Geoscience Reference
In-Depth Information
(a)
(b)
Fig. 5.7
An ephemeral river bed
(Rio Aguas, south-east Spain)
displaying multiple channel sizes
and levels associated with varying
magnitudes of floods. Photographs
(a) and (b) represent the same
cross-section, occupied by a low
magnitude, annual event in (b).
The whole width of the channel
visible here was last activated by a
1 in 500 year storm event in 1973,
documented in Thornes (1974).
5.2.4 Sediment transport by wind
and high transmission losses through the bed of
the river. Transmission losses will vary accord-
ing to the characteristics of the channel-fill
sediments, the length of the flood and the width
of the flood. These will vary downstream. Over-
all water discharge will decrease downstream
as a result of transmission losses. It is thus clear
that ephemeral streamflow is highly complex
and variable in nature.
Although winds in arid environments are no
stronger than those in other regions, the sparse
vegetation protection combined with large
periods of transport inactivity by water mean
that sediment supply is typically abundant and
thus the winds carry more sediment than any
other geomorphological agent (Cooke et al.