Flow and Transport in Regions with Aquatic Vegetation

This review describes mean and turbulent flow and mass transport in the presence of aquatic vegetation. Within emergent canopies, the turbulent length scales are set by the stem diameter and spacing, and the mean flow is determined by the distribution of the canopy frontal area. Near sparse submerged canopies, the bed roughness and near-bed turbulence are enhanced, but the velocity profile remains logarithmic. For dense submerged canopies, the drag discontinuity at the top of the canopy generates a shear layer, which contains canopy-scale vortices that control the exchange of mass and momentum between the canopy and the overflow. The canopy-scale vortices penetrate a finite distance into the canopy, δe, set by the canopy drag. This length scale segregates the canopy into two regions: The upper canopy experiences energetic turbulent transport, controlled by canopy-scale vortices, whereas the lower canopy experiences diminished transport, associated with the smaller stem-scale turbulence. The canopy-scale vortices induce a waving motion in flexible blades, called a monami.National Science Foundation (U.S.) (EAR 0309188)National Science Foundation (U.S.) (EAR 0125056)National Science Foundation (U.S.) (EAR0738352)National Science Foundation (U.S.) (OCE0751358

Hydrodynamics of vegetated channels

This paper highlights some recent trends in vegetation hydrodynamics, focusing on conditions within channels and spanning spatial scales from individual blades, to canopies or vegetation patches, to the channel reach. At the blade scale, the boundary layer formed on the plant surface plays a role in controlling nutrient uptake. Flow resistance and light availability are also influenced by the reconfiguration of flexible blades. At the canopy scale, there are two flow regimes. For sparse canopies, the flow resembles a rough boundary layer. For dense canopies, the flow resembles a mixing layer. At the reach scale, flow resistance is more closely connected to the patch-scale vegetation distribution, described by the blockage factor, than to the geometry of individual plants. The impact of vegetation distribution on sediment movement is discussed, with attention being paid to methods for estimating bed stress within regions of vegetation. The key research challenges of the hydrodynamics of vegetated channels are highlighted.National Science Foundation (U.S.) (Grant No. EAR0309188)National Science Foundation (U.S.) (EAR0125056)National Science Foundation (U.S.) (EAR0738352)National Science Foundation (U.S.) (OCE0751358

Political Entrepreneurship in the Field of Māori Sovereignty in Aotearoa New Zealand

Individual actors have the potential to shape political outcomes through creative use of opportunities. Political entrepreneurship identifies how such actors recognise and exploit opportunities, for personal or collective gain. The existing literature focuses on individuals operating within institutional settings, with less attention paid to other types of actors. In this article, I argue for an expansion of the political entrepreneurship framework, by considering individuals in the electoral and protest arenas. An examination of the field of Māori sovereignty, or tino rangatiratanga, in Aotearoa New Zealand allows exploration of prominent actors’ innovative strategies and practices. The findings highlight the actors’ reliance on identity in mobilising support within the community, to press claims. Broadening the application of political entrepreneurship demonstrates the roles of social, cultural and political capital in influencing outcomes, by identifying opportunities available to individuals embedded in the community and according to the context of the arena

Effects of aquatic and bank-side vegetation on hydraulic performance of small streams

We consider effects of bed and bank-side vegetation on hydraulic resistance of small streams, and develop simple quantitative relationships for predicting and quantifying these effects using the normalized plant characteristics. We conducted two field studies to explore effects of submerged aquatic and bank-side vegetation on stream hydraulics. In the first study, we examined the effects of aquatic plant biomass, stature and architecture on hydraulic conditions in five small streams representing a range of channel dimensions, flows and aquatic plant assemblages. In the second field study, we created experimental floods in a small stream to examine the effects of submerged bank-side vegetation on hydraulic conditions. The results of the studies and the relationships presented in the paper may be used to provide initial estimates of resistance coefficients for hydraulic modelling, predicting effects of aquatic weed management and bank-side planting on flood levels, and designing naturalisation and enhancement projects for small streams

Hydraulic Resistance due to Aquatic Vegetation in Small Streams: Field Study

This technical note examines vegetation effects on hydraulic resistance in small streams and suggests simple quantitative relationships for predicting and quantifying these effects using the plant characteristics with the greatest explanatory power. In particular, we examine the effects of aquatic plant biomass, stature, and architecture on hydraulic performance of five New Zealand streams representing a wide range of channel dimensions, flows, aquatic plant species, and assemblages. Comparisons among the vegetation parameters indicated that ratios of the site-averaged canopy height to the mean flow depth and of the site-averaged plant length to the mean flow depth were the best roughness descriptors. Effects of individual plant species and their characteristic patch patterns were not significant. The data from all sites collapsed around single lines, suggesting that general physical parameters of vegetation should be the primary determinants of hydraulic resistance in streams studied, not species-specific parameters, as often assumed