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Home My WebLink AboutCDP 2022-0031; ADAMS HOUSE; DRAINAGE STUDY; 2023-10-31 Drainage Study Adams Residence Portion of Lot 8, Block C of Map No. 2152 4368 Adams Street Carlsbad, California 92008 Prepared for: Curtis Ling 3667 Adams Street Carlsbad, California 92008 Prepared by: Christensen Engineering & Surveying 7888 Silverton Avenue, Suite “J” San Diego, CA 92126 (858) 271-9901 October 31, 2023 ( Introduction This project involves removal of the existing single-family residence and appurtenances from a portion of Lot 8, Block C, Bellavista, Map No. 2152, 4368 Adams Street, in the City of Carlsbad. Following its removal, a new single-family residence with an accessory dwelling unit and appurtenances, including landscaping, drainage system and retaining walls will be constructed The attached drainage area map is from a topographic survey by Coastal Land Solutions, Inc., dated June 24, 2021. No runoff is tributary to the project parcel and so only runoff generated on site, is the subject of this study. Prior to construction runoff flows to Adams Street, westerly of the site. Following construction, the same pattern will remain. Total runoff from the site increases from 1.33 cfs to 1.84 cfs, an increase of 0.51 cfs. The existing site imperviousness area is 9,781 sf. The project will create/replace 8,825 sf. Impervious area to be retained (not created/replaced) represents 1,951 sf. Total post construction impervious area is 10,528 sf. Runoff from the site is collected in the public storm drain system northerly of the site, at the southeasterly corner of the intersection of Adams Street and Hoover Street. Before and following construction, site runoff does not flow over neighboring properties. The San Diego County Rational Method was used to calculate the anticipated flow for the 100-year storm return frequency event. The drain system was tested and found adequate to convey anticipated runoff. Antony K. Christensen RCE 54021 Exp. 12-31-23 JN A2022-01 10-31-2023 Date Calculations 1. Intensity Calculation (From San Diego County Hydrology Manual, Figure 3-3) Tc = Time of concentration = 1.8(1.1-C)Dist. 1/2 ( S 1/3 ) Since the slope over the area with the greatest elevation change is (39’/268’) 14.6% over the site and the distance traveled is 268 ft and the runoff coefficient is 0.40 (22.9% pre-construction). Post- construction flow is 220’ @ 16.8%, C= 0.50 (38.2% imperviousness post-construction). Tc = 7.3 minutes (pre) Tc = 6.3 minutes (post) IX = 7.44 P6 Duration -0.645 IX = 7.44 P6 Duration - 0.645 Since D = 7.3 Since D = 6.3 IX = 2.06 P6 IX = 2.27 P6 from: San Diego County Hydrology Manual Rainfall Isopluvial Map for 100 year Rainfall Event – 6 Hour P6 (100) = 2.5 The six-hour storm is selected over the 24-hour storm due to its closer approximation to the site’s time of concentration. So: I100 = 2.06 (P6) I100 = 2.27 (P6) I100 = 2.06 (2.5) I100 = 2.27 (2.5) I100 = 5.15 inches (pre) I100 = 5.68 inches (post) 2. Coefficient Determination For residential area From Table 3-1 Soil Type = B Imperviousness pre-construction = 22.9% Imperviousness post-construction = 37.3% From Interpolation: Pre-construction C = 0.40 Post-construction