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HomeMy WebLinkAboutCT 75-04; Lot 91 Map 8302; Hydrology Report; 1989-05-03L ;7 n .,D AND DRAINAGE REPORT HYDROLOGY STUDY LOT 91 OF HAP 8302 FOR IN THE CITY OF CARLSBAD PE 2.89.31 15-q PREPARED FORI ROBERT DAVIS ' CARLSBAD, CALIFORNIA 92009 7014 LLAMA STREET ENGINEERING DEPT. LIBRARY City of Carlsbad 2075 Las Palmas Drive Carlsbad, CA 92009-4859 PREPARED BY I VILLAGE ENGINEERING CORP. 1466 PIONEER WAY, EL CAJON, CA 92020 (619) 588-8559 (619) NO. 28306 n VILLAGE ENGINEERING CORP. PREPARED BY I 1466 PIONEER WAY, EL CAJON, CA 92020 (619) 588-8559 (619) NO. 28306 x-" 3- 07 F 7#// -@p .- ' May 3, 1989 ,W: 0. 89042 July 11, 1989 Robert Davis 7014 Llama Street Carlabad, California 92009 Subject: Hydrology and Drainage Report for a Proposed Single Carlsbad, California. Family Residence, Lot 91, Tract 75-4, Map 8302, 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 waa performed in accordance with your request and our proposal dated April 27, 1989. Architectural Plans well as our conclusions and recommendations, The results of our field investigation and review of the era present.& in the accompanying report. . 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. 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 On Site Conditions Exhibit 4 Exhibit 3 100 Year 24 hr. Precipitation 100 Year 6 hr. Precipitation Exhibit 5 Site Configuration, Brow ditch, Sewer esmt APPENDIX A. Rational Formula Watershed less than 0.5 square miles. B. Site Photo’s 2. Existing Sidewalk under Drain. 1. Existing Brow Ditch. 3. Existing Site Conditions, 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 report for the subject site. The vicinity map for this project is presented on Exhibit Number 1. Exhibit Number 5 shows the To assist in the preparation of this report, we were provided site configuration and the locations of existing Brow Ditch. with preliminary plans that were prepared by Mark Radford, project architect. " PROJECT DESCRIPm 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 Our field investigation was conducted on April 19, 1989, and consisted of visual observations of the existing surface 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 sparse covering of the native grasses and shrubs cover the site. A 15 foot sewer easement is parallel to the west property line and a 20 sewer easement also parallels the northern property line. The surrounding hillside has been changed by the developer to construct the required public improvements and lots, in doing so, the watershed direction has changed and eliminated the major off down the hill travels over the natural ground and graded areas site fiows from coming onto the site. The water that does come 95, than enters Acuna Court, and flows Northwest to the end of the cul-de-sac. There the water enters an existing sidewalk flow into lot 114. 90 and 91 on lot 90 '(see site photo's) and is permitted to sheet - that enter the existing home sites and vacant lots, 93 through - under drain and travels along a concrete brow ditch between lots " The conclusion is the existing site is .54 AC. in size and is located at the northwest end of Acuna Court facing the pacific 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. - area sheet flows in a natural fashion onto lot 114. Therefore, .- - The Recommendations for the site follows the strict guide lines of the soils engineer. c Exhibit 1 Vicinity Map - Exhibit 2 HYDROLOW CALCULATIONS Qtj SITE CONDITIONS Project 2607 ,&?UNA OuFr WO# 89QdL Date 5-1-e Calc: dP- Date: S-/-W CHfE \1P Date 7-1l-m SHT../ofA-SHTS. -"" WQFF COEFFICIENTS (RATIONAL METHODL Q=CIA Developed Areas Coefficient, C Percentages : Land Use Soil Group (1) 104 Single Family A - B C " .40 .45 .50 Multi-Units .45 .50 -60 .70 " Mobil Homes .SO .55 ___ Rural (Lots > .5 AC) .45 .30 .35 .65 Commercial (2) .40 .45 - .70 .75 .80 80 % Impervious .85 "" Industrial (2) .a0 .85 .90 .95 90 % Impervious (S.D. County,IV-A-9, APPENDIX IX-B) c = '55 , - - ACRES X C = CA = */#70 - Time of-Concentration Tc (see drainage basin area) L.0.03 miles Hi.Pt. 364.Pt. 35.7 , bH. //' , L. 165' , S..O667 - SAN DIEGO COUNTY NATURAL WATER SHED *Tc=(11.9 (Lza .385 X 60 = + 10 minutes = Tc- - minutes + 3/5 minutes disturbed basin ( H ) - 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 =CITY OF CARLSBAD *Tc=1.8 (1.1 -C)LA1/2 .385 X 60 = Z,lO (S x 100) ^1/3 + 10 minutes = TC= -8- minutea (or) ___ sf0 +a or 5 minutes disturbed basin. INTENSITY I=7.44 .X (P6orP24) X D^-.645 I= L.50 (6 I = Intensity (in/hr.) 100 vr. P=6 hr. or 24 hr .. Precipitation (in.) 6 D=Duration (min .) 