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HomeMy WebLinkAboutSDP 96-14C; LEGOLAND HOTEL CALIFORNIA; PRELIMINARY DRAINAGE STUDY; 2008-04-14PRELIMINARY DRAINAGE STUDY For LEGOLAND HOTEL CALIFORNIA Carlsbad, CA Date: April 14, 2008 Prepared By: Hofman Planning & Engineering 3152 Lionshead Avenue Carlsbad, CA 92010 RCE 58873 RECEIVED APR 1 ' " CITY OF Cl' PLANI I ,_, Prepared by: jc D - • Legoland Hotel California Drainage Study -.. -.. --- ---- -.. -------.. .. .. --.. -• .. TABLE OF CONTENTS Section 1 . Certification . . . . .. . . . . . . . . . . . .. .. . . .. . .. . .. . . .. . .. .. . . . . . . . . . .. . . .. .. . . . . . . . .. . .. . .. . . . . . 1 Section 2. Project . .. ... . .. . .. .. . .. .. .... .. ... ... . .. .. .. ... ... ... .. .. . ... . . . .. . . .. ... ... ... .. .. . ... . ... ..... 2 Section 2 .. 1 Objective ............................................................................. 2 Section 2 .. 2 Description ............................................................................. 2 Section 2 .. 3 Existing Condition ...... ............ ... ... ... ............ ...... ... ...... .......... 2 Section 2 .. 4 Proposed Condition ....... ..... ...... ...... ... ...... ......... ... ...... 2 Section 3. Methodology .......... ..... ... ...... ... ...... ... . .. ...... ...... ...... ...... ... ......... ... 3 Section 3. 1 Rational Method ...... ......... ............ ... ......... ...... ... ...... .......... 3 Section 4. Summary............................................................................................. 4 Section 5. Hydrology Calculations ......... ...... ......... ... ... . .. ...... ...... ............ .. 5 Section 5. 1 Pre-Developed .... ..... ...... .... ........ ... ... ...... ... ... ... .. .... ... . ..... ... ... . . 5 Section 5.2 Post-Developed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 Attachment A Attachment B Attachment C Attachment D Attachment E Vicinity Map Pre-Developed Hydrology Map Post-Developed Hydrology Map Node Analyses Tables & Charts - • Legoland Hotel california Drainage Study - - -... - -- .. -• - • 41 .. • Section 1 . Certification DECLARATION OF RESPONSIBLE CHARGE I hereby declare that I am the engineer of work for this project, that I have exercised responsible charge over the design of the project as defined in Section 6703 of the Business and Professions Code, and that the design is consistent with current design. I understand that the check of project drawings and specifications by the City of Carlsbad is confined to a review only and does not relieve me, as engineer of work, of my responsibilities for project design. \ ' EXP. 06-30-09 ·'>'-,~ ..• l-·" C 58873 p. G·W-rf-J .l ~rLi-o& DATE .. • Legoland Hotel California Drainage Study - - - .. • -.. --... ... .. • 111 • .. • .. .. Section 2. Project Section 2 .. 1 Oqjective The objective of this study is to determine the stormwater runoff generated in a 100- year event for both the existing and proposed conditions on the site and to determine the need for hydraulic structures. Moreover, this study will also design the proposed storm drain system to effectively control the runoff while mitigating impacts to the downstream storm drain facilities. Section 2 .. 