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Home My WebLink AboutCT 2016-0002; TOWN HOUSE; HYDROLOGY AND STORM WATER MANAGEMENT REPORT; 2018-05-15CITY OF CARLSBAD ENGINEERING DIVISION HYDROLOGY AND STORM WATER MANAGEMENT REPORT FOR TOWN HOUSE 2677 STATE STREET ENGINEER OF WORK JdJ- VINCENT L. SAMPO-RCE 44173 I l(] l ·H ll { i rfil l1 --c::{c(C--- d J OM() )r► }I Ii -L PREPARED BY: SAMPO ENGINEERING, INC. 171 SAXONY ROAD, SUITE 213 ENCINITAS, CA 92024 (760) 436-0660 Town House Standard Development Project MA 18 2 18 L~.1 Sampo Engineering, Inc. 5/15/2018 Introduction: The subject property is approximately 0.225 gross acres and is located at 2677 State Street in the City of Carlsbad. The property has been previously developed as an automotive repair shop, asphalt concrete covers the majority of the site and there is an existing garage on-site. The subject property's storm water runoff sheet flows Westerly & Southwesterly from the State St Right of Way to the existing storm drain inlet located on the westerly property line & Right of Way of the rear alley. The pipe exiting the inlet ties into the existing public 66" RCP that runs South-North along the west side of the rear alley. This project proposes to maintain the historical drainage pattern. The project proposes to construct a 4 story, mixed-use condominium bui lding on State Street, just North of the recently completed Railyard Lofts and campfire projects. This project proposes 8 luxury condominium units and 1,600 sf of ground-level professional office space with 18 residential parking spaces located within an on-grade parking garage. Hydrology Summary: A hydrology study utilizing the Rational Method was performed for the existing and proposed conditions and the results are as follows. The existing condition is composed of l hydrologic basin that includes the entire property. The existing drainage basin has a tributary area of 0.225 AC with a runoff coefficient of C=0.91 and an anticipated flow for the l 00-year storm of 1.43 CFS. The proposed drainage basin, over the same area, produces a runoff coefficient of C=0.92 and an anticipated flow for the 100-year storm of 1.45 CFS. The total site impervious surface area is increased by 276 SF from the existing condition. Thus, the anticipated increase in storm water runoff volume has been calculated as 22 CF. A detention basin is proposed below the parking garage in an effort to mitigate peak storm flows for the total site in the developed condition, refer to attached calculations. Storm Water Quality Summary: The project has been determined to be a "Standard Project" using the City of Carlsbad Storm Water Standards Questionnaire (E-34) and is therefore exempt from priority project requirements. The development proposes to reduce the discharge of pollutants offsite by utilizing Source Control and Low Impact Development (LID) BMP's to the maximum extent practical. Storm water will be treated by installing