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1

On how defining and measuring a channel bed elevation impacts key quantities in sediment overloading with supercritical flow

Eslami Hasan, Yousefyani Hooshyar, Yavary Nia Mohsen, Radice Alessio

Acta Geophysica

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2022

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Vol. 70, no 5

2511--2528

EN

The manuscript presents the results of an aggradation experiment performed in a laboratory channel with supercritical flow. The channel was fed with a stationary sediment load exceeding the transport capacity of the flow in the initial condition, thus inducing sediment aggradation and an increase of the bed slope. The experiment is part of a laboratory campaign mimicking sediment overloading in mountain rivers, a process that can determine increased hydraulic risk levels at key spots. A crucial issue in measuring sediment aggradation is the definition and determination of the bed elevation, this issue being quite relevant in experiments with a relatively large transport capacity, where a thick bed-load layer exists and hinders the possibility to determine with confidence a reference bed elevation. The determination of the bed elevation, in turn, impacts the quantification of a number of properties, including the initial sediment transport capacity of the flow, temporal scales of the aggradation process, water depth and Froude number. The manuscript presents a sensitivity analysis of the results to two extreme definitions for the bed elevation: the first one locates the bed at the upper edge of the bed-load layer, while the second one at the lower edge of the bed-load layer where the particles do not move. The presentation of the two alternatives is focused on the experimental methods they use, consistently with the intent of the special issue. Furthermore, it is demonstrated that the definition of the bed elevation also has a major impact on numerical models of the process. The experimental results have been reproduced numerically, demonstrating that the calibration parameters returning a best fit are also impacted significantly by how the bed is defined. The preferred definition for analyzing an experimental campaign is locating the bed below the bed-load layer.

2

Silting forecast of the planned retention reservoirs within the drainage system in Łączany

Michalec Bogusław, Strutyński Mateusz

Geomatics, Landmanagement and Landscape

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2019

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no. 4

219--230

EN

This paper presents the concept for the location of two dry water reservoirs designed to retain water led through the main ditch (R) of the drainage system in Łączany. The purpose of the work is to develop a forecast for the reduction in the capacity of planned dry water reservoirs. Planned water reservoirs will allow increasing flood protection of drained areas. Based on geodetic measurements in the selected locations, the capacity of planned dry reservoirs was determined, amounting to 4.08 and 115.49 thousand m3, respectively for the U reservoir formed from the flood relief channel, and the R reservoir, located in the lower course of the R ditch. According to the developed forecast, applying the Gončarov formula, the U reservoir would be 50% silted after 134 years, and the R reservoir would be 50% silted after 149 years. The forecast has been prepared using the method recommended by the guidelines, i.e. it was developed as for reservoirs with constant water damming (accumulation). TE values determined using the Churchill method were adopted in the silting forecast. The estimated forecast indicates a long service life of the reservoirs without the need for their desilting. However, the development of a detailed forecast would require a modification of the calculation methodology, taking into account the determination of the capacity of water reservoirs to retain bed load, typical of dry water reservoirs. In the absence of the method, determination of the service life cycle of water reservoirs can be developed as an estimate.

PL

W niniejszej pracy przedstawiono koncepcję lokalizacji dwóch suchych zbiorników wodnych zatrzymujących wodę prowadzoną rowem głównym R systemu odwadniającego w Łączanach. Celem pracy jest opracowanie prognozy redukcji pojemności planowanych suchych zbiorników wodnych. Planowane zbiorniki wodne umożliwią zwiększenie ochrony przeciwpowodziowej terenów odwadnianych. Na podstawie pomiarów geodezyjnych w wytypowanych lokalizacjach określono pojemności planowanych suchych zbiorników, wynoszącą 4,08 i 115,49 tys. m3, odpowiednio dla zbiornika U utworzonego z kanału ulgi i zbiornika R, zlokalizowanego w dolnym biegu rowu R. Według opracowanej prognozy formułą Gončarova zbiornik U zostałby zamulony w 50% po upływie 134 lat, a zbiornik a zbiornik R zostałby zamulony w 50% po upływie 149 lat. Prognoza została opracowana metodą zalecaną przez wytyczne, tj. została opracowana tak jak dla zbiorników o stałym piętrzeniu wody. W prognozie zamulania przyjęto wartości TE określone metodą Churchilla. Szacunkowa prognoza wskazuje na długi okres użytkowania zbiorników bez konieczności ich odmulania. Jednakże opracowanie szczegółowej prognozy wymagało by zmodyfikowania metodyki obliczeń uwzględniające określenie zdolności zbiorników wodnych do zatrzymywania rumowiska właściwą dla suchych zbiorników wodnych. Ze względu na brak tej metody określenie żywotności zbiorników wodnych może być opracowywane jako szacunkowe.

3

Coherent structure dynamics and sediment particle motion around a cylindrical pier in developing scour holes

Link O., Gonzalez C., Gonzalez C., Maldonado M., Escauriaza C.

