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HomeMy WebLinkAboutPD 2018-0031; HUELSEBUSCH RESIDENCE; HYDROLOGY REPORT FOR HUELSEBUSCH RESIDENCE; 2021-05-18 HYDROLOGY REPORT for Huelsebusch Residence 1331 Knowles Avenue PD2018-0031/DWG514-9A/GR2018-0042 City of Carlsbad, California PREPARED FOR: Melody Huelsebusch 1331 Knowles Avenue Carlsbad, Ca. 92008 PREPARED BY: Coastal Land Solutions 577 Second Street Encinitas, CA 92024 (760) 230-6025 DATE: October 3, 2018 Revised: May 18th, 2021 Steven R. Jones, RCE 65124 5-18-21 HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 TABLE OF CONTENTS SECTION Executive Summary 1.0 Introduction 1.1 Existing Conditions 1.2 Proposed Project 1.3 Summary of Results and Conditions 1.4 Conclusions 1.5 References 1.6 Methodology 2.0 Introduction 2.1 County of San Diego Criteria 2.2 Runoff coefficient determination 2.3 Hydrology Model Output 3.0 Existing Conditions Hydrologic Model Output 3.1 Proposed Conditions Hydrologic Model Output 3.2 Detention Volume 3.3 Attachments Existing Condition Hydrology Map (pocket) A1 Proposed Condition Hydrology Map (pocket) A2 Runoff Coefficients for Urban Areas A3 Maximum Overland Flow Length & Initial Time of Concentration A4 Soil Hydrologic Groups A5 Rainfall Isopluvials for 100 year Rainfall Event- 6 hours A6 Rainfall Isopluvials for 100 year Rainfall Event- 24 hours A7 Intensity Duration Design Chart A8 Average Velocity Chart for Overland Flow Time Travel A9 HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Hydrology Study, for 158 Chestnut Avenue, has been prepared to analyze the hydrologic characteristics of the existing and proposed project site, and determine the existing condition offsite hydrologic characteristics that are conveyed through the proposed project site. This report intends to present the methodology and the calculations used for determining the runoff from the project site in both the pre-developed (existing) conditions and the post-developed (proposed) conditions, as well as the offsite areas, produced by the 100 year 6 hour storm. 1.2 Existing Conditions The proposed project property is located east of Coast Highway 101, West of Highway 5, north of Tamarack Avenue, and is located on the north side of Chestnut Avenue, in the city of Carlsbad, as shown on the vicinity map and aerial shown below. Vicinity Map \ . I I I I . -·· \ \ \ . \\ carlsbadViHaoeEJ <r",..• 9 starbucil Carls b ad ,_. BueMV,sta 9 ElementaryScl'lool ij ~ ,,. •.. \ • \ ... 9 P,izaPort \ ~~_. Holiday Park carlsbadParl!.s & Recreation ... .,, \ \ . ,l' ) l Jl \ ./ \ j I \ .. --. ,. .,,,~ ,,,, .. \ \ Carlsbad High School 9 0 \ \ ClleSUIUIAVI \.,, \.,, Elementa~~~'!~ Q I . ., HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 Aerial Map The existing site is a 0.32 acre (14,000 sf) residential lot with a single family residence. In addition to the existing residential structure, the site currently consists of one driveway, wooden fences, an out structure, and miscellaneous hardscape. Existing impervious surface area on the site is 1,934 sf. The percentage of existing impervious surface on the site is 14%. Drainage from the existing site is primarily conveyed in a north and south direction, and sheet flows across the property. Approximately half of the property drains north and discharges to Knowles Avenue. The westerly portion of the front yard drains northwest to Knowles Avenue then eventually to a storm drain at Pio Pico Drive. The easterly portion of the front yard drains northeast to Knowles Avenue then eventually to a storm drain at a low point in Knowles Avenue. This storm drain connects to a storm drain system at Pio Pico Drive, eventually to Buena Vista Lagoon. The Southerly half of the property drains south and discharges to the neighbor’s property. 