krystar downspout filters on all roof downspouts and utilizing a sand oil separator on all runoff collected in the proposed parking garage trench drain. The majority of ( one downspout drains to a planter area) the storm water runoff generated by the new structure will be collected, treated as outlined above, detained in a concrete vault in the parking garage before being released and at the flow rates not to exceed the existing condition into the existing inlet in the rear alley. Town House Standard Development Project 2 Sampo Engineering, Inc. 5/15/2018 DRAINAGE STUDY CALCULATOR EXISTING SITE JN: 16-150 INITIALS: ZL DATE: May 15, 2018 DESCRIPTION: Area = 9,800 SF 0.23 AC ~ = (Pervious)(CO% 1MPER) + (lmpervious)(C.,00% 1MPER) Total Area (690 SF)(0.35) + (9110 SF)(0.95) 9800 SF 0.91 Q = 126.3 ( Watercourse Distance, FT) ~ = 1 1 (Slope,%) I c1 = 1.8(1.1 -C)(D) '12 (S)'/3 1.8"(1.1-0.95)"(126.3JA1/2 (1.1)01/3 2.94 MIN Use 5 min as minimum value 5.00 MIN f!.2 = 1.2 ( 2-Year, 6-Hour lsopluvial) f!. 10 = 1.7 ( 10-Year, 6-Hour lsopluvial) f!.100 = 2.6 ( 100-Year, 6-Hour lsopluvial) l2 = 7.44 P2 Dre, -0645 7.44(1.2)(5)"(-0. 645) 3.16 IN/HR !10 = 7.44 p ,o Dre, -0645 7.44(1. 7)(5)"(-0.645) 4.48 IN/HR f 100 = 7.44 P ,oo Dre, -0645 7. 44(2. 6)(5)"(-0. 645) 6.85 IN/HR Q.2 = CIA (0.91)(3. 16 IN/HR)(0.23 AC) 0.66 CFS Q.10 = CIA (0.91)(4.48 IN/HR)(0.23 AC) 0.94 CFS Q.100 = CIA (0.91)(6.85 IN/HR)(0.23 AC) 1.43 CFS Per San Diego County Hydrology Manual 2003 171 Saxony Road, Suite 213 • Encinitas. CA 92024 • P: 760-436-0660 • F: 760-436-0659 • info@sampoengineering.com DRAINAGE STUDY CALCULATOR PROPOSED SITE JN: 16-150 INITIALS: ZL DATE: May 15, 2018 DESCRIPTION: Area = 9,800 SF 0.23 AC ~ = (Pervious)(CO% IMPER ) + (lmpervious)(C.,00,. ,MPER) Total Area (414 SF)(0.35) + (9386 SF)(0.95) 9800 SF 0.92 Q = 107 77 ( Watercourse Distance, FT) ~ = 0.93 (Slope,%) I ,1 = 1.8(1.1 -C)(D) 112 (S)"3 1. 8(1. 1-0.95)(107. 77)'112 (0.93)'1/3 3.45 MIN Use 5 min as minimum value 5.00 MIN !!.2 = 1 2 ( 2-Year, 6-Hour lsopluvial) e 10 = 1 7 ( 10-Year, 6-Hour lsopluvial) !!.100 = 2.6 ( 100-Year, 6-Hour lsopluvial) 12 = 7.44 P2 Dre, -0645 7.44(1.2)(5)'(-0. 645) 3.16 IN/HR 110 = 7.44 P 10 Dre, -0645 7.44(1. 7)(5)'(-0.645) 4.48 IN/HR 1100 = 7.44 P100 Dre, -0645 7.44(2. 6)(5)'(-0. 645) 6.85 IN/HR .Q2 = CIA (0.92)(3.16 INIHR)(0.23 AC) 0.67 CFS _Q 10 = CIA (0. 92)(4.48 INIHR)(0. 23 AC) 0.95 CFS _Q 100 = CIA (0.92)(6.85 /NIHR)(0.23 AC) 1.45 CFS Per San Diego County Hydrology Manual 2003 171 Saxony Road, Suite 213 • Encinitas, CA 92024 • P: 760-436-0660 • F: 760-436-0659 • info@sampoengineering.com DRAINAGE VOLUME CALCULATOR EXISTING BASIN # 1 VOLUME DESCRIPTION: E.2 E.100 .J!' 100 9,800 SF (Pervious)(Co,. IMPER) + (lmpervious)(C.,00% IMPER ) Total Area 1.2 2.6 ( 2-Year, 6-Hour /sopluvial) ( 100-Year, 6-Hour lsopluvial) Per San Diego County Hydrology Manual 2003 C P2 A C P,oo A PROPOSED BASIN # 1 VOLUME DESCRIPTION: Area = 9,800 SF £ = (Pervious)(C0,.IMPER) + (lmpervious)(C.,00% IMPER ) Total Area E.2 = 1.2 ( 2-Year, 6-Hour lsopluvial) E.100 = 2.6 ( 100-Year, 6-Hour lsopluvial) Per San Diego County Hydrology Manual 2003 .!!'2 = C P2 A .J!' 100 = C P1oo A t.V = .l{ 100 PROPOSED · .l{ 100 EXISITNG (690 SF)(0.35) + (91 10 SF)(0.95) 9800 SF (0.91)(0.1 FT)/9800 SF) (0.91)(0.22 FT)(9800 FT) (414 SF)(0.35) + (9386 SF)(0.95) 9800 SF (0.92)(0. 