Progress report
Fluvial geomorphology
Evan S.J. Dollar
Centre for Water in the Environment, School of Civil and Environmental
Engineering, University of the Witwatersrand, WITS 2050, Johannesburg,
South Africa
I Introduction
Rivers are complex systems. The breadth and scope of research into fluvial
geomor-phology for the two-year period between July 2001 and July 2003 is evidence of this.
It is also evident that river form, process and behaviour can be understood in a
scale-sensitive, hierarchical manner. This requires that the spatial and temporal
complexities of fluvial systems be given due recognition. Thus, while
small-scale process studies are vital, these need to be nested within the context of
broad-scale, long-term studies (cf. Cammeraat, 2002; Fukuoka, 2002; Goudie, 2002; Thorne,
2002; Vandenberghe, 2002; Beckedahl et al., 2002; Kjeldsen et al., 2002; Phillips, 2003a).
Smith et al. (2002) in fact argue that much of the accumulated process knowledge
should be used to bring longer-term and broader-scale perspectives of landscape
change back to prominence.
Fluvial geomorphology is also in a stronger position now than it ever has been.
Research has broadened and strengthened, and the contribution of fluvial
geomor-phology to resolving complex interdisciplinary problems is now widely recognized
(Conacher, 2002; Benda et al., 2002; Frei et al., 2002). This represents both an
opportu-nity and a challenge, as too many policy decisions are made without adequate
consideration of the spatial and temporal complexity of systems; this is an area in
which fluvial geomorphologists can offer crucial insight (Knuepfer and Petersen,
2002).
II Palaeofluvial geomorphology
Most geomorphologists consider that current environmental conditions are strongly
contingent on past processes. Palaeofluvial investigations continue to provide
important clues about the evolution of fluvial systems and the imprint of the past
on present-day forms (Magny, 2001; Moore and Larkin, 2001; Saito et al., 2001; Zaleha
et al., 2001; Bullard, 2002; Garcia-Castellanos, 2002; Hereford, 2002; Kraus, 2002;
Latrubesse, 2002; Lewis, 2002; Liu, 2002; Erskine and Peacock, 2002; Heine and
Heine, 2002; Latrubesse and Kalicki, 2002; Lorenz and Nadon, 2002; Maas and
Mack-lin, 2002; Moore and Blenkinsop, 2002; Pope and Millington, 2002; Rogers and Li,
2002; Ardies et al., 2002; Guccione et al., 2002; Lauriol et al., 2002; Reheis et al.,
2002; Ringrose et al., 2002; Sander et al., 2002; Schildgen et al., 2002; Thomas, D.S.
et al., 2002; Jiongxin, 2003a; Kukulak, 2003; Colman and Bratton, 2003; Manville
and White, 2003; Meisina and Piccio, 2003; Nash and Smith, 2003; Prange and
Loh-mann, 2003; Brandt et al., 2003; Candy et al., 2003; Goodbred et al., 2003; Hou et al.,
2003; Srivastava et al., 2003). Common threads that run through much of the
palaeo-fluvial research is that palaeo-fluvial evolution is effected by multicausal drivers of varying
spatial and temporal dominance and complexity. These drivers include sea-level and
climate changes, tectonic activity, variable sediment supply and transport (Schulte,
2002; Gibbard and Lewin, 2002; Johnson and Warburton, 2002a; Novak and Bjo¨rck,
2002; Wegmann and Pazzaglia, 2002; Wisniewski and Pazzaglia, 2002; Andres et al.,
2002; Ben-David et al., 2002; Formento-Trigilio et al., 2002; Nott et al., 2002; Polyak
et al., 2002; Snyder et al., 2002, 2003; Brooks, 2003; Forsyth and Nott, 2003; Allison
et al., 2003; Benito et al., 2003; Kumar et al., 2003; Mayer et al., 2003; Peka´rova´ et al.,
2003; Rigsby et al., 2003; Wang et al., 2003; Weber et al., 2003) and hydrological
changes (Pisˇu´t, 2002; Magny et al., 2002; O’Sullivan et al., 2002; Viles and Goudie,
2003; Noon et al., 2003). A variety of morphological, lithological, palaeohydrological,
pedogenetical, sedimentological and dating techniques are applied to help elucidate
the evolution of fluvial systems (Dambeck and Thiemeyer, 2002; Latrubesse and
Franzinelli, 2002; Sa´ez and Cabrera, 2002; Stanistreet and Stallhofen, 2002; Bourke
et al., 2003; Rittenour et al., 2003; Sanderson et al., 2003; Zhang et al., 2003).
While palaeofluvial research provides valuable insight into the evolution of fluvial
systems, the imprint of the past on present fluvial behaviour needs to be made
expli-cit to better understand present-day forms and processes. An example of how this
might be achieved is the River Styles approach (Fryirs, 2002; Brierley et al., 2002).
The River Styles approach demonstrates how antecedent controls such as different
valley forms (River Styles) operate under a set of boundary conditions that constrain
form and processes at lower spatial (and temporal) scales. Central to the concept of
River Styles is that geomorphic diversity needs to be recognized in order to compare
like with like, thereby recognizing that different basins/ecosystems have different
levels of resilience and cannot be managed in a homogenous manner. Fryirs (2003)
provides guiding principles for assessing geomorphic river condition through the
application of the River Styles framework.
III Sediment transfer
The transfer of sediment from hillslopes to rivers, flood plains, lakes and transitional
and coastal waters is, in part, a function of sediment delivery. The assessment of
basin sediment budgets (Wasson, 2002; Fuller et al., 2002; Van Rompaey et al.,
2002), sediment delivery (Golosov, 2002) and sediment flux (Jiongxin, 2002; Jones
and Frostick, 2002; Nelson and Booth, 2002; Owens and Walling, 2002; Verstraeten
and Poesen, 2002; Xu and Cheng, 2002; Gangyan et al., 2002; Fontana and March,
2003; Phippen and Wohl, 2003; Donohue et al., 2003; Vanacker et al., 2003) are critical
for fluvial system understanding. Delivery is spatially and temporally highly
vari-able (Macaire et al., 2002) and requires hillslope – channel/flood plain coupling
(Michaelides and Wainwright, 2002; Slattery et al., 2002). Consequently, the
interpret-ation of the stratigraphic record for determining sediment delivery is complicated by
buffering, especially in larger basins (see Castelltort and Van Den Driessche, 2003), as
is the application of techniques for estimating sediment yield (cf. Hancock and
Anderson, 2002; Meadows and Hoffman, 2002; Symader and Roth, 2002; Fuller
et al., 2003).
