This study focuses on modeling hydrological responses of shallow hillslope soil in a headwater catchment. The research is conducted using data from the experimental site Uhlířská in Jizera Mountains, Czech Republic. To compare different approaches of runoff generation modeling, three models were used: (1) onedimensional variably saturated flow model S1D, based on the dual-continuum formulation of Richards’ equation; (2) zero-dimensional nonlinear morphological element model GEOTRANSF; and (3) semidistributed model utilizing the topographic index similarity assumption - TOPMODEL. Hillslope runoff hydrographs and soil water storage variations predicted by the simplified catchment scale models (GEOTRANSF and TOPMODEL) were compared with the respective responses generated by the more physically based local scale model S1D. Both models, GEOTRANSF and TOPMODEL, were found to predict general trends of hydrographs quite satisfactorily; however their ability to correctly predict soil water storages and inter-compartment fluxes was limited. and Studie je zaměřena na modelování hydrologické reakce mělké svahové půdy v pramenné části povodí Nisy, k výzkumu byla použita data z experimentálního povodí Uhlířská. Porovnání různých konceptuálních představ modelování odtoku bylo uskutečněno pro: (1) jednorozměrný model proměnlivě nasyceného proudění S1D; (2) model založený na bezrozměrném nelineárním morfologickém prvku - GEOTRANSF a (3) semi-distribuovaný model využívající principu podobnosti na základě topografického indexu - TOPMODEL. Hydrogramy odtoku ze svahu a změny zásob vody v půdě vypočtené zjednodušenými modely GEOTRANSF a TOPMODEL byly porovnány s odpovídajícími odezvami fyzikálně založeného modelu S1D. Oba modely, GEOTRANSF i TOPMODEL, byly poměrně úspěšné v předpovědi základních trendů hydrogramů odtoku, jejich schopnost správně předpovídat zásoby vody v půdě a toky mezi nimi však byla omezená.
The paper provides an overview of recent hydrology-related research conducted by the Research Institute for Soil and Water Conservation and its predecessors. Research catchments and similar research sites, mostly under agricultural land use, are described. The principal catchments, located in Central and East Bohemian peneplains and highlands (Cerhovický potok near Hořovice, anonymous stream above Černičí near Čechtice, Kopaninský tok near Pelhřimov, and Žejbro near Skuteč with its subcatchments) are described in a greater detail with reference to web presentations (http://www.hydromeliorace.cz/povodi/ index.html). The second part overviews the main research results obtained, prevailingly during the last decade, in the field of catchment hydrology, water quality generation, agronomic measures for protection against nitrate pollution, the effect of tile drainage on extreme flows and water quality, soil water in the vadose zone with preferential flow and the landscape-ecological aspects of water resources protection. It is concluded that some problems could not be solved if the questions were not posed in a hydrological manner. The authors recommend to generalise empirical research results by modelling and to intensify connections between RISWC research and hydrological activities of other institutions. and Práce podává přehled novější historie výzkumu s hydrologickými prvky ve Výzkumném ústavu meliorací a ochrany půdy a v ústavech, které byly jeho předchůdci. Stručně popisuje jednotlivá malá výzkumná povodí a další výzkumné lokality, většinou se zemědělským využitím půdy. Hlavní výzkumná povodí, umístěná v oblasti středočeských a východočeských parovin a pahorkatin (Cerhovický potok u Hořovic, bezejmenný potok nad Černičím u Čechtic, Kopaninský tok u Pelhřimova a Žejbro u Skutče se svými podpovodími), jsou popsána podrobněji s odkazem na prezentace na webu (http://www.hydromeliorace.cz/povodi/index.html). Ve druhé části článku je podán přehled hlavních výsledků výzkumu dosažených převážně v posledním desetiletí v oblasti hydrologického režimu povodí a mechanismů tvorby jakosti vody, agronomických opatření na ochranu před dusičnanovým znečištěním, vlivu drenážních systémů na extrémní průtoky a jakost vod, vody v nenasycené zóně půdy s preferenčním prouděním a krajinně ekologických aspektů ochrany vodních zdrojů. Závěrem se konstatuje, že řadu problémů by nebylo možno vyřešit, kdyby otázky nebyly kladeny hydrologickým způsobem. Autoři doporučují zobecnit empirické výzkumy modelováním a zintenzivnit návaznost výzkumu VÚMOP na hydrologické aktivity jiných institucí.
