20200579 Ver 1_Sand Filter Calculations_20200511

ID#* 20200579 Version* 1
Select Reviewer:*
Katie Merritt
Initial Review Completed Date 05/12/2020
Mitigation Project Submittal - 5/11/2020
Is this a Prospectus, Technical Proposal or a New Site?* O Yes a No
Type of Mitigation Project:*
r Stream r Wetlands G Buffer q Nutrient Offset
(Select all that apply)
Project Contact Information
Contact Name:*
Rebecca Stubbs, PE
Project Information
...................................................................................
ID#:* 20200579
Existing IW
Project Type:
Project Name:
County:
F DMS r Mitigation Bank
Whirligig Station
Wilson
Document Information
Email Address:*
[e-mail]
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Mitigation Information
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WHIRLIGIG STATION - PARKING LOT
IMPROVEMENTS
WILSON, NC
STORMWATER CALCULATIONS
NUTRIENT CREDIT GENERATION
PROJECT NUMBER:
DESIGNED BY:
CW I-19000
H. DEW, PE
R. STUBBS, PE
DATE: APRIL2020
2905 MERIDIAN PARKWAY
DURHAM, NORTH CAROLINA27713
NC LIC. # C-0293
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NARRATIVE > CWI-19000
2905 Meridian Parkway, Durham, NC 27713 / 919. 361. 5000creatingexperiences through experience
WHIRLIGIG STATION
Sand Filter Nutrient Credit Calculations
GENERAL DESCRIPTION
The proposed design for the Whirligig Station – Parking Lots Improvements underground storage and sand filter SCM
was previously approved by the City of Wilson. The original design, signed February 28, 2020, can be found in the
Appendix of this report. The project is located on a lot between Tarboro Street SW and Goldsboro Street SW in the
downtown area of Wilson, North Carolina and is owned by the City of Wilson. The project is within the Neuse River
Basin. The existing site consists of a parking lot area with limited stormwater drainage piping. The proposed design will
include increased stormwater routing of onsite and offsite surface runoff to the SCM which is capturing approximately
8.61 acres of total and impervious area. The associated amount of impervious does not change from the pre-
development to the post-development condition.
CALCULATION METHODOLOGY
These calculations provide the determination of nutrient credits, specifically nitrogen, generated by the sand filter once
constructed. The sand filter design computations per the current NC DEQ MDCs include a correction to the ‘hmax’,
ponding depth value, from the previously provided calculations in the original Stormwater Design Calculations (See
Appendix). The original sand filter nutrient calculations were completed using the North Carolina Stormwater Nitrogen
and Phosphorus Tool (SNAP Tool). However, the design storm size input has been updated in the current report to
reflect the water quality design storm for which the facility is sized. The original calculations were referenced for all
other inputs.
DISCUSSION OF RESULTS
NUTRIENT CREDITS GENERATED
The onsite underground storage and sand filter SCM is capturing approximately 8.61 acres of surface runoff. The sand
filter is designed per MDC standards. Nutrient treatment was not required by the development in the original design,
however, as the sand filter is providing nitrogen treatment in the downtown area, the credits generated have been
calculated to be utilized in the associated MBI. The total generated nitrogen credits were calculated to be 431.23 lbs.
CONCLUSION
If the development on this tract is built as proposed within the original report (see Appendix), then no additional
stormwater control measures are needed to generate the calculated nitrogen credits associated with this project.
However, modifications to the proposed development may require that this analysis be revised. Some modifications
that would require this analysis to be revised include:
1.The proposed site impervious surface differs from the amount accounted for in this report.
2.The post-development watershed breaks change significantly from those used to prepare this report.
The above modifications may result in the assumptions within this report becoming invalid. The computations within
this report will need to be revisited if any of the above conditions become apparent as development of the proposed
site moves forward.
Whirligig Station – Parking Lot Improvements
CWI-19000
Modified Sand Filter Calculations
WHIRLIGIG STATION
CWI-19000
MODIFIED SAND FILTER DESIGN H. DEW, PE
3/17/2020
Determination of Water Quality Volume (WQV)
Note: The following design calculations are based upon requirements from the NCDEQ Minimum Design Critieria.
where,
WQV= water quality volume (CF)
RV = 0.05+0.009(I) where I is percent impervious cover
A = area in acres
P = rainfall (in inches)
Input data:
Total area, A =8.61 acres
Impervious area =8.61 acres
Percent impervious cover, I =100.0 %
Rainfall, P =1.0 inches
Calculated values:
RV = 0.95
WQV = 0.68 acre-ft
=29693 cf.
Sizing is based upon the discounted water quality volume, WQV dis (75% of the total WQV).
WQVdis = 22270 cf.
Size Sand Filter and Sedimentation Chamber
Determine the required Sand Filter Surface Area
The minimum required sand filter surface area is the discounted WQ volume divided by the ponding depth:
Ponding Depth (D) =2.50 ft
ASF = 8,908 sf. (minimum sand filter surface area required)
The minimum sand chamber area must accommodate 50% of the treatment volume.
Design Summary
ASF ≥8,908 sf (minimum total sand and sedimentation chamber surface area)
ASF ≥9,230 sf (total sand and sedimentation chamber surface area provided)
ASand ≥4,454 sf (minimum sand chamber area required)
ASand ≥6,602 sf (minimum sand chamber area provided)
ASed ≥2,628 sf (minimum sedimentation chamber area provided)
D =2.50 ft (maximum WQV dis ponding depth in facility)
A SF = WQV dis / D
WQV = (P)(R V )(A)/12 x 43,560
WHIRLIGIG STATION
CWI-19000
MODIFIED SAND FILTER DESIGN H. DEW, PE
3/17/2020
Determination of Underdrain Sizing
The following design calculations are based upon requirements from the 2009 NC BMP Design Manual.
Compute drawdown through filter bed
where,
A = provided surface area of filter bed (sf)
k = coefficient of permeability of filter media (ft/day)
hF = height of water above filter bed (feet)
dF = filter bed depth (feet)
Input data:
A =6602 sf
k =3.50 ft/day
hF =2.50 ft
dF =2.00 ft
Calculated values:
Q =51993 cf/day
=0.602 cfs
Compute minimum drawdown discharge
WQV =22270 cf
t = 1.667 days
Minimum drawdown, Q = 0.155 cfs
Compute underdrain pipe capacity
Number of rows, n =8
Diameter of underdrains, d =6 inches
Area, A =0.1963 sf
Wetted perimeter, P =1.5708 ft
Slope, S =0.0050 ft/ft
Capacity of one pipe = 0.395 cfs
Total capacity = 3.161 cfs
Assume 50% clogging =1.580 cfs DESIGN ACCEPTABLE
Compute underdrain perforation capacity
3/8-inch perforations spaced 3 inches on center, along 4 longitudinal rows spaced 90 o apart
Number of rows, n =8
Diameter of underdrains, d =6 inches
Length of underdrains, L =40 ft
Number of perforations = 5120 holes
Capacity of one hole = 0.008 cfs
Total capacity = 42.280 cfs
Assume 50% clogging =21.140 cfs DESIGN ACCEPTABLE
Q = A(k)(h F +d F )/(d F )
Project Information
Project Name:Merrimont Park
Submission Date:
Project Area (ft2):377,194 ft2
Disturbed Area (ft2):85,836 ft2
Development Land Use Type:Commercial
Development Activity Type:Existing Dev. Retrofit
Designated Downtown Area?yes
Project Location/Address:211 Tarboro St. SW
County:Wilson
Local Jurisdiction:Wilson
Project Latitude Coordinates:35.724181 N
Project Longitude Coordinates:-77.912967 W
Precipitation Station:Wilson
Physiographic Region:Coastal
Nutrient Management Watershed:Neuse
Subwatershed:Neuse - 03020203
Phosphorus Delivery Zone:Neuse - Contentnea
Nitrogen Delivery Zone:Neuse - Contentnea
Project Designer and Contact Phone
Number / Email:Rebecca Stubbs, PE, [e-mail]
Part of Common Development Plan?yes
Project Owner Type:Local Government
Project Description:
Roof 1.18 0.11 101,282 101,282
Roadway 1.64 0.34 75,318 75,318
Parking/Driveway/Sidewalk 1.42 0.18 200,594 200,594
Protected Forest 0.97 0.03
Other Pervious/Landscaping 2.48 1.07
CUSTOM LAND COVER 1
CUSTOM LAND COVER 2
CUSTOM LAND COVER 3
LAND TAKEN UP BY SCM 1.18 0.11
SIMPLE METHOD Stormwater Runoff Volume Generated, V
Runoff Coefficient, R v V = Pj * Rv * (P/12) * A
Rv = 0.05 + (0.009 *I) where A =
drainage area (ft2)
where I = percent impervious (%)
Pj =
Average Annual Pollutant Load, L P =
L =
where C =
Pre-Project: Post-Project:
A =8.6592 ac A =8.6592 ac
P =47.40 in.P =47.40 in.