2 Description As shown in attachment A, the site is wholly within the parking lot of Legoland California in the city of Carlsbad (APN 211-100-14). The site is bordered by the park to the north and the parking lot to the east west and south. The site is presently a paved parking lot and decorative paving which will be removed . Section 2 .. 3 Existing Condition As shown on attachment B, the site currently drains to the south, into an existing private 36" PVC storm drain. The runoff enters the storm drain through a series of curb inlets in the existing parking islands. Section 2 .. 4 Proposed Condition A new 3-story hotel building as well as incidental utilities, and hardscape improvements is proposed within the parking lot at will span over the existing pedestrian park entrance. As indicated on attachment C, a new private subsurface drainage system will convey the runoff around the hotel building into the existing storm drain system . .. -• .. • .. - .. .. .. ... -... .. .. 41 .. • .. .. .. .. .. .. .. .. Legoland Hotel California Drainage Study Section 3. Methodology .............................................................. . Section 3.1 Rational Method The Rational Method as described in the San Diego County Hydrology Manual, Section 3, (Revised June 2003) shall be used to determine storm runoff . The Rational Method formula is expressed as follows: Q = CIA Where: Q = peak discharge, in cubic feet per second (ds) C = runoff coefficient, proportion of the rainfall that runs off the surface. The coefficient C has no units and is based on the soil group and the percentage of impervious area for the drainage sub-area. Attachment E includes calculations for the percent of impervious area for each drainage sub-area. I = average rainfall intensity for a duration equal to the Tc for the area, (in/Hr.) A = drainage area contributing to the design location, in acres The following values are used in the calculations: Soil Group D from San Diego County Soils Group Map. (See Attachment E) C (Coefficient of Runoff) from Table 3-1. (See Attachment E) 100 year 6 Hr. Rainfall = 2.6" (See Attachment E) 100 year 24 Hr. Rainfall = 4.5" (See Attachment E) The site has be divided into drainage sub-areas as shown on the On-Site Hydrology Maps in Attachments B and C. Basin areas and invert elevations were calculated from the proposed grading plans and the existing topography. Given that the soil around the site is type B and the proposed site is general commercial, the runoff coefficient C is assumed to be 0.80 throughout the site in accordance with table 3-1 of the manual . The time of concentration, Tc, for each sub-area along the drainage path is computed based on the initial time of concentration for the initial area and the travel time to reach the next node. We based the times of concentration on overland flow nomograph shown on figures 3-3 through 3-7 and/or table 3-2 of the manual. The 100-year rainfall intensity was calculated with the intensity duration design chart template (figure 3.1 of the manual). Then, applying the rational method equation, the peak runoff is determined at each node along the drainage path. Q's are tabulated for each sub-area along the drainage path. The node analyses are shown in