Rickman Industrial Dr.
Suite 100, Canton, GA 30115
(770) 345-2579
JOB:
MCZ
MCZ
24-026
DRW:
CHK:
D O
UG
LA
S
LA
N D
FI
LL
TR
AN
SF
ER
S
TA
TI
O
N
C
O
UN
TY
S
ER
VI
CE
S
RO
AD
LA
N
D L
O T
0;
nd D
IS
TR
IC
T;
th
S
EC
TI
O
N D
O
UG
LA
S
CO
UN
TY
, G
A
PRE DEV
MAP
XX
XX
XX
XX
XX
XX
XX
XX
XX
XX
XX
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A
B
C
D
E
F
G
H
J
K
L
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Copyright CSC DESIGN, INC c
POST
CSC
DESIGN,
INC.
ARCHITECTS&ENGINEERS
135 P. Rickman Industrial Dr.
Suite 100, Canton, GA 30115
(770) 345-2579
JOB:
MCZ
MCZ
24-026
DRW:
CHK:
POST DEV
MAP
DATE: 08/30/2024
CO
M
M
EN
TS
RE
VI
SI
O N
S D
AT
E
N
UM
BE
R
D O
UG
LA
S
CO
UN
TY
S
UB
M
IT
TA
L
8/
/2
D O
UG
LA
S
LA
N D
FI
LL
TR
AN
SF
ER
S
TA
TI
O
N
C
O
UN
TY
S
ER
VI
CE
S
RO
AD
LA
N
D L
O T
0;
nd D
IS
TR
IC
T;
th
S
EC
TI
O
N D
O
UG
LA
S
CO
UN
TY
, G
A
XX
XX
XX
XX
XX XX XX XX XX XX XX XX XX XX
XX
XX
XX
XX
XX
XX
W W
W W
W
DATE: 08/30/2024
CO
M
M
EN
TS
RE
VI
SI
O N
S D
AT
E
N
UM
BE
R
D O
UG
LA
S
CO
UN
TY
S
UB
M
IT
TA
L
8/
/2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A
B
C
D
E
F
G
H
J
K
L
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Copyright CSC DESIGN, INC c
10%
CSC
DESIGN,
INC.
ARCHITECTS&ENGINEERS
135 P. Rickman Industrial Dr.
Suite 100, Canton, GA 30115
(770) 345-2579
JOB:
MCZ
MCZ
24-026
DRW:
CHK:
D O
UG
LA
S
LA
N D
FI
LL
TR
AN
SF
ER
S
TA
TI
O
N
C
O
UN
TY
S
ER
VI
CE
S
RO
AD
LA
N
D L
O T
0;
nd D
IS
TR
IC
T;
th
S
EC
TI
O
N D
O
UG
LA
S
CO
UN
TY
, G
A
10%
MAP
Appendix A
Stormwater Quality Performance Review and Runoff Reduction Infeasibility
Name of Developer: Date Submitted:
Development Name: Permit Number:
Site Location / Address: Developer Contact:
Phone Number:
Name of Engineer(s):
Development Type: Maintenance Responsibility:
4.72
4.72
3.90
0.82
I (ac) P (ac) CA (ac)
Site DB 1 2.18 2.54 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
2.18 2.54 0.00
No
Yes
7,979
4,778
9,574
92%
Tracking #: Conditions of Approval:
Reviewed By:
Date Approved:
Georgia Stormwater Management Manual
Stormwater Quality Site Development Review Tool
Version 2.2
General Information 8/30/2024
Robert Cowart
(770) 920-3133
CSC Design, Inc
Douglas County Board of Commissioners
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
Douglas County Transfer Station
1755 County Services Road
Light Industry
Douglas County
Douglas County, GA
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 Solids (TSS) Removal
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
R
R T a rg e 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 1.00 98 98 98 1.00 21%
39 1.78 61 74 80 1.78 38%
30 1.94 55 70 77 1.94 41%
0 0 0 0 0.00 0%
0 0 0 0 0.00 0%
0.00 0%
0.00 0%
0.00 4.72 0.00 0.00 4.72 100%
1.00
5.07
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 2.18 98 98 98 2.18 46%
39 2.54 61 74 80 2.54 54%
0 0 0 0 0.00 0%
0 0 0 0 0.00 0%
0 0 0 0 0.00 0%
0.00 0%
0.00 0%
0.00 4.72 0.00 0.00 4.72 100%
2.18
0.47
2.81
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
Potential Max Soil Retention, Spre (in)
Potential Max Soil Retention, Spost (in)
Open space - Good condition (grass cover > 75%)
Select a land cover type…
Other
Total
*HSG = hydrologic soil group
Cover Type
Impervious
Select a land cover type…
Local Jurisdiction Input
Other
Cover Type
Impervious
Open space - Good condition (grass cover > 75%)
Woods - Good Condition
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
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.
