Огляд матеріалів всеукраїнської науково-теоретичної конференції «Ірраціональне підгрунтя раціональності»

Конференція відбулася 14 квітня 2009 року в приміщенні ПДПУ імені В.Г.Короленка. Організаторами конференції були кафедра філософії Полтавського державного педагогічного університету імені В.Г.Короленка, відділ філософської антропології інституту філософії імені Г.С.Сковороди НАН України, кафедра філософії Київського національного педагогічного університету імені М.П.Драгоманова

Effects of riparian vegetation on experimental channel dynamics

River morphodynamics and sediment transportBank erosion and protectio

Incipient meandering and self-formed floodplains in experiments

River morphodynamics and sediment transportRiver morphology and morphodynamic

Bifurcation instability and chute cutoff development in meandering gravel-bed rivers

Chute cutoffs reduce sinuosity of meandering rivers and potentially cause a transition from a single to a multiple channel river. The channel bifurcation of the main channel and the mouth of the incipient chute channel controls sediment and flow partitioning and development of the chute. Recent channel bifurcation models suggest that upstream bend radius, gradient advantage, inlet step, and upstream sediment supply at the bifurcation are important factors in the evolution of bifurcations. Our objective is to unravel the relative importance of these factors for chute cutoff success and development. We compare results from a morphodynamic three-dimensional (3D) model and a one-dimensional (1D) model with nodal-point relation with field observations of chute cutoffs in a meandering gravel-bed river. The balance between increased gradient advantage and flow curvature upstream of the chute channel bifurcation was systematically investigated with the 1D model. The 3D model runs and the field observations show the development of two types of chute cutoffs: a scroll-slough cutoff and a bend cutoff. The morphodynamic 3D model demonstrates that chutes are initiated when flow depth exceeds the floodplain elevation. Overbank flow and a significant gradient advantage result in a bend cutoff. The outcome of the 1D model shows that channel curvature at the bifurcation determines the success or failure of the chute cutoff when the chute channel is located at the inner bend, as in the case of scroll-slough cutoffs. We conclude that chute initiation depends on floodplain characteristics, i.e., floodplain elevation, sediment composition, and the presence of vegetation. Chute cutoff success or failure is determined by the dynamics just upstream of the channel bifurcation and location of the chute channel in the bend, which determines channel curvature and gradient advantage. These findings have ramifications for the prediction of chute cutoff in a wide range of rivers under natural and managed conditions and for the understanding of stratigraphy and architecture of deposits

Quantifying biostabilisation effects of biofilm-secreted and extracted extracellular polymeric substances (EPSs) on sandy substrate

© Author(s) 2018. Microbial assemblages ( biofilms ) preferentially develop at water-sediment interfaces and are known to have a considerable influence on sediment stability and erodibility. There is potential for significant impacts on sediment transport and morphodynamics, and hence on the longer-term evolution of coastal and fluvial environments. However, the biostabilisation effects remain poorly understood and quantified due to the inherent complexity of biofilms and the large spatial and temporal (i.e. seasonality) variations involved. Here, we use controlled laboratory tests to systematically quantify the effects of natural biofilm colonisation as well as extracted extracellular polymeric substances (EPSs) on sediment stability. Extracted EPSs may be useful to simulate biofilm-mediated biostabilisation and potentially provide a method of speeding up timescales of physical modelling experiments investigating biostabilisation effects. We find a mean biostabilisation effect due to natural biofilm colonisation and development of almost 4 times that of the uncolonised sand. The presented cumulative probability distribution of measured critical threshold for erosion of colonised sand reflects the large spatial and temporal variations generally seen in natural biostabilised environments. For identical sand, engineered sediment stability from the addition of extracted EPSs compares well across the measured range of the critical threshold for erosion and behaves in a linear and predictable fashion. Yet, the effectiveness of extracted EPSs to stabilise sediment is sensitive to the preparation procedure, time after application and environmental conditions such as salinity, pH and temperature. These findings are expected to improve biophysical experimental models in fluvial and coastal environments and provide much-needed quantification of biostabilisation to improve predictions of sediment dynamics in aquatic ecosystems

Bank pull or bar push: what drives scroll-bar formation in meandering river?

One of the most striking features of meandering rivers are quasi-regular ridges of the point bar, evidence of a pulsed lateral migration of meander bends. Scroll bars formed on the inner bend are preserved on the point-bar surface as a series of ridges as meanders migrate, and in the subsurface of the point bar as inclined heterolithic stratification with lateral accretion surfaces. It is necessary to understand the formation and sedimentary architecture of these point bars, which are fundamental geomorphic building blocks of meandering rivers and potential reservoirs for water, oil, and gas. However, it remains unresolved whether the scroll-bar pattern forms in response to outer bend bank erosion during floods (i.e., bank pull), or is forced by bank progradation (i.e., bar push). Here we use experimentally formed meandering rivers with a set of static and migrating bends to isolate the effects of sediment supply to the point bar, bank protection, and forced bank retreat. We find that channel widening caused by bank retreat near the bend apex causes deposition of new scroll ridges along the inner bend point bar, whereas scroll bars cannot be forced by sediment pulses. Thus channel width variations along meander bends cause bank pull, which is necessary for scroll-bar formation. Furthermore, we find that each newly attached scroll bar overlies a nonpermeable layer of finer-grained sediment caused by the temporary flow expansion, which explains the fining-upward tendency of point bars

From nature to lab: scaling self-formed meandering and braided rivers

River morphodynamics and sediment transportRiver morphology and morphodynamic

First experiences with Personal Networks as an enabling platform for service providers

By developing demonstrators and performing small-scale user trials, we found various opportunities and pitfalls for deploying personal networks (PNs) on a commercial basis. The demonstrators were created using as many as possible legacy devices and proven technologies. They deal with applications in the health sector, home services, tourism, and the transportation sector. This paper describes the various architectures and our experiences with the end users and the technology. We conclude that context awareness, service discovery, and content management are very important in PNs and that a personal network provider role is necessary to realize these functions under the assumptions we made. The PNPay Travel demonstrator suggests that PN service platforms provide an opportunity to develop true trans-sector services