HomeMy WebLinkAboutFDP201900016 Calculations 2020-03-30FLOOD STUDY REPORT
JACOBS CREEK
TMP 104-14133
ALBEMARLE COUNTY, VIRGINIA
NOVEMBER 30, 2019
REVISED MARCH 30, 2020
P:
4051 JACOBS
CREEK DRIVE
01 1
��CR�
PROPOSED
BRIDGE
CROSSING
PC,0, �
JACOBS
Y7 CREEK
N
m SCALE
ENGINEERING
VICINITY MAP
OWNER:
TINA TAYLOR AND STEVEN LOWE
4051 JACOBS CREEK DRIVE
SCOTTSVILLE, VA 24590
ENGINEER:
30 SCALE, LLC
MICHAEL MYERS, PE, CFM
434-242-2866
MIKE@30CALE.COM
APPROVED
by the Albemarle County
Community Developpment Department
Date 03/30/2020
File FDP201900016
;1.1i�E. e1.
mane.o�.
Frank V. Pohl, PE, CFM O =F.
C,
M L F. S
Lic. No. 33028
o� 03/30/2 '2U �w
�� sI 9Na 1
TABLE OF CONTENTS
1. PROJECT NARRATIVE 3
2. HYDROLOGIC INFORMATION 4
3. HEC-RAS OUTPUT SHOWING NO INCREASED IN BASE FLOOD ON
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APPENDICES
FEMA FIRMETTE
HEC-RAS OUTPUT SUMMARY TABLES
EXISTING CROSS -SECTIONS (HEC-RAS)
PROPOSED CROSS -SECTIONS (HEC-RAS)
RUNOFF HYDROGRAPHS
NOAA PRECIPITATION CHART
SOILS MAP AND SOIL TYPES
6
1. PROJECT NARRATIVE
Currently, the access to the residence on 4051 Jacobs Creek Drive is limited due to a low and eroding
gravel/dirt access road over three deteriorating culverts at the existing driveway crossing. During most
wet conditions, the access is impassable. The proposal is to remove the culverts and fill, and to
construct an all-weather bridge crossing to improve the access to the property.
The contributing drainage area to the stream crossing is approximately 2.5 square miles, which is below
the 5 square -mile threshold for the ACOE to require permitting. Therefore, no ACOE permit is required
to perform this work. The overall disturbed area is 1,750 sf, which is below the threshold to require an
erosion and sediment control of stormwater management plan under the VESCP and VSMP guidelines.
Also, the crossing is located in the Zone A (Approximate) FEMA Floodplain and the Albemarle County
Water Protection Ordinance Stream Buffer, thereby requiring a flooding analysis to ensure no backwater
effects on upstream properties and a mitigation planting plan.
With the significant upstream drainage area, the shallowness of the stream, and the crossing area being
prone to flooding, the design of the proposed bridge crossing elevates the access approximately 18"
above the current grade, which will provide dry crossing conditions for the majority of storm events.
The mitigation planting requirements are shown on Sheet 3 of the plan set.
Following construction, the proposed bridge crossing will not back water up onto adjacent properties for
the 2, 10 or 100-year storm events. Refer to computations herein to support this.
2. HYDROLOGIC INFORMATION
DRAINAGE AREA = 1,506 AC.
