SW1221003_Stormwater Narrative_20221031

Planning & Project Management / Civil Engineering i Surveying
BROC)KS Soil Science Services 1 Environmental Engineering & Services
ENGIN EERIN G ASS ❑ DIATES 17 Arlington Street 1 Asheville NC 28801 I www.brooksea.com i 828-232-4700
Wk River Townhomes
Sin&, -Family Attached ®evoOo��r ent.
Town of Mills Riven, (Henderson Country
North Carolina
Stormwater and Erosion Control Report
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Original: July 25, 2022
Revised: October 10, 2022
Mark Brooks, PE

TABLE OF CONTENTS
Storm Water & Erosion Control Narrative.......................................................1-4
NOAA Precipitation Charts, Jurisdictional Determination, Subsurface
Exploration and Geotechnical Evaluation, USGS Map & FEMA Map...............Appendix 1
Hydrologic Model and BMP Design.............................................................Appendix 2
Erosion Control Calculations and Specifications .............................................Appendix 3

I ► /_1 V:7_1%I LWO
Project Description
The proposed Mills River Townhomes Single -Family Attached Development is located
on three adjacent parcels known as 2211, 2253 and 2035 Jeffress Road in the Town of
Mills River, North Carolina (Corresponding Henderson County PINs: 9631-79-4210,
9631-77-4946 and 9631-88-2468). The 37.00-acre site will be accessed via two private
roads from Jeffress Road. The proposed development consists of 148 Single -Family
Attached Townhome Units with private driveways and patio's. The community amenities
include a clubhouse, a resort -style pool and cabana, dog run and sports field with
associated parking and sidewalks.
Existing Site Conditions
The entire existing parcel known as 2211 Jeffress Road is currently vacant and
composed of a grass meadow ground cover.
The southern majority portion of the existing parcel known as 2253 Jeffress Road is
currently an agricultural use and composed of row crops. The central portion consists of
linear streams and wetlands with a surrounding brush/weed/grass mixture. The
northern portion is currently a residential/agricultural use and composed of grass
meadow ground cover. This area is accessed via a private asphalt driveway and
consists of a single-family dwelling, accessory building, barn and silo, all proposed to be
removed.
The entire existing parcel known as 2035 Jeffress Road is vacant and composed of a
woods/grass combination with linear streams and wetlands to the east and south.
The soils for the site are classified by the NRCS as a Rosman loam (Ro) with a
Hydrologic Soil Group Type A rating, a Bradson gravelly loam (BaB) with a Hydrologic
Soil Group Type B rating, a Toxaway silt loam (To) and Codorus loam with a Hydrologic
Soil Group Type B/D rating, and a Delanco dillard loam (DeA) with a Hydrologic Soil
Group Type C rating.
The site primarily drains to the existing streams near the center of the site and along the
eastern property lines. For analysis purposes, this drainage basin was split in to three
areas. Drainage Area #1 drains towards the central northern existing wetlands.
Drainage Area #2 drains towards central southern existing wetlands and stream.
Drainage Area #3 drains towards the southern and eastern property line. All drainage
areas ultimately converge and exit the site in the northeast corner of the existing
agricultural field.
U.S. Armv CorDs of Enaineers Jurisdictional Determination:
A Notification of Jurisdictional Determination dated June 1, 2022 is enclosed within. No
impacts to existing streams and wetlands are proposed.
Proposed Developed Conditions
The proposed development is considered high -density and is designed to achieve a
runoff treatment for the first inch of rain. Runoff from impervious areas associated with
buildings, roads with curb & gutter, driveways, sidewalks, and parking areas are

captured to the maximum extent practical and conveyed through storm water pipes to
three separate BMP systems each utilizing BayFilter's as the Primary SCM in
conjunction with underground StormTech chambers for detention. All offsite areas
bypass the proposed BMP systems and are directed into the existing streams which
mimics the existing conditions.
Purpose of Report
The purpose of this report is to demonstrate compliance with NCDEQ Phase II Post
Construction Activities.