Sourcing sediment is also critical for understanding transfer and for targeted
man-agement (Wasson et al., 2002; Cawood et al., 2003). Recent advances in the techniques
for discriminating sediment sources provide valuable tools in this regard (Stefani,
2002; Collins and Walling, 2002; Foster et al., 2002; Jenns et al., 2002; Yeager et al.,
2002; van der Perk and Sla´vak 2003; Di Giulio et al., 2003) and may aid in
distinguish-ing between human-induced and natural, dynamic changes in storage (Klimek, 2002;
Larue, 2002). Valuable lessons have been learnt, as evidence has shown that there is
no simple relationship between event magnitude and sediment yield in basins, nor is
there a simple relationship between river and flood plain sedimentation rates and
event magnitude, duration, frequency or timing. What is clear is that sediment
trans-fer may be asynchronous with disturbance drivers and therefore requires a
long-term perspective. Trimble (1999) provides an excellent example of this. In the
Coon Creek catchment, USA, basin sediment yield has not changed since the
mid-1850s, despite major land use changes. Storage change has provided a buffer that
has decoupled basin sediment yield from land use change. Similarly, Fryirs and
Brierly (2001) have shown that for many of the catchments of southeastern Australia,
alluvial stores are the primary sources of fluvial clastic sediment since European
settlement. In the Bega catchment, however, only 16% of the delivered sediment
has reached the estuary. They argue that this is due to antecedent controls on valley
width that have resulted in the lowland plain acting as sediment sink.
Numerous studies have focused on quantifying sediment loads and rates of
sedimentation in modern systems (Panin et al., 2001; Franzinelli and Igreja, 2002;
Orfeo and Stevaux, 2002; Kothyari et al., 2002; Warne et al., 2002; White et al.,
2002). Examples include estimating the total sediment load delivered from the
Yangtze River (Higgitt and Lu, 2001) to the Three Gorges Project (TGP) in China
(Lu and Higgitt, 2001). It is estimated that 84% of the eroded soil from the catchments
is delivered to the reservoir; the remainder is deposited in valley floor paddy fields.
Cao, S. et al. (2002) estimate the average annual sediment load entering the TGP is 523
million tons. Of this, 47% is sourced from the Jinsha River, one of the main tributaries
of the Yangtze.
Reductions in sediment load are reported for various fluvial systems worldwide
(Chen et al., 2001; Xu, 2002a; Ta et al., 2002; Yang et al., 2002). Jiongxin (2003b) has
shown, for example, that since the 1970s, the sediment flux into the Yellow River
has declined as a result of effective soil control measures in upstream basins.
Simi-larly, the reforestation of basins in Slovenia has reduced sediment loads, resulting
in bed incision and reduced flood plain deposition (Keesstra, 2002). Similar incision
(and associated consequences) has been reported for the Rhone River in France in
response to decreased sediment yields (Kondolf et al., 2002; Arnaud-Fassetta, 2003).
Increased sediment delivery to channels results in the opposite effect: increases in
channel width, bank collapse, increased flood risk, lowering of water tables and the
undermining of bridges and embankments (Kondolf et al., 2002).
IV Channel pattern and morphology
The growth of fluvial geomorphology as a science has led to the description and
analysis of previously unreported channel patterns. For example, Bartholdy and
Billi (2002) report on a river planform ‘type’ in Tuscany, Italy, that is neither straight
nor meandering. These rivers are typically almost straight, with a slightly incised
main channel eroded into a former flood plain. They suggest the term
‘pseudomean-dering’ to describe this channel pattern. Discrimination of channel pattern and
chan-nel pattern change based on planform and process, however, remains an important
area of research (Simpson and Smith, 2001; Zimmerman and Church, 2001; Hudson,
P.F., 2002; Xu, 2002b; Lancaster and Bras, 2002; Mosselman and Sloff, 2002; Shafieefar
and Husseini, 2002; Buhman et al., 2002; Ramonell et al., 2002). Numerical procedures
for predicting pattern are common (Termini, 2002; Vignoli and Tubino, 2002;
Kura-bayashi et al., 2002; Watanabe et al., 2002; Yokoyama et al., 2002), less common are
semi-empirical predictive methods (Richardson and Thorne, 2001; Young et al., 2002).
The prediction of channel morphology has been a pursuit of river practitioners
since the late nineteenth century. Two broad approaches are common: an engineering
approach that favours a numerical, hydrodynamic perspective (Neary et al., 2001; Ma
et al., 2002; Chitale, 2003; Olsen, 2003; Nicklow et al., 2003) and a qualitative,
semi-empirical approach that favours field observation and data collection (Halwas
and Church, 2002). Most numerical models are based on asynchronous solution of
simplified governing equations. This, however, ignores to some extent the strong
relationship between discharge, sediment transport and morphological evolution
of fluvial systems. Cao, Z. et al. (2002) recommend that in order to refine the
model-ling of alluvial rivers, the coupled system of complete governing equations needs to
be synchronously solved.
Investigations into downstream changes in channel morphology continue to
pro-vide important insights into the relationship between discharge descriptors and
channel form parameters (Griffiths, 2002; Radecki-Pawlick, 2002; Molnar and
Ramirez, 2002; Moody and Troutman, 2002; Pitlick and Cress, 2002; Merritt and
Wohl, 2003), and remain critical to modelling and understanding river behaviour.
Amsler and Ramonell (2002), for example, were able to show that increases in
thal-weg sinuosity, channel width and bank erosion were related to high dominant
dis-charges. Heritage et al. (2001), however, reject the notion of a channel-forming
‘dominant’ or ‘bankfull’ discharge for the Sabie River in South Africa. Results
from 23 monitoring sites show that the sections are related to the entire flow regime,
not a single-channel forming discharge. Similarly, Lewin and Brewer (2001) reject the
assumption that it is possible to distinguish between meandering and braided
chan-nels on the basis of bankfull specific stream power and bed material size alone. They
suggest that it is useful to consider the patterning processes that underlie the pattern
scatter on the bankfull stream power/bed material size plots. They argue that
large-scale bedform development and stability is important for meandering and braiding.
Field-based investigations provide valuable empirical data on channel
mor-phology (Wohl and Legleiter, 2003). Thompson and Hoffman (2001), for example,
characterised 145 pools in New England to better understand pool geometry and
sorting characteristics. Pool dimensions were related to drainage area and channel
slope through stream power at larger scales and local hydraulic conditions at finer
scales. Similarly, Jackson and Sturm (2002) found that stream power and unit stream
power were the dominant channel shaping factors in small first- and second-order
forested channels in Washington’s coast ranges in the USA. Buffington et al. (2003)
demonstrate that pools in coarse-grained forest rivers in the USA were formed
mainly by flow obstruction and that their geometry and frequency of occurrence
depended on flow obstruction characteristics. These controls, in turn depended on
a variety of factors, with their relative influence depending on channel type and
location within the drainage basin.
