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Home My WebLink AboutCT 75-04; Acuna Ct; Hydrology Study; 1989-05-03AND DRAINAQE REPORT HYDROLWY STUDY FOR LOT 91 OF MAP 8302 IN THE CITY OF CARLSBAD - ". PE 2.89.31 PREPARED FORI ROBERT DAVIS CARLSBAD, CALIFORNIA 92009 7014 LLAMA STREET ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive Carlsbad, CA 92009-4859 VILLAGE ENQINEERINQ CORP. PREPARED BY I 1466 PIONEER WAY, EL CAJON, CA (619) 588-8559 (619) 447-4747 w May 3, 1989 W.O. 89042 July 11, 1989 Robert Davis 7014 Llama Street Carlsbad, California 92009 Subject: Hydrology and Drainage Report for a Proposed Single Family Residence, Lot 91, Tract 75-4, Map 8302, Carlsbad, California. Reference: Hydrology and drainage Report by Village Engineering Corp. Dateed April 19, 1989. PE 2.89.31 Gentlemen: We are pleased to present the results of our Hydrology and Drainage report for the subject project. This study was performed in accordance with your request and our proposal dated April 27, 1989. The results of our field investigation and review of the are present.ed in the accompanying report. - Architectural Plans well as our conclusions and recommendations, - We appreciate this opportunity to be of professional service. If you have any questions, you are welcome to contact this office at your convenience. - Respectfully Submitted, Village Engineering Corp. Project Designer - Sirous T. Kermani, REC 28306 Project Engineer TABLE OF CONTENTS Page Introduction and Project Description ....................... 1 Purpose and Scope of Project .............................. 1 Findings ................................................... 1 Site Description ....................................... 1 Conclusions and Recommendations ............................ 2 ATTACHMENTS Exhibit 1 Exhibit 2 Vicinity Map Hydrology Calculations Exhibit 2 Hydrology Calculations Exhibit 2a Gutter & Roadway Discharge -Velocity Chart Exhibit 3 100 Year 24 hr. Precipitation Exhibit 4 Exhibit 5 100 Year 6 hr. Precipitation Site Configuration, Brow ditch, Sewer esmt. On Site Conditions Offsite Conditions A. B. C. APPENDIX Rational Formula Watershed less than 0.5 square miles. Site Photo’s 1. Existing Brow Ditch. 2. Existing Sidewalk under Drain. 3. Existing Site Conditions. Basin Map for Offsite Area. HYDROLOGY AND DRAINAGE REPORT SINGLE FAMILY RESIDENCE FOR PROPOSED LOT 91, TRACT 75-4, MAP 8302 CARLSBAD. CALIFORNIA - INTRODUCTION This report presents the results of our Hydrology and Drainage rqqtrt. far *.he muktjpct..ait.e. The vicinit.y map far t.A%a prollaat T? pFRGW#(Rt# RR *b&h&k #wnl?+W 1, P;rLLhlt Wumber 5 ahms tha To assist in the preparation of this report, we were provided site conflguration and the locations of existing Brow Ditch. with preliminary plans that were prepared by Mark Radford, project architect. PROJECT DESCRIPTION This project is located on the north end of Acuna Court, Rancho La Costa, County of San Diego, California. Development of this site is proposed to consist of constructing a single story, wood frame home with raised floors and slab-on- grade construction. PURPOSE AND SCOPE OF PROJECT The purpose of this report is to develop information regarding the on-site Hydrology condition to determine the flow and drainage conditions to receive the proposed development. The scope of this study includes the following: A.) Site Visit B.) Reviewing the recommendations made by Ketchum Engineering C.) Reviewing the Architectural Plans for a Single Family Inc . , Soils Engineer. Resident. FIELD INVESTIGATION consisted of visual observations of the existing surface Our field investigation was conducted on April 19, 1989, and conditions of the on-site and off-site. CONCLUSIONS