HomeMy WebLinkAbout; Sediment Basin Calculations for La Costa Greens; Temporary Sediment Basin Calculations for La Costa Greens; 2003-11-10HUNSAKER
^ASSOCIATES
SAN DIECO, INC.
PLANNING
ENGINEERING
SURVEYING
IRVINE
LOS ANGELES
RIVERSIDE
SAN DIEGO
TEMPORARY SEDIMENT
BASIN CALCULATIONS
for
LA COSTA GREENS
City of Carlsbad, California
Prepared for:
Real Estate Collateral Management Company
c/o Morrow Development
1903 Wright Place
Suite 180
Carlsbad, CA 92008
W.O. 2352-66
November 10, 2003
DAVE HAMMAR
LEX WILLIMAN
ALISA VIALPANDO
10179 Huennekens St.
San Diego, CA 92121
(858) 558-4500 PH
(858)558-1414 FX
www.HunsakerSD.com
lnfo@HunsakerSD.com
Rdyfiiond L. Martin, R.C.E.
Project Manager
Hunsaker & Associates San Diego, Inc.
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TABLE OF CONTENTS
CHAPTER
Temporaiy Sediment Basin Design Criteria i
Temporary Sediment Basin Table II
Sample Calculation III
Basin Exhibit IV
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CHAPTER 1
TEMPOiRARY SEDIMENT
BASIN DESIGN CRITERIA
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Temporarv Sediment Basin Desiqn 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 1 - 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 ofthe 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 = 1.2QA/s 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 into a natural drainage shall be provided with
outlet protection to prevent erosion and scour of the embankment channel.
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CHAPTER 2
TEMPORARY SEDIMENT
BASIN TABLE
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CHAPTER 3
SAMPLE CALCULATION
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Sample Calculation
For Basin 1:
Step 1 - Detemnine the drainage area into the temporary basin (in sq. ft.):
A = 9.\- acrex ^'^^^^'fi^ = 396,396 - ft^
1 - acre
Step 2 - Determine the required volume ofthe basin to hold 1-inch of rainfall, or
as stated in Part 8 of Section A of the State Water Resources Control Board
Order No. 99-08-DWQ, 3600 cubic feet of storage per acre draining into the
sediment basin, (in ft):
VREQUIRED = 396,396 -ft'x 0.083 -ft = 33,033 - ft'
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 6-ft (all dimensions in feet):
Basin bottom dimensions = 82-ft x 57-ft
Basin top dimensions = 94-ft x 69-ft
T = B + 2h, where: T = Top
B = Bottom
h = height = 6-ft
r = 82-K(2x6) = 94-/f
r = 57-^(2x6) = 69-/f
Volume = 33480 ft^
2
2
^BOTTOM =82x57 = 4,674-/?
ATOP = 94 X 69 = 6,486 -/?
V = A^y(. xh = 5580 X 6 = 33,480 - ft
-.3
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V = 33,480 - ft' > V^Q^j^ = 33,033 - ft'
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IV
CHAPTER 4
BASIN EXHIBIT
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