V Channel change
Predicting channel pattern and morphology is, of course, contingent on
understand-ing channel change. The drivers of channel change are widely known (Manville,
2002; Marchetti, 2002; Lach and Wyz´ga, 2002; Lie´bault and Pie´gay, 2002; Maingi
and Marsh, 2002; Talbot and Lapointe, 2002a, b; Lie´bault et al., 2002; Perona et al.,
2002; Thomas, R. et al., 2002; Warburton et al., 2002; Surian and Rinaldi, 2003;
Heroy et al., 2003; Skelly et al., 2003), and predicting morphological change in rivers
and flood plains using numerical methods and GIS/DEM technology is common
(Rosatti, 2002; Basson and Beck, 2002; Cellino and Essyad, 2002; Kassem and
Chaudhry, 2002; Olesen and Tjerry, 2002; Vetsch and Faeh, 2002; Langendoen et al.,
2002; Willems et al., 2002). However, all these methods are influenced by various
degrees of uncertainty, assumptions and choices of model schematization (van
Vuren et al., 2002). Cao and Carling (2002: 470) in fact state that many computational
river models remain ‘. . . at best imperfectly constructed, and worst invalid’. This is
due to the fact that model calibration is often subjective, verification is impossible
and validation does not necessarily establish model truth. They therefore suggest
that high-level expertise, physical insight and experience are critical for meaningful
solutions to be acquired and model limitations properly assessed. It is important to
be aware of the limitations of computational/numerical modelling, as ‘Model
performance is overstated by using the affirmative terms verification and validation,
which can mislead the public and decision-making’. Despite these cautions,
predict-ing change in response to changpredict-ing drivers remains an important goal in fluvial
research (Gautier and Peters, 2002).
Examples of empirical studies of channel change reported in the literature are
numerous. A few are mentioned here. Magilligan et al. (2002) report on geomorphic
changes in response to the 1996 jo¨kulhlaup on Skeioara´rsandur, southeastern
Iceland. The impacts of the jo¨kulhlaup are explained in relation to antecedent
con-ditions, particularly the asymmetric decoupling of the ice front from the sandur
during the recent recession. Channel narrowing following impoundments are also
well known. The style and degree of change, however, depend on the geomorphic
context, type of streamflow regulation and post-impoundment sediment transport
regime (Phillips, 2002). Grams and Schmidt (2002), working in the Green River in
Colorado and Utah, USA, for example, determined that the degree of channel
nar-rowing below the Flaming Gorge Dam in reaches with abundant sediment supply
was proportional to specific stream power. Reaches with the greatest reductions
in specific stream power showed the greatest reductions in bankfull channel
width and vice versa. Hassan and Klein (2002) report on the channel changes of
the Lower Jordan River associated with a drop in the Dead Sea level of 22 m in
the last 70 years. Rapid drops in sea level since the late 1980s have resulted in
major morphological changes and channel incision. Channel widths have narrowed
by almost a factor of four and sinuosity has dropped by 25%. Incision is
coinciden-tal with sea level reductions, with the incision having moved upstream by 11 km
by 1993.
Holistic interpretations of channel changes in the context of past climate changes,
shorter-term human impacts and potential future climate change, however, remain
elusive (cf. Franks, 2002). Effort is being made in this regard, with some success
(Stouthamer and Berendsen, 2001; Clague et al., 2003). This is of significance, as
Brooks et al. (2003) have shown that sound and realistic management programmes
cannot be achieved in rivers and basins without an understanding of long-term
chan-nel and flood plain evolutionary history. From a study of paired catchments in
south-eastern Australia, they demonstrated that the removal of riparian vegetation and
woody debris from the Cann River resulted in orders of magnitude changes in
var-ious channel parameters (e.g., depth, slope and capacity). Importantly, they point
out that management intervention through reintroducing pre-existing riparian
vegetation and woody debris will simply not result in channel recovery, as
nume-rous thresholds were crossed as a result of historical changes. Clearly, channel
change needs to be understood in a historical, evolutionary context, otherwise
the ultimate controls on and changes to river form and process will not be fully
appreciated.
VI Fluvial features
The international literature is replete with descriptions and explanations of diverse
fluvial features (Blair, 2001; Leclair and Bridge, 2001; Prent and Hickin, 2001;
Smith and Pearce, 2001; Yang et al., 2001; Bourke, 2002, 2003; Bridgland, 2002;
Gupta, 2002; Harvey, 2002a; Inbar, 2002; Lowey, 2002; Miall, 2002; Nin˜o, 2002;
Purkait, 2002; Surian, 2002; Wittenberg, 2002; Knighton and Nanson, 2002; Latrubesse
and Stevaux, 2002; Walsh and Hicks, 2002; Bendjoudi et al., 2002; Davis et al., 2002;
De Souza et al., 2002; Hirayama et al., 2002; Kleinhans et al., 2002; Kostic et al.,
2002; Loncke et al., 2002; Makaske et al., 2002; Strasser et al., 2002; Sun et al., 2002;
Tooth et al., 2002a, b; Weissmann et al., 2002; Defina, 2003; Ferguson, 2003; Stock
and Dietrich, 2003; Villard and Church, 2003; Willis and Griggs, 2003; Constantine
et al., 2003; Fielding et al., 2003; Montgomery et al., 2003a; Ra˜doane et al., 2003; Samuel
et al., 2003). Some examples are described below.
Outburst floods produce impressive and dramatic fluvial features. Quaternary
International has devoted an entire edition to this topic – (Volume 90, 2002). Their
role in modifying landscapes has generated considerable interest and debate (Cutler
et al., 2002; Fisher et al., 2002). Since description of the Lake Missoula flood (Baker,
1973), research has demonstrated that these outburst floods were more common
than first thought. For example, Rudoy (2002) reports on Late Pleistocene
super-floods following glacier-dam breaks in southern Siberia. These cataclysmic super-floods
transformed the landscape and resulted in morphological associations of
moun-tainous scablands, similar to those reported in North America. In some locations,
dis-charges of up to 18 000 000 m
3s
21created features such as giant current ripple
marks, giant diluvial ramparts and terrace bars. Maximum unit stream powers of
10 000 000 W m
22are estimated to have occurred, greater than those estimated
for Lake Missoula.
Drylands cover around half the world’s surface, but there is limited information
on dryland rivers (Nanson et al., 2002). A timely book fills this gap (Bull and Kirkby,
2002) and provides a broad overview with a few case studies that will be of interest to
geomorphologists interested in dryland environments. Bullard and Livingstone
(2002) call for greater recognition of the interaction between aeolian and fluvial
sys-tems in dryland areas. They argue that aeolian and fluvial syssys-tems do not operate
independently as commonly perceived, and that their interaction has important
implications for understanding the geomorphology of dryland environments.
A number of innovative techniques have also been developed to aid in the
under-standing of river behaviour. Many of these techniques allows us to address
geo-morphic questions that have not been addressed before (Lane et al., 2002; Lane
and Chandler, 2003; Brasington et al., 2003). Table 1 presents an incomplete list of
some of these techniques.
