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Home My WebLink AboutCT 2017-0007; TAMARACK BEACH HOMES; PRELIMINARY HYDROLOGY STUDY; 2018-02-13.. ... ... ... -... -----------... --... -... ---... ---... -... -... .. ... PRELIMINARY HYDROLOGY STUDY FOR TENTATIVE MAP/ COAST AL DEVELOPMENT PERMIT 438 TAMARACK A VENUE CT 2017-0007 / CDP 2017-0075 / PUD 2017-0006 CITY OF CARLSBAD, CA PREPARED FOR: TOURMALINE PROPERTIES 2079 GARNET A VENUE SAN DIEGO, CA 92109 PREPARED BY: PASCO LARET SUITER & ASSOCIATES, INC. 535 N. HIGHWAY JOI, SUITE A SOLANA BEACH, CA 92075 PH: (858) 259-8212 Prepared: September 20, 2017 Revised: February 13, 2018 TER G. LAWSON, RCE 80356 2-13-18 DATE RECEIVED MAR 01 2018 CITY OF CARLSBAD PLANNING DIVISION -.. -.. -----------... -... ---------------.. -... -- Executive Summary Introduction Existing Conditions Proposed Project Conclusions References Methodology Introduction TABLE OF CONTENTS County of San Diego Criteria City of Carlsbad Standards Runoff Coefficient Determination Hydrology & Hydraulic Model Output Pre-Developed Hydrologic Model Output (I 00-Year Event) Post-Developed Hydrologic Model Output (I 00-Year Event) Detention Analysis (100-Year Event) Appendix Appendix A: Hydrology Support Material PLSA 2760-01 SECTION 1.0 I.I 1.2 1.3 1.4 1.5 2.0 2.1 2.2 2.3 2.4 3.0 3.1 3.2 3.3 4.0 -.. --------.. --------.. -------... ---------.. PLSA 2760-01 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Preliminary Hydrology Study for the proposed development at 438 Tamarack Avenue 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 I 00- year, 6-hour storm . 1.2 Existing Conditions The subject property is located just north of Tamarack Avenue, and is geographically settled between the Coastal Rail Trail and railroad tracks to the west, and Hibiscus Circle, a public street, to the east. The site is bordered by Tamarack Avenue to the south, and Nautical Drive, a private road, to the west and north. A small strip of open space abuts the property to the east, belonging to a parcel that is part of the existing residential development north of the property. The existing site consists of a single-family residence, with a driveway, hardscape, and landscape improvements typical of this type of development. The property is located within the Carlsbad watershed, and, more specifically, the Agua Hedionda Lagoon Hydrologic Area. The existing site is comprised of approximately 0.405 acres. The tributary drainage basin extends beyond the site limits and is approximately 0.45 acres, generally draining in an east to west direction across the property. There does not appear to be any existing storm drain infrastructure located onsite to convey drainage, and runoff sheet flows through the site to the western property line. To the north of the property, existing curb, gutter, and sidewalk improvements prevent offsite runon from entering the site. Drainage does not enter the property from the west, as it is downstream of the subject parcel. Lastly, curb, gutter, and sidewalk improvements in the right-of-way along Tamarack Avenue prevent drainage from entering the site to the south. Runoff leaves the site to the west, where it enters existing public storm drain infrastructure in Tamarack Avenue, and is conveyed south alongside the railroad tracks before ultimately outletting