Geoscience Reference
In-Depth Information
Table 3.4
Perspectives and objectives of river management. (Based on Knighton 1998, p. 330.)
River as hazard
River as resource
Bank protection
Aesthetics
Bridge stability
Agriculture
Deforestation
Conservation
Flood control - channelization, dams
Ecology
Floodplain zonation
Fishery
Land drainage - agricultural drains, road drainage,
Heritage
urban stormwater systems
Contamination of water and sediment
Navigation
Soil erosion and sediment transport
Recreation
Gully development
Rivers as international- to district-level boundaries
Urbanization
Sand and gravel extraction
Water resource - irrigation, industrial and municipal supplies,
power generation
engineering of rivers and floodplains, and sug-
gested that, ideally, river management schemes
should incorporate all of these factors from the
planning stage onwards. The first of these is that
lateral, vertical and downstream connectivity
and relationships between planform, profile and
cross-section should be identified. In other words,
schemes should consider the whole river basin
rather than only local reaches. This premise is
based on the principles that river channels are
three-dimensional, with longitudinal, transverse
and vertical dimensions that are modified in
response to changes in water and sediment fluxes.
The interconnectivity between different parts
of river systems means that change in one part
will eventually result in change within a con-
tiguous part (Knighton 1998). This is clearly
shown in the cases of dam construction, where
trapping of the upstream sediment load leads
to bed degradation and loss of habitat down-
stream (Kondolf 1995; section 3.4.1.3). It is
thus important for engineers to view rivers from
basin, rather than reach, perspectives (Knighton
1998) because by doing so they will be able to
understand the underlying causes for potential
problems, rather than their local (reach-based)
manifestations (Sear et al. 1995).
The second of Gilvear's (1999) recommenda-
tions is that the chronology of events, landforms
and sedimentary deposits in basins over a range
of time-scales be determined for river systems.
James (1999) stressed this time aspect of fluvial
change, because this is highly relevant to the
long-term stability of engineered structures and
flood-risk assessments. Gilvear (1999) suggested
that time-scales of less than 1000 years are
the most significant to managed rivers. Several
studies have demonstrated that river channels
are also extremely sensitive to environmental
change and can adjust very rapidly, from days,
seasons to years (Coulthard et al. 2000). Studies
of fluvial landforms as indicators of stability and
instability, and documentation of sedimentary
histories within river basins, can be carried out
by geomorphologists to aid prediction of future
change (Gilvear 1999).
Recommendation three follows on from two,
in that geomorphology should be linked to envir-
onmental change. By collecting field geomor-
phological data and combining them with other
field (e.g. age dating, pollen analysis, vegetation
mapping) and historical data (e.g. chronicles,
weather diaries; Newson 1992), the fluvial geo-
morphologist can identify the processes (e.g.
climate change) responsible for river landforms,
and predict how rivers may respond to these
processes in the immediate future. Climate change
and the related frequency of extreme events such
as floods and related large-scale sediment transfer
can result in structural changes to rivers and
damage to built structures (such as channels or
dams). Baker (1994) has pointed out that such
