HomeMy WebLinkAboutWPO200800062 Calculations 2008-05-29 SWM #3 SEDIMENT BASIN CALCULATIONS
FOR
HOLLYMEAD TOWNCENTER AREA Al EROSION
May 29, 2008
LOCATION:
Albemarle County, Virginia
Tax Map 32, Parcels 42A & 44
Tax Map 46, Parcel 5
PREPARED BY:
Dominion Development Resources, LLC
172 South Pantops Drive
Charlottesville, VA 22911
P: 434.979.8121
F: 434.979.1681
„4vALTt t
U
JOHN DAVID BEIR.NE JR
Lic. No 042267
ION At
Dominion Development Resources, LLC Page 1
(434) 979 -8121
Hollymead Towncenter Area m
SWM #3 Sediment Basin
Name: DA Sed, 25yr
Type: Modified Rational
HYDROGRAPH INFORMATION
Peak Flow (Qp) = 340.98 (cfs)
Time to Peak (Tp) = 5.00 (min)
Time of Base (Tb) = 12.50 (min)
Volume = 2.9433 (ac -ft)
Time Step = 1.00 (min)
Flow Multiplier = 1.00
RATIONAL HYDROGRAPH INFORMATION
Flow Multiplier = 1.00
Receding Limb Factor = 1.50
APPROXIMATE STORAGE
Maximum Outflow = 0.00 (cfs)
Maximum Storage = 2.9433 (cu ft)
BASIN INFORMATION
WEIGHTED WATERSHED AREA
Description Area CN Runoff Coef
Overall Approximation 53.1800 NA 0.80
TIME CONCENTRATION -- User Defined
Time of Concentration (Tc) = 5.00 (min)
RAINFALL DESCRIPTION
Distribution Type = Synthetic
Total Precipitation = 0.66 (in)
Return Period = 25 (yr)
Storm Duration = 0.08 (hr)
Dominion Development Resources, LLC Page 2
(434) 979 -8121
Hollymead Towncenter Area xi
SWM #3 Sediment Basin
Name: Sed Rtd 25yr
Type: Reservoir: Modified Puls
HYDROGRAPH INFORMATION
Peak Flow (Qp) = 7.73 (cfs)
Time to Peak (Tp) = 13.00 (min)
Time of Base (Tb) = 1440.00 (min)
Volume = 1.1693 (ac -ft)
Time Step = 1.00 (min)
Peak Elevation = 479.7301 (ft)
Detention Time = NA
RESERVOIR STRUCTURE INFORMATION
Number = 2
Name = SWM #3 Sed Basin
Storage Type = User - Defined Area
Maximum Storage = 491134.8412 (cu ft)
Maximum Discharge = 217.74 (cfs)
INFLOW HYDROGRAPH INFORMATION
Number = 26
Name = DA Sed, 25yr
Peak Flow (Qp) = 340.98 (cfs)
Time to Peak (Tp) = 5.00 (min)
Time of Base (Tb) = 12.50 (min)
Volume = 2.9433 (ac -ft)
Flow Multiplier = 1.00
Dominion Development Resources, LLC Page 3
(434) 979 -8121
Hollymead Towncenter Area NI
SWM #3 Sediment Basin
Type : Stand Pipe
Name : Sed Basin
RATING CURVE LIMIT
Minimum Elevation = 475.0000 (ft)
Maximum Elevation = 486.0000 (ft)
Elevation Increment = 0.5000 (ft)
STAND PIPE INFORMATION
ORIFICE INFORMATION
Diameter = 6.00 (ft)
Crest Length = 18.85 (ft)
Effective Crest Length = 14.85 (ft)
Orifice Coefficient = 0.60
Fractional Open Area = 0.83
WEIR INFORMATION
Crest Elevation = 484.0000 (ft)
Weir Coefficient = 3.33
Exponential = 1.50
OPTIONAL WEIR INFORMATION
Type : Rectangular Weir Suppressed #1
WEIR INFORMATION
Crest Length = 2.00 (ft)
Crest Elevation = 481.8000 (ft)
Weir Coefficient = 3.33
Exponential = 1.50
Type : Rectangular Weir Suppressed #2
WEIR INFORMATION
Crest Length = 2.00 (ft)
Crest Elevation = 481.8000 (ft)
Weir Coefficient = 3.33
Exponential = 1.50
Dominion Development Resources, LLC Page 4
(434) 979 -8121
Hollymead Towncenter Area lcr i
SWM #3 Sediment Basin
OPTIONAL ORIFICE INFORMATION
Structure Number : 1
Type : Circular Orifice
OPTIONAL ORIFICE INFORMATION
Diameter = 2.00 (ft)
Invert Elevation = 478.5000 (ft)
Orifice Coefficient = 0.60
Number of Openings = 1
ORIFICE EQUATION
Q = Co *A((2gh) /k) ^0.5
DEFINITIONS
Co = Orifice Coefficient
A = Wetted Area, (cfs)
k = 1
CULVERT INFORMATION
Type : Circular Concrete - Square Edge with Headwall
OUTLET STRUCTURE INFORMATION
Diameter = 48.00 (in)
Invert Elevation = 475.0000 (ft)
Pipe Length = 100.00 (ft)
Slope = 0.09
Manning's n Value = 0.01
Orifice Coefficient = 0.60
Tailwater Elevation = 468.4000 (ft)
Number of Barrels = 1
Dominion Development Resources, LLC Page 5
(434) 979 -8121
Hollymead Towncenter Area AI
SWM #3 Sediment Basin
STAND PIPE STAGE VS. DISCHARGE
Elevation Stage Weirs Orifices Stand Pipe Culvert Total
(ft) (ft) (cfs) (cfs) (cfs) (cfs) (cfs)
475.0000 0.0000 0.00 0.00 0.00 0.00 0.00
475.5000 0.5000 0.00 0.00 0.00 3.09 0.00
476.0000 1.0000 0.00 0.00 0.00 8.93 0.00
476.5000 1.5000 0.00 0.00 0.00 17.35 0.00
477.0000 2.0000 0.00 0.00 0.00 27.49 0.00
477.5000 2.5000 0.00 0.00 0.00 39.17 0.00
478.0000 3.0000 0.00 0.00 0.00 51.37 0.00
478.5000 3.5000 0.00 0.00 0.00 63.91 0.00
479.0000 4.0000 0.00 1.48 0.00 76.45 1.48
479.5000 4.5000 0.00 5.35 0.00 87.96 5.35
480.0000 5.0000 0.00 10.53 0.00 100.53 10.53
480.5000 5.5000 0.00 15.12 0.00 109.10 15.12
481.0000 6.0000 0.00 18.52 0.00 117.84 18.52
481.5000 6.5000 0.00 21.38 0.00 125.98 21.38
482.0000 7.0000 1.19 23.91 0.00 133.62 25.10
482.5000 7.5000 7.80 26.19 0.00 140.85 33.99
483.0000 8.0000 17.51 28.29 0.00 147.72 45.80
483.5000 8.5000 29.52 30.24 0.00 154.29 59.77
484.0000 9.0000 43.46 32.08 0.00 160.59 75.54
484.5000 9.5000 59.09 33.81 17.48 166.65 110.39
485.0000 10.0000 76.25 35.46 49.45 172.50 161.16
485.5000 10.5000 94.80 37.04 90.85 178.16 178.16
486.0000 11.0000 114.65 38.55 139.87 183.64 183.64
Dominion Development Resources, LLC Page 6
(434) 979 -8121
Hollymead Towncenter Area Pr!
