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HomeMy WebLinkAboutTM Creek Sub #1 Drainage Calc Report r►\ //iorinj 4110114 i~ A' WAn THE LAND GROUP, INC. TM Creek Subdivision No. 1 Drainage Calculations Report CfrA 11 7529 ,`b EOF10 CE'NE P. Prepared by: Eugene P. Smith, P.E. August 24, 2015 Landrtape,-1 tthitetturr•Site Planning•Cit'l Engineering•Goff Course Irrigation c Engineering it Graphic C.nmmunication 462 I:.Shore Drive,Ste.100,Eagle,Idaho 83616•I'208.939.4041 I`208.939 4445*tywnv.thrl;trnil ottpinc.rr+ttl (,.\2015\115056\CAD\talcs and Reports\Drainage\115056 Drainage Report'I'YMC1.doe% iI %o THE LAND GROUP, INC, TM Creek Subdivision No. 1 Drainage Calculations Report TM Creek Subdivision No, I is the first phase of a multi phase proposed commercial development. The project is generally located in the NW 1/4 of the NW t/a of Section 14,T.3N., R.1 W.,Boise Meridian,City of Meridian,Ma County,Idaho, on the south side of W.Franklin Road and on the east side of S.Ten Mile Road. This phase will he comprised of 8 commercial lots and I common lot on approximately 6.89 acres. The storm drainage from this project will he intercepted by oil/water skimmer cleanout inlets and discharged to sub-surface seepage trenches. Assumptions used for this drainage report arc as follows: 1) Rational Equation used to estimate storm runoff(Q=C I A) 2) SCS:TR-55 method used to determine Time of Concentration(Tc) 3) Compute weighted average to determine C values; Driveways. C = 0.95; Landscape areas, C = 0.10; Paved portion of the right-of-way,C=0.95, This phase is divided into five(5)runoff collection zones. The Rational Equation was used to determine the peak discharge. This method uses a weighted"C"value,Time of Concentration(Tc)calculated by SCS TR-55 methods, and rainfall Intensity-Duration-Frequency(IDF)curves for the Boise Front(Source: State of Idaho Department of Highways,Surveys and Plans Division,Procedures Manual). The rainfall intensity is determined from the IDF curve where"i" is selected at the calculated Tc and the 1(H)-year return curve_ Contributing area was computed and is depicted on the attached map. The assumption is made that only those areas within the access easements/ROW is included in the drainage area to size the seepage trenches. This is based on the assumption that the individual lots will be self-contained and/or is delayed long after the peak discharge has passed. The peak discharge is used to determine the capacity of the seepage trench, if the calculated Tc is less than 10 minutes,a minimum value of 10 minutes is used to select"I" in the peak discharge calculations. Per ACHD policy, for volume calculations,"1"is determined using Tc of 60 minutes for use in determining the storage requirement. Landscape"I rrhite.lurr•Site Planning•coil Fingineen, •Golf Course!station c-I ngineerm, •Graphic Communication 462 F.Shun. t)r vc,Ste. 100,l:al;tc,Idahn 83616•I'208.939.4041 I'208.9324445•wwu thct mdpnrupinc.c'n G.\,2015\,115056\(:.11)\Calcs and Report.\l)rainat c\_115056 1)rainazc Ri.'purt'I'M(:.1.Jucc L o � et) CD CD LO CD CID N 7. 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C 0 17 V O #3 a C z O H m 5 la o ci C 2 2 'C7 12 E CU •- N 2.1 a' In C Z W CC = ..N r3 V H7 Vyy N < < C-- I- C TM Creek Subdivision No 1 July 9,2015 Drain Time for Infiltration Bed HRS=Required Volume'90% Trench Length'Trench Wldth"Infiltratlon Rate Zone Req'd vol Length Width Mf Rate 1 1,690 41 13 0 8 HRS= 4.33 2 749 29 8 8 HRS= 4.33 3 1,149 45 8 8 HRS= 4 33 4 2,119 55 12 a FIRS= 4 33 5 992 39 8.0 8 HRS= 4.33