VII Flood plains
Flood plains are an integral part of the fluvial system. Much of the work on flood
plains is directed towards understanding present (Brunke, 2002; Middelkoop,
2002; Asselman and van Wijngaarden, 2002; Nicholas and Mitchell, 2003; Lusk
et al., 2003) and past sedimentation rates (Walling and Owens, 2002; Foster, I.D.L.
et al., 2002; Paine et al., 2002; Page, K.J. et al., 2003) and their relationship to the
trans-portation of nutrients, organics (Morozova and Smith, 2003), contaminants (Rowan
and Franks, 2002; Maurice-Bourgoin et al., 2002; Middelkoop et al., 2002), vegetation
(Sims and Thoms, 2002; Webb et al., 2002) and to hydrology (Dyer, 2002; Aalto et al.,
2002). Again, a variety of approaches are adopted in an attempt to understand
flood plain behaviour; from laboratory experiments (Bathurst et al., 2002) to the
longer-term interpretation of flood plain histories (Wasson, 2002). Nanson and
Croke (2002) argue that flood plain research is critical for understanding material
fluxes, contaminant storage, longitudinal and lateral connectivity and riverine
ecol-ogy. They suggest that the following research directions are fundamental to moving
the research field forward: flood plain formation processes, flood plain instability
and changes in flood plain state, scale, the role of vegetation in flood plain systems
and flood plains in interdisciplinary research.
VIII Vegetation
Vegetation plays an important role as an agent in fluvial geomorphology. At finer
scales, this is effected through its influence on local hydraulics that determines
sedi-ment transport. At this scale, vegetation reduces bed shear through absorbing
momentum by drag on the stems (Wilson and Horritt, 2002; Samuels et al., 2002;
Jordanova and James, 2003). This enhances deposition and reduces sediment
trans-port capacity (Helmio¨, 2002; Righetti and Armanini, 2002). Complexity is introduced
through large spatial and temporal variations between different vegetation types,
growth stages, densities and locations (Ja¨rvela¨, 2002a, b; Sellin and van Beesten,
2002; Yoshida and Dittrich, 2002). Flexible vegetation also behaves differently with
stage changes and, as a consequence, roughness becomes variable and dynamic (Shi
Table 1
List of recent techniques applied to understand fluvial system behaviour
Technique Author(s)
Use of World Wide Web Schroder et al. (2002)
Physical models De Boer and Ali (2002); Milana and Tietze (2002); Moreton et al. (2002); Davies et al. (2003) Landscape-genesis (LG) models Al Bakri (2002)
GPS and sonar Chang et al. (2003)
Measuring sediment transport Dinehart (2002); Antonelli and Provansal (2002); Gupta and Cvetkovic (2002); Rakoczi and Szekeres (2002); Sterling and Church (2002); De Bonis et al. (2002); Mu¨ller et al. (2002); Puertas et al. (2002); Rennie et al. (2002); Shteinman et al. (2002)
Hydrodynamic models Thomas and Nicholas (2002); Lee et al. (2002) High resolution survey data Lane et al. (2001); Adriaensen et al. (2002);
Asselman et al. (2002); Hicks et al. (2002); Whited et al. (2002); Baily et al. (2003); Mason et al. (2003)
GIS Ba´rdossy and Schmidt (2002); Puech and Raclot (2002); Dawson et al. (2002); Sinha et al. (2002); Finlayson and Montgomery (2003); Khan and Islam (2003); Vogt et al. (2003)
Remote sensing Gupta and Ping (2002); Toro and Mayerle (2002); Gupta et al. (2002)
Laser Induced Direction and Ranging (LiDAR) French (2003); Charlton et al. (2003) Digital Elevation Models (DEM) Brasington and Smart (2003); Chappell et al.
(2003); Lane et al. (2003); Rippin et al. (2003) Electrical Resistivity Ground Imaging (ERGI) Baines et al. (2002)
Artificial turf maps Steiger et al. (2003)
Tracers Go¨lz (2002); Ferguson and Hoey (2002); Blade et al. (2002); Ferguson et al. (2002); Milan et al. (2002) Cosmogenic nuclides and sediment fingerprinting Bierman and Caffee (2002); Singh and
France-Lanard (2002); Clapp et al. (2002); Nichols et al. (2002); Schaller et al. (2002); Small et al. (2002); Terry et al. (2002); van Wijngaarden et al. (2002a, b, c); Wallbrink et al. (2002); He and Walling (2003); Brocard et al. (2003); Vance et al. (2003) Magnetostratigraphic techniques Tinkler (2001); Auler et al. (2002)
Documentary evidence and oral records Jiongxin (2003a)
Time Domain Reflectometry (TDR) Valle´ and Pasternack (2002)
River measurement techniques Le Roux (2001); Bartley and Rutherfurd (2002); Lindsay and Ashmore (2002)
Magnitude frequency techniques Marren et al. (2002); McKee et al. (2002); Navratil et al. (2002); Rushmer et al. (2002); Heritage et al. (2003)
and Hughes, 2002; Stephan and Gutknecht, 2002). Consideration of the hydraulics of
flow through and over vegetation therefore remains an important field of study, both
experimentally (Rowin´ski and Kubrak, 2002a, b; Bennett et al., 2002; Carollo et al., 2002;
James et al., 2002) and in the field (Baptist and Mosselman, 2002; Goodson et al., 2003).
The important question remains the prediction of velocity profiles in open channels.
At larger scales vegetation is also of importance (Steiger and Gurnell, 2002;
Huisink et al., 2002). At the flood plain scale for example, the importance of
vege-tation in reducing the risk of flooding in the Waal River, the Netherlands, is
recog-nized (van Vuren et al., 2002). At the channel-type scale, Gradzin´ski et al. (2003)
have shown how in-channel vegetation enhances channel aggradation and
contrib-utes to avulsion by blocking channels in the anastomosing upper Narew River in
Poland. Similarly, Gumbricht et al. (2001) have demonstrated that local topographic
features and channel flanking vegetation exert an important influence on the
distri-bution of water in the Okavango Delta, Botswana.
At the reach scale, it is also generally accepted that riparian vegetation increases
bank stability and reduces stream bank erosion through enhancing resistance to
ero-sion (Micheli and Kirchner, 2002a; Murray and Paola, 2003; Hesero-sion et al., 2003;
McKergow et al., 2003). Birkeland (2002) quantified changes in flood power and
riparian vegetation on the Escalante River, Utah, USA. Increased growth in riparian
vegetation (86%), channel widening and flood plain narrowing resulted in an
increase in flood power of between 11 and 53% in the active channel between 1922
and 1988, and a decrease in flood plain flood power of between 44 and 97% for
the same period. At least 20–45% of this decrease was attributed to increased
resist-ance resulting from vegetation growth. Similarly, Micheli and Kirchner (2002b)
report on a study that demonstrated that for the Kern River in California’s Sierra
Nevada, riparian banks with dry meadow vegetation are ten times more susceptible
to erosion than banks with wet meadow vegetation.
