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HomeMy WebLinkAboutPUD 2021-0006; ACACIA BEACH HOMES; PRELIMINARY HYDROLOGY STUDY; 2021-09-13PRELIMINARY HYDROLOGY STUDY FOR PLSA 3580-01 TENTATIVE PARCEL MAP / MINOR SITE DEVELOPMENT PLAN/ COASTAL DEVELOPMENT PERMIT ACACIA BEACH HOMES -245 ACACIA AVENUE MS 2021-0004 / CDP 2021-0036 / PUD 2021-0006 / SDP 2021-0018 CITY OF CARLSBAD, CA PREPARED FOR: RREG INVESTMENTS SERIES, LLC SERIES 1041 5315 AVENIDA ENCINAS, SUITE 200 CARLSBAD, CA 92008 PREPARED BY: PASCO LARET SUITER & ASSOCIATES, INC. 535 N. HIGHWAY 101, SUITE A SOLANA BEACH, CA 92075 PH: (858) 259-8212 Prepared: July 2021 Revised: September 2021 9-13-21 Tyler G Lawson, PE #80352 DATE ~City of Carlsbad SEP 3 0 2021 ~lanning Division Executive Summary Introduction Existing Conditions Proposed Project Conclusions References Methodology Introduction TABLE OF CONTENTS County of San Diego Criteria Runoff Coefficient Determination Hydrology & Hydraulic Model Output Pre-Developed Hydrologic Calculations ( 100-Year Event) Post-Developed Hydrologic Calculations (100-Y ear Event) Pre-Developed vs. Post-Developed Peak Flows (100-Year Event) Appendix Isopluvial Maps Intensity Duration Design Charts Runoff Coefficients Hydrologic Soil Group -USDA Web Soil Survey Pre-Development Hydrology Node Map Post-Development Hydrology Node Map PLSA 3580-01 SECTION 1.0 1.1 1.2 1.3 1.4 1.5 2.0 2.1 2.2 2.3 3.0 3.1 3.2 3.3 4.0 PLSA 3580-01 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Preliminary Hydrology Study for the proposed development at 245 Acacia Avenue, known as Acacia Homes, has been prepared to analyze the hydrologic and hydraulic characteristics of the existing and proposed project site. This report intends to present both 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 produced by the 100-year, 6-hour storm. 1.2 Existing Conditions The subject property is located along Acacia Avenue, northeast of the intersection of Acacia A venue and Garfield Street, in the City of Carlsbad. The site is bound by a combination of existing single-family and multi-family developments to the west, south, and east, as well as Acacia A venue, a public road, to the north. The existing site consists of two-family residences, a driveway, walkways, landscaping, open space consisting of mostly dirt, and miscellaneous improvements typical of this type of development. The project site is located in the Agua Hedionda Hydrologic Area, and, more specifically, the Los Monos Hydrologic Sub-Area (904.31) of the Carlsbad watershed. The subject property has an approximate area of 0.212 acres and is approximately 42.2% impervious in the existing condition. Per the Web Soil Survey application available through the United States Department of Agriculture, the basin is generally categorized to have type B hydrologic soils. Based on the existing impervious area and land use type, a pre-development weighted runoff coefficient of 0.52 was calculated for the subject property using the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. After review of the site edge conditions, existing topography, and adjacent developments, it was determined that there is no additional offsite runon entering the site from the neighboring properties. The existing site can be categorized into one (1) major drainage basin, with one ( 1) primary discharge