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.
Soil water content and actual water repellency were assessed for soil profiles at two sites in a bare and grass-covered plot of a sand pasture, to investigate the impact of the grass removal on both properties. The soil of the plots was sampled six times in vertical transects to a depth of 33 cm between 23 May and 7 October 2002. On each sampling date the soil water contents were measured and the persistence of actual water repellency was determined of field-moist sam-ples. Considerably higher soil water contents were found in the bare versus the grass-covered plots. These alterations are caused by differences between evaporation and transpiration rates across the plots. Noteworthy are the often excessive differences in soil water content at depths of 10 to 30 cm between the bare and grass-covered plots. These differences are a consequence of water uptake by the roots in the grass-covered plots. The water storage in the upper 19 cm of the bare soil was at least two times greater than in the grass-covered soil during dry periods. A major part of the soil profile in the grass-covered plots exhibited extreme water repellency to a depth of 19 cm on all sampling dates, while the soil profile of the bare plots was completely wettable on eight of the twelve sampling dates. Significant differences in persistence of actual water repellency were found between the grass-covered and bare plots.
In Mediterranean ecosystems, special attention needs to be paid to forest–water relationships due to water
scarcity. In this context, Adaptive Forest Management (AFM) has the objective to establish how forest resources have to
be managed with regards to the efficient use of water, which needs maintaining healthy soil properties even after
disturbance. The main objective of this investigation was to understand the effect of one of the AFM methods, namely
forest thinning, on soil hydraulic properties. At this aim, soil hydraulic characterization was performed on two
contiguous Mediterranean oak forest plots, one of them thinned to reduce the forest density from 861 to 414 tree per ha.
Three years after the intervention, thinning had not affected soil water permeability of the studied plots. Both ponding
and tension infiltration runs yielded not significantly different saturated, Ks, and unsaturated, K–20, hydraulic conductivity
values at the thinned and control plots. Therefore, thinning had no an adverse effect on vertical water fluxes at the soil
surface. Mean Ks values estimated with the ponded ring infiltrometer were two orders of magnitude higher than K–20
values estimated with the minidisk infiltrometer, revealing probably soil structure with macropores and fractures . The
input of hydrophobic organic matter, as a consequence of the addition of plant residues after the thinning treatment,
resulted in slight differences in terms of both water drop penetration time, WDPT, and the index of water repellency, R,
between thinned and control plots. Soil water repellency only affected unsaturated soil hydraulic conductivity
measurements. Moreover, K–20 values showed a negative correlation with both WDPT and R, whereas Ks values did not,
revealing that the soil hydrophobic behavior has no impact on saturated hydraulic conductivity.
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.
Soil moisture content was measured by TDR sensors Aqua-Tel-TDR (Automata, Inc., today McCrometer CONNECT) in a loamy Chernozem on carbonate-rich loess substrate. The sensors, wrapped in slurry made of local soil and water, were installed horizontally into pre-made holes. The bias caused by imperfectly filled gaps between the wall of the hole and the sensor surface was reduced by field calibration. The same gaps made it possible to detect the preferential flow in soil macropores, due to which the reflectometric readings were perceivably higher than analogous readings before percolation events and sometimes higher than the native soil porosity. One typical event is presented. It is envisaged that sensors of this type can be used for semi-quantitative estimation of the preferential flux density, e.g. with the help of dual or multiple porous medium models or the momentum dissipation theory. and Vlhkost hlinité černozemní půdy na karbonátovém sprašovém substrátu byla měřena metodou TDR čidly Aqua-Tel-TDR (Automata, Inc., dnes McCrometer CONNECT). Čidla, obalená před osazením pastou z místní zeminy a vody, byla instalována vodorovně do předvrtaných otvorů. Systematická chyba způsobená nedokonale zaplněnými mezerami mezi čidlem a stěnou otvoru byla zmenšena terénní kalibrací. Tytéž mezery umožnily indikovat preferenční proudění v půdních makropórech, díky němuž byla reflektometrická měření citelně vyšší než analogické hodnoty před průsakovou epizodou a někdy i vyšší než pórovitost původní půdy. Je demonstrována jedna typická epizoda. Lze předpokládat, že čidla tohoto typu mohou být použita k semikvantitativnímu odhadu hustoty preferenčního toku, např. za pomoci modelů dvojného nebo vícenásobného pórovitého prostředí nebo teorie rozptylu hybnosti.
The main objective of this study is to develop a model procedure for predicting low flows for a large set of gauged basins located in the Rhine-Meuse area. The methodology is primarily based on the analysis of recession curves, river discharges being essentially provided by groundwater flow during drought period. Our objective is to use recession coefficients in order to calibrate base flow predictions coming out from a groundwater reservoir. Problems related to the temporal variability of recession coefficients are discussed. We come to the conclusion that lows flows prediction can be improved by implementing a new groundwater reservoir into the RR model based on our knowledge of low flow processes. and Cieľom tejto štúdie je návrh procedúry pre predpoveď minimálnych prietokov pre početnú skupinu malých povodí lokalizovaných v oblasti riek Rýn - Meuse. Metóda je založená predovšetkým na analýze výtokových kriviek počas suchého obdobia, keď sú prietoky dotované hlavne podzemnými vodami. Naším cieľom je použitie výtokových koeficientov na kalibráciu predpovede základného prietoku z podzemných zdrojov. Sú tu diskutované problémy súvisiace s časovou zmenou výtokových koeficientov. Prišli sme k záveru, že prognóza nízkych prietokov môže byť zlepšená implementáciou nového rezervoáru podzemných vôd do zrážkoodtokového modelu, založeného na našich poznatkoch o procesoch tvorby nízkych prietokov.