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HomeMy WebLinkAboutCDP 2017-0021; OCEAN STREET RESIDENCE; HYDROLOGY STUDY; 2017-03-24John P. Strohminger HYDROLOGY STUDY 2680 Ocean Street Carlsbad, CA 92008 Shafran Coastal Residence CDP 17- Prepared for: Alan Shafran 1673 Amante Court Carlsbad, CA 92011 Prepared By: John P. Strohminger RCE 55187 dba Pacific Overland Engineering & Surveying 635 Via Columbia Vista, CA 92081 Date: March 24, 2017 Date TABLE OF CONTENTS 1 P . D .. . roJect escnpt1on ............................................................................................................. 2 1.1. Existing Condition .................................................................................................. 2 I .2 . Proposed Condition ................................................................................................ 2 I .3. Soil Characteristics ................................................................................................. 3 2. Rational Method Description .............................................................................................. 3 3. Hydrology Analysis ............................................................................................................ 4 4. Water Quality ..................................................................................................................... 4 5. Hydromodification .............................................................................................................. 4 6. Attachments .......................................................................................... 5 7. References .......................................................................................................................... 6 1. Project Description This project is a 0.08 acre residential parcel located at 2680 Ocean Street in the City of Carlsbad. Ocean Street is a public street that connects with Cypress A venue to the north and Beech A venue to the south. An existing single family residence and detached garage are currently onsite. Proposed improvements consist of a single-family detached dwelling unit, driveway, and replacement retaining wall along the rear property line. The site's APN number is 203-141-10- 00. The legal description is Lot 84 of Map 2037. Attachment 1 shows the Vicinity Map. 1.1. Existing Condition The existing site has a single-family residence, detached garage and driveway at an average elevation of 44 feet above Mean Sea Level (MSL). The elevation of the street fronting the property is slightly lower at 42 MSL. There is a 6 foot high retain wall along the rear property line. To each side of the project are single family residences at the same elevation. To the rear is a parking lot for a condominium project 4 feet higher than the project's rear yard. Storm water from the site surface flows to the street, continues on the surface north along the east side of Ocean Street and on to an inlet 150 feet away. From there the water is conveyed to the Pacific Ocean in an underground conduit. 