Impact of large instream logs on river bank erosion

There has been abundant research into the effect of tree roots on stabilizing river banks, and also on the effect of trees on bed-scour after they have fallen into the stream, but there is little research into the effect of instream logs on bank erosion. Here we develop the hydraulic theory that predicts local and reach scale bank erosion associated with instream logs with various configurations and distributions and conclude that individual log can increase local bank erosion, but multiple logs can reduce overall reach erosion. Where there is consistent bank strength, the local erosion varies in a non-linear way with the angle, size and position of the log. The reach scale effect of multiple logs depends on the distribution of logs and the proportion of the reach occupied by logs. Erosion effects of instream logs are difficult to measure. We are testing the above theory of erosion associated with instream logs in a series of anabranches of different sizes that experience consistent irrigation flows each year (on the Murray River in SE Australia). These channels have high erosion rates, abundant logs, and are like a giant flume that allows us to measure erosion processes, as well as hydraulics, in a controlled setting

Excluding stock from riverbanks for environmental restoration: The influence of social norms, drought, and off-farm income on landholder behaviour

Governments often use voluntary agreements to encourage landholders to adopt environmental practices, such as excluding stock from grazing riverbanks. In Victoria, Australia, government agencies subsidize the adoption of these projects, while landholders are required to continue maintaining stock exclusion indefinitely. In the absence of further financial or legal enforcement, landholder compliance depends on the motivation and decision-making of individual landholders. Social beliefs about the responsibility of landholders to improve the condition of degraded riverine ecosystems, known as social norms, influence farmers to adopt new environmental practices. The influence of social norms on behaviour weakens when people perceived themselves to be constrained. From late 1996 to mid-2010 landholders in Victoria endured more than ten years of drought that has reduced productivity, and income. Drought conditions may influence whether landholders continue to exclude stock over the long-term, despite holding positive social norms. However, behaviour is influenced by perceptions of constraint; landholder perceptions may not reflect drought severity. Perceived drought affectedness may also be related to the amount of income obtained from farm activities. This study examined the relationship between social factors, (including injunctive and descriptive social norms, and symbolic and instrumental social beliefs, perceived drought affectedness, actual drought severity), and the percentage of overall income that landholders obtain from farm activities. A social survey, and assessment of river restoration projects, was conducted with 93 landholders in rural Victoria, Australia. We found that landholders who continue to graze riverbanks hold weaker social norms about excluding stock in drought conditions. Grazing behaviour was explained by social norms, and perceived drought affectedness together. Perceived drought affectedness was best explained by actual drought severity, but also by the amount of income obtained from farming activities, rather than either factor alone. Policy makers should consider using drought relief funding to subsidize the purchase of additional stock feed during droughts to encourage farmers to continue environmental stock exclusion, particularly when farmers rely on farm activities for most of their income

Researching agricultural environmental behaviour: Improving the reliability of self-reporting

Agricultural practices cause many of the environmental problems in river basins. Changing farmer behaviour to adopt more sustainable practices is a key focus of government policy in many countries. There is now a need to assess the effectiveness of projects that promote environmental agricultural behaviour. Most agricultural research that evaluates landholder practices relies on farmers to report about their own behaviour. This behavioural measure, known as ‘self-reporting’, has been widely critiqued because reporting is often biased. Little is known about the reliability of self-reports about environmental behaviour, and even less is known about self-reporting agricultural environmental behaviour. This paper considers the extent that agricultural environmental research relies on self-reported data, presents a case-study comparing farmer self-reports with more reliable observed proxy data, and offers some methods for minimising self-reporting bias, particularly bias related to participant perceptions of social desirability. We compared self-reports about farmer environmental behaviour (preventing cattle from grazing riverbanks) with observed proxy data (e.g., visual evidence of cattle access) and found that more than 60% of self-reports were inaccurate, including both under- and over-reporting of grazing behaviour. We found that self-reporting is less reliable for identifying behavioural determinants compared to using observed proxy data. We also found that farmers experience social pressure to perform environmental behaviours. Thus, we suggest the inaccuracy of self-reported data may be the result of social desirability bias. Substantial investment has been made to assess the effectiveness of government policy for encouraging agricultural environmental behaviour. The success of such programs relies on the accuracy of behavioural data. Agricultural research often depends on self-reported data. Thus, researchers should make efforts to design projects to reduce the likelihood of self-reporting bias

The politicisation of science in the Murray-Darling Basin, Australia:discussion of ‘Scientific integrity, public policy and water governance’

Many water scientists aim for their work to inform water policy and management, and in pursuit of this objective, they often work alongside government water agencies to ensure their research is relevant, timely and communicated effectively. A paper in this issue, examining 'Science integrity, public policy and water governance in the Murray-Darling Basin, Australia’, suggests that a large group of scientists, who work on water management in the Murray-Darling Basin (MDB) including the Basin Plan, have been subject to possible ‘administrative capture'. Specifically, it is suggested that they have advocated for policies favoured by government agencies with the objective of gaining personal benefit, such as increased research funding. We examine evidence for this claim and conclude that it is not justified. The efforts of scientists working alongside government water agencies appear to have been misinterpreted as possible administrative capture. Although unsubstantiated, this claim does indicate that the science used in basin water planning is increasingly caught up in the politics of water management. We suggest actions to improve science-policy engagement in basin planning, to promote constructive debate over contested views and avoid the over-politicisation of basin science

The management of crown river frontages: Upper King River, north eastern Victoria

It is the purpose of this thesis to examine problems in management of the Crown River Frontages of the Upper King River, North-Eastern Victoria. Management, in the context of this study, is defined as the application, by responsible governmental agencies, of legislation enacted in relation to river frontages. This approach provides a 'base level' with which the present condition of the river frontage will be compared. This comparison should provide a degree of explanation as to why the the Crown River Frontages are in their present condition

