Environmental Hydraulics

Abstract:

This Volume arose from XXVI International School of Hydraulics held at Bartlowizna Leisure and Training Center at GoniÄ…dz, Poland, in the period of 19-22 September 2006. The meeting attracted a group of both – top researchers mostly from around Europe, and young scientists.

Abstract:

The roughness geometry function of the interfacial sublayer of a gravel-bed armour layer was measured directly by filling water stepwise into a laboratory flume and indirectly from a digital elevation model (DEM) of the surface. The results of both methods are compared and show that the DEM can be used to reliably estimate the roughness density function for a wide range of the interfacial sublayer. The direct measurements revealed an absolute minimum of porosity at the level of the roughness trough which is significantly smaller than porosity in the undisturbed subsurface and porosity estimates obtained from relationships found in the literature. The significance of the results for hydraulic engineering and ecological applications is highlighted.

Abstract:

The paper addresses the expanded mathematical models (equations) of both conservative and organic (reactive) contaminant transport in a groundwater stream. These models include, except the advection and dispersion processes, both the source (negative) term of reversible sorption and the term of radioactive decay or biodegradation. The term of reversible sorption can be described by linear or non-linear adsorption (desorption) isotherms in relation to statics of this process, whereas the term of radioactive decay or biodegradation can be described by the first-order irreversible rate reactions for the reactive solutes flowing in ground medium.

Abstract:

The numerical solution of two-dimensional advection equation on the irregular curvilinear grid is considered. The simple upstream differencing scheme and TVD (Total Variation Diminishing) schemes are compared. The test solution for rotation of two-dimensional scalar field in the Cartesian and curvilinear coordinates is numerically realized. It was concluded that the results of modeling in both coordinate systems are identical.

Abstract:

The transport of suspended sediment in open channel flows is the key issue of the area of fluvial hydraulics. Traditionally, in classical hydraulics, the phenomenon is analyzed as a one-phase composite system. This paper deals with three different models to calculate the vertical distribution of suspended sediment concentration in open channel flows. These models, i.e. the classical one and two new models are briefly presented. The numerical simulations of the vertical sediment transport using these models are presented and main differences are discussed.

Abstract:

New three-dimensional numerical non-hydrostatic model with a free surface that was designed for modelling the bottom and bank stability subjected by ship propeller jets is presented. Unlike all known models, it describes threedimensional fields of velocities generated by ship propellers, turbulence intensity and length scale in the given domain of arbitrary bottom and coastal topography. Results of simulations are compared with the laboratory experiments.

Abstract:

We report the results of laboratory experiments on water heating/cooling, performed in 5 m long water channel with a slope. About 63 series of photos were analyzed: for 3 locations, for 3 bottom slopes (3.7, 6.7 and 12 degrees) and for different Ra numbers. It was pointed out that there exist two types of mixing characterizing different circulations in the presence of slope: gravity current and undersurface jet; the thermal bar is the region where one type of mixing is replaced by another; the highest speed and flowrate are at the break point; the flow is three-dimensional.

Abstract:

Flow in rivers and on floodplains is complex as it is affected by several interconnected factors such as topography, sediment transport and vegetation characteristics. The resulting processes are explained by the measure “Hartheim” planned for retention purposes at the Upper Rhine river. On the basis of existing formulas and instruments it is demonstrated that a good estimation of the development of the measure is possible. The proposed procedure is a useful tool for estimating morphological developments of restored river sections.

Abstract:

Ecological and eco-touristic importance and the problems of conservation of natural lands around Choghakhor Wetland, located in the Chahar Mahal and Bakhtiari province of Iran, the habitat of many immigrant bird and aquatic creatures, were the main topics of this study; the importance of providing an environmental planning and management plan for this wetland is emphasized. In order to determine priorities according to the status of Choghakhor Wetland, in comparison to the 75 important wetlands of Iran (63 of these have been registered in the Ramsar Convention documents), the five criteria (birds, fish, threatening factors, social-economic problems and conservation status) of the wetland were studied and analyzed, and the macro-invertebrate benthos, including Oligochaeta, Chironomidae and Gammaridae, was surveyed. For Choghakhor Wetland, the result was 80/140, so this wetland got the 8th priority among all other ones. In fact, this classification shows the potential strength of Choghakhor Wetland to have environmental management plan. The results of this study make it clear that construction of a dam is the strongest threatening factor to this habitat and its biodiversity. This clearly shows the necessity of environmental planning and management to assess the impacts in order to establish proper management and wise use of the wetland.