Procedure
Collection System:
The proposed collection system was sized to adequately convey the 25-year, 24-hour
storm. Drainage areas were delineated for each proposed inlet in addition to Rational
`C' coefficients and time of concentration based on the TR-55 method. Energy
dissipation will be handled with riprap pads sized for the 25-year storm. Refer to sheets
C-5.10 & C-5.11 in the provided plan set for a drainage summary. Refer to the
stormwater profiles on sheets C-5.1 & C-5.2 in the provided plan set for a depiction of
the 25-year hydraulic grade line.
Water Quantity:
The SCS Method using a 24-hour, Type II storm was used to determine the pre -
developed and developed annual peak stormwater discharges generated from this site.
The HydroCAD runoff routing program was used to determine these peak flows and
storm volumes as well as routing through the underground StormTech chambers
systems and bypass areas. Stage/discharge rates for the systems were determined
based on storage, culvert, orifices and weir equations within Hydrocad.
Calculations for the 25-year storm event were performed to show the BayFilter's and the
StormTech chambers are adequately sized to pass the 25-year storm event. Rip -rap
aprons are provided along with outlet control structures for primary drainage from basin
areas.
Water Quality:
The Simple Method was used to determine the runoff volume for the first -inch of rainfall.
Treatment is provided for all built -upon area of runoff for 1" treatment design storm.
Calculations per Section B of NCDEQ Stormwater Design Manual are enclosed within.
All structural stormwater treatment systems are designed to have a minimum of 85
percent average annual removal for total suspended solids (TSS) through the use of
adequately sized BayFilter's. The BayFilter's are designed to meet all required General
MDC's.
Seasonal High Water Table (SHWT):
Per NCDEQ MDC guidelines, the lowest point shall be a minimum of two feet above the
SHWT. A Subsurface Exploration and Geotechnical Evaluation prepared by ECS
Southeast, LLP dated May 31, 2022 is enclosed within. The bottoms of all StormTech
systems are at least 2' above the SHWT.

Calculations
Drainage maps are included the plans on sheets C-5.10 & C-5.11 associated with this
project. These maps show the existing and proposed conditions. A summary of the
entire drainage area for the site and each individual drainage area within the site is
included in this report. Erosion Control calculations including sediment basin design are
included in Appendix 3.
Stormwater Results
The following table shows the design volume required to treat the 1" water quality
design storm depth for each BMP. HydroCAD was utilized to customize water quality
storm events to produce the minimum volume required to be treated and produce runoff
rates for each BMP. These volumes and runoff rates were utilized to adequately size
the proposed BayFilter units and StormTech chambers. Refer to Appendix 2 for
HydroCAD calculations.
WQTreatment- Simple Method for Runoff Volume (1" Design Storm Depth)
Detained Area (AC)
Impervious Area (AC)
Pervious Area (AC)
Impervious Percent
Runoff Coefficient
Design Volume (CF)
Proposed Volume (CF)
BMP #11
5.265
3.380
1.885
0.642
0.628
11,998
12,061
BMP #2
1 3.632
2.913
0.719
0.802
0.772
10,177
10,188
BMP #3
1 3.267
2.293
0.975
0.702
0.682
8,083
8,085
TOTALI
1.2.1641
8.586
1 3.578
1 2.146
The following table shows the proposed BMP systems are adequately sized to safely
pass the 25-year, 24-hour storm event.
10-year, 24-hour Storm Event
25-year, 24-hour Storm Event
Peak Water Surface Elevation
Peak Water Surface Elevation
Top of BMP Elevation
BMP #1
2080.49'
2080.65'
2080.75'
BMP #2
2079.23'
2079.44'
2079.50'
BMP #3
2078.69'
2078.90'
2079.50'
Erosion Control Narrative
Erosion and sedimentation control will be provided with measures consistent with the standards
set forth in the NCDEQ Erosion Control Manual. During the first phase of construction, the
limits of disturbance will be delineated and construction entrances/exits will be installed.
