INLAND WATER SURVEY 423 
enables steady observations to be made at depths of 17 ft. or over in high 
velocities. ‘This rod resembles the struts of an aeroplane in section. It is 
also used for soundings. The efficient and safe carrying out of the gauging 
is dependent on the care, skill, and accuracy of a surveyor, who is a practical 
engineer, a rigger and a boatman. 
4. CURRENT METERS, 
There are many good types of meters which record, electrically, the 
revolutions of the meter. 
The essential gauging points are :— 
(a) The care of the meters. 
(6) The careful work of looking out for weeds, leaves, etc., on the 
meter during gauging. 
(c) The frequent calibration of the meters at the National Physical 
Laboratory and the use of several meters. 
5. THE GauGING OPERATIONS AND ACCOMPANYING FIELD Work. 
On a 100-ft. to 300-ft. width of river, the velocities are measured on every 
gauging at each 10-ft. mark on the tallyline, and often at every intermediate 
5 ft. At each of these points, velocities are measured at 6 in., 1 ft., and each 
foot to the bottom, and at intermediate 6 in. near the bottom. 
The time intervals given by the buzzer are entered on the field sheets, 
and also the clock time at the point. 
On shore, the assistant keeps the water level records at the two gauges 
against the clock time. A hook-gauge in a well is used for these water 
levels, and they are plotted for the day. Automatic recorders may be used 
in the future. 
+ During floods, the water levels vary very considerably during the gauging 
day, but the underlying principle of the writer’s method is that each point 
on the river has its separate stage-discharge curve, thus eliminating inac- 
curacies of computation due to varying water level during the gauging day. 
The gauging day thus ends with velocity field sheets and the graphs and 
readings of water levels. 
6. COMPUTATIONS. 
These do not need description in detail, and the whole work centres on 
the Stage-Discharge Diagram at each gauging point on the section. A 
diagram is attached to this Memorandum, giving, for each water level gauged, 
the cusecs passing the point for a 1-ft. width of river and, by intermediate 
markings, the cusecs passing at each foot or 6 in. of depth. The water 
slope is given against the water-level height of the recorder gauge. To this 
diagram is added a diagram of maximum velocities at and near the surface. 
This yields a maximum velocity-stage graph, and, by applying different 
coefficients to these maximum velocities, the coefficients applicable to each 
stage of the river may be judged. 
_ These coefficients are used for the final smoothing of the stage-discharge 
curve of each point, and, finally, the discharges at each 3 in. of water level 
height are transferred to a diagram giving the discharges for the whole river 
section at each 3 in. of water level. The results are also tabulated. On 
these lines, if there is no overflow, the discharge values may be reasonably 
extended to higher floods and approximately to lower low waters. 