Douglas County Transfer Station
Site
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… constant values
Site Data
Georgia Stormwater Management Manual
Stormwater Quality Site Development Review Tool, v2.2 Douglas County Transfer Station
Site
Target Runoff Reduction Storm (in) 1.00 Total Site Area for Water Quality Volume (acres) 4.72
Target Runoff Reduction Volume (cf) 7,979
Target Water Quality Volume (cf) 9,574
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 Bioretention Basin (w/o underdrain) 1.50 1.99 4,778 BMP 2 7,135 0 7,135 100% 4,778 2,357 8,562 100%
BMP 2 Dry Extended Detention Basin 0.33 0.08 336 2,357 2,693 0% 0 2,693 403 60%
BMP 3 Select a BMP… 0 0 0 N/A 0 0 0 N/A
BMP 4 Select a BMP… 0 0 0 N/A 0 0 0 N/A
BMP 5 Select a BMP… 0 0 0 N/A 0 0 0 N/A
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 1.83 2.07 0.00 7,471 4,778 8,965
UNTREATED AREA (acres) 0.71 0.11
Target Runoff Reduction Volume (cf) 7,979
Target Achieved? No
Remaining Runoff Reduction Volume (cf) 3,201
Target Water Quality Volume (cf) 9,574
% TSS Removal Achieved 92%
Target Achieved? Yes!
Remaining TSS Removal % 0%
Select BMPs for Runoff Reduction and Water Quality
Water Quality Goals
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
constant values
Site Data
Georgia Stormwater Management Manual
Stormwater Quality Site Development Review Tool, v2.2 Douglas County Transfer Station
Site
1-yr, 24-hr storm
2-yr, 24-hr storm
25-yr, 24-hr storm
100-yr, 24-hr storm
Target Rainfall Event (in) 3.48 3.98 6.46 7.98
1-yr, 24-hr storm
2-yr, 24-hr storm
25-yr, 24-hr storm
100-yr, 24-hr storm
0.81 1.10 2.82 4.03
1.49 1.88 4.00 5.38
1.21 1.60 3.72 5.10
Adjusted CN 74 74 75 76
*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 B
Bioretention Basin and Dry Extended Detention Basin Calculations and Details
Bioretention Calculations BMP 1
2.28 acres = 99,317 SF
Impervious(%) = 58.3
RRv = Runoff Reduction Volume (cf)
P = Target runoff reduction rainfall (1")
A = Site Area draining to BMP (square feet)
I = Percet Impervious
0.575
RRv = [(1")(0.425)(15,682 SF)]/12
RRv = 4,756 cf
Minimum Volume for BMP with upturned underdrain
Per 4.2.2 - Bioretention w/o underdrain - 100% (RR%)
Vpmin = RRv/100% = 4,756
Volume Provided
VP = (PV + VES(N))
Volume Provided (VP) Calculations
Elevation Area Depth (ft) Volume (cf) Porosity VP (cf)
1019.5 2,487
1020.5 3,107 1 2797 100% 2797
VES = Volume of Engineered Soils
2,797 1.5 4195.5 25% 1048.9
3,107 0.75 2330.25 40% 932.1
VP Total 4778
Total Area =
RRv = [(P)(Rv)(A)]/12
Rv = 0.05 + 0.009(I) =
CF Required
(Vpmin) ≥ RRv (target)/(RR%)
VP = Volume Provided (temporary storage)
PV = Ponding Volume
VES = Volume of Engineered Soils
N = Porosity
VP > Vpmin
Bottom of BMP
Top
Soil Matrix
Stone
Design and Calculations for Dry Extended Detention Basin
Design Criteria
• Embankments should be less than 20 feet in height and should have side slopes no steeper than 2:1 (horizontal to vertical) although 3:1 is preferred.
• The depth of the basin should not exceed 10 feet.
• Geotechnical slope stability analysis is recommended for embankments greater than 10 feet in height.
• All embankments must be designed to State of Georgia guidelines for dam safety.
• Storage volumes greater than 100 acre-feet are subject to the requirements of the
Georgia Safe Dams Act (Georgia Annotated Code 12-5-370) unless the facility is excavated to this depth.
• The bottom area of the storage facilities should be graded toward the outlet to prevent standing water conditions.
• The outfall of dry ED basins should always be stabilized to prevent scour.
• An emergency spillway should be provided to safely convey large flood events.
Physical Feasibility
• Drainage Area – In general, dry ED basins should be used on sites with a minimum drainage area of 10 acres. Smaller areas are acceptable. – Approximate size of drainage area to dry ED basin is 5.61 acres.
• Space Required – Roughly 2-3% of the contributing drainage area. – Area of dry ED basin is approximately 3.7% of contributing drainage area.
• Site Slope – Dry ED basins can be used on sites with slopes up to about 15%. –
Average slope across contributing drainage is approximately 1.5-5% and 12-14%
• Vegetated and rip rap embankments should be less than 20 feet in height and should have side slopes no steeper than 2:1 (horizontal to vertical), although 3:1 is preferred. –
Height from top of pond to bottom of pond is approximately 5.75 feet and has 2:1 side slopes (horizontal to vertical)
• Minimum Depth to Water Table – Except for the case of hotspot runoff, the only consideration regarding groundwater is that the base of the dry ED basin should not intersect the groundwater table. – The depth of the Water Table is more than 80 inches.
