Article

Spatial variability in the timing, nature and extent of channel response to typical human disturbance along the Upper Hunter River, New South Wales, Australia

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Abstract

Prior to European settlement the Upper Hunter River near Muswellbrook, New South Wales was a passively meandering gravel-bed river of moderate sinuosity and relatively uniform channel width. Analyses of floodplain sedimentology, archival records, parish maps and aerial photographs document marked spatial variability in the pattern of channel change since European settlement in the 1820s. Different types, rates and extents of change are reported for seven zones of adjustment along an 8 km study reach. This variable adjustment reflects imposed antecedent controls (buried terrace material and bedrock), which have significantly influenced local variability in river sensitivity to change, as well as contemporary morphodynamics and geomorphic complexity. Local variability in system responses to disturbance has important implications for future river management and rehabilitation. Yes Yes

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... Drought conditions occurred between , in the early 1980s and since the late-1990s. The flood of record occurred in 1955 with a discharge of 5685 m 3 /s and a recurrence interval of 1:100 years (Hoyle et al., 2008). However, other records indicate that the flood of June 1820 may have reached approximately the same levels as the 1955 event and the 1806 and 1870 events may have exceeded the 1955 levels (NSW Water Resources Commission, 1984), albeit under different channel conditions. ...
... Europeans first explored and settled the upper Hunter catchment in the 1820s (Hoyle et al., 2008). Before European settlement, the upper Hunter catchment was inhabited by two Aboriginal tribes, the Kamilaroi and the Wanaruah. ...
... The timing of this secondary incision is unknown. From this evidence, it is safe to assume that the initial phase of bed lowering along Dart Brook occurred early in the twentieth century in response to lowering along the Hunter River (Hoyle et al., 2008). The system continues to respond to this trunk stream influence through the formation of secondary headcuts. ...
Article
Most analyses of river adjustment have focused on parts of catchments where metamorphosis has occurred. This provides a non-representative view of river responses to human-disturbance. Although many rivers have been subjected to systematic land-use change and disturbance, significant variability is evident in the form, extent and consequences of adjustment. This study documents the catchment-wide distribution of river sensitivity and adjustment in the upper Hunter catchment, New South Wales, Australia in the period since European settlement. The spatial distribution and timing of lateral, vertical and wholesale river adjustments are used to assess river sensitivity to change. The type and pattern of rivers, influenced largely by valley setting, have induced a fragmented pattern of river adjustment in the upper Hunter catchment. Adjustments have been largely non-uniform and localized, reflecting the predominance of bedrock-controlled rivers which have limited capacity to adjust and are resilient to change. Less than 20% of river courses have experienced metamorphosis. Phases of reach-scale geomorphic adjustment to human disturbance are characterized as a gradient of primary, secondary and tertiary responses. In general terms, primary responses such as cutoffs or straightening were followed by secondary responses such as channel expansion. These secondary responses occurred between 50–70 years after initial disturbance. A subsequent tertiary phase of river recovery, denoted as a transition from predominantly erosional to predominantly depositional geomorphic processes such as channel contraction, occurred around 70–120 years after initial disturbance. Such responses are ongoing across much of the upper Hunter catchment. Copyright © 2009 John Wiley & Sons, Ltd.
... Research on phases of geomorphic adjustment (and hence sediment reworking) along rivers in the catchment (Hoyle et al., 2008a;) and on the strength of longitudinal bedload sediment supply (Fryirs et al., 2007a,b) only provide a preliminary set of ideas about the sources of sediment in the catchment and whether or not this sediment has been delivered to the Hunter River at Muswellbrook. ...
... Three major phases of river adjustment have been identified in the upper Hunter catchment since European settlement (Hoyle et al., 2008a;Fryirs et al., 2009). The location of these adjustments and analysis of the materials that were reworked provides some guidance as to the primary sediment sources in this catchment. ...
... This recovery phase is characterised by a transition from dominantly erosional to dominantly depositional geomorphic processes as reflected by significant bench formation, floodplain accretion, and channel contraction in many reaches . This is particularly evident along the Hunter River at Muswellbrook where fine-grained vertical accretion on instream benches has resulted in the formation of inset floodplains within the over enlarged macrochannel trench (Hoyle et al., 2008a). Up to 3 m of fine-grained material has also accumulated in deep pools, but an unknown volume has accumulated on gravel bars forming colmation layers along the reach (Hoyle et al., 2008b;Mika et al., 2010). ...
Article
River bed colmation layers clog the interstices of gravel-bed rivers, impeding the vertical exchange of water and nutrients that drives ecosystem function in the hyporheic zone. In catchments where fine-grained sediment supply has increased since human disturbance, understanding sediment provenance and the (dis)connectivity of supply allows practitioners to target sediment source problems and treat them within catchment management plans.Release of alluvial fine-grained sediment from channel bank erosion since European settlement has resulted in the formation of a colmation layer along the upper Hunter River at Muswellbrook, eastern Australia. X-ray fluorescence spectrometry (XRF) and X-ray diffractometry (XRD) are used to determine the elemental and mineralogical signatures of colmation layer and floodplain sediment sources across this 4480 km2 catchment. This sediment tracing technique is used to construct a picture of how suspended sediment supply and (dis)connectivity operates in this catchment. In this system, the primary source areas are subcatchments in which sediments are stored largely in partly confined floodplain pockets, but from which sediment supply is unimpeded and directly connected to the receiving reach. Subcatchments in which alluvial sediment storage is significant — and which contain large, laterally unconfined valleys — are essentially ‘switched off’ or disconnected from the receiving reach. This is because large sediment sinks act to trap fine-grained sediment before it reaches the receiving reach, forming a buffer along the sediment conveyor belt. Given the age structure of floodplains in the receiving reach, this pattern of source area contributions and (dis)connectivity must have occurred throughout the Holocene.
... Localised adjustment occurred within the macrochannel, and significant reach-to-reach variability is evident (c.f. Hoyle et al., 2008;Fryirs et al., 2009). The most notable geomorphic adjustments in the upstream reaches were erosion (e.g., along MCR) and deposition (e.g., in LSR). ...
... Croke et al., 2013b;Grove et al., 2013). Reach-to-reach variability in river responses to flooding and disturbance has been demonstrated elsewhere and been used to forecast where future geomorphic change is most likely to occur (Hoyle et al., 2008;Downs et al., 2013). Along Lockyer Creek the majority of flood-related geomorphic adjustment has occurred within the macrochannel and along its banks. ...
Article
This study aimed to determine the extent of geomorphic change resulting from the catastrophic flood of 2011 in the Lockyer Valley in southeast Queensland and to place these impacts within a history of geomorphic adjustment. Aerial photographs dated from 1933 to 2011, parish maps and historical on-ground photographs dating from 1865 to 1966 were examined for evidence of geomorphic adjustment since European settlement in the first half of the nineteenth century. Eleven forms of geomorphic adjustment were identified in three categories; erosional, depositional, and reorganisational. Only 26% of the Lockyer Creek channel length has been affected by some form of geomorphic adjustment since European settlement. Most of this adjustment was localised and dominated by reorganisation of geomorphic unit assemblages within the macrochannel and sediment deposition on floodplains. No wholesale river change in the form of lateral migration or avulsion has occurred, and the river’s morphology has remained relatively characteristic over time (i.e., morphology remains relatively uniform in a reach-averaged sense). Geomorphic responses to extreme flooding has been minor, and the geomorphic effectiveness of floods in this system (including the 2011 flood) has been limited over the last several hundred years. The system is likely still adjusting to past flooding events that ‘set’ the morphology of the current system (i.e., the macrochannel). A form of event resilience has resulted in this system such that it is less prone to geomorphic adjustment during events than would normally be considered geomorphically effective. As a result, antecedent controls on macrochannel presence and capacity are considered to be first-order controls on contemporary forms and processes in this system. Work is required to test whether the resilience of this system will hold in the future, with more extreme episodes of flooding predicted to occur in this region under future climate change.
... Inevitably, our approach to assessing confinement from remotely sensed data may not detect situations where confining media (e.g. terraces) are buried or where boundaries are subtle and show no surface expression (Hoyle et al., 2008;Fryirs and Brierley, 2010). To improve accuracy in these situations, field verification is required to identify these sorts of buried margins. ...
... In valleys where the channel abuts against secondary confining features, there is still limited capacity to adjust, but the boundaries of the channel may be more erodible depending on the composition of the materials that make up the confining features. In most cases, these margins will be more erodible than the valley margin (Hoyle et al., 2008). ...
... Channel adjustments are driven both by natural (climate driven) and human factors. Human impact has produced remarkable channel changes, such as narrowing, incision, and changes to channel pattern [3][4][5][6][7][8][9]. The most common human interventions include channelization e.g., [10,11], dams e.g., [12][13][14][15][16], sediment mining [17,18], and land-use changes e.g., [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. ...
... Being aware of some limitations, namely that we had to select a main factor for those rivers characterized by multiple causes, and the relatively small size of the dataset, this analysis could be useful to explore possible relationships between causes (e.g., controlling factors) and channel adjustments. Three causes turned out to be the dominant causes in 16 out of 18 rivers (Figures 5 and 6): Gravel and sand mining (river ID: 2, 3,4,8,10,16,17); dams (ID: 5,6,12,14,18); climate change (ID: 7,9,11,15). Channelization and land-use change (coupled with climate change) were identified for the other two rivers of the dataset. ...
Article
Full-text available
Channel adjustments in Iranian rivers have been intense over the last decades due to natural and human factors. Iran has six major basins, all with different climates, from very humid to very arid. This work is a review of the available studies and data about channel adjustments in Iranian rivers, and aims to reconstruct a first outline, at a national scale, of types, magnitude, and causes of adjustments. The results show that most of the rivers have undergone incision (1 to 2 m and, in some cases, up to 6 to 7 m) and narrowing (from 19% to 73%), although widening (from 22% to 349%) has occurred in some rivers. Narrowing is due to dams and sediment mining; widening is due to climate change and sediment mining. Incision is due to gravel and sand mining, dams, channelization, with in-channel mining being the main cause of incision. Channel adjustments have occurred in basins with different climates, but it seems that widening has been more intense in arid and semi-arid climates. Such adjustments have several negative effects (e.g., damage to bridges, degradation of river ecosystems, and instability of banks). The comparison between Iran and other countries shows that narrowing and incision have been the dominant processes in most of the rivers, while damming and in-channel mining have been used as the main controlling factors. Data about adjustments in Iranian rivers are neither homogeneous nor complete for all the rivers. This lack of completeness implies that our understanding of channel changes, and their causes, should be improved by further investigation.
... Inevitably, our approach to assessing confinement from remotely sensed data may not detect situations where confining media (e.g. terraces) are buried or where boundaries are subtle and show no surface expression (Hoyle et al., 2008;Fryirs and Brierley, 2010). To improve accuracy in these situations, field verification is required to identify these sorts of buried margins. ...
... In valleys where the channel abuts against secondary confining features, there is still limited capacity to adjust, but the boundaries of the channel may be more erodible depending on the composition of the materials that make up the confining features. In most cases, these margins will be more erodible than the valley margin (Hoyle et al., 2008). ...
Article
Valley setting and confinement (or lack thereof) are primary controls on river character and behaviour. Although thereare various proxies for valley confinement, direct measures that quantify the nature and extent of confinement are generally lackingand/or inconsistently described. As such they do not lend themselves to consistent analysis over large spatial scales. Here we clearlydefine forms of confinement to aid in quantification of degrees of confinement. Types of margin that can induce confinement aredifferentiated as a valley margin, valley bottom margin, and/or anthropogenic margin. Such margins sometimes overlap and sharethe same location, and in other situations are separated, giving immediate clues as to the valley setting. We apply this frameworkto examples from Australia, United States and New Zealand, showing how this framework can be applied across the spectrum ofriver diversity. This method can help to inform interpretations of reach-scale river behaviour, highlighting the role of antecedentcontrols on contemporary forms and processes. Clear definitions of confinement are shown to support catchment-scale analysis ofriver patterns along longitudinal profiles, and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments(e.g. process zone distribution, lateral sediment inputs and (dis)connectivity).
