In the present study, experiments were conducted in a large-scale flume to investigate the issue of local scour around side-by-side bridge piers under both ice-covered and open flow conditions. Three non-uniform sediments were used in this experimental study. Analysis of armour layer in the scour holes around bridge piers was performed to inspect the grain size distribution curves and to study the impact of armour layer on scour depth. Assessments of grain size of deposition ridges at the downstream side of bridge piers have been conducted. Based on data collected in 108 experiments, the independent variables associated with maximum scour depth were assessed. Results indicate that the densimetric Froude number was the most influential parameter on the maximum scour depth. With the increase in grain size of the armour layer, ice cover roughness and the densimetric Froude number, the maximum scour depth around bridge piers increases correspondingly. Equations have been developed to determine the maximum scour depth around bridge piers under both open flow and ice covered conditions.
In response to the continually increasing sediment concentrations in rivers and lakes, the Ethiopian government is leading an effort where farmers are installing soil and water conservation measures to increase infiltration and reduce erosion. This paper reports on findings from a four year study in the 95 ha Debre Mawi watershed where under the government led conservation works, mainly terraces with infiltration furrows were installed halfway in the period of observation. The results show that runoff volume decreased significantly after installation of the soil and water conservation practices but sediment concentration decreased only marginally. Sediment loads were reduced mainly because of the reduced runoff. Infiltration furrows were effective on the hillsides where rain water could infiltrate, but on the flat bottom lands that become saturated with the progress of the monsoon rain, infiltration was restricted and conservation practices became conduits for carrying excess rainfall. This caused the initiation of gullies in several occasions in the saturated bottomlands. Sediment concentration at the outlet barely decreased due to entrainment of loose soil from unstable banks of gullies in the periodically saturated bottom areas. Since most uphill drainage were already half filled up with sediments after two years, long term benefits of reducing runoff can only be sustained with continuous maintenance of uphill infiltration furrows.
We apply the Linear Storage Model (LSM) to simulate the influence of the evapotranspiration on discharges. High resolution discharge data from two small catchments in the Czech Republic, the Teply Brook and the Starosuchdolsky Brook catchment are used. The results show the runoff process is simpler in a deeper valley of the Starosuchdolsky catchment where the soil zone is deeper and the valley bottom recharges runoff even during very dry periods. Two-soil zone model is adequate to simulate the diurnal runoff variability. Three-soil zone model is needed in the Teply Brook catchment due to the absence of water transport in the most-upper soil zone. Time delays between minimum and maximum discharge during the day reach up to about 20 hours. Evapotranspiration and hydraulic resistances are as high as 14% of catchment daily runoff in the urbanized Starosuchdolsky Brook catchment and 25% of catchment daily runoff in the forested, less impacted Teply Brook catchment.
Soil compaction causes important physical modifications at the subsurface soil, especially from 10 to 30 cm depths. Compaction leads to a decrease in infiltration rates, in saturated hydraulic conductivity, and in porosity, as well as causes an increase in soil bulk density. However, compaction is considered to be a frequent negative consequence of applied agricultural management practices in Slovakia.
Detailed determination of soil compaction and the investigation of a compaction impact on water content, water penetration depth and potential change in water storage in sandy loam soil under sunflower (Helianthus annuus L.) was carried out at 3 plots (K1, K2 and K3) within an experimental site (field) K near Kalinkovo village (southwest Slovakia). Plot K1 was situated on the edge of the field, where heavy agricultural equipment was turning. Plot K2 represented the ridge (the crop row), and plot K3 the furrow (the inter–row area of the field). Soil penetration resistance and bulk density of undisturbed soil samples was determined together with the infiltration experiments taken at all defined plots.
The vertical bulk density distribution was similar to the vertical soil penetration resistance distribution, i.e., the highest values of bulk density and soil penetration resistance were estimated at the plot K1 in 15–20 cm depths, and the lowest values at the plot K2. Application of 50 mm of water resulted in the penetration depth of 30 cm only at all 3 plots. Soil water storage measured at the plot K2 (in the ridge) was higher than the soil water storage measured at the plot K3 (in the furrow), and 4.2 times higher than the soil water storage measured at the most compacted plot K1 on the edge of the field. Results of the experiments indicate the sequence in the thickness of compacted soil layers at studied plots in order (from the least to highest compacted ones): K2–K3–K1.