COMPOSITE CN = 71
TIME OF CONCENTRATION = 92 MIN
DRAINAGE MAP
HYDROLOGIC CALCLLIATIONS
SUMMARY OF SOIL TYPES IN CONTRIBUTING DRAINAGE AREA
SOIL GROUP SUMMARY
DA=
1,506AC
A
B
G
D
TOTALS
LAND AREA
0
434.9
1 3.6
1 1061.1
1,606 AC
SOIL GROUP
SOIL#
SOIL NAME:
ACRES
%
0%
1 29%
1 C%
1 71%
1O0%
C
I
MEADOWVIL.LE
2.0
0.1%
NOTE: PREDOMINANT
SOILS
TYPE IS D
D
16
CODDRUS
40.8
2.7%
D
51B
BUGLEY
157.3
10.4%
COMPOSITE
CM CALCULATIONS
D
51C
BUGLEY
283.1
18.8%
D
51 D
BUGLEY
459.4
30.5 %
AREA AC
GROUP
CN
CN'AREA
D
51E
BUGLEY
26.7
1.8%
OPEN SPACEILAWNS [GOOD}
67
❑
80
6,360
D
52E
BUGLEY
29.8
2.0%
28
3
61
1,708
B
53B
DANRIPPLE
7.6
0.5%
SUBTOTAL
95
7,068
C
55B
DANRIPPLE
1.6
0.1%
B
52B
BUFFSTAT
96.1
6.4%
WOODSIRURAL AREA GOOD
985
D
77
75,845
B
52C
BUFFSTAT
126.7
8.4%
402
B
55
22,110
B
76
DANRIVER LOAM
0.0
0.0%
SUBTOTAL
1,387
97,956
B
17
DANRIVER-CODORUS
17.6
1.2%
B
I BOB
LITTLEJOE
182.7
12.1%
IMPERVIGIJSAREA
B
8OC
L17TLEJCE
4.2
0.3%
ROADSIORIVEWAYS
18
BID
98
1,744
❑
95
HATBORO
68_5
4.5%
HOUSES
8
BID
98
294
D
W
WATER
2.1
0.1%
WATER
3
BID
98
294
SUBTOTAL
24
2,332
TOTALS
1,505 AC
100 O%
TOTAL
1,508 AC
1O7,3ii
71
PRECIPITATION DATA AND TIME OF CONCENTRATION CALL:
NOAA ATLAS 14 DATA
1-YR
2-YR
lO-YR
SO-YR
100-YR
24-HR PRECIPITATION IINI
2.90
3,51
530
756
871
12-HR PRECIPITATION (IN)
2,44
2,92
431
607
695
TYPE OF FLOW
L {FTT
NI ELEV
LO EIEV
SLOPE
TT
SHEET FLOW
200
562
576
3%
12 MEN
SHALLOW CONCENTRATED FLOW
242
576
559
5%
2 MIN
CHANNEL FLOW
13624
553
320
2%
78 MIN
TIME OF CONCENTRATION
92 MIN
PEAK FLOW RATES FROM TR-55
ANALYST.
1-YR
2-YR
10-YR
100-Y8
PEAK FLOW ICFS)
351
1 595
1 1414
1 3204
3. HEC-RAS OUTPUT SHOWING NO INCREASED BASE FLOOD ELEVATION ON ADJACENT
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Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hyd. No. 1
JACOBS CREEK DRAINAGE AREA
Hydrograph type
= SCS Runoff
Storm frequency
= 1 yrs
Time interval
= 2 min
Drainage area
= 1506.000 ac
Basin Slope
= 0.0 %
Tc method
= TR55
Total precip.
= 2.92 in
Storm duration
= 24 hrs
Q (cfs)
400.00
350.00
250.00
04111111111111A
150.00
100.00
50.00
Monday, 12 / 2 / 2019
Peak discharge
= 361.44 cfs
Time to peak
= 774 min
Hyd. volume
= 3,925,205 cuft
Curve number
= 71
Hydraulic length
= 0 ft
Time of conc. (Tc)
= 91.50 min
Distribution
= Type II
Shape factor
= 484
JACOBS CREEK DRAINAGE AREA
Hyd. No. 1 -- 1 Year
Q (cfs)
400.00
350.00
300.00
250.00
200.00
150.00
100.00
50.00
0.00 ' 1 1 1 1" ' ' ' ' ' ' " 0.00
0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560
Hyd No. 1 Time (min)
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hyd. No. 1
JACOBS CREEK DRAINAGE AREA
Hydrograph type
= SCS Runoff
Storm frequency
= 2 yrs
Time interval
= 2 min
Drainage area
= 1506.000 ac
Basin Slope
= 0.0 %
Tc method
= TR55
Total precip.
= 3.54 in
Storm duration
= 24 hrs
Q (cfs)
630.00
540.00
450.00
270.00
180.00
0.00
0 120 240
Hyd No. 1
Peak discharge
Time to peak
Hyd. volume
Curve number
Hydraulic length
Time of conc. (Tc)
Distribution
Shape factor
JACOBS CREEK DRAINAGE AREA
Hyd. No. 1 -- 2 Year
Monday, 12 / 2 / 2019
= 595.40 cfs
= 772 min
= 5,981,331 cuft
= 71
= 0 ft
= 91.50 min
= Type II
= 484
Q (cfs)
630.00
540.00
450.00
360.00
270.00
180.00
i i i I I I I I I "1, 0.00
360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hyd. No. 1
JACOBS CREEK DRAINAGE AREA
Hydrograph type
= SCS Runoff
Storm frequency
= 10 yrs
Time interval
= 2 min
Drainage area
= 1506.000 ac
Basin Slope
= 0.0 %
Tc method
= TR55
Total precip.