in the Agua Hedionda Lagoon and the Pacific Ocean . The 0.45-acre drainage basin for the subject property can be broken down into two minor drainage basins in the existing condition with two discharge locations from the site. Basin A consists of the northern half of the existing structure as well as the entire rear yard, and is approximately 0.34 acres in size and 27.7% impervious. Basin B contains the southern half of the existing residence as well as the front yard, and is approximately 0.11 acres in size and 81.3% impervious. Per the Web Soil Survey application available through the United States Department of Agriculture, the area is generally categorized to have group B soils. Based upon soil type and the amount of existing impervious area onsite, a runoff coefficient of0.43 was calculated for Basin A and 0.78 for Basin Busing the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula Page 1 oflO --------.. ----------------------------- PLSA 2760-01 provided therein. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration was calculated for each basin for the I 00-year, 6-hour storm event. The peak flow rate for the I 00-year, 6-hour storm for Basin A was determined to be 0.73 cfs with a time of concentration of 7.7 minutes, discharging to Nautical Drive (a Private Road) to the west before entering a storm drain curb inlet just south where it is conveyed west via an existing public storm drain. The peak flow rate for the JOO-year, 6-hour storm for Basin B was determined to be 0.57 cfs with a time of concentration of 5.0 minutes, discharging on the surface in the Tamarack A venue curb and gutter to the southwest and traveling west offsite. While the two minor drainage basins discharge to two separate storm drain systems in Tamarack Avenue, both flows enter an existing 84" RCP storm drain approximately 200 feet downstream and are conveyed south to the Agua Hedionda Lagoon. Refer to pre-development hydrology calculations included in Section 3. I of this report for a detailed analysis and the pre- development hydrology map included in Appendix A of this report for existing drainage basin delineation and discharge locations. 1.3 Proposed Project The proposed project includes the demolition of all onsite structures and the construction of five multi-family, detached condominium units with a shared access driveway, and various hardscape and landscape. Site grading along with drainage and utility improvements typical of this type of residential development will also be constructed. The proposed pad elevations range from elevation 46.7 at the northwesterly end of the property to 48.8 at the southeasterly end of the subdivision. Runoff from the proposed development will primarily drain from east to west to mimic existing drainage conditions and the existing onsite topography. A majority of the site and the entirety of the proposed impervious areas will be routed away from proposed structures to a series of storm drain inlets located in the front, side, and rear yards. Private drain pipes will collect all runoff entering each inlet and will route to a centrally located 8" PVC storm drain in the drive aisle. The 8" PVC line will route all onsite drainage south through the site before connecting to the existing storm drain in Tamarack Avenue. The project site will continue