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<br />20 <br /> <br />Stream Classification According to Flow <br /> <br />All streams have been or can be classifJ.ed on the basis of continuity <br />of flow as follows: <br /> <br />(1) Permanent or Perennial Stream. Penl.llnent strellms receive their <br />waters fro. the watershed stream network, from subsurface water, <br />seepage, and from springs. Often the streambed is below the water <br />table for the immediate drainage area and strellm flow may <br />fluctuate according to the water table level. <br /> <br />(2) Intermittent or Ephemeral Stream. Intermittent streams may flow <br />for only part of each year as a result of receJLving surface runoff <br />water during wet periods or periods of snowmell; in mountail10us <br />regions. <br /> <br />(3) Interrupted Streams. Interrupted st,reams are lltreams that flow <br />alternately on and below the surface,. They may disappear :lnto thf< <br />streambed for varying distances onl~' to reappear in a downlltream <br />location. The subsurface flow is usually through coarse sandll, <br />gravels, rubble, or through limes to,,"e and assoe;iated caves and <br />caverns. <br /> <br />(4) Spring Creeks. Spring Creeks are streams that have their ,)rigin <br />fro. underground springs and dischaI'ge directly into an aSllociated <br />stream channel (rheocrene) or into a, small basj,n, pond, or lake <br />(limnocrene). However, when the creek simply flows out of the <br />ground into a wetland, marsh, swamp, bog, etc. it has been termed <br />a helocrene (Bornhauser 1913, Hynes 1970). <br /> <br />Cyclic Variations in Stream Flow <br /> <br />It is well known fro. analyzing large amounts of dSLta from strl!&m <br />gauging atat1.~1;\S that the earth's surface receives varybg amounts of <br />precipitation (humidity), buf that precipitation is cons:tant for thll earth <br />as a whole. A'period of increased humidity in one part of the world is <br />simul,taneously accompanied by reduced humidity elsewhere,. This is "ell <br />substantiated by observations that there are both synchr'onous and <br />asynchronous variation in drainage basin runoff that is geographically <br />localized. Analyses of 60 major river systems in the nc,rthern hemillphere <br />have shown that cycles recur most frequently with period,s of 2 to 3,. 5 to <br />7, 11 to 13, and 22 to 28 years. The 11 to 13 year cycles are normdly <br />regarded as being governed by solar activity whereas shc,rter cycles are not <br />yet adequately explained. However, the 2 to 3 year cycle is observable not <br />only in variations of stream flow but also in the level of the oceans. <br />Silll1lar cycles occur in a number of other geophysical phenomena. <br /> <br />Discharge <br /> <br />.. 'I;~~ ,!IIIount or volume of water flowiXll p.lIt . <br />perlod"'Of U.. 18 tee.ed the discharge (outdow). <br /> <br />liven point in a I:iven.. <br />The stsndard time, unit <br />