Bank Erosion as a Desirable Attribute of Rivers
ABSTRACT Bank erosion is integral to the functioning of river ecosystems. It is a geomorphic process that promotes riparian vegetation succession and creates dynamic habitats crucial for aquatic and riparian plants and animals. River managers and policymakers, however, generally regard bank erosion as a process to be halted or minimized in order to create landscape and economic stability. Here, we recognize bank erosion as a desirable attribute of rivers. Recent advances in our understanding of bank erosion processes and of associated ecological functions, as well as of the effects and failure of channel bank infrastructure for erosion control, suggest that alternatives to current management approaches are greatly needed. In this article, we develop a conceptual framework for alternatives that address bank erosion issues. The alternatives conserve riparian linkages at appropriate temporal and spatial scales, consider integral relationships between physical bank processes and ecological functions, and avoid secondary and cumulative effects that lead to the progressive channelization of rivers. By linking geomorphologic processes with ecological functions, we address the significance of channel bank erosion in sustainable river and watershed management.
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ABSTRACT: This study shows a comprehensive simulation of water and sediment fluxes from the catchment to the reach scale. We describe the application of a modelling cascade in a well researched study catchment through connecting stateof-the-art public domain models in ArcGIS. Three models are used consecutively: (1) the hydrological model SWAT to evaluate water balances, sediment input from fields and tile drains as a function of catchment characteristics; (2) the onedimensional hydraulic model HEC-RAS to depict channel erosion and sedimentation along a 9 km channel onedimensionally; and (3) the two-dimensional hydraulic model AdH for simulating detailed substrate changes in a 230 m long reach section over the course of one year. Model performance for the water fluxes is very good, sediment fluxes and substrate changes are simulated with good agreement to observed data. Improvement of tile drain sediment load, simulation of different substrate deposition events and carrying out data sensitivity tests are suggested as future work. Main advantages that can be deduced from this study are separate representation of field, drain and bank erosion processes; shown adaptability to lowland catchments and transferability to other catchments; usability of the model’s output for habitat assessments.Journal of Hydrology and Hydromechanics 12/2013; 61(4):334–346. · 0.65 Impact Factor
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ABSTRACT: 1. The invertebrates of natural and semi-natural floodplains are diverse, often rare, and important functionally. Early successional patches formed by flood-deposited, coarse, exposed riverine sediments (ERS) are an important habitat in these riparian ecosystems. 2. Extensive channel modifications and engineering works have removed ERS from much of the European river network. This vulnerability, coupled with their role in strengthening biodiversity and associated ecosystem function, makes it important to catalogue remaining ERS distributions and understand controlling factors. 3. This paper aims to: (1) provide the first systematic, modern assessment of the extent and distribution of ERS in England and Wales; (2) characterize geographical and hydrological features of ERS-rich systems; and (3) model the physical and artificial factors determining the complexity and abundance of ERS in England and Wales. 4. River flow regime analysis and generalized linear modelling were combined to identify variables influencing ERS habitat complexity and abundance. 5. ERS predominates in the north and south west of England and Wales, where headwaters are at higher altitudes and substrates are predominantly glacial, alluvial or sedimentary. Local complexity (average number of individual ERS patches per km) was related to stream power and the potential for sediment transport as reflected by stream slope. ERS habitat area declined with the presence of headwater abstraction, but otherwise ERS was not associated with any identified hydrological regime. However, all rivers were strongly seasonal and characterized by sufficient flashiness to ensure high-flow events throughout the year. 6. These results underline the strong natural controls on the distribution and complexity of ERS, but also that habitat provision can be suppressed by human activities, which has implications for conservation practice.Aquatic Conservation Marine and Freshwater Ecosystems 04/2013; 23:924-938. · 1.76 Impact Factor
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ABSTRACT: Environmental legislation in the US (i.e. NEPA) requires defining baseline conditions on current rather than historical ecosystem conditions. For ecosystems with long histories of multiple environmental impacts, this baseline method can subsequently lead to a significantly altered environment; this has been termed a 'sliding baseline'. In river systems, cumulative effects caused by flow regulation, channel revetment and riparian vegetation removal significantly impact floodplain ecosystems by altering channel dynamics and precluding subsequent ecosystem processes, such as primary succession. To quantify these impacts on floodplain development processes, we used a model of river channel meander migration to illustrate the degree to which flow regulation and riprap impact migration rates, independently and synergistically, on the Sacramento River in California, USA. From pre-dam conditions, the cumulative effect of flow regulation alone on channel migration is a reduction by 38%, and 42-44% with four proposed water diversion project scenarios. In terms of depositional area, the proposed water project would reduce channel migration 51-71 ha in 130 years without current riprap in place, and 17-25 ha with riprap. Our results illustrate the utility of a modeling approach for quantifying cumulative impacts. Model-based quantification of environmental impacts allow scientists to separate cumulative and synergistic effects to analytically define mitigation measures. Additionally, by selecting an ecosystem process that is affected by multiple impacts, it is possible to consider process-based mitigation scenarios, such as the removal of riprap, to allow meander migration and create new floodplains and allow for riparian vegetation recruitment.PLoS ONE 01/2014; 9(6):e99736. · 3.53 Impact Factor