Simon and Collinson (2002), however, argue that many studies that consider the
stabilizing effects of riparian vegetation under-represent the importance of
hydro-logical processes, some of which may be detrimental to bank stability. They report
that in some instances, the hydrological effects (pore-water pressure, soil moisture
modification) of trees may in fact reduce bank stability, although the stabilizing
mechanical effects usually offset this. This would suggest that hydrological,
mechan-ical and ecologmechan-ical criteria should be jointly considered in determining the potential
stabilizing and destabilizing effects of riparian vegetation on bank stability.
Integrated research between ecology and geomorphology is gaining momentum
(Viles and Naylor, 2002; Steiger et al., 2003). This endeavour will continue to provide
new insights into both ecosystem behaviour and Earth surface processes (Naylor
et al., 2002). However, as with most integrative endeavours, the issue of dealing
with scale in an appropriate manner is critical to its success. A number of examples
are evidence of this in the recent literature. Brooks and Brierley (2002) have shown,
for example, that over thousands of years, channel capacity, hydraulics, bed load
transport rates and bank erosion are influenced substantially by vegetation and
wood, both within the channel and on the flood plain. Cowell and Dyer (2002)
have shown how impoundments have affected the natural flooding dynamics
along the Allegheny River in Pennsylvania, USA, which in turn has resulted in a
functional change from floods acting as a disturbance (that generates early
succes-sional habitat) to a stressor. Changes in hydrological regime (lower peak discharges,
longer duration) have favoured non-native species resulting in altered composition
and vegetation dynamics. Jeffries et al. (2003) argue that given the importance of
vegetation in fluvial form and process, its pigeon-holing as a dependent variable
(e.g., Schumm and Lichty, 1965) should no longer be accepted.
IX Bank erosion
Bank erosion and its associated consequence, channel migration, has received
con-siderable attention in the literature (Duan, 2001; Darby and Delbano, 2002), and
remains a significant engineering (Shimizu, 2002; Schmautz and Aufleger, 2002)
and environmental concern (Simon and Thomas, 2002; Simon et al., 2002). The
pre-diction of bank erosion remains a priority, but many existing models fail to simulate
this process adequately. Wright et al. (2002) suggest that this is due to the fact that
most models can only simulate one or two components of the bank erosion process
(erosion by water flow; bank collapse under gravity and removal of failed debris)
and cannot account for the influence of secondary currents. Darby et al. (2002)
make a similar point and suggest that these models tend to be limited to steady
state conditions, utilize idealized and nonmechanistic relationships to link bank
ero-sion rates and near-bank velocities through an erodibility coefficient determined by
calibration rather than via the characteristics of the sedimentary environment. Recent
interventions have encouraged the use of vegetative-based approaches in dealing
with the problems associated with bank erosion that offer ecological advantages
and long-term sustainability (Environment Agency, 1999). Not all problems
associ-ated with bank erosion are, however, unidirectional. Couper et al. (2002), for
example, report on negative erosion-pin recordings for some rivers in the UK.
X Woody debris
The role of Coarse and Large Woody Debris (CWD and LWD) across a range of
spatial and temporal scales has been recognized as being significant in channel
form and process studies for nearly two decades. The effect of centuries of ‘riparian
gardening’ in Europe (Montgomery and Pie´gay, 2003) and widespread riparian
veg-etation clearing in North America (Collins et al., 2002) and Australia (Erskine and
Webb, 2003) is startling. Regional differences in wood size, density, shape,
avail-ability, recruitment, character, geomorphic context, river size and pattern exist,
how-ever, that complicate understanding and the modelling of woody debris distribution
and effects (Gurnell et al., 2002; Kraft et al., 2002; Kraft and Warren, 2003).
Montgom-ery and Pie´gay (2003) argue that the key uncertainties related to woody debris are its
influence on pristine rivers and how it controls hydraulics and geomorphological
features in channels of different sizes and regional locations.
The geomorphic impact of woody debris depends on how the wood acts as an
obstruction (distribution and function) and the consequent impact of the obstruction
on local hydraulics and sediment processes (Bocchiola et al., 2002; Wallerstein, 2003;
Daniels and Rhoads, 2003; Hygelund and Manga, 2003), as well as the additional
material that it obstructs and collects (Curran and Wohl, 2003; Webb and Erskine,
2003; O’Connor et al., 2003). This impact can operate at a number of scales, from
affecting local hydraulics and sediment transport at local scales to affecting channel
geometry and morphological features at reach scales (Hughes and Thoms, 2002;
Abbe and Montgomery, 2003; Montgomery et al., 2003b). For example, Marcus et al.
(2002) suggest that for the Snake River, Soda Butte Creek and Cache Creek in the
Greater Yellowstone Ecosystem, USA, the movement of woody debris is perhaps
the opposite of most sediment transport systems in mountains. In first- and
second-order streams, the wood is too large to be moved so that the system is
transport-limited, with floods introducing new material but not removing wood
by downstream transport. In third- and fourth-order streams, the system displays
a form of dynamic equilibrium in that the channel is able to move woody debris
at the same rate it is introduced. In fifth-order and larger channels, the system can
be considered to be supply-limited.
Faustini and Jones (2003) have shown how sediment-limited streams in Oregon
may, when deprived of woody debris, exhibit less morphological variation at the
channel unit scale, store less sediment and release it more rapidly than those with
woody debris. Similarly, Kail (2003) has shown from work on six central European
rivers that structural diversity is greater in woody debris sections at almost all scales.
At the reach scale, woody debris also creates greater variability in the longitudinal
water profile of a river than a similar river without woody debris. Woody debris is
therefore also critical in influencing the diversity and availability of aquatic habitat
(Zika and Peter, 2002; Haga et al., 2002; Lehane et al., 2002). Montgomery and Pie´gay
(2003) conclude that it is time that wood and vegetation assume their place beside
sediment regime (supply and calibre for example) and discharge as a primary control
on the dynamics and morphology of fluvial systems.
XI Sediment transport
The prediction of sediment transport (Cheng, 2002a; Yen, 2002; Abril and Knight,
2002; Cerda` and Garcı´a-Fayos, 2002; Huang and Nanson, 2002; Kleinhans and van
Rijn, 2002; Ogawa and Watanabe, 2002; Wilcock and Kenworthy, 2002; Di Cristo
et al., 2002; Hairsine et al., 2002; Link et al., 2002; Nikora et al., 2002; Nin˜o et al.,
2002; Delleur, 2003; Metivier and Meunier, 2003; Schmeeckle and Nelson, 2003; De
Sutter et al., 2003), particle entrainment, settling velocity and deposition
(Papanico-laou et al., 2001; Malmaeus and Hassan, 2002; Milburn and Prowse, 2002; Wu and
Lin, 2002; Dancey et al., 2002; Paphitis et al., 2002; Seminara et al., 2002; Strom et al.,
2002; Smith and Cheung, 2003; Wu and Chous, 2003; Aguirre-Pe et al., 2003;
Haralam-pides et al., 2003; Nin˜o et al., 2003; Papanicolaou et al., 2003) is of great interest to
flu-vial geomorphologists, but tends to be the domain of river engineers.