to accept runoff from the parcel to the, as the limits of the proposed drainage basin remains exactly the same as in the pre-developed condition. Onsite infrastructure has been sized to account for this additional drainage, while improvements along the east property line have been designed to convey the runon. Similar to the existing condition, the analyzed watershed can be broken down into two minor drainage basins with two separate discharge locations from the site. Basin A consists of the majority of the property, and is approximately 0.40 acres is size and 48.7% impervious. Proposed drainage basin B consists of graded slopes in the front of the property, as well as a portion of the drive aisle and walkways sloping toward Tamarack Avenue, and is approximately 0.05 acres and 14.3% impervious. Based upon soil type and the amount of proposed impervious area onsite, a runoff coefficient of 0.57 was calculated for Basin A and 0.34 for Basin Busing the methodology described in section 3.1.2 of the San Diego County Hydrology Manual and the formula provided therein. Using the Rational Method Page 2 of IO -... -... -------------.. ---... -----------... -.. ... ... PLSA 2760-01 Procedure outlined in the San Diego County Hydrology Manual, a peak flow rate and time of concentration was calculated for the post-development I 00-year, 6-hour storm event. The peak flow rate for the I 00-year, 6-hour storm for Basin A was determined to be 1.10 cfs with a time of concentration of 8.15 minutes discharging to the existing 24" RCP storm drain in Tamarack Avenue. The peak flow rate for the I 00-year, 6-hour storm for Basin B was determined to be 0.12 cfs with a time of concentration of5.0 minutes, discharging on the surface in the Tamarack Avenue curb and gutter to the southwest and traveling west offsite. While the proposed minor drainage basin A discharges to a separate storm drain system in Tamarack Avenue from existing drainage basin A, it can be considered a local diversion, as both flows enter an existing 84" RCP storm drain approximately 200 feet downstream and are conveyed south to the Agua Hedionda Lagoon. Refer to post- development hydrology calculations included in section 3 .2 of this report for detailed analysis and the post-development hydrology map in Appendix A of this hydrology report for proposed drainage basin delineation and discharge locations. In an effort to comply with the City of Carlsbad's storm water standards for Standard Development Projects, the project site will implement source control and site design BMP's where feasible and applicable in accordance with the City of Carlsbad's BMP Design Manual, February 2016 edition. All runoff generated from proposed roofs and hardscape areas will be directed to landscaped areas and grassy swales to disperse drainage onto pervious surfaces. A pervious pavement material is proposed for the drive aisle to minimize proposed impervious area, soil compaction, and promote dispersion. Partial infiltration and evapotranspiration in landscaped areas will assist in slowing peak discharges and in reducing total volume generated during storm events. The drive aisle and onsite landscaped areas will remove sediment and particulate-bound pollutants from storm water prior to leaving the project site. 1.4 Conclusions The proposed