Abstract:

An automatic calculation of eddy viscosity fields for 2-D horizontal hydrodynamic model of Szczecin Bay is discussed. Two methods for turbulent diffusion coefficients are applied – Peclet formula and Smagorinski model. Both are used for steady flow simulations on FEM network in Szczecin Bay. The results of simulation indicate some strength of Smagorinski model over Peclet one in terms of flexibility for describing complex flow conditions. Also mixed formulation has brought interesting results concerning presence of eddy vorticity.

Abstract:

The spread of a passive contaminant in an open-channel reach is considered with use of a two-dimensional advection-diffusion equation with the offdiagonal dispersion coefficients included. This paper presents the calculation of truncation errors, namely numerical diffusion and numerical dispersion for various finite-difference schemes. The accuracy of the considered finite-difference approximations is analysed by deriving and studying the relevant modified partial differential equation.

Abstract:

This paper presents a flood risk analysis of the Warsaw reach of the Vistula river (Poland). We argue that any model of urban area has to be evaluated and calibrated using local performance as well as global measures.
   In this particular flooding estimation problem, the main challenge lies in the very limited amount of available calibration data. This was overcome by an extensive survey of the river channel and floodplains geometry and application of a model with a simplified flow dynamics description, corresponding to the scarcity of data.
   Calibration of the model is based on observed water levels during the flood event in July 1997. Simulations are performed for 10 different events with a specified value of probability of reoccurrence (including uncertainties) estimated by the Institute of Meteorology and Water Management in Warsaw. By combining information about model uncertainties and event occurrence probabilities, it was possible to produce a spatially distributed uncertainty of prediction of water levels along the river reach.

Abstract:

The study presents the results of hydraulic overfall calculations regarding selected weirs. Calculations were carried out with traditional formulas using appropriate discharge coefficients. Then, they were compared with the results of numerical calculations regarding the same devices, treated as a special kind of cross section with an appropriately selected Manning’s roughness coefficient. The analysis presented regards overfalls in the submersion conditions, which allows for calculation of non-uniform motion in subcritical flow conditions. Possibility of simplifying the structure of the numerical overfall model presented in the study by means of maintaining the continuity of the algorithm is of significant importance while carrying out hydraulic calculations of a developed flow section.

Abstract:

In the paper, the analysis of possible causes of embankment failure of Staw Starzycki reservoir located on the Czarna-Bielina river in Tomaszów Mazowiecki is presented. This event happened in March 2005. The hydrological conditions generating the increase of inflow to the reservoir were analysed. On the basis of geological–engineering recognition of embankment body and foundation soil in failure cross-section, the simulation of embankment washout process with determination of final breach parameters and outcome outflow hydrograph were carried out, and compared with the real state. A summary pointing out the direct cause of embankment failure is given.

Abstract:

During winters in Poland, lakes, ponds, rivers, channels, run-of-reservoirs, ditches and streams are covered with ice, which changes significantly the flow and thermal conditions in water bodies. The paper presents a very complicated process of ice formation on stagnant and flowing waters. Various kinds of ice are described together with their consequences for flow and thermal conditions. The possibility to define flow conditions in open channels with ice cover is described. In 1982, a significant flood on WÅ‚ocÅ‚awek Reservoir (Lower Vistula River) appeared, which was caused by the coincidence of unfavourable, extreme hydrological and meteorological conditions. These conditions, as well as the run and consequences of the flood, are described. Detailed field measurements of ice cover and flow were carried out. One-dimensional model for steady nonuniform flow was developed and applied to the conditions existing in 1982 on the WÅ‚ocÅ‚awek Reservoir.