Attachment D . - -Legoland Hotel california Drainage Study -- .. -.. --.. ... .. - --- • .. • - • - • - .. .. ... Section 4. Summary The proposed project will not significantly alter drainage patterns on the site or the surrounding area. Placement of the hotel requires minimal flow diversion. There will be no net an increase to the amount of impervious area. As shown on the results in Attachment D, the existing site runoff is at 72.90 cfs, while the proposed project will increase the volume of runoff to 73.59 cfs. The increase in runoff is negligible and due solely to the diversion around the existing hotel as well as a slight increase in area to the west of the site. A capacity analysis of the existing 36" PVC storm drain shows that the pipe is currently at 58% capacity and is able to handle the increase in volume resulting from this project. (See attachment D) We have determined that the inlet capacities of the proposed storm drain system are sufficient to prevent any ponding during a 100-year storm event. Moreover, we have designed the storm drain system so that the 100-year runoff generated from the proposed development does not significantly impact the downstream facilities any more than the existing condition . ---- - -- -- -.. --- ,_ 4f> ACIFIC -OCEAN ---.. .. .. .. .. --- • ,. ATTACHMENT A VICINITY MAP CITY OF OCEANSIDE CITY OF ENCINITAS ■ NOT TO SCALE CITY OF VISTA ITY OF N MARCOS I I I .----------------- BASIN NOOE DRAINAGE OIR£CnON STORM DRAIN PIP£ -LEGEND ---. l _J r-wApel lllndlcllpe- lnc ~A-ue (780)~· ~ -11:1825 -··-· ... CCN■ULTIN■ !he contents d . NOTICE information of LE ths document constit related entities. ~LANO California :e proprietary ~m',;',:, oonfiden~: ~-:v;ng .,;:":uo:'nt in whole or i~o:ined herein s:i~ ~ the ~;'"' ... prio, ";.:.~~sdosed to oth':.":"" ornia coosent of LEGOLAND ~ S1 E " t-f ~ 1:i AMENDMENT g EGOLAND HOTE SDP # 96-14(C) ~ PRE L CALIFORNIA ~ HYDR8E~EGL YO PED :c MAP Scale: as shown April 14, 2008 Sheet Number ATTACHMENT B I I I I I I I I I ); '-',,,_ .• ',,·,. \ \ --"""'~,. ' _,/,,1,j/1!/l/,·,1. /l--1_.~,·.:_ .. f,i_/,·,i_ ,,I '-',, '\, \, \ " '¾~--~ //I ;,,ii I "' ' --"'-~--' ;~ I "' ~~,/) ) . ~~t ~ ---~ ~~~ __,-// ' "~ I I I //!l I ~/4~~'~'~':::-~ ~, /JI //;111! ! ~J;?.:=::~~~-:.··,.~ "---~" •/if//_ / I •I•/ '<:::::'=-:::,,,,,,, •~ ~~~'.\, :_:1{_;_:,:_,:,;,._i.li/~.:-~_i_:_:_~,-.l.i/1/ I <' c.1 •. ,~,;=~~::::;::::t..,"":./-7}.:~< \\ ---,~~~~,yl/): , . ,,, \ ,\ \-I '-\'. ,,,..._,ox,., _ ___.,:~~~~\\-. ) JI / [J;· / /j ;,c;;,---:::,,,.,,.----, \~<' ~ i ";l: \w\':-:\~ f ! ! I JI I J 0-,~:::_ 1,1 ~/ -~ '-1f§:~·\ ftif 1' / ~V,r",._A/1. ~t.:::?\i'.~ ~.Q~~ttz --' J .._.,,,.__,,, &~, '~ 11 I /, '/ I ' \ 'l '\'\ \ \ ',,\ '\.../ (//!\ \, \\<'\ ' \ : \' \ \ BASIN NODE DRAINAGE DIRECnON STORM DRAIN PIP£ 0 40 LEGEND --, _J --. - 80 I 160 SCALE ,..