SW5221102_Design Calculations (SNAP)_20230414

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Division of Water Resources

Proiect Information
Project Name:
Bryson's Ridge Subdivision Phase 2
04/12/2023
2,269,515 ft2
Submission Date:
Project Area (ft):
Disturbed Area (ft):
263,102 ft2
Development Land Use Type:
Single Family Residential
Development Activity Type:
Development - New
Designated Downtown Area?
no
Project Location/Address:
NC-581
County:
Nash
Local Jurisdiction:
Spring Hope
Project Latitude Coordinates:
35.959961 N
Project Longitude Coordinates:
-78.110970 W
Precipitation Station:
Rocky Mount
Physiographic Region:
Nutrient Management Watershed:
Subwatershed:
Piedmont
Tar -Pamlico
Tar -Pamlico - 03020101
Phosphorus Delivery Zone:
Tar - Pamlico River
Nitrogen Delivery Zone:
Tar - Pamlico River
Kevin Yarnell [phone]
no
Private
Project Designer and Contact Phone
Number / Email:
Part of Common Development Plan?
Project Owner Type:
Project Description:

R = 0.05 + (0.009 * 1)
where I = percent impervious (%)
Average Annual Pollutant Load, L
L= (Pi *Rv*(P/12))*(C*A*2.72)
where C = event mean concentration (mg/L)
PROJECT AREA LAND COVERS
Roof
Roadway
TN
EMC
(mg/L)
1.18
1.64
TP _T Pre-
EMC Project
(mg/L) Area (ft2)
0.11
0.34
Post -
Project
Area (ft)
462,000
195,542
Parking/Driveway/Sidewalk
1.42
0.18
74,533
Protected Forest
0.97
0.03
39,204
39,204
Other Pervious/Landscaping
2.48
1.07
2,230,311
1,462,952
CUSTOM LAND COVER 1
CUSTOM LAND COVER 2
CUSTOM LAND COVER 3
LAND TAKEN UP BY SCM
1.18
1 0.11
1 35,284
LAND COVER AREA CHECK
Net Change of Land Covers (ft): 767,359
Total Project Area Entered (ft): 2,269,515
Total Pre -Project Calculated Area (ft): 2,269,515
Total Post -Project Calculated Area (ft): 2,269,515
Equations Used and Project Area Calculations
SIMPLE METHOD Stormwater Runoff Volume Generated, V
Runoff Coefficient R v V = Pj * Rv * (P/12) * A
where A = drainage area (ft)
Pj = fraction of rain events with runoff
P = average annual rainfall depth (in)
A =
52.1009
ac
A = 52.1009
ac
P =
44.81
in.
P = 44.81
in.
V =
381364
ft3
V = 2708304
ft3
1=
0%
1= 34%
Rv =
0.05
Rv = 0.36
Pi =
0.9
Pi = 0.9
CTN =
2.45
mg/L
CTN = 1.42
mg/L
CTP =
1.05
mg/L
CTP = 0.26
mg/L
LTN =
58.44
Ib/yr
LTN = 240.92
Ib/yr
LTP =
25.05
Ib/yr
LTP = 43.31
Ib/yr

3. SCM Characteristics
Catchment ID 1 1 1
SCM ID 101 TI 102
I
Type of SCM Wet Pond per MDC Wet Pond per MDC
Predominant hydrologic soil B B
group at SCM location
SCM Description I Wet Pond 2 1 Wet Pond 3
Design Storm Size (inches/24hrs)
Percent of Full Size
100%
100%
Hydrologic Value - Percent Annual
Effluent
68%
68%
Hydrologic Value - Percent Annual
Overflow
16%
16%
Hydrologic Value - Percent Annual
ET/Infiltrated
17%
17%
SCM Effluent TP EMC (mg/L)
0.15
0.15
SCM Effluent TN EMC(mg/L)
1.22
1.22
SCM Land Cover TP EMC (mg/L)
0.11
0.11
SCM Land Cover TN EMC (mg/L)
1.18
1.18
Drains to SCM ID
102
0
Catchment Routing
Catchments Draining to Catchments
Draining
to Catchments Draining to
(Source Catchment)
SCM 101
SCM 102
SCM 103
Catchment 1
Catchment 2
Catchment 3
_
Catchment 4
Catchment 5
I
Catchment 6
SCM ID:
Area Draining Directly to
SCM Drainage Area land Covers
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 (ftz)
Allowable Total Land Use
Area to be Treated Based
on Post-Promect Areas
Post -Project Untreated
Land Area (ftz)
Roof 250,250
35,000
285,250
462,000
176,750
Roadway 162,277
18,965
181,242
195,542
14,300
Parking/Driveway/Sidewalk 62,277
7,286
69,563
74,533
4,970
Protected Forest 0
0
39,204
39,204
Other Pervious/Landscaping 685,674
140,699
826,373
1,462,952
636,579
CUSTOM LAND COVER 1
0
0
0
CUSTOM LAND COVER 2
0
0
0
CUSTOM LAND COVER 3
0
0
0
LAND TAKEN UP BY SCM 27,007 8,277
ALAREA DRAINING TO SCM
1,187,485 210,227 0
(ftz):
CATCHMENTAREA(ft): 1,397,712
35,284
35,284
0
1,397,712
2,269,515
871,803

