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Responsibility for flood risk management (FRM) is increasingly being devolved to a wider set of stakeholders, and effective participation by multiple FRM agencies and communities at risk calls for engagement approaches that supplement and make the best possible use of hydrologic and hydraulic flood modelling. Stakeholder engagement must strike a considered balance between participation ideals and the pragmatic realities of existing mechanisms for FRM decision‐making. This article evaluates the potential for using participatory modelling to facilitate engagement and co‐production of knowledge by FRM modellers, practitioners and other stakeholders. Participatory modelling offers an approach that is flexible and versatile, yet sufficiently structured that it can support meaningful representation of scientific, empirical and local knowledges in producing outcomes that can readily be integrated into existing procedures for shared decision‐making. This article frames the qualities of participatory modelling useful to FRM, as being accessible, transparent, adaptable, evaluative and holistic. These qualities are used as criteria with which to assess the practical utility of three popular participatory techniques: Bayesian networks, system dynamics and fuzzy cognitive mapping. Case studies are used to illustrate how each technique might benefit FRM options appraisal and decision‐making. While each technique has potential, none is ideal, and local contexts will guide selection of which technique is best suited to deliver effective stakeholder participation. [ABSTRACT FROM AUTHOR]

Drag forces exerted on cylindrical simulated logs by flowing water are measured in a laboratory flume. Drag coefficient values calculated from these data are presented for a range of log submergence and slenderness values. Drag coefficients for large submergence values are consistent with those previously published. However, at submergence values less than eight element diameters, the observed drag coefficients are consistently higher than those previously published. This discrepancy is due to the additional drag created by stationary surface waves which causes the drag coefficient to increase considerably when a log is positioned near the free surface. This phenomenon, which has not been accounted for in previous studies on large woody debris, is shown to depend on log slenderness, submergence, and Froude number. CE Database keywords: Surface water; Timber; Drag; Submerging.

The pattern of primary isovels, pathways of sediment transport (both bed load and suspended load), and the evolution of channel planform are all strongly affected by secondary currents. The way in which secondary currents affect channel morphology in single-thread meandering rivers is now well understood; however, to date there has been no field-based study of secondary currents in a large, sand-bedded braided river. The River Survey Project of FAP-24, Bangladesh, offered the opportunity to rectify this gap in knowledge through a joint study between the University of Nottingham, Delft Hydraulics, and the Danish Hydraulics Institute. A comprehensive set of field data, including measurements of primary and secondary velocities and channel bed topography, were taken around a braid bar in the Brahmaputra River near Bahadurabad, Bangladesh. An acoustic doppler current profiler was used to measure three-dimensional velocity profiles. The results presented here were taken from two cross sections: at the flow bifurcation upstream of the study bar and at the bend apex of the left anabranch around the study bar. The results demonstrate the presence of large-scale secondary current cells at the flow bifurcation and bend apex.

Many flood-control channels are subjected to expensive and environmentally damaging maintenance practices to control vegetation growth in attempts to preserve flood capacity. However, such maintenance regimes are often based on vague and qualitative guidelines. There is a clear need for physically based methods of predicting the impacts of vegetation growth on flow resistance and flood capacity. In the present note, a numerical hydraulic model is coupled with physically based flow-resistance equations for gravel-bed materials and vegetation roughness elements. The resulting model is capable of simulating stage-discharge curves in channels with arbitrary cross-sectional geometry, gravel-bed materials and bank, and/or floodplain vegetation, including overbank flows. The new model is demonstrated to be capable of closely replicating the stage-discharge curve at a study site on a natural river channel. Finally, the model is demonstrated using examples in which the effects on flood capacity of seasonal vegetation growth are simulated at the study site.

The ability to predict the stability of eroding riverbanks is a prerequisite for modeling alluvial channel width adjustments and a requirement for predicting bank-erosion rates and sediment yield associated with bank erosion. However, there are a number of limitations of existing bank-stability analyses that limit their physical basis and predictive ability. Some of these limitations are addressed through the development of a new bank-stability analysis. The new approach is applicable to steep, cohesive, nonlayered riverbanks that fail along planar failure surfaces. Pore-water and hydrostatic confining pressure terms are included in the analysis. The failure plane is not constrained to pass through the toe of the bank. The predictive abilities of four bank-stability analyses (Lohnes and Handy 1968; Huang 1983; Osman and Thorne 1988; and the present analysis) were assessed using field data. The new analysis is the most successful of the tested analyses in terms of predicting the stability of riverbanks with respect to mass failure.

Many existing morphological models are limited by their inability to account for changing channel width through time. In this and a companion paper, the development and testing of a numerical model of river widening are reported. The new model is applicable to straight, sand-bed streams with cohesive bank materials, and nonuniform bathymetry and width in the longitudinal direction. The flow field is obtained by solving versions of the flow resistance, flow momentum, and continuity equations, which account for the influence of gradually varied flow and lateral shear in the near bank zones. Secondary and overbank flows are excluded. Predicted flows are used to account for streamwise and transverse sediment transport fluxes. Numerical solution of the sediment continuity equation allows temporal variations in bed-material size, bed morphology, and bank geometry to be simulated. Channel widening is simulated by coupling bank stability with flow and sediment transport algorithms. A probabilistic approach is used to estimate the longitudinal extent of mass failures within modeled reaches, and mixed layer theory is used to model the transport of the resulting bed and bank material mixture. Assessment of the accuracy of the new model, discussed in the companion paper, indicates that the new model simulations of widths, depths, and deepening rates are within 15% of observed values, but widening rates are underpredicted by a factor of approximately 3.

