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Home My WebLink AboutCDP 99-49; ARMY NAVY ACADEMY MASTER PLAN; HYDROLOGY STUDY; 2000-02-20RECEIVED HYDROLOGY STUDY DEC 2 0 2000 CITY OF GARLSBAD HOUSING &REDEVELOPIVIENT DEPARTMENT ARMY NAVY ACADEMY CITY OF CARLSBAD CALIFORNIA DCI ENGINEERING, INC. 5100 E. LA PALMA AVE., STE ANAHEIM, CA 92807 (714) 779-3828 1 1 7 ^—> • > TT'^^ v/ ^ PREPARED UNDER THE SUPERVISION OF: DAVID J. MAC ARTHUR, P.E. R.C.E. 12502, EXP. 3-31-2001 PAGE 1 OF 5 PAGES o I n 1 M / 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 QIO. TO DETERMINE THE RUNOFF GENERATED FROM THIS SITE, CALCULATIONS WERE MADE AND FORMATTED PER THE SAN DIEGO COUNTY HYDROLOGY MANUAL AS FOLLOWS: STORM FREQUENCY 1 0 YR. LAND USE PARKING LOT TOTAL LAND AREA 0.51 AC IMPERVIOUS AREA 0.40 AC SOIL TYPE A ASSUME Tc 10 MIN. I = 2.7"/HR FIG. ll-A-2 COEF. OF RUNOFF (DEVELOPED) 0.85 Q = C X A X I Q(DEVELOPED) = 0.85x0.40x2.7=0.92 CFS Q(UNDEVELOPED) 0.6 x 0.40 x 2.7 =0.65 CFS RUNOFF RETAINED ONSITE = 0.27 CFS ESTIMATED DURATION OF STORM 6 HRS RETAINED QIO = 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. I = 4.2'7HR (FIG B-3) COEF. OF RUNOFF 0.65 (ASSUMED) Q = C X A X I QIOO = 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 QIOO 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 PACIFIC AVENUE AREA = 0.18 ACRES NEW BUl^G DRAINAGE AREA = 0.88 AC RECEIVED NOV 2 7 2000 ENGINEERING DEPARTMENT HYDROLOGY STUDY ARiyiY-NAVY ACADEMY ADDITIONS CITY OF CARLSBAD CALIFORNIA DCI ENGINEERING, INC. 5100 E. LA PALMA AVE., STE 117 ANAHEIM, CA 92807 (714) 779-3828 PREPARED UNDER THE SUPERVISTON OF: DAVID J. MAC ARTHUR, P.E. R.C.E. 12502, SXP. 3-31-2001 PAGE 1 OF 6 PAGES DCI ENGINEERING ARMY-NAVY ACADEMY ADDITIONS PAGE 2 OF 6 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 QIO. THE SIZE IS A LITTLE LARGER THAN SHOWN ON THE SITE PLAN .«\ND WOULD BB ABOUT 6 FEET DEEP. TO DETERMINE THE RUNOFF GENERATED FROM THIS SITE, CALCULATIONS WERE MADE AND FORMATTED PSR THE ORANGE COUNTY HYDROLOGY MANUAL AS FOLLOWS: STORM FREQUENCY 10 YR. LAND USS PARKING LOT IMPERVIOUS AREA 0.40 AC ASSUME Tc 10 MIN. 1 = 2.7'7HR (FIG. B-3) COEF. OF RUNOFF (DEVELOPED) 0.85 Q = C X A X I Q(DEVELGPED) = 0.85x0.40x2.7=0.92 CFS Q(UNDEVELOPED) 0.6 x 0.40 x 2.7 =0.65 CFS RUNOFF RETAINED ONSITE = 0.27 CFS REFER TO HYDROGRAPH (SHAPE PER ORANGE COUNTY HYDROLOGY MANUAL) ESTIMATED DU.RATION OF STORM 5 HRS, RETAINED QIO - 0.27 CPS ESTIMATED AREA OF RETENTION BASIN = 3100 S.F. AND AVERAGE DEPTH OF 6', VOLUME = "8,600 CUBIC FEET. THE SECOND LOCATION IS A 5600 S.F.BUILDING ON A 45,000 S.F. SITE FRONTING ON PACIFIC AVENUE. P.OGE 3 OF 6 PAGES THE REQUIRE Q FOR THIS SITE IS BASED ON A 100 YEAR STORM. USING THE SAME GRAPHS, 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. I 4.2"/HR (FIG B-3) COEF. OF RUNOFF 0.65 (ASSUMED) Q = C X A X I QIOO = 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 QIOO 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 1'/SEC, Regtessic.i Equations: Ht)" at (X« Intensity ir. inches/hour, t« duration in minutes] Return Frequency <years). 2 5.702 -0.574 5 7.370 -0.562 10 10.209 -0.S73 25 11.995 -0.S66 SO 13,521 -0.566 100 15.560 -0.573 30 60 100 ISO 360 PRECIPITATION DURATION (MIN) 100 YH !S TH 5 v« 1440 ORANGE COUNTY HYDROLOGY MANUAL B-7 MEAN PRECIPITATION iNTENSITIES FOR NONMOUNTAINOUS AREAS „ Figuf* 8-3 0.50- ARMY NAVY ACADEMY ADDITIONS CARLSBAD, CALIFORNIA HYDROGRAPH PER ORANGE COUNTY HYDROLOGY MAMUAL 10 Y EAR FREQUENCY STORM AVERlAGE IN FLOW OVER 5 .HR. jPER TOTA. INFLOW OVER AVERAGE DEPTH OF vS s- 0 at OD = 0.10 CFS A 5 HR, ptRldD - 18,600 CF RETENTION BASIN = 6.0 FT. TIME IN HOURS HYDROLOGY MAP ARMY^NAVY ACADEMY CARLSBAD. CALIFORNIA PACIFIC AVENUE AREA =^ O.ia ACRES UEU HUll.DlMG AREA = 0.88 AC VP V cfc