Bottom Sill Research Articles

INNOVATIVE BY-PASS SOLUTION FOR IRON GATES I TO RECONNECT THE HISTORICAL MIGRATION ROUTES OF WILD ANADROMOUS STURGEON SPECIES, IN ORDER TO IMPROVE THEIR CONSERVATION STATUS

The anadromous sturgeon species in the lower Danube are currently critically endangered and based on the studies of the INCDPM expert team and the 2022 report of IUCN-SSG (Sturgeon Specialist Group) it appears that the future prospects of these populations are unfavourable. This situation occurs mainly as a result of anthropogenic impacts, especially due to intensive fishing, poaching and hydrotechnical constructions (e.g.: dams, immersed obstacles such as the bottom sill on Bala Branch). The dams interrupted the historical spawning migration routes of these species and the bottom sill can interrupt them in the future. In this context, INCDPM has elaborated an innovative by pass solution for the Iron Gates I, based on the longterm monitoring of ultrasonically tagged sturgeons from the Black Sea to the Iron Gates. This article presents the methodology developed by INCDPM in order to ensure the implementation of the innovative by-pass solution with minimal risk of unseccesful restoration of the historical migration routes. The study aims to present the specific migration conditions and the actual routes, which have been determined by over a decade of in-situ monitoring of ultrasonically tagged specimens. Additionally, simulations of upstream migration will be conducted and GIS maps will be developed to present historical migratory routes, with consideration given to hydrodynamic conditions and climate change scenarios.

Numerical Study on the Influence of Combined Rectification Facilities on the Flow in the Forebay of Pumping Station

The flow pattern of the forebay of the pumping station has a considerable effect on the operating efficiency and stability of the pump unit. A good forebay flow pattern can enable the pump unit to improve efficiency and operating conditions. This study takes a large pumping station as the research object and considers two rectification schemes, namely, a single bottom sill and a “bottom sill + diversion pier”. Without rectification facilities under different start-up schemes, the forebay flow pattern after the addition of rectification facilities is calculated, and the influence of single and combined rectification facilities is analyzed. Results show large-scale undesirable flow structures such as backflow and vortex in the forebay of the original design that without rectification facilities and uneven flow distribution occurs in the operating unit. The addition of a bottom sill in the forebay can control the central water beam from the water diversion pipe. The flow is divided to spread to both sides of the forebay and can be rectified twice after installing the diversion piers. The combined rectifier facility of “bottom sill + diversion pier” is beneficial to disperse incoming flow and make the flow distribution of each unit more uniform. The backflow and vortex inside the forepond are basically eliminated, and the flow state of the forepond is significantly improved.

Laboratory experiments on the influence of stratification and a bottom sill on seiche damping

Abstract. The damping of water surface standing waves (seiche modes) and the associated excitation of baroclinic internal waves are studied experimentally in a quasi-two-layer laboratory setting with a topographic obstacle at the bottom representing a seabed sill. We find that topography-induced baroclinic wave drag contributes markedly to seiche damping in such systems. Two major pathways of barotropic–baroclinic energy conversions were observed: the stronger one – involving short-wavelength internal modes of large amplitudes – may occur when the node of the surface seiche is situated above the close vicinity of the sill. The weaker, less significant other pathway is the excitation of long waves or internal seiches along the pycnocline that may resonate with the low-frequency components of the decaying surface forcing.

Analysis of Underwater Topographic Survey of Stilling Basin Based on Unmanned Survey System

The combination of Global Positioning System‐Real Time Kinematic (GPS‐RTK) and depth sounder is an important technical method of modern underwater topographic survey. In this paper, the combined technology was integrated with unmanned surface vehicle (USV) technology to construct an unmanned survey system suitable for underwater topographic survey in stilling basin, and it was applied to survey the underwater topography of the stilling basin of Tingzikou hydrojunction project. Based on the surveying and mapping data and 3D model, the trend of elevation change of the stilling basin including apron, end sill, antiscour section, and river convergence section was analyzed. The results show that, for the surface outlet stilling basin of Tingzikou, after flood, the structure is complete, the boundaries are clear, the water quality is good, and there is little sediment on the surface of apron from overflow dam section to end sill. Furthermore, no obvious sediment or structural abnormality has been found in the still basin. Affected by the bedrock and cofferdam cobble gravel sediment, the elevation of the antiscour section and the downstream convergence section of the surface outlet stilling basin increased significantly. For the bottom outlet stilling basin of Tingzikou, there is large sediment within a range of 20 m∼40 m from the bottom sill and the maximum height of it reaches 2.04 m, while there is no obvious sediment or structural abnormality in the remaining region of basin. The critical sedimentation height can effectively judge the safety grade of the sedimentation height in stilling basin and provide a reliable support for assessing the overall safety of stilling basin. The application of unmanned survey technology improves the accuracy and timeliness of underwater topography and sedimentation distribution of stilling basin, which has significant application research value and promotion significance.