Changes of steady state water flow rates and the bromide breakthrough were observed in laboratory infiltration experiments done on a sample of compacted sand and on an undisturbed soil sample (Eutric Cambisol). Infiltration-outflow experiments consisted of series of ponded infiltration runs with seepage face boundary condition at the lower end of columns. The initial water contents were different for each run. The results of the experiment done on an undisturbed soil column showed that the flux rates and water contents measured during quasi-steady state differ between infiltration runs. This finding contradicts the standard theory. The fluctuations of the water content during the steady state flow can be ascribed to the variations in volume of the entrapped air. Similarly, bromide breakthrough curves performed during the steady state flow runs differ for the undisturbed soil sample. The same behaviour was not observed in the sample of homogeneous sand. Computer tomography was utilized to characterize the structure of the undisturbed soil sample with focus on potential preferential flow pathways. To formulate more general conclusions, the infiltration outflow and bromide solute transport experiments have to continue with the aim to collect a representative set of data. and Studie sleduje změny ustálených rychlostí proudění a průnikových čar bromidu na vzorku zhutněného písku a na neporušeném vzorku půdy ze skupiny kambisolů. Experimenty sestávaly ze série výtopových infiltrací na horním okraji a s výronovou plochou na spodním okraji vzorků. Počáteční vlhkost byla pro jednotlivé infiltrační běhy různá. Výsledky experimentu uskutečněného na neporušené půdě ukazují, že se vlhkosti a rychlosti proudění během ustáleného proudění lišily pro jednotlivé infiltrační běhy. Tento efekt není ve shodě se standardní teorií. Změny vlhkosti během ustáleného proudění mohou být způsobeny přítomností uzavřeného vzduchu. Pro neporušený půdní vzorek se lišil také tvar průnikových čar bromidu, měřených během ustáleného proudění. Oba efekty nebyly pozorovány pro vzorek zhutněného písku. Počítačová tomografie byla použita k popisu struktury neporušeného půdního vzorku se zaměřením na přítomnost potenciálních cest preferenčního proudění. K tomu, aby bylo možno formulovat obecné závěry, bude nutné získat reprezentativní soubor dat pomocí zde představeného experimentu.
Ice jams in northern rivers during winter period significantly change the flow conditions due to the extra boundary of the flow. Moreover, with the presence of bridge piers in the channel, the flow conditions can be further complicated. Ice cover often starts from the front of bridge piers, extending to the upstream. With the accumulation of ice cover, ice jam may happen during early spring, which results in the notorious ice jam flooding. In the present study, the concentration of flowing ice around bridge piers has been evaluated based on experiments carried out in laboratory. The critical condition for the initiation of ice cover around bridge piers has been investigated. An equation for the critical floe concentration was developed. The equation has been validated by experimental data from previous studies. The proposed model can be used for the prediction of formation of ice cover in front of a bridge pier under certain conditions.
The aim of this paper is to set up the model describing the depletion runoff process when a catchment is supplied only from subsurface water sources and also to describe a transpiration effect when depleted mostly by riparian vegetation considering it as a diurnal process in hot and rainless period. This model is conceived as a simple linear description of all forms of subsurface runoff supplying the stream flow in fully forested the Teply Brook small catchment (district Zdar nad Sazavou, the Czech Republic) for the dry seasons of 2003 to 2007 when the discharges were continuously recorded at the outlet. There are three interconnected soil water zones, represented by the corresponding subsurface storages in the model. Actual evapotranspiration from the riparian part of the catchment is approximated by a special form of the Fourier series. The model simulates a runoff process using seven independent parameters, evapotranspiration is simulated through another four parameters. The paper points out how the model can be successfully implemented in the simulation of diurnal discharge fluctuation on the small forested experimental catchment in dry periods. and Na základě kontinuálně naměřených průtokových dat z období let 2003-2007 byl pro Teplý potok (okres Žďár nad Sázavou) sestaven lineární odtokový model. V článku je podrobně rozebírána hydrologická charakteristika povodí a na příkladech diskutována vhodnost nasazení tohoto třínádržového systému pro popis chování průtoku korytem v bezesrážkových obdobích. Navrhovaný model charakterizuje povodí s pomocí sedmi hydrologických nezávislých parametrů a dalších čtyř parametrů charakterizujících evapotranspiraci. Článek ukazuje, že řešení navrhovaného modelu může s dobrou přesností aproximovat chování odtoku tohoto malého, převážně lesnatého povodí.