1.2. Proposed Condition The proposed project proposes to demolish the existing residence, garage, rear wall, fences and hardscape and replacing them. The improvements and grading will disturb 0.09 acres. The new drainage pattern is virtually the same as the existing drainage pattern. There is a high point in the rear yard; storm flows around both sides of the house and joins at the street. Flows then continue on the surface to the existing inlet mentioned above . 2 1.3. Soil Characteristics The following soil group definitions come from Technical Release 55 (TR-55) by the United States Department of Agriculture: Group A soils have low runoff potential and high infiltration rates even when thoroughly wetted. They consist chiefly of deep, well to excessively drained sand or gravel and have a high rate of water transmission (greater than 0.30 in/hr). Group B soils have moderate infiltration rates when thoroughly wetted and consist chiefly of moderately deep to deep, moderately well to well drained soils with moderately fme to moderately course textures. These soils have a moderate rate of water transmission (0.15-0.30 in/hr). Group C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water and soils with moderately fine to fine texture. These soils have a low rate of water transmission (0.05-0.15 in/hr). Group D soils have high runoff potential. They have very low infiltration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a clay pan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very low rate of water transmission (0-0.05 in/hr). The conservative approach is assuming Group D soils for the site. 2. Rational Method Description The rational method, as described in the 2003 San Diego County Hydrology Manual, was used to generate surface runoff flows, which were then used to size the drainage facilities. The basic equation: Q = CiA C = runoff coefficient (varies with land use) i = Intensity (in/hr) A = Area (acres) The 6 hour and 24 hour rainfall isopluvial maps are found in the 2003 San Diego County Hydrology Manual. Adjusted P6 calculations can be found in the Attachments. Initial travel time calculations (Ti) are based on the overland flow equation given in Figure 3-3 of the County's Hydrology Manual and is limited to the maximum overland flow length in Table 3-2 of the County's Hydrology Manual 3 3. Hydrology Analysis The Zoning for the project is R-15 with a maximum density of 15 dwelling units per acre. Table 3-1 shows the MDR with 14.5 du/ac coupled with a soil type D to have a runoff coefficient "C" of 0.63. From the County Rainfall Isopluvials P6 is 2.5 and P24 is 4.2. The adjusted value for P6 remains 2.5. From Figure 3-1 the resultant rainfall is 5.5 inches per hour. From Table 3-2 MDR coupled with a slope of 2% warrants a maximum overland distance of 80 feet and a Time of Concentration equal to 6.5 minutes. Per the equation in Section 2, Q=CiA, Q=(0.63)(5.5)(0.09) = 0.31 cubic feet per second for both the existing and proposed condition. 