project is able to decrease the total peak runoff generated by the I 00-year, 6-hour storm event from I .30 cfs in the pre-developed condition to 1.22 cfs leaving the project site by increasing the overall flow path and time of concentration for the onsite drainage basin. Implementing various site design BMP's such as a pervious paver drive aisle assist to further reduce the post-developed hydrologic runoff coefficient and volume of discharge. While additional runoff is routed to the 24" RCP storm drain in Tamarack A venue, the existing infrastructure has the capacity to handle the slight increase in demand due to the proposed project. This can also be considered a microdiversion, as runoff leaving the site from both discharge locations comingle several hundred feet downstream. All proposed onsite infrastructure including storm drain piping and area drains have been adequately sized with enough capacity to intercept and convey peak runoff of I. IO cfs generated onsite. Additional calculations and analyses including private storm drain pipe capacity can be found in the Appendix. Based upon the analysis included in this report, the proposed onsite drainage system is adequate to capture and convey runoff from the proposed project and discharge to the appropriate discharge locations. Page 3 oflO ... ----.. ---.. -... -----.. -... ----... ---------... ... ... - PLSA 2760-01 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 "Engineering Standards, Volume 5: Carlsbad BMP Design Manual", revised February 2016, City of Carlsbad Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov. Page 4 oflO ... .. -----------.. ---------------.. .. --.. ---.. PLSA 2760-01 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: 1 = 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 oflO ---------... -------.. -----------------.. -- PLSA 2760-01 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 ofrainfall anticipated from a given storm event (i.e. JOO-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 I 00 feet, and is dependent on land use and slope . 2.3 City of Carlsbad Standards The City of Carlsbad requires a Preliminary Hydrology Study be completed for projects larger than I-acre per Form P-2: Development Permits. The City of Carlsbad has additional requirements for hydrology reports which are outlined in the Grading and Erosion Control Ordinance. Please refer to this manual for further details. 2.4 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 at the end of this section, categorizes the land use, the associated development density ( dwelling units per acre) and the percentage of impervious area. Page 6 of 10 ---.. ---... -.. ----... ---... ... -... -------------... -- PLSA 2760-01 3.0 HYDROLOGY MODEL OUTPUT 3.1 Pre-Developed Hydrologic Model Output (100 Year Event) Pre-Development: *Rational Method Equation Q=CIA Pwo= 2.5 * I O0-Year, 6-Hour Rainfall Precipitation Basin A (Drainage Basin to Storm Drain) Total Area= 14,750 sf~ 0.34 Acres Impervious Area= 4,088 sf~ 0.09 Ac Pervious Area= I 0,662 sf~ 0.25 Ac 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 -0.90, Cn value for developed/impervious surface *Per SDHDM Section 3.1.2 Cn = 0.9 x 4,088 sf+ 0.25 x 10,662 sf= 0.43 14,750 sf Tc= ti+ tt ti@ 80'= 2.0% => 6.5 min from Table 3-2 ofSDCHM for ~14.5 DU/Ac tt => L = 