recording type gauge. Shallow streams and low-flow stages may be waded
and measured with the help of a graduated staff. In alluvial streams with
fast-moving flows the gauge may be suspended from a fixed reference
point, e.g. a bridge parapet wall.
Gauge recordings are indispensable for design purposes and for
hydrological studies. The data are equally valuable for the purposes of
navigational studies and for high (flood predictions) and low (water
quality, aquatic life) water management. Stage readings at a gauging
station combined with discharge measurements yield stage–discharge
(rating curves) relationships (Section 8.4.4).
Telemetry is used to transfer water level data from remote stations,
either continuously or at predetermined intervals (Herschy, 1986).
8.4.3 Bed levels
The simplest method of establishing bed levels is by using a graduated
sounding rod with a base plate fixed at the bottom end. The base plate
prevents the rod from penetrating into the river bed and also helps to keep
it in a vertical position.
The bed topography can also be obtained by sounding techniques
from the water surface. In river engineering bed level measurements have
to be made periodically. The most commonly used sounding instrument is
the echo or supersonic sounder, which can be mounted aboard the survey
332 RIVER ENGINEERING
Fig. 8.5 Water level (stage) recording station