4. Water Quality The project is a Standard Development Project per the completed Storm Water Standards Questionnaire (E-34) provided in the attachments. The project is therefore not required to submit a Stormwater Quality Management Plan (SWQMP). The project is required to incorporate Source Control and Site Design BMP's. The Standard Project Requirement Checklist (E-36) address these BMP's and is included in the attachments. 5. Hydromodification This project is exempt from hydromodification requirements since it is not a Priority Development Project. 4 6. Attachments Includes Vicinity Map, Table 3-1, Isopluvials, Figure 3-1, Table 3-2, E-34 and E-36. 5 0 Ar y an · Novy Acaoemy Boo store 2680 Ocean Street Beach Terrace C Inn Cnrtsbad Mvgcc Park Mel oir Properties 0 Swn·ni's Cofe Carlsbud I l SHEET T!TlE ~PN JOJ-1-1'-C.i \ \ \ \ \ \ \ \ Exist & Proposed Drainage 2680 Ocean Street, Carlsbad, CA 92008 John P Strohmin9er Engineering / / 0ATE:3-26-2017 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 Elcmc11ts %IMPER. A B Undist"ltrbed Nat11ral Terrnin (Natural) Permanent Open S11ace 0"' 0.20 0.25 Low Density Residential (LDR) Residential, 1.0 DU/A or less I 0 0.27 U.32 Low Density Residential (LDR) Rcsidc11lial, 2.0 DU/A or less 20 0.34 0.38 Low Density Residential (I .DR) Residential, 2.9 DU/A or less 25 0.38 0.41 Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 Medium [)ensity Residential (MDR) Residential, 7.3 OlJ/J\ or less 40 0.48 0.51 Medium Density Residentinl (MDR) 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 Resi lcntial (IIDR) Residential, 24.0 DU/A or less 65 0.66 0.67 IJigh Density Residential (II DR) 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. om) General Commercial 85 0.80 0.80 Commen:ial/lndustrial (O.P. Com) Orfiee Professional/Commercial 90 0.83 0.84 Commercial/Industrial (Limited l.) Limited Jndustrial 90 0.83 0.84 Commercial/Industrial (General I.) General Industriill 95 0.&7 0.87 C 0.JO 0.36 0.42 0.45 0.48 0.54 0.57 0.60 0.69 ().'.78 0.78 0.81 0.X4 0.84 0.87 3 6 of26 D 0.35 0.41 0.46 0.49 0.52 0.57 0.60 \of>Jl 0.71 0.79 0.79 U.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 J.1 .2 (rqJrcscnting the pcrvious runoff coefficient, Cp, for the soil type), or for areas that will rcmnin undisturbed in perpetuity. Justification must he given that the area will remain nalurnl forever (e.g., the area is located in Cleveland Nalional Forest). OU/ A = dwelling units per acre NRCS = National Resources Conservation Service 3-6 'I :13-00• - ; I I 'V I' I L·~~· I' j ~ l I I I' l I ( "' " to L--· ... ~. -· ·----~-r,-----,- .'·1 .. ,- 'l. l ·· .. , •, ,•, ·, .... ·· .. ',,,, •· I (J) I 'I _____ J 'r·. • -t" .1 ...·--···· ... ' .... ... 1.J) ( .. >···~--r j_·J t,-,... . ...... -~ .. :.:.l ... :t:!115' 1 ·i 5· .. '. 1"' I • '>•.[ I 1 I . I ' . ··. ,·-1 ... --:.:.::.:.::.::·· ·-. I I .. ' ln , ~I ...__(,,~~ ·. -~ ·--.... · I . ., '·J I f i I o· C ., ... t County of San Diego Hydrology Manua1 Rai11Ji-..1/I f.c;op/u1 iuls IOO Year H~11_f,i1J J,;vt•11f -(dl!!_!u·s ) ·,, '/ -C IS f'o ......... ,11111,,,u,-, . ,.,, .. "~" ....... ·-· ~.~GS '.\', I t.1,. :•n '1,,,1, ("I-,,,!! N ,•;:~~ ~t'!';i!:!:_t"r::~:; ~ 7::-~~·!:; ~.;~:,_~~.