... Development of Bryan Creek can be compared with this well described conceptual model of channel recovery following migration of a sand pulse. The model suggests that, as the tail passes downstream, bed variability increases and a sequence of channel adjustments takes place [40] including: channel contraction, bench formation (benches are stable bank-attached bars that accrete within the over-widened channel) and return of a well-defined low-flow channel [17,41], exhumation of the pre-disturbance bed [42][43][44], stable alternating bars [45], establishment of in-stream vegetation [46,47], and the re-emergence of pools [3,40]. Alternatively, as the sediment supply declines, the river could also resume some other pre-pulse trajectory, such as incision (for example [20,38]). ...
... Development of Bryan Creek can be compared with this well described conceptual model of channel recovery following migration of a sand pulse. The model suggests that, as the tail passes downstream, bed variability increases and a sequence of channel adjustments takes place [40] including: channel contraction, bench formation (benches are stable bank-attached bars that accrete within the over-widened channel) and return of a well-defined low-flow channel [17,41], exhumation of the pre-disturbance bed [42][43][44], stable alternating bars [45], establishment of in-stream vegetation [46,47], and the re-emergence of pools [3,40]. Alternatively, as the sediment supply declines, the river could also resume some other pre-pulse trajectory, such as incision (for example [20,38]). ...
Article
Full-text available
A premise of stream restoration theory and practice is that it is often futile to attempt to restore a stream at the reach scale (10 ¹ –10 ³ metres) until catchment scale problems have been addressed. This study considers reach scale restoration actions undertaken in Bryan Creek, a sand bed river in south east Australia impacted by a sediment pulse, after catchment sediment sources have been addressed. Local scale interventions, which were in-stream sand extraction, fencing to exclude stock and riparian revegetation, were evaluated by quantifying cross-section and thalweg variability, mapping in-stream and riparian vegetation and by classifying the morphology that emerged following each intervention. Following intervention channel reaches moved to one of three distinct states: simple clay bed, eroding reaches dominated by Juncus acutus , and reaches with deep pools and Phragmites australis . Boundaries between the intervention reaches were sharp, suggesting local scale interventions dominate over catchment scale processes. The magnitude and spread of variability metrics were similar between all reaches and differences in variability bore no relation to intervention type, despite the stark difference in post-intervention morphology. These findings suggest that cross-section and thalweg variability metrics are an inadequate proxy for the effectiveness of local scale interventions in accelerating the recovery of sand bed reaches from a bedload pulse. The most important implications for river managers is that local scale interventions can lead to substantial and rapid improvements in condition, and the change in condition of these reaches is almost independent of other reaches. In this case, the key to the pattern of reach scale geomorphic recovery is excluding stock from waterways so that a specific macrophyte can establish, trap sediment and develop pools.
... Erosion of the MBR in response to the 2011 flood event exhibited substantial variation between reaches, similar to other bedrockalluvial rivers (Hoyle et al., 2008;Konsoer et al., 2016;Toone et al., 2014). Bedrock and indurated gravel deposits influence river processes in the catchment through bed stability (Brizga, 2000b;Kemp et al., 2015), partial confinement by the valley margins (represented by the colluvial slope geomorphic unit which experienced little erosion; Table 1), and reinforcement of other geomorphic units such as benches (at non-eroding field sites). ...
... Fig. 9), as it did in many other Australian rivers (Brooks and Brierley, 2000;Brooks et al., 2003;Fryirs et al., 2018). The macrochannel of the MBR was present at the time of European settlement (Kemp et al., 2015), and does not reflect a response to disturbance as found elsewhere in Australia (Hoyle et al., 2008). However erosion did occur on alluvium inset within the macrochannel (1898 photo in Fig. 9; Kemp et al. (2015)). ...
... At large spatial scales adequately quantifying the soil strength component of resisting force is a significant challenge. This component plays a major role in the spatial variation in riverbank erosion behaviour (Hoyle et al., 2008;Konsoer et al., 2016). Catchment scale studies of riverbank erosion commonly use flat depositional areas as a means of identifying erodible soil (Gallant and Dowling, 2003;Wilkinson et al., 2009). ...
... For example the cumulative specific streampower variable was not significant in isolation in the UBR. While these approaches are not adequate to capture the full complexity of within reach variation (Hoyle et al., 2008), they may improve the performance of riverbank erosion modelling at large spatial scales without requiring extensive field data collection. ...
Article
A large proportion of the uncertainty surrounding catchment sediment budget modelling has been attributed to sediment supplied from riverbank erosion. Some of the variables influencing riverbank erosion are bend curvature, specific streampower, riparian vegetation, and in some instances sand and gravel extraction. The empirical relationship between these variables and observed riverbank erosion across 78 km of the Upper Brisbane River, Australia was investigated. No significant relationship was found between curvature, specific streampower and riverbank erosion. The role of riparian vegetation relative to sediment supply from riverbank erosion varied with spatial location, susceptibility of a reach to erosion, and human disturbance such as sand and gravel extraction. Despite not having data on substrate type the model described approximately 37% of the variation in observed riverbank erosion. It appears that inclusion of a management practice factor in riverbank erosion models is justified, where appropriate, and may improve model performance.
... basal lags or fine-grained, cemented materials). Where macrochannels have been described elsewhere, evidence also confirms their lateral confinement by resistant fine grained sediments Hoyle et al., 2008;Powell, 1987) and bedrock (e.g. Heitmuller et al., 2015). ...
... Understanding of channel changes implies a detailed reconstruction of evolutionary trajectory of channel morphology and identification of controlling factors. To explain past river dynamics and infer possible future trends it is crucial to have a sound link between morphological changes and their causes, which can be natural or, quite often, related to human interventions (Liébault and Piégay 2001;Hoyle et al. 2008;Wyzga 2008). The REFORM framework provides the spatial and temporal context for such an analysis, by emphasising integration of information on human pressures and geomorphological processes operating within spatial units from catchment, through landscape units and river segments to the river reaches, their historical changes and thus the cascade of linkages across space and time that influence the hydromorphological character and dynamics of river reaches. ...
Article
This paper focuses on the temporal elements of the REFORM hydromorphological framework, illustrating these elements with an analysis of information from the lower Tagliamento river, Italy. It presents an analysis of historical channel adjustments at segment and reach scales over the last two centuries, reflecting human pressures that are summarised but not fully developed in this paper, and an analysis of data from aerial photographs, topographic surveys, and river flow records. This is followed by an assessment of likely future changes over the period 2012–2035 based upon both a conceptual model founded on the historical analysis and numerical modelling. The Tagliamento river has gone through three main phases of adjustment. The first two phases, characterized by narrowing and incision, were driven primarily by human interventions (i.e. sediment mining and channelization). The most recent phase represents an attempt of the river to achieve a new equilibrium condition and is mainly controlled by flow regime (i.e. frequency and magnitude of formative discharges) and vegetation establishment. As for future channel evolution, both models showed that slight width changes are likely to occur over the period 2012–2035. Channel widening, that could be expected as a response to an excess of unit stream power, will be hampered by vegetation establishment. Finally, the “no intervention” strategy seems to be the best option for leading the river towards a new equilibrium condition and to achieve different goals (e.g. flood mitigation, conservation or improvement of ecological status).
... This is a term used originally by Van Niekirk et al (1999) to describe large channels in southern Africa which have a compound complex morphology. The term has been used in Australia more recently (see Hoyle et al., 2008;Shellberg and Brooks, 2007) to describe rivers which have a compound cross section bounded by late Pleistocene age high floodplain terraces, with numerous inset floodplain and bench features ( Figure 1, Figure 2). In such channels the majority of "modern sediment deposits" (i.e. ...
... To go further back in time, the planform configuration of palaeochannels can be investigated based on their topographic signature in the floodplain and supported by sedimentological and stratigraphic evidence (e.g. Hoyle et al., 2008;Brown et al., 2013). ...
Technical Report
Full-text available
Work Package 2 of REFORM focuses on hydromorphological and ecological processes and interactions within river systems with a particular emphasis on naturally functioning systems. It provides a context for research on the impacts of hydromorphological changes in Work Package 3 and for assessments of the effects of river restoration in Work Package 4. Deliverable 2.1 of Work Package 2 proposes a hierarchical framework to support river managers in exploring the causes of hydromorphological management problems and devising sustainable solutions. The deliverable has four parts. Part 1 (this volume) provides a full description of the hierarchical framework and describes ways in which each element of it can be applied to European rivers and their catchments. Part 2 includes thematic annexes which provide more detailed information on some specific aspects of the framework described in Part 1. Part 3 includes catchment case studies which present the application of the entire framework described in Part 1 to a set of European catchments located in different biogeographical zones. Part 4 includes catchment case studies which present a partial application of the framework described in Part 1 to a further set of European catchments.
... South Africa. The term was first used in an Australian context by Hoyle et al., (2008) to describe the morphology of compound channels bounded by Pleistocene terraces in the Hunter River. There is a growing realisation that understanding the dynamics of these inset deposits is crucial to understanding the transport of sediments from and through catchments (e.g. ...
Article
Full-text available
We present the results of investigations into alluvial deposition in the catchment of the Normanby River, which flows into Princess Charlotte Bay (PCB) in the northern part of the Great Barrier Reef Lagoon. Our focus is on the fine fraction (<~ 63 μm) of alluvial deposits that sit above the sand and gravel bars of the channel floor, but below the expansive flat surface generally referred to as the floodplain. Variously described as benches, bank attached bars or inset or inner floodplains, these more or less flat-lying surfaces within the macro-channel have hitherto received little attention in sediment budgeting models. We use high resolution LiDAR based mapping combined with optical dating of exposures cut into these in-channel deposits to compare their aggradation rates with those found in other depositional zones in the catchment, namely the floodplain and coastal plain. In total 59 single grain OSL dates were produced across 21 stratigraphic profiles at 14 sites distributed though the 24 226 km2 catchment. In-channel storage in these inset features is a significant component of the contemporary fine sediment budget (i.e. recent decades/last century), annually equivalent to more than 50% of the volume entering the channel network from hillslopes and subsoil sources. Therefore, at the very least, in-channel storage of fine material needs to be incorporated into sediment budgeting exercises. Furthermore, deposition within the channel has occurred in multiple locations coincident in time with accelerated sediment production following European settlement. Generally, this has occurred on a subset of the features we have examined here, namely linear bench features low in the channel. This suggests that accelerated aggradation on in-channel depositional surfaces has been in part a response to accelerated erosion within the catchment. The entire contribution of ~ 370 kilotonnes per annum of fine sediment estimated to have been produced by alluvial gully erosion over the last ~ 100 years can be accounted for by that stored as in-channel alluvium. These features therefore can play an important role in mitigating the impact on the receiving water of accelerated erosion.
... 159 To go further back in time, the planform configuration of palaeochannels can be investigated based on their topographic signature in the floodplain and supported by sedimentological and stratigraphic evidence. 160,161 Finally, the chronology of physical pressures should be updated with the dates and extent of river realignment and channel bank and bed reinforcement. This information can come from maps, remote-sensing, and water agency records. ...
Article
The hydrology and geomorphology of most rivers has been fundamentally altered through a long history of human interventions including modification of river channels, floodplains, and wider changes in the landscape that affect water and sediment delivery to the river. Resultant alterations in fluvial forms and processes have negatively impacted river ecology via the loss of physical habitat, disruption to the longitudinal continuity of the river, and lateral disconnection between aquatic, wetland, and terrestrial ecosystems. Through a characterization of geomorphological change, it is possible to peel back the layers of time to investigate how and why a river has changed. Process rates can be assessed, the historical condition of rivers can be determined, the trajectories of past changes can be reconstructed, and the role of specific human interventions in these geomorphological changes can be assessed. To achieve this, hydrological, geomorphological, and riparian vegetation characteristics are investigated within a hierarchy of spatial scales using a range of data sources. A temporal analysis of fluvial geomorphology supports process-based management that targets underlying problems. In this way, effective, sustainable management and restoration solutions can be developed that recognize the underlying drivers of geomorphological change, the constraints imposed on current fluvial processes, and the possible evolutionary trajectories and timelines of change under different future management scenarios. Catchment/river basin planning, natural flood risk management, the identification and appraisal of pressures, and the assessment of restoration needs and objectives would all benefit from a thorough temporal analysis of fluvial geomorphology.For further resources related to this article, please visit the WIREs website.Conflict of interest: The authors have declared no conflicts of interest for this article.