AND RECOMMENDATIONS The finding of the Hydrology report are as follows; The site is apart of a major subdivision in the City of Carlsbad, Map No. 8302, of Tract Map 75-4, produced by Rick Engineering, tract name, “La Costa Estates North”. The site is a rectangular shaped parcel that is located on the northwest end of Acuna Court. Drainage on-site is by sheet flow towards the north and northwest. The site slopes gently downward from Acuna Court. A A 15 foot sewer easement is parallel to the west property line sparse covering of the native grasses and shrubs cover the site. and a 20 sewer easement also parallels the northern property line. The surrounding hillside has been changed by the developer to construct t.he required public impr0vement.s and lots, in doing goI the watershed direction has changed and eliminated the major off site flows from coming onto the site. The water that does come that enter the existing home sites and vacant lots, 93 through down the hill travels over the natural ground and graded areas 95, than enters Acuna Court, and flows Northwest to the end of the cul-de-sac, the existing sidewalk 6 inches, can maintain the flow due to the depth of the Q, is equal to 0.3 with the Velocity of 4.8 f.p.s. and the combined Q=5.06 c.f.8.. There the water enters an existing sidewalk under drain and travels along a concrete brow ditch between lots 90 and 91 on lot 90 (see site photo’s) and is permitted to sheet flow into lot 114. The conclusion in the existing site is .54 AC. in size and is located at the northwest end of Acuna Court facing the pacific area sheet flows in a natural fashion onto lot 114. Therefore, ocean. The drainage area is .34 AC. in size and the remaining the lot will have the water drain into the existing brow ditch by both means of a swale and site area drains. The grading plan down spouts, and swale, as for the swale draining into the brow shows the locations and sizes of the catch basin, drain pipes ditch refer to the landscape plan per building plans, The Recommendations for the site follows the strict guide lines of the soils engineer. Exhibit 2 !uDBaoaLcALcuLmQm . "___ ON SITE CPNDITIONS Project 2607 MCUNA Cou WO# 8W4t Date 5-I-e Calc: 4s Date: S-/-CLCHKD %- Date 7-/I-- SHT./-ofA-SHTS. LOT ________ 41 MAP 830 'TRACT MAP 75-4 AREA PC3 P x - ( /O SCALE) = 034 ACRES STORM FREQUENCY /OO years, DURATION 24- hr. RUNOFF COEFFICIENTS (RATIONAL METHOD) Q=CIA - Developed Areas Percentages : Land Use ""_ /a0 Single Family "" Multi-Units " Rural (Lots > .5 AC) -__ Commercial (2) _" Mobil Homes 80 % Impervious 90 % Impervious "" Industrial (2) (S.D. County,IV-A-9, APPENDIX .40 A Coefficienu Soil Group (1) - B .45 .50 c & - .45 .50 -60 .70 .45 .50 -30 .35 9 55 .65 .70 .40 -75 .45 .80 .85 -80 .85 .90 .95 IX-B) c = JS , ACRES X C = CA = * /870 Time of Concentration "_____ Tc (see drainage basin area) L.U.03 miles Hi .Pt , 364" , Lo.Pt. 35.3 , bH. // ' , L. f65 ' , S..U667 SAN DIEGO COUNTY NATURAL WATER SHED *Tc=(11.9 (L-3)) .385 X 60 = + 10 minutes = Tc= minutes + 3/5 minutes disturbed basin Tc= Time in Hours, L = Distance in Miles or Percentage of a mile, H = Height in feet (S.D. County, IV-A-10, APPENDIX X-A) C = Coefficient, S = Slope - URBAN WATER SHED PER CITY OF CARLSBAD ( H ) *Tc=l.8 (1.1 -C)L"1/2 .385 X 60 = 2, 10 (S x 100) "1/3 + 10 minutes = To= -8- minutes (or) st0 +a or 5 minutes disturbed basin. INTENSITY 1~7.44 X (P6orP24) X DA-.645 I= L.sP (6 I = Intensity (iri/hr,) 100 yr. P=6 hr, or 24 hr. Precipitation (ii.) 6 D=Duration (min .) 24 hr.) I= /0-@(24 hr.) hr , 2*5-incheslOOyr. hr .rQ incheslOOyr , 100 yr. P 6hr .= z*f in., P 24hr .