. Determination of stream flow during the frozen season . 16 Jan. 23, I90E Fig. 10.—Vertical velocity curves under ice cover; average of curves at stations 80, 90,100 for differentstages, Wallkill River at Newpaltz, N. Y. that both threads of mean velocity tend to move downward as thestage increases. (See figs. 9 to 11.) The range in position of mean threads seems to be about thesame for both upper and lower threads, being about depth(with a few exceptions). Moreover, the change in position of thetwo threads is about the same in amount, the average differencebeing of
. Determination of stream flow during the frozen season . 16 Jan. 23, I90E Fig. 10.—Vertical velocity curves under ice cover; average of curves at stations 80, 90,100 for differentstages, Wallkill River at Newpaltz, N. Y. that both threads of mean velocity tend to move downward as thestage increases. (See figs. 9 to 11.) The range in position of mean threads seems to be about thesame for both upper and lower threads, being about depth(with a few exceptions). Moreover, the change in position of thetwo threads is about the same in amount, the average differencebeing of the depth. With very rough ice cover the tendencyis toward greater depression of both mean threads, but it will be VERTICAL VELOCITY 0URVE8. SI noted that they si ill preserve about the same distance apart, viz, depth. (See table on pp. 73-74, and fig. L4,p. 84). POSITION OF MAXIMUM VELOCITY AND RELATION TO MEAN VELOCITY. The average position of maximum velocity is at depth belowthe ice, varying from to depth. In general, it becomes. IN TERMS OF MEAN VELOCITY = Feb. 1305 6AGE HEIGHT NO OFCURVES AvERJkGEDEPTH AVERAGEVELOCITY 4 15 18 21 /.23 6 00 7 7 Feb. 1906 . Mar/906 Alar. 1906 Fig. 11.—Vertical velocity curves under ice cover, showing change in form of curve with change ofstage, Connecticut River at Orford, N. II. lower as the depth and velocity increase and hence as the stageincreases. Rough ice cover tends also to lower the depth of themaximum thread, and when the ice becomes broken and tilted orwhen needle ice accumulates near its under surface the thread maybe considerably below mid depth, indicating a greater effect due toice friction than to that of the stream bed; in other words, thecurve is a complete reversal of the ordinary open-water verticalvelocity curve. ibb 187—07 6 82 STREAM FLOW DURING THE FROZEN SEASON. The average coefficient to apply for obtaining maximum from
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