location leaving the property. Drainage basin EX-1 consists of the entirety of the project site and primarily drains from west to east through the property via sheet flow methods. Based on a study of the existing site topography, there currently exists a cross-lot drainage scenario as runoff leaves the site along the eastern property line before ultimately being conveyed out to Acacia A venue further downstream. Once in the Acacia A venue right-of-way, runoff leaving the site travels east approximately 100 feet toward an existing storm drain inlet. The storm drain inlet is on the south side of Acacia A venue. Surface flow enters the storm drain inlet ultimately are conveyed south to outlet in the Agua Hedionda Lagoon prior to entering the Pacific Ocean. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration was calculated for the 100-year, 6-hour Page 1 of 11 PLSA 3580-01 storm event for the onsite drainage basin. Table 1 below summarizes the results of the Rational Method calculations. I EXISTING DRAINAGE FLOWS DRAINAGE DRAINAGE Q100 lioo AREA AREA (CFS) (IN /HR) (ACRES) EX-1 0.212 0.72 6.59 Table 1. Existing Condition Peak Drainage Flow Rates Refer to pre-development hydrology calculations included in Section 3 .1 of this report for a detailed analysis of the existing drainage basin, as well as a pre-development hydrology node map included in the appendix of this report for pre-development drainage basin delineation and discharge locations. 1.3 Proposed Project _The proposed project includes the demolition of all existing onsite improvements and the . ot\Sktt~siruction of three (3) new multi-family condominium units. The project proposes a 3 ~~ private driveway to provide vehicular access to the proposed garages. Three private onsite wW :S ~ parking stalls interior to the site are also shown for site residents. There arTSwo proposed (~~~va~roposed structures. The northern structur~o be built on a t{ +\,.... ~~ graded 53.5 pad elevation, and the southern structures are to be built on a graded 54.0 and 54.5 pad elevations, respectively. Site grading, drainage and utility improvements typical of this type of multi-family residential development will also be constructed as can be seen on the Preliminary Grading Plan prepared by Pasco, Laret, Suiter & Associates under separate cover. The subject property is approximately 76.9% impervious in the proposed condition. Based on the proposed impervious area and land use type, a post-development weighted runoff coefficient of 0. 7 5 was calculated for the subject property using the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. The proposed site consists of one ( 1) major drainage basin, with one ( 1) primary discharge location from the northeast corner of the property similar to the existing condition. However, the site proposes to discharge water onto Acacia Avenue from the proposed private driveway and from a sidewalk under drain pipe to the northeast. Thus, the onsite drainage basin was further broken down into two areas for analysis based on these discharge locations. Both discharge locations eventually confluence in the Acacia A venue curb and gutter right after leaving the property. Drainage basin PR-1 consists of the majority of the site and will continue to convey runoff generally from a high point in the southeast corner of the site to the Acacia Avenue right- of-way by means of surface flow. A concrete ribbon gutter located at the center of the driveway will also serve to capture and convey drainage to the proposed curb and gutter Page 2 of 11 PLSA 3580-01 along Acacia Avenue. Drainage basin PR-2 consists of the eastern portion of the site and will convey runoff from the project high point directly out to Acacia Avenue. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration were calculated for the 100-year, 6- hour storm event for the onsite drainage basins. Table 2 below summarizes the results of the Rational Method calculations in the post-developed condition. PROPOSED DRAINAGE FLOWS DRAINAGE DRAINAGE Q100 lioo AREA AREA (ACRES) (CFS) (IN /HR) PR-l 0.135 0.53 4.93 PR-2 0.077 0.28 5.28 TOT 0.212 0.81 5.28 Table 2. Proposed Condition Peak Drainage Flow Rates Additionally, drainage will be routed from the rear of the property out to Acacia A venue to alleviate an existing cross-lot drainage scenario discussed in the previous section. Subsequently, the proposed project will increase the Tc and flow length through the property, decreasing intensity to account for the increase in hardscape from the pre- development to post-development condition. Refer to post-development hydrology calculations included in Section 3 .2 of this report for a detailed analysis of the proposed drainage basin, as well as a post-development hydrology node map included in the appendix of this report for post-development drainage basin delineation and discharge locations. In an effort to comply with the City of Carlsbad storm water standards, the proposed site has incorporated LID design techniques to optimize the site layout. Runoff from proposed roofs and new or removed and replaced hardscape areas will be directed to landscaped areas as applicable to disperse drainage to pervious surfaces. The landscaped areas will assist to remove sediment and particulate-bound pollutants from storm water in addition to helping mitigate peak runoff by providing some volume retention, evapotranspiration, as well as slightly increasing the site's overall time of concentration. 1.4 Conclusions Based upon the analysis included in this report, there is a net increase of less than ~0.1 cfs in peak runoff as a result of the proposed development due to the 3,210 square feet of increased hardscape in the proposed condition as compared the existing site. This can be considered negligible, and peak runoff leaving the property in the post-developed condition is mitigated by increasing the time of concentration through the site as well as promoting Page 3 of 11 PLSA 3580-01 incidental infiltration and evapotranspiration. Additionally, as mentioned above the site will alleviate an existing cross-lot drainage scenario by routing runoff from the rear of the property out to Acacia A venue as opposed to the neighboring property to the east. As runoff ultimately reaches an existing storm drain inlet in Acacia A venue, water will not be diverted away from existing drainage patterns. Additionally, runoff produced by the proposed development will not have an adverse effect on the downstream watershed. The proposed site conditions will function to mitigate peak runoff to pre-project conditions, and the slight increase in runoff due to the proposed surface improvements can be considered negligible. The proposed project will be exempt from hydromodification compliance requirements as it does not qualify as a Priority Development Project as defined in the Regional Municipal Separate Storm Sewer System (MS4) Permit and the San Diego County Model BMP Design Manual. 