V =1273878 ft3 V =1273878 ft3
I =100%I =100%
Rv =0.95 Rv =0.95
Pj =0.9 Pj =0.9
CTN =1.40 mg/L CTN =1.40 mg/L
CTP =0.19 mg/L CTP =0.19 mg/L
LTN =111.32 lb/yr LTN =111.32 lb/yr
LTP =15.36 lb/yr LTP =15.36 lb/yr
event mean concentration (mg/L)
Equations Used and Project Area Calculations
fraction of rain events with runoff
average annual rainfall depth (in)
(Pj * Rv * (P/12 )) * (C * A * 2.72)
PROJECT AREA LAND COVERS
TN
EMC
(mg/L)
TP
EMC
(mg/L)
Post-
Project
Area (ft2)
Pre-
Project
Area (ft2)
Net Change of Land Covers (ft2):0
Total Pre-Project Calculated Area (ft 2):
Total Post-Project Calculated Area (ft 2):
Total Project Area Entered (ft 2):377,194
377,194
377,194
LAND COVER AREA CHECK
3. SCM Characteristics
Catchment ID 1 1 1
SCM ID 101 102 103
Type of SCM Sand Filter per MDC -
Closed
Predominant hydrologic soil
group at SCM location D
SCM Description Sand Filter per MDC -
Closed
Design Storm Size (inches/24hrs)1.00
Percent of Full Size 100%
Hydrologic Value - Percent Annual
Effluent 90%
Hydrologic Value - Percent Annual
Overflow 10%
Hydrologic Value - Percent Annual
ET/Infiltrated 0%
SCM Effluent TP EMC (mg/L)0.12
SCM Effluent TN EMC (mg/L)1.20
SCM Land Cover TP EMC (mg/L)0.11
SCM Land Cover TN EMC (mg/L)1.18
Drains to SCM ID 0
Catchment Routing
(Source Catchment)Catchments Draining to
SCM 101
Catchments Draining to
SCM 102
Catchments Draining to
SCM 103
Catchment 1
Catchment 2
Catchment 3
Catchment 4
Catchment 5
Catchment 6
SCM ID:101 102 103
SCM Drainage Area Land Covers Area Draining Directly to
SCM 101 (ft2)
Area Draining Directly to
SCM 102 (ft2)
Area Draining Directly to
SCM 103 (ft2)
Total Land Use Area
Treated By All SCMs (ft2)
Allowable Total Land Use
Area to be Treated Based
on Post-Project Areas (ft2)
Roof 101,282 101,282 101,282
Roadway 75,318 75,318 75,318
Parking/Driveway/Sidewalk 198,466 198,466 200,594
Protected Forest 0 0
Other Pervious/Landscaping 0 0
CUSTOM LAND COVER 1 0 0
CUSTOM LAND COVER 2 0 0
CUSTOM LAND COVER 3 0 0
LAND TAKEN UP BY SCM 0 0
TOTAL AREA DRAINING TO SCM
(ft2):375,066 0 0 375,066 377,194
CATCHMENT AREA (ft2):375,066
Project Summary
377,194 ft2 8.6592 acres
85,836 ft2 1.9705 acres
100%100%
1.77 12.86
15.36 111.32
10.15 96.98
N/A N/A
0.00 0.00
-5.21 -14.35
-5.21 -14.35
Nutrient Export Summary Pre-Project
Whole Site
Conditions
Post-Project
Whole Site
without SCMs
Post-Project
Whole Site with
SCMs
Post-Project
SCM-Treated
Area
Post-Project
Untreated Area
100.0%100.0%100.0%100.0%100.0%
100.0%100.0%100.0%100.0%100.0%
1,273,878 1,273,878 1,273,878 1,266,692 7,187
0%0%0%
1.40 1.40 1.22 1.22 1.42
111.32 111.32 96.98 96.34 0.64
12.86 12.86 11.20 11.19 13.04
0%0%-13%
0.19 0.19 0.13 0.13 0.18
15.36 15.36 10.15 10.07 0.08
1.77 1.77 1.17 1.17 1.65
0%0%-34%
SCM/Catchment Summary
Volume
Reduction (%)TN Out (mg/L) TP Out (mg/L)
TN Out
(lbs/ac/yr)
TP Out
(lbs/ac/yr)
TN Reduction
(%)
TP Reduction
(%)
0.00%1.22 0.13 11.19 1.17 12.94%34.07%
0.00%1.22 0.13 11.19 1.17 12.94%34.07%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
0.00%0.00 0.00 0.00 0.00 0.00%0.00%
P Load Treatment Balance at Site (lb/yr):
Nitrogen Delivery Factor (%):
Owner Type:
Designated Downtown Area?
Subwatershed:
Nitrogen Delivery Zone:
Commercial
yes
Neuse - 03020203
Neuse - Contentnea
Neuse
Neuse - Contentnea
Existing Dev. Retrofit
Merrimont Park
Total Nitrogen Loading Rate (lb/ac/yr)
Total Nitrogen % Change (relative to pre-D)
Project Name:
Project Area (ft2):
Disturbed Area (ft2):
County:
Development Land Use Type:
P Load Treatment Balance at Lake (lb/yr):N Load Treatment Balance at Lake (lb/yr):
Nutrient Management Watershed:
Phosphorus Delivery Zone:
N Load Treatment Balance at Site (lb/yr):
Phosphorus Delivery Factor (%):
Submission Date:
Total Phosphorus Load Leaving Site (lb/yr)
Total Phosphorus Loading Rate (lb/ac/yr)
Percent Built-Upon Area (BUA) (%)
Annual Runoff Volume (ft3/yr)
Annual Runoff % Change (relative to pre-D)
Total Nitrogen EMC (mg/L)
Total Nitrogen Load Leaving Site (lb/yr)
Development Activity Type:
Percent Impervious (for runoff calculation) (%)
Total Phosphorus EMC (mg/L)
Phosphorus Loading Rate Target (lb/ac/yr):
Phosphorus Load Target at Site (lb/yr):
Phosphorus Load Leaving Site w/SCMs (lb/yr):
P Offsite Buy-Down Threshold Loading Rate (lb/ac/yr):
SCM rows in red have a data entry error for the SCM that makes an error in the calculation.
