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Home My WebLink AboutCDP 00-62; Hamilton Residence; Hydrology Study;HYDROLOGY STUDY 8 AUGUST 2001 CITY PROJECT # HAMILTON RESIDENCE CITY OF CARLSBAD Introduction This report was prepared to analyze the difFerence in the storm water discharge generated by the pre developed, and a post developed state, lot ( 2335 Pio Pico Drive APN 156-350-11, City ofCarlsbad . (see Vicinity Map) In addition, we will determine the volume of storm water to be detained onsite, while discharge to the street is controlled by pipe diameter, so as not to exceed the pre- developed storm water discharge from the lot. Discussion The following analysis was performed in conjunction with the San Diego Coimty Hydrology Manual (SDCHM). Unless otherwise indicated all calculation worksheets are from the appendices ofthe SDCHM. To accurately calculate the flow generated by the proposed development ofthis lot. The drainage area is split into 3 sub-areas: AREA "A"; "B" & "C"( EXHIBIT 1) ' Tc's. of 12 minutes was used. ( EXHIBrr H) To calculated average precipitation intensity for this lot -10 year frequency storm, 6 hour & 24 hour duration precipitation maps (EXHIBIT IV & EXHTOIT V ) were utilized. Average Intensity = 2.4 in/hr ( EXHIBIT HI) Soil type: U.S. Dept. of Agriculture soil survey maps were used. This lot is in an area marked MIC, which is a Type A soil. - ( EXHIBIT'S VI and VH ) The rational method (Q=CIA) is used to calculate the flow generated for each respective sub-area. Runoflf values for each sub-area are listed below: Sub-area pre-developed post- developed runoflf coeflHcient (0.3) runoflr coefficient (0.4) Area "A" (0.13 acres) Q = 0.09ftVs Q = 0 12ft^/s Area"B" (0.05 acres) Q = 0.04ft^/s Q = 0.04ft^/s Area"C" (0.02 acres) Q = 0.01ft'/s Q = 001ft'/s TOTAL Q = 0.14ftVs Q = 0.17ft^/s The runoff has increased by 0.03 ft^/s in the developed state. ( EXHEBIT XI) Indicates the runoff coefificients used in the rational method calculation. (EXHIBIT vm and EXHIBIT IX ) graphically indicate the peak "runofD'controlled outflow," for Area "A" and Area "B". The Manning Formula was used to verify that a 3" dia pipe is capable of conveying 0.09 ft7s @ a gradient of 1%. We have calculated the maximum volume of storm water to be detained on the lot is 7.3 ft^, while the flow is discharged in a controlled outlet situation from the lot, which does not exceed the pre-developed situation. Area "A'' ( developed situation ) Maximum incoming flow = 0.12 ft^/s Discharge: 1 x 3" dia pipe = 0.09 ftVs As calculated and indicated on Exhibit Vm, a storage capacity of 7.3 ft^ is required to attenuate the outflow from the lot. We will indicate that the current grading design has the capacity to accommodate the volume of storm water which is to be detained. The area shown hatched in AREA "A"on ( EXHIBIT I) is capable of accommodating a volume of 31.9 ft^ (calculated by average end areas). (EXHIBIT X ) Therefore the required volume can be accommodated within AREA "A" Area "B" ( developed situation ^ Maximum incoming flow = 0.04 ftVs Discharge: 1 x 3" dia pipe = 0.04 ft^/s ( pipe is capable of accommodating 0.09 ft^/s ) Therefore no storm water detention is required within