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.
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.
Ponded infiltration experiment is a simple test used for in-situ determination of soil hydraulic properties, particularly saturated hydraulic conductivity and sorptivity. It is known that infiltration process in natural soils is strongly affected by presence of macropores, soil layering, initial and experimental conditions etc. As a result, infiltration record encompasses a complex of mutually compensating effects that are difficult to separate from each other. Determination of sorptivity and saturated hydraulic conductivity from such infiltration data is complicated. In the present study we use numerical simulation to examine the impact of selected experimental conditions and soil profile properties on the ponded infiltration experiment results, specifically in terms of the hydraulic conductivity and sorptivity evaluation. The effect of following factors was considered: depth of ponding, ring insertion depth, initial soil water content, presence of preferential pathways, hydraulic conductivity anisotropy, soil layering, surface layer retention capacity and hydraulic conductivity, and presence of soil pipes or stones under the infiltration ring. Results were compared with a large database of infiltration curves measured at the experimental site Liz (Bohemian Forest, Czech Republic). Reasonably good agreement between simulated and observed infiltration curves was achieved by combining several of factors tested. Moreover, the ring insertion effect was recognized as one of the major causes of uncertainty in the determination of soil hydraulic parameters.
Infiltration-outflow experiments were performed on undisturbed soil samples of coarse sandy loam simultaneously with the imaging of flow process by means of magnetic resonance (MR) imaging. The flow in soil under study is highly preferential and exhibits time instability of soil hydraulic properties. For the transient part of infiltration runs, fast 2D imaging was used. For the steady state flow and for the equilibrium state after drainage, horizontal 2D imaging and mapping of longitudinal relaxation (T1) was performed. To obtain the information about internal soil structure all samples were imaged by the computer tomography (CT). The results of all the measurements represent a unique data set. For each sample it contains a record of cumulative infiltration and outflow, hydraulic pressure heads and the simultaneous MR visualization of each particular experiment. Suction pressure heads show a good agreement with the propagation of the wetting front in the sample as displayed by the MR at the very beginning of the each infiltration run. Presented data are the result of first experiment, where MR imaging of infiltration into undisturbed soil samples was combined with concurrent monitoring of suction pressure heads. The next step is to use the gained data for modeling of the infiltration in heterogeneous soil. and Uskutečnili jsme infiltračně výtokový experiment na neporušených vzorcích hlinitopísčité půdy za souběžného snímkování metodou magnetické rezonance (MR). Zkoumaná půda vykazuje výrazné preferenční proudění a časovou závislost hydraulických charakteristik. Pro transientní fáze experimentů jsme použili rychlého vertikálního 2D snímkování. Při ustáleném proudění a při rovnovážném stavu byly pořízeny horizontální 2D snímky a bylo provedeno mapování podélné relaxivity (T1). Pro zjištění vnitřní struktury pevné fáze byly všechny vzorky v suchém stavu snímkovány počítačovou tomografií (CT). Výsledkem experimentu je komplexní soubor dat, který kromě snímků MR obsahuje záznam kumulativní infiltrace výtoku a tlakových výšek. Možnosti metody MR jsou demonstrovány na příkladu porovnání sledu 2D snímků MR s měřenými sacími tlakovými výškami během transientní části infiltrace, kde obě měření shodně zaznamenaly postup čela zvlhčení. Prezentovaná data jsou výsledkem prvního snímkování infiltrace do neporušených vzorků půdy pomocí MR v kombinaci se souběžným měřením sacích tlaků. Dalším krokem bude použití takového souboru dat jako podkladu pro modelování procesu infiltrace do půdy.
Temporal variability of the soil hydraulic properties is still an open issue. The present study deals with results of ponded infiltration experiments performed annually in a grid of permanent measurement points (18 spatial and 14 temporal replicates). Single ring infiltrometers were installed in 2003 at a meadow site in the Bohemian Forest highlands, the Czech Republic. The soil at the plot is coarse sandy loam classified as oligotrophic Eutric Cambisol. Soil water flow below infiltration rings has distinctly preferential character.