Perimeter devices such as silt fence and reinforced stabilized outlets will be also be installed for
the entire site. During the next phase of construction, temporary diversions with check dams
and temporary skimmer basins for the northern portion of the site will be installed. The
contractor will begin clearing and grubbing the site and begin construction on the newly rerouted
existing sanitary sewer main. Once the sanitary sewer main is rerouted and approved,
construction will begin on the proposed bottomless culverts. Once the bottomless culverts for
the entrance roadway are complete and approved, mass grading will begin on the northern
portion of the site in order to allow for heavy equipment to access the southern portion without
any stream or wetland impacts. Clearing and grubbing of the southern portion of the site will
begin. Temporary diversions with check dams and temporary skimmer basins for the southern
portion of the site will be installed as import material is brought to the southern portion of the
site. A total of seven temporary skimmer sediment basins are proposed for the site and three of
them will be converted to permanent underground StormTech chamber systems once the site is
stabilized. Temporary diversion swales will convey runoff to the proposed sediment basins to

the maximum extent practical. The rest of the site will utilize sediment fence with reinforced
outlets that are to be placed near the base of the fill slope associated with grading impacts.
Upon completion of the road and utility construction, townhome construction may begin.
Calculations for the temporary skimmer sediment basins can be found in Appendix 4 of this
report. In addition, refer to the associated engineering plans submitted for review.
Recommendations
Brooks Engineering recommends that the proposed development utilize stormwater
management facilities as outlined in this study in order to treat stormwater and prevent
erosion at discharge points per NCDEQ regulations. Routine maintenance will need to
be performed in order for the stormwater management areas to operate as designed.
Refer to the Operations & Maintenance Manual.

Appendix 1

11/12/21, 9:04AM Precipitation Frequency Data Server
NOAA Atlas 14, Volume 2, Version 3
Location name: Mills River, North Carolina, USA*�'°
Latitude: 35.3991°, Longitude:-82.566° � ;
Elevation: 2095.51 ft *
*source: ESRI Maps w,�w ^ y�
-source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1
Average recurrence interval (years)
1
2
5
10
25
50
100
200
500
1000
0.369
0.439
0.526
0.592
0.678
0.743
0.809
0.875
0.961
1.03
5-min
(0.333-0.410)
(0.397-0.487)
(0.474-0.584)
(0.532-0.655)
(0.605-0.750)
(0.659-0.822)
(0.715-0.897)
(0.767-0.972)
(0.833-1.07)
(0.883-1.16)
0.589
0.702
0.842
0.947
1.08
1.18
1.29
1.39
1.52
1.62
10-min
(0.531-0.655)