Wilson Local Jurisdiction:Wilson
Total Phosphorus % Change (relative to pre-D)
Total P Load Reduction Needed (lb/yr):
Nitrogen Loading Rate Target (lb/ac/yr):
Nitrogen Load Target at Site (lb/yr):
Nitrogen Load Leaving Site w/SCMs (lb/yr):
N Offsite Buy-Down Threshold Loading Rate
Total N Load Reduction Needed (lb/yr):
Local Government
102: NA
101: Sand Filter per MDC - Closed
SCM ID and Type
103: NA
201: NA
Catchment 1
Catchment 2
Catchment 3
Catchment 4
Catchment 5
202: NA
203: NA
301: NA
302: NA
303: NA
401: NA
402: NA
403: NA
602: NA
603: NA
501: NA
502: NA
Catchment 6
503: NA
601: NA
Type of SCM:Sand Filter per MDC -
Closed
Area Treated by SCM (ft2):375,066
Percent Impervious of Contributing Watershed (%): 100%
Runoff Coefficient, Rv: 0.95
Inflow Volume (ft3):1,266,692
Incoming Total Nitrogen Concentration (mg/L): 1.40
Annual Incoming Total Nitrogen Load (lbs): 110.66
Incoming Total Phosphorus Concentration (mg/L): 0.19
Annual Incoming Total Phosphorus Load (lbs): 15.28
Total Volume Leaving SCM (ft3):1,266,692
Outgoing Total Nitrogen Concentration (mg/L): 1.22
Annual Outgoing Total Nitrogen Load (lbs): 96.34
Outgoing Total Phosphorus Concentration (mg/L): 0.13
Annual Outgoing Total Phosphorus Load (lbs): 10.07
Annual Volume Reduction by SCM (ft3):0
Annual Volume Reduction by SCM (%): 0%
Annual Total Nitrogen Reduction by SCM (%): 12.94%
Annual Total Nitrogen Reduction by SCM (lb): 14.32
Annual Total Phosphorus Reduction by SCM (%): 34.07%
Annual Total Phosphorus Reduction by SCM (lb): 5.21
L = ((P * Pj * Rv) ÷ (12 )) * (C * A * 2.72)
where L = annual pollutant loading (lbs)
Pj = fraction of rain events that produce runoff (dec)
C = event mean concentration of pollutant (mg/L)
Lout = Vout * EMCout * 6.243ᴇ-5
where Vout = outflow volume (ft3),
EMCout = effluent median concentration (mg/L)
Vout = Vin * (1 - Red)
where Vin = inflow volume (ft3)
Red = volume reduction by SCM (%)
Rv = 0.05 + (0.009 *I),
where I = percent impervious (%)
Supporting Calculations
V = Pj * Rv * A * (P/12),
where A = area of catchment (ft2)
P = average annual rainfall depth (in)
CATCHMENT 1, SCM 101
L = ((P * Pj * Rv) ÷ (12 )) * (C * A * 2.72)
where L = annual pollutant loading (lbs)
Pj = fraction of rain events that produce runoff (dec)
C = event mean concentration of pollutant (mg/L)
Lout = Vout * EMCout * 6.243ᴇ-5
where Vout = outflow volume (ft3),
EMCout = effluent median concentration (mg/L)
Vout = Vin * (1 - Red)
where Vin = inflow volume (ft3)
Red = volume reduction by SCM (%)
Rv = 0.05 + (0.009 *I),
where I = percent impervious (%)
Supporting Calculations
V = Pj * Rv * A * (P/12),
where A = area of catchment (ft2)
P = average annual rainfall depth (in)
Cumulative Catchment Area (ft2):375,066
Composite Catchment Impervious Surface (%):
Composite Runoff Coefficient, Rv:
Cumulative Runoff Volume (ft3):1,266,692
Composite Total Nitrogen Runoff Concentration (mg/L): 1.40
Annual Total Nitrogen Runoff Load (lbs): 110.66
Composite Total Phosphorus Runoff Concentration (mg/L): 0.19
Annual Total Phosphorus Runoff Load (lbs): 15.28
Total Volume Leaving Catchment (ft3):1,266,692
Outgoing Total Nitrogen Concentration (mg/L): 1.22
Annual Outgoing Total Nitrogen Load (lbs): 96.34
Outgoing Total Phosphorus Concentration (mg/L): 0.13
Annual Outgoing Total Phosphorus Load (lbs): 10.07
Annual Volume Reduction by Catchment (ft3):0
Annual Volume Reduction by Catchment (%): 0%
Annual Total Nitrogen Reduction by Catchment (%): 12.94%
Annual Total Nitrogen Reduction by Catchment (lb): 14.32
Annual Total Phosphorus Reduction by Catchment (%): 34.07%
Annual Total Phosphorus Reduction by Catchment (lb): 5.21
CATCHMENT 1
4/6/2020
Wilson
N/A
N/A
100%
100%
(A) (B) (C) (D) (E) (F) (G) (H)
(L) (Where
Applicable)
Untreated
Loading Rate
(lbs/ac/yr)
Treated
Loading Rate
(lbs/ac/yr)
Loading Rate
Target
(lbs/ac/yr)
Reduction
Need
(lbs/ac/yr)
Project Size
(ac)
Offset
Duration (yrs)
Delivery
Factor (%)
State Buy
Down Amount
(lbs)
Local Gov’t
Buy Down
Amount (lbs)
B - C D * E * F * G
12.86 11.20 12.86 -1.66 8.6592 30 100%0.00
(A) (B) (C) (D) (E) (F) (G) (H)
(L) (Where
Applicable)
Untreated
Load Rate
(lbs/ac/yr)
Treated Load
Rate
(lbs/ac/yr)
Loading Rate
Target
(lbs/ac/yr)
Reduction
Need
(lbs/ac/yr)
Project Size
(ac)
Offset
Duration (yrs)
Delivery
Factor (%)
State Buy
Down Amount
(lbs)
Local Gov’t
Buy Down
Amount (lbs)
B - C D * E * F * G
1.77 1.17 1.77 -0.60 8.6592 30 100%0.00
Phone:
Date:
Date:(mm/dd/yyyy)
County:
Wilson
35.724181
-77.912967
100.00%
100.00%
WATERSHED INFORMATION
P Offsite Threshold Rate (lb/ac/yr):
NUTRIENT OFFSET REQUEST
Phosphorus Load Offset Needs
Nitrogen Load Offset Needs
Local Government Authorizing Signature:
Staff Email:
Development Land Use Type:
Development Activity Type:
Commercial
Nitrogen Delivery Factor:
Phosphorus Delivery Factor:
Neuse
Neuse - 03020203
Neuse - Contentnea
Neuse - Contentnea
Staff Name:
Existing Dev. Retrofit
Project Latitude:
Project Longitude:
LOCAL GOVERNMENT AUTHORIZATION
Local Government Name:
N Offsite Threshold Rate (lb/ac/yr):
Pre-Project Built-Upon Area %:
Post-Project Built-Upon Area %:
Nutrient Management Watershed:
Subwatershed:
Nitrogen Delivery Zone:
Phosphorus Delivery Zone:
http://deq.nc.gov/about/divisions/water-resources/planning/nonpoint-source-management/nutrient-offset-
information
Nutrient Management Strategy Watershed - Nutrient Offset Credit Reporting Form
Project Address:
Project Name:
Applicant Name:McAdams
Whirligig Station Parking Lot Improvements
211 Tarboro St. SW
Please complete and submit the following information to the local government permitting your development project
to characterize it and assess the need to purchase nutrient offset credits. Contact and rule implementation
information can be found online at:
PROJECT INFORMATION
Whirligig Station – Parking Lot Improvements
CWI-19000
Appendix – Original Stormwater Design Calculations
WHIRLIGIG STATION
Parking Lot Improvements
Wilson County, NC
STGRMWA.TER
DESIGN CALCULATIONS
February 28, 2020
101
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1906 Nash Street North Wilson, NC 27893-1726
Phone: [phone] Fax: [phone]
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WHIRLIGIG STATION – Parking Lot Improvements
STORMWATER UNDERGROUND STORAGE WITH SAND FILTER
DESIGN CALCULATIONS

GENERAL SITE DESCRIPTION

The proposed project is located between Tarboro Street SW and Goldsboro St SW, City of Wilson in
Wilson County. (Latitude: 35.724181°; Longitude: -77.912967 °). The site is an existing parking area that
is mostly impervious with limited drainage pipe sizes to accommodate all site surface runoff.

The proposed project is will route all site and offsite surface runoff to an underground stormwater treatment
system nutrients and peak flow reduction.

Site Data:
Site Area 1.84+/- acres
Total onsite + offsite drainage area 375,066 sf (8.61+/-) acres
Total Built Upon Area 375,066 sf (8.61+/-) acres
Percent Impervious 100%
Proposed SCM Underground Storage with Sand Filter

UNDERGROUND STORAGESYSTEMPRELIMINARY PLANSNOT FOR CONSTRUCTION

Underground Storage with Sand Filter
Design Calculations

 Stormwater Nitrogen & Phosphorus Tool (SNAP)
 Sand Filter Preliminary Design
 Stormwater Events Equivalent CN value
 Equivalent Impervious Area Calculations
 Underground Storage Pond Design Calculations

Project Information
Project Name:Whirligig Station Parking Lot Improvements
Submission Date:
Project Area (ft2):377,194 ft2
Disturbed Area (ft2):85,836 ft2
Development Land Use Type:Commercial
Development Activity Type:Existing Dev. Retrofit
Designated Downtown Area?yes
Project Location/Address:211 Tarboro St. SW
County:Wilson
Local Jurisdiction:Wilson
Project Latitude Coordinates:35.724181 N
Project Longitude Coordinates:77.912967 W
Precipitation Station:Wilson
Physiographic Region:Coastal
Nutrient Management Watershed:Neuse
Subwatershed:Neuse - 03020203
Phosphorus Delivery Zone:Neuse - Contentnea
Nitrogen Delivery Zone:Neuse - Contentnea
Project Designer and Contact Phone
Number / Email:Ronald Fuentes [phone]
Part of Common Development Plan?yes
Project Owner Type:Local Government
Project Description:
Project Area Land Cover Characteristics
Roof 1.18 0.11 101,282 101,282
Roadway 1.64 0.34 75,318 75,318
Parking/Driveway/Sidewalk 1.42 0.18 200,594 200,594
Protected Forest 0.97 0.03
Other Pervious/Landscaping 2.48 1.07
CUSTOM LAND COVER 1
CUSTOM LAND COVER 2
CUSTOM LAND COVER 3
LAND TAKEN UP BY SCM 1.18 0.11
SIMPLE METHOD Stormwater Runoff Volume Generated, V
Runoff Coefficient, R v V = Pj * Rv * (P/12) * A
Rv = 0.05 + (0.009 *I) where A =
drainage area (ft2)
where I = percent impervious (%)
Pj =
Average Annual Pollutant Load, L P =
L =
where C =
Pre-Project: Post-Project:
A = 8.6592 ac A =8.6592 ac
P = 47.40 in.P =47.40 in.