-;;-so· 240 LEGOL:Jll CALIFORNIA 1 LEGOLAND DRIVE CARLSBAD, CA 92008 (760) 918-5300 Prepared by: NICHOLS BROWN WEBBER AJ.OilTECTS AND 1.ANDSCAP1! PlANNl!RS ,ctCDl&'.Jm8,~NBl«.ln'4'.1'MAlml,,(lll]N ... &G,, tx Tl!l.i'TUaVlI.LBHBATH(++41....i"9.IJC).PA%(+4414'1812aJ r-wApel llrldoalpe- lnc 571-11 HygoloA-,uo Leucadia, CA IIZ024 (780) 943-071!0 IWltl)8l2Qcox.n CA-il:2825 NOTICE The contents of this document constitute proprietary information of LEGOLAND Califorria and/or other related entities. Any party receiving this document does so in confidence and agrees that the information contained herein shall not be duplicated in ¥mole or in part, nor disclosed to others without the express prior written consent of LEGOLAND California. Key Plan CITY SUBMITTALS Description Date r "' i;: ~ t t f ~ I;\ SITE DEVELOPMENT PLAN - AMENDMENT i SDP # 96-14(C) EJ LEGOLAND HOTEL CALIFORNIA §? - -Existing Node Analysis Carrying -Capacity ... Node Basins Area Ac C Tc Min I In/Hr Q100 cfs cfs Conveyance 1 1 18.87 0.82 14.4 3.46 53.59 66.70 36" PVC @. 1.0% .. 2 1,2 19.97 0.82 16.0 3.24 52.97 66.70 36" PVC @. 1.0% 3 3 4.56 0.82 5.0 6.85 25.59 22.62 24" RCP @ 1.0% .. 4 1 Thru 4 28.55 0.82 17.0 3.11 72.90 123.00 36" RCP @ 3.4% - Proposed Node Analysis -Carrying Capacity ¥ Node Basins Area Ac C Tc Min I In/Hr Q100 cfs cfs Conveyance 1 1 18.87 0.82 14.4 3.46 53.59 66.70 36" PVC@ 1.0% -2 2 1.24 0.82 5.0 6.85 6.97 10.50 18" PVC@ 1.0% .. 3 2,3 5.44 0.82 8.0 5.06 22.55 22.62 24" RCP @. 1.0% 4 4 2.71 0.82 6.0 6.09 13.52 14.40 18" PVC@. 2.0% -5 1 thru 5 28.85 0.82 17.0 3.11 73.59 123.00 36" RCP @ 3.4% .. .. .. - --.. ... -... -... .. .... r - __ , ___ ) ______ , ; -;--. ~~---.i...l..-~-+-1-: ...... .. ~~----,~~-+--:-~____,~4-:--_:__:_-H~-___.'.__---H-~----;.-'........'.._~ _ _i_;.+~l---...,......:.._j_,-___:_L _L_i__:_:_;___:___L_j__j__J__:__~_j__~, 2~30• ,.-, - .. ' + ,-.. ;-.. + L LO· ...... ,. :-. . ......... ,-... , ---: .,... r-+-·\ ' -~ : : co : ·-t T ... ;-: :;=::c-----;-------i----··'·-···:·· .. -·-----~----• '_Ll.J..l _::_ ; LJ 3 County of San Diego Hydrology Manual Soil Hydrologic Groups Legend Soil Groups D GroupA -Groups D Data Unavailable DPW ~GIS s1iiGIS (190:Vim91'!~J,U.."-'c~½ln 3'.~Jl]!i:l:li1Jtrf..Jl~S~.m-We Hav~ San Diq1.o Covered! THIS MAP IS PROVIDED WrTHOVTWARRANTY OF ANY KIND, EITHER EXPRESS OR l~ED. INQ.UOING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY ANO FITNESS FOR A PARTICULAR PURPOSE. Copyright SanGIS. All Rights ReseM,d. This products may oontaln Information from the SANOAG Regional Information System wNch C&Mot be ,epn,ducad without tt1e written permission d SANDAG. Thia product may ccntarn lnfonnatkln which has been reproduced ,.;tt, permission granted by Thomas Brothers Maps. 3 Miles I ----•-·-•·······~--~=~=c====ttt==~~~~~L.~tJ2_~L~-}}~J~?~~~~s.1'"J~.~.~t:t.~-t~t.~-l~t,-tf~~~t-j.,:1~7_j_L~f-+::~~;i;i 1;~~J~s:;~=rs~~~;~1w=1;;us::1JjjJt[tttIJ =.?·t••«•: ... =·-·· ····-········; ...... , ... ;'_·~:~-~ .. :.~: .. -~~J . ........ ~..... ' ~ -----i----•-" .. __ H ---------- •f•••-;•-~ .. •.Jl••••••-"•••..L --• I County of San Diego Hydrology Manual Rainfall lsopluvials 100 Year Rainfall Event-6 Hours lsopluvial (inches) DPW ~GIS ~ N 08PD't-nr,r ,:,f P:J;.ic "4tviu Gr~•~ /'rl:lrrr'.~,~~ sftiGIS \Ve Have S:m Diq;n Cc:vcrt<l! ............................... , •. •·····•·······l·························•········'········•·········.• ... ·.·.·.·.· .• 1.·.·.· ... ·.~'·····•············•·······•·······•·······SI+ THIS MAP IS PROvtOED WITHOUT WARRANTY OF ANf KIND, EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANT.ABIUTY ~O FITNESS FOR A PARTICULAR PURPOSE. Cowtghl SanGIS. All Rights Rel8N9d. Thts products may contain Information from the SANOAG Regional Information System which..