AREA "B" Area "C' This area remains unchanged by the development ofthis lot, which drains, as before, directly to the street. Conclusion: The pre-developed outflow was calculated as 0.14 ft\ so the developed drainage discharge cannot exceed this figure. The 0.03 ft /s ( or 7.3 ft^) difference between pre and post developed situations, will be detained on the lot, and the discharge vnll be controlled by limiting the pipe diameter as indicated in the summary below: Discharge from area "A" is via a 3" dia pipe Q = 0.09 ft^/s Discharge from area "B" is via a 3" dia pipe Q = 0.04 ftVs (approach flow is 0.04 ftVs ) Discharge from area "C" is unchanged Q = 0.01 ft^/s Total discharge - developed situation Q = 0.14 ft^/s We have determined that the developed drainage discharge will be not exceed the pre- developed situation, as per the proposed grading plan. X HVDHOUOGV PLAN SAN DIEGO COUNTY DEPARTMENTOF SPECIAL DISTRICT SERVICES APPROVED DESIGN MANUAL URBAN AREAS OVERLAND TIME OF FLOW CURVES DATE APPENDIX X-C INTENSriy-DUKATIO. .tSIGH CHART Directions for Application: 1) From precipitation naps determine 6 hr. and 24 hr. amounts for the selected frequencv. These maps are printed in the County Hydroloay Manual (10, 50 and 100 yr. maps included in the Design and Procedure Manual). 2) Adjust 6 hr. precipitation (if necessary) so that it is within the range of 45% to 65% of the 24 hr. precipitation. (Not applicable to Desert) 3) Plot 6 hr. precipitation on the right side of the chart. 4) Draw a line through the point parallel to the plotted lines. 5) This line is the intensity-duration curve for the location being analyzed. Application Form: 0) Selected Frequency \0 yr. 24 2) Adjusted *Pg= 1.Co 24 in. min. 3) t, = /2.0 4) I = 2'4-ln/hr. *Not Applicable to Desert Region APPCNDIX XI IV-A-14 Rc i scd 1/85 Fl X COUNTY OF SAN DIEGO DEPARTMENT OF SANITATION & FLOOD CONTROL 10-YEAR PREGIPlTATIOfJ 33" cr IS-: iSSPLUl'IALS OF 10-YE/5.R G-|l3Un ,PRE(;iHTpiOij IN ™ fifj IHCH ECIAL STUDIES DRANCH. OFFICE i NATioKA^Jor?^^^'^™'^'^'^ COMMERCE T OCEANIC A.ND AT 30' 2020 18- 116' COUNTY OF SAN DIEGO Jf^^J^'-'ENT OF SANITATION S- FLOOD CONTROL 5* 10-YEAR 24-HOuk PRECiPiTATIOf^ 20-/-ISOPLUVIALS PRECIPiTATIOiJ IfJ IF 10-YEAR 24-HOUR ENTHS OF Afl KICH m ' 33* Prep.jied by U.S. DEPARTMEr T OF COMMERCE nmJ™'' ^•'h'^'''"-:'"^- ADMINISTRATION SPECIAL STUDIES DRANCII. OKFICE OK I o 30' TABLE 11.---INTERPRETATIONS FOR LAND MANAGEMENT--Continued Map symbol Soil Hydro- logic group Erodibility Limitations for conversion from brush to grass LfE LpB LpC LpC2 LpD2 LpE2 LrE LrE 2 LrG LsE LsF Lu LvF3 Md MIC MIE MnA MnB MoA MpA2 MrG MvA MvC MvD MxA OhC OhE OhF OkC OkE PeA PeC PeC2 PeD2 PfA PfC Py Las Flores-Urban land complex, 9 to 30 percent slopes: Las Flores Urban land Las Posas fine sandy loam, 2 to 5 percent slopes to 9 percent slopes-- to 9 percent slopes. to 30 percent to 30 percent Las Posas fine sandy loam. Las Posas fine sandy loam, eroded. Las Posas fine sandy loam, 9 to 15 percent slopes, eroded. Las Posas fine sandy loam, 15 to 30 percent slopes, eroded. Las Posas stony fine sandy loam, slopes. Las Posas stony fine sandy loam, slopes, eroded. Las Posas stony fine sandy loam, 30 to 65 percent slopes. Linne clay