Abstract:

In the present work, the authors turned special attention to bed changes in a river section below hydro-technical structures. To analyse the sediment transport, the authors used a mathematical model taking into account the twodimensional transport. This model was constructed based upon the balance of sediment streams for an elementary volume along the river and diffusion character of the lateral sediment stream. In the paper, the authors present the verification of mathematical model for a straight section of the river. Geometry and hydraulic parameters of the river section were taken after the field measurements based on the Odra river between train and road bridges near to the town KostrzyÅ„.

Abstract:

This paper presents preliminary results from a study considering the parameterisation of coarse-grid 2D flood models to take into account sub-grid scale flow patterns occurring in the urban area. A simulation of a severe flood in an urbanized coastal floodplain is first run using a fine grid that can resolve the flow around and between buildings. Next, the same model is run again using the same underlying topography, although stripped from any buildings, and a set of 7 values of the roughness parameter (Manning’s n), all larger than (or equal to) the value used in the original run. A further set of simulations is carried out using a five-fold increased grid cell size. It is found that while it may be possible to model the overall effects of the buildings using strongly increased roughness parameter values, using a coarse grid otherwise has implications related to the loss of information about the site topography that results in flood flow routes being incorrectly modelled.

Abstract:

Hydrodynamics of aquatic ecosystems is a relatively new, emerging multidisciplinary research area dealing with two key inter-connected issues: (i) physical interactions between flow and organisms (e.g., due to drag forces); and (ii) ecologically relevant mass-transfer-uptake processes (e.g., due to molecular and turbulent diffusion). Owing to physical and biological complexity of boundary conditions in aquatic systems, the conventional hydraulic methodologies are often impracticable and new approaches are required. One of such approaches, the double-averaging methodology, is discussed with particular focus on flows over biologically-modified beds.

Abstract:

The paper presents results of numerical study of flow around a cylindrical pier. Flow complexity with various turbulent flow objects is described: downflow at the upstream side of a pier, horseshoe vortex and vertical wake vortices. The flow model, large-eddy simulation, is formulated on the basis of Navier-Stokes equations. Finite volume method is used for discretization. Second order finite difference schemes were used for equations approximation. A discrete particle motion model was formulated for spherical mass particles. The model allows for interaction between flow and particles. The study resulted in particle  trajectories around a cylindrical pier with a developed scourhole. It indicates that some of the bed particles are caught by strong jet directed towards the surface. The jet is bounded and driven by vertical wake vortices.

Abstract:

Sopot, one of the most renowned recreational cities in Poland, located at the Gulf of GdaÅ„sk coast, is cut by a number of streams collecting the rain water from the moraine hill surrounding the city, and discharging it directly into the sea. The quality of water, due to passage through the urbanized area, is often below required standards, especially due to bacteria pollution. At present, the rain water is discharged directly on the sandy beaches, and in case of high pollution, causes problems for the coastal zone; sometimes it is necessary to close beaches for recreation. The local administration considers re-location of the outfalls seaward to solve the problem. To assess the consequences of the proposed investment, numerical modeling was carried out. The new situation becomes more complicated due to potential construction of the yachts harbor attached to the existing pier. Numerical tests will support the decision to be made.

Abstract:

Numerical algorithm of high accuracy was developed for simulation of rapidly changing unsteady flow in an open channel of arbitrary shape. The algorithm was applied for the estimation of daily regulation of Ob river flow by Novosibirsk Hydroelectric Power Plant on work of Novosibirsk water intakes situated downstream of it.

Abstract:

One-dimensional Fickian dispersion models such as the advection diffusion equation (ADE) are commonly used to analyse and predict concentration distributions downstream of contamination events in watercourses. Such models are only valid once the tracer had entered the equilibrium zone. This paper compares previous theoretical, experimental and numerical estimates of the distance to reach the equilibrium zone with new experimental values, obtained by examining the change of skewness in a tracer profile, downstream of a crosssectionally well mixed source. Closer agreement was found with Fischers’ theoretical estimate than prior experimental and numerical studies.