V = 1273878 ft3 V =1273878 ft3
I = 100%I = 100%
Rv = 0.95 Rv = 0.95
Pj = 0.9 Pj = 0.9
CTN = 1.40 mg/L CTN = 1.40 mg/L
CTP = 0.19 mg/L CTP = 0.19 mg/L
LTN = 111.32 lb/yr LTN = 111.32 lb/yr
LTP = 15.36 lb/yr LTP = 15.36 lb/yr
Net Change of Land Covers (ft2):0
Total Pre-Project Calculated Area (ft2):
Total Post-Project Calculated Area (ft2):
Total Project Area Entered (ft2):377,194
377,194
377,194
LAND COVER AREA CHECK
PROJECT AREA LAND COVERS
TN
EMC
(mg/L)
TP
EMC
(mg/L)
Post-
Project
Area (ft2)
Pre-
Project
Area (ft2)
event mean concentration (mg/L)
Equations Used and Project Area Calculations
fraction of rain events with runoff
average annual rainfall depth (in)
(Pj * Rv * (P/12 )) * (C * A * 2.72)
3. SCM Characteristics
Catchment ID 1 1 1
SCM ID 101 102 103
Type of SCM Sand Filter per MDC -
Closed
Predominant hydrologic soil
group at SCM location D
SCM Description Sand Filter per MDC -
Closed
Design Storm Size (inches/24hrs)2.91
Percent of Full Size 100%
Hydrologic Value - Percent
Annual Effluent 90%
Hydrologic Value - Percent
Annual Overflow 10%
Hydrologic Value - Percent
Annual ET/Infiltrated 0%
SCM Effluent TP EMC (mg/L)0.12
SCM Effluent TN EMC (mg/L)1.20
SCM Land Cover TP EMC (mg/L)0.11
SCM Land Cover TN EMC (mg/L)1.18
Drains to SCM ID 0
Catchment Routing
(Source Catchment)Catchments Draining to
SCM 101
Catchments Draining to
SCM 102
Catchments Draining to
SCM 103
Catchment 1 no
Catchment 2 no
Catchment 3 no
Catchment 4 no
Catchment 5 no
Catchment 6 no
SCM ID:101 102 103
SCM Drainage Area Land Covers Area Draining Directly to
SCM 101 (ft2)
Area Draining Directly to
SCM 102 (ft2)
Area Draining Directly to
SCM 103 (ft2)
Total Land Use Area
Treated By All SCMs (ft2)
Roof 101,282 101,282
Roadway 75,318 75,318
Parking/Driveway/Sidewalk 198,466 198,466
Protected Forest 0
Other Pervious/Landscaping 0
CUSTOM LAND COVER 1 0
CUSTOM LAND COVER 2 0
CUSTOM LAND COVER 3 0
LAND TAKEN UP BY SCM 0
TOTAL AREA DRAINING TO SCM
(ft2):375,066 0 0 375,066
CATCHMENT AREA (ft2):375,066
SCM Characteristics
3. SCM Characteristics
Catchment ID
SCM ID
Type of SCM
Predominant hydrologic soil
group at SCM location
SCM Description
Design Storm Size (inches/24hrs)
Percent of Full Size
Hydrologic Value - Percent
Annual Effluent
Hydrologic Value - Percent
Annual Overflow
Hydrologic Value - Percent
Annual ET/Infiltrated
SCM Effluent TP EMC (mg/L)
SCM Effluent TN EMC (mg/L)
SCM Land Cover TP EMC (mg/L)
SCM Land Cover TN EMC (mg/L)
Drains to SCM ID
Catchment Routing
(Source Catchment)
Catchment 1
Catchment 2
Catchment 3
Catchment 4
Catchment 5
Catchment 6
SCM ID:
SCM Drainage Area Land Covers
Roof
Roadway
Parking/Driveway/Sidewalk
Protected Forest
Other Pervious/Landscaping
CUSTOM LAND COVER 1
CUSTOM LAND COVER 2
CUSTOM LAND COVER 3
LAND TAKEN UP BY SCM
TOTAL AREA DRAINING TO SCM
(ft2):
CATCHMENT AREA (ft2):
SCM Characteristics
Allowable Total Land Use
Area to be Treated Based
on Post-Project Areas (ft2)
Post-Project Untreated
Land Area (ft2)
101,282 0
75,318 0
200,594 2,128
0 0
0 0
0 0
0 0
0 0
0 0
377,194 2,128
Project Summary
377,194 ft2 8.6592 acres
85,836 ft2 1.9705 acres
100% 100%
1.77 12.86
15.36 111.32
10.15 96.98
N/A N/A
0.00 0.00
-5.21 -14.35
-5.21 -14.35
Nutrient Export Summary
Pre-Project
Whole Site
Conditions
Post-Project
Whole Site
without SCMs
Post-Project
Whole Site with
SCMs
Post-Project
SCM-Treated
Area
Post-Project
Untreated Area
100.0%100.0%100.0%100.0%100.0%
100.0%100.0%100.0%100.0%100.0%
1,273,878 1,273,878 1,273,878 1,266,692 7,187
0% 0% 0%
1.40 1.40 1.22 1.22 1.42
111.32 111.32 96.98 96.34 0.64
12.86 12.86 11.20 11.19 13.04
0% 0% -13%
0.19 0.19 0.13 0.13 0.18
15.36 15.36 10.15 10.07 0.08
1.77 1.77 1.17 1.17 1.65
0% 0% -34%
Wilson Local Jurisdiction:Wilson
Total Phosphorus % Change (relative to pre-D)
Total P Load Reduction Needed (lb/yr):
Nitrogen Loading Rate Target (lb/ac/yr):
Nitrogen Load Target at Site (lb/yr):
Nitrogen Load Leaving Site w/SCMs (lb/yr):
N Offsite Buy-Down Threshold Loading Rate
Total N Load Reduction Needed (lb/yr):
Local Government
Submission Date:
Total Phosphorus Load Leaving Site (lb/yr)
Total Phosphorus Loading Rate (lb/ac/yr)
Percent Built-Upon Area (BUA) (%)
Annual Runoff Volume (ft3/yr)
Annual Runoff % Change (relative to pre-D)
Total Nitrogen EMC (mg/L)
Total Nitrogen Load Leaving Site (lb/yr)
Development Activity Type:
Percent Impervious (for runoff calculation) (%)
Total Phosphorus EMC (mg/L)
Phosphorus Loading Rate Target (lb/ac/yr):
Phosphorus Load Target at Site (lb/yr):
Phosphorus Load Leaving Site w/SCMs (lb/yr):
P Offsite Buy-Down Threshold Loading Rate (lb/ac/yr):
Whirligig Station Parking Lot Improvements
Total Nitrogen Loading Rate (lb/ac/yr)
Total Nitrogen % Change (relative to pre-D)
Project Name:
Project Area (ft2):
Disturbed Area (ft2):
County:
Development Land Use Type:
P Load Treatment Balance at Lake (lb/yr): N Load Treatment Balance at Lake (lb/yr):
Nutrient Management Watershed:
Phosphorus Delivery Zone:
N Load Treatment Balance at Site (lb/yr):
Phosphorus Delivery Factor (%):
P Load Treatment Balance at Site (lb/yr):
Nitrogen Delivery Factor (%):
Owner Type:
Designated Downtown Area?
Subwatershed:
Nitrogen Delivery Zone:
Commercial
yes
Neuse - 03020203
Neuse - Contentnea
Neuse
Neuse - Contentnea
Existing Dev. Retrofit
SCM/Catchment Summary
Volume
Reduction (%)TN Out (mg/L) TP Out (mg/L)
TN Out
(lbs/ac/yr)
TP Out
(lbs/ac/yr)TN Reduction (%) TP Reduction (%)
0.00%1.22 0.13 11.19 1.17 12.94%34.07%
0.00% 1.22 0.13 11.19 1.17 12.94% 34.07%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
0.00% 0.00 0.00 0.00 0.00 0.00% 0.00%
602: NA
603: NA
501: NA
502: NA
Catchment 6
503: NA
601: NA
Catchment 3
Catchment 4
Catchment 5
202: NA
203: NA
301: NA
302: NA
303: NA
401: NA
402: NA
403: NA
102: NA
101: Sand Filter per MDC - Closed
SCM ID and Type
103: NA
201: NA
Catchment 1
Catchment 2
SCM rows in red have a data entry error for the SCM that makes an error in the calculation.
