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11.
While many studies have documented pathways of river degradation, few studies have assessed the character, capacity, and stages of river recovery. In this paper, a generic procedure to measure river recovery is developed and applied in Bega catchment, on the south coast of New South Wales (NSW), Australia. The approach is based on analysis of geomorphic units and ergodic reasoning. Historical data and field analyses are used to identify stages of river evolution throughout Bega catchment. From this, stages of river condition and pathways of adjustment are assessed for three river styles at different positions within the catchment. Five categories of river condition are identified. Intact reaches operate in a self-adjusting manner, whereby processes maintain the pre-disturbance geomorphic character of the reach. The processes occurring in restoration reaches maintain and enhance the geomorphic structure of the reach. These reaches are moderately resilient to change. The river has experienced degradation, but has recovered to a condition approximating its pre-disturbance character and behavior. Degraded reaches are still adjusting to disturbance and the processes of recovery have not yet begun. The river is experiencing progressive deterioration away from the structure and function of the pre-disturbance condition. Turning-point reaches are at the transitional stage where they can either recover or revert to a degraded state. Finally, a creation reach has a self-adjusting character and behavior but operates under altered catchment boundary conditions. The character and behavior of the river do not equate to pre-disturbance conditions; rather, the river is well adjusted to the prevailing catchment boundary conditions of water and sediment transfer, and vegetation cover and composition (among many factors). Once these conditions have been identified for each river style, all reaches in a catchment are placed on pathways of degradation and recovery, and predictions made about their direction of change. The three river styles analyzed in Bega catchment demonstrate differing recovery pathways. Some reaches are adjusting toward a restored condition, while others are adjusting toward a new (or creation) condition. The geomorphic recovery potential of each reach is determined by assessing the connectivity of reaches throughout the catchment and interpreting limiting factors to recovery (e.g., water and sediment transfer, vegetation and coarse woody debris [CWD] character and distribution). [Key words: geomorphic river condition, river recovery, river degradation, recovery potential, fluvial geomorphology, river management.] 相似文献
12.
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. 相似文献
13.
‘Out with the Old?’ Why coarse spatial datasets are still useful for catchment‐scale investigations of sediment (dis)connectivity 
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下载免费PDF全文 The increasing popularity of remote sensing techniques has created numerous options for researchers seeking spatial datasets, especially digital elevation models (DEMs), for geomorphic investigations. This yields an important question regarding what DEM resolution is most appropriate when answering questions of geomorphic significance. The highest possible resolution is not always the best choice for a particular research aim, and DEM resolution should be tailored to fit both the scale of investigation and the simplicity/complexity of modelling processes applied to the dataset. We find that DEM resolution has a significant effect on a simple model of bed load sediment connectivity in the Lockyer Valley, Queensland. We apply a simple bed load transport threshold to catchment DEMs at three different resolutions – 1 m, 5 m, and 25 m. We find that using a 1 m resolution DEM generates numerous disconnections along tributary channel networks that underestimates the sediment contributing area, i.e. effective catchment area (ECA), of seven tributary basins of Lockyer Creek. Utilizing a coarser (lower‐resolution) DEM helps eliminate erroneous disconnections, but can reduce the detail of stream network definition. We find that the 25 m resolution DEM provides the best measure of ECA for comparing sediment connectivity between tributary catchments. The utility of simple models and coarse‐resolution datasets is important for undertaking large, catchment‐scale geomorphic investigations. As catchment‐scale investigations are becoming increasingly entwined with river management and rehabilitation efforts, scientists need not embrace an ‘out with the old’ philosophy. Simple models and coarse‐resolution datasets can help better integrate geomorphic research with management strategies and provide inexpensive and quick first‐order insights into catchment‐scale processes that can help focus future management efforts. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
14.