=*in., P6/P24= &3 % < 65% Q = C x I x A, Q _FS$- X -6.ze x a39 J Q = -d:&-- C sf.8. Q=CxIxA, Q= J5 x- /O,w x "-9 ,J4 Q = c.f.s. Runoff: Q = I x CA Altitude Factor = /e u Q Q 100 100 = /.a factor factor = /. 0 """ x 6.50 6 X &&??2 4 Intensity Intensity "/hr . "/hr . CA .. /87u x "" USE Q USE Q 6hr 100 24hr 100 c.f.s. c.f.s. C.f.S. C.f.8. Referencer San Diego County Flood Control Hydrology Manual, January 1985 (1) Soil group maps are available at the offices of the Dept. of Public Works (2) Where actual conditions deviate significantly from the tabulated imperviousness values of 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 caee shall the final coefficient be less than 0.50, for example: Consider commercial on D soil group Actual imperv. = SO%, Tabulated imperv. = EO%, Revised C = 50/80 x 0.85 = 0.53 Exhibit 2 _""" HYDROLOGY CALCULATIONS OFESITE-CONDITIONS """ Developed Areas Land Use cseffieientL-c Soil Group (1) Percentages : A I! c !? .40 .45 .50 .55 .70 .65 .45 .80 .85 Single Family ""_ "_" Multi-Units .45 .50 .60 ""_ Mobil Homes .45 .so * 55 ""_ Rural (Lots > .5 AC) .30 .35 .40 ""_ Commercial (2) .70 * 75 80 % Impervious 90 % Impervious " /@&- Industrial (2) .80 .85 .90 & (S.D. County,IV-A-9, APPENDIX IX-B) c = "LE", ACRES X C = CA = 0.27 """""""""""""""""~ SAN DIEGO COUNTY NATURAL WATER SHED *Tc=(11.9 (LA3))A. 385 X 60 = + 10 minutes = Tc= 8- minutes ( H 1 " e--+ 3/5 minutes disturbed basin Tc= Time in Hours, L = Distance in Miles or Percentage of a mile, H = Height in feet (S.D. County, IV-A-10, APPENDIX X-A) C = Coefficient, S = Slope URBAN WATER SHED PER CITY OF CARLSBAD "_""""""" .Of1 0.27 ,3 *Tc=1.8 (1.1 -c,LL^1/2 .385 X 60 =340f (S x 100) ^1/3 """ 0, 'kr 1 / 0.IC / + 10 minutes = TC= minutes (or) 8.05 + 3 or @minutes disturbed basin. . -. HYDROLOGY .- ." -. -. . . " CALCULATIONS -. - - -. . . . "_ " OFF SITE ". "" CONDITIONS - - "" Hm.3 '* " """"_ INTENSITY I=7.44 X (P6orP24) X D^-.645 I= (6 hr.) I= 7,7S4(24 hr.) r7, 7 (.I' I = Intensity (in/hr.) 100 yr. ~ 100 yr. P=6 hr. or 21 hr. Precipitation (ik.1 6 hr.-Z,r inci1es100yr. ' D=Duration (min.) 24 hr, ?,-i"inchesl00yrf Q 100 Q 100 = 10 factor factor - 1"- USE 9 USE Q 6hr 100 24hr 100 c.f.s. C.f.8. c.f.s. c.f.s. Reference : San Diego County Flood Control Hydrology Manual, January 1985 (1) Soil group maps are available at the offices of the Deet. of Public Works (2) Where actual conditions deviate significantly from the tabulated imperviousness values of 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 0.50, for example; Consider commercial on D soil group - Actual imperv. = 50%, Tabulated imperv. = 80%, - Revised C = 50/80 x 0.85 = 0.53 Exhibit 2 HYDROLOQY """_" CALCULATIONS "_ """ QFF-SrrTE-cQNDlTIQNs RVNQEF_C_oEEEICIENTs-~~A_~IQ~~~-~E~~Q~~ Q=CIA ""__ Developsd-Ageqg """""-I" Coefficient C Land Use Soil Group (1) Percentages : A_ B Single Family .40 - c D Multi-Units .45 .50 .55 ""_ .45 .so .60 .70 Mobil Homes Rural (Lots > .5 AC) -45 .50 .55 .65 ""_ .30 .35 .40 .45 Commercial (2) ""_ .70 .75 .80 80 % Impervious -85 ""_ /OU Industrial (2) -80 .85 .90 90 % Impervious (S.D. County,IV-A-9, APPENDIX IX-B) c = "._""_, 95 ""_ ""_ cbs') ACRES X C = CA = 0.3 L """"""""_""""""""" SAN DIEGO COUNTY NATURAL WATER SHED *Tc=(11.9 (L"311A.385 X 60 = -4 + 10 minutes = Tc= -e minutes ( H 1 _e--+ 3/5 minutes disturbed basin Tc= Time in Hours, L = Distance in Miles or Percentage of a mile, 11 = Height in feet (S.D. County, IV-A-10, APPENDIX X-A) C = Coefficient, S = Slope URBAN WATER SHED PER CITY OF CARLSBAD *Tc=l.8 (1.1 -QL.:YlL2 .385 X 60 = 3.0< ,081 0.7'7 .3 (S x 100) ^1/3 4. 10 minutes = Tc= 0. c?04/ (1. I b -6 minutes (or) 8*05-+ 3 or Qminutes disturbed basin. a ""_"" INTENSITY I=7.44 X (P6orP24) X D^-.645 I= yag (6 hr.) I= 7,7$(24 hr.) 7 (3''' I = Intensitv (in/hr.) 100 vr. - 100 yr. P=6 hr. or 22 hr. Precipitation (ik.1 6 hr. 5 -incheslOOyr. D=Durat ion (min.) 24 hr.