scholarly journals Dune dynamics and roughness under gradually varying flood waves, comparing flume and field observations

2014 ◽  
Vol 39 ◽  
pp. 115-121 ◽  
Author(s):  
J. J. Warmink
Keyword(s):  
Subcritical Water ◽  
Continuous Process ◽  
Flood Management ◽  
Flood Wave ◽  
Flume Experiments ◽  
Bed Forms ◽  
Bed Form ◽  
Dune Height ◽  
Dune Dynamics ◽  
Flood Waves

Abstract. Accurate forecasts of bed forms and their roughness during a flood wave are essential for flood management. Bed forms remain dynamic even under steady discharge and are subject to a continuous process of creations and destructions of individual bed forms. Dune evolution during the rising limb of a flood wave is quite well understood and can be modeled. However, dune evolution during the falling limb remains poorly understood. The objective of this paper is to explain the bed form evolution and roughness during the receding limb of fast flood waves. Therefore, bed profiles of two flume experiments were analyzed in detail and individual dune creations and destructions were classified. The results showed that for fast flood waves in subcritical water flow: (1) dune length grows during both rising and falling limb due to amalgamation of bed forms, (2) dune length has a longer adaptation time than dune height, resulting in short, high dunes during the peak discharge, and (3) this hysteresis difference between dune height and length results in a larger roughness than predicted by equilibrium bed form dimension equations, which may result in a larger roughness of the main channel during floods than expected.

scholarly journals Effect of unsteady flows on the development and magnitude of bed forms

2021 ◽  
Author(s):  
Le Wang ◽  
Alan Cuthbertson ◽  
Gareth Pender ◽  
Zhixian Cao
Keyword(s):  
Unsteady Flow ◽  
Morphological Changes ◽  
Unsteady Flows ◽  
Coarse Sand ◽  
Total Water ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Bed Forms ◽  
Bed Form ◽  
Water Work

<p>Sediment transport and associated morphological changes in alluvial rivers occur primarily under unsteady flow conditions that are manifested as well-defined flood hydrograph events. At present, typical bed forms generated by such unsteady flows is far less studied and, thus, more poorly understood, than equivalent bed forms generated under steady flow conditions. In view of this, the objective of this work is to investigate the development of morphological bed features, and specifically variability in the length, height and steepness of bed forms that develop in a mobile coarse-sand bed layer under unsteady flow hydrographs under zero sediment feed conditions. A series of laboratory flume experiments is conducted within which different flow hydrograph events are simulated physically by controlling their shape, unsteadiness and magnitude. Experimental results indicate that different categories of bed forms such as dunes, alternate bars or transitional dune-bar structures develop within the erodible bed layer when subject to varying hydrograph flow conditions. Examination of relative importance of three parameters used to describe the hydrograph characteristics (i.e. asymmetry, unsteadiness and total water work) on bed form dimensional descriptors (i.e. wavelength, height and steepness) reveals that hydrograph unsteadiness and total water work are the primary and second-order controls on bed deformations or corresponding bed form dimensions. By contrast, hydrograph asymmetry appears to have minimal or negligible influence on bed form development in terms of their type and magnitude. Based on these findings, a physical model was developed and tested to describe the effect of unsteady flow hydrographs with varying unsteadiness and total water work on the nature and size of resulting bed forms that are generated in sand-bed layers. </p>

scholarly journals Application of HEC-RAS model for estimating changes in watercourse geometry during floods

2012 ◽  
Vol 34 (2) ◽  
pp. 63-72 ◽  
Author(s):  
Joanna Markowska ◽  
Jacek Markowski ◽  
Andrzej Drabiński
Keyword(s):  
River Channel ◽  
Groundwater Table ◽  
Water Levels ◽  
Primary Role ◽  
Flood Wave ◽  
Initial State ◽  
Wave Impact ◽  
Groundwater Levels ◽  
Groundwater Level Fluctuations ◽  
Flood Waves

