Special Issue on River Flow Hydrodynamics: Physical and Ecological Aspects

Abstract

As part of the celebration in Minneapolis on May 19–21, 2008, of the 70th year since the St. Anthony Falls Laboratory was first dedicated on November 17, 1938, a minisymposium on the topic of stream restoration fluid mechanics was organized within the inaugural conference of ASCE’s Engineering Mechanics Institute. Ten papers are included in this special issue representing contributions that were made to this minisymposium as well as manuscripts that were solicited from other authors in an effort to expand coverage of the subject. This issue provides the opportunity to review the progress that has been made in some areas of modeling river flow hydrodynamics, with emphasis on physical and ecological aspects. The issue begins with two papers dealing with in-stream structures, including those used for flow training and those that serve as bridge foundations, and their potential effects on river behavior. The first paper, “River Training and Ecological Enhancement Potential Using In-Stream Structures” by Radspinner et al., provides a review of the available literature and engineering design experience. Cross vanes, J-hook vanes, rock vanes, W-weirs, submerged vanes, stream barbs, bendway weirs, spurs, and constructed riffles, which represent the most commonly used instream flow control structures, are considered. Survey results obtained from federal and state agency personnel indicate that in terms of cost, performance, maintenance, and environmental enhancement, in-stream structures are preferable to riprap revetment, dredging, and concrete. Results from case studies and discussions with practitioners highlight the need for better-defined guidelines for the design of these structures. In their paper “Coherent Structure Dynamics in Turbulent Flows Past In-Stream Structures: Some Insights Gained via Numerical Simulation,” Paik et al. review the latest developments in the use of hybrid unsteady Reynolds-averaged Navier-Stokes/large-eddy simulation URANS/LES modeling strategies for simulating turbulent flows around in-stream structures. These computational fluid dynamics CFD techniques are capable of resolving coherent structures, such as the turbulent horseshoe vortex past bed-mounted piers, for a wide range of Reynolds number flows and thus of capturing some intricate aspects of the flow field and associated scour in the vicinity of hydraulic structures. Furthermore, the capability of modeling such structures at ecologically relevant scales is crucial for the development of improved stream restoration designs. The issue continues with a group of three papers that focus on the flow through vegetation hydrodynamics and nutrient uptake in streams. The first of these papers, “Effects of Added Vegetation on Sand Bar Stability and Stream Hydrodynamics” by Rominger