Type of SCM:Sand Filter per MDC -
Closed
Area Treated by SCM (ft2):375,066
Percent Impervious of Contributing Watershed (%): 100%
Runoff Coefficient, Rv: 0.95
Inflow Volume (ft3):1,266,692
Incoming Total Nitrogen Concentration (mg/L): 1.40
Annual Incoming Total Nitrogen Load (lbs): 110.66
Incoming Total Phosphorus Concentration (mg/L): 0.19
Annual Incoming Total Phosphorus Load (lbs): 15.28
Total Volume Leaving SCM (ft3):1,266,692
Outgoing Total Nitrogen Concentration (mg/L): 1.22
Annual Outgoing Total Nitrogen Load (lbs): 96.34
Outgoing Total Phosphorus Concentration (mg/L): 0.13
Annual Outgoing Total Phosphorus Load (lbs): 10.07
Annual Volume Reduction by SCM (ft3):0
Annual Volume Reduction by SCM (%): 0%
Annual Total Nitrogen Reduction by SCM (%): 12.94%
Annual Total Nitrogen Reduction by SCM (lb): 14.32
Annual Total Phosphorus Reduction by SCM (%): 34.07%
Annual Total Phosphorus Reduction by SCM (lb): 5.21
Rv = 0.05 + (0.009 *I),
where I = percent impervious (%)
Supporting Calculations
V = Pj * Rv * A * (P/12),
where A = area of catchment (ft2)
P = average annual rainfall depth (in)
CATCHMENT 1, SCM 101
L = ((P * Pj * Rv) ÷ (12 )) * (C * A * 2.72)
where L = annual pollutant loading (lbs)
Pj = fraction of rain events that produce runoff (dec)
C = event mean concentration of pollutant (mg/L)
Lout = Vout * EMCout * 6.243ᴇ-5
where Vout = outflow volume (ft3),
EMCout = effluent median concentration (mg/L)
Vout = Vin * (1 - Red)
where Vin = inflow volume (ft3)
Red = volume reduction by SCM (%)
Wilson
N/A
N/A
100%
100%
(A) (B) (C) (D) (E) (F) (G) (H)
(L) (Where
Applicable)
Untreated
Loading Rate
(lbs/ac/yr)
Treated
Loading Rate
(lbs/ac/yr)
Loading Rate
Target
(lbs/ac/yr)
Reduction
Need
(lbs/ac/yr)
Project Size
(ac)
Offset
Duration (yrs)
Delivery
Factor (%)
State Buy
Down Amount
(lbs)
Local Gov’t
Buy Down
Amount (lbs)
B - C D * E * F * G
12.86 11.20 12.86 -1.66 8.6592 30 100%0.00
(A) (B) (C) (D) (E) (F) (G) (H)
(L) (Where
Applicable)
Untreated
Load Rate
(lbs/ac/yr)
Treated Load
Rate
(lbs/ac/yr)
Loading Rate
Target
(lbs/ac/yr)
Reduction
Need
(lbs/ac/yr)
Project Size
(ac)
Offset
Duration (yrs)
Delivery
Factor (%)
State Buy
Down Amount
(lbs)
Local Gov’t
Buy Down
Amount (lbs)
B - C D * E * F * G
1.77 1.17 1.77 -0.60 8.6592 30 100%0.00
Phone:
Date:
http://deq.nc.gov/about/divisions/water-resources/planning/nonpoint-source-management/nutrient-offset-
information
Nutrient Management Strategy Watershed - Nutrient Offset Credit Reporting Form
Project Address:
Project Name:
Applicant Name:
Whirligig Station Parking Lot Improvements
211 Tarboro St. SW
Please complete and submit the following information to the local government permitting your development project
to characterize it and assess the need to purchase nutrient offset credits. Contact and rule implementation
information can be found online at:
PROJECT INFORMATION
Staff Name:
Existing Dev. Retrofit
Project Latitude:
Project Longitude:
LOCAL GOVERNMENT AUTHORIZATION
Local Government Name:
N Offsite Threshold Rate (lb/ac/yr):
Pre-Project Built-Upon Area %:
Post-Project Built-Upon Area %:
Nutrient Management Watershed:
Subwatershed:
Nitrogen Delivery Zone:
Phosphorus Delivery Zone:
Development Land Use Type:
Development Activity Type:
Commercial
Nitrogen Delivery Factor:
Phosphorus Delivery Factor:
Neuse
Neuse - 03020203
Neuse - Contentnea
Neuse - Contentnea
Local Government Authorizing Signature:
Staff Email:
Date: (mm/dd/yyyy)
County:
Wilson
35.724181
77.912967
100.00%
100.00%
WATERSHED INFORMATION
P Offsite Threshold Rate (lb/ac/yr):
NUTRIENT OFFSET REQUEST
Phosphorus Load Offset Needs
Nitrogen Load Offset Needs
SAND FILTER PRELIMINARY DESIGN
Water Quality Volume (WQv)
Drainage Area (DA) 375,066.00 sf
Built Upon Area (BUA)375,066.00 sf
BUA/DA 1.00
Runoff Coefficient (Rv) 0.95
Storm Rainfall Depth (Rd)1 in
Water Quality Volume (WQv)29,692.73 cf
Sediment Chamber
Surface Area Required, Asmin.=240*Rv*(DA/43560)*Rd 1,963.16 sf
Surface Area of Sediment Chamber Provided (As)2,459.50 sf
Depth of Sediment Chamber 2.00 ft
Volume of Sediment Chamber 4,919.00 cf
Sand Filter
WQv adj. = 0.75 x WQv 22,270 cf
Ponding depth, (h = 0.5' to 6')6.00 ft
Surface Area Required, Afmin = WQv adj. / h 3,711.59 sf
Surface Area Provided (Af)6,450.50 sf
Sand Filter Depth (D)2.00 ft
WQv adj. surface area (SA = As + Af) 8,910.00 sf
% WQv adj above sand Filter (must be greater than 50%) 72.40 %
Min. required Weir Height above sand filter (WQv adj./SA) 2.50 ft
Provided overflow weir height above sand filter 2.50 ft
Porosity (N)0.40
Equivalent Surface Area for caclulating Volume of voids 2,580.20 sf
Underdrain Pipe
Material PVC
Manning's roughness coefficient (n)0.010
Slope (s)0.005 ft/ft
Pipe size 6.000 in.
Flow capcity 0.516 cfs
Number of pipes 9.00
Total flow (Qdrain)4.64 cfs
Outlet Pipe size (Theoretical) 13.66 in.
USE ====> 12.00 in.
Outlet Pipe Capacity (Qfull)3.27 cfs
Drawdown Rate
Sand Filter Depth provided (D) 24.00 in
Dept of sand above pipe/s 18.00 in
Sand Filter Exfiltration Rate (ER= Qdrain/Af) 21.93 in/hr
Min. Exfiltration Rate (ERmin)2.00 in/hr
Min. Qdrain = ERmin * Af 0.30 cfs
Time to drain sand chamber (T) = D/ER 1.09 hrs
Max. time to drain sand chamber (Tmax) = D/Ermin 12.00 hrs
* Max. drawdown is controlled by the drain pipe outlet capacity
Chamber Areas
Total Storage Volume (from Storm Trap) 130,175.98 cf
Total interior depth of structure 8.33 ft
Equivalent Surface Area (Volume / Depth) 15,621.12 sf
Sediment Chamber surface area 2,459.50 sf
Sand Filter surface area 6,450.50 sf
Overflow Chamber surface area 30.67 sf
Temporary Storage surface area 6,680.45 sf
Stage-Storage Table
Sand Filter Treatment Chamber Temporary Storage Total
Elevation Area (sf) Incremental Area (sf) Incremental Area (sf) Incremental Incremental Storage
Volume Volume Volume Volume Volume
127.00 2580.0 0.0 6,680.0 0.0 0.0 0.0
128.00 2580.0 2580.0 6,680.0 6,680.0 9,260.0 9,260.0
129.00 2580.0 2580.0 8910.0 0.0 6,680.0 6,680.0 9,260.0 18,520.0
130.00 8910.0 8,910.0 6,680.0 6,680.0 15,590.0 34,110.0
131.00 8910.0 8,910.0 6,680.0 6,680.0 15,590.0 49,700.0
131.50 8910.0 4,455.0 6,680.0 3,340.0 7,795.0 57,495.0
132.00 8910.0 4,455.0 6,680.0 3,340.0 7,795.0 65,290.0
133.00 8910.0 8,910.0 6,680.0 6,680.0 15,590.0 80,880.0
134.00 8910.0 8,910.0 6,680.0 6,680.0 15,590.0 96,470.0
135.00 8910.0 8,910.0 6,680.0 6,680.0 15,590.0 112,060.0
135.33 8910.0 2,940.3 6,680.0 2,204.4 5,144.7 117,204.7
Total 5,160.0 Total 56,400.3 Total 55,644.4 Total Storage 117,204.7
Note: Sand Filter area equivalent to 40% of total surface area to account for volume of voids.