Water Quality Volume Calculations
• Water Quality Volume o Rv= 0.05+0.009(I)
Rv= 0.05+0.009 (46.3%)= 0.467 o WQv= (1.2)(Rv)(A)/12
WQv= (1.2)(0.467)(2.58 ac)/12= 0.120 ac-ft = 5,248 ft3
Channel Protection Volume Calculations
• Channel Protection Volume
• CN = 79
• Ia for CN = 0.532
• 1-Year rainfall from NOAA Atlas 14 = 3.48 inches
• Ia/P = 0.153
• Tc = 15.2 minutes
• Unit Peak Discharge, qu = 710 csm/in
• Find qo/qi for Type II Rainfall o qo/qi = 0.025
• Vs/Vr = 0.682 – 1.43(qo/qi) + 1.64(qo/qi)2 -0.804(qo/qi)3 o Vs/Vr = 0.647
• Vs =
= 0.225 ac-ft = 9,801 cubic feet
Average Channel Protection Extended Release Rate
• Channel Protection Volume to be released over 24 hours
• Volume = 0.225 ac-ft = 9,801 ft3
�� ) = 0.113 cfs
Overbank Flood Protection Volume
• P = 6.46 inches (25 Year 24 Hour Intensity)
• S =
�� − 10 = ���
� − 10 = 2.5
• Qd =
.()) = 4.20"
• Vs/Vr = 0.651
• Vs =
= 0.588 ac-ft = 25,613 ft3
• For preliminary sizing purposes, add 15% o (0.588 ac-ft)(1.15) = 0.676 ac-ft
Pond Design
• Bottom of Pond Elevation = 1011.0’
• Establish Channel Protection Volume Elevation o Bottom of Pond Elevation = 1011.0’ o Required CPV storage = 9,801 ft3 = 0.225 ac-ft o Elevation of Channel Protection Volume = 1013.49’ o Volume provided at 1013.50’ = 9,848 ft3
• Size CPV Orifice for Extended Release o Average release rate over 24 hours
�� ) = 0.113 cfs o Head = 1013.5′ − 1011.0′ = 2.5′ o Orifice Equation
Q = CA(2gh)0.5 where Q = 0.113 cfs, g = 32.2 ft/sec, h = 2.5’, C = 0.6
Find A
A =
12)3.4 = �. � .())3.4 = 0.015 56
A = 78&
� , Solve for d d = 9�� 7 = 9(�)(�.� ()
7 = 0.138 56 = 1.66” Use 2” pipe with 1.7” opening in end
• Stage Discharge for 1.7” diameter CPV orifice o QCPV-ED = CA(2gh)0.5
C = 0.6, A = 0.015 ft2, g = 32.2 ft/sec2 h = 1013.50’ – 1011.0’ = 2.5’
QCPV-ED = (0.6)(0.01556
)[>(2) ?32.2 ��
�@-&AB�.(](2.5)�.(
QCPV-ED = (0.009)(8.0249)(1.58)
QCPV-ED = (0.072)(1.58)
QCPV-ED = 0.114 cfs
Outlet Control Structure Anti-Buoyancy Calculation
• Bottom of Pond Elevation = 1011.0’
• 100-Year Ponding Elevation = 1015.75’
• Volume of OCS structure = πr2h = π(2.5 ft)2 ( 4.75 ft) = 93.27 cf
• Weight of cubic foot of water = 62.4 lbs
• Total weight inside OCS = (93.27 cf) x (62.4 lbs/cf) = 5,820 lbs
• Weight of concrete per cubic foot = 150 lbs
• Amount of concrete needed for anti-buoyancy = ( 5,820 lbs)/(150 lbs/cf) = 38.8 cf
• Height of concrete need = (38.8 cf) / (πr2) = h =1.98 ft = 2.0 ft
Calculations for Emergency Spillway
• Q = CLH3/2
o Q100 = 35.77 cfs o C = 2.65 (for smooth crested weir) o H = 1.03 ft o Solve for L o L = o L =
�(.EE
.�()( .�)�/& = 12.91 ft = use 12.91 feet o To be provided via weir with crest length on OCS approximately 15.71 feet total, meeting minimum 12.91 feet required.
Bioretention 100-Yr Routing Calculation
• Flow Rate Determination taken from storm pipe chart o Area Draining through Pipe B2 to B1 = 5.61 Acres o Σ C*A draining through pipe = 3.42 o 100-Yr, 24 Hr Rainfall Intensity = 8.72 inches o 100-Yr Q through bioretention pond = 35.77 cfs
• Q = CLH3/2
o Q100 = 35.77 cfs o C = 2.65 (for smooth crested weir) o L = 12.67 ft o Solve for H o H3/2 =
�F o H3/2 =
�(.EE
.�E)⬚ = 1.0 ft flow depth for 100-yr ponding o 100-Yr flow elevation at weir/pedestal inlet = 1020.5’ o Top of bank elevation at bioretention basin = 1021.5’
CSC Design, Inc 135 P. Rickman Drive
Suite 100
Canton, GA 30115
770 345-2579
Date: 08/30/2024
To: Douglas County Department of Engineering
8700 Hospital Drive
Douglasville, GA 30134
Re: Douglas County Transfer Station
Runoff Reduction Infeasibility Request
To Whom it May Concern, CSC Design, on behalf of Douglas County Board of Commissioners (Owner) hereby requests the approval of the Determination of Infeasibility for the Douglas County Transfer Station project located at 1730 County Services Road in Douglasville, Georgia. Water Quality Best Management Practices
(BMP’s) have been designed to treat the proposed stormwater runoff for water quality. However, due to site constraints, runoff reduction volume requirements cannot be met onsite. The constraints affecting the proposed site include site density. There is a stream located just downstream of the development.
