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�! � <br /> SC$ 1VESTERN 1VASHINGTON RUNOFF CURVE NUMBERS <br /> ( <br /> � SCS WESTERN WASHINGTOM1 RUNOFF CURVE NUMBERS (Published by SCS in 1982) <br /> RunoH curve numbers for selecled agricuilural, suburban ar4 urban land use lor Typc Ia <br /> � rainlatl tlistribulion„24•hour storm duration. <br /> . CURVE NUMBERS BY <br /> HYDROLOGIC SOIL GROUP <br /> LANC� USE DESCRIPT�ON A B � � <br /> Cultivated land(1): winter cond'aion 86 91 �9: 95 <br /> Mountain apen areas: low growing brush and grasslands 74 82 89 g2 � <br /> Meadow or pasture: 65 7A 'PS 89 <br /> Wood or lorest lantl: undisturbed or oider second growlh 4p 6y ;- g� �-- <br /> Wood or forest larxi; young second growth or brush SS �2 B� 86 <br /> Orchard: withcovercrop -Bi 88 g4 <br /> Open spaces,lawns, pyrks, gdl courses, cerneteries, <br /> landswping. <br /> good cond'rtion: grass cover on 75Y, <br /> or more ofthe area 68 gp O � <br /> fair.condition: grass cover on 50% <br /> • Io 75% ol the area �� g� �� 92 <br /> Gravel rwds and parking lots � 76 85 89 91 <br /> Dirt roeds arW parking lots � 72 62 87 89 <br /> � Impervious surlaces, pavement, roots, eic. 98 93 99 98 <br /> � Open vrdter �ies: lakes, wetlands. ponds, etc. t00 t00 t00 <br /> Single Family Residentiai (�) — <br /> Dwelling Unft/Gross Acre % Impervious (3) <br /> 1.0 DU/GA �5 Separate curve number <br /> . 1.5 Dll/GA 20 shall be selectecl <br /> 2.0 DU/GA 25 for pervious and <br /> 2.5 DU/GA 30 impervious portiqn <br /> 3.0 DU/GA ' 34 0l the sice a Casin <br /> • 3.5 DU/GA 38 <br /> a.0 OU/GA 42 <br /> 4.5 DU/GA qg <br /> 5.0 DU/GA 48 <br /> 5.5 DU/GA Sp <br /> � 6.0 DU/GA 54 <br /> 6.5 DU/GA �q <br /> 7.0 DU/GA 56 <br /> Planned unh developmenls, % impervious <br /> corxlominiums, apartments, must be camputed <br /> � commerCia� business and <br /> iMustrial areas. ' <br /> (t) For a more detailed descrip�ion ol ag�icul�ural laixl use curve numbers reler to Nalional Eny�neering <br /> � HaMbook, Section 4, Hydrdogy, Chapler 9, August 1972. <br /> (2) Assumes rool and driveway runoH is direcied into street/storm system. <br /> (J) The remaining pe�•ious areas�(lawn) are considered to 1�+in good contliiion lor these curve r.umbers. <br /> \ <br /> � <br />