HomeMy WebLinkAboutCDP 99-49; Army and Navy Academy; Hydrology Study;HYDROLOGY STUDY
ARMY-NAVY ACADEMY ADDITIONS
CITY OF CARLSBAD
CALIFORNIA
DCi ENGINEERING, INC.
5100 E. LA PALMA AVENUE
SUITE 117
ANAHEIM, CALIFORNIA 92807
714.779.3828
PREPARED UNDER THE SYUPERVISION OF:
DAVID J. MACARTHUR, P.E.
R.C.E. 12502, EXP. 3-31-2001
PAGE 1 OF 5 PAGES
DCI ENGINEERING
ARMY-NAVY ACADEMY ADDITIONS
PAGE 2 OF 5 PAGES
DISCUSSION
THE EXISTING SITE CONSISTS OF TWO SEPARATE AREAS THAT ARE
PART OF A LARGER EXISTING DEVELOPMENT. THE FIRST AREA IS A
PARKING LOT AND RETENTION BASIN. THIS PARKING LOT HAS A LARGE
AMOUNT OF LANDSCAPING THAT HAS BEEN FACTORED INTO THE RUNOFF
CALCULATIONS. THE RETENTION BASIN HAS BEEN SIZED TO HOLD THE
DIFFERENCE IN RUNOFF VOLUME BETWEEN THE DEVELOPED AND UNDEVELOPED
Q1 0.
TO DETERMINE THE RUNOFF GENERATED FROM THIS SITE, CALCULATIONS
WERE MADE AND FORMATTED PER THE SAN DIEGO COUNTY HYDROLOGY MANUAL
AS FOLLOWS:
STORM FREQUENCY
LAND USE
TOTAL LAND AREA
IMPERVIOUS AREA
SOIL
ASSUME Tc
I = 2.7'7HR
COEF. OF RUNOFF (DEVELOPED)
Q =
Q(DEVELOPED) =
Q{UNDEVELOPED)
10 YR.
PARKING LOT
0.51 AC
0.40 AC
TYPE A
10 MIN.
FIG. ll-A-2
0.85
C X A X I
0.85 X 0.40 X 2.7 = 0.92 CFS
0.6 X 0.40 X 2.7 =0.65 CFS
0.27 CFS RUNOFF RETAINED ONSITE =
ESTIMATED DURATION OF STORM 6 HRS
RETAINED Q10 = 0.27 CFS (3600 x 6hr) = 5832 CF
ESTIMATED AREA OF RETENTION BASIN = 2186 S.F. AND AVERAGE DEPTH
OF 3', VOLUME = 5880 CUBIC FEET.
PAGE 3 OF 5 PAGES
THE SECOND LOCATION IS A 6600 S.F.BUILDING ON A 45,000 S.F. SITE
FRONTING ON PACIFIC AVENUE.
THE REQUIRED Q FOR THIS SITE IS BASED ON A 100 YEAR STORM. USING
THE GRAPH (11-A-7), A 100 YEAR STORM WILL GENERATE ABOUT 4.2'7HR.
STORM FREQUENCY 100 YR
LAND USE SCHOOL
IMPERVIOUS AREA 15% (TOTAL AREA =1.03 AC)
ASSUME Tc 10 MIN.
1 = 4.2"/HR (FIG B-3)
COEF. OF RUNOFF 0.65 (ASSUMED)
2 ^ C X A x I
= 0.65 X 1.03 X 4.2 = 2.8 CFS
ASSUME 15% DRAINS FROM BUILDING INTO AN EARTH SWALE =0.28 CFS
THE REMAINING Q100 COLLECTS AT THE SOUTH EAST CORNER OF THE
BUILDING AND IS CARRIED TO A SIDEWALK CULVERT FOR A COMBINED FLOW
INTO THE STREET OF 2.8 CFS. A 4' WIDE CULVERT WOULD RESULT IN A
VELOCITY OF LESS THAN I'/SEC.
HYDROLOGY MAP
ARMY=NAVY ACADEMY
CARLSBAD, CALIFORNIA