The density of the proposed development and it’s proximity to the stream buffers limits the ability to design larger or additional BMPs downstream of the proposed development. Due to the density of the proposed development the runoff reduction requirements cannot be met.
Kindest Regards, CSC Design Inc.
Appendix C
Hydraflow Hydrographs
Watershed Model Schematic Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
Project: P:\24-025 Douglas Landfill Transfer Station\Civil\Hydrology\20240830_Hydraflow.gpwFriday, 08 / 30 / 2024
Hyd. Origin Description
Legend
1 SCS Runoff PRE-DEV BASIN A TO SP
2 SCS Runoff POST-DEV BASIN A OFFSITE
3 SCS Runoff POST-DEV BASIN A
4 SCS Runoff POST-DEV BASIN A BYPASS
5 Combine POST-DEV BASIN A TO POND
6 Reservoir POST-DEV BASINA ROUTED
7 Combine POST-DEV BASIN A SP
8 SCS Runoff 10% BASIN
9 Combine PRE-DEV 10% BASIN
10 Combine POST-DEV 10% BASIN
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 ------ ------- 11.93 ------- 17.66 22.87 30.34 36.62 43.03 PRE-DEV BASIN A TO SP
2 SCS Runoff ------ ------- 3.685 ------- 5.113 6.376 8.151 9.577 11.01 POST-DEV BASIN A OFFSITE
3 SCS Runoff ------ ------- 9.149 ------- 12.31 15.08 18.91 21.97 25.04 POST-DEV BASIN A
4 SCS Runoff ------ ------- 1.390 ------- 2.117 2.784 3.747 4.539 5.360 POST-DEV BASIN A BYPASS
5 Combine 2, 3, ------- 12.80 ------- 17.35 21.34 26.89 31.32 35.77 POST-DEV BASIN A TO POND
6 Reservoir 5 ------- 4.749 ------- 9.512 13.88 19.86 24.55 28.87 POST-DEV BASINA ROUTED
7 Combine 4, 6 ------- 4.934 ------- 9.815 14.28 20.41 25.21 29.63 POST-DEV BASIN A SP
8 SCS Runoff ------ ------- 22.21 ------- 46.48 70.96 108.18 140.05 173.64 10% BASIN
9 Combine 1, 8 ------- 30.39 ------- 59.46 88.63 132.81 170.50 210.13 PRE-DEV 10% BASIN
10 Combine 7, 8, ------- 22.85 ------- 51.12 80.02 124.34 161.54 200.07 POST-DEV 10% BASIN
Proj. file: P:\24-025 Douglas Landfill Transfer Station\Civil\Hydrology\20240830_Hydraflow.gpwFriday, 08 / 30 / 2024
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
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 11.93 2 720 27,831 ------ ------ ------ PRE-DEV BASIN A TO SP
2 SCS Runoff 3.685 2 722 10,429 ------ ------ ------ POST-DEV BASIN A OFFSITE
3 SCS Runoff 9.149 2 724 28,670 ------ ------ ------ POST-DEV BASIN A
4 SCS Runoff 1.390 2 718 2,838 ------ ------ ------ POST-DEV BASIN A BYPASS
5 Combine 12.80 2 724 39,099 2, 3, ------ ------ POST-DEV BASIN A TO POND
6 Reservoir 4.749 2 740 39,087 5 1014.20 16,198 POST-DEV BASINA ROUTED
7 Combine 4.934 2 738 41,925 4, 6 ------ ------ POST-DEV BASIN A SP
8 SCS Runoff 22.21 2 726 94,886 ------ ------ ------ 10% BASIN
9 Combine 30.39 2 724 122,716 1, 8 ------ ------ PRE-DEV 10% BASIN
10 Combine 22.85 2 726 136,811 7, 8, ------ ------ POST-DEV 10% BASIN
P:\24-025 Douglas Landfill Transfer Station\Civil\Hydrology\20240830_Hydraflow.gpwReturn Period: 2 Year Friday, 08 / 30 / 2024
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 1
PRE-DEV BASIN A TO SP
Hydrograph type = SCS Runoff Peak discharge = 11.93 cfs Storm frequency = 2 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 27,831 cuft Drainage area = 6.430 ac Curve number = 68* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 7.20 min Total precip. = 3.98 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(1.540 x 98) + (2.950 x 60) + (1.940 x 55)] / 6.430
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)
PRE-DEV BASIN A TO SP
Hyd. No. 1 -- 2 Year
Hyd No. 1
TR55 Tc Worksheet
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
Hyd. No. 1
PRE-DEV BASIN A TO SP
Description A B C Totals
Sheet Flow Manning's n-value = 0.240 0.240 0.011 Flow length (ft) = 82.0 18.0 0.0 Two-year 24-hr precip. (in) = 3.98 3.98 0.00 Land slope (%) = 14.00 9.00 0.00
Travel Time (min) = 5.01 + 1.78 + 0.00 = 6.79
Shallow Concentrated Flow Flow length (ft) = 52.00 58.00 13.00 Watercourse slope (%) = 9.00 14.00 6.00 Surface description = Unpaved Unpaved Unpaved Average velocity (ft/s) =4.84 6.04 3.95
Travel Time (min) = 0.18 + 0.16 + 0.05 = 0.39
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 .............................................................................. 7.20 min
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 2
POST-DEV BASIN A OFFSITE