Rivers with discontinuous watercourses are part of the spectrum of river diversity. Chain-of-ponds types contain irregularly spaced, steep-sided ponds that are separated by preferential flow paths on swampy valley fill. They often contain endangered ecological communities and are receiving greater attention for conservation and restoration. Very little is known about how these river types form, how they have evolved and how they function. Here we present the Late-Quaternary evolution of one of the last remaining large-scale chain-of-ponds systems in Australia, the Mulwaree Ponds. The chain-of-ponds was fully formed by 4.5 ka, with the position and alignment of the ponds being related to the position of pools of a palaeo-river that is up to 100 ka old. Contemporary hydrogeomorphic processes are insufficient to create the ponds, but sufficient to maintain and keep them open. The phases of evolution for this chain-of-ponds system are synchronous with Late-Quaternary changes in fluvial activity documented for other rivers in southeastern Australia. The ponds at Mulwaree have significant preservation potential over thousands of years. In the current landscape they are rare forms, providing significant grounds for conservation and protection of their distinctive geodiversity. © 2020 John Wiley & Sons, Ltd. 相似文献
15.
Temperate Highland Peat Swamps on Sandstone (THPSS) and Coastal Upland Swamps in the Sydney Basin (CUSSB) are listed as endangered ecological communities under Australia's national and state legislation. They are threatened by a range of human and climate impacts. Across the region there are 3208 individual, valley-bottom, elongate-shaped, upland swamps that drain first- or second-order drainage lines and small catchment areas (mean?=?0.25?km2). They occur at a median distance of 57?km from the coast in areas with an average annual rainfall of 1505?mm/year and average annual temperature of 15°C. Those closer to the coast occur on elevations as low as 160?m a.s.l., and those further from the coast, on plateau country, occur up to 1172?m a.s.l. (median 634?m a.s.l.). The valleys that contain these swamps terminate downstream at a valley constriction or bedrock step, behind which alluvial materials have accumulated, and peat has formed to produce relatively steep swamps (median slope 6.2 per cent). Understanding the spatial distribution and physical attributes of these systems, and having the accompanying maps as a resource, is critical for development of sound, well-informed conservation, rehabilitation and monitoring programs, and for analysing the ecosystem services they provide. 相似文献
16.
The worldwide availability of digital elevation models (DEMs) has enabled rapid (semi-)automated mapping of earth surface landforms. In this paper, we first present an approach for delineating valley bottom extent across a large catchment using only publicly available, coarse-resolution DEM input. We assess the sensitivity of our results to variable DEM resolution and find that coarse-resolution datasets (90 m resolution) provide superior results. We also find that LiDAR-derived DEMs produce more realistic results than satellite-derived DEMs across the full range of topographic settings tested. Satellite-derived DEMs perform more effectively in moderate topographic settings, but fail to capture the subtleties of valley bottom extent in mild gradient, low-lying topography and in narrow headwater reaches. Second, we present a semi-automated technique within ArcGIS for delineating valley bottom segments using DEM-derived network scale metrics of valley bottom width and slope. We use an unsupervised machine-learning technique based on the k-means clustering algorithm to solve a conundrum in GIS-based geomorphic analysis of rivers: the delineation of valley bottom segments of variable length. The delineation of valley bottom segments provides a coarse-scale entry point into automated geomorphic analysis and characterization of river systems. © 2020 John Wiley & Sons, Ltd. 相似文献
17.
Extensive valley fills at the base of the escarpment in upper Wolumla Creek, on the south coast of New South Wales, Australia, have formed from a combination of ‘cut and fill’ processes. The valley fills comprise series of alternating, horizontally bedded sand and mud units, reflecting reworking of detritus from deeply weathered granites of the Bega Batholith. Sand units are deposited as sand sheets or splays on floodplain surfaces or in floodouts that form atop intact valley fill surfaces downstream of discontinuous gullies. Alternatively, sands are deposited from bedload and form bars or part of the valley floor within channel fills. Organic-rich mud units are deposited from suspension in swamps or in seepage zones at the distal margin of floodouts. Within 5 km of the escarpment, valley deposits grade downstream from sand sheet and splay deposition in floodouts, to mud deposition in swamp and seepage zones. Radiocarbon dates indicate that virtually the entire valley fill of upper Wolumla Creek was excavated prior to 6000 years BP . Remnant terraces are evident at valley margins. The valley subsequently filled between 6000 years BP and 1000 years BP producing valley fills around 12 m deep, but no greater than 300 m wide. Reincision into the valley fill, on a scale smaller than the present incision phase, is indicated at around 1000 years BP , following which the channel refilled. Portion plans dated from 1865 refer to the study area as ‘Wolumla Big Flat’, and show large areas of swampy terrain, suggesting that the valley fill had re-established by this time. Within a few decades of European settlement the valley fill incised once more. Upper Wolumla Creek now has a channel over 10 m deep and 100 m wide in places, draining a catchment area of less than 20 km2. © 1998 John Wiley & Sons, Ltd. 相似文献
18.