= 5.34 in
Storm duration
= 24 hrs
Q (cfs)
1414.00
1212.00
1010.00
•1. 11
404.00
202.00
0.00
0 120 240
Hyd No. 1
Peak discharge
Time to peak
Hyd. volume
Curve number
Hydraulic length
Time of conc. (Tc)
Distribution
Shape factor
JACOBS CREEK DRAINAGE AREA
Hyd. No. 1 -- 10 Year
Monday, 12 / 2 / 2019
= 1413.60 cfs
= 770 min
= 13,051,370 cuft
= 71
= 0 ft
= 91.50 min
= Type II
= 484
Q (cfs)
1414.00
1212.00
1010.00
•1. 11
404.00
202.00
i v_i I I I I I I 1 0.00
360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2020
Hyd. No. 1
JACOBS CREEK DRAINAGE AREA
Hydrograph type
= SCS Runoff
Storm frequency
= 100 yrs
Time interval
= 2 min
Drainage area
= 1506.000 ac
Basin Slope
= 0.0 %
Tc method
= TR55
Total precip.
= 8.74 in
Storm duration
= 24 hrs
Q (cfs)
3206.00
2748.00
2290.00
1832.00
1374.00
458.00
0.00
0 120 240
Hyd No. 1
Peak discharge
Time to peak
Hyd. volume
Curve number
Hydraulic length
Time of conc. (Tc)
Distribution
Shape factor
JACOBS CREEK DRAINAGE AREA
Hyd. No. 1 -- 100 Year
Monday, 12 / 2 / 2019
= 3203.54 cfs
= 770 min
= 28,707,800 cuft
= 71
= 0 ft
= 91.50 min
= Type II
= 484
Q (cfs)
3206.00
2748.00
2290.00
1832.00
1374.00
916.00
458.00
i I� I I I I I I I I � 0.00
360 480 600 720 840 960 1080 1200 1320 1440 1560
Time (min)
NOAA Atlas 14, Volume 2, Version 3
' Location name: Scottsville, Virginia, USA*
Latitude: 37.9259*, Longitude:-78.4397°
n: 338.19 ft""
Elevation:
* source: ESRI Maps-
n+
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
11 PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1 11
recurrence interval
10 11 25 1 50 1 100 1 200 1 500 1 1000
0.345
0.407
0.474
0.537
0.604
0.658
0.706
0.751
0.802
0.844
5-min
(0.311-0.384)
(0.366-0.452)
(0.426-0.525)
(0.483-0.596)
(0.541-0.668)
(0.586-0.726)
(0.626-0.780)
(0.661-0.829)
(0.700-0.887)
(0.731-0.937)
0.551
0.650
0.759
0.859
0.963
1.05
1.12
1.19
1.27
1.33
10-min
(0.496-0.613)
(0.586-0.723)
(0.683-0.842)
(0.772-0.952)
(0.862-1.06)
(0.933-1.16)
(0.995-1.24)
(1.05-1.31)
( 1.11-1.40)
( 1.15-1.48)
0.689
0.818
0.960
1.09
1.22
1.33
1.42
1.50
1.60
1.67
15-min
(0.620-0.766)
(0.737-0.909)
(0.864-1.07)
(0.976-1.21)
(1.09-1.35)1
(1.18-1.46)
(1.26-1.57)
1 (1.32-1.66)
1 (1.39-1.77)
1 (1.45-1.85)
0.945
1.13
1.36
1.58
F 2.00
2.17
2.34
2.54
2.70
30-min
(0.850-1.05)
1 (1.02-1.25)
1 (1.23-1.51)
1 (1.42-1.75)
1 (1.78-2.21)
(1.93-2.40)
1 (2.22-2.81)
(2.34-3.00)
1.18
1.42
1.75
2.05
2.41
2.71
2.99
3.28
3.64
3.95
60-min
(1.06-1.31)
(1.28-1.58)
(1.57-1.94)
(1.84-2.27)
1 (2.41-2.99)
(2.65-3.30)
(2.89-3.62)
(3.18-4.03)
(3.42-4.38)