Project Summary
Project Name:
Bryson's Ridge Subdivision Phase 2
2,269,515 ft 52.1009 acres Submission Date:
263,102 ftZ 6.0400 acres April 12, 2023
Project Area (ft):
Disturbed Area (ft):
County:
Nash
Local Jurisdiction:
Spring Hope
Development Land Use Type:
Single Family Residential
Owner Type:
Private
Development Activity Type:
Development - New
Designated Downtown Area?
no
Nutrient Management Watershed:
Tar -Pamlico
Subwatershed:
Tar -Pamlico - 03020101
Phosphorus Delivery Zone:
Tar - Pamlico River
Nitrogen Delivery Zone:
Tar - Pamlico River
Phosphorus Delivery
Factor (%):
100%
Nitrogen Delivery
Factor (%):
100%
Phosphorus Loading Rate Target (Ib/ac/yr):
0.83
Nitrogen Loading Rate Target (Ib/ac/yr):
4.62
Phosphorus Load Target at Site (lb/yr):
43.31
Nitrogen Load Target at Site (lb/yr):
240.92
Phosphorus Load Leaving Site w/SCMs (lb/yr):
25.75
Nitrogen Load Leaving Site w/SCMs (lb/yr):
171.70
P Offsite Buy -Down Threshold Loading Rate (lb/ac/yr):
N/A
N Offsite Buy -Down Threshold Loading Rate
N/A
Total P Load Reduction Needed (lb/yr):
0.00
Total N Load Reduction Needed (lb/yr):
0.00
P Load Treatment Balance at Site (lb/yr):
-17.56
N Load Treatment Balance at Site (lb/yr):
-69.22
P Load Treatment Balance at Lake (lb/yr):
-17.56
N Load Treatment Balance at Lake (lb/yr):
-69.22
Net land use change is greater
than Disturbed Area. Verify
Disturbed Area.
Nutrient Export Summary
Pre -Project
Whole Site
Conditions
0.0%
0.0%
Post -Project Post -Project Post -Project
Post Project
Whole Site Whole Site with SCM-Treated
Untreated Area
without SCMs SCMs Area
33.8% 33.8% 40.9% 22.5%
32.3% 32.3% 38.4% 22.5%
Percent Impervious (for runoff calculation) (%)
Percent Built -Upon Area (BUA) (%)
Annual Runoff Volume ft3/ r
381,364
2,708,304
2,134,234
1,394,842
739,392
Annual Runoff % Change (relative to re-D)
0%
610%
460%
Total Nitrogen EMC (mg/L)
2.45
1.42
1.29
1.23
1.40
Total Nitrogen Load Leaving Site (lb/yr)
58.44
240.92
171.70
107.09
64.61
Total Nitrogen Loading Rate (Ib/ac/yr)
1.12
4.62
3.30
3.34
3.23
Total Nitrogen % Change (relative to pre-D)
0%
312%
194%
Total Phosphorus EMC (mg/L)
1.05
0.26
0.19
0.16
0.26
Total Phosphorus Load Leaving Site (lb/yr)
25.05
43.31
25.75
13.57
12.18
Total Phosphorus Loading Rate (Ib/ac/yr)
0.48
0.83
0.49
0.42
0.61
Total Phosphorus % Change (relative to pre-D)
1 0%
73%
3%