Abstract:

In the paper, flow routing process in a river system within the context of real-time flood forecasting is discussed. Adaptation of St. Venant model for peak flow forecasting in a river system with the presence of uncontrolled inflow was introduced. The principal idea of the presented approach is to separate forecast of the peak flow discharge from the peak occurrence time. An illustrative example based on historical flow data taken from Raba river demonstrates the efficiency of the presented method.

Abstract:

In the paper the results of the sensitivity analysis of the rainfall-runoff model are presented. Calculations were made on the basis of the nonlinear reservoir model. The influence of the three basic catchment parameters – roughness, length and slope on the outflow hydrograph – was investigated. It was noticed that in the assumed range of parameters the time to the peak outflow is independent of their values. The time to peak is influenced by the rainfall hyetograph shape. The peak outflow depends on a certain combination of catchment parameters called the catchment characteristic. The impact of this characteristic depends on rainfall properties. The obtained results allow to develop the formula to estimate rainfall characteristic influence on the peak outflow without a need of the rainfall-runoff model application.

Abstract:

Three-layer sediment transport model was originally developed for hydrodynamic conditions induced by waves and currents in coastal zones (Kaczmarek 1999). With some modifications, the model can be applied for the description of transport and vertical sorting of graded sediment in rivers. Both theoretical approach and some chosen results of the study are presented in the paper.

Abstract:

The primary objective of flood frequency analysis (FFA) is the estimation of upper quantiles of probability distribution. Because of the fact that many natural events, river flows in particular, have a physical lower bound at zero, one can doubt whether the lower bound is the best third parameter for flood frequency models. Maybe, assuming the lower bound as zero and introducing a second shape parameter for getting greater flexibility is more adequate? In this paper the background and arguments for using two shape parameters instead of the lower bound parameter are presented. Three ways of introducing the second shape parameter are considered in respect to the commonly used FF models, and Gamma distribution serves as an example. Besides, one outlines the selection procedure of the best fitted probability distribution model for the two competing models, i.e. the three-parameter distribution with lower bound parameter and its counterpart, the two-shape-parameter distribution lower bounded at zero.

Abstract:

An appropriate application of the one-dimensional convective-dispersive equation for modelling of tracer breakthrough curves depends on the understanding of physical phenomena related to solute behaviour at the inlet and outlet boundaries and at the discontinuities of the system. Questions of the correct mathematical representation of the boundary conditions and of the relevant tracer injection and detection modes are discussed within the context of tracer tests in constructed wetlands. The discussed issues are illustrated by examples of tracer tests performed in two constructed wetlands of different types: a subsurface flow system and a pond. The appropriateness of the semi-infinite solution of the CDE for the pulse injection and detection of the tracer in the flux is discussed and some questions that require more elaboration are outlined.

Abstract:

The simulation of solute transport in rivers is frequently based on numerical models of the Advection-Dispersion Equation. The construction of reliable computational schemes, however, is not necessarily easy. The paper reviews some of the most important issues in this regard, taking the finite volume method as the basis of the simulation, and compares the performance of several types of scheme for a simple case of the transport of a patch of solute along a uniform river. The results illustrate some typical (and well known) deficiencies of explicit schemes and compare the contrasting performance of implicit and semi-Lagrangian versions of the same schemes. It is concluded that the latter have several benefits over the other types of scheme.

Abstract:

The multiple scales of landscape topography produce a wide distribution of groundwater circulation cells that control the hydro-geological environments surrounding geological repositories for nuclear waste. The largest circulation cells tend to discharge water into major river reaches, large freshwater systems or the nearby Baltic Sea. We investigated numerically the release of radionuclides from repositories placed in bedrock with depths between 100 to 2000 meters in a Swedish coastal area and found that leakage from the deeper positions emerges primarily in the major aquatic systems. In effect, radionuclides from the deeper repositories are more rapidly transported towards the Sea by the stream system compared to leakage from more shallow repositories. The release from the shallower repositories is significantly retained in the initial stage of the transport in the (superficial) landscape because the discharge occurs in or near low-order streams with high retention characteristics. This retention and residence time for radioactivity in the landscape control radiological doses to biota and can, thus, be expected to constitute an essential part of an associated risk evaluation.