1.42
1.70
2.11
2.49
2.97
3.37
3.77
4.18
4.74
5.20
2-hr
(1.25-1.61)
(1.50-1.93)
(1.86-2.39)
(2.20-2.82)
(2.60-3.34)
(2.94-3.80)
(3.27-4.24)
(3.60-4.70 )
( 4.03-5.33)
( 4.39-5.87)
1.54
1.85
2.29
2.71
3.22
3.67
4.11
4.56
5.16
5.68
3-hr
(1.36-1.76)
(1.63-2.11)
(2.02-2.62)
(2.38-3.09)
(2.82-3.66)
(3.18-4.16)
(3.54-4.65)
(3.90-5.16)
( 4.37-5.85)
( 4.75-6.44)
1.95
2.34
2.88
3.42
4.10
4.71
5.33
6.00
6.91
7.73
6-hr
(1.73-2.22)
(2.07-2.66)
(2.54-3.27)
1 (3.00-3.88)
1 (3.58-4.64)
1 (4.08-5.31)
1 (4.58-6.02)
(5.10-6.77)
(5.79-7.80)
(6.39-8.73)
12-hr
2.44
(2.16-2.80)
2.92
(2.58-3.34)
3.61
(3.18-4.13)
4.31
(3.78-4.91)
5.23
6.07
1 (5.24-6.89)
6.96
(5.94-7.88)
F 9.33
1 (7.70-10.5)
10.6
(8.62-12.0)
24-hr
2.90
(2 .60-3.26)
3.51
(3.15-3.95)
4.48
(4.01-5.04)
5.30
(4.73-5.95)
6.52
(5.78-7.30)
7.56
(6.66-8.45)
8.71
(7.61-9.71)
9.98
(8.63-11.1)
11.9
( 10.1-13.2)
13.5
( 11.3-15.0)
3.40
4.12
5.24
6.17
7.50
8.63
9.84
11.2
13.1
14.7
2-day
(3.06-3.81)
1 (3.71-4.61)
1 (4.71-5.86)
1 (5.53-6.88)
1 (6.68-8.35)
1 (7.63-9.58)
1 (8.64-10.9)
1 (11.3-14.6)
(12.5-16.4)
3.62
4.38
5.57
6.55
7.96
9.15
10.4
11.8
13.8
15.5
3-day
(3.28-4.02)
1 (3.98-4.87)
1 (5.04-6.18)
1 (5.92-7.26)
1 (7.16-8.81)
1 (8.17-10.1)
1 (9.25-11.5)
1 (12.0-15.3)
(13.4-17.2)
3.84
4.65
5.90
6.93
8.42
9.67
11.0
12.5
14.6
16.4
4-day
(3.51-4.24)
(4.24-5.13)
(5.38-6.51)
(6.30-7.63)
(7.63-9.26)
(8.71-10.6)
(9.86-12.1)
( 11.1-13.7 )
(12.8-16.1)11
(14.2-18.1)
4.45
5.35
6.69
7.79
9.37
10.7
12.1
13.6
15.8
17.6
7-day
(4 .08-4.86)
(4.92-5.85)
(6.14-7.31)
(7.13-8.51)
(8.53-10.2)
(9.67-11.7)11
( 10.9-13.2)
( 12.1-14.9 )
(13.9-17.3)11
( 15.3-19.3)
10-day 5.04 6.05 7.47 8.62 10.2 11.6 13.0 14.5F 16.6 18.3
(4.65-5.46) (5.58-6.56) (6.89-8.09) 1 (7.93-9.34) 1 (9.39-11.1) 1 (10.6-12.5) 1 (11.8-14.1) 1 (14.8-18.0) (16.2-20.0)
5.5
20-day 6 236.14 7.44 8552 8.97-610.3 10. -111.7 11 8-13.6 13.10-15.0 14.13-16.6 1515-18.2 17.12 0.3 182 - 2.0
30-day 8.18 9.70 11.5 12.8 14.6 15.9 17.2 18.5 20.2 21.4
(7 .69-8.72) (9.13-10.3) (10.8-12.2) (12.0-13.6) 1 (13.7-15.5) 1 (14.9-16.9) 1 (16.0-18.3) (17.2-19.7) 1 (18.6-21.6) 1 (19.7-22.9)
45-day 10.2 12.1 14.2 15.7 17.6F 19.1 20.5 21.8F 23.6 24.8
(9.66-10.9) (11.4-12.8) (13.3-15.0) (14.8-16.6) (16.6-18.7) (17.9-20.2) A (19.2-21.7) 1 (21.9-25.1) (23.0-26.5)
60-day 12.1 14.2 16.4 18.0 20.1 21.7 23.1 24.5 26.3 27.5
(114-12.8) (13.4-15.0) (15.5-17.3) (17.0-19.0) (19.0-21.2) (20.4-22.9) (21.7-24.4) (23.0-25.9) (24.5-27.8) (25.6-29.3)
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 NOAAAtlas 14 document for more information.