92' .1.E = 1.6' tt= [ { l l .9(L/5,28O)"3 }/.1.E]"O.385 tt= [ { 11.9(92/5,280)"3}/1.6]"0.385 = 0.020 0.020 x 60 = 1.2 Min. Tc= 6.5 + 1.2 = 7.7 Min P6= 2.5 1 = 7.44 x P6 x D·0645 I= 7.44 X 2.5 X 7.7-0 645 ~ 4.98 in/hr !too~ 4.98 in/hr Q100= C*l*A Q100 = 0.43 x 4.98 in/hr x 0.34 Ac= 0.73 cfs Page 7 of 10 -----.. ----.. ----------------------.. ---- PLSA 2760-01 Basin B (Southern Drainage Basin to Tamarack Avenue) Total Area= 4,923 sf-+ 0.11 Acres Impervious Area= 4,002 sf-+ 1.68 Ac Pervious Area= 921 sf-+ 1.39 Ac 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 -0.90, Cn value for developed/impervious surface *Per SDHDM Section 3.1.2 Cn = 0.9 x 4,002 sf+ 0.25 x 921 sf= 0.78 4,923 sf Tc =5.0 Min *Minimum Tc per SDCHM r = 7.44 x P6 x D·0645 r = 7.44 x 2.5 x 5.o-0645 "' 6.59 in/hr !100"' 6.59 in/hr Q100 = C*l*A Q100 = 0.78 x 6.59 in/hr x 0.11 Ac= 0.57 cfs Page 8 oflO -------... -... -----------... ... -----------... .. -.. PLSA 2760-01 3.2 Post-Developed Hydrologic Model Output (100-Year Event) Post-Development: *Rational Method Equation Q=CIA P100= 2.5 • I 00-Year, 6-Hour Rainfall Precipitation Basin A (Drainage Basin to Storm Drain in Tamarack) Total Area= 17,293 sf-+ 0.40 Acres Impervious Area= 8,423 sf-+ 0.20 Ac Pervious Area= 8,870 sf-+ 0.20 Ac 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 -0.90, Cn value for developed/impervious surface *Per SDHDM Section 3.1.2 Cn = 0.9 x 8.423 sf+ 0.25 x 8,870 sf= 0.57 17,293 sf Tc= Ti+ Tt Ti =6.S min *Per SDCHM Table 3-2 for -14.5 DU/ Ac Tt = :ETt1 + Tt2 + TtJ _ 11.9 (liso ~) (1.49(R2/351/2)1 ( S 3)0.385 Tt -1.2 ft + 110.0ft/ 0.013 ( 1.49(R2/3 51/2)1 + 48.0ft/ 0.013 Tti = 110 ft/ (*4.21 ft/s) = 0.435 min TtJ = 48 ft/ (*4.21 ft/s) = 0.190 min *Velocity/ travel time though 6" PVC pipe *Velocity/ travel time though 6" PVC pipe Tt = (0.017 hrs + 0.007 hrs + 0.003 hrs) x 60 min = 1.65 min Tc= Ti+ Tt = 6.5 min+ 1.65 min= 8.15 min P6= 2.5 1 = 7.44 x P6 x D·0645 I= 7.44 X 2.5 X 8.JS-0645 ;,; 4.81 in/hr Q100 = C*l*A Qwo = 0.57 x 4.81 in/hr x 0.40 Ac= 1.10 cfs Page 9 oflO -----... -... -.. ---.. .. ... -------... ---... .. 1111 ----.. .. ... .. Basin B (Drainage Basin to Tamarack Avenue) Total Area= 2,379 sf-+ 0.055 Acres Impervious Area= 341 sf-+ 0.01 Ac Pervious Area= 2,038 sf-+ 0.045 Ac Cn, Weighted Runoff Coefficient, -0.25, Cn value for natural ground, Type B Soils PLSA 2760-01 *Per San Diego Hydrology Design Manual (SDHDM) Section 3.1.2 -0.90, Cn value for developed/impervious surface *Per SDHDM Section 3.1.2 Cn = 0.9 x 341 sf+ 0.25 x 2,038 sf= 0.34 2,379 sf Tc =5.0 Min *Minimum Tc per SDCHM r = 7.44 x P6 x D·0645 r = 7.44 x 2.5 x 5.o-0645 "" 6.59 in/hr lwo"' 6.59 in/hr Qwo = C*l*A Qwo = 0.34 x 6.59 in/hr x 0.055 Ac = 0.12 cfs Pre-Development vs. Post-Development (Undetained -Total Site RunofO Pre-Development (Basin A) Qwo= 0.73 cfs Pre-Development (Basin B) Q100 = 0.57 cfs Pre-Development (Total Site) Q100 = 1.30 cfs Post-Development (Basin A) Q100 = 1.10 cfs Post-Development (Basin B) Q100 = 0.12 cfs Post-Development (Total Site) Q 100 = 1.22 cfs Delta 0.37 cfs Delta -0.45 cfs Delta *-0.08 cfs *Total overall site runoff reduced in proposed condition from pre-development Page 10 of 10 ----.. ----.. ----------.. --... ---.. .. ---- 11111 -... ... ... APPENDIX A Hydrology Support Material +t 1 -t-t . + t+ t LUt : j-j- 1 ¢:>-l---+-i-4 +-+ f C') I . .._ .. r r ;t-. + + -4-c-I -:-: t + : H-f ttthll I t ·-t--+--+-+ L + ~+= ro + + ... -++ f t • t ~. J· ~ ,-+lf I ,-. + =1 rt t ·j • :: rrr t + + + Lt t ' ' j ~ i • j I l : r 1 1 +-t-' t t ~ . + . ... • + , I . -+--+--i--.L -t -W--~+ t +-+- -+-t-+ + + +--,~~~ t-+f-t +_ \---+--+ ( -. I 1 • l '•J +-- L~t---l---t~-t--+-io--t- +-t-++t-+ f-t+-+T+-rt --+-+ ... +-+-+-~ . t I -+-+- t t + ; <O -= ..... +--t-............... rt t +-... + I I t+~+-~+- ·,-. . . . • r + +-~ • f I -~•-.. ...... # ..... ---, . .. . . " . --,-,, . • !.-+-----+ . . ' . . : . . ' !-, .... __ ,, -,-----,- t tn ++4 t + + i-t-t--+-+ ~ +-+-l--+--+-+t--++ 33•3rJt +++-+~ ++++•+tr+ +i + l- \ Lttt l~ ', i t \ l}t+ tt . ·• ' /-.1---+.,.r-+t--+ + + ~ t i , • • I . . . . + 1 ••• : : • ' -3,,j15' ________,.._ .. ........J ...+-----:.•------. . 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N 4 E s 3 0 3 ~ THIS MAP IS PROVIDED WITHOlJT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INClUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANT ABILITY AND FITNESS FOR A PARTICULAA PURPOSE. ~ SanGlS. Al Rights R......,od. Thi$ p,oduCtS may oonta,, -.nation from the SANDAG Regional lmormation System ""1idl cannot bo --the written pennisslon of SANOAG. -product mayoonta,, lnfotmatlonwhlcl, has been ---granted byll-anas -....Maps. Miles ) ' ' ....... ...., ) .... 10.0 9.0 8.0 70 )' 6.0 5.0 ~ I f~ r--., .. : f"" 4.0 3.0 I 2.0 I -:l 0 ~ Q) .c ) ~ 1.0 ~0.9 ~0.8 s .!: 0.7 ~ i I 0.6 =. 0.5 04 ' 0.3 I I 02 0.1 ; ~ I I ""' I I I I I l I ...... ', ' ' ""-.. ' .... .... ..... . .... .... .. .... , .... ........... '~ 'i. ~ r-...., .. r... .. ... "" "'i.. ... ~ ~ .... , ""• .... i...., r..... . .. ""' ""i., ~ ~ .. .. 1-.. ... __ ~ ' ' .... ...... ~, ~ I .. ' I= 3.2 in/hr ..... ' ... .. ' ... ... r... "" '~ ,.. ... ~ ... """' ~ 'i... 'i., ~ ... , .. , .... .... " .. ' "", .. ..... t.., "' " ~ I tc 20min T l illlll Tl 111111 5 6 7 8 9 10 15 20 30 Minutes I I I .. ' .. ,, ,, ", ' ,, " ' " ' .. ' ~ ', 40 50 Duration EQUATION I = 7.44 P5 D-0.64S I = Intensity (in/hr) P5 = 6-Hour Precipitation (In) D = Duration (min) " ........ ' .... ......... I !',, ... . , ..... .... ' .... .. ...... ... .... .... .... ... .. ,, ' ~ ... ... ...... r-t~ " .... ", "'i-. """' , I ,: ,~ ' .. , I'.._ ' .. ........ . ..... .... .... 1 ..... " 'i.... .... 2 .. r ""..i... ' ...... ~' I 'i. ~ r ~ ~ ~ ~, • 3 Hours ~, I I - ' 4 I I I I I I I 5 6 'fl l !;; ,::, ~ 6.0 "§: 5.5 g 5.0 g 4.55' 4.0 ~ 3.5 ~ 3.0 2.5 2.0 1.5 1.0 Intensity-Duration Design Chart -Example Directions for Appllcation: (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 yrmaps included in the Design and Procedure Manual). (2) Adjust 6 hr precipitation (if necessary) so 1hat 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 Fonn: (a) Selected frequency 50 year (b) Ps = 3 in., P24 = ~ ,;s = 54.5 %<2l 24 (c) Adjusted P6<2) = _3_ in. (d) tx = 20 min. (e) l = ~in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. PS 1 1.5 L 2.5 3 3.5 . 4 4.S l 5 1 5.5 II- Duration I 1 T 1 I I I 1 1 1 I 1 1 1 5 ~63 ~9~.27.6'94?"> ·:~•'1"·'"·"·1714.49 15.81 ? 2.12~ 3.1814~4 5.30 6.36 7.42 8..:48_9.54 1Q,~:<h 11~66 12.12 10 1.68 ~~_J.37 4.2_1105 5,90 6.74 _?:.58 8.42 9.27 10.11 15 1.30 1,95 2.59 3.24 3.89 4 54 5.19 5,84 6.49 7.13 7,76 20 1.oa 1.62'2.1s;2.e9 3.2313.n 4.31 4.85 s.39 ·s .93 1 s.4¥ 25 J>-~ 1.40 1.87 2.3:!