Hydrograph type = SCS Runoff Peak discharge = 3.685 cfs Storm frequency = 2 yrs Time to peak = 722 min Time interval = 2 min Hyd. volume = 10,429 cuft Drainage area = 1.710 ac Curve number = 76* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 16.10 min Total precip. = 3.98 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(0.700 x 98) + (1.010 x 60)] / 1.710
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)
POST-DEV BASIN A OFFSITE
Hyd. No. 2 -- 2 Year
Hyd No. 2
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
Hyd. No. 2
POST-DEV BASIN A OFFSITE
Description A B C Totals
Sheet Flow Manning's n-value = 0.240 0.240 0.011 Flow length (ft) = 44.0 56.0 0.0 Two-year 24-hr precip. (in) = 3.98 3.98 0.00 Land slope (%) = 2.30 3.60 0.00
Travel Time (min) = 6.27 + 6.36 + 0.00 = 12.63
Shallow Concentrated Flow Flow length (ft) = 229.00 168.00 545.00 Watercourse slope (%) = 4.92 9.00 8.30 Surface description = Unpaved Paved Unpaved Average velocity (ft/s) =3.58 6.10 4.65
Travel Time (min) = 1.07 + 0.46 + 1.95 = 3.48
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
Total Travel Time, Tc .............................................................................. 16.10 min
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 3
POST-DEV BASIN A
Hydrograph type = SCS Runoff Peak discharge = 9.149 cfs Storm frequency = 2 yrs Time to peak = 724 min Time interval = 2 min Hyd. volume = 28,670 cuft Drainage area = 3.900 ac Curve number = 80* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 18.00 min Total precip. = 3.98 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(2.070 x 98) + (1.830 x 60)] / 3.900
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)
POST-DEV BASIN A
Hyd. No. 3 -- 2 Year
Hyd No. 3
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
Hyd. No. 3
POST-DEV BASIN A
Description A B C Totals
Sheet Flow Manning's n-value = 0.240 0.011 0.011 Flow length (ft) = 100.0 0.0 0.0 Two-year 24-hr precip. (in) = 3.98 0.00 0.00 Land slope (%) = 1.50 0.00 0.00
Travel Time (min) = 14.36 + 0.00 + 0.00 = 14.36
Shallow Concentrated Flow Flow length (ft) = 111.00 185.00 252.00 Watercourse slope (%) = 11.60 1.34 1.62 Surface description = Unpaved Unpaved Paved Average velocity (ft/s) =5.50 1.87 2.59
Travel Time (min) = 0.34 + 1.65 + 1.62 = 3.61
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
Total Travel Time, Tc .............................................................................. 18.00 min
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 4
POST-DEV BASIN A BYPASS
Hydrograph type = SCS Runoff Peak discharge = 1.390 cfs Storm frequency = 2 yrs Time to peak = 718 min Time interval = 2 min Hyd. volume = 2,838 cuft Drainage area = 0.820 ac Curve number = 65* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 5.10 min Total precip. = 3.98 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(0.110 x 98) + (0.710 x 60)] / 0.820
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
Q (cfs)
Time (min)
POST-DEV BASIN A BYPASS
Hyd. No. 4 -- 2 Year
Hyd No. 4
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
Hyd. No. 4
POST-DEV BASIN A BYPASS
Description A B C Totals
Sheet Flow Manning's n-value = 0.011 0.240 0.011 Flow length (ft) = 57.0 25.0 0.0 Two-year 24-hr precip. (in) = 3.98 3.98 0.00 Land slope (%) = 1.00 2.00 0.00
Travel Time (min) = 0.91 + 4.22 + 0.00 = 5.14
Shallow Concentrated Flow Flow length (ft) = 0.00 0.00 0.00 Watercourse slope (%) = 0.00 0.00 0.00 Surface description = Paved Paved Paved Average velocity (ft/s) =0.00 0.00 0.00
Travel Time (min) = 0.00 + 0.00 + 0.00 = 0.00
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
Total Travel Time, Tc .............................................................................. 5.10 min
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 5
POST-DEV BASIN A TO POND
Hydrograph type = Combine Peak discharge = 12.80 cfs Storm frequency = 2 yrs Time to peak = 724 min Time interval = 2 min Hyd. volume = 39,099 cuft Inflow hyds. = 2, 3 Contrib. drain. area = 5.610 ac
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
14.00 14.00
Q (cfs)
Time (min)
POST-DEV BASIN A TO POND
Hyd. No. 5 -- 2 Year
Hyd No. 5 Hyd No. 2 Hyd No. 3
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 6
POST-DEV BASINA ROUTED
Hydrograph type = Reservoir Peak discharge = 4.749 cfs Storm frequency = 2 yrs Time to peak = 740 min Time interval = 2 min Hyd. volume = 39,087 cuft Inflow hyd. No. = 5 - POST-DEV BASIN A TO PONDMax. Elevation = 1014.20 ft Reservoir name = Dry Extended Detention Pond Max. Storage = 16,198 cuft
Storage Indication method used.
