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4118 API'UIlD KYDaOI.OOY The nmoff cocfticieot is also dependent on tbe cbaractet 8Dd cooditioo of tbe soil. The iDfilttation rile decreases as raiufall continues. IIId is also influenced by tbe antecedent moisture condition of tbe soil. Other factors influeDCing tbe nmoff coefficient are J'linfall intensity. proximity of tbe water table. degree of soil <:ompactioo. porosity of tbe subsoil. veletatioo. JroUIIIl slope. 8Dd clepressioa stonge. A reasonable c:oeffic:ient must be chosen to represent tbe intepatcd effectl of all tbese factors. Sugested coefficients for various surface types as used in Austin, Texas are liVeD in Table 15.1.1. Ra1D18IIlnteDllty The rainfall inteDsity i is t/J drainage basin or subbasi ninfall duration IIId IetUn is equal to tbe time of co The mum period is eltabl as . desiJD panmetcr. Runoff is assumed tl entire watcrsbed is coabit is tbe time for . drop oh to tbe point of inlmSt. I- tbe aitic:al time of CODCen consider. The time of con, tbe sum of tbe inlet time t reach the sewer inlet), and the outer point: TABLE 15.1.1 RUIIOlf coefIIdents for .. 10 the ndoul method lIdun Portod (Jan) CIIIr.- ol.m- 2 5 I' 25 51 I_ .. a~ h,!1 AIpIIaIlic 0.73 0.77 0.81 0.86 0.90 0.95 1.00 ConcreIeIroof 0.75 0.80 0.83 0.88 0.92 0.97 1.00 Gtaa _ (IawnI, pIIIb. ....) Pbor cmtdirioro (arus ..,.. less _ so.. of Ibe Ilea) FIaI. G-2.. 0.32 0.34 0.37 0.40 0.44 0.47 0.58 A..-qe, 2-7" 0.37 0.40 0.43 0.46 0.49 0.53 0.61 Sloop. over 7.. 0.40 0.43 0.45 0.49 0.52 0.55 0.62 F_ t:rNIdiJiDII (arus ..,.. OIl 5O'lIo II> 75.. ollbe Ilea) 1'Ial,G-:z.. 0.25 0.28 0.30 0.34 0.37 0.41 0.53 A..-qe, 2-7.. 0.33 0.36 0.38 0.42 0.45 0.49 0.58 Stoep, 0'" 7.. 0.37 0.40 0.42 0.46 0.49 0.53 0.60 Good cmtdition (arus ..,.. bqer _ 75.. of Ibe ....) 1'Ial, G-2.. 0.21 0.13 0.25 0.19 0.32 0.36 0.49 A....,.. 2-7.. 0.19 0.32 0.35 0.39 0.42 0.46 0.56 Sloop, 0... 7.. 0.34 0.37 0.40 0.44 0.47 0.51 0.58 V.........,.. CUllivated Laud Flat. G-2.. 0.31 0.34 0.36 0.40 0.43 0.4' 0.57 A..-qe, 2-'" 0.35 0.38 0.41 0.44 0.48 0.51 0.60 Stoep, over 7" 0.39 0.42 0.44 0.48 0.51 0.54 0.61 -...ntan.. FIaI. G-:z.. 0.25 0.28 0.30 0.34 0.37 0.41 0.53 A..-qe, 2-,.. 0.33 0.36 0.38 0.42 0.45 0.49 0.58 Stoep, 0'" 7.. 0.37 0.40 0.42 0.46 0.49 0.53 0.60 FoRItIWoodJands 1'Ial. G-Z" 0.22 0.25 0.211 0.31 0.35 0.39 0.48 A..-qe.2-7" 0.31 0.34 0.36 0.40 0.43 0.47 0.56 Stoep, 0... 7.. 0.3.5 0.39 0.41 0.45 0.48 0.52 0.58 -= 11Ie val... in the ..... .. the _ used by the City III _. Teus. Vsed wiIb petIlIisIimI. The flow time is JiveD by when: ~ is tbe 1enJllt of velocity in the pipe. The inlet time, or tim can be obtained by experil fotD111las such as those lisl flow routes for cliffmnl ( concentration 1IIDOIII1be Ii time of c:oncentratioo of th, Because tbe lII'eaS Ct small. it is also customary under similar conditions. In the surface increases, 8Dd il traYd increases and as 1m, detennined on tbe basis of computation. DnlDage Area The size and shape of 1be , be determined. The area m, or by field surveys where conloUr interval il too areat