HomeMy WebLinkAboutCT 04-16; LA COSTA GREENS NEIGHBORHOOD 1.06 & 1.07; TEMPORARY SEDIMENT BASIN CALCULATIONS; 2005-09-271•
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I HUNSAKER
7&ASSOCIATES 1
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- : SAN DIEGO, INC.
PLANNING -
- ENGINEERING
: SURVEYING
TEMPORARY SEDIMENT
I IRVINE BASIN .CALCULATIONS, LOS ANGELES
- RIVERSIDE for
SAN DIEGO LA COSTA GREENS
I- NEIGHBORHOODS 1.6 &1.7
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City- ofCárlsbad, California
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Prepared for.
Real Estate Collateral Management Company-
do Morrow Development'
1903 Wright Place
I Suite 180 -.
1 Carlsbad, CA 92008
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W.0. 2352-115
I September 27, 2005
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- Hunsaker & Associates
San Diego, Inc.
DAVE HAMMAR Exp. 000106 I
DAN SMITH
VIALPAND CIVI Ra6dond L. Martin, R.C.E.
FCA Vice President.
I RAY MARTIN -
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- :10179Huenn6k6 St.
San Diego, CA 92121
(858) 558-4500 PH
(858) 558-1414 F AN kG H:EPORTSO3211 15 Gens 1.06 .0A03-Basin.d
.&2352-1l5 9/27I20053:14
I'nfo@HunsakerSD.com. I www.HunsakerSD.com
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La Costa Greens - Neighborhoods 1.6 & 1.7'
Temporary Sediment Basin Calculations
Temporary Sediment Basin Design Criteria
Per Part 8 of Section A of the State Water Resources Control Board Order No 99-
08-DWQ, "sediment basins shall, at a minimum, be designed as follows"
Option I - Pursuant to local ordinance for sediment basin design and
maintenance, provided that the design efficiency is as protective or
more protective of water quality than Option 3
OR
Option 2 — Sediment basins, as measured from the bottom of the
basin to the principle outlet, shall have at least capacity equivalent to
3,600 cubic feet of storage per acre draining into the sediment basin.
The length of the basin shall be more than twice the width, of the basin.
The length is determined by measuring the: distance between the inlet
and the outlet; and the depth must not be less than three feet nor
greater than five feet for safety reasons and for maximum efficiency.
OR
Option 3 -,Sediment basins shall be designed using the equation As =
I .2QNs where As is the minimum surface area for trapping soil
particles of a certain size; Vs is the settling velocity of the design
particle size chosen, and Q=CIA where I is the precipitation intensity
for a 10-year, 6-hour rain event and A is the area draining to the
sediment basin in acres. The design particle size shall be the smallest
grain size determined by wet sieve analysis, or the fine silt sized (0.01
mm) particle, and the Vs used shall be 100 percent of the calculated
settling velocity. The length is determined by measuring the distance
between the inlet and the outlet; the length shall be more than twice
the dimension as the width; the depth shall not be less than three feet
nor greater than five feet for safety reasons and for maximum
efficiency. The basins shall be located on the site where it can be
maintained on a year-round basis and shall be maintained on a
schedule to retain the two feet of capacity.
In addition, the text states that a sediment basin shall have a means for dewatering
within 7-calender days following a storm event. The outflow from a sediment basin
that discharged intoa natural drainage shall be provided with outlet protection to
prevent erosion and scour of the embankment channel.
AH ah H:\REP0R1S123521115 Greens 1.08 & l.07A03.0asjndoc
WOO 2352.115 9/27/2005 2:32 PM
I
La Costa Greens — Neighborhoods 1.6 A. 1.7
Temporary Sediment Basin Calculations
Sample Calculation
For Basin 1: . .
I Step I - Determine the drainage area into the temporary basin (in ft):
I A=.21.44— acre x43560 =933,926—ft 2 1—acre
I Step 2 - Determine the required volume of the basin to hold 1-inch. of rainfall (0.083-
ft), or as stated in Part 8 of Section A of the State Water Resources Control Board
I . Order No. 99-08-DWQ, 3600 cubic feet of storage per acre draining into the
sediment basin, (in ft): .
1 .V)ziQ = 933,926 -ft.2 x0.083 -ft = 77,516—ft3
Step 3 - By trial-and-error determine basin's bottom and top dimensions along with
the volume contained by those dimensions, use 2:1 slope and a basin depth of 5-ft
(all dimensions in feet):
Basin bottom dimensions 191-ft (L) x 74-ft (W)
' Basin top dimensions = 201-ft (L) x 84-ft (W) . .
T=B+2h, where: T=Top
BBottom
height 5-ft
TL =74+(2x5)=84—ft
T=191+(2x5)=201—ft
1
Volume =6,516ft3
ABOfl.OM' =74x191=14,134—ft2
ATOP =84x201= 16,884—ft2
I AA VG = (14,134±16,884)
= 15,509 —ft 2
V=AAVG xh'=1.5,509x5=77,545—ft 3 .
:.V=77,545—ft 3 ~VREQUfD =77,516_ft
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AH aS H:/.REPORTS/2352\I 15 Greens 1.05 & I .O7rA038asln.doc
WOO 2352-115 9/27/2005 2:32 PM
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TEMP
BASIN
ID
AREA
A
(ac)
AREA
A
(ft)
REQUIRED
VOLUME
VR (ft)
REQUIRED
VOLUME
VR (yd 3)(ft)
BASIN BOTTOM BASIN TOP BASIN
DEPTH
(ft)
BASIN
VOLUME
V (ft)
BASIN
VOLUME
V (yd 3)
LENGTH WIDTH
(ft)
LENGTH
ft)
WIDTH
(ft)
1 21.4 933,926 77,516 2,871, 191 74 201 84 5 77 545 2,872
2 77 335,848 27,875 1,032 100 48 110 58 5 27,950 1,035
3 143 620,730 51521 1,908 136 68 146 78 5 51,590 1,911
4 72 313196 25,995 963 96 47 106 57 5 26,385 977
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& ASSOCIATES ..
SAN DIEGO, INC ..
PLANNING 10179 Huennekens Street ..
ENGINEERING San Diego, Ca 92121 .. ...- .
SURVEYING PH(858)558-4500. FX(838)558-1414
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R: \0385\&Eng\Exhibits\Ex 10_ BASIN EXHIBIT.dwg[2086]Sep-26-2005: 15: 53