Abstract Groundwater table levels in a river valley depend, among other factors, on meteorological and hydrogeological conditions, land use and water levels in watercourses. The primary role of a watercourse is to collect surface and groundwater, and it becomes an infiltrating watercourse at high water levels. Changes in groundwater levels and the range of these changes depend chiefly on the shape, height and duration of the flood wave in the river channel. The assessment of flood wave impact on groundwater was based on long-term measurements of groundwater levels in the Odra valley and observations of water levels in the river channel. Simulations were performed with the use of in-house software FIZ (Filtracja i Zanieczyszczenia; Filtration and Contamination), designed for modelling unsteady water flows within a fully saturated zone. A two-dimensional model with two spatial variables was employed. The process of groundwater flow through a porous medium, non-homogeneous in terms of water permeability, was described with Boussinesq equation. The equation was solved with the use of finite element method. The model was applied to assess groundwater level fluctuations in the Odra valley in the context of actual flood waves on the river. Variations in groundwater table in the valley were analysed in relation to selected actual flood water levels in the Odra in 2001-2003 and 2010. The period from 2001 to 2003 was used to verify the model. A satisfactory agreement between the calculated and the measured values was obtained. Based on simulation calculations, it was proved that flood waves observed in 2010 caused a rise in groundwater table levels in a belt of approximately 1000 metres from the watercourses. It was calculated that at the end of hydrological year 2009/2010, the highest growths, of up to 0.80 m, were observed on piezometers located close to the Odra river channel. The passage of several flood waves on the Odra caused an increase of subsurface retention by 3.0% compared to the initial state.

scholarly journals Experimental determination of the flood wave transformation and the sediment resuspension in a small regulated stream in an agricultural catchment

2017 ◽  
Vol 21 (11) ◽  
pp. 5681-5691 ◽  
Author(s):  
David Zumr ◽  
Tomáš Dostál ◽  
Jan Devátý ◽  
Petr Valenta ◽  
Pavel Rosendorf ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Initial Conditions ◽  
Sediment Resuspension ◽  
Early Spring ◽  
Wave Transformation ◽  
Flood Wave ◽  
Water Saturated ◽  
Artificial Flood ◽  
Long Channel ◽  
Flood Waves

Abstract. This paper presents the methodology used for artificial flood experiments conducted in a small artificial, trained (regulated) channel on the Nučice experimental agricultural catchment (0.5 km2), central Czech Republic, and the results of the experiments. The aim was to monitor the transformation of the flood wave and the sediment transport within the channel. Two series of experiments were carried out in contrasting initial conditions: (a) in September, when the stream banks were dry, the baseflow was negligible, and the channel was fully overgrown with vegetation; and (b) in March, when the stream banks were almost water saturated, the baseflow was above the annual average, and there was no vegetation present. Within each campaign, three successive flood waves, each with an approximate volume of 17 m3 and peak flow of ca. 40 L s−1, were pumped into the upper part of the catchment drainage channel. The transformation of the flood wave and the sediment transport regime within an approximately 400 m long channel section were monitored by measuring the discharge, the turbidity, and the electrical conductivity in three profiles along the stream. On the basis of the results, it was concluded that there is a considerable amount of deposited sediment, even in the well-trained and straight channel that can be re-mobilized by small floods. Part of the recorded sediment therefore originates from the particles deposited during previous soil erosion events. The flood waves initiated in dissimilar instream conditions progressed differently – we show that the saturation of the channel banks, the stream vegetation and the actual baseflow had a strong influence on the flood transformation and the sediment regime in the channel. The sediment moves quickly in winter and early spring, but in the later part of the year the channel serves as a sediment trap and the resuspension is slower, if dense vegetation is present.

scholarly journals The role of flood wave superposition for the severity of large floods

2019 ◽  
Author(s):  
Björn Guse ◽  
Bruno Merz ◽  
Luzie Wietzke ◽  
Sophie Ullrich ◽  
Alberto Viglione ◽  
...  
Keyword(s):  
Flood Wave ◽  
Data Set ◽  
Discharge Data ◽  
Main River ◽  
Wave Superposition ◽  
Triple Points ◽  
Flood Peaks ◽  
The Impact ◽  
Flood Waves

