Editorial

Abstract

By the end of the nineteenth century the first hydraulic laboratories had been established, mostly in the current technical universities. Physical modelling allows insight into the complex interactions between water flow and hydraulic structures. Hydraulic physical modelling became an effective support tool in solving complex hydraulic problems. Results from model tests acted as a driving force for further theoretical developments of analytical and later also numerical methods. Today the development of mathematical models and numerical simulations, as a cheaper and faster approach, decreases the significance of hydraulic laboratory tests but cannot fully substitute for physical modelling. Physical modelling is still used in solving very complex problems and in the verification of new developed mathematical and numerical models. Mathematical models often need input parameters that can only be determined through physical modelling. Therefore, both physical modelling in hydraulic laboratories and mathematical and numerical models are complement and irreplaceable in practical design and research work in hydraulic engineering today. This issue of Water Management illustrates the implementation of experimental and numerical methods and their combinations in solving typical hydraulic problems.Two papers in this issue discuss local scour around bridge piers, including interference of water flow, structure and river bed sediments. Local scour is often a reason for bridge collapse and is therefore also a topic with great public interest. The problem of scouring is a complex topic dependent on a large number of parameters. These different parameters are discussed in the first two papers.The paper by Chreties et al. (2013) presents the influence of flow conditions on local scour around pier groups. The authors chose physical modelling and concentrate their research on equilibrium scour depth with 'no memory' effect -scour depth does not depend on the flow conditions used to obtain the actual scour state. The results confirm that sediment characteristics are the most dominant factor defining form and depth of the scour hole.The experimental results also demonstrate that the 'no memory' hypothesis is valid for pier groups where the pier cap does not interfere with the flow.The second scour paper (Dehghani et al., 2013) is a detailed study of scouring around bridge piers under unsteady flow conditions. The authors chose to use a three-dimensional numerical model, combining Navier-Stokes equations and the sediment continuity equation. In the study, stepwise defined hydrographs with different peak discharges and period shapes were used, simulating timedependent scour development around a circular pier. The suggested numerical procedure provides good agreement with scour depth measured in the experiment and could be applied to assess scour development in real flood, unsteady state, conditions. The paper by Wallerstein and Arthur (2013) deals with the estimation of trash screen blockage by organic and manmade debris. More than 100...