... In contrast, while we found differences between revegetated and open sites in height above and distance from the channel, these do not appear to influence species composition in this study. This is likely due to the fact that very few floods of sufficient magnitude have inundated these surfaces since they were revegetated (Hoyle et al. 2008;Fryirs et al. 2009). Most floodplains in these areas have not been inundated since the floods of 1978 and 1955, prior to the establishment of any revegetation we assessed and too infrequently to have an impact on herbaceous communities (Lyon & Sagers 1998). ...
Article
Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.
... For example, Leigh and Webb (2006) documented incision driven by large floods during the first part of the Holocene prior to anthropogenic disturbances; whereas, Macklin et al. (1992) linked floods caused by a wetter climate to land use change as a cause of incision-suggesting that anthropogenic disturbance alone is not always the cause of recent incision (Macklin et al., 2010). Moreover, the influence of human disturbances is variable because of a given system's relative sensitivity such that some systems respond faster and with greater impact than others (Hoyle et al., 2008). ...
... Understanding of channel changes implies a detailed reconstruction of evolutionary trajectory of channel morphology and identification of controlling factors. To explain past river dynamics and infer possible future trends it is crucial to have a sound link between morphological changes and their causes, which can be natural or, quite often, related to human interventions (Liébault and Piégay 2001;Hoyle et al. 2008;Wyzga 2008). The REFORM framework provides the spatial and temporal context for such an analysis, by emphasising integration of information on human pressures and geomorphological processes operating within spatial units from catchment, through landscape units and river segments to the river reaches, their historical changes and thus the cascade of linkages across space and time that influence the hydromorphological character and dynamics of river reaches. ...
Article
Prediction requires use of models (e.g. conceptual, physical, analytical or numerical models). Uncertainty associated with any kind of model and complexity of fluvial systems, specifically of braided rivers, are major issues to be taken into account. This means that we should be aware that prediction of channel morphology has inherent limitations since results of any model are affected by a degree of uncertainty and braided rivers are very complex systems that exhibit self-organized critical behaviour. In this work a long braided reach (33 km in length) of the Tagliamento River (north-eastern Italy) is analysed. This large gravel-bed river (average channel width was 760 m in 2009) underwent notable channel adjustments due to human interventions (i.e. sediment mining and channelization) in the past. Our aim is to explore future channel evolution taking into account different scenarios of flow regime and sediment supply at catchment and reach scale. Two different modelling approaches were combined: (i) a conceptual model based on a historical analysis of channel changes over the last 200 years and controlling factors and (ii) numerical modelling, using a reduced complexity model (CAESAR). According to the conceptual model channel widening will take place in the future, though the evolutionary trajectory will depend on magnitude and frequency of formative discharges. For instance assuming that flow regime in the next years will be similar to that in the period 1993-2009, channel width will increase up to 1020 m in 2080 (in this case an average widening rate of 3.7 m/yr is assumed). From this conceptual model different future trajectories could be derived, for instance more intense channel widening is predicted if an increase in magnitude and frequency of formative discharges is assumed. The numerical modelling, using constant conditions for flow regime and different conditions for sediment supply (i.e. scenarios), showed that channel widening will continue in the next decades, independently from sediment management strategies. As expected, widening turned out to be more intense in the scenario where bank protections were removed (w = 1230 m) compared to the scenario where upstream sediment input was reduced (w = 1130 m). This work should be taken as an attempt to predict channel morphology evolution over long spatial and temporal scales (i.e. tens of km and tens of years) that are rarely considered in river modelling. Such scales are very relevant for river management. Because uncertainty can be very high in modelling long river reaches over several decades, it is worth using different models to reduce uncertainty. The results of the two models used in this study turned to be very coherent, thus increasing reliability of the predictions.
... The dataset used in this study can be considered good, comparing it with those used in similar studies (e.g., Winterbottom, 2000;Liébault et al., 2002;Hoyle et al., 2008;Swanson et al., 2011). A detailed evolutionary trajectory was reconstructed for channel width, and a quantitative analysis of controlling factors was feasible. ...
Article
Interpretation of channel changes is not always straightforward since it requires a detailed reconstruction of the evolutionary trajectory of channel morphology, a quantitative analysis of controlling factors and, finally, identification of links between evolutionary trajectories and controlling factors. The aim of this paper is to explain channel adjustments and controlling factors in the Tagliamento River, a large gravel-bed river in northeastern Italy. Traditional methods for studying historical channel changes (i.e., use of aerial photos, topographic data) were employed, but numerical modelling turned out to be very useful for the quantification of bedload transport and for supporting interpretation of past changes and likely future channel evolution.River channel underwent three main phases of adjustment over the last 200 years. The first two phases, from the end of the nineteenth century to the early 1990s, were characterized by narrowing (channel width decreased from 1250 to 540 m) and incision (about 1 m); and the third phase, from the 1990s to present day, by widening (from 540 to 600 m) and slight aggradation (about 0.2 m).Combining evolutionary trajectories of channel morphology and analysis of controlling factors we argue that the long-term channel evolution of the Tagliamento River was driven mainly by human intervention at the reach scale (i.e., sediment mining and channelization). Changes in sediment supply in the catchment area had no, or minor, effects in the study reach. The most recent changes (i.e., widening and slight aggradation) are explained as a response to past disturbances that have produced a remarkable change of channel geometry and an increase of unit stream power in the reach. Magnitude and frequency of formative discharges are a key driving factor of the intensity of recent changes, while this was not the case during the previous phases of adjustment.
... Re-establishing the riparian trees may not be sufficient to contain the modified, wider and deeper channel in its new configuration; this outcome is considered to be unlikely but it is possible that the newly established hydraulic regime of the modified channel (faster flood flows) may overwhelm the vegetation and scour out a new equilibrium channel cross-section (cf. Brooks and Brierley 1998;Erskine and Green 2000;Hoyle et al 2008;Hubble 2001). On a geological time-scale, continued erosion of these valleys is expected -albeit at a geologically slow rate. ...
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Riverside vegetation is a significant factor influencing the occurrence and progress of streambed and riverbank erosion. Recent riparian management practice in Australia has focussed on re-establishing or maintaining native riparian vegetation in order to control or prevent erosion as well as regenerate or preserve the complex variety of in-stream and riverside habitats. This work presents an integrated review of field and experimental studies conducted in eastern Australia that evaluate native vegetation's role in mass failure of riverbanks. Several results of these studies have general application and include the following: (1) The presence of riparian forest on riverbanks significantly reduces the likelihood of erosion by mass failure due to reinforcement of riverbank soils by tree roots and this reduced likelihood of mass failure enables a narrower channel cross-section than would otherwise be the case for many Australian coastal streams. (2) A number of Australian tree species have apparently evolved roots that seek the permanent, summer water table in order to survive prolonged dry spells, these root systems are particularly effective in mass failure mitigation due to rooting depths that are commonly greater than 5 m and are sometimes well in excess of 20 m. (3) The so-called "Root-Area-Ratio method" of calculating the shear strength of root-reinforced soil using root tensile strength data and Waldron's [Waldron, L.J., 1977. The shear resistance of root-permeated homogenous and stratified soil. J. Soil Sci. Soc. Am. 41, 843-849] and Wu et al.'s [Wu, T.H., McKinnell, W.P., Swanston, D.N., 1979. Strength of tree roots and landslides on Prince of Wales Island, Alaska. Can. Geotech. J. 16,19-33] simple root model leads to significant overestimation of the actual root-reinforcement due to (a) breakage or pull-out of roots that taper and narrow beneath the shear plane such that individual roots do not achieve the tensile strength calculated on the basis of root diameter at the shear plane; and/or (b) the fact that the soil mass fails progressively along the length of potential shear plane rather instantaneously across the entire shear plane. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
... Inset alluvial surfaces, including genetic floodplains and benches, reflect relationships with more frequent fluvial processes (Woodyer, 1968;Nanson and Croke, 1992;Croke et al., 2016). Such channel forms have been observed in a range of climatic settings where hydrological variability is high, including subtropical and temperate Australia (Hoyle et al., 2008;Croke et al., , 2013a, South Africa (van Niekerk et al., 1999;Heritage et al., 2001), tropical monsoonal rivers in India (Gupta, 1995;Rajaguru et al., 1995) and the Caribbean (Ahmad et al., 1993) and the semi-arid regions of North America (Heitmuller et al., 2015). Observations in subtropical south-east Queensland (SEQ) suggest many of the rivers in this region are constrained by macrochannel boundaries (Shellberg and Brooks, 2007;Croke et al., , 2013aKemp et al., 2015). ...
Article
Along the eastern margin of Australia, hydrological variability reaches a peak in the subtropics of south-east Queensland and many rivers have entrenched characteristics. To address the nature of entrenchment and the relationship with adjacent alluvium, this paper presents the results of detailed chrono-stratigraphic analysis of alluvial units in the partly confined mid-reaches of Lockyer Creek, Australia. Four sites were investigated using topographic, sedimentological and chronological data. Radiocarbon and single grain optically stimulated luminescence dating indicate a large proportion of the valley fill reflects a major phase of aggradation of fine-grained alluvium from ca. 35 ka throughout the Last Glacial Cold Period. Synchronous incision of Pleistocene alluvial fills between 11.5 and 9.3 ka suggests the current entrenched Lockyer Creek formed in response to changes in late Quaternary climate. Holocene floodplains set within the entrenched Pleistocene valley floor have basal ages of ca. 7.5 ka, but whose proximal margins are still actively accreting. This Holocene fill has accreted over the mid- to late Holocene but overlaps with the contemporary hydrological regime. The sedimentary nature of the Holocene fill appears to be related to persistent antecedent controls in the form of bedrock and terrace constriction.
... Rustomji et al. (2009) identified hydrologically-variable basins along the eastern coast of Australia as those with high Flash Flood Magnitude indices (FFMI) and a high Q50:Q2 flood quantile ratio. In these settings, the dominant channel form is often referred to as a 'macrochannel' or compound channel-in-channel which displays multiple inundation surfaces and has been described in subtropical and temperate Australia (Hoyle et al., 2008;Croke et al., , 2013a, South Africa (van Niekerk et al., 1999;Heritage et al., 2001), India (Gupta, 1995;Rajaguru et al., 1995), the Caribbean (Ahmad et al., 1993) and the semi-arid regions of North America (Heitmuller et al., 2015). Two key issues often confound the success of catchment management and strategic re-vegetation plans in these settings; (1) identifying the active channel bank and bank top and, (2) determining where riparian vegetation could contribute most to ameliorating flood problems such as reducing flood velocities and enhancing sediment trapping. ...
Article
In perennial stream settings, there is abundant literature confirming that riparian vegetation affects flood hydrology by attenuating the flood wave, enhancing deposition and reducing bank erosion. In contrast, relatively little is known about the effectiveness of riparian vegetation during floods in hydrologically-variable regions. The dominant channel form in these settings is often referred to as a 'macrochannel' or compound channel-in-channel which displays multiple inundation surfaces where it is often difficult to identify the active channel bank and bank top. This study uses the inundation pattern of recent flood events in the Lockyer Valley of South East Queensland (SEQ), Australia to present a framework which specifically considers the interaction between inundation frequency and trapping potential on a range of inundation surfaces. Using hydrological modelling and a consistent definition of floodplains and within-channel features, it outlines five key priority areas for the placement of riparian vegetation to alleviate common flood problems within the catchment. The highest priority for the placement of riparian vegetation to ameliorate the effects of small-moderate floods is on within-channel benches. For out-of-macrochannel flows, riparian vegetation is most effective on genetic floodplains which occupy the largest spatial extent within the valley. In particular, it identifies the need for, and benefits of, revegetation in spill out zones (SOZ) which occur where upstream channel capacity is larger and flow is funnelled at high velocity onto the floodplain downstream. This study highlights the importance of understanding the key geomorphic processes occurring within a catchment and developing effective catchment management plans to suit these conditions.