Abstract. The severity of floods is shaped not only by event and catchment specific characteristics but also depends on river network configuration. At the confluence of relevant tributaries to the main river, flood event characteristics may change depending on magnitude and temporal matching of flood waves. This superposition of flood waves may potentially increase flood severity. However, this aspect is up to now not analysed for a large data set. To fill this gap, the role of flood wave superposition in determining flood severity is investigated. A novel methodological approach to analyse flood wave superposition is presented and applied to mean daily discharge data of 37 triple points from the four large river basins in Germany and Austria (Elbe, Danube, Rhine and Weser). A triple point consists of the three gauges at the tributary as well as upstream and downstream of the confluence to the main river. At the triple points, differences and similarities in flood characteristics are jointly analysed in terms of temporal matching and magnitudes of flood peaks. At many analysed confluences, the tributary peaks arrive consistently earlier than the main river peaks, but mostly high variability in the time lag is detected. No large differences in temporal matching are detected for floods of different magnitudes. In the majority of the cases, the largest floods at the downstream gauge occur not because of a perfect temporal matching of tributary and main river. In terms of spatial variability, the impact of flood wave superposition is site-specific. Characteristic patterns of flood wave superposition are detected for the flood peaks in the Danube, where peak discharge largely increases due to inflow from the alpine tributaries. Overall, we conclude that the superposition of flood waves is not the driving factor of flood peak severity in Germany, but a few confluences bear potential of strong flood magnifications in the case of temporal shift in flood waves.

scholarly journals Analysis of physical mechanisms of human body instability for the definition of hazard zones present in emergency action plans of dams. Case study: Santa Helena Dam, Bahia

RBRH ◽  
2019 ◽  
Vol 24 ◽  
Author(s):  
Luan Marcos da Silva Vieira ◽  
Andrea Sousa Fontes ◽  
André Luiz Andrade Simões
Keyword(s):  
Human Body ◽  
Buoyancy Force ◽  
Flood Wave ◽  
Hazard Management ◽  
Physical Mechanisms ◽  
Adaptive Ability ◽  
Definition Of ◽  
The Individual ◽  
Flood Waves

ABSTRACT The impacts caused by flood waves due to dam ruptures usually cause irreversible damages to the resident population, and, the loss of body equilibrium in floods contributes to aggravate this scenario. In this context, this work aimed to analyse the influence of consideration of physical mechanisms that cause instability in the human body on the definition of hazard zones. Therefore, it was developed simulation of the propagation of the flood wave due to the hypothetical rupture of Santa Helena Dam in Bahia, using the hydrodynamic model HEC-RAS. The results of flow velocities and heights were related and compared to different criteria of hazard zonings and mechanisms that cause body instability. It was verified that the consideration of instability mechanisms of the human body can contribute to hazard management, through the knowledge of areas in which different individuals may topple or slide. It was confirmed that in supercritical flow regimes is more likely for the individual to slide and that in subcritical regimes the individual will topple. Moreover, the consideration of parameters such as buoyancy force and the angle related to the human body's adaptive ability in a flooding influence on the definition of zones.

scholarly journals Possibilities of Controlling the River Outlets by Weirs on the Example of Noteć Bystra River

2020 ◽  
Vol 12 (6) ◽  
pp. 2369
Author(s):  
Joanna Wicher-Dysarz ◽  
Ewelina Szałkiewicz ◽  
Joanna Jaskuła ◽  
Tomasz Dysarz ◽  
Maksymilian Rybacki
Keyword(s):  
Flood Hazard ◽  
A Priori ◽  
Effective Control ◽  
Flood Wave ◽  
Extreme Hazards ◽  
Longitudinal Profiles ◽  
Maximum Flows ◽  
The City ◽  
Flood Waves