SWM #3 Sediment Basin
Name: SWM #3 Sed Basin
RATING CURVE LIMIT
Minimum Elevation = 471.0000 (ft)
Maximum Elevation = 486.0000 (ft)
Elevation Increment = 0.5000 (ft)
STAGE STORAGE INFORMATION
Storage Method: User - Defined Storage
Number Elevation Area Ave Area Volume Cumulative Volume
(ft) (sq ft) (sq ft) (cu ft) (cu ft)
1 474.4900 0.0000 0.0000 0.0000 0.0000
2 478.5000 38502.0000 19251.0000 77196.5100 77196.5100
3 480.0000 41810.8500 40156.4250 60234.6375 137431.1475
4 482.0000 56483.6900 49147.2700 98294.5400 235725.6875
5 484.0000 63770.2400 60126.9650 120253.9300 355979.6175
6 486.0000 71361.4600 67565.8500 135131.7000 491111.3175
DISCHARGE INFORMATION
Type: Trapezoidal Weir
Name: Emergency Spillway
Type:
Name: Sed Basin
RESERVOIR STAGE STORAGE /DISCHARGE
Elevation Stage Area Storage Discharge
(ft) (ft) (sq ft) (cu ft) (cfs)
478.5000 7.5000 38502.0000 77220.0337 0.00
479.0000 8.0000 39604.9500 96746.7712 1.48
479.5000 8.5000 40707.9000 116824.9837 5.35
480.0000 9.0000 41810.8500 137454.6712 10.53
480.5000 9.5000 45479.0600 159277.1487 15.12
481.0000 10.0000 49147.2700 182933.7312 18.52
481.5000 10.5000 52815.4800 208424.4187 21.38
482.0000 11.0000 56483.6900 235749.2.112 25.10
482.5000 11.5000 58305.3275 264446.4655 33.99
483.0000 12.0000 60126.9650 294054.5387 45.80
483.5000 12.5000 61948.6025 324573.4305 59.77
484.0000 13.0000 63770.2400 356003.1412 75.54
484.5000 13.5000 65668.0450 388362.7124 110.39
485.0000 14.0000 67565.8500 421671.1862 161.16
485.5000 14.5000 69463.6550 455928.5624 190.08
486.0000 15.0000 71361.4600 491134.8412 217.74
Maximum Storage = 491134.8412 (cu ft)
Maximum Discharge = 217.74 (cfs)
Dominion Development Resources, LLC Page 7
(434) 979 -8121
1992
3.14
TEMPORARY SEDIMENT BASIN DESIGN DATA SHEET
(with or without an emergency spillway)
Project r R ilea J a m t e 4 �{ A\
Basin # E (. w sS Location E 're;.5-f, rIc 5 (5‘"-) M - '1)
Total area draining to basin: S3 ,1 acres.
Basin Volume Design
Wet Storage:
1. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres).
67 cu. yds. x 53.\S acres =3 I-43,0G cu. yds. ( 7 - 1 6
2. Available basin volume = ''3 ,6"3 cu. yds. at elevation III 50. (From
storage - elevation curve)
3. Excavate cu. yds. to obtain required volume *.
* Elevation corresponding to required volume = invert of the dewatering
orifice.
4. Available volume before cleanout required.
33 cu. yds. x Vi)' acres = I' Mcu. yds.
5. Elevation corresponding to cleanout level = '\2 -•c1`k .
(From Storage - Elevation Curve)
6. Distance from invert of the dewatering orifice to cleanout level = 5.5 \ ft.
(Min. = 1.0 ft.)
Dry Storage:
7. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres).
67 cu. yds. x 5 1 acres = 3 5 3. %%cu. yds.
III - 112
1992 3A4
8. Total available basin volume at crest of riser* = Mln's3.6lcu. yds. at
elevation 1Q7,4 ,pO . (From Storage - Elevation Curve)
* Minimum = 134 cu. yds. /acre of total drainage area.
9. Diameter of dewatering orifice = in.
10. Diameter of flexible tubing = ' 6 in. (diameter of dewatering orifice
plus 2 inches).
Preliminary Design Elevations
11. Crest of Riser = ,c
Top of Dam =
Design High Water = '-5(�. O0
Upstream Toe of Dam = 471_00
Basin Shape
12. Length of Flow L =
Effective Width We 1,
If > 2, baffles are not required
If < 2, baffles are required t ; 54'GA
Runoff
13. Q = 1`k 2. cfs : 0 (From Chapter 5)
14. Q = Z \ S. cfs c, (From Chapter 5)
Principal Spillway Design
15. With emergency spillway, required spillway capacity Q = Q = cfs.
(riser and barrel)
Without emergency spillway, required spillway capacity Q = Q = Z 1 L \cfs.
(riser and barrel)
III - 113
1992 3.14
16. With emergency spillway:
Assumed d vaflahle he (-h) _- -M ft. (Using Q
h = Cres -emergency Spillway Elevalion, - Crest of Riser Elevation
Without emergency spillway:
Assumed available head (h) = \ . 0 ft. (Using Q
h = Design High Water Elevation - Crest of Riser Elevation
17. Riser diameter (D = - 4 in. Actual head (h) = , 5 ft.
(From Plate 3.14 -8.)
Note: Avoid orifice flow conditions.
18. Barrel length (1) = I o o ft.
Head (H) on barrel through embankment = 19.0 ft.
(From Plate 3.14 -7).
19. Barrel diameter = \`\ in.
(From Plate 3.14 -B [concrete pipe] or Plate 3.14 -A [corrugated pipe]).
20. Trash rack and anti- vortex ,device
Diameter = inches.
Height inches. y ' . - ` ,,, T rn, s k VLc, c K
(F,rb�m Table 3.14 -D).
c fbrn 2 c - - -aran. eve v -k,
Emergency Spillway Design 3 41"•4•
GN 2 \eJc.t--; on c)' 4 479.1 - S 'Vw C a ' A- . tO N c_ n)\ o s
21. Required spillway capacity Q = Q25 - Q = \ a ( cfs. �(
22. Bottom width (b) = \ O ft.; the slope of the exit channel (s) =
ft. /foot; and the minimum length of the exit channel (x) = •
ft.
(From Table 3.14 -C). -
• III - 114
1992 3.14
Anti -Seep Collar Design
23. Depth of water at principal spillway crest (Y) = ft.
Slope upstream face of embaankriient (Z) = :1. q( q
Slope of principal spill .: ybarrel (S = % v
Length of bar - in `saturated zone (L = ft.
24. Num I - of collars required ,., =-„, dimensions =
from Plate 3.14 -12).
Final Design Elevations
25. Top of Dam = -- `\ c ,
Design High Water = 1.}
Emergency Spillway Crest = 1-}-
Principal Spillway Crest = g''!' °c)
Dewatering Orifice Invert = , A 1- -1 S, , 5 0
Cleanout Elevation = t:.1`q 7 - , c 1
Elevation of Upstream Toe of Dam
or Excavated Bottom of "Wet Storage
Area" (if excavation was performed) = 411.a0
III - 115
2 ct
u) O_ 0;
N Q Q
CC v) N N N N N N N N N N ■ to co
200000000 (D (6
OuJ wwwwwww OO
a_ ti co Co o Co ,- CO CO CO Ln CO k
W N CO 6) r- .- M .- O O O .:
o O O O O O"
0 co 6) N.- h CO CO V C7) LO LO
V Ln ,- CO In CO O If) 6) CO l -
0 O N 4 Ln O CO O N Ln " --
N- N N O so N CO CO N- O CO
O O CO CO CO O CO CO V CO M N
- f: CO O (0 Cfl Ln N Ln LO Ln
d
u7 W
0
,
m II c
c c
'E
I-- CO O V O N V CO LO N
• W L) CO C7) 0 0 N O N N 6) ,
O O O ,- O 0 0'
U
N Lip
O O W V Co c u - ) C - CO 0 ()
CL II > N N (Ni M V L() Ln
C
O Co N LO N N co d' CO CO ..
C a- N N M M vf dr V LO
0 0 0 0 0 0 0 0 0 0 0
c N
• L 0 N CO
4
■ t 1 > N
W
co LO LO LO LO LO LO LO Lf In Ln = ,
. 2.
V 0 0 0 0 0 0 0 0 0 0 0-
c4 • 6 0 0 0 0 0 0 0 0 0 0"
U c
t 66666 0 0 0 0 0 0
C) o 4 4 4 4 4 v v v r` N
N- - '
W 0 0 0 0 0 0 0 0 0 0 0
m
a o o 0 0 0 0 0 0 0 0 0
N o
"C F 00000000000
O
itS sr) co 6) O N LO CO V f-- N f- P..M..
CO 6) CO 6) N d" CO CO
Ce O
O M V V CO Is O CO 6
c0 (6 II
CO ~ o 00
,
6 N
J —
N o sn
0
O
0 11
Ca Q
if) 6) 6) O N LO CO V f� N f�
o N CO Cr) CO 6) N V LC) o0
Ws 0 O c- M V V O N N 6
0
0 CO N O CO CO V N 0 O) 6)
U N Lri Lti Lt) V 4 V V V V C7 C7
N O h V' V' M o Co co f` O,
30 Ln LC i Co N-: 00 6) 6) O T 1- V
a
R d' CO N 6) CO CO N N N N CO •
• U O M CO O t` N N CO CO
Q O O O ,- N Ni Ni
CV Q
C O L C O O CO L M CO M 0 CO
I- c O co N N N CO CO CO 1 N LO
C
- O O O O O O O O O O O
O V
o V V V V V V d" V ,
U 0 0 0 0 O O 0 0 0 0 0
(o 6) co f� co 6) 4 N CO LO
< r- h CO CO dt CO CO CO CO N V
O 0 0 0 0 0 0 0 0 0 0 <-
Q .r 04 0 V to Co N- co 6) O 0
1- +
0 CV "
r F-
0 x N CO vt LO CO N- CO 0) 0
EROSION AND SEDIMENT CONTROL NARRATIVE
FOR
HOLLYMEAD TOWNCENTER AREA Al
May 23, 2008
LOCATION:
Tax Map 32 Parcels 44,45
Tax Map 46 Parcel 5
Rivanna District, Albemarle County, Virginia
v1LT,f ,
�� Gfjp �'f �
0
OWNER & DEVELOPER JOHN DAVID BEIRNE JR
HM Acquisition Group, LLC Lic. No. 042267
PO Box 5548
Charlottesville VA, 22905 / <
SStONAL EN 0
PREPARED BY:
Dominion Development Resources, LLC
172 S Pantops Dr.
Charlottesville, VA 22911
434.979.8121
(F) 434.979.1681
1
A. MINIMUM STANDARDS (MS):
All applicable Virginia Erosion and Sediment Control Regulations and Minimum Standards
shall be adhered to during all phases of construction. These include, but are not limited to
the following:
1. STABLIZATION OF DENUDED AREAS:
Permanent or temporary soil stabilization shall be applied to bare areas within seven days
after final grade is reached on any portion of the site. Temporary soil stabilization shall be
applied within seven days to denuded areas that may not be at final grade, but will remain
dormant or undisturbed for longer than 30 days. Permanent stabilization shall be applied
at areas that are to be left dormant for more than 1 year.
2. STABILIZATION OF SOIL STOCKPILES:
During construction of the project, soil stockpiles shall be stabilized or protected with
sediment trapping measures. The applicant is responsible for temporary protection and
permanent stabilization of all soil stockpiles on site as well as soil intentionally transported
from the project site.
3. PERMANENT VEGETATIVE COVER
A permanent vegetative cover shall be established on denuded areas not otherwise
permanently stabilized. Permanent vegetation shall not be considered established until a
ground cover is achieve that, in the opinion of the county Inspector, is uniform and mature
enough to survive to inhibit erosion.
4. TIMING & STABILIZATION OF SILT TRAPPING MEASURES:
Sediment basins and traps, perimeter dikes, sediment barriers and other measures
intended to trap sediment shall be constructed as a first step in any land disturbing activity
and shall be made functional before upslope land disturbance takes place.
5. STABILIZATION OF EARTHEN STRUCTURES:
Stabilization measures shall be applied to earthen structures such as dams, dikes and
diversions immediately after installation.
6. SEDIMENT TRAPS AND BASINS:
A sediment basin shall control surface runoff from disturbed areas that is comprised of
flow from drainage areas greater than or equal to three acres. The sediment basin shall
be designed and constructed to accommodate the anticipated sediment loading for the
land disturbing activity. The outfall device or system device shall take into account the
total drainage area flowing through the disturbed area to be served by the basin.
7. CUT AND FILL SLOPES:
Cut and fill slopes shall be designed and constructed in a manner that will minimize
erosion. Slopes that are found to be eroding excessively within one year of permanent
stabilization shall be provided with additional slope stabilizing measures until the problem
is corrected.
8. CONCENTRATED RUN -OFF DOWN CUT OR FILL SLOPES:
Concentrated runoff shall not flow down cut or fill slopes unless contained within an
adequate temporary or permanent channel, flume, or slope drain structure.
2
9. WATER SEEPS FROM A SLOPE FACE:
Whenever water seeps from a slope face, adequate drainage or other protection shall be
provided.
10. STORM SEWER INLET PROTECTION:
All storm sewer inlets that are made operable during construction shall be protected so
that sediment -laden water cannot enter the conveyance system without first being filtered
or otherwise treated to remove sediment.
11. STABILIZATION OF OUTLETS:
Before newly constructed stormwater conveyance channels are made operational,
adequate outlet protection and any required temporary or permanent channel lining shall
be installed in both the conveyance channel and receiving channel.
12. WORK IN LIVE WATERCOURSES:
When work in a live watercourse is performed, precautions shall be taken to minimize
encroachment, control sediment transport and stabilize the work area to the greatest
extent possible during construction. Nonerodible material shall be used for the
construction of causeways and cofferdams. Earthen fill may be used for these structures if
armored by nonerodible cover materials.
13. CROSSING A LIVE WATERCOURSE:
When a live watercourse must be crossed by construction vehicles more than twice in any
six month period, a temporary stream crossing constructed of nonerodible materials shall
be provided.
14. APPLICABLE REGULATIONS:
All applicable federal, state and local regulations pertaining to working in or crossing live
watercourses shall be met.
15. STABILIZATION OF BED AND BANKS
The bed and banks of a watercourse shall be stabilized immediately after work in the
watercourse is completed.
16. UNDERGROUND UTILITIES:
Underground utilities shall be installed in accordance with the following standards in
addition to other criteria:
a. No more than 500 linear feet of trench may be opened at one time.
b. Excavated material shall be placed on the uphill side of trenches
c. Effluent for dewatering operations shall be filtered or passed through approved
sediment trapping device, or both, and discharged in a manner that does not adversely
affect flowing streams or offsite property.
d. Material used for backfilling trenches shall be properly compacted in order to minimize
erosion and promote stabilization.
e. Restabilization shall be accomplished in accordance with these regulations.
f. Applicable safety regulations shall be complied with.
3
17. CONSTRUCTION ACCESS ROUTES:
Where construction vehicle access routes intersect paved public roads, provisions shall be
made to minimize the transport of sediment by vehicular tracking onto paved surfaces.
Where sediment is transported on to a public road surface, the road shall be cleaned
thoroughly at the end of each day. Sediment shall be removed by shoveling or sweeping
and transported to a sediment control disposal area. Street washing shall be allowed only
after sediment is removed in this manner. This provision shall apply to individual lots as
well as to larger land disturbing activities.
18. TEMPORARY E &S CONTROL MEASURE REMOVAL:
All temporary erosion and sediment control measures shall be removed within 30 days
after final site stabilization or after temporary measures are no longer needed, unless
otherwise authorized by the local program authority. Trapped sediment and the disturbed
soil areas resulting from the disposition of temporary measures shall be permanently
stabilized to prevent further erosion and sediment.
19. ADEQUACY OF RECEIVING CHANNELS:
Properties and waterways downstream from the development site shall be protected from
sediment deposition, erosion and damage, due to increases in volume, velocity and peak
flow rates of stormwater runoff for the stated frequency storm of 24 -hour duration.
B1. PROJECT DESCRIPTION:
The purpose of this project is for the continuation the construction of Meeting St. Total
area of disturbance is 27.21 Acres.
B2. EXISTING SITE CONDITIONS:
The site has been mass graded under previously approved erosion plan. The site is
grassed with moderate slopes.
B3. ADJACENT AREAS:
The site is bounded to the South by U.S. Route 29, to the East by Towncenter Drive, to
the North by commercial areas, and to the West by residential districts.
B4. SOIL DESCRIPTIONS:
According to the Albemarle County Soils Survey conducted by the United States
Department of Agriculture Soil Conservation Service, the primary soil types that may be
disturbed during this scope of work have been identified as the following:
1. Elioak Loam (27B) — Permeability is moderate, surface runoff and the hazard of
erosion is moderate. Hydrologic group C, K factor .28
2. Elioak Silt Loam (28C3) — Permeability is moderate, surface runoff is rapid and
the hazard of erosion is severe. Hydrologic group C, K factor .28
3. Glenelg Loam (34C) — Permeability is moderate, surface runoff is rapid and the
hazard of erosion is severe. Hydrologic group B, K factor .43
4. Hazel Loam (39D) — Permeability is moderately rapid, surface runoff is rapid and
the hazard of erosion is severe. Hydrologic group C, K factor .24
4
5. Louisburg Sandy Loam (47C) — Permeability is rapid, surface runoff is rapid, and
the hazard of erosion is severe. Hydrologic group B, K factor .24
6. Louisburg Sandy Loam (47D) — Permeability is rapid, surface runoff is rapid, and
the hazard of erosion is severe. Hydrologic group B, K factor .24
7. Pacolet Sandy Loam (65B) — Permeability is moderate, surface runoff is rapid,
and the hazard of erosion is severe. Hydrologic group B, K factor .28
8. Pacolet Sandy Loam (65C) — Permeability is moderate, surface runoff is rapid
and the hazard of erosion is severe. Hydrologic group B, K factor .28
B5. CRITICAL AREAS:
Critical slopes, streams and wetlands are the critical areas for this project. The contractor
shall take care to prevent sediment from entering into the stream.
B6. EROSION AND SEDIMENT CONTROL MEASURES:
Unless otherwise indicated, all erosion and sediment control practices will be constructed
and maintained according to the minimum standards and specifications as set forth in the
Virginia Erosion and Sediment Control Handbook, latest edition. The minimum standards
of the Virginia Erosion and Sediment Control Regulations shall be adhered to unless
otherwise waived or approved by variance.
SILT FENCE (SF) — 3.05
Silt fencing will be installed as a first step in construction activities. Location and
details are shown on the plans.
TEMPORARY DIVERSION DIKE (DD) — 3.09
A temporary diversion dike will be installed before site grading begins, for the purposes of
diverting storm and sediment -laden runoff to the appropriate outlet or trapping facility.
Location and details are shown on the plans.
TEMPORARY SEDIMENT BASIN (ST) — 3.14
A temporary sediment basin will be installed before site grading begins, for the purpose of
detaining sediment -laden runoff from disturbed areas. Location and details of the
sediment basins are shown on the plans.
DUST CONTROL (DC) — 3.39
A variety of methods are available to prevent surface and air movement of dust from
exposed soil surfaces and reduce the presence of airborne substances which may
present health hazards, traffic safety problems or harm animal or plant life.
B7. PERMANENT AND TEMPORARY STABILIZATION:
SURFACE ROUGHENING — 3.29
Disturbed areas to be seeded and mulched shall be left in a roughened condition to help
decrease runoff velocities and aid in the establishment of vegetation.
TOPSOILING — 3.30
5
Topsoil may be stripped from the area to be graded and stockpiles for later use. All
stockpiles which will be left dormant for more than 30 days shall be temporarily seeded. A
topsoil stockpile may be selected onsite by the developer and shall be temporarily
protected with surrounding silt fencing.
TEMPORARY SEEDING — 3.31
Temporary soil stabilization shall be applied within 7 days to denuded areas that may not
be at final grade, but will remain dormant (undisturbed) for longer than 30 days and less
than 1 year. This includes, but is not limited to areas such as soil stockpiles. Seeded
areas shall be limed when necessary at a rate of 2 tons per acre, and fertilized at a rate of
450 lbs. per acre of 10 -20 -20 (10 lbs. per 1,000 square feet) or equivalent. A Temporary
Seeding Schedule is attached for proper seed selection.
PERMANENT SEEDING — 3.32
A perennial vegetative covering shall be established on disturbed areas within 7 days of
being brought to final grade on areas not otherwise protected. Selection of the seed
mixture shall depend on the time of year it is to be applied according to the Permanent
Seed Schedule as shown on the drawing. Seeded areas shall be Timed when necessary
at a rate of 2 tons per acres, and fertilized at a rate of 1,000 lbs. per acre of 10 -20 -10 (10
lbs. per 1,000 square feet) or equivalent.
MULCHING — 3.35
All seeded areas shall be mulched with straw immediately following seeding operations.
Straw mulch shall be applied at a rate of two tons per acre.
B8. SOIL STOCKPILES AND BORROW AREAS
No offsite activities are expected for this project.
B9. STORM WATER MANAGEMENT:
Any increase in stormwater runoff as a result of land disturbing activity will be minimal. The
existing sediment basin (SWM 3) will provide temporary stormwater detention.
B10. MAINTENANCE SCHEDULE:
A program of maintenance for the erosion and sediment controls specified in this narrative
and shown on the plans are recommended as follows:
1. The Site Superintendent or his representative shall make a visual inspection of all
erosion and sediment controls on a daily basis until the site is stabilized and especially
after a heavy rainfall to assure that all controls are in place and that none have been
damaged. Any damaged control shall be repaired prior to the end of each workday to
include re- seeding if necessary.
2. All silt trapping devices shall be cleaned out at 50 percent capacity and sediment shall
be disposed of by spreading on site or hauling away if not suitable for fill.
3. Gravel outlets shall be checked regularly for sediment buildup that may prevent
drainage. Controls shall be inspected and repaired after each rainfall and cleaned if
sediment has accumulated to half of the device's original height.
4. All earthen structures such as diversion dikes and berms shall be checked daily during
construction for breaching by equipment. Repairs shall be made immediately.
5. Silt fences shall be checked after each rainstorm to assure they have not fallen or
become clogged with silt. All repairs shall be made immediately.
6. All seeded areas shall be inspected regularly to see that good stand is maintained.
Areas will be re- fertilized and re- seeded as necessary.
6
7. After construction operations have ended and disturbed areas have been stabilized, all
berms and sediment - trapping devices may be removed after removal, the ground shall
be restored to its natural or proposed condition to include establishment of permanent
vegetation. Removal of any control is contingent upon approval of the County
Inspector.
7
SWM #3 SEDIMENT BASIN CALCULATIONS
FOR
HOLLYMEAD TOWNCENTER AREA Al EROSION
May 29, 2008
LOCATION:
Albemarle County, Virginia
Tax Map 32, Parcels 42A & 44
Tax Map 46, Parcel 5
PREPARED BY:
Dominion Development Resources, LLC
172 South Pantops Drive
Charlottesville, VA 22911
P: 434.979.8121
F: 434.979.1681
O �� �
U y'
JOHN DAVID BEIRNE JR
Lic. No. 042267
Dominion Development Resources, LLC Page 1
(434) 979 -8121
Hollymead Towncenter Area Al
SWM #3 Sediment Basin
Name: DA Sed, 25yr
Type: Modified Rational
HYDROGRAPH INFORMATION
Peak Flow (Qp) = 340.98 (cfs)
Time to Peak (Tp) = 5.00 (min)
Time of Base (Tb) = 12.50 (min)
Volume = 2.9433 (ac -ft)
Time Step = 1.00 (min)
Flow Multiplier = 1.00
RATIONAL HYDROGRAPH INFORMATION
Flow Multiplier = 1.00
Receding Limb Factor = 1.50
APPROXIMATE STORAGE
Maximum Outflow = 0.00 (cfs)
Maximum Storage = 2.9433 (cu ft)
BASIN INFORMATION
WEIGHTED WATERSHED AREA
Description Area CN Runoff Coef
Overall Approximation 53.1800 NA 0.80
TIME CONCENTRATION -- User Defined
Time of Concentration (Tc) = 5.00 (min)
RAINFALL DESCRIPTION
Distribution Type = Synthetic
Total Precipitation = 0.66 (in)
Return Period = 25 (yr)
Storm Duration = 0.08 (hr)
Dominion Development Resources, LLC Page 2
(434) 979 -8121
Hollymead Towncenter Area - A1
SWM #3 Sediment Basin
Name: Sed Rtd 25yr
Type: Reservoir: Modified Puls
HYDROGRAPH INFORMATION
Peak Flow (Qp) = 7.73 (cfs)
Time to Peak (Tp) = 13.00 (min)
Time of Base (Tb) = 1440.00 (min)
Volume = 1.1693 (ac -ft)
Time Step = 1.00 (min)
Peak Elevation = 479.7301 (ft)
Detention Time = NA
RESERVOIR STRUCTURE INFORMATION
Number = 2
Name = SWM #3 Sed Basin
Storage Type = User - Defined Area
Maximum Storage = 491134.8412 (cu ft)
Maximum Discharge = 217.74 (cfs)
INFLOW HYDROGRAPH INFORMATION
Number = 26
Name = DA Sed, 25yr
Peak Flow (Qp) = 340.98 (cfs)
Time to Peak (Tp) = 5.00 (min)
Time of Base (Tb) = 12.50 (min)
Volume = 2.9433 (ac -ft)
Flow Multiplier = 1.00
Dominion Development Resources, LLC Page 3
(434) 979 -8121
Hollymead Towncenter Area Al
SWM #3 Sediment Basin
Type : Stand Pipe
Name : Sed Basin
RATING CURVE LIMIT
Minimum Elevation = 475.0000 (ft)
Maximum Elevation = 486.0000 (ft)
Elevation Increment = 0.5000 (ft)
STAND PIPE INFORMATION
ORIFICE INFORMATION
Diameter = 6.00 (ft)
Crest Length = 18.85 (ft)
Effective Crest Length = 14.85 (ft)
Orifice Coefficient = 0.60
Fractional Open Area = 0.83
WEIR INFORMATION
Crest Elevation = 484.0000 (ft)
Weir Coefficient = 3.33
Exponential = 1.50
OPTIONAL WEIR INFORMATION
Type : Rectangular Weir Suppressed #1
WEIR INFORMATION
Crest Length = 2.00 (ft)
Crest Elevation = 481.8000 (ft)
Weir Coefficient = 3.33
Exponential = 1.50
Type : Rectangular Weir Suppressed #2
WEIR INFORMATION
Crest Length = 2.00 (ft)
Crest Elevation = 481.8000 (ft)
Weir Coefficient = 3.33
Exponential = 1.50
Dominion Development Resources, LLC Page 4
(434) 979 -8121
Hollymead Towncenter Area Al
SWM #3 Sediment Basin
OPTIONAL ORIFICE INFORMATION
Structure Number : 1
Type : Circular Orifice
OPTIONAL ORIFICE INFORMATION
Diameter = 2.00 (ft)
Invert Elevation = 478.5000 (ft)
Orifice Coefficient = 0.60
Number of Openings = 1
ORIFICE EQUATION
Q = Co *A((2gh) /k) ^0.5
DEFINITIONS
Co = Orifice Coefficient
A = Wetted Area, (cfs)
k = 1
CULVERT INFORMATION