-be reproduced without the wrtttsn pennlsalon ol SANDAG. This product may oontafn Information which haa been reproduced -.1th pennlsalon granted by Thomas 8-Mapo. s 3 0 3 Miles ~- I I I County of San Diego Hydrology Manual Rainfall lsop/uvials 100 Year Rainfall Event-24 Hours lsopluvial (inches) DPW ~ ...... GIS ~ D9J'W.-:,r:T'JIP:J;.c~ Gcc,;i-,~ fr.f-~.,"IV'x• ,':-'r.vr~ \X:c Ha--~ San Dicg(, Covc:rtd! THIS MAP IS PROV10EO WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INQ..UOING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY ANO FITNESS FOR A PARTICULAR PURPOSE. Copyright S..GIS. All Rights -- This products may oontaln lnfoonatlon from the SAND,_G Regional Information System which cannot be reproduced wtthout the wrttten permission ol SAND.-\G. This product may contain Information which has been reproduced wtth permission granted by lhomas -Maps. Miles '~ffifflffifflID] I I I 11111111111111111111111 II 111 I llll~llllllllill I I I I I I I I I 111I II111111111111 .u ;:::1'. ,..._ ..., ...... ,..._ ,._, ""...,.._ •._ "".. EQUATION 6.0 ..,_ .. ...," ._,, "', I = 744 P60-0.645 . '' .... ' .. .. """' ~ ~ . 5 o ... .., I = Intensity (in/hr) . l""'.. .... I',. .... I-,. I,," l"t,. I r-,.,1'-. ,::,"-I'-.,._ i.. i,. " ~ ~ " P6 = 6-Hour Precipitation {in) 4.o N. .... ..._ :-... "' · I .. D = Duration (min) I f' l"'r-,., •~"" to.., " I • i-... ..., ' "' " r-.,... i,. I',! . "~ 3.0 : ..,. ... " ~ I "'--'"' "'"ti-'j,, ,., ~ m.l 1 "' ; .. I", "r l'I', l llllil lllllllllllll • , I 1111 I """ I' ... ,,...,,.. 2 · 0 , I I I l .... r-,. .. I ~ / ,. r-,.l'r-,. ""' ... ,.. 1111111 er, I" ~I".. ~ , ... r... 1• if I'.. .. i" I"" ...... .. "~ !:; 'C' i"""'.., ~" ~ i"'r,,. i•.,. .... ~r JI ::1 r-.._ " I"',... I"',.. '°'r ~r ('I> 0 ,~.. f-. ,~ .... ,... I" 0 ~ I"~ .., ..... ' " 6.0 "§: i ~ ,. r,,. r,,. I" f"' 5.5 i g 1 0 r r . '"" 5.0 g ·-,,...,,, J'IIII ;:o,9 r-. rs 4.5 5 :'!: ..... ,. I" 0 ~0.8 r,. rs " 4.0 ~ .!!lo1 -"" "'" ~ · 35,e ,. ~. l l illllllllfl illllllil ll""'-U IIIIIII IIII\\\ I N . o.e: : : : : : : : : : : : : 11 I I I I I I I 111111111111111111 I I~ IIIIIIIIIIIIIIIT 1" ..,..,"' 11 n 1 '.:I~ 3-0 0 5:l I I l I I I I I I I I I II II I II 11111111111111 I 11 111 11 111""'.11111111111 1"', ••t I I I I I I I I I \ I I I I I ::Li I I I I I I I I I II IIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIHln~l-1'' '1-2.0 1.5 0.2 1.0 t· -l+HHf+Hl!+Hl+HH-H-H-H+l+HH-HH+H+HHHH-+·H-H-HtHt+l+ttltHHH~ 0.1 I I I 111 1 1111 ttttttttttttttttWtlfiltlttffi1±ttttttttttttttttttttttl 11111 ttttttttttttttttttlll 6 7 8 9 10 15 20 30 Minutes 40 50 2 3 Hours 4 5 6 5 Duration Intensity-Duration Design Chart -Template Directions for Application: (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. {S) This line is the intensity.cturation curve for the location being analyzed. Application Fonn: (a) Selected frequency loo year {b) p6 = ~ in., P24 = ~ .:6 = ~7 7 %(2) 24 (c) Adjusted p6<2> = ~ in. (d) tx = __ min. (e) I = ___ in./hr . Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. :;~,ati~ ·•··-~-t-;i5.l·~--pr;-f : ~r-T ~--~ -\5 1 s;s ·:.~-~~ 1. -. .5 _2c6.3_ 3_ .. 95J5271' 6~9t7.90!922. ! 10·5· 4i1 l.86, 13.17 14.49, 15.