The limitations of sediment and bed load equations are widely known and
predic-tions of all transport formulae show large uncertainties. Difficulties introduced by
sediment packing, variability of the near-bed turbulent velocity field, modification
of the velocity field by upstream protruding grains and variable supply mean that
a universal transport equation has not been developed. Field measurements of
sedi-ment transport confirm the limits of applying transport equations for prediction
(Pearce et al., 2003). Obtaining reliable field data are almost impossible, particularly
when evidence of extreme events does not survive (Coppus and Imeson, 2002; Sheets
et al., 2002). Despite these challenges, researchers continue to develop new models
for prediction (Cheng, 2002b; Le Roux, 2002; Richardson, 2002; Hunziker and Jaeggi,
2002; Monteith and Pender, 2002; Nagy et al., 2002; Pen˜a et al., 2002; Ribberink et al.,
2002; Wongsa et al., 2002; Wilcock and Crowe, 2003; Yang and Lim, 2003). Lisle and
Church (2002) suggest that a better understanding of transport – storage relations
may improve predictive model capacity in the future.
Studies that emphasize the collection of field data are rare, but important (Eaton
and Lapointe, 2001; Habersack and Laronne, 2002; Hayes et al., 2002; Julien et al.,
2002; Rodr´iguez et al., 2002; Ryan et al., 2002). These studies add much to our
under-standing of river behaviour. Some examples are presented below. Martin (2003)
pre-sents results from a study in which bed load transport formulae are evaluated
against field data collected over a 10-year period along an 8-km-long study reach
on the Vedder River, British Columbia, Canada. Martin (2003) found that the
Bag-nold stream power formula and the Meyer – Peter and Muller formula
underpre-dicted gravel transport for the period of record. Interestingly, however, the
simple stream power correlation captured the downstream pattern of deposition
best. Bagnold’s formula was found to most realistically predict bed load transport,
although Martin (2003) indicates that no one formula predicts best under all
conditions.
Johnson and Warburton (2002b) measured the annual sediment budget of a UK
mountain torrent. They found that over the period of 1 year, 184 tonnes of sediment
was removed from a 2.4 ha study area. Channel (70%) and bank (25%) sources
domi-nated the supply, with surface processes and rockfall on hillslopes accounting for
only 5% of the total budget. Konrad et al. (2002) report on spatial patterns of bed
material entrainment by floods using bed tags. They showed that although the
prob-ability of bed material entrainment was approximately uniform over a gravel bar
during individual floods and independent from flood to flood, regions of stability
and instability occurred at some bars over the course of a season.
XII River and flood plain hydraulics
Knowledge of the hydraulics of open channel flow including flow resistance (Bathurst,
2002; Katul et al., 2002), flow types (Crowley, 2002; Ferro and Carollo, 2002; Biron
et al., 2002; Jordanova et al., 2002), velocity and turbulence (DeVries, 2002; Lee and
Ferguson, 2002; Babaeyan-Koopaei et al., 2002; Chen and Chiew, 2003) and the role
of flood plains in open channel flow (Carling et al., 2002) is of obvious importance
to the fluvial geomorphologist. A recent two-volume proceedings from the River
flow 2002 conference in Belgium (Bousmar and Zech, 2002a, b) covers three major
topics in this regard. These are the hydrodynamics of river flow (overbank flows
and flood propagation, resistance determination and interactions with vegetation,
river engineering, rapid transients and dam-break hydraulics and interactions
between river hydraulics and ecology), sediment transport in rivers (river
mor-phology and morphodynamics, scour and techniques of sediment transport
model-ling) and methods and techniques (laboratory techniques and application of remote
sensing and GIS technology to river modelling). The main message that emerges
from the proceedings is that current river management requires practitioners and
managers both to protect human lives and properties, while at the same time
main-taining river function for a variety of purposes (including ecological). There is also
recognition that there is a need to manage rivers in sympathy with their natural
operation, rather than focusing on traditional river engineering approaches (cf. de
Vriend, 2002). An additional focus of the proceedings related to ecohydraulics, a
field of study that seeks to integrate water resource development with the
sustain-able utilization of aquatic ecosystems (Caruso, 2001; Leclerc, 2002; Clifford et al.,
2002; Franks et al., 2002). However, the tools that are available to convert habitat
time series (habitat regime) into meaningful operating rules require considerable
validation and refinement. Of particular importance is the development of a
concep-tual framework to create a common understanding of the relationship between
eco-logical and physical subsystems (Franzin et al., 2002).
XIII River management and remediation
Human activities have influenced rivers for millennia (World Commission on Dams,
2000; Taylor and Kesterton, 2002; Asmal, 2002; Doyle et al., 2003; Thomas, D.S., et al.,
2004). As a result, widespread changes to fluvial systems have taken place (Bonacci
and Roje-Bonacci, 2003; Landwehr and Rhoads, 2003; Dennis et al., 2003; Ellery et al.,
2003). Recognition of these impacts, and the need for management intervention has
led to fluvial geomorphologists applying their skills to a variety of river management
and remediation efforts. This importance is reflected in the literature [Dorn (2002),
for example, makes the point that the most cited geomorphological literature in
the 1990s related to river research with a biological emphasis]. Four recent books
on this topic (Anthony et al., 2001; Kondolf and Pie´gay, 2003; Sear et al., 2003; Gordon
et al., 2004) also reflect this interest.
Management and remediation of rivers requires decision-makers to intervene in
a manner that is beneficial to people and the environment (Goodwin, 2001; Feng
et al., 2001; Gregory, 2002; Kurashige, 2002; Thompson, 2002a, 2003; Archer and
Newson, 2002; Bhuiyan and Hey, 2002; Falkenmark and Folke, 2002; Larsen and
Greco, 2002; Sato and Watanabe, 2002; Simon and Darby, 2002; Williams and Archer,
2002; Islam et al., 2002; Mount et al., 2002; Newson et al., 2002; Pedroli et al., 2002;
Poole et al., 2002; Ward et al., 2002; Spaliviero, 2003; Cioffi and Gallerana, 2003;
Amos et al., 2003). This means managing ecosystem functionality (Frothingham
et al., 2002) and the integration of physical, chemical and biological characteristics
of a river at appropriate scales (Dovciak and Perry, 2002; Graf et al., 2002; Poudevigne
et al., 2002; Cadenasso et al., 2003; Sauvage et al., 2003). The management of rivers as
‘integrated ecosystems’ (Rodda, 2001) comprises at least four interacting subsystems:
the active channel, flood plain (or, where absent, macro-channel), alluvial aquifer
and riparian vegetation (Poole et al., 2002). Together these comprise the integrated
fluvial system, emphasizing the importance of lateral and longitudinal connectivity
and interdependence. Four broad themes are considered under river management
and remediation. These are: river landscape and classification, ecological water
requirements, the European Water Framework Directive and river restoration and
remediation. Each of these will be discussed in turn.