Evaluating the Effect of the Hydrotechnical Works from the Danube’s Caleia Branch on the Spawning Migration of Sturgeons

Over the years, to maintain navigation along the Danube, the implementation of a series of hydrotechnical works was imposed in order to ensure the continuity of economic activities. Between 2011 and 2014, one such project was built in the vicinity of the county of Braila, on a secondary branch of the Danube - The Caleia branch. The main goal was to redistribute water discharge from the secondary channel to the main branch by construction of a bottom sill. The bottom sill and subsequent discharge redistribution led to hydrodynamic alterations caused by increased water current velocities. These modifications of the hydrodynamic regime may affect the migration of anadromous sturgeon species that swim from the Black Sea to spawn upstream, therefore making the monitoring of the impact paramount. Considering the fact that the anadromous migrating species are internationally protected species, by a series of agreements and conventions, and that the stocks of the species are still in decline, a complex monitoring program was implemented in the affected area. This study presents important information regarding the site utilization during spawning migration and an evaluation of the behavior of sturgeons tagged with ultrasonic transmitters that migrated upstream over the bottom sill. During the monitoring period, the studies show that five sturgeons passed the bottom sill during their upstream migration, swimming against maximum water current velocities of 2.5 m/s.

Numerical Modelling of Pollutant Dispersion in the Lower Danube River

This paper presents the numerical modeling results of the pollutant dispersion in the Danube riverbed, using experimental data recorded monthly on the Borcea - Bala - Old Danube sector, for a 2 years period. The water samples were collected from the left bank, center and right bank of the river, and the follwing indicators were analyzed: lead, nickel, chromium, cadmium and copper. Heavy metals were determined by atomic absorption spectrophotometry with graphite furnace (GFAAS). Numerical modeling was performed using Delft3D software, taking into account a reference situation (a scenario regarding the pollutant dispersion for known concentrations) and a scenario that simulates an accidental pollution (where the concentrations of pollutants were increased by 50 % compared to the values corresponding to Class V of water quality according to M.O. 161-2006). In order to properly assess the pollutant dispersion, the construction of the numerical model was developed taking into account a number of complex hydraulic works (bottom sill, dredging operations on the Danube in the area of confluence and downstream, on the whole width of the fairway). The results of numerical modeling generated the pollutant dispersion maps and the dispersion coefficients (indicating the transport of substances). Higher levels of the monitored indicators were observed on Borcea, caused by water coming from different sources of pollution (industry, agriculture, etc.) and discharged at a low flow, limiting the dilution.

Urban flood modeling using shallow water equations with depth-dependent anisotropic porosity

The shallow water model with anisotropic porosity conceptually takes into account the unresolved subgrid-scale features, e.g. microtopography or buildings. This enables computationally efficient simulations that can be run on coarser grids, whereas reasonable accuracy is maintained via the introduction of porosity. This article presents a novel numerical model for the depth-averaged equations with anisotropic porosity. The porosity is calculated using the probability mass function of the subgrid-scale features in each cell and updated in each time step. The model is tested in a one-dimensional theoretical benchmark before being evaluated against measurements and high-resolution predictions in three case studies: a dam-break over a triangular bottom sill, a dam-break through an idealized city and a rainfall-runoff event in an idealized urban catchment. The physical processes could be approximated relatively well with the anisotropic porosity shallow water model. The computational resolution influences the porosities calculated at the cell edges and therefore has a large influence on the quality of the solution. The computational time decreased significantly, on average three orders of magnitude, in comparison to the classical high-resolution shallow water model simulation.