STORM EXISTING POST DEV'T POST DEV'T REDUCTION SCM WS EL SCM OUTLET POST DEV'T
EVENT CONDITIONS W/O SCM WITH SCM %FLOW EQUIV. CN
1-YR 29.82 CFS 29.82 CFS 8.15 CFS 73%129.82 8.13 CFS 71.0
10-YR 56.48 CFS 56.48 CFS 11.19 CFS 80%131.82 11.15 CFS 52.6
25-YR 70.70 CFS 70.70 CFS 12.38 CFS 82%132.95 12.33 CFS 45.8
100-YR 97.22 CFS 97.22 CFS 18.66 CFS 81%134.91 18.59 CFS 39.0
DRAINAGE BASIN SUMMARY
Post SCM - 1 yr Storm
Description Area (sf)CN Area x CN
Impervious surface 212,932.1 98.0 20,867,345.80
Lawn/Grassed area 164,261.9 36.0 5,913,428.40
Total Area 377,194.0 71.0 26,780,774.20
Post SCM - 10 yr Storm
Description Area (sf)CN Area x CN
Impervious surface 100,990.7 98.0 9,897,088.60
Lawn/Grassed area 276,203.3 36.0 9,943,318.80
Total Area 377,194.0 52.6 19,840,407.40
Post SCM - 25 yr Storm
Description Area (sf)CN Area x CN
Impervious surface 59,621.0 98.0 5,842,858.00
Lawn/Grassed area 317,573.0 36.0 11,432,628.00
Total Area 377,194.0 45.8 17,275,486.00
Post SCM - 100 yr Storm
Description Area (sf)CN Area x CN
Impervious surface 18,251.3 98.0 1,788,627.40
Lawn/Grassed area 358,942.7 36.0 12,921,937.20
Total Area 377,194.0 39.0 14,710,564.60
EQUIVALENT IMPERVIOUS AREA CALCULATION
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 8
Equivalent Impervious
Hydrograph type = SCS Runoff Peak discharge = 8.154 cfs
Storm frequency = 1 yrs Time to peak = 12.03 hrs
Time interval = 2 min Hyd. volume = 22,990 cuft
Drainage area = 8.660 ac Curve number = 71
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 2.91 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 2 4 6 8 10 12 14 16 18 20 22 24 26
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 (hrs)
Equivalent Impervious
Hyd. No. 8 -- 1 Year
Hyd No. 8
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 8
Equivalent Impervious
Hydrograph type = SCS Runoff Peak discharge = 11.17 cfs
Storm frequency = 10 yrs Time to peak = 12.03 hrs
Time interval = 2 min Hyd. volume = 34,071 cuft
Drainage area = 8.660 ac Curve number = 52.6
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 5.45 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 2 4 6 8 10 12 14 16 18 20 22 24 26
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 (hrs)
Equivalent Impervious
Hyd. No. 8 -- 10 Year
Hyd No. 8
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 8
Equivalent Impervious
Hydrograph type = SCS Runoff Peak discharge = 12.43 cfs
Storm frequency = 25 yrs Time to peak = 12.03 hrs
Time interval = 2 min Hyd. volume = 39,313 cuft
Drainage area = 8.660 ac Curve number = 45.8
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 6.81 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 2 4 6 8 10 12 14 16 18 20 22 24 26
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 (hrs)
Equivalent Impervious
Hyd. No. 8 -- 25 Year
Hyd No. 8
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 8
Equivalent Impervious
Hydrograph type = SCS Runoff Peak discharge = 18.68 cfs
Storm frequency = 100 yrs Time to peak = 12.03 hrs
Time interval = 2 min Hyd. volume = 57,400 cuft
Drainage area = 8.660 ac Curve number = 39
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 9.35 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
0 2 4 6 8 10 12 14 16 18 20 22 24 26
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
21.00 21.00
Q (cfs)
Time (hrs)
Equivalent Impervious
Hyd. No. 8 -- 100 Year
Hyd No. 8
Hydraflow Table of Contents 18-501 Whirligig Parking Lot.gpw
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Watershed Model Schematic...................................................................................... 1
Hydrograph Return Period Recap............................................................................. 2
1 - Year
Summary Report......................................................................................................................... 3
Hydrograph Reports................................................................................................................... 4
Hydrograph No. 1, SCS Runoff, Existing to UGS..................................................................... 4
Hydrograph No. 2, SCS Runoff, Existing Offsite...................................................................... 5
Hydrograph No. 3, Combine, Existing...................................................................................... 6
Hydrograph No. 4, SCS Runoff, Proposed to UGS.................................................................. 7
Hydrograph No. 5, SCS Runoff, Proposed to Offsite............................................................... 8
Hydrograph No. 6, Reservoir, UGS.......................................................................................... 9
Pond Report - UGS............................................................................................................10
Hydrograph No. 7, Combine, Proposed.................................................................................11
10 - Year
Summary Report.......................................................................................................................12
Hydrograph Reports.................................................................................................................13
Hydrograph No. 1, SCS Runoff, Existing to UGS...................................................................13
Hydrograph No. 2, SCS Runoff, Existing Offsite....................................................................14
Hydrograph No. 3, Combine, Existing....................................................................................15
Hydrograph No. 4, SCS Runoff, Proposed to UGS................................................................16
Hydrograph No. 5, SCS Runoff, Proposed to Offsite.............................................................17
Hydrograph No. 6, Reservoir, UGS........................................................................................18
Hydrograph No. 7, Combine, Proposed.................................................................................19
25 - Year
Summary Report.......................................................................................................................20
Hydrograph Reports.................................................................................................................21
Hydrograph No. 1, SCS Runoff, Existing to UGS...................................................................21
Hydrograph No. 2, SCS Runoff, Existing Offsite....................................................................22
Hydrograph No. 3, Combine, Existing....................................................................................23
Hydrograph No. 4, SCS Runoff, Proposed to UGS................................................................24
Hydrograph No. 5, SCS Runoff, Proposed to Offsite.............................................................25
Hydrograph No. 6, Reservoir, UGS........................................................................................26
Hydrograph No. 7, Combine, Proposed.................................................................................27
100 - Year
Summary Report.......................................................................................................................28
Hydrograph Reports.................................................................................................................29
Hydrograph No. 1, SCS Runoff, Existing to UGS...................................................................29
Hydrograph No. 2, SCS Runoff, Existing Offsite....................................................................30
Hydrograph No. 3, Combine, Existing....................................................................................31
Hydrograph No. 4, SCS Runoff, Proposed to UGS................................................................32
Hydrograph No. 5, SCS Runoff, Proposed to Offsite.............................................................33
Hydrograph No. 6, Reservoir, UGS........................................................................................34
Hydrograph No. 7, Combine, Proposed.................................................................................35
1 2
3
4 5
6
7
1
Watershed Model Schematic Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Project: 18-501 Whirligig Parking Lot.gpw Thursday, 02 / 27 / 2020
Hyd.Origin Description
Legend
1 SCS Runoff Existing to UGS
2 SCS Runoff Existing Offsite
3 Combine Existing
4 SCS Runoff Proposed to UGS
5 SCS Runoff Proposed to Offsite
6 Reservoir UGS
7 Combine Proposed
Hydrograph Return Period Recap
2
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 ------ 29.68 ------- ------- ------- 56.21 70.36 ------- 96.75 Existing to UGS
2 SCS Runoff ------ 0.196 ------- ------- ------- 0.371 0.464 ------- 0.638 Existing Offsite
3 Combine 1, 2 29.82 ------- ------- ------- 56.48 70.70 ------- 97.22 Existing
4 SCS Runoff ------ 29.68 ------- ------- ------- 56.21 70.36 ------- 96.75 Proposed to UGS
5 SCS Runoff ------ 0.196 ------- ------- ------- 0.371 0.464 ------- 0.638 Proposed to Offsite
6 Reservoir 4 8.125 ------- ------- ------- 11.15 12.33 ------- 18.59 UGS
7 Combine 5, 6 8.147 ------- ------- ------- 11.19 12.38 ------- 18.66 Proposed
Proj. file: 18-501 Whirligig Parking Lot.gpw Thursday, 02 / 27 / 2020
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hydrograph Summary Report
3
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 29.68 2 720 86,336 ------ ------ ------ Existing to UGS
2 SCS Runoff 0.196 2 716 456 ------ ------ ------ Existing Offsite
3 Combine 29.82 2 720 86,791 1, 2 ------ ------ Existing
4 SCS Runoff 29.68 2 720 86,336 ------ ------ ------ Proposed to UGS
5 SCS Runoff 0.196 2 716 456 ------ ------ ------ Proposed to Offsite
6 Reservoir 8.125 2 734 86,315 4 129.82 31,217 UGS
7 Combine 8.147 2 734 86,771 5, 6 ------ ------ Proposed
18-501 Whirligig Parking Lot.gpw Return Period: 1 Year Thursday, 02 / 27 / 2020
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 1
Existing to UGS
Hydrograph type = SCS Runoff Peak discharge = 29.68 cfs
Storm frequency = 1 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 86,336 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 2.91 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
4
0 2 4 6 8 10 12 14 16 18 20 22 24
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
Q (cfs)
Time (hrs)
Existing to UGS
Hyd. No. 1 -- 1 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 2
Existing Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.196 cfs
Storm frequency = 1 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 456 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 2.91 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
5
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (hrs)
Existing Offsite
Hyd. No. 2 -- 1 Year
Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 3
Existing
Hydrograph type = Combine Peak discharge = 29.82 cfs
Storm frequency = 1 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 86,791 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 8.660 ac
6
0 2 4 6 8 10 12 14 16 18 20 22 24
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
Q (cfs)
Time (hrs)
Existing
Hyd. No. 3 -- 1 Year
Hyd No. 3 Hyd No. 1 Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 4
Proposed to UGS
Hydrograph type = SCS Runoff Peak discharge = 29.68 cfs
Storm frequency = 1 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 86,336 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 2.91 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
7
0 2 4 6 8 10 12 14 16 18 20 22 24
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
Q (cfs)
Time (hrs)
Proposed to UGS
Hyd. No. 4 -- 1 Year
Hyd No. 4
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 5
Proposed to Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.196 cfs
Storm frequency = 1 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 456 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 2.91 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
8
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (hrs)
Proposed to Offsite
Hyd. No. 5 -- 1 Year
Hyd No. 5
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 6
UGS
Hydrograph type = Reservoir Peak discharge = 8.125 cfs
Storm frequency = 1 yrs Time to peak = 12.23 hrs
Time interval = 2 min Hyd. volume = 86,315 cuft
Inflow hyd. No. = 4 - Proposed to UGS Max. Elevation = 129.82 ft
Reservoir name = UGS Max. Storage = 31,217 cuft
Storage Indication method used.