Progress, problems and prospects in Australian river repair

Effective river restoration requires an integrative approach among researchers, managers and stakeholders, grounded in sound science. Using Australia as a case study, we examined contemporary responses to the following three global challenges for river management: first, to base management practice on 'best available science' (BAS); second, to integrate diverse, discipline-bound knowledge within cross-disciplinary and trans-disciplinary approaches; and third, to achieve adaptive management based on monitoring and evaluation. Analysis of 562 papers from the six Australian national stream-management conferences held since 1996 provided insight into the rapidly growing area of management, and the degree to which these three challenges are being met. The review showed that discipline-bound abiotic or biotic science was the focus of 46% of papers. Cross-disciplinary science, defined as the integration of biophysical sciences, was presented in 36% of papers, and trans-disciplinary science, defined as the merging of biophysical science with social and economic perspectives, in 17%. Monitoring and evaluation results were presented in only 12% of papers, whereas applications of adaptive management were reported in a mere 2%. Although river management has been transformed in recent decades, much remains to be done to create a holistic foundation for river restoration that links biophysical science to social science and economics.13 page(s

Using Structure-from-Motion Photogrammetry to Improve Roughness Estimates for Headwater Dryland Streams in the Pilbara, Western Australia

There are numerous situations where engineers and managers need to estimate flow resistance (roughness) in natural channels. Most estimates of roughness in small streams come from humid areas. Ephemeral streams in arid and semi-arid areas have different morphology and vegetation that leads to different roughness characteristics, but roughness in this class of stream has seldom been studied. A lack of high-resolution spatial data hinders our understanding of channel form and vegetation composition. High resolution structure-from-motion (SfM)-derived point clouds allow us to estimate channel boundary roughness and quantify the influence of vegetation during bankfull flows. These point clouds show individual plants at centimetre accuracy. Firstly, a semi-supervised machine learning procedure called CANUPO was used to identify and map key geomorphic features within a series of natural channels in the Pilbara region of Western Australia. Secondly, we described the variation within these reaches and the contribution of geomorphic forms and vegetation to the overall in-channel roughness. Channel types are divided into five reach types based on presence and absence of geomorphic forms: bedrock; alluvial single channel (≥cobble or sand dominated); alluvial multithread; composed of either nascent barforms or more established; stable alluvial islands. Using this reach classification as a guide, we present estimates of Manning’s roughness within these channels drawing on an examination of 650 cross sections. The contribution of in-channel vegetation toward increasing channel roughness was investigated at bankfull flow conditions for a subset of reaches. Roughness within these channels is highly variable and established in-channel vegetation can provide between a 35–55% increase in total channel roughness across all channel types. This contribution is likely higher in shallow flows and identifies the importance of integrating vegetation and geomorphic features into restorative practices for these headwater channels. These results also guide Manning’s selection for these semi-arid river systems and contribute to the vegetation-roughness literature within a relatively understudied region

River Channel Relocation: Problems and Prospects

River relocation is the diversion of a river into an entirely new channel for part of their length (often called river diversions). Relocations have been common through history and have been carried out for a wide range of purposes, but most commonly to construct infrastructure and for mining. However, they have not been considered as a specific category of anthropogenic channel change. Relocated channels present a consistent set of physical and ecological challenges, often related to accelerated erosion and deposition. We present a new classification of river relocation, and present a series of case studies that highlight some of the key issues with river relocation construction and performance. Primary changes to the channel dimensions and materials, alongside changes to flow velocity or channel capacity, can lead to a consistent set of problems, and lead to further secondary and tertiary issues, such as heightened erosion or deposition, hanging tributaries, vegetation loss, water quality issues, and associated ecological impacts. Occasionally, relocated channels can suffer engineering failure, such as overtopping or complete channel collapse during floods. Older river relocation channels were constructed to minimise cost and carry large floods, and were straight and trapezoidal. In some countries, modern relocated channels represent an exciting new challenge in that they are now designed to replicate natural rivers, the success of which depends on understanding the characteristics, heterogeneity, and mechanisms at work within the natural channel. We discuss shortcomings in current practice for river relocation and highlight areas for future research for successful rehabilitation of relocated rivers

The daily-scale entrance dynamics of intermittently open/closed estuaries

Intermittently open/closed estuaries (IOCE) are a dynamic form of estuary characterised by periodic entrance closure to the ocean. Entrance closure is a function of the relative balance between on and offshore sediment transport with closures occurring during periods of low fluvial discharge whereby the estuary ebb-tidal prism is reduced. Although the broad scale processes of entrance closure are becoming better understood, there remains limited knowledge on channel morphodynamics during an individual closure event. In this study, the entrance dynamics of three IOCE on the coast of Victoria, Australia, were monitored over a daily timescale following both artificial and natural openings. The influence of changing marine and fluvial conditions on the relative sedimentation rate within the entrance channel was examined. IOCE in Victoria showed two distinct modes of entrance closure: (a) lateral accretion, whereby the estuary gradually closes by longshore drift-driven spit growth during low river flows; and (b) vertical accretion, where the channel rapidly aggrades under high (> 2 m), near-normal waves. During storms, when fluvial discharge and wave heights simultaneously increase, large swells will not always close the mouth due to an increase in the ebb-tidal prism. The estuary water depth and the maximum channel dimensions following opening were not proportional to the opening duration, with this being a function of the wave and fluvial conditions occurring following lagoon drainage. Based on the findings of this work, implementing a successful artificial entrance opening is dependent on reduced onshore sedimentation rates which occur when wave energy is low (< 2 m Hs) relative to river flow. Copyrigh