Acta Geophysica

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2012

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Vol. 60, no. 6

1689-1719

EN

Recent investigations on the dynamics of the turbulent horseshoe vortex system (THV) around cylindrical piers have shown that the rich coherent dynamics of the vortical structures is dominated by lowfrequency bimodal fluctuations of the velocity field. In spite of these advances, many questions remain regarding the changes of the flow and sediment transport dynamics as scour progresses. In this investigation we carry out laboratory experiments to register the development of the scour hole around a cylindrical pier in a fine-sand bed (d50 = 0.36 mm). We use the bathymetry measured in the experiment to simulate the flow field employing the detached-eddy simulation approach (DES), which has shown to resolve most of the turbulent stresses around surface-mounted obstacles. From these simulations we compare the dynamics of the THV to the flat-bed case, and analyze the effects on particle transport and sediment flux using the Lagrangian particle model of Escauriaza and Sotiropoulos (2011b) to study the impact of the changes of the flow on the sediment dynamics.

4

3D numerical simulation of particle-particle collisions in saltation mode near stream beds

Moreno P., Bombardelli F.

Acta Geophysica

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2012

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Vol. 60, no. 6

1661-1688

EN

The importance of particle-particle collisions in sediment saltation in the bed-load layer is analyzed herein by means of numerical simulation. The particle saltation theoretical/numerical model follows a Lagrangian approach, and addresses the motion of sediment particles in an open channel flow described by a logarithmic velocity profile. The model is validated with experimental data obtained from the literature. In order to evaluate the importance of the phenomenon, simulations with and without particle-particle collisions were carried out. Results for two different sediment concentrations are presented, namely 0.13% and 2.33%. For each concentration of particles, three different flow intensities were considered, and trajectories of two different particle sizes, within the sand range were computed. Changes in particle rotation, particle velocity, and angle of trajectory before and after particle-particle collisions appear to be relatively important at lower shear stresses, whereas they decrease in significance with increasing flow intensities. Analyses of the evolution in time of the second order moment of particle location suggest that inter-particle collisions introduce transverse diffusion in saltating particles in the span-wise direction.

5

Mathematical modelling of bedload transport over partially dry areas

Lanzoni S.

Acta Geophysica

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2008

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Vol. 56, no. 3

734-752

EN

The paper describes the derivation of a depth-averaged, two-dimensional form of the sediment balance equation, suitable to study the morphodynamics of movable sediment beds even when the flow depth attains values comparable to bed irregularities. This equation is derived by double-averaging in time and in space the instantaneous three-dimensional sediment balance equation. For this, a proper phase function is introduced, which depends on the statistics of bed topography. The structure of the macroscopic volumetric sediment discharge vector resulting from the averaging procedure is discussed for the case of dominant bedload transport. The theoretical framework developed within the paper sets the stage for a proper parametrization of the physical processes acting at spatial scales smaller than those usually resolved by depthaveraged numerical models.

6

Przepustowość koryt potoków górskich w terenie zabudowanym

Michalik A., Książek L., Bąk Ł., Dudkowski T., Tekielak T.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2004

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Vol. 13, No. 1

42--51

EN

Mountain streams crossing an urban area have typical for communication and hydraulic structures such as small bridges, foot-bridges, culverts, outlets of drains etc. Their construction and location can act on flow capacity. In this paper an estimation of hydraulic conditions of three mountain streams is presented. There are Ryta, Rzyczanka and Porębski creeks crossing by the Andrychów municipality. For urban sections of each creek them measurements were carried out. They were concerning the longitudinal profiles, cross-sections, and grain size distributions of the bed material. An inventory of hydraulic and hydrobiological structures has been made too. Results were used to calculate the most important hydraulic magnitude such as probable great flows. stage-discharge curves and intensity of bed load transport, It has made possible to determine the stable and unstable section of the creeks. The K-KOMSUM, PRZEPŁYW and HEC-RAS software were applied. It has been ascertained that the investigated streams have a constant capacity. On the Ryta and the Porębski creeks geological structure favour natural deeping of the channels and the Rzyczanka creek does not have deformations thanks to the hydraulic structures.

7

Transport rumowiska wleczonego i skład jakościowy osadów dennych Potoku Jałowieckiego w Beskidzie Makowskim (Karpaty polskie)

Radecki-Pawlik A., Florencka N.

Inżynieria Środowiska / Akademia Górniczo-Hutnicza im. S. Staszica w Krakowie

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2001

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T. 6, z. 2

385-397

PL

W pracy przedstawiono wyniki badań chemicznych rumowiska dennego zgromadzonego w łachach korytowych potoku górskiego płynącego przez zlewnię położoną na obszarze wiejskim pod kątem ewentualnej akumulacji metali ciężkich w występujących w korycie potoku utworach aluwialnych. Stwierdzono, że największa ilość akumulowanych pierwiastków chemicznych odkłada się w rumowisku najdrobniejszym, w miejscach ocienionych naturalnymi wychodniami skalnymi, gdzie wymiana materiału następuje wyłącznie podczas przepływów ponadkorytowych i jest to Pb oraz Cd. Dodatkowo wykonano obliczenia transportu rumowiska wleczonego metodą Parkera oraz unoszonego metodą DRUSLE.

EN

The paper presents the field research of heavy metals accumulation in point bars and sediments. The research was undertaken in Jałowiecki mountain stream - Polish Carpathian mountainous region. It was found that in some tiny sediments situated within shadow of mega-clusters or rocks there is a tendency to accumulate heavy metals, especially Pb and Cd. Additionally bed load transport was calculated using Parker method and suspended load using DR-Usle concept.