Geoscience Reference
In-Depth Information
3
Fluvial environments
Karen Hudson-Edwards
3.1
et al. 1997; Benito et al. 1998; Knighton 1998;
Leeder 1999; Miller & Gupta 1999; Bridge
2003). This chapter summarizes, updates and
builds on this work, and, specifically, highlights
the ever increasing effects of anthropogenic
activity on sedimentation in rivers.
INTRODUCTION
Rivers are arteries for the transport and storage
of physically and chemically weathered material
from continents, through estuaries, and ulti-
mately to oceans; they thus play a major role in
the Earth's biogeochemical cycling of materials,
and influence the Earth's climate. Rivers are
found in every corner of the world, and in every
climatic zone. Both natural processes and anthro-
pogenic exploitation of natural resources from
prehistoric times through to the present day have,
however, had a very significant impact on the
hydrology, sediment regime and contamination
of rivers world-wide. During the Quaternary, for
example, river systems have experienced con-
siderable natural hydrological variability due to
deglaciation and sea-level change, and human
activity has left very few rivers in a pristine state,
except perhaps for some in Canada, Amazonia,
the Congo Basin and Siberia (Meybeck 2003).
This chapter describes the nature of fluvial
sedimentary environments, types and sources of
sediments in these environments, processes and
impacts of natural and anthropogenic disturbance
events on river sediment fluxes and effects, man-
agement of fluvial sedimentary environments and,
finally, issues concerning fluvial environments
that need to be addressed in the future. The chap-
ter draws on the voluminous fluvial geomor-
phological, sedimentological, environmental and
archaeological literature. For further informa-
tion, the reader is referred to this literature, and
to the many excellent topics and topic chapters
on fluvial sedimentary environments, and the
background information and references contained
therein (Richards 1982; Brown 1997; Thorne
3.1.1 Definition and classification of fluvial
environments, and relevance to environmental
sedimentology
The word 'fluvial' pertains to a stream or river,
the existence, growing or living in or about a
stream or river, or something that is produced by
a river (Bates & Jackson 1980). Fluvial environ-
ments occur on every continent on Earth and in
every climatic zone (Fig. 3.1), and thus are often
classified according to climate, with arid, semi-
arid, temperate (cool), temperate (Mediterranean)
and tropical types known (e.g. Jansen & Painter
1974). Rivers are also classified by their flow
regimes, with perennial (flowing every year,
throughout the year), intermittent (flow for only
part of a year, every year, usually during or
after a wet season) and ephemeral (occasional
flow) types defined. Intermittent and ephemeral
rivers often occur in Mediterranean or tropical
environments, whereas perennial rivers occur in
temperate regions.
'Fluvial sediments' are those sediments that
consist of material transported by, suspended
in, or laid down by a stream (Bates & Jackson
1980). They are important sources of nutrients,
contaminants and other solid materials to
downstream fluvial, estuarine and coastal envir-
onments. Millions of tonnes of sediment are trans-
ported annually to oceans (Table 3.1), with the