The results are marked with substantial interannual changes of observed infiltration rates. Considering just the results from the initial four years of the study, the temporal variability did not exceed the spatial variability detected in individual years. In later years, a shift to extremely high infiltration rates was observed. We hypothesize that it is related to structural changes of the soil profile possibly related to combined effect of soil biota activity, climatic conditions and experimental procedure. Interestingly, the temporal changes can partly be described as fluctuations between seemingly stable infiltration modes. This phenomenon was detected in the majority of rings and was found independent of the initial soil moisture conditions.
Soil water repellency causes at least temporal changes in the hydrological properties of a soil which result in, among other things, suboptimal growing conditions and increased irrigation requirements. Water repellency in soil is more widespread than previously thought and has been identified in many soil types under a wide array of climatic conditions worldwide. Consequences of soil water repellency include loss of wettability, increased runoff and preferential flow, reduced access to water for plants, reduced irrigation efficiency, increased requirement for water and other inputs, and increased potential for non-point source pollution. Research indicates that certain soil surfactants can be used to manage soil water repellency by modifying the flow dynamics of water and restoring soil wettability. This results in improved hydrological behavior of those soils. Consequently, the plant growth environment is also improved and significant water conservation is possible through more efficient functioning of the soil. and Vodoodpudivosť pôdy spôsobuje prinajmenšom dočasné zmeny v hydrologických vlastnostiach pôdy, ktoré okrem iného môžu viesť k suboptimálnym podmienkam rastu rastlín a k zvýšenej potrebe závlah. Vodoodpudivosť pôdy je rozšírenejší jav, ako sa pôvodne predpokladalo; bola identifikovaná v mnohých pôdnych typoch a klimatických podmienkach na celom svete. Dôsledkom vodoodpudivosti pôdy je strata zmáčavosti, zvýšený povrchový odtok a preferenčné prúdenie, znížená dostupnosť vody a iných vstupov pre rastliny, znížený účinok závlah, zvýšené požiadavky na vodu a iné vstupy, ako aj zvýšené riziko plošného znečistenia. Výskum naznačuje, že niektoré povrchovo aktívne látky (soil surfactants) môžu upraviť vodoodpudivosť pôdy obnovením omáčania a modifikáciou dynamiky vody. Výsledkom je zlepšenie hydrologických vlastností pôdy. Podobne, výsledkom je zlepšenie prostredia pre rast rastlín, zvýšenie retencie vody v pôde a teda aj efektívnejšia funkcia pôdy.
An understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants.
Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above
strongly heterogeneous and highly permeable deposits and thus are prone to preferential flow and enhanced pollutant
transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon
suburbs (France) established over a highly heterogeneous glaciofluvial deposit covering much of the Lyon region. An investigation
of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic
properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was
used to identify the effects of individual lithofacies that constitute the deposit. Multiple scenarios that considered different
levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied
after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies
triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly
for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on
their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways,
the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective
hydraulic conductivity of the heterogeneous transect.
The application of Brilliant Blue FCF tracer enables to identify flow types in multi-domain porous systems of soils via analyses of morphologic parameters of stained objects occurring in dye pattern profiles, as they represent the footprint of flow processes which occurred in soil during both the infiltration and the redistribution of dye solution. We analysed the vertical dye pattern profiles exposed for different time lengths, and revealed temporal evolution of dye solution redistribution leading to changes in flow types. The field experiment was performed with the Brilliant Blue tracer (the 10 g l–1 concentration) applied on 1m x 1m surface of the Dystric Cambisol. The top litter horizon had been removed before 100 l of the tracer was applied. Four vertical profiles were excavated on the experimental plot (always 20 cm apart) at different times after the irrigation had been finished: 2 hours (CUT 2), 24 hours (CUT 24), 27 hours (CUT 27) and 504 hours (CUT 504). The analyses of the dyed patterns profiles showed the spatio-temporal changes in the dye coverage, surface area density, average BB concentration, and stained path width, which allowed us to specify three stages of dye solution redistribution history: (i) a stage of preferential macropore flow, (ii) a stage of strong interaction between macropore-domain and soil matrix leading to the generation of heterogeneous matrix flow and fingering flow types, and (iii) a final stage of dye redistribution within the soil body connected with leaching of BB caused by meteoric water. With increasing time, the macropore flow types convert to mostly matrix-dominated FTs in the upper part of the soil profile. These results were supported by soil hydrological modelling, which implied that more than 70% of the soil moisture profiles variability among CUT 2–CUT 504 could be explained by the time factor.