1 River and landscape classification
It is common knowledge that hierarchical landscape classification is a useful means
to organize, interpret and understand complex systems such as fluvial landscapes
(Vannote et al., 1980; Ward and Stanford, 1995; Wu and Loucks, 1995; Tockner et al.,
2000; Berman, 2002; Poole, 2002; Wright and Li, 2002; Pess et al., 2002; Ralph and
Poole, 2003). Two broad types of classification system are evident: structure-based
classification systems (cf. Jensen et al., 2001; Berman, 2002) and process-based
classi-fication systems (cf. Montgomery, 1999; Winter, 2001; Berman, 2002; Church, 2002).
Both approaches have strengths and weaknesses (see Berman, 2002 for a full
descrip-tion). Both approaches, however, recognize that a hierarchical system helps deal
with the complexity and variability of river systems and the importance of spatial
and temporal scale. Hierarchical classification systems recognize that river channels
and flood plains are inextricably linked to the landscape and that basin features and
scale-specific disturbance processes influence ecosystems at multiple scales and
influence response and recovery times. Importantly, connectivity vector strength
(longitudinal, lateral, vertical and temporal) between system components drives
system heterogeneity and hence biotic distribution and pattern (Montgomery, 1999;
Berman, 2002). These discontinuities (Rice et al., 2001) at multiple scales generate
‘patches’ that represent distinct structural and process units and result in the
hetero-geneous distribution in space and time of biotic and abiotic environmental resources.
These influence the flow of materials through the system. For a river system,
struc-tural and process patches at different scales form a nested, interactive hierarchy
(Berman, 2002). Patch dynamics and geometry play a critical role in the distribution
of biota (Crook et al., 2001). River and landscape classification methods must attempt
to capture this complexity through partitioning ecosystem variability and
deter-mining patch response to disturbance at multiple scales. Identifying and
delineating unique landscape classes therefore needs to account for the following
(Berman, 2002):
1 catchment influences on river structure and resource dynamics;
2 disturbance and recovery processes influencing the strength of connectivity
vectors, resource dynamics and biotic pattern; and
3 hierarchy, scale and patch dynamics influence on energy and materials flow
through the system.
Furthermore, classification systems need to capture that fact that large-scale factors
constrain the structure and function of patches at smaller-scales and that small-scale
factors shape the structure and function of patches at larger scales. This is needed to
predict biotic pattern and distribution and to diagnose system impairment
(Fausch et al., 2002). Classification must also allow for the prediction of human
impacts on natural disturbance processes that alter the relationships between
patches and the resource dynamics including the availability, delivery, transport
and processing of materials fundamental to biotic communities (Berman, 2002).
Berman (2002) considers that at the core of classification is the ability to categorize
across scales those ecosystem processes driving the discontinuous distribution of
biotic and abiotic resources. These concepts are not new to the fluvial
geomorphol-ogist (cf. Schumm and Lichty, 1965). The challenge remains developing a
hierarchi-cal, scale-based classification system that can meet the requirements of ecological
and geomorphological theory and the operational requirements of management
intervention.
2 Ecological water requirements
An important tool in river management and remediation is the determination of
Ecological Water Requirements (EWR) or Environmental Flow Allocations (EFA)
for rivers. Demands placed on a variety of specialists, including fluvial
geomorphol-ogists to predict these EWRs are reflected in the amount of ‘air-time’ given to this
topic in the literature (cf. Rood et al., 2003; Special issue of Rivers Research and
Appli-cation (Volume 19, 2003)). Naiman et al. (2002) argue that the ecosystem is a
legiti-mate user of water and that one of the challenges to river science is forecasting
the consequences of changing water regimes, especially as environmental issues
related to water escalate over the next two to three decades. The determination of
these requirements has progressed to the point where the information requirements
need to be nested within the context of adaptive management, integrated
ecosys-tem-based perspectives and increasing public participation (and scrutiny) (Hillman
and Brierley, 2002; Thoms and Sheldon, 2002). (Some have questioned whether
EWRs of rivers can be effectively integrated with management objectives,
socio-economic demands or a water market system (cf. Doupe´ and Pettit, 2002; Ladson
and Finlayson, 2002).) This requires information about changes from a ‘natural
con-dition’ or ‘virgin state’. While numerous indices are available to characterize
hydro-logical changes from a reference condition (Indicators of Hydrohydro-logical Alteration)
(cf. Olden and Poff, 2003) these are lacking from a geomorphological and ecological
perspective.
3 European Water Framework Directive
A third important focus in river management and remediation is the European Water
Framework Directive (WFD) (European Union, 2000). The main objective of the WFD
is the achievement of a ‘good water status’ (Chave, 2001) through preventing further
deterioration of water bodies and protecting and enhancing the status of aquatic
ecosystems and associated wetlands. Fluvial geomorphology is central both to
the design and implementation of the WFD (Newson, 2002; Raven et al., 2002; BSI,
2003; Sear et al., 2003). This requires the description, monitoring and prediction
of river channel conditions and behaviour; a major challenge, as discussed earlier.
In Europe, the WFD recognizes the importance of considering hydromorphology
in river management and protection. This includes consideration of:
.
the extent of modification of the flow regime;
.
the extent to which water flow, sediment transport and the migration of biota are
impacted by artificial barriers; and
.
the extent to which the morphology of the river has been modified; including the
constraints to the free movement of a river across its flood plain.
Chave (2001) makes the point that the WFD implicitly recognizes that certain
com-mon hydromorphic features will emerge that will enable the ecosystem to flourish
where there is no human intervention. The WFD therefore provides both an
oppor-tunity to entrench the position of fluvial geomorphology in applied studies, but also
offers a challenge to ensure that the ‘science’ is appropriate, transparent and
accoun-table. Monitoring and auditing are critical in measuring the success (and learning) of
the WFD (cf. Osterkamp, 2002; Thorne, 2002; Bash and Ryan, 2002; Downs and
Kondolf, 2002; Walker, J. et al., 2002).