1.3 Proposed Project The intent of this project is to remove the entire existing residence, grade and build a new single family residence, construct concrete driveway, hardscape, re- vegetate graded area, and install a new water meter. HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 The proposed impervious surface area on the site is 3,440 sf. The percentage of proposed impervious surface on the site is 29%. The proposed increase in impervious surface is 1,506 sf, a 78% increase. The drainage from the proposed development will be facilitated by overland sheet flow, drainage swales, and a downspout pipe system to direct roof runoff to a 1550 gallon cistern storage tank. The cistern storage tank will collect and detain roof runoff via downspouts. Downspouts will be installed with a first flush diverter per City BMP manual Appendix I-7, and E.7. The storm water from the tank will be used to water the landscape, lawn areas, planter areas, and irrigate the yard. These vegetated areas will treat the storm water. Overflow from the cistern storage system will be at the down spout locations. Overflow will discharge onto concrete surfaces and be directed towards the back yard. Runoff from the driveway is directed to a swale along the westerly side yard where it will be treated prior to discharge off site. Runoff from yard area and portions of the side yard drain north and discharges to Knowles Avenue. Runoff from the backyard will drain south and maintain existing runoff conditions. A runoff coefficient for Medium Density Residential (MDR) will be used to determine the proposed runoff for a future residential building development. 1.4 Summary of Results Hydrologic analysis of the existing (pre-developed) and proposed (post- developed) condition of the site is included in this report as section 3.1 and 3.2 respectively. The hydrologic analysis is used in this report to approximate a peak flow at an assumed point of discharge in the existing condition, to quantify a pre and post developed condition peak flow. This assumption is made to develop a model that generates conservative peak flows to ensure that the storm drain system will be capable of safely conveying stormwater. The following summarizes the peak discharges at two points of discharge that resulted from performing hydrologic analysis of the project site in both the proposed developed and existing condition: Point of Discharge Existing Conditions Developed Conditions Runoff Coefficent 0.52 0.56 Q100 (cfs) Tc (min.) AREA Q100 (cfs) Tc (min.) AREA Front Yard (Northeast 1) 0.18 9.83 0.085 0.26 8.1 0.099 HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 Front Yard (Northwest 7) 0.15 8.85 0.067 0.17 11.15 0.070 Backyard 4 0.36 10.32 0.168 0.36 10.36 0.166 The project site hydrologic models for both the pre- and post-developed conditions encompass a total area of 0.32 acres. Evaluating the two models, the proposed development will increase the amount of runoff from the project site by 0.10 cfs or 14%. Front yard (northeast) drainage will increase slightly by 0.08 cfs. This increase is only happens when the cistern detention system overflows. Front yard (northwest) drainage will increase slightly by 0.02 cfs. This increase is based on new driveway, and hardscape areas. Backyard drainage will remain the same. 1.5 Conclusions As stated in section 1.4, the project site hydrologic models for both the pre- and post-developed conditions encompass a total area of 0.32 acres. Evaluating