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<br />EM 1110-2-1406
<br />5 Ian 60
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<br />6--09. HORIZONTAL DRAINAGE. W'cl" llOl",s..ntal drainage is inadequate (as in the Great
<br />Plains, in contrast to the mountainous ,un 0" Western United States), the delay to runoff
<br />caused hy the snowpack may he much larger tha 11 for the vertical transit of water through the pack
<br />alone. Present knowledge does not pern' (",',d',ation of this effect, but it could be treated as an
<br />additional time delay to runoff to be imorporatcd in the routing of streamflow through basin
<br />storngC'.
<br />
<br />6--10. COMPUTATION OF UQUID.W"..TElt RF,QUIREMENTS. The apparent "loss" of
<br />water input (eit.her rainfall or snownlt'!U 111 conditioning the snowpark to produce runoff is the
<br />sum of the equivalent. cold (UTlH'I\t. .ill 11l('hrsJ and thp liquid-w<lter deficiency. This may be
<br />expressed as
<br />
<br />Sp=lr,.~Sf
<br />
<br />(27)
<br />
<br />\""h('1'c lllc is the liquid \\-nlel' tn rll;Si~ tll(' tt'mpc'rature of the p:H~k to 00 C., Sf is the liquid water
<br />dl'flrirllcy of 111r sn::-wpnrk, and )1:..."", is the' '(l)('rn~nnent" storflgr. i;:l inches, in that it is not available
<br />for runoff until 1 hI' ':,Hnq):lck is llldted. Each term is ('xpressed in inches of liquid water. Equation
<br />26 (pal'. (J-l);j) ,](,J, I.\f fC'\\ ;'Jtll'Il ill thc form
<br />
<br />TV = T\',T, (28)
<br />, 1uO
<br />
<br />wllPrD n"o 1" the initial Wall'I' equivalent of the snowpack in inches, and Ts is the average snowpack
<br />f('I1lPNUt'II'\ in C( '. !.I'low zeI'o. Additional storage of liquid watcr to satisfy the liquid-water
<br />(klici(\n('y H;:t.\' Lr~ (,~pI'essed as
<br />
<br />s _ j; (].\" -+.]")
<br />/-1UO Q' '.c
<br />
<br />(29)
<br />
<br />wh,'!'" f; is the liquid-water deficiency in percent. For cases whcre the snowpaek is initially dry,
<br />j; is {'qual toj~', the liquid-water-holding capacity.
<br />
<br />6-11. EXA:\lPLE OF CO:\1PUTATION. As a guide for computing the storage potential of the
<br />,no\\'pack, t]", following hypothetical example shows the variation that may be expected for a
<br />d('('fl I1lidwintel' snowpack covering three elevation zones, in anticipation of a rain-on-snow event:
<br />
<br />i I F:kyationzonc, ft, msl
<br />, i
<br />, t'nit Symbol
<br /> i 6,OO()-5,000 5,OOlH,OOO 4,000-3,000
<br /> I Inchcs_ _ I 150 100 50 D.
<br /> ,- I
<br /> g/CCu___ -- i 0.35 0.38 0, 40 p.
<br /> Inche'L_ _ i 52 38 20 lVo'
<br /> oC______ -- -4 -2 0 T..
<br /> PerccIlL___i 4 4 4 f"
<br /> "
<br /> I Percent_ _ __ , 0 I 0 1 J,.
<br /> , Pcrc:ent_ 4 4 3 1'v'
<br />i - --I lVc.
<br /> Inche~_ __ L 30 O. 47 0
<br />I In('hc~L _ 53.3 I 38. 5 20.0 lV,+lV,.
<br /> ---I I
<br /> Inche:'L _ __ ! 2. 13 L 54 0.60 Sf.
<br /> Inche~ _ ----, 3.43 2.01 O. GO Sp=S,+lVc'
<br /> ! I
<br />
<br />HeTll
<br />
<br />lnitial f'1l0W dcpth__
<br />Init1:d snow density_
<br />Initial :-nowpack water equint/cnL
<br />Initial "now temperature ________
<br />Liquid-water-holding c[l.p[l.eity ___ _ __
<br />Initial liquid-water c:orJtt'llL_
<br />Initial liquid-water ddieicllcy _ ___
<br />Cold eoutl'llt of t'lImyp:\l'k______
<br />"-all'r equivalent nt 00 C ________
<br />Liquid water defieiency___ ________
<br />Total liquid water rl'quiremenL
<br />
<br />UI
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<br />The temporary storage of water ill tmnsit woul<1 be ill addition to the nmounts shown in the above
<br />example. ASSUlllillg th,lt the maximum free water for the snowpack us a whole is 10 percent (a
<br />near maximulll vallle for d('('p mountain 5no\\'p"ck5), the \\':ltrr in transit \Vould reprcsent 6 percent
<br />of t.he sllowpack water (lqUiVUlellt.. As a lllllXillllllU, the transitory ~tor<lge would amount to about
<br />1.2 inches in th(' lowest elevation ZOIl(', <ll\d about ;3,2 inches in the highest zone, if the inflow is
<br />of suffjeient duration to establi:-;h all equilibrium with outflow,
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<br />23
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