C= 0.50 3. Volume calculations Q = CIA Areas of Drainage Pre-Construction Area of site (no runon) ES = 0 6480 Acres Post-Construction Area of site flowing to Curb outlet 2 RNE = 0.2086 Acres Area of site flowing to Curb outlet 1 RW = 0.1629 Acres Area of site flowing westerly G = 0.0444 Acres Area of site flowing to Adams St REM =0.2321 Acres Q100 (ES) = (0.40) (5.15) (0.648) Q100 (RNE) = (0.50) (5.68) (0.2086) Q100 (RW) = (0.50) (5.68) (0.1629) Q100 (G) = (0.50) (5.68) (0.0444) Q100 (REM) = (0.50) (5.68) (0.2321) Q100 (ES) = 1.33 cfs Q100 (RNE) = 0.59 cfs Q100 (RW) = 0.46 cfs Q100 (G) = 0.13 cfs Q100 (REM) = 0.66 cfs Total 1.84 cfs 4. Discussion Pre-construction the site runoff flows westerly to Adams Street. Following development, the site will continue to convey its runoff to Adams Street. There is a calculated increase of 0.51 cfs for the 100- yr return frequency event following development, and is conveyed to the same public storm drain, located in Adams Street as it is before development. See the attached printout for velocity of runoff at the two curb outlets. APPENDIX Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Oct 31 2023 CURB OUTLET# 1 (D 39) Rectangular Highlighted Bottom Width (ft) = 3.00 Depth (ft) = 0.07 Total Depth (ft) = 0.25 Q (cfs) = 0.460 Area (sqft) = 0.21 Invert Elev (ft) = 100.00 Velocity (ft/s) = 2.19 Slope(%) = 1.50 Wetted Perim (ft) = 3.14 N-Value = 0.013 Grit Depth, Ye (ft) = 0.10 Top Width (ft) = 3.00 Calculations EGL (ft) = 0.14 Compute by: Known Q Known Q ( cfs) = 0.46 Elev (ft) Section Depth (ft) 101 .00 ----r-----r-------.------..------~--------.---------r------.--------,-1.00 100.75 --+-----+-----+-----+------+-----+-----+----+------!-0.75 100.50 ---+-----+-----+-----+------+-----+-----+----+------+-0.50 100.25 ----i'---.......-----+----+------+-----+-----+----...... --....... -0.25 100.00 --+------+-----+----+------+---....... ----+----+------f-0.00 99. 75 ---+-----+--------+------+-----+-----+----+------+--0.25 0 .5 1.5 2 2.5 3 3.5 4 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Oct 31 2023 CURB OUTLET# 2 (D 40) Rectangular Highlighted Bottom Width (ft) = 3.00 Depth (ft) = 0.08 Total Depth (ft) = 0.25 Q (cfs) = 0.590 Area (sqft) = 0.24 Invert Elev (ft) = 100.00 Velocity (ft/s) = 2.46 Slope(%) = 1.50 Wetted Perim (ft) = 3.16 N-Value = 0.013 Grit Depth, Ye (ft) = 0.11 Top Width (ft) = 3.00 Calculations EGL (ft) = 0.17 Compute by: Known Q Known Q ( cfs) = 0.59 Elev (ft) Section Depth (ft) 101 .00 ----r-----r-------.------..------~--------.---------r------.--------,-1.00 100.75 --+-----+-----+-----+------+-----+-----+----+------!-0.75 100.50 ---+-----+-----+-----+------+-----+-----+----+------+-0.50 100.25 ----i'---.......-----+----+------+-----+-----+----...... --....... -0.25 ---------------~7 --------------= =- 100.00 --+------+-----+----+------+---....... ----+----+------f-0.00 99. 