The concept of a ‘dominant discharge’, i.e. a steady discharge giving rise to
the same pattern of meanders, slope and channel geometry as the annual
sequence of discharges, is frequently used. It can be defined as bankful
discharge, or a discharge of a certain return period, or perhaps best as the
discharge associated with the ‘bed building water level’ at which the
largest total volume of sediment transport per year occurs, and is deter-
mined as shown in Fig. 8.4.
8.4 River surveys
8.4.1 MappingThe river engineer needs reliable maps for river investigations and for the
design and execution of engineering works. Maps compiled by the usual ter-
restrial surveying techniques are often incomplete and unreliable, but aerial
photographic techniques and satellite images can provide accurate valuable
data on river systems.
8.4.2 Water levels (stages)Water levels or stages are obtained from gauges (non-recording or record-
ing types) installed at gauging stations. Figure 8.5 shows an automatic
RIVER SURVEYS 331
Fig. 8.4 Bed-building (dominant) stage (discharge)