the two models, the proposed development will increase the amount of runoff from the project site by 0.10 cfs or 14%. The increase in runoff will be mitigated by installing a 1550 gallon cistern storage tank detention facility on site. The required detention volume is V= 117 cubic feet or 900 gallons. Calculations are based on City BMP Design Manual, Appendix B.3.2 Design Capture Volume (DCV), See section 3.3. Storm water from the tank will be used to irrigate the yard, planter area, lawn areas, and vegetation. Storm water runoff is directed into vegetated drainage swales, prior to discharge off site. It is anticipated that the proposed development will maintain the historic discharge locations of the existing drainage patterns. The proposed drainage system will safely convey the entire 100-year peak flow generated by onsite runoff. 1.6 References “San Diego County Hydrology Manual”, revised June 2003, County of San Diego, Department of Public Works, Flood Control Section. “San Diego County Stormwater Urban Mitigation Plan (SUSMP)”, revised August 2012, County of San Diego. HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 2.0 METHODOLOGY 2.1 Introduction The hydrologic model used to perform the hydrologic analysis presented in this report utilizes the Rational Method (RM) equation, Q=CIA. The RM formula estimates the peak rate of runoff based on the variables of area, runoff coefficient, and rainfall intensity. The rainfall intensity (I) is equal to: I = 7.44 x P6 x D-0.645 Where: I = Intensity (in/hr) P6 = 6-hour precipitation (inches) D = duration (minutes – use Tc) Using the Time of Concentration (Tc), which is the time required for a given element of water that originates at the most remote point of the basin being analyzed to reach the point at which the runoff from the basin is being analyzed. The RM equation determines the storm water runoff rate (Q) for a given basin in terms of flow (typically in cubic feet per second (cfs) but sometimes as gallons per minute (gpm)). The RM equation is as follows: Q = CIA Where: Q= flow (in cfs) C = runoff coefficient, ratio of rainfall that produces storm water runoff (runoff vs. infiltration/evaporation/absorption/etc) I = average rainfall intensity for a duration equal to the Tc for the area, in inches per hour. A = drainage area contributing to the basin in acres. The RM equation assumes that the storm event being analyzed delivers precipitation to the entire basin uniformly, and therefore the peak discharge rate will occur when a raindrop, which falls at the most remote portion of the basin, arrives at the point of analysis. The RM also assumes that the fraction of rainfall that becomes runoff or the runoff coefficient C is not affected by the storm intensity, I, or the precipitation zone number. In addition to the above Rational Method assumptions, the conservative assumption that all runoff coefficients utilized for this report are based on type “D” soils. HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 2.2 County of San Diego Criteria As defined by the County Hydrology Manual dated June 2003, the rational method is the preferred equation for determining the hydrologic characteristics of basins up to approximately one square mile in size. The County of San Diego has developed its own tables, nomographs, and methodologies for analyzing storm water runoff for areas within the county. The County has also developed precipitation isopluvial contour maps that show even lines of rainfall anticipated from a given storm event (i.e. 100-year, 6-hour storm). One of the variables of the RM equation is the runoff