... This is often because of the influence of internal resistance in the system; whether channel or boundary (Knighton, 1999). In most cases, the contemporary channel may be set within a much larger macrochannel of variable capacity with limited space to adjust (Fryirs et al., 2009(Fryirs et al., , 2015Hoyle et al., 2008). This imparts an event resilience to the system such that the river undergoes only localised geomorphic adjustment during high magnitude events that would elsewhere produce significant geomorphic activity (Costa and O'Connor, 1995;Crozier, 1999;Fryirs et al., 2015;Lisenby and Fryirs, 2016;Magilligan et al., 2015;Miller, 1990;Wolman and Gerson, 1978). ...
... These understandings are required to differentiate the causes from the symptoms of degradational influences. Sometimes field analyses that 'look beneath the surface' reveal findings that do not fit with current explanations, thereby requiring an alternative interpretation (e.g., Hoyle et al., 2008;Roering et al., 2013). A quirky piece of evidence can transform an interpretation in the quest to develop a rational and logical argument to create knowledge with an appropriate supporting evidence base. ...
Article
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The process of interpretation, and the ways in which knowledge builds upon interpretations, has profound implications in scientific and managerial terms. Despite the significance of these issues, geomorphologists typically give scant regard to such deliberations. Geomorphology is not a linear, cause-and-effect science. Inherent complexities and uncertainties prompt perceptions of the process of interpretation in geomorphology as a frustrating form of witchcraft or wizardry – a dark art. Alternatively, acknowledging such challenges recognises the fun to be had in puzzle-solving encounters that apply abductive reasoning to make sense of physical landscapes, seeking to generate knowledge with a reliable evidence base. Carefully crafted approaches to interpretation relate generalised understandings derived from analysis of raw data with field observations/measurements and local knowledge to support appropriately contextualised place-based applications. In this paper we develop a cognitive approach (Describe-Explain-Predict) to interpret landscapes. Explanation builds upon meaningful description, thereby supporting reliable predictions, in a multiple lines of evidence approach. Interpretation transforms data into knowledge to provide evidence that supports a particular argument. Examples from fluvial geomorphology demonstrate the data-interpretation-knowledge sequence used to analyse river character, behaviour and evolution. Although Big Data and machine learning applications present enormous potential to transform geomorphology into a data-rich, increasingly predictive science, we outline inherent dangers in allowing prescriptive and synthetic tools to do the thinking, as interpreting local differences is an important element of geomorphic enquiry.
... Research in Southeast Queensland (SEQ) has highlighted that the riverine response to extensive high-magnitude flooding in recent years was largely affected by the presence of entrenched river channels, termed macrochannels [44][45][46][47][48][49]. Macrochannels were first described in the South African Sabie River [50,51], but similar channel forms have been identified elsewhere [52][53][54]. Such streams feature large, compound river channels where multiple alluvial units are inset within a broader, entrenched channel ( Figure 1). ...
Article
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In the tectonically stable rivers of eastern Australia, changes in response to sediment supply and flow regime are likely driven by both regional climatic (allogenic) factors and intrinsic (autogenic) geomorphic controls. Contentious debate has ensued as to which is the dominant factor in the evolution of valley floors and the formation of late Quaternary terraces preserved along many coastal streams. Preliminary chronostratigraphic data from river terraces along four streams in subtropical Southeast Queensland (SEQ), Australia, indicate regionally synchronous terrace abandonment between 7.5–10.8 ka. All optically stimulated luminescence ages are within 1σ error and yield a mean age of incision at 9.24 ± 0.93 ka. Limited samples of the upper parts of the inset floodplains from three of the four streams yield near-surface ages of 600–500 years. Terrace sediments consist of vertically accreted fine sandy silts to cohesive clays, while top stratum of the floodplains are comprised of clay loams to fine-medium sands. The inundation frequency of these alluvial surfaces depends on their specific valley setting. In narrow valley settings, where floodplains comprise <5% of the valley floor, terraces are inundated between the 20 and 50-year annual exceedance probability (AEP) flood, while in wide settings (floodplains >20%), the terraces are no longer inundated. Floodplain inundation frequencies also vary between these settings by an order of magnitude between 5- to 50-year AEP, respectively. The correlation of terrace abandonment within SEQ with fluvial and palaeoenvironmental records elsewhere in the subtropics, and more broadly across eastern Australia, are an indication that terrace abandonment has primarily been driven by climatic forcing. Contemporaneous channel incision in the early Holocene may have been driven by an increasingly warmer and wetter environment in SEQ, with a climate commensurate with the delivery of more extreme weather events. Following channel incision, many streams in SEQ have been largely confined to their entrenched “macrochannel” form that remains preserved within the valley floor.
... Since these earlier studies, it has become apparent that a single CEM cannot be universally applied to an entire catchment because of reach-scale differences in the nature and sensitivity of the channel to adjust to a disturbance as governed by such factors as sediment supply, local hydrologic regime, channel and valley gradient, the nature of the bed and bank materials, and vegetation cover [20], among other parameters. Herein, we examine the channel evolutionary changes associated with the ADE that was initiated by land-use changes in the Big Harris Creek basin for the major types of process zones, including deeply incised channels, entrenched alluvial channels (within narrow and wide valleys), and alluvial channels with riparian wetlands (Figure 1; Table 1). ...
... Since these earlier studies, it has become apparent that a single CEM cannot be universally applied to an entire catchment because of reach-scale differences in the nature and sensitivity of the channel to adjust to a disturbance as governed by such factors as sediment supply, local hydrologic regime, channel and valley gradient, the nature of the bed and bank materials, and vegetation cover [20], among other parameters. Herein, we examine the channel evolutionary changes associated with the ADE that was initiated by land-use changes in the Big Harris Creek basin for the major types of process zones, including deeply incised channels, entrenched alluvial channels (within narrow and wide valleys), and alluvial channels with riparian wetlands (Figure 1; Table 1). ...
Article
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Big Harris Creek, North Carolina, possesses a geomorphic history similar to many drainages in the southern Appalachian piedmont, and was used herein as a representative example of the influence of European settlement on contemporary channel form and processes. The integrated use of historical, dendrogeomorphic, stratigraphic, and cartographic data shows that the conversion of land-cover from a mix of natural conditions and small farms to commercial cotton production in the late 1800s and early 1900s led to significant upland soil erosion, gully formation, and the deposition of legacy sediments on the valley floor. Aggradation was followed by catchment-wide channel incision in the mid-1900s in response to reforestation and the implementation of soil conservation measures. Collectively, the responses form an aggradational-degradational episode (ADE) that produced the geomorphic framework for the contemporary processes operating along the drainage network. Defined, characterized, and mapped process zones (stream reaches of similar form and process) show that the type, intensity, and evolutionary sequence of geomorphic responses varied within the catchment as a function of the position along the drainage network, the erosional resistance of the underlying bedrock, and the valley characteristics (particularly width). Understanding the spatially variable influences of the ADE on contemporary, reach-scale geomorphic processes provides valuable insights for restoration as it helps inform practitioners of the sensitivity and ways in which the reach is likely to respond to future disturbances, the potential impacts of processes on proposed manipulations intended to achieve the project’s restoration goals, and the potential risk(s) involved with channel reconstruction. The latter is strongly controlled by geotechnical differences between erosionally resistant precolonial deposits and easily eroded legacy sediments that locally form the channel banks following the ADE.
... This is often because of the influence of internal resistance in the system; whether channel or boundary (Knighton, 1999). In most cases, the contemporary channel may be set within a much larger macrochannel of variable capacity with limited space to adjust (Fryirs et al., 2009(Fryirs et al., , 2015Hoyle et al., 2008). This imparts an event resilience to the system such that the river undergoes only localised geomorphic adjustment during high magnitude events that would elsewhere produce significant geomorphic activity (Costa and O'Connor, 1995;Crozier, 1999;Fryirs et al., 2015;Lisenby and Fryirs, 2016;Magilligan et al., 2015;Miller, 1990;Wolman and Gerson, 1978). ...
... In this study, we assumed that several soil classes existed prior to agricultural development and considered them as Pre-European settlement soil classes. European settlement of the Hunter Valley began in the 1820s (Hoyle et al., 2008). There are still tracts of land which have native vegetation and which have not been cultivated. ...
Article
The concept of soil security has been proposed with the dimensions of capability, condition, capital, connectivity, and codification of soil. However, it remains a challenge to accurately and efficiently assess the soil's capability and condition as a function of soil change. The idea of genoform and phenoform was proposed 20 years ago and recently revitalized. Herein, we were inspired by these concepts to develop a general approach and concepts of genosoils and phenosoils for distinguishing the soil changes within soil mapping units as affected by human activities. Across a 220 km² district with a diversity in landforms, parent materials, and land use types, we generated maps of Pre-European (soil classes that existed prior to agricultural development) soil classes using a digital soil mapping approach. Based on the land use change, Pre-European genosoils and present genosoils and phenosoils were identified and mapped within each of the Pre-European soil classes. The measured topsoil (0–10 cm) and subsoil (40–50 cm) properties have shown differences between the present genosoils and phenosoils. By objectively calculating the distances between the present genosoils and phenosoils in a principal component space using a recently published comprehensive soil classification system, several present phenosoils displayed significant differences among several soil properties (distance >8% of overall distance) and were redefined as new genosoils. The approach has successfully mapped genosoils and phenosoils within Pre-European soil classes at the district scale and identified shifts between present genosoils and phenosoils. It showed potential in detecting areas of soil changes due to human activities. Future work is required to separate seasonal fluctuations from long-term variations in NDVI and improve land use classification using remote sensing data. The method developed here can be applied in areas without remnant vegetation to separate the soil condition from capability by gauging phenosoils against genosoils.
... Repeated aerial surveys allowed the quantification of morphodynamic processes (Pasquale et al., 2011;Gilvear et al., 1995) and short-to mid-term changes due to human alterations (Marston et al., 1995;Hoyle et al., 2008). More recently, the uncertainties and limitations of aerial pictures for setting up terrain models (e.g. to eliminate vegetation) in river science (compare to Gao, 2009) were overcome with the use of reach-to catchment-scale light detection and ranging (LiDAR) river survey (Charlton et al., 2003;Hilldale and Raff, 2008). ...
Article
Balkan rivers are described as hotspots of biodiversity due to the limited glaciation to a few high-altitude cirques during the last ice age. Although many studies have examined local-scale highlights in biota and biodiversity, an overall hydro-morphological characterization and development assessment of these rivers during the Holocene are missing. Aim of the presented study is to put together the present and recent river dynamics and Quaternary landscape development for a comprehensive understanding of geomorphic processes and the current river morphological characteristics of the Vjosa river. This was done by linking satellite imagery and hydro-dynamic modelling to read the landscape, i.e., to determine the development of landscape units, and (i) the active channel, (ii) the active floodplain and (iii) the morphological floodplain. The digital terrain of the Vjosa River catchment, as an example of the Balkan rivers, was based on a 25 m × 25 m digital elevation model, and hydrodynamic numerical analysis was conducted with a one-dimensional step-backwater model. The application of this assessment approach enabled a clear differentiation of four different sections along the longitudinal profile of the Vjosa—mainly differentiated by the slope and partially corresponding with the confluence of tributaries. We also found that periods of glaciation imposed a strong impact on the hydro-morphological characteristics of the Vjosa River. In particular, the delineation of the active channel and the active floodplain exhibited two different morphological reaches. The first reach exhibits a clear incision of the river into fluvial deposits when the historical sediment supply was high, and the second reach occurs downstream where the current sediment supply is equal or higher than that during the Pleistocene or earlier periods. These differences in hydro-morphological development exert a strong impact on the floodplain development and the human use of these reaches. Thus, despite the given uncertainties due to the lack of bathymetric accuracy, the hybrid assessment approach is useful for the hydro-morphological characterization of the Vjosa river and the identification of landscape forming processes on the catchment scale.
... Therefore, active channel responses are often the consequence of multiple stimuli (e.g., Downs et al., 2013). Although there are several studies trying to link geomorphic adjustments to multiple human disturbances using long term data sets (e.g., Hoyle et al., 2008;Zilian and Surian, 2012;Bollati et al., 2014;Scorpio and Rosskopf, 2016;Downs and Piégay, 2019), the segregation of multiple stimuli remains a challenging task (e.g., González del Tánago et al., 2016). Within this context, the overall aim of this paper is to analyse the geomorphic responses of a mountain river reach (Upper River Cinca, Southern Pyrenees) in relation to natural and human disturbances or influences during almost a century: the period 1927-2015. ...