(0.634-0.779)
(0.759-0.935)
(0.851-1.05)
(0.964-1.20)
1 (1.05-1.31)
1 (1.14-1.43)
1 (1.22-1.54)
(1.32-1.70)
(1.39-1.82)
0.737
0.883
1.07
1.20
1.37
1.50
1.63
1.75
1.91
2.04
15-min
(0.664-0.818)
(0.797-0.980)
(0.960-1.18)
1 (1.08-1.33)
1 (1.22-1.52)
1 (1.33-1.66)
1 (1.44-1.80)
1 (1.54-1.95)
(1.66-2.14)
(1.75-2.29)
1.01
1.22
1.51
1.74
2.03
2.26
2.49
2.73
3.04
3.30
30-min
(0.910-1.12)
1 (1.10-1.35)
1 (1.36-1.68)
1 (1.81-2.24)
1 (2.00-2.50)
(2.20-2.76)
(2.39-3.03)
(2.64-3.40)
(2.83-3.71)
1.26
1.53
1.94
2.26
2.70
3.06
3.43
3.82
4.37
4.81
60-min
(1.14-1.40)
(1.38-1.70)
(1.75-2.15)
(2.03-2.50)
(2.41-2.99)
(2.71-3.38)
(3.03-3.80)
(3.35-4.25)
(3.79-4.88)
(4.13-5.41)
1.48
1.79
2.26
2.64
3.16
3.59
4.04
4.52
5.19
5.73
2-hr
(1.33-1.64)
(1.62-1.99)
(2.03-2.50)
(2.36-2.92)
(2.81-3.50)
(3.17-3.98)
(3.54-4.48)
(3.93-5.01)
(4.45-5.79)
(4.87-6.44)
1.59
1.91
2.40
2.80
3.38
3.86
4.38
4.93
5.74
6.41
3-hr
(1.43-1.77)
(1.73-2.13)
(2.16-2.66)
(2.51-3.11)
(3.00-3.75)
(3.41-4.29)
(3.82-4.86)
(4.26-5.50)
(4.89-6.44)
(5.39-7.22)
2.01
2.40
2.96
3.43
4.13
4.72
5.35
6.05
7.06
7.92
6-hr
(1.84-2.22)
(2.19-2.64)
(2.69-3.25)
(3.12-3.77)
(3.71-4.53)
(4.21-5.18)
(4.73-5.90)
(5.29-6.68)
(6.07-7.84)
(6.71-8.84)
2.53
3.02
3.70
4.25
5.01
5.64
6.28
6.96
F 7.90
8.65
12-hr
(2.32-2.76)
(2.77-3.29)
(3.39-4.04)
(3.89-4.64)
(4.57-5.47)
(5.12-6.16)
(5.67-6.88)
(6.23-7.65)
(6.99-8.74)
(7.58-9.65)
3.02
3.61
4.44
5.10
6.01
6.75
7.51
8.30
9.40
10.3
24-hr
(2.80-3.26)
1 (3.35-3.92)
1 (4.11-4.81)
(4.71-5.51)
(5.54-6.49)
(6.19-7.29)
(6.86-8.10)
(7.54-8.96)
(8.46-10.2)
(9.17-11.1)
3.59
4.28
5.21
5.95
6.97
7.79
8.64
9.51
F 10.7
11.7
2-day
(3.35-3.86)
(3.99-4.61)
(4.85-5.60)
(5.53-6.39)
(6.45-7.48)
(7.19-8.36)
(7.94-9.28)
(8.70-10.2)
(9.72-11.6)
(10.5-12.6)
3.83
4.56
5.51
6.25
7.27
8.08
8.91
9.75
F 10.9
11.8
3-day
(3.58-4.10)
(4.26-4.89)
(5.14-5.90)
(5.83-6.69)
(6.75-7.78)
(7.48-8.65)
(8.22-9.55)
(8.95-10.5)
(9.93-11.7)
(10.7-12.8)
4.07
4.84
5.80
6.56
7.58
8.37
9.18
9.99
11.1
12.0
4-day
(3.81-4.35)
(4.53-5.17)
(5.42-6.19)
(6.13-7.00)
(7.05-8.08)
(7.77-8.94)
(8.49-9.82)
(9.20-10.7)
(10.1-11.9)
(10.9-12.9)
4.76
5.64
6.76
7.65
8.86
9.82
10.8
11.8
F 13.2
14.2
7-day
(4.46-5.09)
(5.29-6.04)
(6.33-7.23)
(7.16-8.18)
(8.26-9.46)
(9.13-10.5)
1 (10.0-11.5)
1 (10.9-12.6)
(12.0-14.1)
(12.9-15.3)
5.45
6.44
7.64
8.59
9.88
10.9
11.9
13.0
F 14.4
15.5
10-day
(5.14-5.78)
(6.08-6.85)
(7.22-8.12)
(8.10-9.12)
(9.28-10.5)
(10.2-11.6)
1 (11.1-12.7)
1 (12.1-13.8)
(13.3-15.3)
(14.2-16.6)
7.40
8.70
10.1
11.2
12.6
13.7
14.7
15.7
17.0
18.0
20-day
(7.02-7.81)
(8.25-9.20)
(9.57-10.7)
(10.6-11.8)
(11.9-13.3)
(12.9-14.4)
1 (13.8-15.5)
1 (14.8-16.6)
(15.9-18.1)
(16.7-19.1)
9.07
10.6
12.2
13.3
14.8
15.9
16.9
17.8
F 19.0
19.9
30-day
(8.62-9.55)
(10.1-11.2)
(11.6-12.8)
(12.6-14.0)
(14.0-15.6)
(15.0-16.7)
1 (15.9-17.8)
1 (16.8-18.8)
(17.9-20.1)
(18.6-21.1)