4 River restoration and remediation
It has been recognized that while whole river training methods have brought many
advantages (e.g., flood control), many disadvantages have also resulted, for example,
continuous degradation of the bed, impacted aquatic ecosystems (Marti, 2002),
groundwater recharge and social concerns (Ono, 2002). As a consequence, ecologically
acceptable remediation has gained momentum as an approach (cf. River Restoration
Centre, 2002). However, there is also a pragmatic realization that complete ‘restoration’
of fluvial systems is seldom attainable, nor desirable. The real questions are what is an
acceptable rate of change and how sustainable is the change? The fourth broad theme
therefore considers the recent contribution of fluvial geomorphology to river
remedia-tion efforts (Hudson, H.H., 2002; Lenzi, 2002; Logan and Furse, 2002; Parsons and
Gilvear, 2002; Boon et al., 2002; Filipe et al., 2002; Walker et al., 2002; Williams et al.,
2002; Environment Agency, 2003; Zimmerman et al., 2003). Examples of river
remedia-tion approaches that consider the importance of ecosystem funcremedia-tionality and the
con-tribution of fluvial geomorphology in resolving these issues comes from five continents
(cf. Meyer, 2001; Thompson, 2002b; Florsheim and Mount, 2002; Steveaux and Takeda,
2002; Jonker et al., 2002; McGinness et al., 2002; Rowntree and du Plessis, 2003; Walters
et al., 2003). A limitation of many river remediation projects, however, has been that
they have tended to be small-scale in nature, without adequate consideration of the
drainage basin linkages that provide the template for remediation and rehabilitation
(Gregory and Chin, 2002).
An example of a basin-scale perspective to river management and remediation is
the River Styles approach (as described earlier). The approach provides a typology
upon which spatial and temporal linkages of biophysical processes are assessed
within a drainage basin (Brierley et al., 2002). River character and behaviour are
recorded and the capacity for each river reach to adjust varies with each Style.
This is important, as different rivers will respond differently to imposed changes.
For example, despite the fact that the Toledo Bend Reservoir impounds 74% of
the Sabine basin in the USA, minimal geomorphic impacts were experienced
below the impoundment (Phillips, 2003b). This would suggest that the reach was
transport-limited before impoundment; thus reduced sediment supply after
impoundment had a limited effect on the channel boundary. Impacts therefore
need to be interpreted within a broader geomorphic context. This illustrates the
value of the River Styles framework in that it assesses geomorphic river condition
and recovery potential in the context of the evolutionary pathways of the systems.
The approach is also one of few that successfully manages to cross scale boundaries
and provide a reasoned, integrated and implementable scale-based approach for
river management and remediation.
The aforementioned discussion illustrates the point that there is a need to
recog-nize that predictions in geomorphology tend to be qualitative and imprecise.
Fur-thermore, the ability of the discipline to apply experimental and laboratory data
are limited, and repeatable observations and falsifying hypotheses are few because
each geomorphic situation is unique (cf. Schumm, 1991; Benda et al., 2002). Even
where quantitative approaches are applied (particularly in the field of sediment
transport and hazard forecasting), these are only appropriate at limited scales
and domains. Benda et al. (2002) point out, for example, that sediment transport
is difficult to predict accurately (even though it may be done with precision) because
of the problems mentioned earlier. Furthermore, accurate predictions are unlikely
because larger-scale processes constrain smaller-scale processes. For example,
hydrodynamic and hydromorphological models that seek to predict changes in
the physical dimensions of channels rely on sediment input information from
the contributing basins, another unresolved issue. Similar problems exist in
pre-dicting the effects of land use changes on fluvial systems. It could be argued
that, a rigorous, defensible scale-based conceptual approach to prediction (and
management) is preferable to a precise, yet conceptually flawed scale-less
numeri-cal approach.
XIV Ecohydrology
It is widely acknowledged that hydrology plays a critical role in present-day fluvial
systems and associated ecosystems (Arscott et al., 2001; Bonnel, 2002; Caruso, 2002;
Collier, 2002; Alfredsen and Tesaker, 2002; Bovee and Scott, 2002; Brown and Ford,
2002; Bunn and Arthington, 2002; Prowse and Conly, 2002; Wu and Wang, 2002; Annear
et al., 2002; Bond et al., 2002; Cortes et al., 2002; Dugger et al., 2002; Gibbins et al., 2002;
McIntosh et al., 2002; Parkinson et al., 2002; Peel et al., 2002; Prowse et al., 2002; Rech et al.,
2002; Smolders et al., 2002; Wanner et al., 2002; Hughes and Rood, 2003). This
recog-nition has evolved into the field of ecohydrology. Evidence derived from
palaeohydro-logical studies (Runge, 2002; Barker et al., 2002; Uliana et al., 2002; St George
and Nielson, 2003; Keefer et al., 2003; Russell et al., 2003) can also help contextualize
present-day problems through reconstructing past processes; shifts, for example, in
ecotonal zones (cf. Starkel, 2002). There has also been recognition that there is a
linkage between streamflow variability, precipitation and climate forcing (e.g.,
ENSO) (Chiew and McMahon, 2002; Jones and Woo, 2002; Woo and Thorne, 2003)
that should be of considerable interest to geomorphologists, hydrologists and
ecolo-gists alike.
Models are being developed, for example, to assist in providing rapid estimates of
the ecological instream flow requirements of rivers (Hughes and Hannart, 2003).
Eco-hydrology has close links with fluvial geomorphology (cf. Marani et al., 2001) and
hydraulics (cf. Walker et al., 2002; Booker, 2003; Odeh, 2003; Rowland et al., 2003). In
fact, the concept of ecogeomorphology has also been mooted (Thoms and Parsons,
2002). While there is some debate as to exactly what ecohydrology is, there is
consen-sus that there is a need for research into the interface between ecology and hydrology
(Black et al., 2002). This is reflected in the recent launching of the International Journal on
Ecohydrology and Hydrobiology and a special edition in the Hydrological Sciences Journal
dedicated to ecohydrology. The special edition contains five broad discussion papers
(Kundzewicz, 2002; Nuttle, 2002; Moir et al., 2002; Porporato and Rodriguez-Iturbe,
2002; Zalewski, 2002) that may be of interest to fluvial geomorphologists.
XV Conclusions
Fluvial geomorphology has much to offer both as a science, and as input into
mana-ging complex river systems. One of its strengths is that it views the world as a nested
hierarchical system, in which consideration of spatial and temporal scale provides
the context for understanding system behaviour. This presents a useful perspective
that adds considerable value and offers much insight into interpreting a natural
world characterized by complex multiscale and multidimensional problems. The
breadth of research considered in this review demonstrates that within this broad
systems umbrella, there is space for the continuum of spatial and temporal scales
of research that, considered together, offers a potentially holistic understanding
of river behaviour. Much of the future progress in fluvial geomorphology will
rest on its ability to understand and interpret the links within and connectivity
between patches of fluvial forms and processes at different spatial and temporal
scales.
Acknowledgements
Many thanks to my wife Lynette who has helped with sourcing much of the
reviewed material and helping in the laborious task of editing and checking the
manuscript.
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