Mathematical modelling of shallow flows: closure models drawn from grain-scale mechanics of sediment transport and flow hydrodynamics

Canadian Journal of Civil Engineering 36(10) 1605–16Mathematical modelling of river processes is, nowadays, a key element in river engineering and planning. River modelling tools should rest on conceptual models drawn from mechanics of sediment transport, river mechanics, and river hydrodynamics. The objectives of the present work are (i) to describe conceptual models of sediment transport, deduced from grain-scale mechanics of sediment transport and turbulent flow hydrodynamics, and (ii) to present solutions to specific river morphology problems. The conceptual models described are applicable to the morphologic evolution of rivers subjected to the transport of poorly sorted sediment mixtures at low shear stresses and to geomorphic flows featuring intense sediment transport at high shear stresses. In common, these applications share the fact that sediment transport and flow resistance depend, essentially, on grain-scale phenomena. The idealized flow structures are presented and discussed. Numerical solutions for equilibrium and nonequilibrium sediment transport are presented and compared with laboratory and field data

Turbulence in Rivers

The study of turbulence has always been a challenge for scientists working on geophysical flows. Turbulent flows are common in nature and have an important role in geophysical disciplines such as river morphology, landscape modeling, atmospheric dynamics and ocean currents. At present, new measurement and observation techniques suitable for fieldwork can be combined with laboratory and theoretical work to advance the understanding of river processes. Nevertheless, despite more than a century of attempts to correctly formalize turbulent flows, much still remains to be done by researchers and engineers working in hydraulics and fluid mechanics. In this contribution we introduce a general framework for the analysis of river turbulence. We revisit some findings and theoretical frameworks and provide a critical analysis of where the study of turbulence is important and how to include detailed information of this in the analysis of fluvial processes. We also provide a perspective of some general aspects that are essential for researchers/ practitioners addressing the subject for the first time. Furthermore, we show some results of interest to scientists and engineers working on river flows

Geomorphic dam-break flows. Part I: conceptual model

Proceedings of the Institution of Civil Engineers - Water Management 163 Issue WM6This paper presents a one-dimensional conceptual model for simulating geomorphic dam-break flows. The model is based on conservation laws drawn from continuum mixture theory that are integrated over the flow depth,assuming that the f10w is composed of two transport layers. Closure equations were derived from the review and reanalysis of previous studies on granular flow,debris f10w and sheet flow. The sediment transport is modelled assuming capacity regime. The c10sure equation coefficients are estimated based on a large set of experiments available in the literature. The validity of the model is discussed by computing the most relevant dimensionless parameters. The model is expected to simulate adequately the friction at the wave front and the sheet flow throughout the wave profile. Ultimately, although the problem incorporates complex phenomena,the model can be easily implemented by practising engineers for simulating one- dimensional geomorphic dam-break flows. The implementation and the verification of the adequacy of the model for simulating these flows are presented in a 'companion paper

Geomorphic dam-break flows. Part I: conceptual model

Proceedings of the Institution of Civil Engineers - Water Management 163 Issue WM6This paper presents a one-dimensional conceptual model for simulating geomorphic dam-break flows. The model is based on conservation laws drawn from continuum mixture theory that are integrated over the flow depth,assuming that the f10w is composed of two transport layers. Closure equations were derived from the review and reanalysis of previous studies on granular flow,debris f10w and sheet flow. The sediment transport is modelled assuming capacity regime. The c10sure equation coefficients are estimated based on a large set of experiments available in the literature. The validity of the model is discussed by computing the most relevant dimensionless parameters. The model is expected to simulate adequately the friction at the wave front and the sheet flow throughout the wave profile. Ultimately, although the problem incorporates complex phenomena,the model can be easily implemented by practising engineers for simulating one- dimensional geomorphic dam-break flows. The implementation and the verification of the adequacy of the model for simulating these flows are presented in a 'companion paper

Geomorphic dam-break flows. Part II: numerical simulation

Proceedings of the Institution of Civil Engineers - Water Management 163 Issue WM

Current status and management of coffee leaf rust in Brazil

In Brazil, coffee leaf rust, a fungal disease caused by Hemileia vastatrix Berk. et Br., was first detected in Coffea arabica in January 1970, in the southern region of Bahia state. Today, the disease is present in virtually all arabica and conilon (Coffea canephora) coffee-growing areas of Brazil, and continues to threaten coffee production with losses that range from 30 to 50 %. The disease is usually less severe at elevations above 1,200 m, where the environment is less conducive for the rust. Disease risk is increased in arabica coffee compared to conilon, and lower production is expected in the year following an epidemic due to early defoliation and drying of branches. Several varieties were developed in the country using sources of resistance from germplasm collections in Portugal. However, very few are completely resistant, instead exhibiting various levels of partial resistance. The disease is currently managed through the use of protectant and systemic fungicides including copper, triazoles and strobilurins that should be applied following rules of decision that vary according to the risk scenario. A review of the biology and epidemiology of coffee rust in Brazil is presented and the best management practices for controlling the disease based on advances in breeding for resistance and crop protection are discussed