The possibility of effective control of selected dams in the Noteć Bystra river is analyzed. Such a control is expected to permit inundation of selected arable areas, e.g., peat grasslands, to avoid flooding of the city of Czarnków and the terrains located downstream. The chosen case study is the reach of the Noteć River between the dams Pianowka–Mikolajewo–Rosko. The analysis was made on the basis of simulations of the flow and regulation of dams in flood conditions. The flow peaks of hypothetical flood waves were designed according to the directions of the ISOK project (Informatyczny System Osłony Kraju przed nadzwyczajnymi zagrożeniami—IT System of the Country’s Protection Against Extreme Hazards) as the maximum flows over 10-years (p = 10%), 100-years (p = 1%), and 500-years (p = 0.2%). The obtained results are presented as longitudinal profiles of the water surface, maps of inundated areas and maps of inundated soils. The main conclusion is that the robust control of dams reduces the peak of flow during flood wave propagation and forces inundation of the a priori selected areas. It helps to decrease the spatial range of the flood hazard and significantly reduces risk related to floods.

Bed forms in turbulent channel flow

2004 ◽  
Vol 57 (1) ◽  
pp. 77-93 ◽  
Author(s):  
Albert Gyr and ◽  
Wolfgang Kinzelbach
Keyword(s):  
Orange Peel ◽  
Turbulent Channel Flow ◽  
Secondary Flows ◽  
The Self ◽  
Self Organization ◽  
3 Dimensional ◽  
Bed Forms ◽  
Bed Form ◽  
Separation Zones ◽  
Grain Diameter

Bed forms in channels result from the interaction between sediment transport, turbulence and gravitational settling. They document mechanisms of self-organization between flow structures and the developing structure of the bed. It is shown that these mechanisms can be characterized by length scales of the sediment, the bed form and the flow structure. Three types of interaction can be distinguished: 1) The first type of mechanisms can be observed at beds of sediment with grain diameter smaller than the typical structural dimension of turbulence. It is shown how with increasing hydraulic loading of the bed a hydraulically smooth surface develops structures, which turn from “orange peel” to stripe and arrowhead patterns and finally into ripples. This group of bed forms is limited to a grain diameter of d+=12.5 in viscous units. In the regime of the stripe structures drag reduction occurs. 2) If grains or bed forms reach a height, which leads to separation, a completely different regime prevails, which is determined by the self-organization of separation zones. A prominent example for these bed forms are dunes. 3) Demixing processes, secondary flows and roughness contrasts finally lead to the development of longitudinal and transverse banks. All three mechanisms are explained on the basis of kinematic models and documented by experimental data. Emphasis is put on the two-dimensionalization of bed forms in a highly 3-dimensional (3D) turbulent flow, which is traced back to the self organization of vortex systems. This review article contains 55 references.

scholarly journals Effects of Vegetation Density and Arrangement on Sediment Budget in a Sediment-Laden Flow

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1412 ◽  
Author(s):  
Jin-Fu Li ◽  
Samkele Tfwala ◽  
Su-Chin Chen
Keyword(s):  
Evolutionary Process ◽  
Extreme Weather Events ◽  
Vegetation Density ◽  
Flume Experiments ◽  
Weather Events ◽  
Structural Resistance ◽  
Bed Form ◽  
Flexible Vegetation ◽  
Crucial Information ◽  
Vertical Velocity Profile

Understanding the effects of riparian vegetation under sediment-laden flow is becoming crucial due to the increase in frequency of extreme weather events. This study designed three densities and nine random distributions of bent flexible vegetation in flume experiments under sediment-laden flow. Sediments were continually added to the flume at a rate of 21 kg/h to simulate a natural river environment in a sediment-laden flow. The results showed that the evolutionary process of bed form under sediment-laden flow could be divided into four stages: scouring, development, recovery, and deposition stages, forming a dynamic cycle. Dunes were formed and backwater caused them to develop upstream, while structural resistance developed the dunes downstream. Contrary to clear water regime, sediments were deposited upstream of the vegetation area and scour occurred behind the vegetation. In addition, the vertical velocity profile showed to be dependent on the vegetation structure and four clear zones were identified: fixed, bent, canopy, and developed zones. The findings from this study provide crucial information towards river management through understanding the diverse vegetation effects under sediment-laden flows.

Sign in / Sign up

Export Citation Format

Share Document