SCWCatchment Summary
Volume
SCM ID and Type Reduction (%) TN Out (mg/L)
Catchment 1 29.16% 1.23
FTP Out (mg/L)
TN Out -F TP Out
Obs/ac/yr) (lbs/ac/yr) TN Reduction (%) TIP Reduction (%)
3.34 0.42 39.24% 56.387
0.16
101: Wet Pond per MDC
16.88%
1.26
0.17
4.12
0.55
27.08%
44.26%
102: Wet Pond per MDC
16.88%
1.23
0.16
3.34
0.42
20.40%
29.14%
103: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
Catchment 2
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
201: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
202: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
203: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
Catchment 3
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
301: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
302: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
303: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
Catchment 4
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
401: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
402: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
403: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
Catchment 5
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
501: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
502: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
503: NA
0.00%
0.00
0.00
0.00
0.00
0.00%
0.00%
Catchment 6 0.00% 0.00
601: NA 0.00% 0.00
602: NA 0.00% 0.00
603: NA 0.00%-1 0.00
0.00
0.00
0.00
0.00%
0.00%
0.00
0.00
0.00
0.00%
0.00%
0.00
0.00
0.00
0.00%
0.00%
0.00 0.00
0.00
0.00 %
0.00 %
SCM rows in red have a data entry error for the SCM that makes an error in the calculation.

Nutrient Management Strategy Watershed - Nutrient Offset Credit Reporting Form
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.
http://deg. nc.gov/about/divisions/water-resources/planning/nonpoint-source-management/nutrient-offset-
information
PROJECT INFORMATION
Applicant Name:
Project Name: Bryson's Ridge Subdivision Phase 2
Project Address: NC-581
Date: (mm/dd/yyyy)
Development Land Use Type:
Single Family Residential
County: Nash
Development Activity Type:
Development - New
Pre -Project Built -Upon Area %:
0.00%
Project Latitude:
35.959961
Post -Project Built -Upon Area %:
32.26%
Project Longitude:
-78.11097
WATERSHED INFORMATION
Nutrient Management Watershed:
Tar -Pamlico
N Offsite Threshold Rate (lb/ac/yr):
N/A
Subwatershed:
Tar -Pamlico - 03020101
P Offsite Threshold Rate (lb/ac/yr):
N/A
Nitrogen Delivery Zone:
Tar - Pamlico River
Nitrogen Delivery Factor:
100%
Phosphorus Delivery Zone:
Tar - Pamlico River
Phosphorus Delivery Factor:
100%
NUTRIENT OFFSET REQUEST
Nitrogen Load Offset Needs
(A)
(B)
(C)
(D)
(E)
(F)
(G)
(H) (L) (Where
Applicable)
Untreated
Treated
Loading Rate
Reduction
Project Size
Offset
Delivery
State Buy Local Gov't
Loading Rate
Loading Rate
Target
Need
(ac)
Duration (yrs)
Factor (/°)
Down Amount Buy Down
(Ibs/ac/yr)
(Ibs/ac/yr)
(Ibs/ac/yr)
(Ibs/ac/yr)
(Ibs) Amount (Ibs)
B-C
D-E-F-G
4.62
1 3.30
1 4.62
1 -1.33
52.1009
30
100%
0.00
Phosphorus Load Offset Needs
(A)
(B)
(C)
(D)
(E)
(F)
(G)
(H) (L) (Where
Applicable)
Untreated
Treated Load
Loading Rate
Reduction
Project Size
Offset
Delivery
State Buy Local Gov't
Load Rate
Rate
Target
Need
(ac)
Duration (yrs)
Factor (/°)
Down Amount Buy Down
(Ibs/ac/yr)
(Ibs/ac/yr)
(Ibs/ac/yr)
(Ibs/ac/yr)
(Ibs) Amount (Ibs)
B-C
D"E"F"G
0.83
1 0.49
1 0.83
1 -0.34
52.1009
30
100%
0.00
LOCAL GOVERNMENT AUTHORIZATION
Local Government Name:
Staff Name:
Staff Emai
Local Government Authorizing Signature: