HomeMy WebLinkAboutSDP199200052 Calculations Major Amendment, Final Site Plan 1994-07-14 (3) ELIMASSOCI - IES Consulting " ";ineers and Land Surveyors
Route 1 Box 251
Free Union VA 22940
804 978 1409
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March 11, 1994
Mr. Don Franco 4"' E ; El / ED
Department of Engineering
County of Albemarle MAR 1 4 1994
Charlottesville, VA. 22902
Re: CHRISTIAN AID AMENDED SITE PLAN Planning Dept.
Dear Mr. Franco:
I am enclosing the following for your review/approval:
. Revised Drawing AM 3, EXCAVATION, GRADING, ROADWAYS. The Detention
Pond is the major item added.
. Drawing AM 4, RUNOFF AND EROSION WORK SHEET.
. Module 3. Existing Conditions - Pre 1989 development
. Module 6. ROC Measures required - Proposed 1994 development.
I would appreciate your comments on the enclosed, and, in the meantime
revisions to Drawing AM I - SITE PLAN, are being finalized. This. Dwg.
along with the remaining ROC modules ( 1,2 4, 5, 7, 8,& 9) , will be
submitted with all necessary documents, drawings etc. to the Planning
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Department within the next several days.
I will appreciate hearing from you.
Sincerely,
cc: Yolanda Hipski William Finley, P E
Civil/Sanitary Design •Site Planning•Erosion/Drainage Control Plans •Land Surveying
MODULE 3 RUNOFF FLOW FOR EXISTING CONDITIONS/PRE 1989 CONSTRUCTION
AREA #,COVER/SOIL TYPE/AVG SLOPE C Tc i A-ACRES C-WEIGHTED REMARKS
IA BRUSHWOOD/36B&14D/14% 0.15 2.8 0.029871 FLOWS TO 2*4 CULVERT
II GRASS,WEEDS,WOODED/19D/12`k 0.12 2.3 0.019630 " "
III, BRUSHWOOD,GRASS/19D/12% 0.15 2.24 0.023897 " " "
IVA BRUSHWOOD,GRASS/14E/11% 0.15 1.3 0.013869 " " " •
IVB ROOF6%,ASP.5%,GRS89%/14E/5% 0.23 0.97 0.015867 " "
VA BRUSHWOOD/19C/18% 0.15 2.4 0.025604 " "
VB ..._( ROOFI5*,ASPHALT1496,GRASS58%
....( GRASS-GRAVEL 13%/19C/10% 0.36 22 4 2.05 0.052489 " " "
VIXJP-B WCODED70RASS30%/19D/7% INCLUDED UNDER IIB FLOWS TO 2X4 CULVERT
TOTALS 4.1 14.06 0.181230
SITE RUNOFF AT 2X4 CULVERT= 10.44721
SUB AREA RUNOFF FLOWING OFF-SITE TO OTHER AREAS EAST AND WEST
AREA# COVER/SOIL TYPE/AVG SLOPE C Tc i ACRES Qcfs
I BRUSHWOOD/36B&14D/15% 0.15 20 4.2 0.77 0.4851
VI GRASS80%,ASPHALT2096/19C/3% 0.3i 20 4.2 1.1 1.4322
VDOT-A GRS73%,ASPHALT27%/19C/3% 0.34 11 5.5 0.464 0.86768
TOTALS 2.334 2.78498 cfs TO POINTS OTHER THAN 2X4 CULVERT
TOTAL PRE 1989 CONSTRUCTION RUNNOFF 13.23 cfs
MODULE 3.(cant.)RUNOFF CHARACTERISTICS FOR EXISTING CONDITIONS (SEE MODULE 3.A_1_ FOR SOIL TYPE/COVER)
SED. LD. Ls-tons/ac/yr Lp-tons/ac/yr
AREA ACRES K R S% L Ls FACT. P C Sd SUB AREA WEIGHTED WEIGHTED
IA 2.8 0.26 175 14 440 2.7 NA 1 0.001 0.26 0.031941 0.006360 0.000038
II 2.3 0.24 175 12 610 4.4 NA 1 0.001 0.24 0.044352 0.007255 0.000043
III 2.24 0.24 175 12 600 4 NA 1 0.002 0.24 0.08064 0.012847 0.000077
IVA 1.3 0.26 175 7.3 680 2 NA 1 0.002 0.24 0.04368 0.004038 0.000024
IVB 0.97 4.4 680 1 100 0.24 0.012 0.000827 0.000004
VA 2.4 ' 0.24 175 6 840 2 NA 1 0.003 0.225 0.0567 0.009678 0.000058
VB 2.05 0.24 9 900 3 100 0.225 0.03375 0.004920 0.000029
VDOL'-B (INCLUDED IN IIB)
NOTE:
SUB AREAS VI,AND VDOT-A HAD NO NEW OR PROPOSED DEVELOPMENT AFFECTING Ls AND Lp AND RUNNOFF IS OFF SITE TO BROONLEY ROAD.
TOTAL 14.06 ACRES Ls & Lp= 0.045929 0.000275 T/ac/y
= 91.85910 0.551154 Lbs/ac.
TIs = 0.645769 Tons/yr (culver
Illi
ODULE 6 ROC MEASURES REQUIRED
:TOTAL POST CONSTRUCTION RUNOFF (unrttrolled) FROM SUB AREAS (see DWG AM 4) WHICH LEAVES SITE THRCUGH 2*4 CULVERT
iREA #,COVER/SOIL TYPE/AVG SLOPE C Tc i A-ACRES C (weighted) REMARKS
iA BRUSHWOOD/36B&14D/14* • 0.15 2.8 0.029871 IA THRU VB FLOW TO 2*4 CULVERT.
:I ASPH4%,GRASS.96%/19D/25% 0.18 2.3 0.029445
[II BRUSH&GRS989%ASPH2%/19D/12% 0.18 2.24 0.028677
[VA BRUSHWOOD,GRASS/14E/7.6% 0.17 1.3 0.015718
NB ROOF13%,ASPh.4286,GRS4596/14E 0.56 0.97 0.038634
IA BRUSHWOOD/19C/18% 0.17 2.4 0.029018
FB ....( ROOFIS%,ASPHALT16%,GRASS56%
....( GRASS-GRAVEI, PRK_/19C/13% 0.38 .22 4 2.05 0.055405 THIS AREA IS MOST RE240TE
FOOT-B WOODED70%GRASS30%/19D/7% INCLUDED UNDER IIB
EMUS: 4.1 14.06 acres 0.226770
SITE RUNOFF (uncontrolled) AT 2*4 CULVERT = 13.07244 cfs
8. SUB AREA RUNNOFF FLOWING OFF-SITE AT POINTS OTHER THAN THE 2*4 CULVERT
AREAL, COVER/SOIL TYPE/AVG SLOPE C Tc i A ACRES. RUNOFF CFS ' REMARKS
I BRUSHWCOD/36B&14D/15% 0.15 20 4.2 0.77 0.4851 FLOWS OFF-SITE EAST.
VI GRASS80%,ASHPALT20%/19C/2.5 0.31 20 4.2 1.1 1.4322 FLOWS OFF-SITE WEST
VDOT-A GRS5996,ASPHALT41%/19C/3% 0.41 11 5.5 0.464 1.04632 " " " "
MIMS 2.334 acres 2.96362 cfs
t TAL POST CONSTRUCTION RUNOFF (uncontrolled) = 16.03606
TOTAL PRE CONSTRUCTION RUNOFF (see MCCULE 3) , = 13.22759 cfs
DIFFEERNCE 2.80847
C. PERMANENT ROC MEASURES:
C_1.EnSTING CISTERN SW OF CHURCH RECEIVES CHURCH CCMPLE/ ROOF RUNOFF = 0.8 cfs
C.2_RUNOFF TO BE RETAINED/CONTROLLED = 2.00847 cfs
C.3.CONTROLL MEASURE DESIGN:
1U Mill77F PRE & POST DEVELOPMENT RUNOFF AN OPEN BASIN DETENTION POND WILL BE CONSTRUCTED TO INTERCEPT
RUNOFF FROM SUBBASIN IVB (Qi), AND DISCHARGE AT THE REQJIRED CONTROLLED RATE (Co).
C.3.1.RUNOFF FROM SUBBASIN IV B (=Q INTO DEL'ENLZON PONLkQi)
FREQUENCY C i A CFS CSM
l0yr 0.56 6 0.97 3.2592 2150.4
100yr 0.56 8.5 0.97 4.6172 3046.4
3:2-OUTFLOW FROM DETENTION POND (= Qo cfs) -
FREQUENCY Qi cfs RETAINED Qo cfs CSM REMARKS
10yr 3.2592 2 1.2592 830.8123 H=4'; 4 1/2" orfice
100yr 4.6172 2 / 0 2.6/4.6 1715/3035 At H=5', Qo through riser Qi/100yr
3.3-SPILLWAY DESIGN:
a. RISER: DESIGN RISER FOR QQi/100yr. N h=1.5'; Q=3.782*D"2*H; @ D=15" Q= 8.864531 cfs, > Qi/100yr, 15" CMP OK
b. DEWATERING ORIFICE: USE A REENTRANT TUBE TYPE ORFICE, SCH. 40 STEEL, 12" TOE: K=.73, TACK WELDED TO
15'RISER 4.0'BELOW RISER CREST. DESIGN ORIFICE TO DISCHARGE go/10yr EE H=4.0',
Q(gpn)=19.636*K(D""2)*(H".5 ), D = ((1.26*448.8)/(19.636*.73*(4".5))".5 = 4.441286 "; USE 4 1/2" i. d. QRIFICE
PERFORATED POLYETHYLENE DRAINAGE TUBING, COMPLYING WITH ASTM F667 AND AASHN M294, SHALL ATTACH TO
THE ORIFICE WITH A 'FERNCO-STYLE' COUPLING AND EXTEND UPWARD TO THE RISER CREST AND BE SECURED TO THE
RISER WITH ADEQUATE STRAPPING. A POLYETHYLENE CAP SNAIL BE PLACED ON THE TUBE AT THE 10yr DESIGN CREST.
c. BARREL: USE 15" CMP, AS PER COUNTY SPECS. CHECK FLOW: V=1.486/n*R".667*S ".5, R ).3125, S=.02, V= 3.869534
Q=AV=3.1416*1.25"2/4*3.86 =4.736792 > 4.62(Qi&Qo/100yr), 15" CMP @ 5=.02 OK
d. ANTI-VORTEX DEVICE - SEE POND DETAILS IN SECT. C.5 BELOW.
e. ANTI-SEEP COLLAR- 15" BARREL SLOPE = 1.6%, SATUATED L = 30 ft. FROM VS&ECHB,PLATES 1.26k&1,
ONE CM COLLAR, 48'*48", 16ga. SEE, PLATE 1.26m FOR DETAILS.
4.POND DESIGN:
a. DAM: THE DAM SHALL BE CONSTRUCTED NW OF THE NEW ADMIN. BLDG. IN AN AREA WHERE EXISTING TOPOGRAPHY AND SOIL ARE BEST
SUITED FOR CONSTRUCTION. THE APPROXIMATE LOCATION AND ELEVATIONS ARE INDICATED ON DWGS. AM 1 & 3, BUT THE BASELINE. FO
. CONSTRUCTION LAYOUT WILL BE ESTABLISHED AFTER CLEARING AND GRUBBING IN THE INDICATED GENERAL AREA IS COMPLETED.
THE ENGINEER, SOILS ENGINEER, AND CONTRACTOR WILL JOINTLY DETERMINE THE MOST FEASTBLF LOCATION FOR THE C/L OF DAM,
BASED ON THE SOIL, ROCK ETC. ENCOUNTERED WRING THE CLEARING AND GRUBBING OF THE AREA. THE FOLLOWING DESIGN AND/OR
AND/OR CONSTRUCTICN INFORMATICN, HOWEVER, WILL BE ADHERED T0, INCLUDING:DIMENSIONS, VOLUMES, ELEVATION DIFFERENTIALS,
SLOPES, LAYOUT AND ARRANGEMENT OF ACCESSORIES ETC.
- HEIGHT (AFTER COMPACTION/SETTLEMENT OF FILL): U.S.= 8.6'; D.S.(TOP OF DAM TO TOE OF FILL) 10'+/-
- WIDTH OF TOP:=10;'
- SLOPES: DAM=3:1, SIDES=3:1 TO TOP OF DAM, 2:1 TO EXISTING GRADE ABOVE THAT ELEVATION.
- CORE: EXCAVATE TRENCH, 6'-8' WIDE, 70 IMPERVIOUS MATERIAL FROM WATERLINE TO WATERLINE (1'ABOVE RISER CREST)..
b. SPORAGE: BASED ON Qi AND Qo GIVEN IN C.3.2. ABOVE, Qi/10yr STORAGE RFQUIREM NTS ARE AS FOLLOWS:
- DRAINAGE AREA (SUBBASIN IVB)= 0.97 AC.
- SOIL TYPE IS CHESTER LOAM, K= 32-42, HYDRAULIC GROUP = B
- CURVE NUMBER (CN), WEIGHTED AVERAGE = % CN =
, ROOF,PAVING 0.55 98 54
GRASS 0.45 61 27
CN = 81
- RAINFALL DEPTH(SCS PET. 5-10)= 5.5"
- RUNOFF DEPTH(SCS PLT. 5.12)= 3.4"
- Vs/Vr:
Qo/Q=823/2151 (RE: C.3.1 & 2. ABOVE)= .38
Vs/Vr(SCS PLT.5.19, GRAPH B)= 0.36
Vs=0.36*3.4= 1.224 ACRE IN.=1.224*0.97/12= 0.098616 ACRE FT = STORAGE RED. FOR Qi/10yr.
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5. BASED ON THE ABOVE, THE DAM AND SPILLWAY commons WILL CONSIST OF THE FOLLOWING:
Anti Vortex Device per- 10' _y
Top of Dam, 640
_//_//_//_//
Design High Water 638 = 100yr crest
V
Perforated CM top . _ • 6 rebar
Polyethlyne - o c, b w 10'
lyr crest 636.5 cap 24"CMP
Perforated polyethylene ' 15" — — Storage Volume=0.097 3
Drainage Tubing - 6" d car acre ft: ( see C,4.)
NOTE: 1
1.5' Fernco style Tack FILL MATERIAL, INCLUDING CORE, TO BE 1
coupling weld APPROVED BY SOILS ENGINEER, PLACED.
_ IN LAYERS NOT EXCEEDING 6", AND MADE TO I -
IeMatering orifice, ech. _ A DENSITY OF 96t COMPACTION (SEE SPECS).
10 eteel,12"lo¢g,4.5" f ' I
l.d., c/I elev. 632.5EX Inc. 631.4 Anti seep collars
(-/ / / / / / / / / / / / / / / / /
Inv. elev. 630.2 1
631.4 2' 6" ) ` _ 1
30" x 30" x 1/4" ) I Toe, 630 +/- • 4rj
steel plate )
iS" CMP 4_CQRE, EXCAVATE 10 IMPERVIOUS MATERIA
'-— ——1 WATER LINE TO WATERLINE (el 636.5)
POND & DEWATERING SYSTEM DETAILS
NTS
.6 DIVERSION CHANNEL (DV) DESIGN
DIVERSION CHANNELS WILL BE CONSTRUCTED TO CONVEY SUBBASIN NB FLOW INTO THE DEITZETCI POND.