Article
In this paper we analyse the geomorphic response of a mountain river (Upper Cinca River, Central Southern Pyrenees) in relation to multi-scale disturbances during almost a century (i.e., 1927–2015). The integration of multiple geomorphic descriptors (i.e., morphology and topography) and disturbances (i.e., floods, land use changes, dams, embankments and gravel mining activities) allows better understanding of the cause-effect relations and their significance. The paper presents a novel methodology integrating the application of SfM-MVS algorithms to historical imagery to extract multitemporal channel topography and morphology; and the use of statistical tools to infer on the existence of significant trends and breakpoints in the temporal evolution of the geomorphic descriptors and disturbances. Results show that afforestation was the main land use change exhibited between 1957 and 2015, although mainly concentrated during 1977–2015. Annual runoff presented a general negative trend with a wet (1959–1983) and dry period (1983–2015). Extensive gravel mining occurred after flood events, together with channel engineering works such as the construction of embankments. These disturbances, together with the construction of three small dams in the headwaters, had a direct impact on lateral connectivity by confining and constraining channels and concentrating flows, resulting inchannel incision and stability. The evolution of the disturbances, process changes and geomorphic descriptors indicated that, during the last century, the river channel is in a transient state, in which the magnitude of the changes oscillate. The river is adjusting to the disequilibrium imposed by multi-scale disturbances acting at different temporal and spatial scales by means of two contrasting channel states. First, Channel State 1 (1927–1984) was characterised by having high geomorphic activity and channel incision. Conversely, Channel State 2 (1984–2015) was characterised, by having a low geomorphic activity, when channel constraining was the dominant process and incision was more localised and marginal. The results of the Upper Cinca may be relevant to infer in future fluvial metamorphosis associated with the effects of global change on water and sediment fluxes in mountain catchments, and to assist objective-based rehabilitation measures of rivers subjected to multi-scale disturbances.
... Generally, such models are temporally focused on the synchroneity of channel responses with a series of possible causal drivers for change in a style reminiscent of the timeline evaluation in a 'fluvial audit' (Sear et al., 1995;examples in Fig. 6). The notable difference here was that the channel responses are often quantified, and so too the drivers for change, and there is frequently a measure or judgment of the 'intensity' of association between responses and the inferred drivers of change (e.g., Hoyle et al., 2008;Pont et al., 2009;Ziliani and Surian, 2012;Downs et al., 2013;Sarker et al., 2014). The primary exception to the 'fluvial audit' style of figure arises where a time-sequence trajectory of cross-sectional changes are provided (e.g., Pont et al., 2009, Fig . ...
Article
Evidence for the proposed Anthropocene epoch in fluvial geomorphology hinges on the influence of human activities relative to natural forcing. However, research on cause-effect understanding in river channel evolution has rarely focused on the cumulative impact of multiple drivers for change, limiting insights. Systematic review of 25 recent studies professing to explain reach-scale channel responses to cumulative impacts of human activities and natural forcing over the recent past (ca. 1880–2005)reveals some consistencies in spatio-temporal response across various catchment sizes (median 3000 km ² )in mostly industrialized nations. Common drivers for change include changing flood and flow regimes, dam construction, changing land uses and forest cover, bank protection and instream aggregate mining. Recent channel evolution has predominantly involved narrowing, incision and terrace development, reduced bed sediment storage, lower activity rates and simplified channel geometries. Rates of channel change frequently peaked 1955–1990, providing some support for the Anthropocene ‘Great Acceleration’. Evidence here suggests that many river systems are now in morphologically-novel configurations, coinciding temporally with dramatic recent declines in global freshwater aquatic biodiversity. Sustainable approaches to freshwater management must acknowledge these configurations, placing emphasis on process-based approaches to river ecosystem health in which sediment cascades are reconceived to reflect altered longitudinal and lateral connectivity. However, the reviewed studies are driven largely by expert judgment, depicting cause-effect associations through summary conceptual models based on spatial proximity and temporal synchronicity, providing insufficient scientific proof for the Anthropocene based on the ‘overwhelming’ impact of human factors. More conclusive cause-effect statements will require hypothetic-deductive approaches, explicit functional criteria and best-practice environmental model building. Geomorphologists should now move beyond the ‘phase of discovery’ and develop rigorous proofs for cause-effect relationships of cumulative impact; this may be enhanced by developing an avowedly ‘Anthropocene’ perspective in which rivers are viewed critically as socio-biophysical systems co-evolving with human activity.
... Maps of the former may be feasible using remote sensing to map spatially distributed grain size (e.g., Carbonneau et al., 2005;Pearson et al., 2017;Woodget & Austrums, 2017), but the latter will continue to require traditional field analyses (cf. Hoyle et al., 2008). If a source of lag deposits is identified, then assessment of a river's connectivity to the source and the timescale for the legacy Figure 2. Conceptual model showing the time space scales across which larger-than-average grain lag deposits are supplied to a river system and their subsequent influence upon fluvial morphodynamics. ...
Article
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Larger‐than‐average grain deposits in gravel bed rivers potentially exert a distinctive influence upon fluvial morphodynamics and flow resistance. They are products of historical contingency, sourced from rare events that supply atypically coarse material. Larger‐than‐average grain lag deposits are emblematic attributes of the Tongariro River, New Zealand. They are deposited on bar edges and heads. Derived from lahar valley floor deposits that subsequently became terraces, these materials are less likely to be reworked across a range of flows compared to other bar material. Conceptual models that consider channel configuration and incorporate distributions of particle mobility and flood flows are necessary to assess the role of larger‐than‐average grain deposits on river morphodynamics.
Chapter
Reservoirs, dams, and diversions are vital for securing water supplies, producing hydroelectric power, and controlling floods. However, the changes they impose on the fluvial processes of downstream rivers, mainly reflecting reduced sediment loads and lower flood magnitudes, can be dramatic. A ‘typical’ model of channel response with bed degradation immediately below a dam and channel narrowing farther downstream shows complex variations at the reach scale and between rivers. Complete readjustment can take hundreds of years so that many reaches show sequences of transient states. The factors influencing such complex channel changes in space and time are examined and management/restoration options, including dam removal, are discussed.
Article
Human disturbance induces significant geomorphic changes to river systems. In eastern Australia, land‐use practices such as clearance of forests and riparian vegetation, and removal of wood from channels in the 19th and 20th centuries induced widespread geomorphic impacts. However, since the 1970s there has been a noticeable shift in the geomorphic condition of many rivers in eastern New South Wales (NSW). This transition to a recovery trajectory reflects a reduction in land‐use pressures and improved farming practices on the one hand, and adoption of recovery enhancement approaches to river conservation and rehabilitation by management authorities on the other. Monitoring and tracking changes in condition by state government agencies involves identifying when geomorphic recovery is occurring so that decision‐support frameworks can determine whether river management is required, where, when and how much to intervene to enhance river recovery and when to opt‐out of management because the system requires little (or no) intervention. Here we document procedures that are used to manage process‐based, recovery enhancement in NSW. Following a brief review of river change in eastern NSW since European settlement, we outline an approach to identify and measure key geomorphic indicators of river recovery for different river types. We use case studies to demonstrate examples of geomorphic river recovery, prior to showing how state government agencies in NSW are monitoring trajectories and rates of recovery. Broader implications of this ‘good news story’ are discussed.
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Most Italian rivers have experienced widespread channel adjust- ments over the last 100 years, mainly in response to a range of human activities. The aim of this paper is to show how knowledge of channel ad- justment and reconstruction of evolutionary trajectory are or can be used in river management and restoration. The first part of the paper deals with channel adjustments and summarizes the results of recent studies carried out on twelve rivers in northern and central Italy. The second part illustrates three examples of application. The selected rivers have undergone almost the same processes in terms of temporal trends. Initially, river channels underwent a long phase of narrowing (up to 80%) and incision (up to 8-10 m), which started at the end of the 19th century and was very intense from the 1950s to the 1980s. Then, over the last 15-20 years, channel widening and sedimenta- tion, or bed-level stabilization, have become the dominant processes in most of the rivers, though channel narrowing is still ongoing in some reaches. Channel adjustments were mainly driven by human actions, but the role of large floods was also notable in some cases. Different human interventions have been identified as the causes of channel adjustments (sediment mining, channelization, dams, reforestation and torrent control works). Such interventions have caused a dramatic alteration of the sediment regime, whereas effects on channel-forming discharges have seldom been observed. The first example of application concerns a new methodology designed for assessing the hydromorphological condition of Italian rivers and for monitoring their condition through time. This methodology is required in the context of the Water Framework Directive (2000/60/EC) which aims to assess the ecological status of rivers not only using biological and chemical elements, but also hydromorphological elements. The second example illustrates the potential of channel recovery in five gravel-bed rivers of north-eastern Italy. After defining four categories of channel taking into account recent evolution, it was analysed how differ- ent sediment management strategies could affect future channel dynamics. We concluded that even though both reach and basin-scale interventions may be carried out, it is likely that channels will not recover to the morphology they exhibited in the first half of the 20th century, since sediment yield and connectivity will remain less than during the 19th century and the first half of the 20th century. The last example deals with solu- tions for promoting future sustainable management of sediment and channel processes in the Magra River catchment. Knowledge of channel evolution and its causes was used as a basis for defining channel and sediment management strategies, coupled with quantification of bedload transport and bed sediment budget, and the identification of areas most suitable for potential sediment recharge.
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This progress report on the discipline of fluvial geomorphology reviews 134 papers, 112 of which were published in Earth Surface Processes and Landforms (ESPL) during the calendar years of 2008 and 2009. It continues where the last report for 2006 and 2007 (Stott, 2010) ended. Papers are again grouped by themes to cover 10 subdisciplines within the subject area. The themes were chosen by classifying all geomorphological articles published in ESPL for the same period, of which 38% were within the subject area of fluvial geomorphology. Themes (in order of number contributing to the total) were: fluvial sediment transport; soil erosion and control; modelling the fluvial environment; river management, restoration and effects of vegetation on fluvial systems; gully and hillslope sediment transfer; river regulation, channel change and human influences; advances in methodology in fluvial geomorphology; fluvial hydraulics; fluvial chronology; and bank erosion in fluvial systems. The 2006–2007 and 2008–2009 periods are compared and it was found that broadly the same themes retained their popularity (in terms of numbers of papers published) as in the previous report for 2006–2007.
Article
Large-scale reservoirs change downstream water and sediment conditions, causing adaptive adjustments in erosion and deposition along the riverbed, ultimately impacting sandbar morphology. This study examined the sandy reaches downstream of the China Three Gorges Project along the Yangtze River for river erosion and siltation, riverbed morphology, beach evolution, and other physical processes over the past 40 years, to explain the evolution of river geomorphology under human activities, such as reservoirs, improvement projects, and sand mining. The Shashi reach is approximately 52 km in length; it is the first sandy riverbed downstream of the China Three Gorges Dam. Analysis of topographic data from 1975 to 2018 showed that decreased sediment from the basin resulted in increased riverbed erosion (93.1%, in low-water channel), with sand mining activities destroying the integrity of the central bar. Simultaneously, total sandbar area decreased, thalwegs deepened, river morphological coefficients decreased, and the riverbed became narrower and deeper. The erosion and deposition patterns of the Shashi reach beach and channel have changed from “low shoal erosion-high shoal deposition” to “both low and high shoal erosion”. Additionally, waterway engineering has changed sandbar boundaries, and impacted the evolution of interactions among beach groups. Under quasi-natural conditions, strong interactions occur in sandbar evolution, such as the development of the Taipingkou Channel Bar (TPKCB), which led to Lalinzhou Point Bar (LLZPB) erosion, tail section widening, as well as Sanbatan (SBT) shrinkage and recession of its eastward edge. Owing to the implementation of waterway engineering, the linkage between the TPKCB and the upper section of the LLZPB weakened. The widening of the lower section of the latter has caused the SBT to shrink further and shift westward. Changes in the morphologies and dynamic axes of upstream beach groups have resulted in a sharp reduction of incoming sediment causing the downstream Jinchengzhou Point Bar (JCZPB) to gradually evolve into a shrunken channel bar.