coefficient, C. The runoff coefficient is dependent on the percent of impervious surface, land use, and soil type, and the County of San Diego has developed a table of Runoff Coefficients for Urban Areas to be applied to basin located within the County of San Diego. The table categorizes the land use, the associated development density (dwelling units per acre) and the percentage of impervious area. Each of the categories listed has an associated runoff coefficient, C, for each soil type class. The County has also illustrated in detail the methodology for determining the time of concentration, in particular the initial time of concentration. The County has adopted the Federal Aviation Agency’s (FAA) overland time of flow equation. This equation essentially limits the flow path length for the initial time of concentration to lengths of 100 feet or less, and is dependent on land use and slope. 2.3 Runoff Coefficient Determination As stated in section 2.2, the runoff coefficient is dependent on percent impervious surface, land use, and soil type, and the County of San Diego has developed a table of Runoff Coefficients for Urban Areas to be applied to basin located within the County of San Diego. Table 3-1, included in the appendix, categorizes the land use, the associated development density (dwelling units per acre) and the percentage of impervious area. The total number of dwellings proposed is 1, and the total developed lot area is roughly equal to 0.32 acres. The dwelling unit per acre (DU/A) ratio is equal 3.12 DU/A which corresponds to Medium Density Residential DU/A of 4.5 or less on table 3-1. Assume soil type is D, the runoff coefficient is 0.52. For the both the existing and proposed development on site conditions, a weighted C value is determined by the percentage of impervious and pervious surfaces. The runoff coefficient of 0.90, for impervious surface, and 0.45 for pervious surface are used. HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 3.0 Hydrology Calculations 3.1 Existing Conditions Hydrology Calculations Existing runoff coefficient = (1,934sf)(0.90) x (12,006)(0.45)/14,000sf = 0.52 Front Yard Runoff (Northwest) Flow across initial sub area A, nodes 3 to 2: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Area) C= 0.90 (184 s.f.) + 0.45 (861 s.f.) 1,045 s.f. C=165 s.f.+387 s.f. 1,045 s.f. C= 0.53 A= 0.024 acres L= 20 ft S = (130.33-130.06)/20 = 1.3% Ti = 9.15 min. (Table 3-2) I100 = 4.46 in/hr Qnode2 = CAI = (0.53)(0.024)(4.46) = 0.06 cfs Flow across sub area B nodes 2 to 7: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Area) C= 0.90 (176 s.f.) + 0.45 (2,613 s.f.) 2,613 s.f. C=158 s.f.+1,175 s.f. 2,613 s.f. C= 0.51 A=0.061 acres L= 62ft HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 S = (130.06-129.13)/62 = 1.5% V = (vegetation) = 1.5 ft/s T(flow) = (62ft / 1.5 ft/s)/ 60 s/m = 0.68 min Tc = Ti + T(veg) = 9.15 min.+ 0.68 min. = 9.83 minutes I100 = 4.25 in/hr Qnode7= [CAa + CAb ] I100 = [0.53 (0.024) + 0.51(0.061)] 4.25 Qnode7 = 0.18 cfs Front Yard Runoff (Northeastt) Flow across initial sub area A, nodes 8 to 1: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Area) C= 0.90 (336 s.f.) + 0.45 (2,582 s.f.) 2,918 s.f. C=302 s.f.+1,162 s.f. 2,918 s.f. C= 0.50 A= 0.067 acres L= 75 ft S = (130.25-129.50)/75 = 1% Ti = 8.85 min. (Table 3-2) I100 = 4.56 in/hr Qnode1 = CAI = (0.50)(0.067)(4.56) = 0.15 cfs HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 Back Yard Runoff Flow across initial sub area C, nodes 6 to 5: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Area) C= 0.90 (38 s.f.) + 0.45 (659 s.f.) 697 s.f. C=34 s.f.