1.5 References "San Diego County Hydrology Manual", revised June 2003, County of San Diego, Department of Public Works, Flood Control Section. "San Diego County Hydraulic Design Manual", revised September 2014, County of San Diego, Department of Public Works, Flood Control Section "City of Carlsbad Engineering Standards, Volume 5: Carlsbad BMP Design Manual (Post Construction Treatment BMPs) ", revised February 2016 "Low Impact Development Handbook-Stormwater Management Strategies", revised July 2014, County of San Diego, Department of Public Works Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov. Accessed September 2, 2020 Page 4 of 11 PLSA 3580-01 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: Where: r = 7.44 x P6 x o-0645 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: Where: Q=CIA 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 that 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. Page 5 of 11 PLSA 3580-01 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 only upon 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 under 100 feet, and is dependent on land use and slope. The time of concentration minimum is 5 minutes for purposes of calculating rainfall intensity per the County of San Diego Hydrology Manual requirements. 2.3 Runoff Coefficient Determination As stated in section 2.2, the runoff coefficient is dependent only upon 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, included in the Appendix of this report, categorizes the land use, the associated development density ( dwelling units per acre) and the percentage of impervious area. For this study, a weighted runoff coefficient was used for both the pre-project and post- developed site in accordance with the equation provided in Section 3 .1.2 of the County of San Diego Hydrology Manual. The weighted runoff coefficient is a function of the total impervious and pervious surface areas in the existing and proposed conditions. Page 6 of 11 PLSA 3580-01 3.0 HYDROLOGY MODEL OUTPUT 3.1 Pre-Developed Hydrologic Model Output (100-Year Event) Pre-Development: *Rational Method Equation Q=CIA P100= 2.5 * 10O-Year, 6-Hour Rainfall Precipitation Basin EX-1 Total Area= 9,250 sf-+ 0.212 Acres Impervious Area= 3,905 sf -+ 0.089 Acres Pervious Area= 5,345 sf-+ 0.123 Acres Cn, Weighted Runoff Coefficient -0.25, Cn value for natural ground, Type B soils * Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2 -0.9, C value for developed/ impervious surface * Per SDHDM Section 3.1.2 Cn = 0.9 x 3,905 sf+ 0.25 x 5,345 sf= 0.52 9,250 sf Tc= 5.0 Min I = 7.44 x P6 x D-0-645 *Minimum Tc for Rainfall Intensity per SDHDM *Rainfall Intensity Equation I= 7.44 x 2.5 x 5.o-0645 ;::; 6.59 in/hr Q100 = 0.52 x 6.59 in/hr x 0.212 Ac= 0.72 cfs Page 7 of 11 PLSA 3580-01 3.2 Post-Developed Hydrologic Model Output (100-Year Event) Post-Development (without considering HMP/BMP treatment): *Rational Method Equation Q=CIA P100= 2.5 * 100-Year, 6-Hour Rainfall Precipitation Total Site Total Area= 9,250 sf ➔ 0.212 Acres Impervious Area= 7,115 sf ➔ 0.163 Acres Pervious Area= 2,135 sf ➔ 0.049 Acres Cn, Weighted Runoff Coefficient -0.25, Cn value for natural ground, Type B soils * Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2 -0.9, C value for developed/ impervious surface * Per SDHDM Section 3.1.2 Cn = 0.9 x 7,115 sf+ 0.25 x 2,135 sf= 0.75 9,250 sf Basin PR-1 Total Area= 5,905 sf ➔ 0.135 Acres . 