11.6
13.5
15.2
16.4
17.9
19.0
20.0
20.9
F 21.9
22.6
45-day
(11.0-12.1)
(12.9-14.2)
(14.5-15.9)
(15.7-17.2)
(17.1-18.8)
(18.1-20.0)
1 (19.0-21.0)
1 (19.8-21.9)
(20.7-23.1)
(21.4-23.9)
13.9
16.1
18.0
19.4
21.0
22.1
23.1
24.0
25.1
25.8
60-day
(13.2-14.6)
(15.4-17.0)
(17.2-18.9)
(18.5-20.4)
(20.0-22.1)
(21.1-23.3)
(22.0-24.3)
(22.8-25.3)
(23.8-26.4)
(24.4-27.2)
Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for
a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are
not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=35.3991 & Ion =-82.5660&data=depth&units=english&series=pds 1 /4

11 /12/21, 9:04 AM
Precipitation Frequency Data Server
25
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Pas -based depth -duration -frequency (DDF) curves
Latitude: 35.3991 Longitude:-82.5660'
------------
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1 2 5 lfl 25 50 100 200 500 1000
Average recurrence interval (years)
NOAA Atlas 14, Volume 2, Version 3 Created (GMT): Fri Nov 12 14:04:20 2021
Back to Top
Maps & aerials
Small scale terrain
Average recurrence
mlerva I
{years}
— 1
2
— 5
— 10
— 25
50
100
200
500
1000
Duration
— 6-min —
2-day
— 10-min —
3-day
15-min —
d-dmy
— 3C�-min —
7-day
— 6 Wain —
i o-day
— 2fir —
20-day
— 3-rr —
30-day
— Bfir —
45-day
— 12-n r —
60-day
24-nr
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.htmI?Iat=35.3991 &Ion=-82.5660&data=depth&units=engIish&series=pds 2/4

11 /12/21, 9:04 AM Precipitation Frequency Data Server
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Large scale terrain
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11 /12/21, 9:04 AM
Precipitation Frequency Data Server
Back to Top
US Department of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
National Water Center
1325 East West Highway
Silver Spring, MD 20910
Questions?: HDSC.Questions noaa.gov
Disclaimer
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11/12/21, 9:05 AM Precipitation Frequency Data Server
NOAA Atlas 14, Volume 2, Version 3
Location name: Mills River, North Carolina, USA*�'°
Latitude: 35.3991°, Longitude:-82.566° � ;
Elevation: 2095.51 ft *
*source: ESRI Maps w,�w ^ y�
-source: USGS
POINT PRECIPITATION FREQUENCY ESTIMATES
G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley
NOAA, National Weather Service, Silver Spring, Maryland
PF tabular I PF graphical I Maps & aerials
PF tabular
PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hourp
Duration
Average recurrence interval (years)
1
2
5
10
25
50
1 100
100
200
500
1000
4.43
5.27
6.31
7.10
8.14
8.92
9.71
10.5
11.5
12.4
5-min
(4.00-4.92)
1 (5.69-7.01) 11
(6.38-7.86) 11
(7.26-9.00)
1 (7.91-9.86)
1 (8.58-10.8)
1 (9.20-11.7)
(10.00-12.9)
1 (10.6-13.9)
3.53
4.21
5.05
5.68
6.48
7.10
7.72
8.32
9.12
9.73
10-min
(3.19-3.93)
1 (4.55-5.61) 11
(5.11-6.29) 11
(5.78-7.17)