- ?? 0 incheslOOyr . P 6hr.=Z,< in., P 24hr.=-6-c-in., P6/P24=--@"% < 65% Q = C x I x A, Q = , ?< x -41.- x 0.33 : Q = /a< c.f .s. Q = C x 1 x A, Q = -L".-- 6 x _____ 7~75"~ """ a33 # * Q = 2.4 c.f.s. R_unoffL&"-I-x-CA Altitude Factor = //a Q - - """ /f x " 4 L"" $ 6 "/hr. /of3 C.f.S. Q 100 fact r In en 'ty 100 factor Intensity = """ /I B x 3.7" 24 "/hr. CA = 2,48 c.f.s. x _QL3"%" = USE Q = /#S@ C.f.8. USE Q = 2,50 C.f.8. 6hr 100 24hr 100 Reference: San Diego County Flood Control Hydrology Manual, January 1985 (1) Soil group maps are available at the offices of the Dept. of Public Works (2) Where actual conditions deviate significantly from the tabulated imperviousness values of 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 0.50, for exampler Consider commercial on D Soil group Actual imperv. = SO%, Revised C = 50/80 x 0.85 = 0.53 Tabulated imperv. = 80%, """ Developed Areas Land Use """_""L" Coefficient C Soil Group (1) Percentages : t! B Single Family .40 - c !2 -"" .45 .50 -55 Mu1 t i-Uni t s Mobil Homes .45 .50 .60 .70 .45 4 50 .55 "-" "_" 106 Rural (Lots > .5 AC) ""_ .30 .35 .40 & ""_ Commercial (2) .70 .75 .80 .85 ""_ Industrial (2) .80 .85 .90 .95 (S.D. County,IV-A-9, APFENDIX IX-B) 80 % Impervious 90 % Impervious c = """"9 . e4 ACRES X C = CA = -[,09 Time of Concentration Tc (see drainage basin area) L.oLL$$- miles Hi .Pt .-3!.kL2" Lo .Pt *-3za-, bH.-fQ "_, L .-2AS-, s .-L/.-ZA% """"""""__""""""""_ SAN DIEGO COUNTY NATURAL WATER SHED *Tc=(11.9 (LA3))A.385 X 60 = a + 10 minutes = Tc= -f, minutes """ ( H ) - e--+ 3/5 minutes disturbed basin Tc= Time in Hours, L = Distance in Miles or Percentage of a mile, i! = Height in feet (S.D. County, IV-A-10, APPENDIX X-A) C = Coefficient, S = Slope basin. minutes = TC= 12 e94minutes (or) 8 + 3 or 5 minutes . HYDROLOGY CALCULATIONS "~ OFF SITE ~ CONDITIONS /9/L@H 'c " ""_"" INTENSITY I=7.44 X (P6orP24) X DA-.645 I= 3.57 (6 hr.) I= g, 71 (24 hr.) ,", I '/IK I = Intensity (in/tlr .) 1UO yr. P=6 hr. or 24 hr. Precipitation (in.) 6 hr. z,( inchss100yr. ' D=Duration (min.) 24 hr .-~,Q--incheslOOyr. """_ 100 yr. P 6hr.= 2,5 in., P 24hr-.= f,O in., P6/P24= 63 % < 65% Q=CxIxA, Q= 45 x ""_ 3,57x """ 2#4Z. t Q = 3.89 C.f.s. Q=CxIxA, Q= W X s.2/_ X ZJt; Q = 6-2zC.f.s. RunoffL-Q_?-I-x-CA Altitude Factor = -_A-p _____ Q = -L L'o "" x """" 3057 6 "/hr. Q = // f7 X 5. 71 24 "/hr. CA = 6,ZZ 100 factor Intensity x """"" /.09 = """_" 3, 89 C.f.8. 100 factor Intensity """"_ c.f.s. USE Q = """_" 4.0 C.f.8. USE Q = -6, 25- c.f.8. 6hr 100 24hr 100 Reference : San Diego County Flood Control Hydrology Manual, January 1985 (1) Soil group maps are available at the offices of the Dept. of Public Works (2) Where actual conditions deviate significantly from the tabulated imperviousness values of 80% or multiplying 80% or 90% by the ratio of actual imperviousness to 90%, the values given for coefficient C, may be revised by the tabulated imperviousness. However, in no case shall the commercial on D soil group final coefficient be less than 0.50, for exampler Consider Actual imperv. = SO%, Revised C = 50/80 x 0.85 = 0.53 Tabulated imperv. = EO%, 2 Oh t" 1.5' -+ n : ,0175 2 O/n Oeplh RESIDENTIAL STREET ONE SIDE ONLY v = 4.s-f.p.s. SAN OIEGO COUNTY DEPARTMENT OF SPECIAL DISTRICT SERVICES APPROVED /3. DATE *,I 'APPENDIX X-D GUTTER AND ROADWAY DISCHARGE-VELOCITY CHART DESIGN MANUAL IV-0- 13 - 0 m . p1 p1 Exhibit 3 100 Year 24 hr. Precipitation "I < - I u Y $ 11-A- I3 0 N .... Exhibit 4 100 Year 6 hr. Precipitation s u 5 J U I I Ii-.A- ,'- I I - - Exhibit 5 Site Configuration, Brow ditch, Sewer esmt. - I - -.. . .. _I ;I the drainage area in the acres tributary to