Geoscience Reference
In-Depth Information
extreme events may not be predicted by using
statistical analysis of hydrological data, because
they are periodical on a scale outside of these
relatively short-term data. Baker et al. (1983)
suggested that careful, combined geomorpho-
logical and palaeohydrological studies of palaeo-
flood hydrology and sedimentary deposits can
help to elucidate these patterns, to help predict
the real flood risk and potential hazard, and to
make long-term plans for river systems.
Gilvear's fourth point is that engineers should
recognize the links between landforms and pro-
cesses in establishing and controlling fluvial
ecosystems. Pools, riffles, undercut banks and
backwaters are vital habitats for many riverine
species. In fact, hydrogeomorphological variables
have been shown to be more important than
vegetation in terms of controlling species popu-
lations (Bickerton 1995). Vegetation, in turn, is
controlled by sediment type, organic matter con-
tent and stability, as well as hydraulic factors.
Efforts at restoring riverine wetland ecology that
focus on re-establishing pre-existing landforms
by removing unnecessary sediment or adding
structures to encourage the formation of habitat-
friendly landforms (Brookes 1992) are generally
the most successful.
As sediment transfer is a key process that
links engineering and fluvial geomorphology
(Sear et al. 1995), an understanding of the
sources, distribution and sinks of sediment is
fundamental to engineering and management
practices. Having the tools to provenance sus-
pended sediment in river systems is therefore of
vital importance in controlling erosion-sensitive
areas, monitoring and maintaining water and
sediment quality, and developing geomorpho-
logical models (Walling 1990). Furthermore,
knowledge of the influence of hydraulic factors
on channel change, sediment transport processes,
sediment budgets and deposition and storage of
sediment, on a variety of time-scales, is necessary
to improve river engineering and reduce hazards
such as floods (Anthony & Julian 1999).
River management thus ideally involves the
collaboration of engineers and fluvial geomor-
phologists, as well as end-users and managers
of the river's hazards and resources. Although
many schemes are focused primarily on the pro-
tection, enhancement and effective use of water
supplies, they also cover the important issue
of sediment management. Factors include the
erosion and sedimentation, reducing contam-
ination, restoring habitats (see below) and pro-
tecting productive floodplain zones. Because
water and sediment transfer in river basins are
intimately connected, many types of manage-
ment involve both. Today, for example, climate
change and other factors are forcing govern-
ments to adopt 'soft' engineering options for
rivers, particularly in the developed world, with
the creation of washlands (involving removal or
addition of sediment) as a means of flood con-
trol (Newson 1992).
One branch of river management, river re-
storation, has seen increasing growth since its
inception in the 1980s (Gore 1985). Restoration
involves the creation of sustainable geomorpho-
logical features that are favourable habitats
for riverine biota to recover from damage or to
re-establish (Newson 1992). Methods include
construction of habitats, management of riparian
zones, restoration of hydrological stability and
improvement of water quality (Newson 1992;
Gilvear 1999). Although many schemes involve
the creation of stable landforms (pools, stable
riffles), increasingly, the importance of ephemeral
forms such as bars, splays and scours is being
recognized (Marston et al. 1995). Other methods,
including revegetation, reduction of channel
banks to reduce erosion and restoration of
meanders, are also important (Newson 1992).
3.6
FUTURE ISSUES
A large number of issues face fluvial environ-
ments in terms of sedimentation and sediment
quality. Some of the most important of these are
outlined below.
3.6.1 Impacts of climate change
The predicted changes in temperature, precipita-
tion and other global-warming-related effects
on sedimentary systems are outlined in Chapter