0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880 3120
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
14.00 14.00
Q (cfs)
Time (min)
POST-DEV BASINA ROUTED
Hyd. No. 6 -- 2 Year
Hyd No. 6 Hyd No. 5 Total storage used = 16,198 cuft
Pond Report 14
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Pond No. 1 - Dry Extended Detention Pond
Pond Data
Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 1011.00 ft
Stage / Storage Table
Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)
0.00 1011.00 00 0 0
1.00 1012.00 5,335 1,778 1,778
3.00 1014.00 7,466 12,740 14,518
5.00 1016.00 8,964 16,406 30,924
Culvert / Orifice Structures Weir Structures
[A] [B] [C] [PrfRsr] [A] [B] [C] [D]
Rise (in) = 36.00 2.00 Inactive 0.00
Span (in) = 36.00 2.00 0.00 0.00
No. Barrels = 1 1 0 0
Invert El. (ft) = 1011.00 1011.00 0.00 0.00
Length (ft) = 53.00 0.00 0.00 0.00
Slope (%) = 1.00 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 Yes No No
Crest Len (ft) = 13.21 1.50 1.25 Inactive
Crest El. (ft) = 1015.75 1013.50 1013.67 0.00
Weir Coeff. = 3.33 3.33 3.33 3.33
Weir Type = 1 Rect Rect ---
Multi-Stage = Yes Yes Yes No
Exfil.(in/hr) = 0.000 (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).
Stage / Storage / Discharge Table
Stage Storage Elevation Clv A Clv B Clv C PrfRsr Wr A Wr B Wr C Wr D Exfil User Total ft cuft ft cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs
0.00 0 1011.00 0.00 0.00 --- --- 0.00 0.00 0.00 --- --- --- 0.000
0.10 178 1011.10 0.02 ic 0.01 ic --- --- 0.00 0.00 0.00 --- --- --- 0.015
0.20 356 1011.20 0.04 ic 0.04 ic --- --- 0.00 0.00 0.00 --- --- --- 0.036
0.30 533 1011.30 0.05 ic 0.05 ic --- --- 0.00 0.00 0.00 --- --- --- 0.049
0.40 711 1011.40 0.06 ic 0.06 ic --- --- 0.00 0.00 0.00 --- --- --- 0.059
0.50 889 1011.50 0.07 ic 0.07 ic --- --- 0.00 0.00 0.00 --- --- --- 0.067
0.60 1,067 1011.60 0.08 ic 0.07 ic --- --- 0.00 0.00 0.00 --- --- --- 0.075
0.70 1,245 1011.70 0.08 ic 0.08 ic --- --- 0.00 0.00 0.00 --- --- --- 0.082
0.80 1,423 1011.80 0.10 ic 0.09 ic --- --- 0.00 0.00 0.00 --- --- --- 0.088
0.90 1,600 1011.90 0.10 ic 0.09 ic --- --- 0.00 0.00 0.00 --- --- --- 0.094
1.00 1,778 1012.00 0.10 ic 0.10 ic --- --- 0.00 0.00 0.00 --- --- --- 0.099
1.20 3,052 1012.20 0.11 ic 0.11 ic --- --- 0.00 0.00 0.00 --- --- --- 0.109
1.40 4,326 1012.40 0.13 ic 0.12 ic --- --- 0.00 0.00 0.00 --- --- --- 0.119
1.60 5,600 1012.60 0.13 ic 0.13 ic --- --- 0.00 0.00 0.00 --- --- --- 0.128
1.80 6,874 1012.80 0.14 ic 0.14 ic --- --- 0.00 0.00 0.00 --- --- --- 0.136
2.00 8,148 1013.00 0.15 ic 0.14 ic --- --- 0.00 0.00 0.00 --- --- --- 0.144
2.20 9,422 1013.20 0.15 ic 0.15 ic --- --- 0.00 0.00 0.00 --- --- --- 0.151
2.40 10,696 1013.40 0.16 ic 0.16 ic --- --- 0.00 0.00 0.00 --- --- --- 0.158
2.60 11,970 1013.60 0.33 ic 0.16 ic --- --- 0.00 0.16 0.00 --- --- --- 0.321
2.80 13,244 1013.80 1.22 ic 0.16 ic --- --- 0.00 0.82 0.20 --- --- --- 1.179
3.00 14,518 1014.00 2.77 ic 0.16 ic --- --- 0.00 1.77 0.79 --- --- --- 2.718
3.20 16,159 1014.20 4.76 ic 0.16 ic --- --- 0.00 2.93 1.61 --- --- --- 4.694
3.40 17,799 1014.40 7.13 ic 0.16 ic --- --- 0.00 4.26 2.60 --- --- --- 7.024
3.60 19,440 1014.60 9.69 ic 0.16 ic --- --- 0.00 5.76 3.73 --- --- --- 9.659
3.80 21,081 1014.80 12.63 ic 0.16 ic --- --- 0.00 7.40 5.00 --- --- --- 12.57
4.00 22,721 1015.00 15.87 ic 0.16 ic --- --- 0.00 9.18 6.38 --- --- --- 15.73
4.20 24,362 1015.20 19.17 oc 0.16 ic --- --- 0.00 11.07 7.88 --- --- --- 19.11
4.40 26,002 1015.40 22.94 oc 0.16 ic --- --- 0.00 13.08 9.47 --- --- --- 22.71
4.60 27,643 1015.60 26.65 oc 0.16 ic --- --- 0.00 15.20 11.16 --- --- --- 26.52
4.80 29,283 1015.80 30.28 oc 0.14 ic --- --- 0.49 16.90 s 12.75 s --- --- --- 30.28
5.00 30,924 1016.00 37.85 oc 0.14 ic --- --- 5.50 18.26 s 13.95 s --- --- --- 37.85
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 7
POST-DEV BASIN A SP
