Flow hydrodynamics across open channel flows with riparian zones: implications for riverbank stability

Riverbank vegetation is of high importance both for preserving the form (morphology) and function (ecology) of natural river systems. Revegetation of riverbanks is commonly used as a means of stream rehabilitation and management of bank instability and erosion. In this experimental study, the effect of different riverbank vegetation densities on flow hydrodynamics across the channel, including the riparian zone, are reported and discussed. The configuration of vegetation elements follows either linear or staggered arrangements as vegetation density is progressively increased, within a representative range of vegetation densities found in nature. Hydrodynamic measurements including mean streamwise velocity and turbulent intensity flow profiles are recorded via acoustic Doppler velocimetry (ADV)—both at the main channel and within the riverbank. These results show that for the main channel and the toe of riverbank, turbulence intensity for the low densities (λ ≈ 0 to 0.12 m−1) can increase up to 40% compared the case of high densities (λ = 0.94 to 1.9 m−1). Further analysis of these data allowed the estimation of bed-shear stresses, demonstrating 86% and 71% increase at the main channel and near the toe region, for increasing densities (λ = 0 to 1.9 m−1). Quantifying these hydrodynamic effects is important for assessing the contribution of physically representative ranges of riparian vegetation densities on hydrogeomorphologic feedback

Predicting wind turbine blade loads using vorticity transport and RANS methodologies

Two computational methods, one based on the solution of the vorticity transport equation, and a second based on the solution of the Reynolds-Averaged Navier-Stokes equations, have been used to simulate the aerodynamic performance of a horizontal axis wind turbine. Comparisons have been made against data obtained during Phase VI of the NREL Unsteady Aerodynamics Experimental and against existing numerical data for a range of wind conditions. The Reynolds-Averaged Navier-Stokes method demonstrates the potential to predict accurately the flow around the blades and the distribution of aerodynamic loads developed on them. The Vorticity Transport Model possesses a considerable advantage in those situtations where the accurate, but computationally efficient, modelling of the structure of the wake and the associated induced velocity is critical, but where the prediction of blade loads can be achieved with sufficient accuracy using a lifting-line model augmented by incorporating a semi-empirical stall delay model. The largest benefits can be extracted when the two methods are used to complement each other in order to understand better the physical mechanisms governing the aerodynamic performance of wind turbines

Sudden Floods, Prudential Regulation and Stability in an Open Economy

We develop a dynamic stochastic model of a middle-income, small open economy with a two-level banking intermediation structure, a risk-sensitive regulatory capital regime, and imperfect capital mobility. Firms borrow from a domestic bank and the bank borrows on world capital markets, in both cases subject to an endogenous premium. A sudden flood in capital flows generates an expansion in credit and activity, and asset price pressures. Countercyclical regulation, in the form of a Basel III-type rule based on real credit gaps, is effective at promoting macroeconomic stability (defined in terms of the volatility of a weighted average of inflation and the output gap) and financial stability (defined in terms of the volatility of a composite index of the nominal exchange rate and house prices). However, because the gain in terms of reduced volatility may exhibit diminishing returns, a countercyclical regulatory rule may need to be supplemented by other, more targeted, macroprudential instruments.