1.8*(1.1-0.75)*J100 ft Ti=------,,------ \!1.0% *Per SDCHM Figure 3-3, Initial Tc Ti= 6.30 min Tt = Tt1 *Overland flow to eastern PL Tt = 11.9(s~!o ~t) ( f 3)0.385 I 0.3 ft *Per SDCHM Figure 3-4, in hours Tt1 = 0.0126 hr* 60 min I 1 hr= 0.75 Min Tc= Ti+ Tt1 = 6.30 Min+ 0.75 Min= 7.05 Min I= 7.44 x P6 x D-0•645 *Rainfall Intensity Equation 1 = 7.44 x 2.5 x 1.05-0•645 ;::; 5.28 in/hr Q100 = 0. 75 x 5.28 in/hr x 0.135 Ac= 0.53 cfs Page 8 of 11 PLSA 3580-01 Basin PR-2 Total Area= 3,345 sf.+ 0.077 Acres . 1.8*(1.1-0.75)*✓100 ft T1=---.....,....--------- \;1.0% *Per SDCHM Figure 3-3, Initial Tc Ti= 6.30 min Tt = Tt1 *Overland flow to eastern PL ( 3)0.385 11.9( 100ft) Tt = 5280 ft I 1.1 ft *Per SDCHM Figure 3-4, in hours Tt1 = 0.026 hr * 60 min/ 1 hr = 1.54 Min Tc= Ti+ Tt1 = 6.30 Min+ 1.54 Min= 7.84 Min I= 7.44 x P6 x o-0645 *Rainfall Intensity Equation I= 7.44 X 2.5 X 7.84-0645 ~ 4.93 in/hr Q100 = 0. 75 x 4.93 in/hr x 0.077 Ac = 0.28 cfs Page 9 of 11 PLSA 3580-01 3.3 Pre-Developed vs. Post-Developed Peak Flows (100-Year Event) Total Pre-Development (Discharge Leaving Site) Basin EX-1 Q100 = 0. 72 cfs *Discharging from the site at the northeast corner to Acacia A venue Total Q100 = 0.72 cfs Total Post-Development (Discharge Leaving Site) Basin PR-1 Q100 = 0.53 cfs *Discharging from the site to Acacia Avenue via proposed private driveway Basin PR-2 Q100 = 0.28 cfs *Discharging from the site to Acacia A venue via proposed private driveway Total Q100 = 0.81 cfs Pre-Development vs. Post-Development (Discharge Leaving Site): Delta Pre-Development Q100 = 0. 72 cfs Post-Development Q100 = 0.81 cfs 0.09 cfs increase Page 10 of 11 PLSA 3580-01 4.0 APPENDIX Page 11 of 11 ib C") 0 r--,-,- in ,- 0 r--,-.... b in 0 s:I" 0 c'b r--,-,-.... ..... . -·\, ... .. . .... , ............ ... b C") 0 (0 ..... .... ····• ...... . . . . . •· . 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CoP)'l'ight SanGIS. All Rights Reserved. This products may contain Information from the SANDAG Regional lnfonnation System Vlltilch camot be reproduced without the wri1len pennlsslon of SANDAG. Thil product may contain lnfonnatlon which has been reproduced with pennlsslon granted by Thomas --- Miles 10.0 9.0 8.0 7.0 ... ::, 0 ~ (I) .r:. 6.0 5.0 4.0 3.0 2.0 g 1.0 ';:o.9 ~0.8 (I) ~0,7 0.6 0.5 0,4 0.3 0.2 0,1 1' "i-,.. 1' "'i--. ' "i.... X " I'. I .. "i.... .,...., ' ' I', ~ "r.... " ' .... ' I I I • I ----+-- ~ 5 6 ........ r,... ..,"", ... ...... -:, .. ........ "'r-,. ....... ... ,.., "'"' ... "" ........ < r-...._ .. , .... "' .... "" ,..,,. ""' ........ ..... .... "' .... ' .. "' ... .. ,.., .. ... ........ ,..,., ..,.., ~ ' "', ..... "'" ... .. ........ ... "'"' .. ' ...... ,..,., "', ........ ~ .. ... ,1 ........ r-..., r-."' ~ ""'i-, .... "' .... .. , .. ........ "" ' i..., ....... "'~ ... , ...... "'"' "'"' ~ .. - ' __ ,_ --- 7 8 9 10 15 20 ~~ ~ .. ~~ ~ .... ~~ ~ .. ~ ~~ ~~ .. ~~ ~~~ ~ 30 Minutes I : j j ~ .. ' ~ .. .. .. .. ..