75 ---+-----+--------+------+-----+-----+----+------+--0.25 0 .5 1.5 2 2.5 3 3.5 4 Reach (ft) AE Feet SDDO 4D00 EQUATION Tc = (1~t)0.385 Tc == Time of concentration (hours) L = Watercourse Distance (miles) .6.E = Change in elevation along effective slope line {See Figure 3-S)(feet) 3000 3D00 0.5 ' ' ' ' 30 20 300 5 200 AE L SOURCE: Callfomia Division of Highways (1941) and Kirplch (1940) Nomograph for Determination of Tc Hours Minutes 4 3 2 1 ' ' ' Tc so 40 30 20 18 16 14 12 10 9 8 7 6 5 4 3 Time of Concentration (Tc) or Travel Time (Tt) for Natural watersheds FIGURE ~ I-UJ UJ u. z UJ (.) z <! I-Cl) 0 UJ CJ) a:: :::> 0 (.) a:: UJ I-<! ~ 2.50% slope--#, 2.0--+-----#111 100 t-----'-1~-5~---+-~--------~-~-411~:#~~~-#-- 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 20 Cl) LU I-:::, z ~ z LU :E i= ~ 0 -' u. 0 z <{ ....I a:: LU > 0 FIGURE Rational Formula -Overland Time of Flow Nomograph 3.3 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 & 1 .t: g1.o :o.s -~0.8 s .E0.7 0.6 0.5 0.4 0.3 0.2 0.1 -,....,-~ ....... , ' I l' -,.... .... .... '" "i,.. r-.. 1'. .... ~ "", ""r,... ... , ..... r-.. N... .... .. , ..... " .. ... .. ........ "" .1, ""~ ... . ... r..., '" ... r,... . ... ~ .. I' - .. "" i-.., "' :-.... ,, I ' ' • .. N.. ....... ... I= 3.2in/hr I .... I r... I" .. .... ... " ~ ... r ""~ .. , :-...., . ""' ~ "~ l ... ~ "' ..... i•" :..,..._ .. I "'t-,. "'I', I I ~ .. " I ~ I I 1 I I I I I l -,--- -l.-I I -:-----·-· -w -------·•--. ----. I i 1c = 20min ' 11111111 I I I 11111111 . ' 5 6 7 8 9 10 15 20 30 Minutes ! I l ! I I I .. { .. .. ~ I ... ~ I ~ h ~ I j .. I I I I .. I I i ' . - 40 50 1 Duration I I I 11 I f I ' f I I I i 11 I l ! I 11 I I i I Ii EQUATION l I = ?.44 Ps o·0.645 I I Intensity (in/hr) I = i P5 = 6-Hour Precipitation {in) I I D :: Duration {min) I I I I I I I I I l I I I t"'r-.. I I I I', .. , ... I I I I', .... ~ 'i-, I', , .. ~ I• .... ~ I . "" ... I" .... ~,;, ~ ~ ! I :..,r-, I• .... ~N,. , .. 'r--r-t ~ ~ ' """ :..,r-, 1'-i,,. ~ I ~ II! I I", "" r i I ' r--, I I J I', ~r--l I j "i' I ,.. .. I I "'r--N, 11 I , .. ""· I I "" !"1 i f I•• I "'I' I i n I N I' I' I I I ~ ~ . ' I I I ; I I I I I I -1--·->---.... -+ .. l·J I I ----I :, I I I i ,1 I I I ,l I I I I I 111111111111!11 I I I 111 llil 2 3 4 5 6 Hours 91 :t a C: ... 1J iil !l. 6.og, 5.5 g- 5.0 ::, 4.5 S-n 4.0 g 3.5~ 3.0 2.5 2.0 1.5 1.0 Intensity-Duration Design Chart -Example Directions for Application: (1) From precipitation maps determine 6 hr and 24 hr amounts ror 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 fine through the point parallel to the plotted lines. (5) This line is the intensity-duration curve for the location being analyzed . Appllcatfon Form: (a) Selected frequency _§9__ year p (b) Ps = _3_ in., P24 = ~ -~ = 54.5 %12) 24 (c) Adjusted p6<2> = _3_ in. (d) Ix= ~ min. (e) I = _R_ in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. PG ; 1 1.5: 2· . 2.5 3 3.S 4 4.5 : S 5,5 : 6 Duration • I I ; l I I I ·1 I : I I • • I ·5 2.63 ,=!-951 s.27: 6.59 J.90 9.22po.54. tl.86! 13.11: 14.49, 1s.a1 7 2.12 3.18;4.24!5.30 6.36·7.42: 8.◄8. 9.54 10.60:11.66,12.72 ·10 1.s8 j2.~i3·.~tI~-?.t_:.s~~fs~.~1-~..?4 :.t.~~J-~:~i~ ?.-_~1_;1~ . .1.1 ts uo . 1.95:l!.5~'. 3.24, 3.11914.54! 5.19_. 5.~; 6_,_4?. ,7,13 i .!?~ 20 1.08 ·1.62:2.15'2.69 3.23 3.77; 4.31 -4.85 ! 5.39, 5.931 6.-16 25 o.93 • 1.40'. 1.a1: 2.33: 2.80; 3~27[ :iia. ;fao I •i:ti'i ; ·s: fa I s:so 30 o.83 ;1.24;i.6f2.01:2.49:2.so1 i3.~2: 3,73 ! 4.i5 [ 4.56 i 4.98 40 0.69 _ 1.03. 1.38_ 1.72 _2.01:2.41: 2.76. 3.10 i 3.45 '. 3.79; 4.13 so 0.60 ,o.soi 1.19, 1.49: 1.19:2.09: 2.39, 2,69: 2.98 I 3.