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234 STORMWATER MANMGEMENT ALTERNATIVES FOR WATER OUALIN IMPROVEMENI <br />T�BLE 7.3 Approximele Setlling Velocilies tor Various Sedlmenl Pacltcles <br />Diameter <br />mm µm' <br />8-10 5000-10,00U <br />0.5-1 500-1000 <br />0.25-0.5 250-500 <br />0.08-0.1 80-100 <br />0.002-0.05 2-50 <br />< O.00Ul � 2 <br />Type ot Particle <br />�� <br />Gravel <br />Coarsesand <br />Medium sand <br />Fine sand <br />Silt <br />qay <br />Saurce: U.S. Dep�rtment ot Aericulture 1981. <br />'µm - 0.001 mm or about 1/u•� of an inch. <br />$etlling <br />Veiairy <br />100-200 tt/min <br />15-20 tt/min <br />2-10 ft/min <br />30-SOft/h <br />1-2 ft/h <br />0.005-0.01 ft/day <br />TABLE 7.4 Sp�erica� Pacel�k Diameters and Settlini ��elocities Calculalcd Usio� <br />Stoka I.�w wflh Speciflc Gn�iq' o[ 2.65 and 20° C Velairy ([t/9 <br />let (µm) <br />Diameter (µm) <br />Veiairy (ft/s) <br />S 0.00�19 <br />10 0.00029 <br />12 0.00042 <br />15 0.00066 <br />20 0.0012 <br />� 0.0018 <br />Sourcu: Melcom and New (1975). <br />Diame <br />� <br />30 <br />40 <br />50 <br />60 <br />80 <br />100 <br />particles in urban runoff with average sc <br />ma Table 7.5. <br />Design Storm Slzing <br />. some resecvoirs, engineers have form� <br />�ent removal (Brune, 1953). 'I'hese are <br />a specific location and specific design fl� <br />i and sediment removal estimate tor the <br />Stortnwater particles may be discrete or f <br />11ing mechania can be used to esti arti <br />:ncies. For discrete nonflocculating p <br />�n each other, Stokes law can be used to <br />nplif��ing assumptions using Stokes law <br />�nnw�ater ponds, such as discrete nonfl <br />3uted velocity vectors, P��B floW+ and cor. <br />n1:es the bottom. Nevertheless, the settlin <br />les are important for some design and for <br />l���������..�. <br />0.00'-7 Most particles that settle with velocitia � <br />0.�7 daign should be effectively removed, where <br />0.007J h <br />0.011 ° <br />0.019 u0 � �e <br />0.0?9 <br />TABLE 7S PereeMaie of Particle Mass in SlormWater as Related <br />to M•enae Setl�tc6 Velairy <br />Perant ot Mass <br />in Urban Runaft <br />0-20 <br />20-40 <br />40-60 <br />60-80 <br />80-lOD <br />pverage Settlmg <br />Vdociry (tt/h) <br />� <br />0.33 <br />1.5 <br />7.0 <br />70.0 <br />Sourct: Adapted from U.S. Emironmental Proteaion ABency (19831• <br />e co = design settling velocity, ft/h <br />ha = depth of settling, ft <br />rr = pond detention time, h <br />the pond detention time is <br />V <br />0 <br />�d � 3600� <br />. ta � detention time, h <br />' Vp = volume of pond, ft3 <br />Q= outflow rate based on a desiE <br />3600 m seconds per hour <br />a pond overflow rate of <br />QX3� <br />OR = A <br />OR = overflow rate, ft/h <br />A = surtace area, ft� <br />