+296 s.f. 697 s.f. C= 0.47 A= 0.016 acres L= 30 ft S = (130.23-129.93)/30 = 1% Ti = 9.60 min. (Table 3-2) I100 = 4.32 in/hr Qnode5 = CAI = (0.47)(0.016)(4.32) = 0.032 cfs Flow across sub area D nodes 5 to 4: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Lot Area) C= 0.90 (1,198 s.f.) + 0.45 (5,423 s.f.) 6,621 s.f. C=1,078 s.f.+2,440 s.f. 6,621 s.f. C= 0.53 A=0.152 acres L= 78ft S = (129.93-128.23)/78 = 2.1% V = (vegetation) = 1.8 ft/s T(flow) = (78ft / 1.8 ft/s)/ 60 s/m = 0.72min HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 Tc = Ti + T(veg) = 9.60 min.+ 0.72 min. = 10.32 minutes I100 = 4.13 in/hr Qnode4 = [CAC + CAD ] I100 = [0.47 (0.016) + 0.53(0.152)] 4.13 Qnode4 = 0.36 cfs HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 3.2 Proposed Conditions Hydrologic Model Output Proposed Runoff Coefficient = (3,440sf)(0.90) + (10,560sf)(0.45)/14,000 = 0.56 Front Yard Runoff (Northwest) Flow across initial sub area A, nodes 3 to 2: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Sub Area) C= 0.90 (500 s.f.) + 0.45 (93 s.f.) 593 s.f. C=450 s.f.+42 s.f. 593 s.f. C= 0.83 A= 0.013 acres L= 45 ft S = (132.33-129.83)/45 = 1% Ti = 9.6 min. (Table 3-2) I100 = 4.32 in/hr Qnode2 = CAI = (0.83)(0.013)(4.32) = 0.046 cfs Flow across sub area B nodes 2 to 7: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Sub Area) C= 0.90 (1,193 s.f.) + 0.45 (1,279 s.f.) 2,472 s.f. C=1,073 s.f.+575 s.f. 2,472 s.f. C= 0.67 A=0.057 acres L= 70ft S = (129.83-129.13)/56 = 0.5% V = (bare ground) = 0.75 ft/s HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 T(flow) = (70ft / 0.75 ft/s)/ 60 s/m = 1.55 min Tc = Ti + T(bare) = 9.6 min.+ 1.55 min. = 11.15 minutes I100 = 3.60 in/hr Qnode7 = [CAa + CAb ] I100 = [0.83(0.013) + 0.67(0.057)] 3.60 Qnode7 = 0.17 cfs Front Yard Runoff (Northeast) Flow across initial sub area C, nodes 8 to 1: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Lot Area) C= 0.90 (938 s.f.) + 0.45 (3440 s.f.) 4,378 s.f. C= 844 s.f.+ 1548 s.f. 4,378 s.f. C= 0.55 A= 0.099 acres L= 70 ft S = (130.33-129.13)/70 = 1.7% Ti = 8.1 min. (Table 3-2) I100 = 4.82 in/hr Qnode1 = CAI = (0.55)(0.099)(4.82) = 0.26 cfs HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 Back Yard Runoff Flow across initial sub area D, nodes 6 to 5: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Sub Area) C= 0.90 (0 s.f.) + 0.45 (1,040 s.f.) 1,040 s.f. C=0 s.f.+ 468 s.f. 1,040 s.f. C= 0.45 A= 0.024 acres L= 37 ft S = (130.33-129.93)/37 = 1% Ti = 9.60 min. (Table 3-2) I100 = 4.32 in/hr Qnode5 = CAI = (0.45)(0.024)(4.32) = 0.048 cfs Flow across sub area E nodes 5 to 4: C = 0.90 (Area impervious) + 0.45 (Area pervious) (Sub Area) C= 0.90 (1,325 s.f.) + 0.45 (4,881 s.f.) 6,206 s.f. C= 1,192 s.f.+ 2,196 s.f. 6,206 s.f. C= 0.54 A=0.142 acres L= 82ft S = (129.93-128.23)/82 = 2% V = (vegetation) = 1.8 ft/s T(flow) = (82ft / 1.8 ft/s)/ 60 s/m = 0.76min Tc = Ti + T(veg) = 9.60 min.+ 0.76 min. = 10.36 minutes HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 I100 = 4.11 in/hr Qnode4 = [CAD + CAE ] I100 = [0.45(0.024) + 0.54(0.142)] 4.11 Qnode4 = 0.36 cfs HYDROLOGY REPORT for 1331 Knowles Avenue 1550 Huelsebusch Residence 4/4/20 3.3 Detention Volume Refer to City BMP Manual, Appendix B.3.2 Design Capture Volume (DCV) 6 hour precipitation = 2.5 inches Runoff Volume = 2.5 inches x area x runoff coefficient Site Area = 14,000 square feet Existing Runoff Coefficient C = 1,934(.90) + 12,066(0.45)/14,000 = 0.52 Proposed Runoff Coefficient C = 3,440(0.90) + 10,560(0.45)/14,000 = 0.56 Detention Capture Volume Required = (2.5)(14,000)(0.56-0.52)/12 =117 c.f. Detention Capture Volume Proposed = 200 c.f. = 1,500 gallons lU 2U COASTAL LAND SOLUTIONS, INC. 577 SECOND STREET ENCINITAS, CA 9202~ PH (760) 230-6025 FAX (7601 230-6026 ..