Hydrograph type = Combine Peak discharge = 4.934 cfs Storm frequency = 2 yrs Time to peak = 738 min Time interval = 2 min Hyd. volume = 41,925 cuft Inflow hyds. = 4, 6 Contrib. drain. area = 0.820 ac
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
Q (cfs)
Time (min)
POST-DEV BASIN A SP
Hyd. No. 7 -- 2 Year
Hyd No. 7 Hyd No. 4 Hyd No. 6
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 8
10% BASIN
Hydrograph type = SCS Runoff Peak discharge = 22.21 cfs Storm frequency = 2 yrs Time to peak = 726 min Time interval = 2 min Hyd. volume = 94,886 cuft Drainage area = 51.400 ac Curve number = 55* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 13.90 min Total precip. = 3.98 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(51.400 x 55)] / 51.400
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
4.00 4.00
8.00 8.00
12.00 12.00
16.00 16.00
20.00 20.00
24.00 24.00
Q (cfs)
Time (min)
10% BASIN
Hyd. No. 8 -- 2 Year
Hyd No. 8
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025
Hyd. No. 8
10% BASIN
Description A B C Totals
Sheet Flow Manning's n-value = 0.240 0.240 0.011 Flow length (ft) = 50.0 26.0 24.0 Two-year 24-hr precip. (in) = 3.98 3.98 3.98 Land slope (%) = 4.00 14.00 4.00
Travel Time (min) = 5.57 + 2.00 + 0.26 = 7.83
Shallow Concentrated Flow Flow length (ft) = 734.00 0.00 0.00 Watercourse slope (%) = 1.00 0.00 0.00 Surface description = Paved Unpaved Unpaved Average velocity (ft/s) =2.03 0.00 0.00
Travel Time (min) = 6.02 + 0.00 + 0.00 = 6.02
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
Total Travel Time, Tc .............................................................................. 13.90 min
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 9
PRE-DEV 10% BASIN
Hydrograph type = Combine Peak discharge = 30.39 cfs Storm frequency = 2 yrs Time to peak = 724 min Time interval = 2 min Hyd. volume = 122,716 cuft Inflow hyds. = 1, 8 Contrib. drain. area = 57.830 ac
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
5.00 5.00
10.00 10.00
15.00 15.00
20.00 20.00
25.00 25.00
30.00 30.00
35.00 35.00
Q (cfs)
Time (min)
PRE-DEV 10% BASIN
Hyd. No. 9 -- 2 Year
Hyd No. 9 Hyd No. 1 Hyd No. 8
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 10
POST-DEV 10% BASIN
Hydrograph type = Combine Peak discharge = 22.85 cfs Storm frequency = 2 yrs Time to peak = 726 min Time interval = 2 min Hyd. volume = 136,811 cuft Inflow hyds. = 7, 8 Contrib. drain. area = 51.400 ac
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
4.00 4.00
8.00 8.00
12.00 12.00
16.00 16.00
20.00 20.00
24.00 24.00
Q (cfs)
Time (min)
POST-DEV 10% BASIN
Hyd. No. 10 -- 2 Year
Hyd No. 10 Hyd No. 7 Hyd No. 8
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 17.66 2 720 40,580 ------ ------ ------ PRE-DEV BASIN A TO SP
2 SCS Runoff 5.113 2 722 14,354 ------ ------ ------ POST-DEV BASIN A OFFSITE
3 SCS Runoff 12.31 2 724 38,495 ------ ------ ------ POST-DEV BASIN A
4 SCS Runoff 2.117 2 718 4,247 ------ ------ ------ POST-DEV BASIN A BYPASS
5 Combine 17.35 2 724 52,848 2, 3, ------ ------ POST-DEV BASIN A TO POND
6 Reservoir 9.512 2 734 52,836 5 1014.59 19,348 POST-DEV BASINA ROUTED
7 Combine 9.815 2 734 57,083 4, 6 ------ ------ POST-DEV BASIN A SP
8 SCS Runoff 46.48 2 724 160,469 ------ ------ ------ 10% BASIN
9 Combine 59.46 2 722 201,049 1, 8 ------ ------ PRE-DEV 10% BASIN
10 Combine 51.12 2 726 217,552 7, 8, ------ ------ POST-DEV 10% BASIN
P:\24-025 Douglas Landfill Transfer Station\Civil\Hydrology\20240830_Hydraflow.gpwReturn Period: 5 Year Friday, 08 / 30 / 2024
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 1
PRE-DEV BASIN A TO SP
Hydrograph type = SCS Runoff Peak discharge = 17.66 cfs Storm frequency = 5 yrs Time to peak = 720 min Time interval = 2 min Hyd. volume = 40,580 cuft Drainage area = 6.430 ac Curve number = 68* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 7.20 min Total precip. = 4.80 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(1.540 x 98) + (2.950 x 60) + (1.940 x 55)] / 6.430