~! ___ ····-1 _g_: 1 L 3:.!..8 l 4,24 ~30 s.36 I 1 ,42: 8.48 j 9.54 • 1 o,so _11.66, 12. 12 10 t_,(;tl_ ~~p_,3114.211s.os,~.~L.?,?i+1·sa__;_~,:4~ . .!!-2-? .• JCl_,!_! 15 1.30 1.95 2.59 3.24 3.89 4.541 5.19 5.84 : 6.49 7.13 ! 7.78 --20 -1-:-os-1.62 2.1s. 2.69 3231 3.171431 ·• -1.s5 l s.:fii 5.93 ns:;fif 25 0.93 I 1.40 1:a1 ! 2~33 °2.801 1 3.271 3.73 4.20 r<J:67 15:i:f 5.60 30 .... -.o.·.03 1.2-i1.1.u j 2.01 ;2.49 ).9()[ 3,32 t· 3.73 [ 4 !5 4.56 4.98 '-----~ .. 0~69 ' .. ·.03 .. 1.38J 1.7.2,2.07.2.411 .. 2.76 ···3.10 ; 3.45. 3.7·9 · "_ ... 1.3 50 o.oo o._90 U9: 1.49, 1.79~2_.09 2.39 i 2,6~, 2.sa_ 3,~~ 3,~ ---60 0.53 0.80 Ul6! 133 j 159, 1.86i 2.12 1 2.39 j 2.65 2.92 3.18 --.. !!C! _Q:4._~o.·_,st. 9 .. ·~-1-'•Q2 __ · .i.1.231_1,.43._1 ... , ..• 63 ... LB<! .• ;. 2 .. ,°" .. -.. -· .. 2,25 _ 2.4. ___ s .. __ 120 o.34 o.s1 o.68 o.85j1.02p .19t 1.36 I 1.5311.10 l 1.87 i 2.04 .... _!!!(.! .!?:fil _o~4 00~_9 OJ~. o.~, 103: 1. t 8 1.32 1 1.41 1 1,e2 ;_1.76_ ·· -.---.= i;t~~~-~-t;.ji:Jt.;:r~Ill·~:~_ 11 ~:!:j_--::~l.tl!_ 1.--~.~~. _ 300 0.19 ,0,28 0.38! 0.47 0.56 0.66 0.75 . 0.85 , 0.94 . 1.03 , 1.13 -· 360 0 .11 !o.2sfo.3il 0:-42 i'oso i6.s8: o.a1 1 o.1s·1 ·o."a4·' o-:-s21 1.00 FIGURE @] I I I I I I I I San Diego County Hydrology Manual Date: June 2003 • I I I i I I f I • i i I a l Section: Page: Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Type NRCS Elements Coun Elements %IMPER. A B Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 Low Density Residential (LDR) 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 (MDR) 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 (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 High Density Residential (HDR) Residential, 24.0 DU/ 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 (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 I I 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 I t 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 t I *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 i I ' I I I I lij w u. ~ w t) z .:: rn i5 w ~ ::::> ~ w ~ 3: ' ' • t I I .I i 1 l 4 I j • I i I j • 100 I 1,5 I U./'i// / I ~JJ' § § ✓I .....-"F 130 (/J ~ z I» I ■ I I I I~ -' 41"" v~ I .....,..,.-1 I ~ 20 ~ 0 y~,--,-., ,-~ w :E i= ~ u. 10 ~ ~ a: w ~ -0 EXAMPLE: Given: Watercourse Distance (D) = 70 Feet Slope (s) = 1.3 % Runoff Coefficient (C) = 0.41 Overland Flow Time (T) = 9.5 Minutes T= 1.8(1.1-C)VD 3\fs SOURCE: Airport Drainage, Federal Aviation Administration, 1965 F'IGURE Rational Formula -Overland Time of Flow Nomograph 3-3 . ' i l i I -.. .. .. .. "" .. .. --.. .. .... .. -... .. - - - - .. San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 12 of26 Note that the Initial Time of Concentration should be reflective of the general land-use at the upstream end of a drainage basin. A single lot with an area of two or less acres does not have a significant effect where the drainage basin area is 20 to 600 acres. Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in hydrology studies. Initial Ti values based on average C values for the Land Use Element are also included. These values can be used in planning and design applications as described below. Exceptions may be approved by the "Regulating Agency" when submitted with a detailed study. Table 3-2 MAXIMUM OVERLAND FLOW LENGTH (LM) & INITIAL TIME OF CONCENTRATION (Ti) Element* DU/ .5% 1% 2% 3% 5% 10% Acre LM Ti LM Ti LM Ti LM Ti LM Ti LM Ti Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9 LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4 LDR 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 LDR 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 5.6 MDR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3 MDR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8 MDR 10.9 50 8.7 65 7.9 80 6.9 90 6.4 100 5.7 100 4.5 MDR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3 HDR 24 50 6.7 65 6.1 75 5.1 90 4.9 95 4.3 100 3.5 HDR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7 N.Com 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G.Com 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4 O.P./Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 Limited I. 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General I. 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 100 1.9 *See Table 3-1 for more detailed description 3-12 ---.. ... .. -- .. -.. .. ... .. - - .. .. -- - -- ~E Feet 5000 4000 EQUATION Tc = (1~!3)0.385 Tc L ~E = Time of concentration (hours) = Watercourse Distance (miles) = Change In elevation along effective slope line (See Figure 3-5)(feet) 3000 2000 1000 ' soo' ' 400 ' JOO 200 100 30 20 10 5 '~ ,~?), ~/4> ' ' ' ' ' ' ' ' SOURCE: California Division of Highways (1941) and Kirpich (1940) L MIies Feet '1 . 3000 0.5 ' 2000 1800 1600 1400 JOO 200 L ' Nomograph for Determination of ' ' Tc Hours Minutes ' ' ' Tc 50 40 30 20 18 16 14 12 10 9 8 7 6 5 4 3 Time of Concen1ration (Tc) or Travel Time (Tt) for Natural watersheds FIGURE 3-4 - -.. .. .. - -.. .. - - - ---.. - --- .. ... ---/ ----i------------------L--------------------1 Watershed Divide -r .6.E I Effective Slope Line Design Point (Watershed Outlet) •-----------------L----------------- Area "A" = Area "B" SOURCE: California Division of Highways (1941) and Kirpich (1940) FIGURE Computation of Effective Slope for Natural Watersheds 3-5 .. -.. ... - - -- ... ... -.. .. - - --- .. --- ... - Q) a. 0 en Q) ~ u5 0 l.--1B--+I 1 ..-n = .015-+-~---2% _ -n = .0175 -----....::..::... ____ _,! 2% Concrete Gutter Paved RESIDENTIAL STREET ONE SIDE ONLY 20 -;-------1---.... --+---+--+~r+--t-➔~~"""-------1-----+----+----t-...- 18--f-------t----j ..... -+----+---++➔--f-➔--IHf--..;::,,,,._ 16 ~-------+-#---,+;::::a.-::1----1~-+-+--+--l~I----.....;:...._,; 14 ~--------t,----;----+-+P.....t~+-t-illHl--------==-t~+----,l-----i--#-1----+ 10 ...,. ______ ,_-+-------11----1---4---4--4-,j~-'--.,__..;::,,~ 9 -+----J~=t===----=::~--l-+---l~+-1:........i---1--+------=::::....~~----J---l-+-.:::::..i--1- 8 -t---- 7---- 5 1.0 ~---,,-----+--1-'----+-;;:,,,,,,:c; 0.9 --f....;::""#<o:=-----t-#---+----+-..;:,,.~-+--f-➔--IHt-~~----+if----~. 0.8 ~"""".l~--....;:: ..... ::---fljf------11----+---+-l-::o+o::---+--+-+-.... +--...... ::-----, ..... -------------+- 0.7 ~#---------j~;;:,,,,,"- 0.5 2 3 4 5 6 7 8 9 10 20 30 40 50 Discharge (C.F.S.) EXAMPLE: Given: Q = 10 S = 2.5% Chart gives: Depth= 0.4, Velocity= 4.4 f.p.s. SOURCE: San Diego County Department of Special District Services Design Manual FIGURE Gutter and Roadway Discharge -Velocity Chart 3-6