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Flow field in shallow waters, which is characterized by its complex mixing process and inherent dynamic nature, is interesting mainly due to its practical importance (e. g. in free flushing operation and sedimentation in large reservoirs). 3D numerical models make it possible to track two-dimensional large turbulence coherent structures, which are the dominant phenomenon in shallow reservoirs flow field. In the present study a fully three-dimensional numerical model SSIIM that employs the Finite Volume Approach (FVM) was utilized to reproduce the 3D flow field. Various shallow reservoir geometries with fixed and deformed equilibrium bed were considered. The measurements by Large-Scale Particle Image Velocimetry techniques (LSPIV) and Ultrasonic Doppler Velocity Profiler (UVP) over the flow depth were used for model validation. Outcomes revealed reasonable agreement between the simulated and measured flow velocity field even when an asymmetric flow pattern exists in the reservoir.

River widening is commonly used as a solution for the rehabilitation of rivers with the main purposes of allowing the river to adjust to its natural dynamics and to improve riparian and instream habitat for flora and fauna, by increasing the heterogeneity in substrate, flow and morphology. Local widening may also be used for confluences rehabilitation as, for many of them, the heterogeneity and fragmentation of the river system were severely affected by previous human interventions. Local tributary widening amplifies the morphodynamic processes, enhancing the diversity in sediment substrate, flow velocities and flow depths. In addition, widening should neither affect aspects such as water level in the tributary nor in the main channel, which is an important consideration for flood safety. The aim of this paper is to analyze the differences in terms of bed morphology and flow dynamics induced by different confluence angles in widen channel confluences.

The trap efficiency of a shallow reservoir depends on the characteristics of the inflowing sediments and the retention time of the water in the reservoir, which in turn are controlled by the reservoir geometry. With the purpose of controlling the trapped and flushed sediments in shallow reservoirs, the effects of the geometry on sediment deposition and removal were investigated with systematic physical experiments. The geometry shape factor is an important factor to predict the flow and sediment deposition in the reservoir. The evolution of trap efficiency has an increasing or decreasing effect according to the geometry shape factor and flow patterns. The channel formed during flushing attracts the jet and stabilizes the flow structures over the entire reservoir. Empirical formulas to describe the relationship between the geometry shape factor and sediment trap efficiency as well as flushing efficiency were developed.

One of the common measures for river bank protection is the installation of riprap. There are several methods to design riprap appropriately, which are however generally limited to dumped medium size blocks. Nevertheless, an additional resistance against erosion can be achieved by individually placing blocks in one or several layers instead of dumping them arbitrarily. An experimental investigation has thus been performed to study the stability of large blocks which are compressed as a river bank protection. Tests were carried out including one layer of stones as well as two layers, to evaluate the influence of the riprap layering (e.g. riprap thickness) on the bank stability. The effect of the thickness on the stability of ripraps is investigated in a 10 m long and 1.2 m wide tilting flume, with a rough fixed bed. Riprap median particle size was D50 = 37 mm. Testing was conducted for channel longitudinal slopes 0.015 and 0.030 and riprap bank inclinations of 27, 31 and 35 degrees. The riprap was installed on the top of a wide grain size distribution filter. Supercritical flow conditions were considered, given the steep channel slope. The complete removal of the riprap in a section under a constant discharge was defined as the failure criterion. The riprap failure threshold discharge was determined based on the series of tests with duration of maximum 180 minutes. In each test, riprap transport rate was measured every minute while the stones were tracked by a video camera and collected in a sediment trap at the channel end. The time of total failure was defined by standard video-image processing techniques. A time based analysis of failure was performed and first results revealed that, for similar conditions, the second layer stabilizes the riprap significantly and delays the time for total failure. Nonetheless, transport rate was found to be increased in this latter situation.

The Klingnau reservoir, situated in north Switzerland, suffers from sedimentation in its left enlargement. The dam is placed in the Aare River about 1 km upstream of its confluence with the Rhine. Due to natural conservation and flood protection reasons, it has been sought for decades to slowdown the sedimentation process in the reservoir. For this purpose, 20’000 m3 of deposited material will be excavated by suction dredge and injected downstream into the Rhine. The objective of the present study is firstly to spot the best place for the material injection downstream. It is then aimed to assure that this injected material will not deposit along the Rhine River down to the Birsfelden dam. The latter is situated 60 km downstream of Klingnau and is the last reservoir on the Rhine River in Swiss territory. To accurately simulate the sedimentation process, one and two-dimensional numerical models are applied. It is confirmed that the majority of injected material stays in suspension and can be transported through the Rhine River down to Birsfelden.