~8: :1.sa 60 0.53 0.80-1.06 1.33 · 1.59 1.86, 2.12 2.39: 2,65 1 2.92 I 3.18 ~() 0.◄1 0.61:0.82: 1.02 1.23: 1.43' t.63: 1.84 i 2.04 '. 2.25 '. 2.45 120 o.34 ;o.51 20.ii8;0.ss:1.02:1.19[ 1.36: 1.53) 1.io; ·1.ai ! 2.il4 J59 .. <>,?.9 _0.44:0'.59:0,73;().88,1.03. 1.18, 1.32; 1.47 • 1,62 I 1.76 1eo 0.26 ,0.39:o.5?, o.~5 _().1e:o.91 ! 1.04. ue; t3_1 : 1,4~ J t.5! 240 0.22 :o,33(0:431 o.54 J>.65,o.1s, o.137: o.98 ! 1.o_s, 1.,.~. !,:30 300 0.19 -0.28-0.38• 0.47 .0.5610.661 0.75 • 0.85 i 0.94; 1.03: 1.13 360 0.11 :o.2s' o.33: 0.42 • ci.so • o.sa: o.67 : o.i5 ;-1ia4 ' 6~s2 ' 1.00 FIGURE @] 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 O* 0.20 0.25 Low Density Residential (LOR) Residential, 1.0 DU/A or less IO 0.27 0.32 Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 Medium Density Residential (MOR) Residential, 4.3 OU/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, I 0.9 DU/A or Jess 45 0.52 0.54 Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 High Density Residential (HOR) Residential, 24.0 OU/A or less 65 0.66 0.67 High Density Residential (HDR) 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 (0.P. Com) Office Professional/Commercial 90 0.83 0.84 Commercial/Industrial (Limited l.) Limited Industrial 90 0.83 0.84 Commercial/Industrial (General l.) 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 33'0(]' Orange County 8 Riverside County ,-., M ~ 33"30' 33'15' ... '2-:5 ·····••••••••••••••••••• 32'30' County of San Diego Hydrology Manual Rai,?fh/1 Jsoplm·i<,/s !00 Year l{:iinl:!11 En.'nt • (1 I lours ls<~p!uvial (inches) DP\V ~GIS r, ._ .•.•• t,. :,.: "*' 'I,;:•~ . t~'.~•;;,:'•: •1:,. :?> /,1•.1• ,• <':•:,;•':'-~·,:::," .;~!/ • , .... ~ ......... ,... ,.. ~•.:.•,•, . . .. . . ,, :,--.I·• • s 3 0 3 Miles 33 20' Orange .-·~ County • •• '··" /,./ • , R;ven,;de County .. .. ., :: .. . ....... <·· .. \ '• ....... ::,,, 33"'15' ••• ~ •• \ •... · . . .. ·······•··· .. 33'0ti' 32'45' C 32'30' County of San Diego Hydrology Manual Rainfall !sop/111·iufs • f I11:vcnt -'-I I-lours 100 Yl'at' !tarn a . - s 3 0 --3 Miles DRAINAGE AREA MAPS PRE-DEVELOPMENT DRAINAGE AREA MAP I I I \ \ I \ I I I I /1 I I I - t:J I I I I I I ~/ / / I I ?-j □ . 72.3 c;;j( 0 c;;j( \ I\ i . 70.8 I\ I 4l l \ I, /1 11 \ \ 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 I I I I 1 I. I \ 87.3 \ TW \ J ~ \ ~% \ '\ 1 \\ 9 \ "v I \ ,v \ ----- \ \ \ '-----,_\ \ / \ \ \ \ \ PM NO 8524! \ \ l :t:. I 111.9 -J_i~ ( J--\I AREA "ES" (GREEN) 0.6480AC I PARCEL l ENTIRE SITE FLOWS WESTERLY TO ADAMS ST \J I ;-'{ >< r ,r \ f ! I I I ; '/, I ) I 1 ~ ) \ 0-0 ~ \ I ~' \ I \ ;\ /4 s \\ ,, _--j -~ ----~ -V--I ,--·<" I ----\ -----,, \ I \ • 1~ 't '\ ) \ \ I A I i y ) \\ ,( ) I I J ! . 115.4 \ \ \ ~ SCALE: 1" • 20' POST-DEVELOPMENT DRAINAGE AREA MAP I I I I I I \ I \ I \ I \ I ,, I -1 I __ J,, I 1 I I I \ \ \ I \ I - AREA "REM" (GREEN) 0.2321 AC (1,0110 SF) ONSITE FLOWING WESTERLY BY SURFACE FLO AREA "G" (YELLOW) 0.0444 AC (1,934 SF) ONSITE FLOWING WESTERLY i I I I I \ \ \ AREA "RNE" (RED) 0.2086 AC (9 JJ87 SF) AREA FLOWING TO CURB OUTLET# 2 (041) AREA "RW" (BLUE) 0.1629 AC O JJ96 SF) AREA FLOWING TO CURB OUTLET #1 (040) SCALE: 1" = 20' \ \ I I ) I ,\ 'i\ \ \ \ \ \ I \