1 FT)/9800 SF) (0.92)(0.22 FT)/9800 SF) (1983.SFT)-(1962 FT) JN: 16-150 INITIALS: ZL DATE: May 15, 2018 9800 SF 0.91 0.10 FT 0.22 FT 891.8 CF 1962.0 CF 9800 SF 0.92 0.10 FT 0.22 FT 901.6 CF 1983.5 CF 22 CF Detention vault shall be constructed to have a minimum volume of 22 CF As shown on the Preliminary Grading Plan. Detention volumes as stated above are J designed to detain the increase stormwater runoff In the 100-year peak storm event from the newly proposed development. Detention Vault Volume = S'X 6' X 1' = 30CF>22CF ---- 171 Saxony Road, Suite 213 • Encinitas, CA 92024 • P: 760-436-0660 • F: 760-436-0659 • info@sampoengineering.com ORIFICE CALCULATIONS FOR TOWN HOUSE Eq: =Q=CA ✓ 2gh Where: Q100 = Existing 1.43 cfs C = 0.67 A = cross-sectional area of orifice (ft2) g= 32.2 ft/s2 d = diameter of orifice or pipe (ft) h = I ft max (per plans) Solve for A= area of orifice A= 0 = 1td2 C✓2gh 4 Solve ford d= ( ..!Q \ 112 1rC✓2gh) ( 4(1.43) \ 1t(0.67)(64.4 X 1)112 ) 7.0" 112 = 0.582ft Provide 8" pipe with 7" orifice 171 Saxony Rd #2 13 ♦ Encinitas, CA 92024 ♦ P: 760.436.0660 ♦ F: 760.436.0659 ♦ info@sampoengineering.com Page ll ROUTING CALCS AND STRUCTURE CAPACITY FOR TOWN HOUSE Q100 EXISTING 1.43 CFS Q100 PROPOSED 1.45 CFS CONCRETE DETENTION STRUCTURE V100 = 1983.5 FT3 ________ ........... _______ _ 1.45 FT3 SEC l MIN ~ 22.8MIN 60 SEC ) 0.02 FT3 SEC X 60 SEC =1.2 FT3 /MIN 1 MIN 1.2 FT3 /MINX 22.8 MIN= 27.4 FT3 CONCRETE DETENTION STRUCTURE CAPACITY PROPOSES 6FT X 5 FT X 1 FT= 30 FT3 17 1 Saxony Rd #2 13 ♦ Encinitas, CA 92024 ♦ P: 760.436.0660 ♦ F: 760.436.0659 ♦ info@sampoengineering.com P age 11 . . '. < ' . ... . . • . t • ./ .:· '. .' ··:... .. -· .. -,' .. .. . ., · ....... :·'' ,, ~ . :• ", ' , -. -(;!. -. ·_ . '. .: i: :.ii)-·. ; y.;:,:::.i::--. ·. .. . ~ ' . , ' -· ~ i. 1. ' .• • "..9. • ffi ~~; · 7(-~' A~-i · '., -l . .-· i-c:c~ _.,.,- ..::: ~ ~ .. ···~. ''I>"- • o• 01,- -<o> ;.. 0 N 0 b N II It .... ~-< (.) U) / • ... . ~ VICINITY MAP N NTS LEGEND WA 1ER COORS£ APN: 203 054 10 ........IIJtiAIIII tl/SSORllr I r' BASIN C= 092 l1f»=6.85 IN/HR A=0.23 AC 0100=1.45 CFS ~ _ -,;N56V1'o1"W 1~36: --, ir . 1 I ™ ~~-------_-_...JJ ~ "kl ~11 ~ ~r--=-:: = TRAm TIii[ • .,. t ·. · . . • -:--'i1. , " J· \ .... :-_.. -;. . ~---··.,''.: .• L '-....;..•-•·· , ,. . j a' 'v S}118(1 N55'58'25''[ 128.42' APN: 203-054-07 -- -... - CY ~ 1 o· .. PROPERTY BOUNDARY 20 40 ,--1 I SCALE: l" = 20' ~cti ~ ~ I! D.CI <'S z ~ ~I~ I~ <b ""'w ..,.~ CITY OF CARLSBAD ji ""~ ;; f PRlPO$J DRAINAGE UAP FrYi m ~ ,Si~ TOWN HOUSE 26 77 STA TE STREET ~q-,~&1~ '4~-~~ '~ ~