Chapter
Remote data have frequently been used in fluvial geomorphology to observe landforms and derive geomorphological data such as water depth, grain size, and digital elevation models. This article reviews the types and historical development of remote data used in fluvial geomorphology and introduces examples of recent applications. The focus is on raw remote data and their derivatives, and both classic and recent techniques. Further consideration is given to current problems with the use of remote data in fluvial geomorphology and related future perspectives.
Article
One of the main drivers of overbank fine deposition and floodplain formation is the hydrological connectivity between the channel and the floodplain. Channel correction (i.e., groyne field construction within the main flow channel and secondary channel disconnections) and flow regulation can typically lead to a disconnection of riverine floodplains and disturbances that directly affect terrestrialisation. Channel correction and flow regulation can sometimes occur successively, and it is challenging to distinguish the roles of each. This work attempts to assess the respective effects of two phases of channel regulation (correction versus flow regulation) on floodplain terrestrialisation by comparing three bypassed reaches of the Rhône, France (Pierre-Bénite, Péage-de-Roussillon and Donzère-Mondragon). We applied a transversal methodology coupled with GIS analysis (old maps, Orthophotos, DEM's, etc.) to understand processes of channel-planform evolution, conducted a sediment survey (metal rod) to assess floodplain terrestrialisation, and performed sediment sampling (manual auger) to obtain surface sediment metal content levels (X-ray Fluorescence and Inductively Coupled Plasma Mass Spectrometry). We found a general trend of channel narrowing within the three reaches, among which approximately 40% was found to be associated with correction works while 20% was attributed to flow lowering caused by channel bypassing. The number of flowing channels in all sections declined significantly, and local anabranching reaches evolved into very stable single thread channels. Overbank sedimentation declined significantly over the period, with very high sedimentation levels observed immediately after correction works and with very low sedimentation levels observed after diversion. We also found overbank flooding (in the number of days per year) decreased while fine sediment thickness increased. Similarly, the highest concentrations of metals (Zc, Pb, and Cu) were found to be associated with a low connection frequency and vice versa. When similar 2-staged terrestrialisation patterns are observed in all three reaches, they differ in chronology and driving factors because of their longitudinal positioning and specific local conditions.
Article
The adjustment of natural landscapes relates to the interaction between the rate,magnitude, and continuity of the various agents of change, and the resistance of earthsystems to alteration in the past and present. Three general categories encompass thenature of these interactions: continual (e.g. gravity-driven) adjustment, uniformitariansystems (those subjected to periodic pulses of adjustment), and disturbance-dominatedsystems (wherein singular events leave a lasting footprint on the landscape) (Schumm,1988). Previous models of geomorphic change have tended to focus on uniformitariansystems using a quantitative approach (e.g. Wolman and Miller, 1960). This paperoutlines some deficiencies of quantitative, uniformitarian models, and introduces aqualitative method, the "disturbance geomorphology model", to treat landscapeadjustment in the context of the continuum presented above. Several case studies ofgeomorphic adjustment are given as examples of the disturbance geomorphologyapproach. Finally, I argue that reconciliation between qualitative and quantitative modelsis possible when qualitative models are used as the theoretical framework within whichspecific, quantitative analyses can be based; while predictive capability is a product of thequantitative aspects of the study, geographic and temporal context is provided by anappropriate qualitative conceptualization of the problem, such as the disturbancegeomorphology model discussed herein.
Chapter
Human impacts do not directly alter the fundamental hydraulic and geomorphic processes such as the mechanics of sediment transport, erosion, and deposition along rivers. However, human disturbance modifies the spatial distribution and rate of these processes. This chapter first presents a summary history of human interactions with river systems. This is followed by an appraisal of direct human impacts (impacts of dams and inter-basin transfers, channelisation programmes, removal of riparian vegetation and wood, sand/gravel extraction and impacts of rehabilitation schemes) and indirect human impacts (water abstraction, urbanisation, mining and other indirect factors) upon rivers. Finally, river responses to human disturbance are framed in relation to recovery notions, adding a further layer of complexity to the river evolution diagram.
Article
Reservoirs, dams, and diversions are vital for securing water supplies and controlling floods, but the changes in fluvial processes they impose on downstream rivers, dominated by reduced sediment loads and lower flood magnitudes, can be dramatic. A 'typical' model of channel response with bed degradation immediately below a dam and channel narrowing further downstream shows complex variations at the reach scale and between rivers. Complete readjustment can take hundreds of years so that many reaches show sequences of transient states. The factors influencing such complex channel changes in space and time are examined and management/restoration options are considered.
Article
Remote data have frequently been used in fluvial geomorphology to observe landforms and derive geomorphological data such as water depth, grain size, and digital elevation models. This chapter reviews the types and historical development of remote data used in fluvial geomorphology and introduces examples of recent applications. It deals with raw remote data and their derivatives, and both classic and recent techniques. It also discusses current problems with the use of remote data in fluvial geomorphology and related future perspectives.
Article
To evaluate the effects of reservoir construction on the geomorphology of downstream reaches, a case study is performed on the Three Gorges Reservoir (TGR) by comparing data collected before and after impoundment of the reservoir. This study focuses on a 1,183‐km‐long reach downstream from the TGR and investigates the temporal and spatial characteristics and patterns of geomorphic adjustment in the downstream reaches. The amount of erosion in flood plain channels and the annual average intensity of erosion in downstream reaches after 12 years of impoundment are larger than the predicted values before the impoundment of the TGR. The maximum intensity of erosion was found at 410 km from the dam, with an average thalweg incision of 1.5 m, and the main zone of erosion migrated approximately 80 km downstream. At both preimpoundment and postimpoundment, erosion occurred the along beaches and channels in the Yichang–Chenglingji reach. The pattern of erosional channels and depositional river floodplain changed to erosional channels and erosional river floodplain in the Chenglingji–Hankou reach after the trial impoundment stage. In the Hankou–Hukou reach, the erosional channels and depositional river floodplain pattern changed to erosional deep channels, erosional low beaches, and depositional high‐river floodplain during the early impoundment stage. After the trial impoundment stage, erosion continued in the deep channels, but minor deposition occurred on the river floodplain. Moreover, the discharge of clear water increased, and the duration from middle to low‐water levels increased, leading to more concentrated erosion in low‐water channels. The intensity of the erosion along the river floodplain decreased due to the shortened duration of high‐water levels and reduced human activity.
Article
Evolution of perception of riparian landscapes.- The perception and representation of the riparian landscape have changed throughout history, not only among general population, but also among specialists, scientists, technicians and artists. These changes in the way of how to study these territories can be divided in several subfields like uses, interests, needs and technologies for taking profit of natural resources. Analysis, characterization and interpretation of perception of landscapes have been focused on the Mediterranean rivers of Catalonia (NE Spain) over the last three centuries.
Article
Passive riparian revegetation techniques are important tools in river rehabilitation. However, the utility of the sediment seed bank as a passive riparian regeneration option is poorly understood. After modelling a range of flows for field‐surveyed cross sections, a glasshouse seedling emergence experiment was undertaken to compare the effects of simulated flow duration on seedling emergence of desirable riparian species that occur on benches of the gravel‐bedded Hunter River near Muswellbrook, New South Wales. The duration of inundation did have an effect (although not always significant) on seed germination for most species. The most successful simulated flood conditions differed among species, with the control treatment (no inundation) resulting in the most germination for only two of the 10 species examined. These findings suggest that although environmental flows for the sole purpose of stimulating the riparian seed bank in order to facilitate regeneration of desirable riparian species would be largely ineffective and complicated by differing inundation responses among species, seed bank stimulation using environmental flows could be a value‐added benefit from flows allocated for other purposes. As such, consideration of flow duration is worthy of inclusion in environmental flow allocation planning.
Article
This study investigated the influence of the Three Gorges Dam (TGD) on the evolution of nearby channels in the Yangtze River (Changjiang River) system in order to better understand of the environmental impact of large‐scale reservoir operations. From 2003–2017, the amounts of runoff and sediment transport in the Yangtze River were reduced by 3.3–14.5% and 67.8–92.7%, respectively, relative to 1955–2002 before the TGD was operational. Topographic measurements of the middle reaches (Yichang to Hukou) of the Yangtze River were analyzed from 1975–2017, during which time the cumulative erosion of the flood channel was 22.78×108m3, and the dry channel accounted for 90.3% of the erosion. Following commissioning of the TGD, the scouring intensity of the sandy gravel section near the dam initially increased then decreased, whereas the scouring intensity of sandy sections away from the dam continued to increase. Beaches on convex banks of curved sections were scoured, and deep channels on concave banks became silted. In braided sections, the braids tended to shrink, and the diversion ratio of the main branch during dry seasons reduced, resulting in frequent branch alternation. Compared to changes in the downstream river channels of other large reservoirs worldwide, scouring from the TGD is extensive. The findings of this study are significant for river channel regulation and waterway planning in the Yangtze River and worldwide.
Article
Assessment of River Styles, accompanied by time series analysis of historic imagery and geomorphic change detection techniques are used to explain the capacity for river adjustment (geomorphic sensitivity) in relation to the distribution of stream power along 3000 km of channels (3rd Strahler order and greater) to better inform management initiatives in the Waipā catchment, the largest tributary of the Waikato River on the North Island of Aotearoa, New Zealand. Unlike most dynamically adjusting physical landscapes of Aotearoa, most reaches within the Waipā catchment are resistant to geomorphic change. Only 3% of the studied river length has experienced significant planform adjustment since the 1950s and is considered highly sensitive to adjustment. Contemporary alluvial dynamism is largely restricted to gravel bed reaches in high energy rivers within the piedmont zone. The capacity for lateral adjustment in headwater stream courses is restricted by the imprint of past volcanic activity. Further downstream capacity is also limited because of terrace constraints as a result of post-glacial base-level fall, and the entrenchment of the Waikato Fan. Anthropogenic modifications in the catchment include drained wetlands, straightened channels, reinforced banks and emplaced artificial levees (stopbanks) in the few reaches that were prone to adjustment. Highlighting geomorphologically-sensitive reaches at the catchment-scale helps to better prioritise rehabilitation efforts and to support the design and implementation of proactive management plans.
Article
Full-text available
Soil erosion is a serious issue in Australia and this paper attempts a continental synthesis of erosion, fluvial sediment transport and sediment delivery to the coast. Continental soil erosion is estimated to be 28 × 10 9 t year -1 of which about 50% is from sheet and rill erosion and the remainder from gully and river channel erosion. The rill and sheet erosion is 19% of Pimentel's global estimate from 5% of the world land area. Modern rates of erosion have increased by a factor of up to 145 compared to the natural rates before human disturbance. River transport rates are relatively low due to inefficient sediment delivery in keeping with the arid and low lying nature of the continent. Much of the river sediment is derived from gully sources and while sheet and rill erosion are high, little of this material is delivered to rivers. The modern flux to the oceans is about 302 × 10 6 t year -1 or 2% of the estimated global flux (Milliman & Syvitski, 1992) which appears approximately double that pre-human disturbance. The continental sediment delivery ratio is 3%.
Conference Paper
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This paper examines the patterns of sediment transport in rivers in terms of the sources of sediment and its transport and deposition through the river network. The analysis is in the context of dramatic human influences on river sediment transport and how they might influence freshwater ecosystems. The review of Australian work shows that erosion of hillslopes and stream banks has greatly increased in historical times, supplying vast quantities of sediment to rivers, much of which is still stored within the river system. The stored sediment will continue to effect in-stream and estuarine ecosystems for many decades. In most Australian catchments the dominant source of sediment is streambank erosion. An analysis of historical channel widening suggests that a conceptual framework of relative stream power can explain the diversity of behaviour observed in the numerous case studies. Sediment delivery through catchments is considered first in a generic whole network sense, which emphasizes the crucial role played by riverine deposition in determining catchment sediment budgets. A method is then presented for analysing the diverse spatial patterns of sediment storage in any river network. Finally, the paper considers the temporal changes to channel morphology in response to a human-induced pulse of sediment.