__2.80 3.27 3,13 4.20 . 4.67 .5.13 2:._60 _30 0.83 1.24J l.66.2.07.,L2,49,2.90 3µ_.3.~.+4.15 4_:!i6..._~ 40 o.69 1.03 1.38 1.n 2.01 2.41 2.16 s.10 3.45 3.79 4.13 SO 0.60 0.90~ 1.19~ 1~ J..1?,$-~-~-..1 2_,__&Jt 2.98 3.28 ...... 3.58 60 0.53 0.801 1 06 1.33 159, 1.86j 2.12 2,39 2.65 2.92 3.18 0.41 10.61 .0.82 1.~ 1.23 1_.431 (6:!_ 1.~-t:2.04 ,.2~~ 2.45 o.34 !o.51Jo.eaj°.as 1.021119 t.36 1.53 1.10 1.87 2.04 0.29 l°'«}Q;.0.59 0.731 0,si:+rt~~ 1~ 1.47 ..!.:..61 _).76 I 0~ o~Jo·~ o.~,.,o-?! 0,!)1 UM I ua 1.31 1_,:44 1.57 0.22 _t°•~I0.43 0-~~65U>,7~0!J7 j 0.98 1~Q.S-1.,~'Tf~ 0.19 o.281Q,38Jt,u;o.56+:<>:_~T Q.75 j 0.ss , 0.94 , 1,03-+-1.13 o.11 Jo.2s1o.33 0.42 o.so,o.sa o.67 o.75 o.84 o.92 1.00 I' 3 -2 .E San Diego County Hydrology Manual Date: June 2003 Table 3-1 Section: Page: RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Type NRCS Elements Coun Elements % IMPER. A 8 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 (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 Medium Density Residential (MOR) Residential, I 0.9 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 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 12 of 26 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 (T1) 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 . . .. . . . . -.. . ••: t .;-; ••: t ·•• .. ·•• t ••: :, ·•• ., ... , ... ·••"' ... .,.,., ... , .. ••:"'-• . ::f!.;e . .-;, I . •• ,J •• ... " ~ . .. , . ,. t • C '\ ,. . .,.,;· .. .. • .. .. . .,,......,. . 0 . · c:l)' . ,. ~\\ ~ (:, ,. I, ~ -,. t Ill~. '(\ ,. ~ ..... ~ ~e,'+-~~( :: ~~ -S-. ~-' IS'(' \ ~ \, !),--le C" . .. 'br,'¥-.,,. 'b( -'\'b~ \. '\ 'S l!l~ ~~~"::_.;. \ \:•- ,;-;, I ... ,., .. , ·1:. :, I .. ~:- . . . .. I . ... --• . . .. . Hydrologic Soil Group-San Diego County Area, California MAP LEGEND MAP INFORMATION Area of Interest (AOI) D Area of Interest (AOI) Soils Soil Rating Polygons A D AID B ....... D B/D 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 --Conservation Service Cl C • CID • D • Not rated or not available Water Features Streams and Canals Transportation ++i -----~ 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 10, Sep 12, 2016 Soil map units are labeled (as space allows) for map scales 1 :50,000 or larger. Date(s) aerial images were photographed: Nov 3, 2014-Nov 22,2014 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. 9/6/2017 Page 2 of 4 Hydrologic Soil Group-San Diego County Area, California Hydrologic Soil Group Hydrologlc Soll Group-Summary by Map Unit -San Diego County Area, Callfomla (CA838) Map unit symbol Map unit name I Rating I Acres lnAOI Percent of AOI MIC Marina loamy coarse B 1.0 sand, 2 to 9 percent slopes ~ J-Totals for Area of Interest 1.0 ~~ 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 D) and three dual classes (AID, BID, and CID). 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, 8/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 :iiiii Conservation Service Web Soil Survey National Cooperative Soil Survey 100.0% 100.0°/o j 9/6/2017 Page 3 of 4 Hydrologic Soil Group-San Diego County Area, California Component Percent Cutoff: None Specified Tie-break Rule: Higher USDA Natural Resources :iiiiii Conservation Service Web Soil Survey National Cooperative Soil Survey 9/6/2017 Page 4 of 4 .. "" ... ~ ... .. • ,. .. " • ... .. .. -.. • .. -~ ~ .r· s s s " I "\ '. " \ s ". \ s \ POR.LOT5 MAP9825 < " \ \ s 'l! ~@ " ~i '5'6. \~ ·. I ·. . \ s \ ' \ct < POR. LOT5 MAP9825 ._________.,-, s s " s s .toldw .tillll21al TCUliWJ'E 438 T,tJ,WUCX\CIV!l\l!EPORTSlll'f'OG~-HYDRO.""V s EXISTING HYDROLOGY EXHIBIT 438 TAMARACK AVENUE / (45.TFG) Q ... 