LABORATORY STUDY ON COMPARISON OF THE SCOUR DEPTH AND SCOUR LENGTH OF GROUNDSILL WITH THE OPENING AND WITHOUT THE OPENING

River bed control structure what so called groundsill or bottom sill is built for controlling a river bed to remain stable against degradation. Unlike other river obstacles, the presence of groundsill might cause sediment retention upstream of the structure; hence it reduces the supply of sediment to the downstream part of the river. At some extent, the above situation might create unexpected negative impact, not only cease the sediment migration but also disable fish migration, as well as the utilization of river for navigation. This paper presents the hydraulic investigation on various models of groundsill, i.e. groundsill without the opening and groundsill with a certain type of the opening. Series of laboratory experiments were conducted on an open channel flow of 0.75m width and longitudinal slope of 0.05%. There were two types of groundsill, i.e. groundsill without the opening with 0.75m width and 0.05m height, and groundsill with the opening of 0.39m width and 0.005m height of crest at the opening and 0.05m at the wings. Various flow rates were then introduced, necessary data were taken, and the hydraulic phenomena were studied. The results showed that groundsill without the opening produced non-dimensional (relative to the channel width) scour depth of 0.036, and scour length of 0.253. Groundsill with the opening produced scour depth of 0.013 and 0.024 near the downstream end of the wing section and the opening respectively. The scour length of the groundsill with the opening is 0.080 and 0.293 near the downstream end of the wing section and the opening section respectively. Moreover, it can be noted that the presence of the scour depth and scour length of the groundsill with the opening was generally much smaller rather than that of groundsill without the opening. The above results give the evidence that groundsill with the opening is much friendlier and also more suitable for the environment needs.Keywords: control structure, environmentally sound, groundsill, hydraulic phenomenon

Free-Surface Flow Over River Bottom Sill: Experimental and Numerical Study

This paper reports on a laboratory study that was performed in an experimental model in the Technological Educational Institute of Thessaly. The current research work examines the water surface profile variation in abruptly altered open channel topography. The objective is to investigate the effects of river bottom sills on flow depth for river control protection against floods. A rectangular bottom sill with one edge rounded was placed on the bottom of a rectangular, horizontal, laboratory open flume and measurements were performed of free-surface flow depth over the bottom sill, under steady flow conditions, for different inflow discharges. Moreover, the HEC-RAS simulation model was used to numerically simulate the water surface variation over the rectangular bottom sill, under steady flow conditions. A mixed flow regime simulation was performed in order to validate the transition from subcritical to supercritical flow conditions. The computed flow depth variation over the rectangular bottom sill was compared with the obtained experimental measurements in order to demonstrate the accuracy of the performed measurements. The presented experimental data may be used to assist in the development of new and the verification and refinement of existing river hydraulic numerical simulation models, particularly those which use non-hydrostatic pressure distribution.

Researching on the Single Lock Chamber Automatic Layout Algorithm

Arrange the ships reasonable as much as possible in the lock chamber, can help improving the traffic ability and the utilization rate of the lock. At present, it is not enough for the factors that considered in the automatic layout algorithm, such as: the safety distance between the ships, ship bottom sill depth. The algorithm can be further optimized. This paper will present a new automatic layout algorithm for single chamber which is able to enhance the efficiency of the chamber space and improve the traffic ability.

Accurate vertical profiles of turbulent flow in z‐layer models

AbstractThree‐dimensional hydrodynamic z‐layer models, which are used for simulating the flow in rivers, estuaries, and oceans, suffer from an inaccurate and often discontinuous bottom shear stress representation, due to the staircase bottom. We analyze the governing equations and clearly show the cause of the inaccuracies. Based on the analysis, we present a new method that significantly reduces the errors and the grid dependency of the results. The method consists of a near‐bed layer‐remapping and a modified near‐bed discretization of the k − ε turbulence model. We demonstrate the applicability of the approach for uniform channel flow, using a schematized two‐dimensional vertical model and for the flow over a bottom sill using the Delft3D modeling system.