RUNOFF INTO THE CHANNELS WILL BE AS FOLLOWS: Q(WESP DV)=2.74cfs, S=.08'/ft, R=.44, n=.07y A=2.0,
V=1.49/.07*(.44'.667)**9.08'.5) = 3.481898 fps < 4fps OK
Q = AV = 2*3.48 = 6.96 (l0yr runoff), > 100yr runoff, OK
Q(EAST DV)= DESIGN FOR TOTAL IV B RUNNOFF AT LOWER FWD=4.62cfs(
S= .96'/ft, A= 2.0, R=.0.44 ,n=.07,
' V=1.49/.07*.44'.667*.96'.5=3.814229 fps < 4fps OK
Q=2*3.8= 7.6 cfs > 100yr Qi OK
USE SAME CHANNEL CROSS SECTION FOR EAST & WEST DV AS SHOWN ON DWG AM 3, SECT. A-A
.7.STORMWATER CONVEYANCE CHANNEL DOWNSTREAM FROM DETENTION PCND - DESIGN
Q= Qi/100yr. = 4.62cfs, S= .21'/ft., DESIGN TRAPEZOIDAL CHANNEL, .25' DEPTH WITH RIPRAP.
SELFFCP RIPRAP FROM VDH&T PLATE 1.37b, DEPTH = 0.25', S=.21'/ft, 3:1 SIDE SLOPES
RR d =0.55=6.6", SIZE CHANNEL(see cross section below): A=4*.25+(3*.25'2)= 1.1875 ft sq
50
V (Mannings equa.) = 1.49/.30*((1.1875/(4+(2*.25*(10)'.5))".667)*(.21".5) = 8.585076 fps
VOA Qo/100yr) = 4.621/1.1875 = 3.890526 fps OK
I
•._r:a .25'_` I' 3
RR d =0,07= 6.6" T�/0'l Yr�I�I-4r�1
50 / L- 4'
SCC CROSS Sa riON
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C.8.FLARED END SECTION: OUTLET PROTECTION - 15" CMP BARREL
TAILWATIII DEPTH: Qo/100yr= 4.621= 1.49/.03*((4D+30'2)/(4+(2D*(10".5))))".67*(.21'.5)*(4Dt3D'2)
D(tailwater depth)= 0.1634 ft < 1/2 PIPE(BARREL) DIAMETER = MINNI01 TAILw
La _ 1.4
?Caelsoritti;40!NTI We,
1 •••.:�:!i It')
PIPE SIZE 0=00 100YR of. left. W ft. La ft. d ft.
1 2 50
15 4.62 3.75 5.26 10 0.55
9.PERIMETER CONTROL, TEMPORARY.
norm SILT FINNING TO DETAIN SIMENF DURING CCNSTRI)LTICN AS SHOWN CN DWG. AM I.
SYNTHETIC FIBER FOR FENCES SHALL HAVE A FLOW RATE OF 0.3 gal/sq ft/min, AND A TENSILE STRENGTH(
301b./lin..in. MATERIAL SHALL HAVE ULTRAVIOLET RAY INHIBI7ERS AND STABLIZERS TO ENSURE 6 mos. L
FENCING SHALL BE REMOVED AS SOCK AS UPSIDPE AREAS ARE STABLIZED.
.10SEEDING - TEMPORARY (Re: VA. S&E Control HID Spec 1.65):
ALL DISTURBED/EXPOSED AREAS WHICH WILL NOT BE FIRE E GRADED FOR PERIODS OF 30 DAYS, QI IC RE, SHAL
LINE-PULVERTEM AGRICULTURAL 2 tcns/ac
FERTILZER-10-20-20 450 lb/ac
SEED- RYE/Secale cereal 170 lbs/ac
MUICH(wheat or oat straw) 2 tons/ac ( see VA. E&S Control HL1d. Bk. spec 1.75)
SEEDING= PERMANENT ( Re: va. S&E Control RB Spec 1.66) ALL DISTURBED AREAS.
LIME Same as above
FERTILIZER-5-20-10 1000 lbs./ac
SEED- Crown Vetch 20 lb/ac
Perennial Ryegrass 16 lbs/ac
Redtop 2 lbs/ac