Chapter
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Channel response to alternating flood regimes mainly involves widening during floods with recovery by contraction during drought. The magnitude of widening during floods is functionally related to bank resistance with the greatest increases occurring on rivers or on sections of a river with the most erodible boundary sediments (usually sands) and least vegetation. Similarly subsequent contraction is greatest where there is a large supply of bed material and wash load, or where there is a suitable nucleus for sedimentation. -after Authors
Article
Full-text available
IN carbon dating of material included in fluviatile deposits, it is usually assumed that either there is little age difference between the dateable material and the fluvial deposit, or that the 14C sample and the deposit in which it is contained are sufficiently old for the age difference to be of little consequence. We report here on how a series of dates on charcoal from the bed of the Macdonald River, New South Wales, Australia, casts doubt on these assumptions and indicates that serious errors can occur in relating the radiocarbon ages of charcoal samples to the fluvial deposits in which they lie.
Article
Full-text available
Analysis of the contemporary geomorphology, vegetation and in-channel wood within the relatively pristine Thurra River in southeastern Australia provides insight into river behaviour prior to European disturbance. This sand-bed river has an extremely low channel capacity with a pronounced pool–riffle morphology. Lateral migration rates are low (11–24 mm a−1), as are floodplain aggradation rates (average = 0·27 mm a−1). Sedimentological evidence is used to place contemporary channel dynamics within a 16 ka evolutionary framework. The floodplain has continuously aggraded over this interval, despite a number of avulsions and numerous meander cutoffs. Avulsions occur on a timeframe of once in 5 ka or more, while cutoffs occur around once in 1 ka. The morphology and evolution of the Thurra River are appraised in terms of a mediated equilibrium condition, in which channel capacity, hydraulics, bedload transport rates, bank erosion rates and in-channel deposition are substantially influenced by vegetation and wood within the channel and on the floodplain. Copyright © 2002 John Wiley & Sons, Ltd.
Article
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River rehabilitation and management activities in the upper Hunter catchment, New South Wales over the last 50 years are presented from both a geomorphic and social perspective. 517 riverwork projects have been implemented in the upper Hunter catchment from 1952-2000. Nineteen different types of works were used. Projects were concentrated along laterally-unconfined rivers and were largely implemented after major phases of geomorphic river change. Since 1952, river management activities have evolved from an engineering-based paradigm towards an ecosystem-based approach. However, the same types of works were applied across all types of river. Riverworks addressed the symptoms, not the causes of river change, focusing upon bank erosion rather than bed instability. Findings from interviews with local landholders are used to appraise the community's knowledge, views and opinions on riverwork projects and management actions. Several fundamental challenges to successful rehabilitation are identified, including alienation, communication, ownership and use of science in management and decision-making processes. The results confirm the concept that effective rehabilitation and management require meaningful collaboration between all stakeholders. The evolution of rehabilitation techniques, use of science and community perspectives discussed provide insight into the long-term outcomes of past management activities. By assessing the outcomes of rehabilitation investments, a constructive way forward can be achieved which integrates the science of river management, community values and involvement in rehabilitation processes. Findings presented suggest that in the upper Hunter catchment, true rehabilitation is yet to begin.
Article
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Prior to significant European settlement of the area in the 1850s, lower Bega River on the South Coast of NSW had a narrow, relatively deep channel lined by river oaks. The river had a suspended or mixed load, with platypus habitat available in pools. Banks were fine-grained and relatively cohesive (silts and clays), as was the floodplain, which graded to a series of valley-marginal swamps and lakes. Extensive evidence from maps and portion plans, archival photographs, bridge surveys, and anecdotal sources, complemented by field analysis of floodplain sedimentology (including radiocarbon-dated samples) and vegetation remnants are used to document the dramatic metamorphosis in the character and behaviour of lower Bega River in the latter half of the nineteenth century. By 1926 the channel had widened extensively (up to 340%) and shallowed in association with bed aggradation by coarse sandy bedload. Floodplain accretion was dominated by fine to medium sands, with some coarse sand splays.
Article
This paper outlines the successful development of river improvement techniques to arrest bank erosion in the non-tidal reaches of rivers in New South Wales. These techniques consist basically of river training, whereby the river is guided on a suitable course by low barriers installed in the river bed. Tree growth and major snags obstructing the selected waterway are removed. The popular assumptions that such works increase the velocity of flow, cause flooding downstream and destroy the natural environment of rivers, are critically examined and refuted.
Article
Outlines relevant approaches in geomorphology and approaches developed in other disciplines as a basis for establishing what is required in fluvial geomorphology and how sensitivity may be defined in relation to river channel adjustments. These discussions introduce the application of river channel sensitivity in river management policies. -from Authors
Article
Geomorphic thresholds were defined initially as the condition at which there is a significant landform change without a change of external controls such as base level, climate and land use. Subsequently, through usage, the definition has been broadened to include abrupt landform change as a result of progressive change of external controls. Therefore, it is now appropriate to recognize both intrinsic and extrinsic geomorphic thresholds. If the threshold conditions can be recognized, not only will different explanations for some landforms emerge but also the ability to identify incipiently unstable landforms and to predict their change will be of value to land managers and engineers. -from Author
Article
The general concepts generated by modern studies of geomorphological processes are examined in terms of their utility for models of long-term landform evolution. The work is summarized by four fundamental propositions of landform genesis. These include the idea that each set of environments is represented by constant processes and characteristic landforms which tend to persist over time. 'Geomorphological' time is divided into the time taken to attain this characteristic state and the time over which it persists. The systems and forms are subject, over Io2-Io5 years, to perturbations caused by high magnitude-low frequency events, environmental change and internal structural instabilities which initiate change. The responses to these impulses are complex and include damped, sustained and reinforcing changes taking place by ubiquitous, linear or diffusive propagation which reflect the sensitivity of the landscape to change. This sensitivity is dependent on the path density of the process and the strength of the coupling between the system components and has two end members, mobile-sensitive systems and slowly responding-insensitive areas. Some of the results include the concepts of (i) relief and pattern persistence; (2) stagnancy of development and the hypothesis of unequal activity; (3) convergence of form; (4) the concept of transient forms; (5) stability-instability phases and episodic landscape evolution, which together form a coherent framework for long-term landform evolution. Davis's great mistake was the assumption that we know the processes involved in the development of land forms. We don't; and until we do we shall be ignorant of the general course of their development.
Book
This book outlines a generic set of procedures, termed the River Styles Framework, which provides a set of tools for interpreting river character, behavior, condition, and recovery potential. Applications of the framework generate a coherent package of geomorphic information, providing a physical template for river rehabilitation activities. management and restoration of rivers is a rapidly growing topic for environmental scientists, geologists and ecologists - this book provides a learning tool with which to approach geomorphic applications to river management describes the essential geomorphological principles underlying river behaviour and evolution demonstrates how the River Styles Framework can turn geomorphic theory into practice, to develop workable strategies for restoration and management based on real case studies and authors extensive experience applicable to river systems worldwide synthesises fluvial geomorphology, ecology and management.
Article
The late Holocene of south-eastern Australia was typified by stable climate, vegetation and sedimentary regimes, in relative equilibrium with Aboriginal land use and fire management. The arrival of Europeans, with the associated vegetation clearance, introduction of exotic plants and animals, notably for grazing and agriculture and a change in fire regimes, resulted in changes in vegetation and sedimentary patterns. Impacts varied in type and magnitude through the region and evidence of impacts that is preserved varies with sedimentary setting. Here we take a number of proxy measures of vegetation change, fire history, erosion and weathering from six sediment sections across south-eastern Australia and use an index to measure overall rate of change. This shows that the vegetation and environmental systems of south-eastern Australia have been very sensitive to human impact following European settlement.
Article
Investigations of the hydrology and geomorphology of recent floods from the rapid failure of two small upland dams document the unusually large peak boundary shear stress and peak stream power per unit area for each flood. Downstream consequences to alluvial channels and floodplains, however, were minimal. Lack of geomorphic change is attributed to the short duration of the floods, which lasted about six and sixteen minutes each. Distribution of stream power over hydrographs of eight exceptional floods is constructed from channel geometry, discharge rating curves, and flood hydrographs; the resulting curve is defined as a stream-power graph. A stream-power graph gives a better portrayal of the potential for a flood to be geomorphically effective than simple statements of flow magnitude. From stream-power graphs, total energy expended over a flood hydrograph can be computed. Total flood energy may not be a sensitive measure of geomorphic effectiveness without consideration of channel and floodplain resistance. A conceptual model combining flow duration, peak stream power per unit area, flood energy, and alluvial and bedrock thresholds may represent the effectiveness of floods and can distinguish among such cases as (a) floods of long duration, moderate to large energy expenditure, but low peak stream power per unit area. These floods are ineffective in causing significant landform changes in alluvial or bedrock channels; (b) floods of medium to long duration, with medium to large total energy expenditure, and large peak stream power per unit area. These are believed to be the most effective geomorphic floods in any kind of channel because of the optimal combination of peak flood power, duration, and total energy expenditure; and (c) floods of very short duration, low total energy expenditure, but large peak stream power. These floods are also ineffective agents of geomorphic change in spite of record values of peak stream power per unit area because of their short duration, and resulting low energy expenditures.
Article
The watershed (catchment) approach provides a powerful conceptual model for quantitatively evaluating the structure, function and change within a landscape or region. The values and limitations of this approach are considered in this paper, with particular reference to the Hubbard Brook watershed–ecosystem model. The need for informed long-term (sustained) research is stressed; a haphazard collection of data is rarely valuable. Team-building efforts will be needed increasingly in the future to enhance the success of multidisciplinary teams tackling large and complex environmental problems.
Article
The relationship between form and function has been a central organizing principle in biology throughout its history as a formal science. This concept has been relevant from molecules to organisms but loses meaning at population and community levels where study targets are abstract collectives and assemblages. Ecosystems include organisms and abiotic factors but ecosystem ecology too has developed until recently without a strong spatially explicit reference. Landscape ecology provides an opportunity to once again anneal form and function and to consider reciprocal causation between them. This ecomorphologic view can be applied at a variety of ecologically relevant scales and consists of an investigation of how geomorphology provides a structural template that shapes, and is shaped by ecological processes. Running water ecosystems illustrate several principles governing the interaction of landscape form and ecological function subsumed by the concept of “Functional Ecomorphology”. Particularly lucrative are ecosystem-level interactions between geologic form and biogeochemical processes integrated by hydrologic flowpaths. While the utility of a flowpath-based approach is most apparent in streams, spatially explicit biogeochemical processing pervades all landscapes and may be of general ecological application.
Article
1. As rivers and streams are patchy and strongly hierarchical systems, a hierarchical patch dynamics perspective can be used as a framework for visualising interactions between structure and function in fluvial landscapes. The perspective is useful for addressing fundamental attributes of lotic ecosystems, such as heterogeneity, hierarchy, directionality and process feedback occurring across spatial scales and for illustrating spatio-temporal linkages between disparate concepts in lotic system ecology such as the River Continuum Concept, the Serial Discontinuity Concept, the Flood Pulse Concept and the Hyporheic Corridor Concept.
Article
Long flood records for the Hawkesbury-Nepean River have been used to define alternating flood-(FDRs) and drought-dominated regimes (DDRs). In the former, flood magnitudes and frequencies are higher with mean annual flood discharges (Q2.33) from 2 to 4 times greater than for the latter. If channel size is assumed to be related to some level(s) of discharge, then such regime variations create the potential for channel change or adjustments. Surveys since 1863 at Penrith provide some insight into adjustments related to regime changes. In FDRs channel widths generally increase and depths decrease, while in DDRs, these changes are reversed. Human impacts in and beyond the channel modify the nature of adjustment or response»
Article
Within a few decades of European settlement, channel incision transformed discontinuous river courses throughout Wolumla catchment, on the south coast of New South Wales, Australia. The development of continuous channels greatly increased sediment delivery from the catchment. This paper documents the character, timing and proportion of sediment sourced from upland valley fills, channel expansion sites, and gully networks. Volumes of material transferred from these sources are compared with estimates of sediment eroded from hillslopes, and the movement of sediment off the slopes to the valley floor is assessed. Although disturbance of slopes resulted in significant movement of materials, most of this material has been stored on-slope, in trapped tributary fills and along lower order drainage lines. The slopes are effectively decoupled from the channel. Sediment accumulation in farm dams over the past few decades has been negligible. Around 75% of the total volume of material released from creeks in Wolumla catchment since 1865, i.e., 5500ž103 m3, has been derived from channel incision into valley fills at the base of the escarpment. Sediment flushing occurred within a few decades of catchment disturbance. Bedrock confinement in the middle and lower catchment resulted in very efficient downstream transfer of materials. Although gully networks and channel expansion sites have released a relatively small volume of material, these sources are the greatest contemporary source of sediment in Wolumla catchment.