the design point. :I Runoff Cocfficient, C i ! Appendix IX'lists the estimated coefficicnts for both undeveloped and dcvel6ped.aress. For rural areas which includes all drainage areas 1~ith.a development density less than one dwelling unit per acre, the coefficient is based mainly on the soil group alone. Select the appropriate coefficient from Appendix IX. For urban areas ~ ! select an appropriate coefficient for each type of land use. Xulti- i !; I ply this coefficient by the pcrccntage of the total area included in that class. The sum of these products is the weightcd runoff coefficient. ?!aps showing the various soil groups are'on filc I in the dffise of Sanitation and Flood Control. Rainfall Intensity, - I Intensity - duration - frequency curves applicable to all areas within San Diego County are given in Appendix XI, Time of Concentration, Tc 'The time of concentration.is the time required for runoff to flow from the most remote part of the watershed to the outlet point under consideration. Nethods of calculation differ for natural watersheds (non-urbanized) and for urban drainage systems. Also. when designine storm drain systems, the designer must consider-the possiblility that an existing natural watershed may become urban- ized during the useful life of the storm drain system. . (a) Natural IVatersheds: Obtain Tc from Appendices X-A and X-8 (b) Urban drainage systems: In the case of urban drainage s)-stems, the time of concentration at any point within the drainage area 1'. is the inlet tine or the time required for the storm water - 1 IV-A-4 , , i _. Rev.5/81 I .. I i $"i$ I .. - 4 3,. X mast.cr plan of drainage and flood control facilities for the County ' ,' !I ,; .. of San Diego has been adopted for the Flood Control Districts. Zones I through 4 have comprehensive plans and Zone 5 has a plan for the Sorrego Springs area. The flood discharges indicated in these plans will normally bc n.cceptable and should be used in all design work. Rapidly developing arcas from time to time may warrant additional stud:; and Flood Control District reports should be consulted. .::,, . ., . , . ,.r .. It ' 5. ?;atersheds n.5 Square Miles - 15 Square Niles a. U. S. Soil Conscrvation Service unit hydrograph may be used.* .,<,. , ,: 8 b. Storm duration of 6 to24 hours are appropriate for developing flood '< ,'i, .. discharges for SO znd 100-year storms. The Sanitation and Flood ContrDl's Hydrology Z!anual should be consulted for short duration !. c ,,,. 1 rainfall used in developing discharges for this size watersheds. ,". I ,~ . ,, : ., ,. ,i I c. hlodificd rational nc:!~ods by routing sub-watersheds may be used. t d. I.clcnl arcs flood conrrol rcports, prepared for the Flood Control Ufstric:, vi11 take prccedencc over the above described methods. . Katzrsheds Lcss. than 0.5 Square Nil0 Methd of Computing Runoff - Use :he E3tiOnal Formula Q = CIA where: .I 4 is the peak rate of flow in ccbic feet per second . C is a runoff coefficient expressed as that percentage of rainfall which .,, becomes surface runoff. .. - .. Refer to "Hydrology - Engineering Handbook, Section 4," U. S. Soil Conservation Serricr, available in San Diego County Flood Control Office. .. IV-A-3 , I, a ' Rev. Val .. . 1. Site Photo’s Existing Brow Ditch. Running along the south and southwest property on lot 90. .- 1. Existing Brow Ditch. Running along the south and southwest property on lot 90. J 3. Exitting Site Conditions. Looking East to West. 3. Existing Site Conditions. Looking from the Northwest cor. to the Eaat at the Cul-de-sac. Site Photo”s 2. Existing Sidewalk under Drain. Located at the end of the existing cal-de-sac, on lot 90. Off site conditions, does not flow onto the existing site.