1 (6.30-7.85)
1 (6.82-8.55)
1 (7.30-9.25)
1 (7.90-10.2)
1 (8.35-10.9)
2.95
3.53
4.26
4.79
5.48
6.00
6.50
7.00
7.65
8.14
15-min
(2.66-3.27) 11
(3.19-3.92) 11
(3.84-4.73) 11
(4.30-5.30) 11
(4.88-6.06)
1 (5.32-6.63)
1 (5.74-7.20)
1 (6.14-7.78)
1 (6.63-8.55)
1 (6.98-9.16)
2.02
2.44
3.03
3.47
4.06
4.52
4.98
5.45
6.09
6.59
30-min
(1.82-2.24) 11
(2.20-2.71) 11
(2.73-3.36) 1
1 (3.62-4.49)
1 (4.00-4.99)
1 (4.40-5.52)
1 (4.78-6.05)
1 (5.28-6.81)
1 (5.65-7.41)
1.26
1.53
1.94
2.26
2.70
3.06
3.43
3.82
4.37
4.81
60-min
(1.14-1.40) 1
1 (1.75-2.15) 11
(2.03-2.50) 11
(2.41-2.99)
1 (2.71-3.38)
1 (3.03-3.80)
1 (3.35-4.25)
1 (3.79-4.88)
1 (4.13-5.41)
0.739
0.896
1.13
1.32
1.58
1.79
2.02
2.26
2.59
2.87
2-hr
(0.665-0.819)
(0.808-0.992)1
1 (1.41-1.75)
(1.59-1.99)
1 (1.77-2.24)
1 (1.97-2.51)
1 (2.23-2.90)
1 (2.44-3.22)
0.529
0.637
0.799
0.932
1.13
119
1.46
1.64
1.91
2.13
3-hr
(0.477-0.590)
(0.575-0.709)
(0.719-0.887)
(0.835-1.03)
(0.999-1.25)
1 (1.13-1.43)
1 (1.27-1.62)
1 (1.42-1.83)
1 (1.63-2.14)
1 (1.79-2.40)
0.336
0.400
0.493
0.573
0.689
0.787
F 0.894
1.01
1.18
1.32
6-hr
(0.307-0.370)
(0.365-0.440)
(0.450-0.542)
(0.520-0.630)
(0.620-0.757)
(0.703-0.865)
(0.790-0.985)
(0.883-1.12)
1 (1.01-1.31)
1 (1.12-1.48)
0.210
0.250
0.307
0.353
0.416
0.468
0.521
0.578
0.656
F 0.718
12-hr
(0.193-0.229)
(0.230-0.273)
(0.282-0.335)
(0.323-0.385)
(0.379-0.454)
(0.425-0.511)
(0.470-0.571)
(0.517-0.635)
(0.580-0.726)
(0.629-0.801)
0.126
0.151
0.185
0.212
0.250
0.281
0.313
0.346
0.391
0.428
24-hr
(0.116-0.136)
(0.140-0.163)
(0.171-0.200)
(0.196-0.230)
(0.231-0.270)
(0.258-0.304)
(0.286-0.337)
(0.314-0.373)
(0.353-0.423)
(0.382-0.464)
0.075
0.089
0.109
0.124
0.145
0.162
0.180
0.198
0.223
0.243
2-day
(0.070-0.080)
(0.083-0.096)
(0.101-0.117)
(0.115-0.133)
(0.134-0.156)
(0.150-0.174)
(0.165-0.193)
(0.181-0.213)
(0.202-0.241)
(0.219-0.263)
0.053
0.063
0.076
0.087
0.101
0.112
0.124
0.135
0.151
0.164
3-day
(0.050-0.057)
(0.059-0.068)
(0.071-0.082)
(0.081-0.093)
(0.094-0.108)
(0.104-0.120)
(0.114-0.133)
(0.124-0.145)
(0.138-0.163)
(0.149-0.177)
0.042
0.050
0.060
0.068
0.079
0.087
0.096
0.104
0.116
0.125
4-day
(0.040-0.045)
(0.047-0.054)
(0.056-0.065)
(0.064-0.073)
(0.073-0.084)
(0.081-0.093)
(0.088-0.102)
(0.096-0.111)
(0.106-0.124)
(0.114-0.134)
0.028
0.034
0.040
0.046
0.053
0.058
0.064
0.070
0.078
0.085
7-day
(0.027-0.030)
(0.031-0.036)
(0.038-0.043)
(0.043-0.049)
(0.049-0.056)
(0.054-0.062)
(0.060-0.069)
(0.065-0.075)
(0.072-0.084)
(0.077-0.091)
0.023
0.027
0.032
0.036
0.041
0.045
0.050
0.054
0.060
0.064
10-day
(0.021-0.024)
(0.025-0.029)
(0.030-0.034)
(0.034-0.038)
(0.039-0.044)
(0.043-0.048)
(0.046-0.053)
(0.050-0.057)
(0.055-0.064)
(0.059-0.069)
0.015
0.018
0.021
0.023
0.026
0.028
0.031
0.033
0.035
0.037
20-day
(0.015-0.016)
(0.017-0.019)
(0.020-0.022)
(0.022-0.025)
(0.025-0.028)
(0.027-0.030)
(0.029-0.032)