~~;_:~.:;: * ... ll(lt(ll.,,OAIKllh'Jf¥Jllf1tt•i1 u'IHAr Ntllo'tx.U,,.._ .. 'IJ\f ·~,-., .. u'\.IJl"""•"•-......i. ,.,,,~......,..,,_,, ...... "','I" ..... ,_ W.W!u.1111~··"""'' .. ~ W I: !.:::"~::::;-... ~~;_;Z!:' 1"-r-·>#•..,,---.., If-, ..... ,., ... .., .... _,,,, __ ,...,,..,.,,.,,,_.....,,.., ... _ ,_, ___ ,._, 1,,_,,~,,_. .. ,,, ........ s 3 O 3 Milos ~ _j '! . I I' I, :13·00 i I ! I 1 ' I I I ' I 1?",!!;1 - '' l I' . :1?'!!0' I' ' ti t .L-:...,-1,} I <\ I\• (I) \\• t;,\ l I i I I: I i .I ii I --, ....--1-----l- ~!? ! 1 ,~ I :! I ' I I I :.l..,-1, b 0 ~ ! -!---.!.---"--l..--· ,1 j I ~! 1o ;: I • I ·-rt · ·-h j· -~--1' <') lo ::; I ___ L .. ·-' , . I i . __ '._ . :.1,-i__ 'lo Ir I I .. I !'! I I ' · 33•:10· ' ) 0 r. :.1 :~ County of San Djcgo Hydrology Ma11ual l?oi11/ul/ lsoplu viulx I_ ··i l. -(.' --· G.IS r,_, .............. ,~,.~ ~~-GIS '\\·, 11. ,. ·,, i)1q•11t u,, n ,I! N 1tr,1A1•!:ll'>~J','11)(_11·M111(,u1 ,.,11,nt111/1'ft.T i.1111~•11111.-ilt>tf'fff','' * t'IIIIIUIOth"~\ll'"'-'!P.1111'1:•ll._1Ul111f\.l .. MI.IIWAMfiN!llfi "' ""'"' 1W1f1':;ft/f) IIUIJ rn11r.s-~,,111 Al'AIU•·1a.N1 ,..., .. r,~ ,...,.--.,.1-•lr'l..,,.f\VhH•,r,,..., \V 1: ~:7:£:f]~~~7::~.~;i:J~~.!-.. "' 1,,1 ...... ~-.. -~~---""':'1:.-:~,-·'1 -.i- s 3 0 3 Miles l"2"'.i,, _; 10.0 9.0 0.0 7.0 6.0 5.0 4.0 3.0 2. 0 -.::-::J i C: 1-0 C 9 >,o. £: ~o. 6 ~o .E . 7 ' " 1-,. "'l'I.."' 'r... .... " 1', ' ......... .:-.. I",. 'r,.. ... " ....1', .... I',. i"i,.. "'r- " . ,-.. . r-.1" t-.,. 1," "~ r-.. 1'. ... " ,., ~ -i",,~ ' ... r, --I~ .... ' :,..~ ""' .. ~ .... .. ... .. ~ EQUATION ~+-J~d--1~~-.;A*f*pt.;:1"1-l;HtfitttHtffim-t-HiiHttttttttil I ... 7.44 P6 o -0.645 ~c--++~1-+~.H,~r!:-f:!N::~~"!t-lR"fq:rl'MffitiHtttittltttflittttt I = Intensity (In/hr) ' ' "i.. 'i-. ', 1, ':-.. .. ~ ~ .. ... ' ~~ "'r-,. "' ~ ~ ~ "" :,.." .. ~I ~k .... P6 = 6-Hour Precipitation (in) W-l-+~W~)j...jf--+~tt~!-fl~~d'R-i~mfHqtittttl-ttttll o = Duration (min) ' ·, i-,.' i' .. .. .. "'k I i .... ..... N. ""'~ I k~ .. ~ ... I ~ I'-.... . j "" ~ "'~ i--., r~ ~ ~ .... i', ... "r,.. I ,_ ~~ " I ~ r--..._ I ~ r,.. .... r-.. '"'r, " ""' I' "-. , ... r-, I• ,..,., "'r-l "'~ ~ I i--.. , .. "" .... .... ... " r I', ... . 1,.."'i-.i,.. ... 't-.. 'i.. i.. ... .... , i..i.. " " ' .... I',, "i.. I " ~ l,k~ r,..."' ..... "'r,,. ' 1, i-. .. 1'-. I', I 0.3 _~--__ ;_ ---1-----1-__ .,.,_ •• 1---_: -~~ -: ---- 0.2 -~'-1-----·---- l--l-,i--f-1---t-~I--1-, --- . -... .,-- •I-----L--: ·-~ ,, : •. ~ - ... 1111.•L•.Ll.l.i.1 0 _111 t--t-I--.. _j_"".j..j .. ",W.j.J,f!_1',\ . t =t =t:11::.t=-1-,_-1,_e--1.--1-'--1---1---1----1--++-+t++·1+1-l+11-1·1·l1 i+UI-IHl·~-\:i+'.i~':~+:1ti.'.~f11+'¼\t~l+H·f+IH+-·-+_+_+,_+_+,_-t_+·1 ... ·1-t-t+HHt lrH-t-tttfl!t-·-1--1--• -----··--· 5-, 1---,__ ------i......l-l.-1-1,-1-1--H-· l-l--l---lf-~-1--1-+-I---1--_,_._,...._,,..._.. _ _,., •.. ........... M-H·•"+l>++I • -,-l-------• · ... ,.., ........ ,. .. ..._,.,., ll+ll+Hl-H.J.HHl-1--11-+-+·++-H+I-H+HH·Hl+H+l+HII l--!--l-1-J.-l--l-+-H-l-1-•-..... , .i..i..w.