24 “ hr , Z#s incheslOOyr . hr.rinches100yr. 100 yr. P 6hr .=x in., P 24hr .=-in., P6/P24-: &3 % < 65% Runoff: Q = I x CA Altitude Factor = /. Q Q = -- ha x 6.50 6 “/hr. /,zz C.f.8. = LW C.f.8. 100 factor Intensity *I870 Q 1.U X /O.W 24 “/hr. -” CA x 100 factor Intensity USE Q = /.z5 C.f.8. USE Q = 2.0 C.f.S. - - 6hr 100 24hr 100 - Reference I January 1985 (1) Soil group maps are available at the offices of San Diego County Flood Control Hydrology Manual, the Dept. of Public Works (2) Where actual conditions deviate 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 final coefficient be less than 0.50, for example: Consider commercial on D soil group - significantly from the tabulated imperviousness values of 80% or Actual imperv. = SO%, Tabulated imperv. = EO%, Revised C = 50/80 x 0.85 = 0.53 - 0 N Exhibit 3 100 Year 24 hr. Precipitation -I < " w - E; 11-A-13 Exhibit 4 100 Year 6 hr. Precipitation -9 < U " " s II-A- 7 .. i 0 lr I- O z . Em - - :hibit 5 Site Configuration, Brow ditch, Sewer esmt - . .. , . .. _.- 1 I 2. \<:~tr.rsllcds Over 15 Square Niles, Excepting Najor Rivers i_r x. #\ ma;t.cr plan of drainage and flood control facilities for the County of San Dicgo has been adopted for the Flood Control Districts. Zones 1 through J have conprehensive plans and Zone 5 has a plan for the Borrego Springs area. The floud discharges indicated in these plans wi!l normally be n,cccptable and should be used in all design work. Rapidly developing arcs from time to time may warrant additional study and Flood Control District reports should be consulted. 3. :.;'atersheds 0.5 Square Niles - 15 Square Miles a. U. S. Soil Conservation Service unit hydrograph n2y be used.* b. Storm duration of 6 to24 hours are appropriate for developing flood discharges for 50 and 100-year storms. The Sanitation and Flood ContrDl's Hydrology Z!anual should be consulted for short duration rainfall used in developing discharges for this size watersheds. c. Vodificd ratiansl nct!~ods by routing sub-watersheds may be used. (1. I.ocn! area flood conr?ol reports, prepared for the Flood Control Uistrict, tiill take prccedencc over the above described methods. 4. . .pi.+%rsk* L-m than,B.S Square Wi,lrt ... ., L/ - Nethod of Compting Runoff Usc the, Rational Formula Q = CIA where: 9 is the peak rate of flow in ccbic feet per second . - C is a runoff coefficieni expressed as that percentage of rainfall which Leccmes surface runoff. * Rcfer co "Hydrology - Engineering Handbook, Section 4," U. S. Soil Conservation Scrvlcr. available in San Diego County Flood Control Office. Rev. 5/81 IV-A-3 - I is the avcragc. rai.nfa11 illtensity ill inches per hour for a storm - duration equal to the tjmc of concentration (Tc) of the,contributing Jrainage area. - A ik the drainage area in the acres tributary to the design point. Runoff Coefficient, I C Appendix IX lists the estimated coefficicnts for both undcveloped and dcvel6ped.areas. For rural areas which includes all drainage areas with.3 development density less than one dwelling unit per acre, the coefficient is based mainly on the soil group alone. Select the approprlate coefficient from Appendix IX. For urban areas select an appropriate coefficient for each type of land use. Nulti- ply this coefficient by the pcrccntage of the total area included in chat class. The sum of these products is the weighted runoff coefficient. !!aps shoxing the various soil groups are.on filc in the 6ffice 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 runo'ff to flow from the most remote part of the watershed to the outlet point under consideration. Methods of calculation differ for natural watersheds (non-urbanized) and for urban drainage systems. Also, when designing storm drain systems, the dcsigner must consider.the possiblility that an existing natural watershed may become urban- ized during the useful life of the storm drain system. . (a) Natural Xatersheds: Obtain Tc from Appendices X-A and X-B (b) Urban drainage systems: In the case of urban drainage systems, ! the time of conccntration at any point within the drainage area is given by 7 s T. c Tf where'; 1'. is the inlet tine or the time required for the storm water C 1 1 - IV-A-4 ! " Rev.S/81 .. . Site Photo's 1. 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. 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. 3. Existing Site Conditions. Looking East to Wost. 3. Eximtiny Site Conditions. Looking from the Northwest cor. to the East at the Cul-de-sac.