9
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
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
Q (cfs)
Time (hrs)
UGS
Hyd. No. 6 -- 1 Year
Hyd No. 6 Hyd No. 4 Total storage used = 31,217 cuft
Pond Report 10
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Pond No. 1 - UGS
Pond Data
Contours -User-defined contour areas. Conic method used for volume calculation. Begining Elevation = 127.00 ft
Stage / Storage Table
Stage (ft) Elevation (ft) Contour area (sqft) Incr. Storage (cuft) Total storage (cuft)
0.00 127.00 9,260 0 0
1.00 128.00 9,260 9,259 9,259
2.00 129.00 9,260 9,259 18,518
2.01 129.01 15,590 123 18,641
3.00 130.00 15,590 15,433 34,074
4.00 131.00 15,590 15,588 49,662
5.00 132.00 15,590 15,588 65,250
6.00 133.00 15,590 15,588 80,839
7.00 134.00 15,590 15,588 96,427
8.00 135.00 15,590 15,588 112,016
8.33 135.33 15,590 5,144 117,160
Culvert / Orifice Structures Weir Structures
[A] [B] [C] [PrfRsr] [A] [B] [C] [D]
Rise (in)= 18.00 12.00 12.00 0.00
Span (in)= 18.00 12.00 12.00 0.00
No. Barrels = 1 1 1 0
Invert El. (ft)= 127.00 127.00 127.00 0.00
Length (ft)= 181.00 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 Yes No
Crest Len (ft)= 11.00 3.00 0.00 0.00
Crest El. (ft)= 133.00 134.00 0.00 0.00
Weir Coeff.= 3.33 3.33 3.33 3.33
Weir Type = 1 Rect Rect ---
Multi-Stage = Yes Yes No 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).
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00
Stage (ft)
0.00 127.00
2.00 129.00
4.00 131.00
6.00 133.00
8.00 135.00
10.00 137.00
Elev (ft)
Discharge (cfs)
Stage / Discharge
Total Q
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 7
Proposed
Hydrograph type = Combine Peak discharge = 8.147 cfs
Storm frequency = 1 yrs Time to peak = 12.23 hrs
Time interval = 2 min Hyd. volume = 86,771 cuft
Inflow hyds. = 5, 6 Contrib. drain. area = 0.050 ac
11
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
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 (hrs)
Proposed
Hyd. No. 7 -- 1 Year
Hyd No. 7 Hyd No. 5 Hyd No. 6
Hydrograph Summary Report
12
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 56.21 2 720 168,005 ------ ------ ------ Existing to UGS
2 SCS Runoff 0.371 2 716 887 ------ ------ ------ Existing Offsite
3 Combine 56.48 2 720 168,892 1, 2 ------ ------ Existing
4 SCS Runoff 56.21 2 720 168,005 ------ ------ ------ Proposed to UGS
5 SCS Runoff 0.371 2 716 887 ------ ------ ------ Proposed to Offsite
6 Reservoir 11.15 2 736 167,984 4 131.82 62,410 UGS
7 Combine 11.19 2 736 168,871 5, 6 ------ ------ Proposed
18-501 Whirligig Parking Lot.gpw Return Period: 10 Year Thursday, 02 / 27 / 2020
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 1
Existing to UGS
Hydrograph type = SCS Runoff Peak discharge = 56.21 cfs
Storm frequency = 10 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 168,005 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 5.45 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
13
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
Q (cfs)
Time (hrs)
Existing to UGS
Hyd. No. 1 -- 10 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 2
Existing Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.371 cfs
Storm frequency = 10 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 887 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 5.45 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
14
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (hrs)
Existing Offsite
Hyd. No. 2 -- 10 Year
Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 3
Existing
Hydrograph type = Combine Peak discharge = 56.48 cfs
Storm frequency = 10 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 168,892 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 8.660 ac
15
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
Q (cfs)
Time (hrs)
Existing
Hyd. No. 3 -- 10 Year
Hyd No. 3 Hyd No. 1 Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 4
Proposed to UGS
Hydrograph type = SCS Runoff Peak discharge = 56.21 cfs
Storm frequency = 10 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 168,005 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 5.45 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
16
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
Q (cfs)
Time (hrs)
Proposed to UGS
Hyd. No. 4 -- 10 Year
Hyd No. 4
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 5
Proposed to Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.371 cfs
Storm frequency = 10 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 887 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 5.45 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
17
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (hrs)
Proposed to Offsite
Hyd. No. 5 -- 10 Year
Hyd No. 5
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 6
UGS
Hydrograph type = Reservoir Peak discharge = 11.15 cfs
Storm frequency = 10 yrs Time to peak = 12.27 hrs
Time interval = 2 min Hyd. volume = 167,984 cuft
Inflow hyd. No. = 4 - Proposed to UGS Max. Elevation = 131.82 ft
Reservoir name = UGS Max. Storage = 62,410 cuft
Storage Indication method used.
18
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
Q (cfs)
Time (hrs)
UGS
Hyd. No. 6 -- 10 Year
Hyd No. 6 Hyd No. 4 Total storage used = 62,410 cuft
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 7
Proposed
Hydrograph type = Combine Peak discharge = 11.19 cfs
Storm frequency = 10 yrs Time to peak = 12.27 hrs
Time interval = 2 min Hyd. volume = 168,871 cuft
Inflow hyds. = 5, 6 Contrib. drain. area = 0.050 ac
19
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
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 (hrs)
Proposed
Hyd. No. 7 -- 10 Year
Hyd No. 7 Hyd No. 5 Hyd No. 6
Hydrograph Summary Report
20
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 70.36 2 720 211,792 ------ ------ ------ Existing to UGS
2 SCS Runoff 0.464 2 716 1,118 ------ ------ ------ Existing Offsite
3 Combine 70.70 2 720 212,910 1, 2 ------ ------ Existing
4 SCS Runoff 70.36 2 720 211,792 ------ ------ ------ Proposed to UGS
5 SCS Runoff 0.464 2 716 1,118 ------ ------ ------ Proposed to Offsite
6 Reservoir 12.33 2 736 211,771 4 132.95 80,081 UGS
7 Combine 12.38 2 736 212,889 5, 6 ------ ------ Proposed
18-501 Whirligig Parking Lot.gpw Return Period: 25 Year Thursday, 02 / 27 / 2020
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 1
Existing to UGS
Hydrograph type = SCS Runoff Peak discharge = 70.36 cfs
Storm frequency = 25 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 211,792 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 6.81 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
21
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
Q (cfs)
Time (hrs)
Existing to UGS
Hyd. No. 1 -- 25 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 2
Existing Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.464 cfs
Storm frequency = 25 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 1,118 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 6.81 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
22
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (hrs)
Existing Offsite
Hyd. No. 2 -- 25 Year
Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 3
Existing
Hydrograph type = Combine Peak discharge = 70.70 cfs
Storm frequency = 25 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 212,910 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 8.660 ac
23
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
Q (cfs)
Time (hrs)
Existing
Hyd. No. 3 -- 25 Year
Hyd No. 3 Hyd No. 1 Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 4
Proposed to UGS
Hydrograph type = SCS Runoff Peak discharge = 70.36 cfs
Storm frequency = 25 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 211,792 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 6.81 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
24
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
Q (cfs)
Time (hrs)
Proposed to UGS
Hyd. No. 4 -- 25 Year
Hyd No. 4
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 5
Proposed to Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.464 cfs
Storm frequency = 25 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 1,118 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 6.81 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
25
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.05 0.05
0.10 0.10
0.15 0.15
0.20 0.20
0.25 0.25
0.30 0.30
0.35 0.35
0.40 0.40
0.45 0.45
0.50 0.50
Q (cfs)
Time (hrs)
Proposed to Offsite
Hyd. No. 5 -- 25 Year
Hyd No. 5
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 6
UGS
Hydrograph type = Reservoir Peak discharge = 12.33 cfs
Storm frequency = 25 yrs Time to peak = 12.27 hrs
Time interval = 2 min Hyd. volume = 211,771 cuft
Inflow hyd. No. = 4 - Proposed to UGS Max. Elevation = 132.95 ft
Reservoir name = UGS Max. Storage = 80,081 cuft
Storage Indication method used.
