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HomeMy WebLinkAboutSDP 2018-0020; 540 CHESTNUT AVE; HYDROLOGY STUDY 540 CHESTNUT AVENUE CARLSBAD, CA; 2020-09-25Hydrology Study 540 Chestnut Ave Carlsbad, CA 92008 APN: 204-091-13 V2018-001 0 SDP20 18-0020 GR2020-0009 DWG 523-6A 2ak- Initial DOW RECrTVED SEP 30 2020 Prepared For: LAND DEVELCIPMENT BG Consolidated, LLC ENGINEEPNINIG 1441 Montiel Road, Suite 115 Escondido, CA 92026 (760) 746-4955 Prepared By: Civil Dandworks Civil Laridworks Corporation 110 Copperwood Way Suite P, Oceanside CA, USA 92058 760-908-8745 CLW No.: 1263D; September 25, 2020 Drainage Study 540 Chestnut SFR September 25, 2020 Carlsbad, CA TABLE OF CONTENTS Section INTRODUCTION..........................................................................................................................2 DESIGN CRITERIA AND ASSUMPTIONS................................................................................2 DISCUSSION.................................................................................................................................3 ExistingConditions ...... . .............................................................................................................. 3 ProposedConditions...................................................................................................................4 ANALYSIS and CONCLUSION...................................................................................................4 DECLARATION OF RESPONSIBLE CHARGE.........................................................................5 REFERENCES...............................................................................................................................6 ATTACHMENTS ATTACHMENT 1— LOCATION MAP ATTACHMENT 2— PRECIPITATION MAPS AND SOIL MAP ATTACHMENT 3— EXISTING HYDROLOGY CALCULATIONS ATTACHMENT 4— PROPOSED HYDROLOGY CALCULATIONS ATTACHMENT 4B - PROPOSED CWILD CALCULATIONS ATTACHMENT 5— HYDROLOGY MAP - EXISTING CONDITIONS ATTACHMENT 6— HYDROLOGY MAP - PROPOSED CONDITIONS Page 1 Drainage Study 540 Chestnut SFR September 25, 2020 Carlsbad, CA INTRODUCTION The purpose of this study is to determine storm water runoff and site drainage of a 100-year storm event for the proposed single-family home and accessory dwelling unit located at 540 Chestnut Ave, Carlsbad, CA 92008. The project area is approximately 3,000 square feet or 0.080 acres. The parcel in question is currently vacant. In addition to the single-family home and accessory dwelling unit, this development also proposes other site development features. Sewer and water services, storm drains, a new driveway, pervious pavement, and site landscaping are all proposed with this development. The existing site is relatively flat. The elevations range from 50 to 54 feet above mean sea level. There are no slopes on the existing site that are greater than 25%. See Attachment 1 for the Site Location and Vicinity Maps. DESIGN CRITERIA AND ASSUMPTIONS The site soil classification as hydrologic soil type B. See Attachment 2. Per the San Diego County Hydrology Manual (2003) Rainfall Isopluvial Map (See Attachment 2): 100 Year Rainfall Event— 6 hours P6= 2.7 inches/hour 100 Year Rainfall Event— 24 hours P24= 4.5 inches/hour Per the San Diego County Hydrology Manual (2003) Table 3.1: Hydrologic calculations were performed using the CIVILCAD/CIVILDESIGN Engineering software version 7.6 per methods as outlined within the San Diego Hydrology Manual (2003). The hydrology calculations for proposed and existing conditions may be found within the hydrology calculations section of this report. Page 2 Drainage Study 540 Chestnut SFR September 25, 2020 Carlsbad, CA DISCUSSION EXISTING CONDITIONS The existing site is currently undeveloped. The vacant lot has been cleared and grubbed multiple times, but vegetation continues to grow onsite. Currently, the site has two hydrologic drainage basins. The largest drainage basin, EX-1, is flows