=iU EXISTING CONDITION HYDROLOGY MAP \ \ \ \ \ \ \ I I \ \ \ \ I I Q~0.15 CFSI I EXF129.50 ----( --------------\ ------I ', I '\ \ ) ---/ ---,, KNOWLES AVENUE ,,,--·13 _.. 0---------------I ,,,-I I I -' I ', \ / o o',, o \ / , EX=12~.13 I ', \ I '-1 \ \ \ 1"-----~i-------+----~.----...;';..-,------------...-i I0=0.18 \;Fs] ' \ I I I \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ EX=128.23 0=0.36 CFS \ \I \ >< I >< I >< I \ \ 4 \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0 0 \ \ \ \ \ \ I E i I I I I I I I I I ~-~-' IAREA E = Q.067 AC \ \ \ 0 \ I I I I I I I \ I... (._,,., "----/S--\ . , s.._ \ --:' 1.!?i-\ \ '\ \ \ \ I \ \ I I I I I I I I \ .-,/\ .. \ I I . 0 \ \ \ I I I ' ' ' ' ' ' '\ '\ \ \ \ I B I I AREA B = 0.061 ACI I I I I I I I f~o/ ..f?/ cf) <or\, :/1 // ' ) V/ EX=130.25 AREA D = 0.152 ACI ~--'\ / I I I I I I I \ I 0 \ -~ II (/) 0 "' II _J fe.X=+~p,06---------11 \ \ \ ,: A \. 0 AREA A -0.024 AC IMPERVIOUS \AREA=184 sf \ \ EX=130.33 \ I I _.. -'---C IAREA C = 0.016 AC '\ \ '\ \ " \"/o ./ . ~ ,,, 6 \f".:°-'. ><----)(~ \ 0 0 \ \ ' ' 0 \ EX=130.23 LEGEND ITEM HYDROLOGY NODE SUB AREA NAME FLOW PATH SUB-BASIN BOUNDARY SUB-BASIN AREA PROPERTY BOUNDARY EXISITING TOPOGRAPHY EXISTING CONTOURS SYMBOL 2 A I 0.24 acl - - --255-- - -Al GRAPHIC SCALE 1··-10· 0 10 20 30 C'J,~ COASTAL LAND SOLUTIONS, INC. (I; IL~ 577 ~COr«l STlEET OCINITAS. CA 92024 PH (760) 23Q-6025 FAX (760) 230-8:l26 CLS#1550 \ \ PROPOSED CONDITION HYDROLOGY MAP \ \ \ \ \ I I \ \ ' (---------------\ -------' -,, I ' '----·.ta KNOWLES A_:'~l'.jY~' 7 ------------0 o-._ ,,.----/ Q POST DEVELOP-EP}-O':.t"-7-eFS-~~----T'------,----_____,,,_,. _____ _,,,_ _____ _,,L....,.!·1~/----Q PRE DEVELOPED)=0.15'CfS I :'\1 / .,. / FS=129.1f / .,,, ,, I -' I --) I I I I I I I I I I I I I I I I I I I I I I I I I I r M : 'ii ti \ I .() ® .-+----~I'-,, I Al EA B = 0.057/AC / I ' \ /o o',, o , / , EX=129.13 I ', \ \ / ',, G)~\~-----------/ Q POST DEVELOPED)=0.26 CFS ',, / Q PR!:: DEVELOPED =0.18 CFS ',, / ' ',, / /\¥ .·· c/~;\ //11 ·1----1 I ,I .1· <D .I' ~ I ' , ·, FS=lr29;8:J_ L_ . I • 0 I I I I I . I I I I I ' I--\ \ . ,-\ J / -u I I I I 0 ~. . I i!/\1/ ' / I I I I© IARkA C = 0.099 ACI I I I I I ) x---x---0 0 0 b EX=128.23 1/,. I I Q POST DEVELOPED)=0.36 CFS Q'PRE DEVELOPED)=0.36 CFS I LEGEND ITEM HYDROLOGY NODE SUB AREA NAME FLOW PATH SUB-BASIN BOUNDARY SUB-BASIN AREA BUILDING FOOTPRINT PROPOSED CONCRETE HARDSCAPE PROPERTY BOUNDARY PROPOSED CONTOURS EXISTING CONTOURS EXISTING TOPOGRAPHY SYMBOL 0 0 1024 acl •--. ., .. --25!:J--------255----A2 San Diego County Hydrology Manual Date: June 2003 Table 3-1 Section: Page: RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient "C" Soil Type NRCS Elements County Elements %IMPER. A B Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 Low Density Residential (LOR) Residential, 1.0 DU/A or less 10 0.27 0.32 Low Density Residential (LOR) Residential, 2.0 DU/A or less 20 0.34 0.38 Low Density Residential (LOR) Residential, 2.9 DU/A or less 25 0.38 0.41 Medium Density Residential (MOR) Residential, 4.3 DU/A or less 30 0.41 0.45 Medium Density Residential (MOR) Residential, 7.3 DU/A or less 40 0.48 0.51 Medium Density Residential (MOR) Residential, 10.9 DU/A or less 45 0.52 0.54 Medium Density Residential (MOR) Residential, 14.5 DU/ A or less 50 0.55 0.58 High Density Residential (HOR) Residential, 24.0 DU/A or less 65 0.66 0.67 High Density Residential (HOR) Residential, 43.0 DU/A or less 80 0.76 0.77 Commercial/Industrial (N. Com) Neighborhood Commercial 80 0.76 