~ ~ ~ .... .. ~ ~ i .. ~ ~ ~ i .... ~ "~ I ~ ~ .. .. ~ ~ ~ I i "~ ! ~ T i .... "~ I ~ ' i I I I I + I i i 40 50 Duration I = I = P5 = D = EQUATION 7.44 P5 o-0.645 Intensity (in/hr) 6-Hour Precipitation (in) Duration (min) r,,.. r--.. .. ~ r,,.. ... ........ ~ r,,.. ........ .. .. .... ..... .... .... ~ .. .... ........ r,,.. "' ~ .... ........ r--.. .. .... .... ' .... 'i.... ........ 2 ..... .... ... .. "' ... r-.., "' I" .. .. ~ .. ... .. "'"' .. ~ .. ...... "'" ~ .. r-., "' .. ~ .. -.. .. .. I', .. ...... .. -I', ... .. ... ~~ ..... '"' .. ~ I" .. ~~ '"i,, "' .... ~ .. 3 Hours 4 5 6 Cf' ::r 0 !:; -0 ca 0 6.0 f 5.5 6" 5.0 ::, 4.5 s" 0 4.0 ffi 3.5 ~ 3.0 2.5 2.0 1.5 1.0 Directions for Appllcatlon: ( 1) From precipitation maps determine 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. Appllcatlon Form: (a) Selected frequency ___ year p (b) P6 = __ in., P24 = __ 'P 6 = %(2) 24 (c) Adjusted P6<2l = __ in. (d) 1x = __ min. (e) I = ___ in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. P6 1.5 2·2.S 3 3.5 4 4.5 5 5.5 6 Duration I I I I I -, I I I -f I s....,,.2 .... 63.,,..... 3,,...95~_"""s""21""'."""6""'.s""'9-."""1.""90,,...""'9""'.22"""": 1""'0"'".54,,,_. 1""'1"'".86.,,....,: 1""'3""".1"""1""": 1""'4""".4""9""". 1""s"".8-,-11 7 2.12 . 3.18; 4.24. 5.30. 6.36J.42i 8.48. 9.54. 10.60[ 11.66; 12.72 10 1.68 . 2 53: 3.37. 4.21 , 5.05. 5.90 l 6.74 • 7.58 ~ 8042 : 9.27 , 1~.11 15 1.30 , 1.95, 2.59. 3.24, 3.89, 4.54: 5.19, 5.84. 6.49 l 7.13 [z.78 20 1.oa . 1.62. 2.15. 2.69. 3.23. 3.n; 4.31 . 4~ ; 5.39 1 5.93 : 6.46 25 o.93 . , .40. 1.87. 2.33 . 2.ao. 3.21, 3.73 . 4.20 ; 4.67 l 5.13 : 5.60 30 0,83 , 1.24, 1.66 • 2,07, 2.49, 2.90, 3.32 i 3.73 • 4.15 • 4.56 I 4.98 40 0.69 . 1.03, 1.38. 1,72. 2.07. 2.41 1 2.76. 3.10. 3.45 3.79: 4.13 50 0.60 0.90 1.19 1.49 1.79 2.09! 2.39 2.69 2.98 3.28: 3.58 eo o.53 :oao: 1.00: 1.33: 1,59: 1.86: 2.12 ; 2.39; 2.ss 2.92; 3.18 90 0.41 .0.61; 0.82. 1.02. 1.23; 1.43\ 1.63; 1.84; 2,04 2.25; 2.45 120 0.34 , 0.51 I 0.68; 0.85, 1.02: 1.19l 1.36 i 1.53. 1.70 1,87 1 2.04 150 o.29 , 0.44 l o.59. o.73 . 0.88: 1.03; 1.18 , 1.32 ; 1.47 . 1.62 ~ 1J6_ 1ao o.2s,0.39\0.52.o.s5_o.78,0.91l 1.04: 1.18; 1.31, 1.44, 1.57 240 0.22 .o.33;0.43. 0.54 .o.s5.o.1s: o.87. o.98: 1.oa. 1.19: 1.30 300 0.19 . 0.28, 0.38 '. 0.47. 0,56. 0.66. 0.75 . 0.85 l 0.94 • 1.03 : U3 360 0.17 0.25·0.33 042 0.50 0.58 0.67 • 0.75 0.84 0.92' 1.00 FI RE Intensity-Duration Design Chart· Template 3-1 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 Count 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 1.) Limited Industrial 90 0.83 0.84 Commercial/Industrial General I. General Industrial 95 0.87 0.87 3 6 of26 C D 0.30 0.35 0.36 0.41 0.42 0.46 0.45 0.49 0.48 0.52 0.54 0.57 0.57 0.60 0.60 0.63 0.69 0.71 0.78 0.79 0.78 0.79 0.81 0.82 0.84 0.85 0.84 0.85 0.87 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 I-w w u. z w (.) z <( I-(/) i5 w (/) a:: ::::::, 0 (.) a:: w I-<( ~ 2.50% slope--1, 2.0-+-----11 100---~1=·--r------c--r---:.I~---- 0 EXAMPLE: Given: Watercourse Distance (D) = 70 Feet Slope (s) = 1.3% Runoff Coefficient (C) = 0.41 Overland Flow Time (T) = 9.5 Minutes SOURCE: Airport Drainage, Federal Aviation Administration, 1965 T= 1.8(1.1-C)VD 3Vs (/) w I-::::::, z 20 ~ z w ~ i= ~ 0 _. u. C 10 z :5 a:: w > 0 FIGURE Rational Formula -Overland Time of Flow Nomograph 3.3 Hydrologic Soil Group-San Diego County Area, California 33" gB"N Map Scale: 1:553 if printed