south west towards Tyler Street and enters the cross gutter at the intersection of Tyler St and Chestnut Ave. The smaller drainage basin, EX-2, flows east onto Roosevelt Street. The Roosevelt Street flow path raps around, onto Chestnut Avenue, and enters the same cross gutter and travel path as basin EX-1. In general, all flow conveys west, where it travels down Chestnut Avenue and enters an existing curb inlet at the end of the Street. Below is a summary of pre-develoDment criteria for the subiect oroøertv: TABLE 1: 100 YEAR PRE-DEVELOPMENT CRITERIA Node C Tc (Mm.) Area (acre) Q100 (cfs) V100 (fps) 103 0.25 11.67 0.073 0.08 1.47 202 0.25 5.00 0.007 0.01 0.40 TOTAL 0.080 0.09 Page 3 Drainage Study 540 Chestnut SFR September 25, 2020 Carlsbad, CA PROPOSED CONDITIONS The site proposes a single-family home, accessory dwelling unit, driveway, storm drains, and pervious pavement. The impervious area is increasing with this development because the site is currently vacant. All efforts will be made to reduce the impact of this development. All proposed pavement onsite will be made pervious in order to mitigate the impacts of development. Because of the limited lot space and building requirements, pervious pavement is the best and most efficient was to mitigate the increased impervious area. The development will maintain the same drainage characteristics. The majority of the flow, in PR-I, will discharge to Tyler Street and a smaller amount, in PR-2, will discharge to Roosevelt Street. The flows will still confluence offsite and enter the existing inlet at the west end of Chestnut Avenue. The proposed hydrologic conditions are summarized below: TABLE 2: 100 YEAR POST-DEVELOPMENT Node C Tc (Mm.) Area (acre) Q100 (cfs) V100 (fps) 103 0.65 5.72 0.069 0.32 3.55 203 0.49 5.11 0.011 0.04 3.04 TOTAL 0.080 0.36 1 The proposed development without detention will increase peak flow rates by 0.27 cfs. ANALYSIS AND CONCLUSION A hydrologic analysis has been conducted for the subject for a 100 year storm event. The peak flow offsite will increase by 0.27 cfs with this development. This increase is very small with respect to the entering the existing inlet located on Chestnut Avenue. It is anticipated that the proposed development will not result in any adverse impacts to the existing public storm system. The development was mitigated to the greatest extent possible with the use of pervious pavement. Due to the limited lot size and proposed building footprint, pervious pavement is the only feasible option for mitigation. Page 4 Drainage Study 540 Chestnut SFR September 25, 2020 Carlsbad, CA DECLARATION OF RESPONSIBLE CHARGE I, hereby declare that I am the Engineer of Work for this project, that 1-have exercised responsible charge over the design of the project as defined in section 6703 of the business and professions code, and that the design is consistent with current standards. I understand that the check of project drawings and specifications by the County of San Diego and City of Carlsbad is confined to a review only and does not relieve me, as Engineer of Work of my responsibility for project design. ENGINEER OF WORK: Civil Landworks Corporation / 110 Copperwood Way Suite P, ff , Oceanside CA, USA 92058 if No. C070066 \EXP.09/30/22/ OF COWV David V. Caron R.C.E. 70066 Exp. 9-30-22 9-25-2020 Date Page 5 Drainage Study 540 Chestnut SFR September 25, 2020 Carlsbad, CA REFERENCES City of Carlsbad Storm Water Manual 2008. San Diego County Hydrology Manual (June 2003). San Diego County Drainage Design Manual (July 2005). Web Soil Survey, San Diego Area, California. United States Natural Resource Conservation Service. CIVILCADD/CIVILDESIGN Engineering Software, © 1991-2006 Version 7.6. San Diego County Control Division 2003 Manual Rational Hydrology Study. Page 6 ATTACHMENT 1 LOCATION MAP CLW No.: 1263D September 25, 2020 ATTACHMENT 2 PRECIPITATION MAPS AND SOIL MAP CLW No.: 1263D September 25, 2020 Hydrologic Soil Group—San Diego County Area, California Chestnut Ave Hydrologic Soil Group Map unit symbol Map unit name Rating ] Acres in AOl Percent of AOl MIC Manna loamy coarse sand, 2 to 9 percent slopes B 2.4 100.0% Totals for Area of Interest 2.4 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and 0) and three dual classes (A/D, BID, and G/). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (AID, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition USDA Natural Resources Web Soil Survey 6/5/2018 WIiiiiiiiiii Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—San Diego County Area, California Chestnut Ave Component Percent Cutoff. None Specified Tie-break Rule: Higher Natural Resources Web Soil Survey 6/5/2018 Conservation Service National Cooperative Soil Survey Page 4 of 4 ATTACHMENT 3 EXISTING HYDROLOGY CALCULATIONS CLW No.: 1263D September 25, 2020 EX1 San Diego County Rational Hydrology Program CIVILCADD/CIVILDESIGN Engineering Software,(c)1991-2012 Version 7.9 Rational method hydrology program based on San Diego County Flood Control Division 2003 hydrology manual Rational Hydrology Study Date: 06/10/20 ------------------------------------------------------------------------ ********* Hydrology Study Control Information ********S* Program License Serial Number 6313 Rational hydrology study storm event year is 100.0 English (in-lb) input data Units used Map data precipitation entered: 6 hour, precipitation(inches) = 2.700 24 hour precipitation(inches) = 4.500 P6/P24 = 60.0% San Diego hydrology manual 'C' values used ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Process from Point/Station 101.000 to Point/Station 102.000 USER DEFINED FLOW INFORMATION AT A POINT User specified 'C' value of 0.250 given for subarea Rainfall intensity (I) = 4.288(In/Hr) for a 10.0 year storm User specified values are as follows: TC = 10.96 mm. Rain intensity = 4.29(In/Hr) Total area = 0.073(Ac.) Total runoff = 0.080(CFS) Process from Point/Station 102.000 to Point/Station 103.000 IRREGULAR CHANNEL FLOW TRAVEL TIME Depth of flow = e.147(Ft.), Average velocity = 1.471(Ft/s) Irregular Channel Data ----------------------------------------------------------------- Information entered for subchannel number 1 Point number 'X' coordinate 'Y' coordinate 1 0.00 6.00 2 15.00 0.00 3 30.00 6.00 Manning's 'N' friction factor = 0.035 ----------------------------------------------------------------- Sub-Channel flow = 0.080(CFS) ' flow top width = 0.737(Ft.) velocity= 1.471(Ft/s) area = 0.054(Sq.Ft) Froude number 0.955 Upstream point elevation = 50.800(Ft.) Downstream point elevation = 48.100(Ft.) Flow length = 63.000(Ft.) Travel time = 0.71 mm. Time of concentration = 11.67 mm. Depth of flow = 0.147(Ft.) Average velocity = 1.471(Ft/s) Total irregular channel flow = 0.080(CFS) Irregular channel normal depth above invert elev. = 0.147(Ft.) Average velocity of channel(s) = 1.471(Ft/s) EX1 End of computations, total study area e.073 (Ac.) ATTACHMENT 4 PROPOSED HYDROLOGY CALCULATIONS CLW No.: 1263D September 25, 2020 PR1 San Diego County Rational Hydrology Program CIVILCADD/CIVILDESIGN Engineering Software, (c)1991-2012 Version 7.9 Rational method hydrology program based on San Diego County Flood Control Division 2003 hydrology manual Rational Hydrology Study Date: 06/10/20 ------------------------------------------------------------------------ $*$****** Hydrology Study Control Information Program License Serial Number 6313 ------------------------------------------------------------------------ Rational hydrology study storm event year is 100.0 English (in-lb) input data Units used Map data precipitation entered: 6 hour, precipitation(inches) = 2.700 24 hour precipitation(inches) = 4.500 P6/P24 = 60.0% San Diego hydrology manual 'C' values used Process from Point/Station 101.000 to Point/Station 102.000 * USER DEFINED FLOW INFORMATION AT A POINT User specified •C' value of 0.626 given for subarea Rainfall intensity (I) 7.114(In/Hr) for a 100.0 year storm User