The term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies. However, considerable confusion remains regarding its definition and quantification, especially as it relates to fluvial systems. This confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately. Extreme flood events provide a useful framework to assess variability in connectivity, particularly the connection between channels and floodplains. The catastrophic flood of January 2011 in the Lockyer valley, southeast Queensland, Australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes. High resolution aerial photographs and multi‐temporal LiDAR digital elevation models (DEMs), coupled with hydrological modeling, are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls. Longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel–floodplain connectivity. The major control on connectivity was significant non‐linear changes in channel capacity due to the presence of notable macrochannels which contained a > 3000 average recurrence interval (ARI) event at mid‐catchment locations. The spatial pattern of hydrological connectivity was not straight‐forward in spite of bankfull discharges for selected reaches exceeding 5600 m3 s–1. Data indicate that the main channel boundary was the dominant source of sediment while the floodplains, where inundated, were the dominant sinks. Spatial variability in channel–floodplain hydrological connectivity leads to dis‐connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains. Consideration of such variability for even the most extreme flood events, highlights the need to carefully consider non‐linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative ‘connectivity index’. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
Recognition of the degraded state of rivers across the world has prompted the development of management programmes which promote river repair through rehabilitation practices. Efforts to date have emphasised concerns for biophysical attributes of rivers to the relative exclusion of socio-cultural values. Ultimately, the process of river repair must move beyond this technical focus and incorporate collective societal engagement, participation and ownership. However, the inherent complexities of informing and managing this process limit the prospects that engagement will be translated into an effective and sustained practice. This qualitative case study research analyses the community’s knowledge, views and opinions regarding geomorphic river change and river works projects undertaken in the Upper Hunter catchment, New South Wales, Australia. The responses and views expressed by the participants highlight how ineffective communication and limited understanding of past river work practices has inhibited the connection and ownership between the people and their river. Essentially, historical river management was viewed as a technical process that failed to incorporate social values and aspirations, and which gave inadequate consideration to local knowledge and experience. Participants identified the need to address both diversity and commonality in vision-building and the need for greater confidence and transparency in river science and management. In light of these responses, this paper argues for the adoption of a geo-social, transdisciplinary approach to river rehabilitation. 相似文献
20.
An approach for measuring confinement and assessing the influence of valley setting on river forms and processes 下载免费PDF全文
下载免费PDF全文 Valley setting and confinement (or lack thereof) are primary controls on river character and behaviour. Although there are various proxies for valley confinement, direct measures that quantify the nature and extent of confinement are generally lacking and/or inconsistently described. As such they do not lend themselves to consistent analysis over large spatial scales. Here we clearly define forms of confinement to aid in quantification of degrees of confinement. Types of margin that can induce confinement are differentiated as a valley margin, valley bottom margin, and/or anthropogenic margin. Such margins sometimes overlap and share the same location, and in other situations are separated, giving immediate clues as to the valley setting. We apply this framework to examples from Australia, United States and New Zealand, showing how this framework can be applied across the spectrum of river diversity. This method can help to inform interpretations of reach‐scale river behaviour, highlighting the role of antecedent controls on contemporary forms and processes. Clear definitions of confinement are shown to support catchment‐scale analysis of river 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). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献