26
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
Q (cfs)
Time (hrs)
UGS
Hyd. No. 6 -- 25 Year
Hyd No. 6 Hyd No. 4 Total storage used = 80,081 cuft
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 7
Proposed
Hydrograph type = Combine Peak discharge = 12.38 cfs
Storm frequency = 25 yrs Time to peak = 12.27 hrs
Time interval = 2 min Hyd. volume = 212,889 cuft
Inflow hyds. = 5, 6 Contrib. drain. area = 0.050 ac
27
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
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 (hrs)
Proposed
Hyd. No. 7 -- 25 Year
Hyd No. 7 Hyd No. 5 Hyd No. 6
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 1
Existing to UGS
Hydrograph type = SCS Runoff Peak discharge = 96.75 cfs
Storm frequency = 100 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 293,608 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 9.35 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
29
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
90.00 90.00
100.00 100.00
Q (cfs)
Time (hrs)
Existing to UGS
Hyd. No. 1 -- 100 Year
Hyd No. 1
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 2
Existing Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.638 cfs
Storm frequency = 100 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 1,550 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 9.35 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
30
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.10 0.10
0.20 0.20
0.30 0.30
0.40 0.40
0.50 0.50
0.60 0.60
0.70 0.70
0.80 0.80
0.90 0.90
1.00 1.00
Q (cfs)
Time (hrs)
Existing Offsite
Hyd. No. 2 -- 100 Year
Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 3
Existing
Hydrograph type = Combine Peak discharge = 97.22 cfs
Storm frequency = 100 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 295,157 cuft
Inflow hyds. = 1, 2 Contrib. drain. area = 8.660 ac
31
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
90.00 90.00
100.00 100.00
Q (cfs)
Time (hrs)
Existing
Hyd. No. 3 -- 100 Year
Hyd No. 3 Hyd No. 1 Hyd No. 2
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 4
Proposed to UGS
Hydrograph type = SCS Runoff Peak discharge = 96.75 cfs
Storm frequency = 100 yrs Time to peak = 12.00 hrs
Time interval = 2 min Hyd. volume = 293,608 cuft
Drainage area = 8.610 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 10.00 min
Total precip. = 9.35 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
32
0 2 4 6 8 10 12 14 16 18 20 22 24
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
90.00 90.00
100.00 100.00
Q (cfs)
Time (hrs)
Proposed to UGS
Hyd. No. 4 -- 100 Year
Hyd No. 4
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 5
Proposed to Offsite
Hydrograph type = SCS Runoff Peak discharge = 0.638 cfs
Storm frequency = 100 yrs Time to peak = 11.93 hrs
Time interval = 2 min Hyd. volume = 1,550 cuft
Drainage area = 0.050 ac Curve number = 98
Basin Slope = 0.0 % Hydraulic length = 0 ft
Tc method = User Time of conc. (Tc) = 5.00 min
Total precip. = 9.35 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
33
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Q (cfs)
0.00 0.00
0.10 0.10
0.20 0.20
0.30 0.30
0.40 0.40
0.50 0.50
0.60 0.60
0.70 0.70
0.80 0.80
0.90 0.90
1.00 1.00
Q (cfs)
Time (hrs)
Proposed to Offsite
Hyd. No. 5 -- 100 Year
Hyd No. 5
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 6
UGS
Hydrograph type = Reservoir Peak discharge = 18.59 cfs
Storm frequency = 100 yrs Time to peak = 12.27 hrs
Time interval = 2 min Hyd. volume = 293,587 cuft
Inflow hyd. No. = 4 - Proposed to UGS Max. Elevation = 134.91 ft
Reservoir name = UGS Max. Storage = 110,662 cuft
Storage Indication method used.
34
0 2 4 6 8 10 12 14 16 18 20 22 24 26
Q (cfs)
0.00 0.00
10.00 10.00
20.00 20.00
30.00 30.00
40.00 40.00
50.00 50.00
60.00 60.00
70.00 70.00
80.00 80.00
90.00 90.00
100.00 100.00
Q (cfs)
Time (hrs)
UGS
Hyd. No. 6 -- 100 Year
Hyd No. 6 Hyd No. 4 Total storage used = 110,662 cuft
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Hyd. No. 7
Proposed
Hydrograph type = Combine Peak discharge = 18.66 cfs
Storm frequency = 100 yrs Time to peak = 12.27 hrs
Time interval = 2 min Hyd. volume = 295,137 cuft
Inflow hyds. = 5, 6 Contrib. drain. area = 0.050 ac
35
0 2 4 6 8 10 12 14 16 18 20 22 24 26
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
21.00 21.00
Q (cfs)
Time (hrs)
Proposed
Hyd. No. 7 -- 100 Year
Hyd No. 7 Hyd No. 5 Hyd No. 6
Hydraflow Rainfall Report 36
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020 Thursday, 02 / 27 / 2020
Return Intensity-Duration-Frequency Equation Coefficients (FHA)
Period
(Yrs)B D E (N/A)
1 61.3089 12.1000 0.8801 --------
2 73.0076 12.6000 0.8788 --------
3 0.0000 0.0000 0.0000 --------
5 72.3690 12.4000 0.8323 --------
10 71.3089 12.0000 0.7930 --------
25 67.3330 11.1000 0.7441 --------
50 59.3755 9.9000 0.6892 --------
100 56.4628 9.2000 0.6543 --------
File name: Wilson NC NOAA ATLAS 14.IDF
Intensity = B / (Tc + D)^E
Return Intensity Values (in/hr)
Period
(Yrs) 5 min 10 15 20 25 30 35 40 45 50 55 60
1 5.04 4.02 3.36 2.89 2.55 2.28 2.07 1.89 1.74 1.62 1.51 1.42
2 5.87 4.71 3.95 3.42 3.01 2.70 2.45 2.24 2.07 1.93 1.80 1.69
3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5 6.72 5.44 4.60 4.00 3.55 3.20 2.92 2.68 2.49 2.32 2.18 2.05
10 7.54 6.15 5.22 4.57 4.07 3.68 3.37 3.11 2.89 2.70 2.54 2.40
25 8.52 6.96 5.94 5.22 4.67 4.24 3.89 3.61 3.36 3.16 2.98 2.82
50 9.23 7.56 6.48 5.71 5.13 4.68 4.31 4.01 3.76 3.54 3.35 3.18
100 9.95 8.17 7.02 6.21 5.60 5.12 4.73 4.41 4.14 3.91 3.71 3.53
Tc = time in minutes. Values may exceed 60.
Rainfall Precipitation Table (in)
Precip. file name: P:\_CADD\Hydraflow Precipitaion & Rainfall Intensity Data\Wilson NC NOAA ATLAS 14.pcp
Storm
Distribution 1-yr 2-yr 3-yr 5-yr 10-yr 25-yr 50-yr 100-yr
SCS 24-hour 2.91 3.53 0.00 4.56 5.45 6.81 8.00 9.35
SCS 6-Hr 2.10 2.51 0.00 3.12 3.75 4.60 5.39 6.23
Huff-1st 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Huff-2nd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Huff-3rd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Huff-4th 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Huff-Indy 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Custom 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Contents continued...18-501 Whirligig Parking Lot.gpw
IDF Report..................................................................................................................36
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