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FLOOD07755
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Last modified
1/25/2010 7:12:42 PM
Creation date
10/5/2006 3:11:14 AM
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Template:
Floodplain Documents
County
Statewide
Basin
Statewide
Title
Engineering and Design Runoff from Snowmelt
Date
1/5/1960
Prepared By
US Army Corps of Engineers
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />Ie <br /> <br />e <br /> <br />e <br /> <br />EM 1110-2-1406 <br />5 Jan 60 <br /> <br />3 <br />~ <br />u <br />~ <br /><< <br />~ <br />~ <br />" <br />< <br />~ <br />z <br />o <br />N <br /><< <br />o <br />x <br />< <br />62 <br /> <br /> <br />iLEGE <br />Cur" es g;ve'lh~orel co/ vo/ves i t Dir~cf:-s%~adiON n onl <br />calc /q1~t~6"~ 'Nlof1fud~-":,,,,_~Oirecll-so";!r Ius dif'rf'USe <br />and or on ~/evolloh or~'P rox. I I sky rddiaflo . <br />52 f'f. Mst(Of'lerlH~Ck.) _l_ r----+-- ' <br />, I L -+ I I ' <br />-- L- - _--1, =r~ l--- +- -- ---L I <br />, I I , <br />~__ -c- -- -+-1-- - -~- - --1- <br />SO'I~opeI25'1 -H -I- '--L i L <br />L' I l' I / <br />, I' I <br />1----'-rr-r--1--i--:/7 - I <br />- - - 1- rt-i---'//1-1-- -i- <br />T ,- ..;.>., --- -'--+-1 <br />Hor/z nlol E'osf or Vesf sf, pes:! I <br /> <br />z <br />o <br />~ <br />~ <br />o <br />< <br /><< <br />o <br />~ <br /> <br /> <br />w <br />> <br />~ <br />< <br />" <br />w <br /><< <br /> <br />I <br />I <br /> <br />~ <br />w <br />. <br />o <br />" <br />~ <br /> <br />- --1--[ / <br />--1-L~f- <br />/ ' <br />- -= _J--- , ------ <br /> <br />z <br />o <br /> <br />z <br />2 <br />. <br />" <br />< <br /><< 0 <br /> <br />JAN <br /> <br />Figure S. Seasonal mriation of proportional dear sky solar radiation on north and south slopes, relative to a horizontal <br />surfan'. (From "Der Rinfluss ria Strahlun!J unci deT TemperatllT auf den Schmelzprozess der Sneedeck," by <br />Rncin lIoeck.) <br /> <br />on n horizontal surface is u function of the surface slope angle to north or sout.h, t.he latit.ude, the <br />SC',lSOIl, and tIte lllllount of diffuse sky radintion relative t.o din~ct solar radiation. .Figure 3 shows <br />the srfl3oIl:d v,l.riation of that ratio, for slope angles of 250 north and south, at latitude 460;30' N, <br />as detcI'IIlitl(\d hy Hoeck.6 <br />FOl"est ('0\"('1" also plays fin important part in the amount of solar energy that reaches the snow <br />surface. Consideriug ouly coniferous forest, the transmission percentage vnries \vith the type, <br />density, and condition of trcrs. The transmission also varies with the season, because of variation <br />in shading effect of the trees with the solar altitude. The determination of the amount of sunshine <br />transmitted through the forest is nt bpst an approximation. Figure 4 shmvs a mean transmission <br />curve for daily insolation amounts, rxpresscd in terms of forest canopy density. It will later be <br />shown that, for basin application, the transmission coefficirIlt and forest eanopy density can be <br />combined into a single factor, F, which is termed the effective forest cover. <br /> <br />2-05. ALBEDO. The lllbedo (a), or reflectivity, of tbe snowpaek varies over a considerable <br />range find thus is important in estimating the amount of solar t'Ilergy absorbed by the pack. <br />Albedo is expressed as the percent of reflected shortwave radilltion to that incident on the snow <br />surface. Values range from more thfin 80 percent for new-full en snow to as little as 40 percent <br />for melting, late-season snow. The melt equivalent from shortwave radiation, J.1rs, in inches <br />per day is <br /> <br />M (I-a)I, <br />. ,,= 2mB <br /> <br />(2) <br /> <br />where a is the albrdo expressed as a decimal fraction, Ii the daily incident solar radiation in langleys, <br /> <br />5 <br />
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