Numerical simulation of flow pattern with sill in the front inflow forebay of pumping station

There are recirculation zones and vortexes in the forebay of pumping stations which effect the flow pattern and reduce the efficiency of the pump.The incompressible N-S equations are solved by the finite volume method. The Realizable k-ε turbulence model and the SIMPLE algorithm for pressure-velocity coupling are used. The flow pattern of bottom sills with different positions is calculated. Large recirculation zones and the serious bias flow occur on the both sides in the forebay when there is nothing in the forebay, as well as, flow conditions of sideway pump stations is also bad due to mainstream compression .There is a large recirculation zone and serious bias flow when the bottom sill is too far from the sumps. On the other hand, the flow pattern of sump is badly affected when it is too close to the sumps. The flow pattern is improved when the bottom sill is installed in the right position.There is optimized location where the flow will be pumped uniformly into the sump. The results indicate that the calculation results show a good agreement with the test results. The research results can be applied in the similar forward diffuse forebay of pumping stations.

Research on the Measures of Improve the Flow Pattern of the Forebay of City Intake Water Pumping Stations

City intake water pumping stations are restricted by bank slope conditions of water source areas and land use restrictions etc. Intake structures are difficult to be arranged in accordance with the requirements of hydraulic conditions. Therefore, adverse flow phenomena such as bias flow, recirculation and vortex are easier to generate in the forebay.The adverse flow imparts an adverse effect upon the pump inlet condition, so as to negatively influence safe operation of the pumping station. Physical models were tested according to layout characteristics of a city intake water water pumping station to research the reasons of bad flow conditions occurred in the caisson type forebay. The study found that the bottom sill in the forebay would improve the inflow pattern. The test results showed that the sump of the pumping station could effectively improve the flow pattern in the forebay and improve the efficiency of the pump operation.

Experimental Study on the Flow Pattern Modifying in the Fore Bay of large Urban Side Inflow Pumping Stations

The flow pattern in the fore bay and sump of large urban side inflow pumping station is worse which causes machine vibration, lower efficiency and other server problems. According to pumping station features, some engineering measures can improve effectively the intake flow patterns in the fore bay and the inlet conditions of pumps. In this paper, the reasons for the bad flow pattern are analyzed on the basis of model test of the fore bay of Wuhaogou pumping station of Qingcaosha water resource project which is the major security project of Shanghai World Expo 2010. The methods were discussed to the inlet flow patterns and the influence of the inlet flow patterns, and the measures which are multi-water distribution holes and bottom sill and guide piers were put forward to ameliorate the flow pattern in the paper. The model test results showed that the measures were valuable in ameliorating flow patterns and the inlet conditions of pumps. The engineering measures to improve the flow pattern in the fore bay are developed by the consideration of the analysis results and the features of pumping station layout.

Interfacial waves in two-layer exchange flows downslope of a bottom sill

An experimental study was conducted to examine the interfacial waves in two-layer exchange flows downslope of a bottom sill. The objective of the study was to understand the generation mechanisms of different interfacial waves and the generation conditions and development of Kelvin–Helmholtz (KH) instabilities in spatially varying flow field. During the flow regime of the steady maximal exchange, low-frequency oscillation of the density interface above the sill crest was observed, which resulted in periodic piling and releasing of the lower-layer fluid. This low-frequency oscillation led to the development of large-scale downslope waves that caused significant interfacial entrainment. The periodic time of those piling and releasing events was found to be inversely proportional to the square root of the reduced gravitational acceleration and to be related to the baroclinic forcing of the basin internal seiching. During late sub-maximal exchange, regular and frequent KH instabilities were generated at the interface down the slope at bulk Richardson number of approximately 0.07–0.21, which is considerably larger than previous theoretical predictions for parallel flows with a sharp density interface. Two different growth patterns of those KH instabilities were observed. Measurements of their initial growth rate and the wavelength were also obtained and compared to the theoretical predictions.