Type : Circular Concrete - Square Edge with Headwall
OUTLET STRUCTURE INFORMATION
Diameter = 48.00 (in)
Invert Elevation = 475.0000 (ft)
Pipe Length = 100.00 (ft)
Slope = 0.09
Manning's n Value = 0.01
Orifice Coefficient = 0.60
Tailwater Elevation = 468.4000 (ft)
Number of Barrels = 1
Dominion Development Resources, LLC Page 5
(434) 979 -8121
Hollymead Towncenter Area Al
SWM #3 Sediment Basin
STAND PIPE STAGE VS. DISCHARGE
Elevation Stage Weirs Orifices Stand Pipe Culvert Total
(ft) (ft) (cfs) (cfs) (cfs) (cfs) (cfs)
475.0000 0.0000 0.00 0.00 0.00 0.00 0.00
475.5000 0.5000 0.00 0.00 0.00 3.09 0.00
476.0000 1.0000 0.00 0.00 0.00 8.93 0.00
476.5000 1.5000 0.00 0.00 0.00 17.35 0.00
477.0000 2.0000 0.00 0.00 0.00 27.49 0.00
477.5000 2.5000 0.00 0.00 0.00 39.17 0.00
478.0000 3.0000 0.00 0.00 0.00 51.37 0.00
478.5000 3.5000 0.00 0.00 0.00 63.91 0.00
479.0000 4.0000 0.00 1.48 0.00 76.45 1.48
479.5000 4.5000 0.00 5.35 0.00 87.96 5.35
480.0000 5.0000 0.00 10.53 0.00 100.53 10.53
480.5000 5.5000 0.00 15.12 0.00 109.10 15.12
481.0000 6.0000 0.00 18.52 0.00 117.84 18.52
481.5000 6.5000 0.00 21.38 0.00 125.98 21.38
482.0000 7.0000 1.19 23.91 0.00 133.62 25.10
482.5000 7.5000 7.80 26.19 0.00 140.85 33.99
483.0000 8.0000 17.51 28.29 0.00 147.72 45.80
483.5000 8.5000 29.52 30.24 0.00 154.29 59.77
484.0000 9.0000 43.46 32.08 0.00 160.59 75.54
484.5000 9.5000 59.09 33.81 17.48 166.65 110.39
485.0000 10.0000 76.25 35.46 49.45 172.50 161.16
485.5000 10.5000 94.80 37.04 90.85 178.16 178.16
486.0000 11.0000 114.65 38.55 139.87 183.64 183.64
Dominion Development Resources, LLC Page 6
(434) 979 -8121
Hollymead Towncenter Area Al
SWM #3 Sediment Basin
Name: SWM #3 Sed Basin
RATING CURVE LIMIT
Minimum Elevation = 471.0000 (ft)
Maximum Elevation = 486.0000 (ft)
Elevation Increment = 0.5000 (ft)
STAGE STORAGE INFORMATION
Storage Method: User - Defined Storage
Number Elevation Area Ave Area Volume Cumulative Volume
(ft) (sq ft) (sq ft) (cu ft) (cu ft)
1 474.4900 0.0000 0.0000 0.0000 0.0000
2 478.5000 38502.0000 19251.0000 77196.5100 77196.5100
3 480.0000 41810.8500 40156.4250 60234.6375 137431.1475
4 482.0000 56483.6900 49147.2700 98294.5400 235725.6875
5 484.0000 63770.2400 60126.9650 120253.9300 355979.6175
6 486.0000 71361.4600 67565.8500 135131.7000 491111.3175
DISCHARGE INFORMATION
Type: Trapezoidal Weir
Name: Emergency Spillway
Type:
Name: Sed Basin
RESERVOIR STAGE STORAGE /DISCHARGE
Elevation Stage Area Storage Discharge
(ft) (ft) (sq ft) (cu ft) (cfs)
478.5000 7.5000 38502.0000 77220.0337 0.00
479.0000 8.0000 39604.9500 96746.7712 1.48
479.5000 8.5000 40707.9000 116824.9837 5.35
480.0000 9.0000 41810.8500 137454.6712 10.53
480.5000 9.5000 45479.0600 159277.1487 15.12
481.0000 10.0000 49147.2700 182933.7312 18.52
481.5000 10.5000 52815.4800 208424.4187 21.38
482.0000 11.0000 56483.6900 235749.211 25.10
482.5000 11.5000 58305.3275 264446.4655 33.99
483.0000 12.0000 60126.9650 294054.5387 45.80
483.5000 12.5000 61948.6025 324573.4305 59.77
484.0000 13.0000 63770.2400 356003.1412 75.54
484.5000 13.5000 65668.0450 388362.7124 110.39
485.0000 14.0000 67565.8500 421671.1862 161.16
485.5000 14.5000 69463.6550 455928.5624 190.08
486.0000 15.0000 71361.4600 491134.8412 217.74
Maximum Storage = 491134.8412 (cu ft)
Maximum Discharge = 217.74 (cfs)
Dominion Development Resources, LLC Page 7
(434) 979 -8121
1992 3.14
TEMPORARY SEDIMENT BASIN DESIGN DATA SHEET
(with or without an emergency spillway)
Project U It 2a, J `i 4 t_ eA 4° � { a A l
Basin # E CS w M 's\ Location s--f; r\c 5
Total area draining to basin: S a 1 acres.
Basin Volume Design
Wet Storage:
1. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres).
67 cu. yds. x 5 acres = 3 3 O 6 cu. yds. ( ? ( . 9 � �t c 0, 1-c
2. Available basin volume = 7 (3 p7,$3cu. yds. at elevation 7775(.)). (From
storage - elevation curve)
3. Excavate cu. yds. to obtain required volume *.
* Elevation corresponding to required volume = invert of the dewatering
orifice.
4. Available volume before cleanout required.
33 cu. yds. x %3 acres = I" yds.
5. Elevation corresponding to cleanout level = ���Z.�j� .
(From Storage - Elevation Curve)
6. Distance from invert of the dewatering orifice to cleanout level = 5.c3 \ ft.
(Min. = 1.0 ft.)
Dry Storage:
7. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres).
67 cu. yds. x k°0 acres = 3 5 6 6Acu. yds.
