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<br />e <br /> <br />e <br /> <br />e <br /> <br />EM 1110-2-1406 <br />5 Ian 60 <br /> <br />ary, rt-':3ulting ill gCllcl'all~T snhfrt'('zing t.crl1pcrntm'C's through the pack. By the end of ~fnr('h, <br />the }wat deficit within the pack hnd been on'rcomc find tIle tl'lllpeflllUrr was uniformly at {Jo C. <br />(rxccpt for the surfnt'p ('J'll~t, layer at. night). Thr sIlo\\~pa('k I'<'mairH,d in this condition for the <br />l'{'lllnind(\r of the llll'lt. periud. DCllsities within the snowpilck arr shown 10 in(TeUSr with time <br />and with drpth. Changes in d(,llsity take piner slowly ::ftt't' th() initinl ('OlllpadioTl of the succC's- <br />siye laYNS of new snow. It should be' noted tllfll the J'(')alj\"('ly intc[]:-;(' rainfall of !lanuufY 8 <br />and n did not prodlleC' slid den cli,mges ill ~no\V dpnsity, flnd that I]H~ illdiyidllal snuw horizon <br />lll<lrkcrs shO\n'd no P,Ht jcuL1r SC~ttl(,Illl'llt at. tlwL timC'_ <br /> <br />6-05. THE COt]) CO:'\TE.'IIT OF THE S.'IIOWPACK. ror the <,valuation of runo!}' potential <br />ill the \\-il1tel' and early spring months) the hydl'ologl::;t is prilllarj]y intpl'(\sted ill the tempera- <br />ture ,tlltl dt'Ilsit.v profiles of the sllowpack and how the.y afi't,ct 111(\ "cold ('ont('ntlJ of thl~ STIm\". <br />The cold content. is ddined as the heat required pCI' unit area to raise the temperature of thr <br />~nowpll{'k to 00 C. It. is convenient to expI'(\s::; it ill illch(;~ uf liquid ",atrl' (produced at the Sllf'- <br />facr by ('iiller rilin or Jllclt.) \\"hicl1, upon freezing within 1 he pack, will \varrn the pack to no c. <br />h~~ th(' l'(']PllSL' of its latent heat of fusion. The rdationship may be cxpressL'd as <br /> <br />TV = pl)'[~ <br />C }{jO <br /> <br />(2G) <br /> <br />whe1't' Ire is the cold content in equivalent inches of liquid water, p is density in grams per cubic <br />centiml'tl'l', J) is the depth in ill C'11(\S, and T8 is the uveruge snowpack (or snow layer) tl\!llperature <br />deficit. Iwlow ()O C. <br /> <br />&-06. UQt:ID WATER IN Si'lOW, As indicated earlieT, liquid water may exd in the suowpack <br />in the following furms: <br />(1) IIY!JI'oscopic u'atcr ilnd cOJFillar?J water, which is not available to runofT until the snow <br />rryst:lls have lll.dted. <br />(2) Gl'ai'itatiunaI1cater, which is in transit through the snowpack under the influPIlcc of <br />i!I'llvity. <br />ThC' liquid water in the snowpack is customarily detcrminrd by the calorimetric method (see <br />p:1r. 2--0:1). Figure 8 shows the diurnal varintion of free watrr content of t.he sno\v) at various <br />l(\,~('ls ,\"ithin it typical melting snowpnck in the springtime. This diagraIll shows that) after <br />draillugr of gravitational water during the night, the fI'('e .water ranged from 2 to 5 perccnt. <br />During' tlIP (hy, th('~ free water was as llluch ns 10 IH'I'c('nt) due to the melt water in transit <br />through the p:lck. <br /> <br />6-07. LIQUID WATER REQUIREl\1Ei'lTS TO PRODUCE RU:'\'OFF. For 11 snowpaek to yield <br />runoff, it is IlC'cessary first that its liqllid-watrr-holding capacity be s,ltisfieu. The differf'I1cc <br />het\v{'f'n the liquid-waLer-holding ('apa('ity (.I" p) and tlle liquid-\vateT cont.ent (fp) determines t.he <br />liquid-watl'r deficiency (f' ,)" The liqllid-wuter-holdillg capacity (fop) is defined as the maxi- <br />lIlUIIl amount of llygroticopic and capillary l\'ate1' the pack c!tr1 hold against gr<l\"it,y. Tllis capac- <br />ity is u fUIldioJl of STlO\q):t('k conditioll, but it g(,Jl('r;lll.\~ falls within th(~ l'llngr of :2 to [) IH'lTcut <br />of the total \\TaU'r {'qujyalcllt. of t1w snO\qHlck. For an initinlly cold (subfr('('zing) snowpack, <br />the total \I"atl'r (or eqlliyalent hmt) required to condition the snowpack to produee runoff is the <br />sum of the cold content and the liquid water deficiency, <br /> <br />6-08. VERTICAL DHAINAGE. After the liquid-water conditioning of the snowpaek has taken <br />place, the transit of water thruugh the pack is mostly yertically duwnward tu the ground-snow <br />interface. Ice pbnes within the sllowpack, hO\vcvcr) t.end to deflect the path intermittently, <br />th('rcby !'('."ultillg ill llIl irregularly st('ppcd pattl\l'n. The net storage effeeL on wat.f'r dt'flining <br />through the snowpack is it time rid"y 10 runoff, in the order of :1 to "1 hours of storage time for <br />moderately deep packs. Plate 2 shows the sno\\rpack inflow and outflow rela.tionship fot' typical <br /> <br />21 <br />