Back to Top
PF graphical
PD5-based depth -duration -frequency (DDF) curves
Latitude: 37.92590, Longitude:-78.43970
30
25
c
L 20
++
a
a
0 15
n
v 10
a!
a.
a
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E
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ion
30
25
C
20
a
v
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0
a
'g 10
a
5 •- . -
0
1 2 5 10 25 50 100 200 500 1000
Average recurrence interval (years)
NOAA Atlas 14, volume 2, Version 3 Created (GMTY Tue Nov 12 1&02:37 2019
Back to Too
Average recurrence
inlerval
(yeara)
— 1
2
— 5
— 10
25
50
100
200
500
1000
Duration
— 5-min
— 2-day
— I D-min
— 3-day
15-min
— 4 a8y
— 30-min
— 7-0ay
— O"in
— IO-Oay
— 2-hr
— 20-day
— 3fir
— 30-aay
— 6-nr
— 45-day
— 12-�1r
— 60-aay
— 24-hr
Maps & aerials
Small scale terrain
Large scale terrain
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Washinaton. D.C.'�'- •nni
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5tauntrn
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Large scale map
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Harrk,onburg
SLwnl••i
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acksburg ;,Roanoke
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100km / Nor}al
60mi rrJ
Back to Too
US Department of Commerce
National Oceanic and Atmosoheric Administration
National Weather Service
National Water Center
1325 East West Highway
Silver Spring, MD 20910
Questions?: HDSC.Questionsla.noaa.gov
Disclaimer
51 B
IDG
62B
55B(
51D 80B
y
A.' 5 c
51 B
51
6 2B
62-B
A
'C �,,-62C
B
51 C -1
21 51 JC
7 90
51
B
62C
F 80B
-51-
1D A
80�_B
80B
Custom Soil Resource Report
Map Unit Legend
Map Unit Symbol
Map Unit Name
Acres in AOI
Percent of AOI
1 B
Meadowville silt loam, 2 to 7
2.0
0.1 %
percent slopes
2.7%
16
Codorus silt loam, 0 to 2
40.8
percent slopes, occasionally
flooded
51 B
Bugley channery silt loam, 2 to
157.3
10.4%
7 percent slopes
51 C
Bugley channery silt loam, 7 to
283.1
18.8%
15 percent slopes
51 D
Bugley channery silt loam, 15 to
459.4
30.5%
25 percent slopes
51 E
Bugley channery silt loam, 25 to
26.7
1.8%
45 percent slopes
52E
Bugley very channery silt loam,
29.8
2.0%
25 to 45 percent slopes
53B
Danripple loam, 2 to 7 percent
7.6
0.5%
slopes
55B
Danripple loam, 2 to 7 percent
1.6
0.1%
slopes, rarely flooded
62B
Buffstat silt loam, 2 to 7 percent
96.1
6.4%
slopes
62C
Buffstat silt loam, 7 to 15
126.7
8.4%
percent slopes
76
Dan River loam, 0 to 2 percent
0.0
0.0%
slopes, occasionally flooded
77
Dan River-Codorus complex, 0
17.6
1.2%
to 2 percent slopes,
occasionally flooded
80B
Littlejoe silt loam, 2 to 7 percent
182.7
12.1 %
slopes
80C
Littlejoe silt loam, 7 to 15
4.2
0.3%
percent slopes
95
Hatboro silt loam, 0 to 2 percent
68.5
4.5%
slopes, occasionally flooded
W
Water
2.1
0.1 %
Totals for Area of Interest
1,506.1
100.0%
Map Unit Descriptions
The map units delineated on the detailed soil maps in a soil survey represent the
soils or miscellaneous areas in the survey area. The map unit descriptions, along
with the maps, can be used to determine the composition and properties of a unit.
0