Dam-Break Flow in the Presence of Obstacle: Experiment and CFD Simulation

The aim of this paper is to present an experimental and numerical investigation of dam-break flow over initially dry bed with a bottom obstacle. This test case highlights not only the bottom slope effects but also those of abrupt change in channel topography. Dam-break flow was applied in a smooth prismatic channel of rectangular cross-section over a trapezoidal bottom sill on the downstream bed. The present study scrutinized the formation and propagation of negative bore behind the sill. The flow was numerically simulated by the VOF-based commercially available CFD program, Flow-3D, solving the Reynolds Averaged Navier Stokes equations with the k-ε turbulence model (RANS) and the Shallow Water Equations (SWE). To validate CFD models an experiment was carried out. Using an advanced measuring technique, digital image processing, the flow was recorded simply through the glass walls of channel; thus, continuous free surface profiles were acquired synchronously with three cameras along the channel. The adopted measuring technique is non-intrusive and yields accurate and valuable results without flow disturbances. Comparison of the computed results with experimental data shows that RANS model reproduces the flow under investigation with reasonable accuracy while simple SWE model indicates some discrepancies particularly in predicting the negative wave propagation.

CFD modelling approach for dam break flow studies

Abstract. This paper presents numerical simulations of free surface flows induced by a dam break comparing the shallow water approach to fully three-dimensional simulations. The latter are based on the solution of the complete set of Reynolds-Averaged Navier-Stokes (RANS) equations coupled to the Volume of Fluid (VOF) method. The methods assessment and comparison are carried out on a dam break over a flat bed without friction, a dam break over a triangular bottom sill and a dam break flow over a 90° bend. Experimental and numerical literature data are compared to present results. The results demonstrate that the shallow water approach, even if able to sufficiently reproduce the main aspects of the fluid flows, loses some three-dimensional phenomena, due to the incorrect shallow water idealization that neglects the three-dimensional aspects related to the gravity force.

Effects of topography on the cumulative mixing efficiency in exchange flows

Buoyancy‐driven, hydraulically controlled two‐layer exchange flows were established in a laboratory flume with a lateral constriction and a bottom sill placed at its midpoint. The shear flow was unstable within the constriction, and the overall amount of turbulent mixing was determined from measurements of vertical density profiles after the exchange. The potential energy changes are used to evaluate the mixing efficiency (or flux Richardson number), defined as the fraction of the available potential energy released into kinetic energy that is converted to potential energy through irreversible mixing. Mixing efficiencies asymptote at large Reynolds numbers to values of 8% for a sill with sloping sides and 11% ± 1% for both a weir with vertical sides and the same constriction with no bottom topography. The latter is identical to the value previously reported for shorter, smoothly varying lateral constrictions. Thus, all controlled exchanges examined here undergo less mixing than implied by the commonly assumed maximum turbulent mixing efficiency of 20%, and the actual efficiency is insensitive to the form of the topography. This result implies that calculations of the global energy balance of the ocean may need to be reevaluated.

Experiments of dam-break wave over a triangular bottom sill

The IMPACT project addressed the assessment and reduction of risks from extreme flooding caused by natural events or the failure of dams and flood defence structures. It was funded by the European Commission (EC), started in November 2001 and lasted for 3 years. This paper presents a dam-break flow experiment in a channel with a triangular bottom sill (the bump), that was part of the IMPACT benchmarking programme (WP3: flood propagation). This test case highlights some key issues linked to the propagation of dam-break waves on dry bed in the presence of a bed slope. Two types of measurement devices were used to obtain the evolution of the water depth. First, three water level gauges were used to obtain the time evolution of the water level at three different locations around the bump. Then, using high speed digital cameras, the flow was filmed through the glassy walls of the channel, resulting in a continuous experimental surface profile by combining the images acquired at different locations along the channel. An automated procedure was designed to measure the water depth from the digital images. This procedure has been successfully validated by comparison with the gauge records. Finally, all those measurements form a data set that can be used for the validation of numerical models.

On the radiation and diffraction of linear water waves by a rectangular structure over a sill. Part I. Infinite domain of finite water depth

The effects of a bottom sill on the hydrodynamic coefficients, wave force, and reflection and transmission coefficients of a rectangular structure floating on the free surface are analyzed in this paper by use of a semi-analytical method. Linearized water wave theory and the method of separation of variables are applied to obtain analytical expressions for the diffracted and radiated wave potentials. The unknown coefficients in the obtained expressions are determined by use of the eigenfunction expansion matching method. To verify the obtained expressions and the proposed method, a comparison of the analytical results with those obtained by the boundary element method is made and very good agreement is achieved, which shows that the analytical expressions for the radiated and diffracted potentials are correct. By use of the present analytical solution, several results for the hydrodynamic coefficients, wave force, reflection and transmission coefficients are given.