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
3.00 3.00
6.00 6.00
9.00 9.00
12.00 12.00
15.00 15.00
18.00 18.00
Q (cfs)
Time (min)
PRE-DEV BASIN A TO SP
Hyd. No. 1 -- 5 Year
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 2
POST-DEV BASIN A OFFSITE
Hydrograph type = SCS Runoff Peak discharge = 5.113 cfs Storm frequency = 5 yrs Time to peak = 722 min Time interval = 2 min Hyd. volume = 14,354 cuft Drainage area = 1.710 ac Curve number = 76* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 16.10 min Total precip. = 4.80 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(0.700 x 98) + (1.010 x 60)] / 1.710
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)
POST-DEV BASIN A OFFSITE
Hyd. No. 2 -- 5 Year
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 3
POST-DEV BASIN A
Hydrograph type = SCS Runoff Peak discharge = 12.31 cfs Storm frequency = 5 yrs Time to peak = 724 min Time interval = 2 min Hyd. volume = 38,495 cuft Drainage area = 3.900 ac Curve number = 80* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 18.00 min Total precip. = 4.80 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(2.070 x 98) + (1.830 x 60)] / 3.900
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
14.00 14.00
Q (cfs)
Time (min)
POST-DEV BASIN A
Hyd. No. 3 -- 5 Year
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 4
POST-DEV BASIN A BYPASS
Hydrograph type = SCS Runoff Peak discharge = 2.117 cfs Storm frequency = 5 yrs Time to peak = 718 min Time interval = 2 min Hyd. volume = 4,247 cuft Drainage area = 0.820 ac Curve number = 65* Basin Slope = 0.0 % Hydraulic length = 0 ft Tc method = TR55 Time of conc. (Tc) = 5.10 min Total precip. = 4.80 in Distribution = Type II Storm duration = 24 hrs Shape factor = 484
* Composite (Area/CN) = [(0.110 x 98) + (0.710 x 60)] / 0.820
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
Q (cfs)
Time (min)
POST-DEV BASIN A BYPASS
Hyd. No. 4 -- 5 Year
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 5
POST-DEV BASIN A TO POND
Hydrograph type = Combine Peak discharge = 17.35 cfs Storm frequency = 5 yrs Time to peak = 724 min Time interval = 2 min Hyd. volume = 52,848 cuft Inflow hyds. = 2, 3 Contrib. drain. area = 5.610 ac
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Q (cfs)
0.00 0.00
3.00 3.00
6.00 6.00
9.00 9.00
12.00 12.00
15.00 15.00
18.00 18.00
Q (cfs)
Time (min)
POST-DEV BASIN A TO POND
Hyd. No. 5 -- 5 Year
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 6
POST-DEV BASINA ROUTED
Hydrograph type = Reservoir Peak discharge = 9.512 cfs Storm frequency = 5 yrs Time to peak = 734 min Time interval = 2 min Hyd. volume = 52,836 cuft Inflow hyd. No. = 5 - POST-DEV BASIN A TO PONDMax. Elevation = 1014.59 ft Reservoir name = Dry Extended Detention Pond Max. Storage = 19,348 cuft
Storage Indication method used.
0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640 2880
Q (cfs)
0.00 0.00
3.00 3.00
6.00 6.00
9.00 9.00
12.00 12.00
15.00 15.00
18.00 18.00
Q (cfs)
Time (min)
POST-DEV BASINA ROUTED
Hyd. No. 6 -- 5 Year
Hyd No. 6 Hyd No. 5 Total storage used = 19,348 cuft
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 7
POST-DEV BASIN A SP
Hydrograph type = Combine Peak discharge = 9.815 cfs Storm frequency = 5 yrs Time to peak = 734 min Time interval = 2 min Hyd. volume = 57,083 cuft Inflow hyds. = 4, 6 Contrib. drain. area = 0.820 ac
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)
POST-DEV BASIN A SP
Hyd. No. 7 -- 5 Year
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2025 Friday, 08 / 30 / 2024
Hyd. No. 8
10% BASIN
Hydrograph type = SCS Runoff Peak discharge = 46.48 cfs Storm frequency = 5 yrs Time to…
This is the start of the file's text. The full file is on GovTribe.
File details come from the government source that posted it. Updated .