>.._..,_......,...._.., . ..i_,......,, H--1--lf-~-Hf-l-H--·~·1-1-11-1~-l~-Hi.J.1.lll -·-+--+-+-t-t·--·-I--L-'---IH-··1-1--1--Hl!-H-- 0.1 I-J-4-l-..j....;H--+-LL...LI+J-LL-4-lll..W.i.J.4lllllJJ.IJ.lf--U-l..lfJW..U+w-.U.W.J..U.L1JJ.1.Li....i..-t-J..J...:....i..4L.U.J.J-tJ.1J.J-'-f-L~ 6 6 7 8 9 10 15 20 30 40 50 2 J 4 5 6 Mlm,tes Hours Duration 7' I g ... ,:J ii) 6.0 i 5.5 ~ 5.0 g 4.5 '§' 4.0 i 3.5 - 3.0 2.5 2.0 1.5 1.0 Intensity-Duration Design Chart -Template 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 u,at it is within the range of 45°/4, to 65% of the 24 hr precipitation (not applicaple to Desert) . (3) Plot 6 hr precipitation on t110 right side of the chart . (4) Draw a line through the point parallel to the plotted ·1ines. (5) This line lg the Intensity-duration curve for the location being analyzed . Appllcatlon Form: (a) Selected frequency !DO year 2 -4 2. p._ r-1 (b) P6 = ~ in., P24 ::: _, __ .~ = _:> ___ %(2) z ~ 24 (c) Adjusted Pl?l = · in. (d) t = U '1? min. X --- (e) I = ~ in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. ·,,a 1 1 11.s l· 2 : 2.s • 3 -. 3.!i 4 --i:il ... ii .... ,. s.s : a · Ournllon • I I i I ; I j ·, ; I I : j i' .. , I . I , · ::-J _2.63 ~:~~16~?16 6~.: 7.90 19.22 10.54; 11.80113.'7 14.40 15.01 7 ?,1..~.l~.1!.l 4.,2~ j [.30 ;!J.3~ 7.4-2 8.48 ' 9.54 ! 10.60 11.iiii 12:f:a 1_0 !)~!!. ?-~~ §_.3?; :1.21 1_1!;05 5.90 6.74 T 750 ' 8.42 9.27 iii.fr 15 1.30 1.9G 2.59• 3.2•1 13.UO 4.5'1 5.19 5.04 • 6.49 7.13 7~76. 20 foci 1.o;fffs: 2 ire :i-?-~ 5.r[ 4_.:iJ 1 .fl!s , ~:i~ . !i._jlff s.4il ..~6 . 0.93 !.,_:101 .!:.87. ;_?.~~ .~_.H!) 3.2!. 3.73 I 4.~f? i .:1_.67 5.!_3 5~Q .... JR _Q.8_3 10g~_1.aa]_2.01:2.40 _?;_99 !1·:!.~I E:3 I ~,1~. 4.~6 4.88 19. .Q,~ l._«1_3 1_._38. 1.72 :2·?712.41 2.7~-• 3.!0 /-"§. 3.J~ .1-!3. _ ~o . Q.GO [.~I 1._19 : 1.49 I 1.1912.0~ 2.39 ! 2.so 2.~. 3.2a 3.58 __ 0~ _Q.?3 0.80 )-~_: 1.33 ,· 1 .. 59 1 1.86 2.12 1' ;!.~9 I 2_,65 .. ,'..!12 -~.)~ 90 0.41 0.61 0.82 1.02 1.23 1A3 1.63 1.84 12.0<1 2.25 2.45 --120 ··o'.3~· fiff ififo ; 0.85 ]i .o2 1 I" 1.36 I 1.53 _ 1.70 .' {ij7 °2.0il .. _ ... 1.so 0.20 OAil o.59 I_0.731.Q:~~ 1,_o-9 , 1...!_6_1 f_.~f, .. ~.-i'7J _),G,~ ... 1.1~ . ..... ...l!!Q .Q~ . .Q::l..9 .Q2.li o.~540.1s o.s1 1.o.1 J .. 1_0 .. l:~t J 1~41 .. 1.-E. ·-···-_2~0 E? _O,!!.:~ 0.-1_?. Q_.~4 10.~~ 0.7~ 0.6~ 0Jl8. 1 LO~ .. 1 )~ • !,~ 300 0.10 0.28 0.30 0.41J0.5G 1>.136 0.7t, 0.65 I 0.94 i 1.03 1.13 · .. 3 ,fo o.i i o.2s,o.:fa Io.~.! ro.r.o ti.so o.si 0.1s : o:a;;·; o.92 1.00 F I 3-1 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 ,vl1ere 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. The6e Yalues can be used in planning and design applications as described belov,1. Exceptions may be approved by the "Regulating Agency'· when submitted \vith a detailed study. Table 3-2 MAXIMUM OVERLA.ND FLO"' LENGTH (LM) & INITIAL TIME OF CONCENTR.I\..TION (Ti) Element* DU/ .5 % 1% 2% 3% 5% 10% Acre LM Ti LM Ti LM Ti L'-1 Ti L t-.1 Ti LM Ti Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9 LDR I 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 1 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