loam, 9 to 30 percent slopes Linne clay loam, 30 to 50 percent slopes Loamy alluvial land Loamy alluvial land-Huerhuero complex, 9 to 50 percent slopes, severely eroded: Loamy alluvial land Huerhuero Made land Marina loamy coarse sand, 2 to 9 percent slopes Marina loamy coarse sand, 9 to 30 percent slopes Mecca coarse sandy loam, 0 to 2 percent slopes Mecca coarse sandy loam, 2 to 5 percent slopes Mecca sandy loam, saline, 0 to 2 percent slopes Mecca fine sandy loam, 0 to 2 percent slopes, eroded— Metamorphic roclc land Mottsville loamy coarse sand, 0 to 2 percent slopes Mottsville loamy coarse sand, 2 to 9 percent slopes Mottsville loamy coarse sand, 9 to 15 percent slopes — Mottsville loamy coarse sand, wet, 0 to 2 percent slopes. Olivenhain cobbly loam, 2 to 9 percent slopes -- Olivenhain cobbly loam, 9 to 30 percent slopes Olivenhain cobbly loam, 30 to 50 percent slopes Olivenhain-Urban land complex, 2 to 9 percent slopes: Olivenhain Urban land Olivenhain-Urban land complex, 9 to 30 percent slopes: Olivenhain Urban land Placentia sandy loam, 0 to 2 percent slopes Placentia sandy loam, 2 to 9 percent slopes Placentia ssmdy loam, 5 to 9 percent slopes, eroded Placentia sandy loam, 9 to 15 percent slopes, eroded— Placentia sandy loam, thick surface, 0 to 2 percent slopes. Placentia sandy loam, thick surface, 2 to 9 percent slopes. Playas D D D •D D D D D D D C C B D <S> A B B B B D A A A D D D D D D D D D D D D D Moderate 2- Moderate 2- Moderate 2- Moderate 2- Moderate 1- Moderate 1- Moderate 1- Severe 1— Moderate 2- Severe 1— Severe 16— Severe 1 — Severe 1— Severe 2— Severe 2— Severe 16 Severe 16 Severe 16 Severe 16 Severe 1— Severe 2— Severe 2— Severe 2— Severe 2 Severe 16— Severe 16~ Severe 1— Severe 9— Severe 9— Severe 9— Severe 9— Severe 16-- Severe 16— Moderate 2 Slight. Slight. Slight. Slight. Slight. Moderate. Moderate. Moderate. Moderate. Moderate. Slight. Severe. Severe. Slight. Slight. Severe. Slight. 4/ Slight. 4/ Slight. 4/ Slight. 4/ Slight. Slight. Moderate. Slight. Slight. Slight. Slight. Slight. Slight. See footnotes at end of table. 36 O. 2D,. + 4- Area. "A -5 rn ^ X cr 0,20.. O,o£. o Ik C5 ^or -VU, 5^ht4 Post l)e\Kj|op20l •for Ai-^'a ' ^> Ho l^eleiA-Vfoi^ l^ii^Trecj/A?/~/}»^'^B'^ A L 0,25- 6 ect i IQ.S Rres. c 1,3 •Ct'^ ±i3 X 22' "jAilM TABLE 2 RUNOFF COEFFICIENTS (RATIONAL METHOD) DEVELOPED AREAS (URBAN) Land Use Coefficient, C Soi1 Group"(1) Residential: Single Family A B .45 C .50 D .55 Muiti-Uni ts M .50 .60 .70 Mob i1e homes .50 .55 .65 Rural (lots greater than 1/2 acre) .35 .40 .45 Commerci al(2) SO^i Impervious .70 .75 .80 .85 Industriai (2) 90% Impervious .80 .85 .90 .95 NOTES: ^'^Soil Group inar)S are available at the offices of the Department of Public Works. (2)where actual conditions deviate significantly from the tabulated impervious- ness yaluesof 80% or 90%. the values given for coefficient C. may be revised by multiplying 80% or 90% by the ratio of actual imperviousness to the tabulated imperviousness. However, in no case shall the final coefficient be less than O.50. For example: Consider commercial property on D soiI.group. Actual imperviousness = 50% Tabulated imperviousness = 80% Revised C =50 ^ 0.85 = 0,53 80 APPENDIX I X-B Rev. 5/81