Article
In many catchments in southeastern Australia, alluvial stores have been the dominant source of sediments mobilised in the period since European settlement. In Bega catchment, on the South Coast of New South Wales (NSW), this has been reflected by dramatic changes to river morphology. Extensive volumes of material have been released and efficiently flushed to the lowland plain, with a sediment delivery ratio of almost 70%. However, only 16% of these alluvial sediments have been flushed through to the estuary, as antecedent controls on valley width have resulted in the lowland plain acting as a large sediment sink. The changing nature of sediment source, transfer and accumulation zones has varied markedly from subcatchment to subcatchment. The volume of material supplied to the lowland plain from differing subcatchments is not related to subcatchment area. Rather, the pattern of river types dictates the spatial variability in storage and transfer. Over 67% of sediment released has been sourced from just 25% of the catchment, from subcatchments characterised by large valley fills (cut and fill River Style) that previously stored extensive volumes of material at the base of the escarpment. These parts of Bega catchment were especially sensitive to disturbance. Sediment exhaustion from these parts of the catchment, and from river courses elsewhere, has major implications for the geomorphic recovery potential of rivers, constraining what can be realistically achieved in terms of river rehabilitation.
Article
The concept of thresholds in geomorphology is developed with reference to several different systems. Thresholds are classified as transitive or intransitive, according to whether a change of geomorphic state or process is caused by a persistent change of external boundary conditions or by a relatively short‐lived perturbation of boundary conditions. Lags enter the system when a geomorphic change persists for some time after disruption of boundary conditions. The concepts are first developed with reference to a simple physical system where water changes state from water to ice, or vice versa. Geomorphic examples discussed range from small‐scale rapid changes on sandy surf beaches, through larger‐scale fluvial examples, to the case of semi‐arid dune systems. Use of the concept focuses attention on climatic questions such as geomorphic change: climatic change or climatic perturbation?
Article
The influence of altered fire regimes on the denudation of a catchment is determined from alluvial deposits of the last 10,000 yrs and by monitoring runoff and erosion before and after a wildfire. An increase in fire frequency beginning at 3,000–4,000 yrs BP, as a result of intensified Aboriginal burning, did not change the mechanisms or rates of denudation nor did it cause widespread alluviation as suggested by others. The results of monitoring show that before and after mild fires there is insufficient runoff on most slopes to entrain sediment. Only after intense fires are runoff and erodibility increased enough to significantly accelerate erosion. Conditions are then identified which are most likely to lead to accelerated erosion from altered fire regimes in other catchments.
Article
Cattle grazing practices in the western United States have contributed to widespread riparian degradation resulting in unstable channel morphologies and the loss of fish habitat. Because of prolonged disturbance, numerous riparian areas on both public and private lands have been fenced to exclude cattle in order to promote vegetation establishment and riparian improvement. We selected four gravel-bedded, steep alluvial streams in eastern Oregon with cattle exclosures greater than 14 years old for an analysis of geomorphic adjustments following the removal of cattle grazing. We compare channels inside exclosures and in adjacent grazed reaches to identify the salient stream channel properties that respond to the removal of riparian stresses and to document the magnitude of these changes. Results indicate that significant changes occur, with reductions in bankfull dimensions and increases in pool area being the most common and identifiable changes. At all four sites, bankfull widths are narrower by 10 to 20 percent, and the percentage of channel area occupied by pools is higher in the exclosure by 8 to 15 percent. The increase in pool area is primarily offset by a reduction in the percent glide area. Not all of the channel properties demonstrate adjustment, indicating that perhaps 14 years is an insufficient duration for these variables to adjust.
Article
A number of investigations have been undertaken by the New South Wales Water Resources Commission to determine the regional and compound effects of large scale extractive industries on the stability of the Hunter River, New South Wales. Sedimentologic studies of bed material suggest that the Hunter River upstream of Denman has an armoured gravel bed that is immobile during regulated releases from Glenbawn Dam but is disrupted by moderate but less than bankfull flows. Annual bedloadyields have been computed by the bedload rating-flow duration technique for five river gauging stations. Approximate sand and gravel budgets for selected reaches of the Hunter River demonstrate that the present annual extraction rate from temporary sediment storages within the channel greatly exceeds the transport rate upstream of Denman and is approximately equal to the transport rate downstream of Denman. River degradation is imminent if extractive industries continue operating in the channel of the Hunter River
Article
Abstract Highly structured habitats, those with complex or heterogeneous physical structure, commonly contain more species than simply structured ones. However, tests of this relationship have been hampered by habitat-specific definitions and measurements of habitat structure and, in stream studies, by insufficient information on spatial variation in faunal abundances. We sampled the fauna of 90 stones collected from an order 4 section of the Taggerty and Steavenson Rivers, southeastern Australia. The spatially nested sampling design encompassed three spatial scales (sites within the same stream order, riffles at the same site and groups of stones within the same riffle) but no temporal replication, as we were only able to sample once. Habitat structure of stones was quantified by measuring the amount and type of epilithon on stones, together with stone shapes, sizes, textures and surface complexities. For the latter two attributes, we used a new method, involving image analysis, which can be used to quantify habitat structure in comparable ways in other systems. Species richness (S) was related to some measures of habitat structure, being higher on stones with a rough texture and weakly related to the amount of epilithon present. Total numbers of individuals (N) were also higher on rough stones, and faunal composition (as quantified by hybrid multidimensional scaling) was related to abundance of epilithon. However, flow environments, as quantified by water velocities and depths, were also related to faunal composition. Riffles varied in both faunal densities and near-bed flow environment, but not in any consistent way. Such variability means that individual riffles cannot be reasonably used to ‘represent’ stream sections or orders, an assumption commonly made in stream studies. Neglect of such issues has also resulted in poor conceptual integration between large- and small-scale studies in stream ecology.
Article
Peak rainfalls and peak runoff rates per unit area are comparable over a worldwide spectrum of climates. However, while the magnitude of the external contribution of energy or force in diverse regions is similar, the impact on the landscape varies markedly between regions. Absolute magnitudes of climatic events and absolute time intervals between such events do not provide satisfactory measures of the geomorphic effectiveness of events of different magnitudes and recurrence intervals. Although geomorphic processes are driven by complex sets of interrelated climatic, topographic, lithologic, and biologic factors, the work done by individual extreme events can be scaled as a ratio to mean annual erosion and the effectiveness of such events in forming landscape features can be related to the rate of recovery of channel form or mass wasting scars following alteration by the extreme event. Thus, a time scale for effectiveness may relate the recurrence interval of an event to the time required for a landform to recover the form existing prior to the event.
Article
Extensive river training works were undertaken on the upper Hunter River, Australia between 1956 and 1978 in response to rapid lateral migration and channel widening caused by a series of large floods between 1949 and 1955. River training involved artificial cutoffs, extensive realignment, structural bank protection works and tree planting. Channel length and hence sinuosity (ratio of channel length to valley length) decreased throughout each of six reaches located in the 78.9 km long study area as a direct result of the artificial cutoffs and realignment. Although the overall length reduction was less than 5%, one section experienced a 17% reduction. Localized channel straightening directly increased slope, decreased roughness and consequently increased flow velocity. The structural works have generally succeeded, converting an actively migrating stream into a laterally stable channel. Largely because of channel straightening and reduced sediment supply by floodplain reworking, the river has responded by eroding its bed by up to 1.1 m since the 1950s. Bed erosion preferentially removed the sand and fine gravel fraction producing an armour layer of coarse gravel. This armour layer halted further erosion by protecting the underlying fine material and is now only episodically mobilized by floods with return periods greater than 5.6 years on the annual maximum series. Unfortunately degradation was not predicted before the river training works were undertaken and it was only the fortuitous formation of the bed armour layer which prevented the degradation from becoming a major problem.
Article
Drastic channel adjustments have affected the main alluvial rivers of Tuscany (central Italy) during the 20th century. Bed-level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations. Changes in channel width were investigated by comparing available aerial photographs (1954 and 1993–98).Bed incision represents the dominant type of vertical adjustment, and is generalized along all the fluvial systems investigated. The Arno River system is the most affected by bed-level lowering (up to 9 m), whereas lower incision (generally less than 2 m) is observed along the rivers of the southern part of the region. Human disturbances appear to be the dominant factors of adjustments: the main phase of vertical change occurred during the period 1945–80, in concomitance with the phase of maximum sediment mining activity at the regional scale.The second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel. Based on measurements of channel width conducted on aerial photographs, 38% of the reaches analysed experienced a narrowing greater than 50% of the initial channel width. The largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region.A regional scheme of channel adjustments is derived, based on initial channel morphology and on the amounts of incision and narrowing. Different styles of channel adjustments are described. Rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing; in contrast, sinuous-meandering channels mainly adjusted vertically, with a minor amount of narrowing. Copyright © 2003 John Wiley & Sons, Ltd.
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This paper reviews some of the major developments in the study of channel changes during this century and offers comment on the direction of future research. Topics addressed include the relation of channel equilibrium to time-scale, the process relations of the formal theory of equilibrium channel-morphology, regime theory and hydraulic geometry, complex channel response, human-induced channel adjustments, and channel changes of the Holocene and Pleistocene. It is argued that our perspective on the fluvial system would benefit greatly from research focused on channel changes during the last several hundred years rather than for shorter or longer time-scales.
Article
The occurrence of two ‘rare’ floods (August 1973, August 1977) in the Plynlimon experimental catchments has confirmed the susceptibility of small upland catchments to summer flooding and provided clues to complications in the geomorphological interpretation of floods in terms of their magnitude and frequency. Magnitude may be treated both in terms of work and effectiveness; the emphasis here is on effectiveness, as revealed by simple surveys. The first Plynlimon flood was more effective on slopes and the second in channels, despite peak discharges of similar return periods and almost identical rates of work revealed by bedload trapping. Effectiveness/frequency studies are likely to require a much more detailed approach, subdividing both the characteristics of the flood and the spatial elements of the affected catchments; a simple slope/channel subdivision is found to be suitable for accounts of effectiveness found in the literature on British floods this century. Effectiveness studies also require regular surveys throughout the recovery period following major flooding; in upland catchments these surveys should concentrate on identifying threshold phenomena and illustrating the relationship between effectiveness and work assessments of magnitude.
Article
Incised channels are those in which an imbalance between sediment transport capacity and sediment supply has led to degradation of their beds. This is a frequent response to stream channelization, changes in land use, or lowering of base level. If the degradation causes a critical bank-height threshold to be exceeded, which is dependent on the geotechnical properties of the bank materials, then bank failure and channel widening follow. Interdependent adjustments of channel slope and cross-sectional area occur until a new state of dynamic equilibrium with the imposed discharge and sediment load is attained. These geomorphic adjustments can be described and quantified by using location-for-time substitution and a model of channel evolution can be formulated. Three approaches to rehabilitation of the degraded channels are possible; geomorphic, engineering and rational. The rational approach, which integrates elements of both the engineering and geomorphic approaches, is based on the channel evolution model, and it generally involves control of grade, control of discharge, or a combination of both.
Article
1. Within a few decades of European disturbance in the mid-nineteenth century, river character and behaviour were transformed in Bega catchment on the south coast of New South Wales, Australia. Ecological impacts of geomorphic changes to river structure and function throughout the catchment are assessed. 2. At the time of European settlement, many water courses in Bega catchment were discontinuous, with extensive swamps along middle and upper courses. Following a series of direct and indirect human impacts, channels became continuous in the middle and upper parts of the catchment, as extensive valley fills at the base of the escarpment were incised. Along the lowland plain, the channel widened by over 300%, fundamentally altering the relationship between the channel and its adjacent flo