CURRENT METERS 59 



LOW WATER MEASUREMENTS 



\t m.mx -taiion* ill,- x.-I.M-itx ..i th<- nxer at low stages is so 

 Miiall that it may be advisable to find a section nearby in which 

 the -iit may be made by wading. 1 



measurrmi UK th< m. t< i <>n the rod (Fig. 3) is the moat 

 satisfactory. 



In rder to obtain a suitable section, it may be necessary 

 to cut off part of tin il.,\% |>y damming the stream and modify- 

 ing the channel so as to get sufficient depth and velocity for 

 measuring. 



MEASUREMENTS UNDER ICE 



When a discharge measurement is to be made under ice, it 



i> first neeear> lo find a ..... I iiifa-iirinj: >eeii.,n. Sti. h a 

 reconnoissance can best be made by a hydrographer who is 

 familiar with the stream and x%h. knows where he will find 

 sections of the stream with smooth beds. 



A hole is first chopped through the ice at the center of the 

 stream at a section being investigated. If this hole shows that 

 litil.- or no xlu-h ice is present, and the velocity is measurable, 

 tuith. i implications should be made at each side. It has been 

 found ti (><< of >lu-h <>r anchor ice are most com* 



moidx found just above an open place on the n \.-r-. 



After the measuring section has been selected a hole is 

 chopped through the ice at each measuring point, and the depth 

 ami velocity determined \Nith the meter on the rod. Where the 

 depth and velocity are too great the work will have to be done 

 x\ith the meter >u-pended on the meter cable. 



Ice measurements are usually made by the .2 and .8 method, 

 ami -.in. -nines by vertical curves. The soundings should be 

 made to determine the depth from the bottom of the ice to the 

 hed of !' MI and the meter observations taken at .2 and 



.8 of this depth. In all other respects ice measurements are 

 made and computed in the same way as open water measure- 

 ments. 



The special jointed ice chisel, ice-measuring stick and 

 inving bag, generally used in connr. -ti..n xsith ice measure- 

 are illustrated in Fig. 33. 