on A portrait(B.5" x 11") sheet N ---===-----======Meiers 0 5 10 2J :ll A ----=====---------========Feet 0 25 50 100 150 Map projection: Web Mercator Qimer Cll0!1:linat:es: WGS84 Edge tics: UTM Zone llN WGS84 USDA Natural Resources -1FF Conservation Service Web Soil Survey National Cooperative Soil Survey 7/1/2021 Page 1 of 4 Hydrologic Soil Group-San Diego County Area, California MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons D A D AID DB BID D C D CID D D D Not rated or not available Soil Rating Lines A AID -B -BID C CID -D ,. " Not rated or not available Soil Rating Points A AID ■ B ■ BID USDA Natural Resources ziii Conservation Service □ C CID ■ D □ Not rated or not available Water Features Streams and Canals Transportation +-+-+ Rails -Interstate Highways -US Routes Major Roads Local Roads Background • Aerial Photography Web Soil Survey National Cooperative Soil Survey The soil surveys that comprise your AOI were mapped at 1 :24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection , which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: San Diego County Area, California Survey Area Data: Version 15, May 27, 2020 Soil map units are labeled (as space allows) for map scales 1 :50,000 or larger. Date(s) aerial images were photographed: Jan 24, 2020-Feb 12, 2020 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. 7/1/2021 Page 2 of 4 Hydrologic Soil Group-San Diego County Area, California Hydrologic Soil Group Map unit symbol Map unit name Rating Acres inAOI Percent of AOI MIC Marina loamy coarse B sand, 2 to 9 percent slopes 0.7 Totals for Area of Interest 0.7 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 D) and three dual classes (ND, BID, and C/D). 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 (ND, 8/D, or CID), 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 iiiliiii Conservation Service Web Soil Survey National Cooperative Soil Survey 100.0% 100.0% 7/1/2021 Page 3 of4 Hydrologic Soil Group-San Diego County Area, California Component Percent Cutoff: None Specified Tie-break Rule: Higher USDA Natural Resources ;iiiiiii Conservation Service Web Soil Survey National Cooperative Soil Survey 7/1/2021 Page 4 of 4 \ I I " \ N I '-I ---- \ \ \ Ii \... ~ I I f "' 01_I -- ',::--- LEGEND PROPERTY BOUNDARY CENTERLINE OF ROAD ADJACENT PROPERTY LINE PUBLIC RIGHT-OF-WAY BASIN BOUNDARY FLOW LINE IMPERVIOUS AREA --- / _J,:r'-:- 30' 60' ------ --- / - w ~ w °' 0 z 0 0 .... "' e-: < T l'o:: ~ --...... \ TC=5: 20 ! FL=:J1.1., • I (527F~;l, t:L~..::.'.t.i 7· ' ------------------- I I LITTW r-. PROJECT SITE SHEET MAP 1803 APN.· 204-240-07-00 T xz 49 < FLOWS OVER ., Z4C4 xc94 / :+ E ,_ . =-" PROPERTY TO EAST Q100 TOTAL \ c~S.81,---__.--, =072CFS --1 ) I "" c;:'9----~ r ! -----:; 7'.'.f7 -@::c.u.t....i t E r=== t-...L=...-1:: I ""'1 EL'"4 F-,, rj H fit ----j if', A K _ __ _ I.I' ,~·. 9' .. • /"'~. • 5 F,CONCt'.ETE BLOCK RETAINING t y -o • T.v=51.o • V\;AL' xs0.6 X504 ~,..,)----~-----...... ------------\ (52.4 FG) \ I TV\/=5~ .3 ~ B't/=4:9.9 N 34'03'15" W 150.00' --/51.4 FG) X S1.2 BASIN EX-1 AREA = 9,250 SF (0.212AC) Cn =0.52 I st:'=53.-- I °CA1'0PY 18' ~!v\!::53.5 II 8'!~=~ -, -," 5F.,.. \'VOO'J t:ENCE ON 'NALL ✓-~ j 1'2' "--~ :,_---°fT1=54 .1 _.J ·---~----,-:,~-~-~.., BW=S3 7 , 30· I 7 v\'=53 S ~ 1 --...... '-.. 