The slope-area method is extensively used in
In a river carrying a discharge of 142 m3/s, the stage at a station A was 3,6 m and the water surface slope was 1 in 6000. If during a flood, the stage at A was 3.6 m and the water surface slope was 1 in 3000, what was the flood discharge (approximately)?
Discharge is directly proportional to
For a given stream the rating curve applicable to a section is available. To determine the discharge in this stream, the following data are needed
The stage of river carrying a discharge of Q m3/sec at a point is 10 m and slope of water surface is (1/4000). The discharge of a flood at the same point and same stage of 10 m with a water surface slope of (1/1000) will be
When a routine and regular information of the discharge of a stream is desired, it is usually obtained
As floodwave passess a given section of a river, life lime of occurrence of the maximum stage and that maximum discharge will be such that
The surface velocity at any vertical section of a stream is
Calibration of a current meter for use, in channel flow measurement is done in a
The relation between the stream velocity and revolutions per second of the current meter is called the calibration equation. The calibration equation is unique to each instrument and is determined by towing the instrument in a special tank called towing tank. Towing' tank is a long channel containing still water, with arrangements for moving a carriage longitudinally over its surface at constant speed. The current meter to be calibrated is mounted on the carriage with the rotating element immersed to a specified depth in the water body in the tank. The carriage is then towed at a predetermined constant speed(v) and the corresponding average value of revolutions per second (Ns) of the instrument determined. This experiment is repeated over the complete range of velocities and a best-fit linear relation in the form of the equation v = aNs + b where a, b are constants of the current meter.
If Vs = surface velocity of a stream at a vertical, the average velocity V in the vertical will be about
In the case of large rivers, a number of equidistant vertical sections of the total width of flow are identified, for the purpose of finding by numerical integration, the total discharge on any day. On each section, the mean velocity is taken as the arithmetic average of two typical depths on that section. Then the mean velocity is worked out for that section. Usually, the mean velocity of any section, corresponds to which one of the following?
(V represents the point velocity at the given section and the depth such as 0.1 d, 0.2d.... etc.)
In shallow stream of depth up to about 3.0 m, the average velocity,
This is called single point observation.
In moderately deep streams the velocity is observed at two points.
In rivers having large flood flows, only surface velocity (Vs) is measured within a depth of about 0.5 m from the surface. The average velocity = kVs where k is in the range of 0.85 to 0.95.