0.13CFS NAUTICAL DRfVE- s (PRJVA1E} /' --------- Q1/JO:Q.57CFS / BAS/NA AR.EA= 14,751JSF {0.34AC} en~·o.43 s ' s / ~ --\.__ TAMARACK AVENUE PLAN VIEW-EXISTING HYDROLOGY SCAl.£:!":!O' s POR. LOT5 MAP9825 .,,.,, I I '--~ '--"'-,. ~ ,~ • t "' s s \ ~ \ ~\ ~\ \ ~Q \ 0"' ~ LEGEND =---MJ.W:,ENTLOTUNEIRIGHT-0'-WAY """"-"'""""" -'""'"""""' """"""""",,,, EXJSTN$A..OWPA1H ··-···- """"'"""""- EXISTN3.IFE1MXISAREA W///M BASIN A -AR.EA CALCULATIONS a,,s,wATOTAI.AREA U,75/JSF(D.:U.4C/ MS/NA ll'EIMCtlSAREA ,.r&SF MSIIAl'BMOUSAREA !O,B&'SF li.ll'EIMCIUS 27,,S o, 0.43 BASIN 8-AREA CALCULATIONS 8ASIH8TOTAI.AREA 4)123SF(O!llrC) 8ASIH B.M'EIMO!JSAREA 8ASIH B PEJMOUS AREA ......... " _,._._. " ' """ m, 81.311, , .. GIIN'HICSCAI.£ l":10" " ~ ~ PASCO LAREY SUITER & ASSOCIATEBI CML EH81NEERIN8 + LANO PU.NNINII + LAND IUIIVEYINII SHHan:llftlp1Nfl01,. ... A. ..._._.CA '2075 plalSUSUJl:l j l'.IUUM,4111 I~- PI.Sot2llill-lll .. "' .. ... .. • ,. JI. 1' J. ,, • .. ll ' .. A & .. - " \ , , " I ". \ '. " I , ", \ . POR. LOTS MAP9825 ' , I \ ' " 'l! 12@ c,.,: " §t C, \1 " ", \ ' ,_ I ~ \ , ", , , ....______..., , ' POR. LOTS MAP9825 , 01001 0.12as • ~=:~-,: -'--- 1 J:Lbo, J:it,ol27ll0 TOCIRIWN: 438 T~~7SIH'r'D'ia~.dlov s PROPOSED HYDROLOGY EXHIBIT 438 TAMARACK AVENUE ,/ ' NAU11CAL DRIVE (PRNATE) I ,/ I ""' ., .. .~ .. "- I. 41.SFI. ~ ----. / -j..,._;.-" .. , -"'-----\· / I ' 1:1 ' TAMARACKAVENUE !I! ~ 'I I «JJJEIH QIOO ~ 1.10 CF$ -,-----·-+~-:.~ PLAN VIEW. PROPOSED HYDROLOGY SCA!E'.f":10' ; F I F I POR. LOT5 MAP9825 _,,, '---.... "' ~ 4Ulf> \ ~\ it\ ~Q \ ~~ "' LEGEND """" -,,,,,_ NJJN:ENTwr IJE IRIGHT-0"-WAY """""""""" DRAfi4GE MSl4 80!.NWIY """""""""''-" """""'""""" PROPOSEDFI.OWPA1H ··-···- """""'""'""'M<COON """""'""""""""' tv½?ffA PROPOSED PEIMOUS PA,BIB#T BASIN A -AREA OOCULATIONS TOTAI.BAS/HNIEA ,,_.......,._ ""'"""""""" """"""'""'. 0, BASIN B -AREA CALCULATIONS 17.NJSF """' 8,8roSF ~" OY TOTAl.8'\&WAREA 2,379SF IIAS'o' IMPEIMOUSAREA 3'1 SF 81.SWl'EJMCtlSAREA .ZD.VSF IY'EIMOl.lSAREA5 14.~ 0, "" GilAPHIC SCALE 1•: !O' '" '" • ~ PASCO LARET SUITER & ASSOCIATESI CML £N81NEERIN8 + LANO PI.ANNIN8 + LANO 8UIIVEYIN8 "'~Jl!tbarlH, ... A. SC1Jaaaa.m,CA'2015 lplt. UI.Ut.12121 ts UUSUll:I I~ Pls,\2180-01 Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 30® by Autodesk, Inc. Monday, Feb 12 2018 8-in PVC Pipe Capacity Circular Diameter (ft) Invert Elev (ft) Slope(%) N-Value Calculations Compute by: Known Depth (ft) Elev (ft) = 0.67 = 40.00 = 1.00 = 0.013 Known Depth = 0.66 Highlighted Depth (ft) = 0.66 Q (cfs) = 1.224 Area (sqft) = 0.35 Velocity (ft/s) = 3.47 Wetted Perim (ft) = 2.1 0 Crit Depth, Ye (ft) = 0.53 Top Width (ft) = 0.00 EGL (ft) = 0.85 8" PVC pipe at 1.0% has capacity (1 .22 cfs) to convey peak runoff generated onsite of 1.1 cfs. Section 41 .00 ~-----------------~------------ 40.75 --+-----------------+-------------- 40.50 --+-----------------~'----------~-- 40.25 --+-----------------.+\--------------+-- 39.75 __,_ _________________ .L,_ ___________ _ 0 Reach (ft)