In his criticism of my book Člověk a pravidla [Man and rules], Michal Ivan scrutinized my notion of implicit rule, concluding that it is flawed. In this contribution, I defend my approach, explaining the notion in greater detail. I state that my talk about the existence of an implicit rule refers to the social setting in which some kinds of social (especially linguistic) actions are governed by normative attitudes of the members of the society. These normative attitudes institute the propriety which make instances of actions of the kinds either correct or incorrect; hence people can follow or violate the rule, the rule can come into being, develop, and fade away - without it being explicitly articulated., Ve své kritice své knize Člověk Pravidla [ Člověk a pravidla ], Michal Ivan prozkoumány mé pojem implicitního pravidla, k závěru, že je chybné. V tomto příspěvku obhajuji svůj přístup a podrobněji vysvětluji pojem. Prohlašuji, že můj rozhovor o existenci implicitního pravidla odkazuje na sociální prostředí, ve kterém jsou některé druhy společenských (zejména jazykových) akcí řízeny normativními postoji členů společnosti. Tyto normativní postoje zakládají vhodnost, která činí případy těchto činů správné nebo nesprávné; lidé tak mohou pravidlo dodržovat nebo porušovat, pravidlo může vzniknout, rozvinout se a zmizet - aniž by to bylo výslovně vyjádřeno., and Jaroslav Peregrin
The aim of the paper is to discuss the ersatz theory of Lewis’s impossible worlds, point out its undeniable benefits and demonstrate its costs. Firstly, I present two approaches to Lewis’s impossible worlds taken as constructions out of possibilia. Secondly, I evaluate the proposals using the Lewisian criteria of success concerning the well defined conception of analysis. Although appealing, I do not find the proposals fully persuasive. Thirdly, I discuss the objection from an ad hoc distinction between possible and impossible worlds. I conclude that the objection does not present a special problem for the Lewisian theory. Finally, I motivate a theory of extended modal realism, to wit, modal realism enriched with concrete impossibilia., Cílem práce je diskutovat ersatzovou teorii Lewisových nemožných světů, poukázat na její nepopiratelné výhody a prokázat její náklady. Za prvé, předkládám dva přístupy k Lewisovým nemožným světům, které jsou považovány za konstrukce z možností. Zadruhé hodnotím návrhy s použitím Lewisovských kritérií úspěchu, které se týkají dobře definované koncepce analýzy. I když se mi líbí, nepovažuji návrhy za přesvědčivé. Za třetí, diskutuji o námitce z ad hoc rozlišení mezi možnými a nemožnými světy. Z toho vyvozuji, že námitka nepředstavuje zvláštní problém pro Lewisovu teorii. Nakonec motivuji teorii rozšířeného modálního realismu, vtipu, modálního realismu obohaceného o konkrétní nemožnost., and Martin Vacek
This paper presents a novel framework to use artificial neural network (ANN) for accurate forecasting of river flows at higher lead times. The proposed model, termed as sequential ANN (SANN), is based on the heuristic that a mechanism that provides an accurate representation of physical condition of the basin at the time of forecast, in terms of input information to ANNs at higher lead time, helps improve the forecast accuracy. In SANN, a series of ANNs are connected sequentially to extend the lead time of forecast, each of them taking a forecast value from an immediate preceding network as input. The output of each network is modified by adding an expected value of error so that the residual variance of the forecast series is minimized. The applicability of SANN in hydrological forecasting is illustrated through three case examples: a hypothetical time series, daily river flow forecasting of Kentucky River, USA and hourly river flow forecasting of Kolar River, India. The results demonstrate that SANN is capable of providing accurate forecasts up to 8 steps ahead. A very close fit (>94% efficiency) was obtained between computed and observed flows up to 1 hour in advance for all the cases, and the deterioration in fit was not significant as the forecast lead time increased (92% at 8 steps ahead). The results show that SANN performs much better than traditional ANN models in extending the forecast lead time, suggesting that it can be effectively employed in developing flood management measures.