In this paper the numerical model presented in the companion paper is tested and applied. Assessment of model accuracy was based on two approaches. First, predictions of evolution of a 13.5 km reach of the South Fork of the Forked Deer River, in west Tennessee, were compared to observations over a 24-yr period. Results suggest that although the model was able to qualitatively predict trends of widening and deepening, quantitative predictions were not reliable. Simulated widths and depths were within 15% of the corresponding observed values, but observed change in these parameters at the study sites were also close to these values. Simulated rates of depth adjustment were within 15% of observed rates, but observed rates of channel widening at the study sites were approximately three times those simulated by the model. In the second approach, the model was used to generate relationships between stable channel width and bank-full discharge. The model was able to successfully replicate the form of empirically derived regime-width equations. Simulations were used to demonstrate the model's ability to obtain more realistic predictions of bed evolution in widening channels.

The field of hydraulics should be improved because of the important role it plays in water resource management. One of the pressing issues in hydraulics is flood control. Engineers must develop measures to protect man and the environment from the negative impact of floods. A multidisciplinary approach called the Flood Action Plan (FAP) has been established as a tool for flood management. The FAP aims to reduce the damaging effects of floods by developing effective flood control and water management strategies.

Anthropogenic litter (solid manufactured waste) is an understudied but pervasive element of river systems worldwide. Its physical structure generally differs from natural substrates, such as gravel and cobbles (hereafter rocks). Consequently, anthropogenic litter could influence ecological communities in urban rivers by providing novel habitats.This study compares the macroinvertebrates recorded on anthropogenic litter with those on rocks to test whether the different substrates support distinct communities. Macroinvertebrates were collected from individual rocks and anthropogenic litter, predominantly plastic, metal, and glass, in three U.K. rivers.Macroinvertebrate communities on anthropogenic litter were consistently more diverse than those found on rocks, reflecting its greater surface complexity, but the density of macroinvertebrates was similar among substrates. The community composition also varied between substrates, with five taxa only recorded on anthropogenic litter. Community differences largely reflected greater abundances of common taxa on anthropogenic litter, which were relatively insensitive to environmental quality. Plastic and fabric anthropogenic litter communities were the most dissimilar to those on rocks, probably due to their flexibility, which could replicate the physical structure of aquatic macrophytes.Our findings indicate that anthropogenic litter supports a distinct and diverse community of macroinvertebrates in urban rivers, which are otherwise relatively homogenous in habitat structure.Removal of anthropogenic litter from urban rivers may not be beneficial for local biodiversity. Understanding the functional habitats provided by anthropogenic litter could help better manage urban rivers to replace habitat lost through urbanisation. [ABSTRACT FROM AUTHOR]

Blue‐Green Infrastructure (BGI) is recognized as a viable strategy to manage stormwater and flood risk, and its multifunctionality may further enrich society through the provision of multiple cobenefits that extend far beyond the hydrosphere. Portland, Oregon, is an internationally renowned leader in the implementation of BGI and showcases many best practice examples. Nonetheless, a range of interdisciplinary barriers and uncertainties continue to cloud decision making and impede wider implementation of BGI. In this paper, we synthesize research conducted by the "Clean Water for All" (CWfA) research project and demonstrate that interdisciplinary evaluation of the benefits of Portland's BGI, focusing on green street bioswales and the East Lents Floodplain Restoration Project, is essential to address biophysical and sociopolitical barriers. Effective interdisciplinary approaches require sustained interaction and collaboration to integrate disciplinary expertise toward a common problem‐solving purpose, and strong leadership from researchers adapt at spanning disciplinary boundaries. While the disciplinary differences in methodologies were embraced in the CWfA project, and pivotal to providing evidence of the disparate benefits of multifunctional BGI, cross‐disciplinary engagement, knowledge coproduction, and data exchanges during the research process were of paramount importance to reduce the potential for fragmentation and ensure research remained integrated. Research Impact Statement: Interdisciplinary research in Portland, Oregon USA, provides an enhanced evidence base to justify adoption of Blue‐Green Infrastructure (BGI) for sustainable flood risk and stormwater management. [ABSTRACT FROM AUTHOR]

Stephen E. Darby and Colin R. Thorne's riverbank-stability analysis is based on planar failure analysis which is no longer used by geotechnical engineers. The circular failure surface analysis is considered to be more appropriate. The application of stability charts based on a circular failure analysis is better than the planar failure analysis shown by Darby and Thorne. Moreover, the stability analyses were done only on the prefailure and postfailure geometry during low flows. This might be very different at the actual time of failure.