0.77 Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 Commercial/Industrial (O.P. Com) Office Professional/Commercial 90 0.83 0.84 Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 C 0.30 0.36 0.42 0.45 0.48 0.54 0.57 0.60 0.69 0.78 0.78 0.81 0.84 0.84 0.87 3 6 of26 D 0.35 0.41 0.46 0.49 0.52 0.57 0.60 0.63 0.71 0.79 0.79 0.82 0.85 0.85 0.87 *The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area is located in Cleveland National Forest). DU/A= dwelling units per acre NRCS = National Resources Conservation Service 3-6 A3 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 12 of26 Note that the Initial Time of Concentration should be reflective of the general land-use at the upstream end of a drainage basin. A single lot with an area of two or less acres does not have a significant effect where the drainage basin area is 20 to 600 acres. Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in hydrology studies. Initial Ti values based on average C values for the Land Use Element are also included. These values can be used in planning and design applications as described below. Exceptions may be approved by the "Regulating Agency" when submitted with a detailed study. Table 3-2 MAXIMUM OVERLAND FLOW LENGTH (LM) & INITIAL TIME OF CONCENTRATION (Ti) Element* DU/ .5% 1% 2% 3% 5% 10% Acre LM Ti LM Ti LM Ti LM Ti LM Ti LM Ti Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9 LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4 LDR 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 LDR 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 5.6 MDR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3 MDR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8 MDR 10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7 100 4.5 MDR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3 HDR 24 50 6.7 65 6.1 75 5.1 90 4.9 95 4.3 100 3.5 HDR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7 N.Com 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G.Com 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4 O.P./Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 Limited I. 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General I. 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 100 1.9 *See Table 3-1 for more detailed description 3-12 AL/ b "' ;:.. ,-0 I)) Cl .,... - 0 Cl (Q I)) -:) 32•45• ------+-----------.; 32•30• b ~ "' ;:.. ;:.. b r,, b ~ p :' "' .... ~ ~ CD 33 15' 3•00· 3 "O CD ::!. ~ (") 0 C: :::, '< 32•45• 32•30• County of San Diego Hydrology Manual Soil Hydrologic Groups Legend Soil Groups LJ GroupA ~ GroupB D Groupe D GroupD D Undetermined LJ Data Unavailable DPW --CGIS ~,,,..,•~~~--f "~•· • ....., ... k.-P,,,•'· N THlS lrMP ISPROVJOED WITHOUT W~TYOF ANVKIND, EITHER EXPR£88 4 ORIW'UEO, INCL.UCMNG,BVTNOTUMITEOTO, THE M"UEDWAARANTIES OF MEACHAHTABILJlY ~ FmESS FOA.APARTIClA.ARPURPOSE. (;oWIGhlSn318.M Rlvl'ta'---1, s TrN~irayoonlllnrobffallan,-..h~R ...... E :-"""-!:"o1~"-~.........i.,. TrN~iray_..,INDrTT-.lon....,,,._.....,.,'111!11 ,..,....i:,w.-clt,yn.an-.-.._.. 3 0 3 Miles ,~- . · .... __ .... 33•15;~----+-7 ~;-;,-'--,;r.=f:;;.7".:ic>ir-"'--\-.....,("""=-.--++---f-------3,,c-'-v+-:,---~~..:,,,..~-----:...,--,f---:--:.,-~=\--___,c----l-----33°15' '.'2":5· ...................... ! 33°00' -0 I)) Cl -· --· Cl 0 Cl a> I)) -:) 32°45' -----t--------~ 32°30' 0 "' 1" ~ ~ •...... .... -- 32°30' 8 "' g ~ ":' 1-. "' ~ ~ County of San Diego Hydrology Manual Rainfall Isopluvials 100 Year Rainfall Event-6 Hours lsopluvial (inches) DPW ¢GIS ~1,;,•..;::,,(E,:,.1 :..-... ,,._....... ....... ,r -~, +.