CURRENT METERS 75 



To insure accurate? marking, all gages should be subdivided, 



li\ means of a steel tap > engineer'- ! \-l. The 



zero of all gages should be .. r<*d to a fixed datum, 



and the ivl.iti.m tliu r-:.ih! 1 be checked frrtjurntly 



by means of an ! ! \.-l. 



HI. (imilM. \\ VII K -I V.I Kl .|s,| K. 



Recording water stage registers make a record of stage, 

 either continuously by a m\ . (he coordinates of win. h indicate 

 the time .tnd the stage, or by a device that prints at stated inter- 

 vals of time. Tli.- i--riih.il parts of tin- nvonlmg gage are: 

 i I i A float which rises and falls with the surface of the water; 



(2) A device for transferring the vertical m<ii<>n of the float 

 to the record. < nh.r directly or through a reducing mechanism; 



(3) The recording device; and (4) The clock. 



Curley recording water stage registers are described in 

 detail on pages 77 to 130. 



BENCH MARKS 



The value of all streamflow records depends so intimately 

 upon the constant relation l><-t\\< <-n /,-ro of the gage and the 

 -i. in. .11 1>< m h mark that too much care cannot be taken to injure 

 the permanence of this relation. 



Two independent bench marks at M li station are desirable. 



The\ >hould le H,, locateil that the\ \\ill not l.f dam.t-.-.l l.\ 

 Hi MM U or nther t\m--. \i ln-idp- -t.ihoi^ .it li-a-t onr 1>. -IH h 

 mark should he apart from tin- -tin. hire. Where trees are 

 axailahle, a trark -pik.- \\ith tin- front edge of the head up- 

 turned, makes a useful bench mark. In a localit\ \%ith"iit 

 timhcr the United States Geological Survey type bench mark 

 (Fig. 40 I i- .i\ .nl.ii.l.-. |',i ><>t it. dig a hole of -mall diameter 

 \\ith a post hole digger, well below frost line. Place in die 

 hole a piece of .'i-im h pipe and fill the hole with concrete: fill 

 the pipe with cement mortar, into which set the bench mark 