specified values are as follows: TC = 5.00 mm. Rain intensity = 7.11(In/Hr) Total area = 0.069(Ac.) Total runoff = 0.320(CFS) Process from Point/Station 102.000 to Point/Station 103.000 PIPEFLOW TRAVEL TIME (Program estimated size) Upstream point/station elevation = 50.200(Ft.) Downstream point/station elevation 47.500(Ft.) Pipe length = 155.00(Ft.) Slope = 0.0174 Manning's N = 0.013 No. of pipes = 1 Required pipe flow = 0.320(CFS) Nearest computed pipe diameter = 6.00(In.) Calculated individual pipe flow = 0.320(CFS) Normal flow depth in pipe 2.76(In.) Flow top width inside pipe = 5.98(In.) Critical Depth = 3.44(In.) Pipe flow velocity = 3.64(Ft/s) Travel time through pipe = 0.71 mm. Time of concentration (TC) = 5.71 mm. End of computations, total study area = 0.069 (Ac.) PR2 San Diego County Rational Hydrology Program CIVILCADD/CIVILDESIGN Engineering Software, (c)1991-2e12 Version 7.9 Rational method hydrology program based on San Diego County Flood Control Division 2003 hydrology manual Rational Hydrology Study Date: 06/10/20 ------------------------------------------------------------------------ Hydrology Study Control Information ****S***** Program License Serial Number 6313 ------------------------------------------------------------------------ Rational hydrology study storm event year is 100.0 English (in-lb) input data Units used Map data precipitation entered: 6 hour, precipitation(inches) = 2.700 24 hour precipitation(inches) = 4.500 P6/P24 = 60.0% San Diego hydrology manual 'C' values used ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Process from Point/Station 201.000 to Point/Station 202.000 USER DEFINED FLOW INFORMATION AT A POINT User specified 'C' value of 0.540 given for subarea Rainfall intensity (I) 7.114(In/Hr) for a 100.0 year storm User specified values are as follows: IC = 5.00 mm. Rain intensity = 7.11(In/Hr) Total area = 0.011(Ac.) Total runoff = 0.040(CFS) ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Process from Point/Station 202.000 to Point/Station 203.000 PIPEFLOW TRAVEL TIME (Program estimated size) ' Upstream point/station elevation = 50.400(Ft.) Downstream point/station elevation = 49.600(Ft.) Pipe length = 20.00(Ft.) Slope = 0.0400 Mannings N = 0.013 No. of pipes = 1 Required pipe flow = e.040(CFS) Nearest computed pipe diameter = 3.00(In.) Calculated individual pipe flow = 0.040(CFS) Normal flow depth in pipe = 0.97(In.) Flow top width inside pipe 2.80(In.) Critical Depth 1.43(In.) Pipe flow velocity = 2.90(Ft/s) Travel time through pipe = 0.11 mm. Time of concentration (IC) = 5.11 mm. End of computations, total study area = 0.011 (Ac.) ATTACHMENT 5 HYDROLOGY MAP - EXISTING CONDITIONS CLW No.: 1263D September 25, 2020 V LEGEND SUBDIVISION BOUNDARY EXISflNG CONTOUR (MAJOR) EXISTING CONTOUR (MINOR) l.w OR HYDROLOGIC BASIN BOUNDARY HYDROLOGIC FLOW PATH EX- 1 BASIN NUMBER F0--l7 J AREA (ACRES) NODE NUMBER (20.00) ELEVATION (FEET) OFFSITE DRAINAGE ATTACHMENT 5 10 0 10 20 GRAPHIC SCALE SCALE: 1"— 10' Civi an works C) 110 COPPERWOOD WAY, SUITE F, OCEANSIDE, CA 92058 Cl PH: 760-908-8745 • info@civillandworks.com rei I :1 i l q' Iiii: ii g o .ie ATTACHMENT 6 HYDROLOGY MAP - PROPOSED CONDITIONS CLW No.: 1263D September 25, 2020 OT 30 BLOCK 30 MAP 775 155 31 36.24'E 1 40.00' _ e 51 .5H®(502 SO61FG I? N5531'36"E 140.0 0' Lij O g' - "w - LLJ L DOWNSPOUT DO WNS POUT \5077F N PR- 1 lWMCDnl IT DOWNSPOUT OWNSPOL'T7 _ I -•--•.•- 1 1 0069 I DOWNSPOUT L_ D OWNSPOUT _ N5531'36"E 14000 50.621G '"-(508) I (50.4) V100=3.04 FPS / u PR-2 / [--- L?22LJ I L=27' 711 LOTS 17 & 18 R/W TCT 107 MAP 775 LEGEND SUBDIWSION BOUNDARY EXI.SThvG jf) EXISTING CONTOUR (MINOR) HYDROLOGIC BASIN BOUNDARY HYDROLOGIC FLOW PATH PR-1 BASIN NUMBER I 0.17 AREA (ACRES) (F~ NODE NUMBER (20.00) ELEVATION (FEET) OFFSITE DRAINAGE ATTACHMENT 6 PROPOSED HYDROLOGIC 10 0 10 20 I I GRAPHIC SCALE SCALE: 1"— 10' Civil andworks 40 110 COPPERWOOD WAY, SUITE F, OCEANSIDE, CA 92058 04 PH: 760-908-8745 • info@civilIandworks.com