·- N TMIS loW' IS PROVIDED WmtoUTWARRNfTY OF Nff KJND, EITHER EXPRESS + ORIMPUEO,NCU.DNO,SUTNOTI.MTEDTO,TIEIMPUEDWAflAAHTIES OF MERDWfTABIUTY NCI FllNESS FOR A PARTICI.I.AA PURPOSE. ~lrGIS.AIRlgla,_.._._ s lNl~lnl!t'ODl'llllninlllmlllonllam,_SNIIWi~ ~a,.i.,i-.Ndlcam•......-i,.._,. ....... ,-lllillllonol!INEAO. Thla~~o:nalk'lblnlloflwt'Kllt.NM~wlll PllfflMlgni,.-~11-........... 3 0 3 Miles ~ 33°15 0 M ;:.. cc --· - io ;:.. io .., 1D .. :~/· ·-::::.~'.;:~<.:::· . .. .: .... . .. · 33•00· -----+---'--s,0,· ----::-::-:---:::::-:~W=~~..::::..,_4.4'--:¾-~~:..S.,_.:.==------1..,,,;.~"-I---H-----!:.....i--++---;.;'/+.c.~---4---....:.+---1t-~--'"~A --+-i--- ;;::i~;j~\{t .l 3°00' 3 "O CD :::!. ~ (") 0 C: ::, ~ 32°45' ----~--------f~~~~~~~~~:.J::.~=-=~;t::.:~:=i-J.,...~__:__~4\.=»i.~~LJ~~~----.-.-i-•• • 2°45" ~~,\. ~ r--~~ · !_f_.l L ... ·· Me 32°30' 32°30' g io g io ~ ~ ;:.. ~ ~ :' ~ ~ ~ County of San Diego Hydrology Manual Rainfall Isopluvials 100 Year Rainfall Event-24 Hours lsopluvial (inches) N llllSIMP ISPRO'IIDEDWmtOVTWAM>HTYOFNttKNl, E!Tl-lER E>CPftEU 0A; -..UEO, HCUJOINO, IIJT NOT L.MTm TO, ntE lriFUED WARIWfflES s OF Mf.lDWITMUTY N«l Fl'TNEII FOR A PARTICIJ.AA PURPOSE. ~a.oil.,.,_..~ lhle..,.._,,_,,_,..,~"""'NIWIDAOR...,. E=°'~.,...,,....~ .... n....-,a;,,.,,-~whlc:tlt.. ..... ~ ... ,.,,...,....,~n-............ 3 O 3 Miles ,._ 7 5 6 7 t) 9 10 15 20 30 40 50 Minutes Duration , I Ii 2 3 4 5 Hours i I I I i I l I I i ' , Tl! [I ii Ji 11 I -1.0 6 Intensity-Duration Design Chart -Template Directions for Application: (1) From precipitation maps detem1ine 6 hr and 24 hr amounts for the selected frequency. These maps are included in the County Hydrology 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 applicaple 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: (a) Selected frequency ___ year p (b) P6 = in., r 24 = _§__ = %(2) ----'P24 -- (c) Adjusted r 6{2) = __ in. (d) Ix : ___ min. (e) I = ___ in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. P6 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 -Duration I I I I I ·1 I I I I I 5 2.63 3.95 5.27 6.59 7.90 9.22 10.54 11.86 13.17 14 49 15.81 7 2.12 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.60 11.66 12.72 10 1.68 2.53 3.37 4,21 5.05 5.90 6.74 7.58 8.42 9.27 10, I 1 15 1.30 1.95 2.59 3.24 3.89 4.54 5.19 5.84 6.49 7.13 7.78 20 1.08 1.62 2.15 2.69 3.23. 3.77 4.3 4.85 5.39 5.93 6.46 -25 0.93 1.40 1.87 2.33 2.80 3.27 J.73 4.20 4.67 5.13 5.60 30 0.83 1.24 1.66 2.07 2.49. 2.90 3.32 3.73 4.15 4.56 4.98 40 0.69 1.03 1.38 1.72 2.07 2.41 2 76 3.10 3.45 3.79 4.13 50 0.60 0.90 1.19 1.49 l.79°2.09 2.39 2.69 2.98 3.28 3.58 60 0.53 0.80 1.06 .33 1.59 1.86 -2.12 2.39 2.65 2.92 3.18 90 0.41 0.61 0.82 1.02 1.23 1.43 1.63 1.84 204 2.25 2.45 ·120 0.3-1 0.51 0.68 0.85 1.02 1.19 1.36 1.53 1.70 1.87 2.04 150 0.29 0,44 0.59 0.73 088 1.03 1.18 1.32 1.47 1.62 1 76 180 0.26 0.39 0,52 0.65 0.78 0.91 1.04 1.18 1.31 1.44 1.57 240 022 0.33 0.43 0.54 0.65 0.76 0.87 0.98 '1.08 1.19 1.30 300 0.19 o.2a· o.38 0.47 0.56. 0.66 0.75 0.85 0.94 1.03 1.13 360 0.17 o.2s· o.33 0.42 0.50. 0.58 0.67 0.75 0.84 0.92 1.00 FI GU RE @] AS 50 r----r--.-.....-.,....._--r-...-r-T""T""1'"'"""'.-rn-"-.....--,,.---.-~-,n--,r-r-~J...-,-~~=11r--rr-1-, I I I I I I I ' , , J I I I I ~ • J 0.5 L---L-L.....L./----L---A.--'-.L...L...L..L..L..J....IUJ.U.U..L.-/....,_,..___._......I--L-.L..--l---1-..l.--1-L...L..L..LLJ..U.I-~--' 0.1 0.2 0.3 0.5 1 2 3 5 10 20 velocity (ft/sec) Reprinted from SCS TR-55-1975. TR:-55-1986 c0:t1tains a simi- lar graph for shallow-concentrated flow over paved and unpaved surfaces, but it does not contain this particular graph. Figure 20.4 SGS Average Velocity Chart for Overland Flow Travel Time A9