(0.031-0.035)
(0.033-0.038)
(0.035-0.040)
0.013
0.015
0.017
0.018
0.021
0.022
0.023
0.025
0.026
0.028
30-day
(0.012-0.013)
(0.014-0.016)
(0.016-0.018)
(0.018-0.019)
(0.019-0.022)
(0.021-0.023)
(0.022-0.025)
(0.023-0.026)
(0.025-0.028)
(0.026-0.029)
0.011
0.012
0.014
0.015
0.017
0.018
0.018
0.019
0.020
0.021
45-day
(0.010-0.011)
(0.012-0.013)
(0.013-0.015)
(0.014-0.016)
(0.016-0.017)
(0.017-0.018)
(0.018-0.019)
(0.018-0.020)
(0.019-0.021)
(0.020-0.022)
0.010
0.011
0.013
0.013
0.015
0.015
0.016
0.017
0.017
0.018
60-day
(0.009-0.010)
(0.011-0.012)
(0.012-0.013)
(0.013-0.014)
(0.014-0.015)
(0.015-0.016)
(0.015-0.017)
(0.016-0.018)
(0.017-0.018)
(0.017-0.019)
Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).
Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a
given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not
checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.
Please refer to NOAA Atlas 14 document for more information.
Back to Top
PF graphical
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11 /12/21, 9:05 AM
Precipitation Frequency Data Server
I161616I6161
10.000
C
41
1.000
C
GJ
a-�
C
� 0.100
L
Ld
a 0.010
PD5-based intensity -duration -frequency (IDF) curves
Latitude: 35.3991', Longitude:-82.5660'
0.0011
t t Jr t L N N O r{4 N rq rq rq N rq N Alb A q r, O O O Ln O
,1 r-1 rn w 1-4N rn v Ln
Duration
100.000
10.000
L
k
1.000
w
c
e
0.100
4.1
49
0.010
0.0011 1 1 1 1 1 1 1 1 1
1 2 5 10 25 50 100 200 500 1000
Average recurrence interval (years)
NOAA Atlas 14, Volume 2, Version 3 Created (GMT): Fri Nov 12 14:05:242021
Back to Top
Maps & aerials
Small scale terrain
Average recurrence
interval
{years}
— 1
2
— 5
— 14
— 25
54
100
200
500
1000
Duration
— 6-min —
2-day
— 14-min —
3-day
15-min —
d-dmy
— 30-rnw —
7-day
— 5 Wain —
10-day
— 2fir —
20-day
— 3-hr —
30-day
— Bfir —
45-day
— 12-nr —
60-day
24-nr
https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.htmI?Iat=35.3991 &Ion=-82.5660&data=intensity&units=english&series=pds 2/4

11 /12/21, 9:05 AM Precipitation Frequency Data Server
ro
at or
KIYO9
M oun Orr
3km
2mi
Large scale terrain
Kingsport' Bristol
Johnson city, 0
Winston-Sales
Knoxville
S & N-It MitcIell
NORTH
Chad
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100km SOUTH CARO
Large scale map
... Kingsport
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Greenville
U
100km
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Large scale aerial
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Precipitation Frequency Data Server
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National Oceanic and Atmospheric Administration
National Weather Service
National Water Center
1325 East West Highway
Silver Spring, MD 20910
Questions?: HDSC.Questions noaa.gov
Disclaimer
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