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SUMMARYNumerical methods have become well established as tools for solving problems in hydraulic engineering. In recent years the ÿnite volume method (FVM) with shock capturing capabilities has come to the fore because of its suitability for modelling a variety of types of ow; subcritical and supercritical; steady and unsteady; continuous and discontinuous and its ability to handle complex topography easily.This paper is an assessment and comparison of the performance of ÿnite volume solutions to the shallow water equations with the Riemann solvers; the Osher, HLL, HLLC, ux di erence splitting (Roe) and ux vector splitting. In this paper implementation of the FVM including the Riemann solvers, slope limiters and methods used for achieving second order accuracy are described explicitly step by step. The performance of the numerical methods has been investigated by applying them to a number of examples from the literature, providing both comparison of the schemes with each other and with published results. The assessment of each method is based on ÿve criteria; ease of implementation, accuracy, applicability, numerical stability and simulation time. Finally, results, discussion, conclusions and recommendations for further work are presented.

(2014) 'Experimental investigation into the impact of a liquid droplet onto a granular bed using three-dimensional, time-resolved, particle tracking.', Physical review E., 89 (3). 032201.Further information on publisher's website:http://dx.doi.org/10.1103/PhysRevE.89.032201Publisher's copyright statement:Reprinted with permission from the American Physical Society: Physical Review E 89, 032201 c 2014 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. An experimental investigation into the interaction that occurs between an impacting water droplet and a granular bed of loose graded sand has been carried out. High-speed imaging, three-dimensional time-resolved particle tracking, and photogrammetric surface profiling have been used to examine individual impact events. The focus of the study is the quantification and trajectory analysis of the particles ejected from the sand bed, along with measurement of the change in bed morphology. The results from the experiments have detailed two distinct mechanisms of particle ejection: the ejection of water-encapsulated particles from the edge of the wetted region and the ejection of dry sand from the periphery of the impact crater. That the process occurs by these two distinct mechanisms has hitherto been unobserved. Presented in the paper are distributions of the particle ejection velocities, angles, and transport distances for both mechanisms. The ejected water-encapsulated particles, which are few in number, are characterized by low ejection angles and high ejection velocities, leading to large transport distances; the ejected dry particles, which are much greater in number, are characterized by high ejection angles and low velocities, leading to lower transport distances. From the particle ejection data, the momentum of the individual ballistic sand particles has been calculated; it was found that only 2% of the water-droplet momentum at impact is transferred to the ballistic sand particles. In addition to the particle tracking, surface profiling of the granular bed postimpact has provided detailed information on its morphology; these data hav...

Hydrological catchments today are largely the product of human activity. They have been engineered. The negative impacts of some of this engineering such as deforestation and agriculture intensification need to be addressed but the solution is not simply a matter of doing the opposite, for example through afforestation or moving to less-intensive farming. We propose a catchment systems engineering (CSE) approach that utilizes and expands on existing catchment-based approaches, combining interventions that work with or mimic natural processes with traditional "hard" engineering to provide a practical route to improved catchment function. The approach is predicated on the need to take an holistic view of catchments and to make proactive interventions that provide and enhance multiple ecosystem services. CSE seeks to address problems that are international in scope, recognizing the need to understand better how hydrological processes have changed due to human activity and how those changes influence frequency, duration, and severity of environmental problems such as floods, droughts, and poor water quality. The emphasis is placed on how we can act to engineer catchment systems to a safer functionally appropriate level utilizing measures such as nature-based solutions alongside traditional engineering structures. CSE is the means to provide multiple ecosystem services while recognizing trade-offs between reducing flood and drought risk directly, improving water quality and creating healthy habitats for wildlife. By targeting local hydrological flow pathways in defined spatial and temporal windows (e.g., during rainfall events at key locations such as riparian zones), CSE can deliver holistic water resource management now.

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A generic Nutrient Export Risk Matrix (NERM) approach is presented. This provides advice to farmers and policy makers on good practice for reducing nutrient loss and is intended to persuade them to implement such measures. Combined with a range of nutrient transport modelling tools and field experiments, NERMs can play an important role in reducing nutrient export from agricultural land. The Phosphorus Export Risk Matrix (PERM) is presented as an example NERM. The PERM integrates hydrological understanding of runoff with a number of agronomic and policy factors into a clear problem-solving framework. This allows farmers and policy makers to visualise strategies for reducing phosphorus loss through proactive land management. The risk of pollution is assessed by a series of informed questions relating to farming intensity and practice. This information is combined with the concept of runoff management to point towards simple, practical remedial strategies which do not compromise farmers ability to obtain sound economic returns from their crop and livestock.

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