Most sediment transport equations overestimate the bedload transport rate by several times when applied to mountain rivers. This is due to the fact that the presence of large relatively immobile boulders, which disrupt the flow, is generally not taken into account. Sediment transport in steep channels with boulders was herein investigated using 41 laboratory experiments carried out on a tilting flume for three slopes (S = 6.7%, 9.9%, and 13%). Sediment transport, mean flow velocities and morphology-describing variables were measured regularly during the experiments. The sediment transport capacity is clearly decreasing with dimensionless boulder distance and is better estimated in terms of critical discharge for incipient motion of mobile sediments than in terms of bed shear stress. A sediment transport formula based on excess discharge relative to a critical value, which depends not only on the channel slope but also on the boulder spatial density, is herein developed.

In-stream vegetation is a dominant influence on water and sediment conveyance, flow velocities and three-dimensional flow structure in lowland rivers during spring and summer. In order to maintain key river functions, weed management practices are employed in many parts of the world. The primary aim of the research reported in this paper is to improve understanding of the effect of weed management practice on flow variables using a Three-Dimensional (3D) finite-volume model, applied before and after weed cutting. The model developed is based on the double-averaging methodology i.e. Double-Averaged continuity and Navier-Stokes equations (DANS), which includes drag terms, form-induced momentum fluxes, blockage (porosity) and turbulence effects due to both the gravel river-bed and in-stream vegetation. The work was carried out on a 105 m reach of the River Lambourn at Boxford, UK. The model predictions of velocity and turbulent kinetic energy are used to investigate the flow behaviour throughout the reach both before and after weed cuts. Model performance is assessed by comparing the predicted results with measured data. The results show the ability of the model to capture the spatially–averaged flow field in gravel-bed rivers dominated by in-stream vegetation.

Can a direct hydraulic jump also be generated if the surface roller is substituted with a corresponding inset? This and related questions are considered in the note, to understand the role of the roller. Based on recent findings relating to the classical hydraulic jump, its modification using bottom and surface insets is reconsidered using laboratory experimentation. The results of these tests are reported below using mainly photography and basic hydraulic computations. It is further demonstrated that the roller may not be separated from the hydraulic jump in a free surface arrangement. This would greatly simplify observations, because the standard two-phase flow including an air-water mixture flow would become a one-phase flow consisting of only water flow. The implications of this result are discussed. This work has exploratory character and should stimulate a further discussion on the main flow features of direct hydraulic jumps. © 2010 International Association for Hydro-Environment Engineering and Research.

This paper recommends design considerations in order to prepare the Assault Variant for urban warfare. The future battlefield will be the urban arena. Underdeveloped countries are producing vast urban slums at an alarming rate. Suspended in underprivileged conditions such as poverty, starvation, and disease, this class will seek change through radical means creating regional crisis. With the United States politically and economically engaged throughout the globe, such a crisis may threaten U.S. interests requiring a military response. Additionally, our adversaries realize the futility in challenging the U.S. military on open, unrestricted ground; therefore, they will seek to degrade U.S. abilities in the restrictive terrain of cities. Though designed for long range, direct fire engagements, history has shown that tanks have excellent utility in urban fighting. This has been proven again during recent experiments designed to create effective urban tactics. The MEEEV Program's Assault Variant will replace the premier capabilities of the M1A1 Main Battle Tank in the year 2020. The Assault Variant's design supports the concepts within Expeditionary Maneuver Warfare - Seabasing, Ship to Objective Maneuver, and Sustained Operations Ashore - creating a smaller, lighter, and more logistically efficient design. Of concern is that this design is not appropriate for fighting in urban areas. Conclusion: in order to prepare the Assault Variant for likely urban warfare, this paper offers sensible urban-minded recommendations to the Assault Variant's firepower, protection, mobility, and command and control systems, as well as its training regimen.

Standards and Applications of an Ecosystem Diversity Framework