III - 112
1992 3.14
8. Total available basin volume at crest of riser* = / cu. yds. at
elevation `Val ,00 . (From Storage - Elevation Curve)
* Minimum = 134 cu. yds. /acre of total drainage area.
9. Diameter of dewatering orifice = 2.4 in.
10. Diameter of flexible tubing = 2 in. (diameter of dewatering orifice
plus 2 inches).
Preliminary Design Elevations
11. Crest of Riser = ,p 0
Top of Dam = `���' "
Design High Water = y-Ysm. 00
Upstream Toe of Dam = 471.00
Basin Shape
12. Length of Flow L =
Effective Width We 1,
If > 2, baffles are not required
If < 2, baffles are required
Runoff
13. Q = Hio 2. cfs, 0 (From Chapter 5)
14. Q = 7 \ C cfs 3, G , (From Chapter 5)
Principal Spillway Design
15. With emergency spillway, required spillway capacity o = Q = cfs.
(riser and barrel)
Without emergency spillway, required spillway capacity Q = Q25 = 2. cfs.
(riser and barrel)
III - 113
1992 3.14
16. With emergency spillway:
Ass meu d ilable heat-= ft. (Using Q
h = Cres ergency Spillway Elevation..,. - Crest of Riser Elevation
Without emergency spillway:
Assumed available head (h) = \ • U ft. (Using Q
h = Design High Water Elevation - Crest of Riser Elevation
17. Riser diameter (D = 3 in. Actual head (h) = . ft.
(From Plate 3.14 -8.)
Note: Avoid orifice flow conditions.
18. Barrel length (1) = 1 ft.
Head (H) on barrel through embankment = 19.0 ft.
(From Plate 3.14 -7).
19. Barrel diameter = \`‘ in.
(From Plate 3.14 -B [concrete pipe] or Plate 3.14 -A [corrugated pipe]).
20. Trash rack and anti - vortex _device
Diameter = inches.
Height = inches. " Trek
(F� m Table 3.14 -D).
Erriergency Spillway Design . pcson eil�� _ „ n o ` o`k ` f e cxcv
e_- \QJ --; 0 ,1'S c `ii,o A. &rv! o
21. Required spillway capacity Q = Q25 - Q = 1 a Cj cfs. 1 �' Vi
P
22. Bottom width (b) = ft.; the slope of the exit channel (s) =
ft. /foot; and the minimum length of the exit channel (x) =
ft.
(From Table 3.14 -C).
III - 114
1992 3.14
Anti -Seep Collar Design
23. Depth of water at principal spillway crest (Y) = ft.
Slope upstream face of embankment (Z) _ :1.
Slope of princie al spill .. y b v
arrel (S = %
3c : (
Length of bar - in saturated zone (L = ft.
24. Num I - of collars required'=,, dimensions =
from Plate 3.14 -12).
Final Design Elevations
25. Top of Dam = `- \`g, ,\
Design High Water = 419.13
Emergency Spillway Crest = t 1
Principal Spillway Crest = g '-R . o °
Dewatering Orifice Invert = * 50
Cleanout Elevation = \C ' f
Elevation of Upstream Toe of Dam
or Excavated Bottom of "Wet Storage
Area" (if excavation was performed) = '11.0D
III - 115
o_ 0-
.,
CO
E E ,
co
E
a)
( i ) ■ . . 1 , . . . tow-
12 0 0 0 0 c) 0 0 c) m m 4
OWWWWWWWW00
o_ r-- cn co o CD ,- CO CO CO co co
N CO CT) rt c- c- CO 0) 0)
W . .
0
' n ;
..'
Cr O N- 1* CO (0 rd rt 0) 10 LO
c
N- N x 0 LO N CO CO 1.--- o co
o
CO cc; cc) cc) cc) cri cri cri cri 7;
-
a.
co w
o) 1 1
c c o c
. E ,
a) 0_ N- CO C5) cr 0 N cr OD LO N
W LO CO C3) 0 0 N 0 CO CO 0)
r..= 0
o
0
co co o ,- ap o co
CI_ • 11 •---.
c ----
o co N 10 •Y N- CO dr CO CO
O 6 6 6 6 6 6 6 6 6 6
C .
N Y....
0 CO
_C On TD CO
.4= N
Ft -' 11 >
R S U J C
M CY) LC) LO LC) 10 LO LO 10 to to co , ..
0 Ti
a) o oo o o (Do c) o o o;').--
—
1 6 0 0 0 0 0 0 0 0 0 0
CD 5
C.)
c .
..0 _
(..) c ) c ) c -.) o c 3 c ) c ) c ) c ) cD c3
4-,
CD ,
o o o o o co co o o o 0
CL CE cj dr N- 1- (N c C) CO 0 0
• 0 000000000c-
U) 6 0 0 0 0 0 0 0 0 0 0
- u)
0
Ce 0 6 ,- cci 4 4 cci N-: cc; c.c) a) -
To
CO
C.0 o 0
CV >-
6
_1 Tc)
C u
u) o
N-
C.)
at 0
C.) If) N 0 CO CO dr N cr 0 CD)
(/) ,
0
0 I--
13 —
co .:71 CO Csl 0) CO CO N A N N C.0 '
O L) CD CO CY) ' 0 (Y) Pr-- r CO CO 0)
0
0 N
' ch N-- N CO OD
< c:, c ; co
6 6 ,- ,- cNi cs.i c• i -
cu <
(0 c LO CO 00 LO CO N CO 0 CO
0
C OCONN x N LC)
- ci 6 6 6 6 6 6 ci 6 6 6
o 6 6 6 0 0 6 6 6 6
(..) 6
co c) co r--- co 0) 4 N CO 10 c- ,
< N tr CD CD 'Cr CO CO 00 CO N Cr ,
O 6 6 6 6 6 6 6 6 6 6 .-
CO cr (0 CD r- co CD 0 00
(NO
1 +
(1) 1-
.,---
o N
... 0 0 - % - r N co 4 co co h. co cs) o
- u) ...... ,-- ,-- ,- ,- (--q
I-
0