2' '=54 ~ _J LOT 1 MAP 1747 X54.2 APN: 204-24/J.09-iJ0 BASIN EX-1 -AREA CALCULATIONS ----------TOTAL SITE AREA 9,250 SF (0.212 AC) &\\\\I BASIN EX-1 TOTAL AREA BASIN EX-1 IMPERVIOUS AREA BASIN EX-1 PERVIOUS AREA % IMPERVIOUS Cn TIME OF CONCENTRATION 9,250 SF (0.212 AC) 3,905 SF (0089AC) 5,345 SF (0.123 AC) 42.2% 0.52 5.0 MINLITES (PER SDCHM) I : I ~f/1'-~ GARAGIE I I I ~ ', IJ -r ---f"T'i? I / ---.__j CONCRETE "/ "'-. ___, ---, I --PROJECT SITE SHEET __/ FLOWS,0~ ) PROPERTY TO EAST___/ GRAVEL X • o (51.1 FG) \s," X 51 <. .>'. 51.6 X51 X 5~ 5 GRAPHICSCALE 1"=10' 10 0 10 20 30 '5 I X 5' " r Lq'r 4 MAP 1747 ' I L __________ _ POR. LOT10 BLOCKQ MAP 1803 APN: 204-240-12-00 APN: 204-24/J.12-00 EXISTING HYDROLOGY EXIHIBT 245 ACACIA AVE CARLSBAD, CA 92008 PASCO LAREY SUITER ~ ~SS©tC!~1rlES San Diego I Solana Beach I Orange County Phone 858.259.8212 I www.plsaengineering.com \ \ \ L. I \ \ 1 \ "-~ $ "" I ' ---- 1~ IE 'J=37 1 -------- 50.4 FS Q/00=0.28 CFS QTOT=0.81 CFS I I I -;r-. 'E In\ ;c"'!.P I I \!::::!/L=LQ. O I TCc<<:¾Y FL=4S.J1 I TC=-1037I F --t9_L\:l r NODE PR-102 53.0 FS 1/ / / I J ----------------CONCRETE LOT 10 APN: 204-240-07-00 ~- MAP 1803 .----- >'.Z·-(,..: X41).. BV~::48.8-,.,.......-·,C\-----... -----~ I I I I I I 1 ~-- ,-sw::,_,,9_7 ~ ~ I -~-1 ~ f <'" ~ _ ----·~ I -sG--,, ___ ---.-37""C ~~....It .., e-w ►.1 1-!!!!liC~ __ ;:;,'#J::::.lti? M "L~& M M * -- _,-~--g'·\ . 0 ..I~ • 5 F-CONCRET:: 3LOCK R::TAINING -----.IL ------1 r.••~~~ T~~•3r , -=~=u ~ ----,.... W=~ ,_ 3\V=50.9 i NODE'PR-202""L-,r---NODE PR-201 0 TV'/=51 3 ill " ""-, 53.1 TG X o-• 50 b _, 0 53 .4-FL X 50.4 8W=49:9 "Ii '---, ';j ", 51/)E , \ ~, ----:::.-':::::::_ ---~ I •. i I . • ,' V=53.4 ---N=S3 =,. Ll B\_1 =53.5-----...., 'i I '---~~____-c:: -liiii,;.';:;t;;;;;; -~3§iil2 ~ N34'03'15"W 15000' '~ - I -..::::=-__,_ L1 = 35' I I X54.2 "' APN· 204-240-09-00 ~-cc---~ ...,.f---- >< L1 = 100' BASIN PR-2 AREA= 3,345 SF (0.212 AC) Cn = 0.75 BL C LL .34'02'01" W 150 00' -----5..--BV/1=53 4 \ T1A =54 1 _1, x 53.8 "' B\'1=54 1 "-I ~ / / 1 - SHl=D I I ' I I ,,----I I X5C' P. • - >< GRAVEL N 'WALL ~, B\N=53.5\1 TW=54.11 ~ 3W=54.2 I I 11 BASIN PR-1 AREA = 5,905 SF (0.212 AC) Cn =0.75 -1 " X 50 2 LOT3 ,.________ \ / / "' ( _/ 5,,------ I X 51.6 l SHEJ \ ', ' r-----------i I I I I' NODE PR-100 54.:_4-l;l~l FL ( ' I I LOT4 , MAP 174? POR. LOT 10 BLOCKQ MAP 1803 APN: 204-240-12-00 ---- ---T LOT 1 MAP 1747 I I LOT2 MAP 1747 APN. 204-240-10-00 / r '-i 1------1-,I J 1/ :1 ~ MAP 1747 '¾..~~-/~-------- / LEGEND PROPERTY BOUNDARY CENTERLINE OF ROAD ADJACENT PROPERTY LINE PUBLIC RIGHT-OF-WAY BASIN BOUNDARY FLOW LINE PROPOSED IMPERVIOUS AREA -------- &\\\\I I PLAN VIEW -POST-DEVELOPMENT NODE MAP SCALE. 1" = 10' HORIZONTAL TOTAL SITE -AREA CALCULATIONS TOTAL SITE AREA 9,250 SF (0.212 AC) SITE TOTAL AREA 9,250 SF (0.212 AC) SITE IMPERVIOUS AREA 7,115SF (0.163AC) SITE PERVIOUS AREA 2,135 SF (0.049AC) % IMPERVIOUS 76.9% Cn 0.75 -----------, BASIN PR-1 -AREA CALCULATIONS BASIN PR-1 TOTAL AREA Cn TIME OF CONCENTRATION 5,905 SF (0.136 AC) 0.75 7.05 MINUTES (PER SDCHM) BASIN PR-2 -AREA CALCULATIONS BASIN PR-1 TOTAL AREA Cn TIME OF CONCENTRATION 3,345 SF (0.077 AC) 015 8. 71 MINUTES (PER SDCHM) GRAPHIC SCALE 1" = 10' 10 0 10 20 30 PROPOSED HYDROLOGY EXHIB IT 245 ACACIA AVE CARLSBAD, CA 92008 PASCO LARET SUITER ~ fa\~~©leifa\'ii"IE~ San Diego I Solana Beach I Orange County Phone 858.259.8212 1 www.plsaengineering.com