Hydrological monitoring in small headwater catchments provides the basis for examining complex interrelating hydraulic processes that govern the runoff generation. Contributions of different subsurface runoff mechanisms to the catchment discharge formation at two small forested headwater catchments are studied with the help of their natural isotopic signatures. The Uhlirska catchment (Jizera Mts., Czech Republic) is situated in headwater area of the Lusatian Neisse River. The catchment includes wetlands at the valley bottom developed over deluviofluvial granitic sediments surrounded by gentle hillslopes with shallow soils underlain by weathered granite. The Liz catchment (Bohemian Forest, Czech Republic) is situated in headwater area of the Otava River. It belongs to hillslope-type catchments with narrow riparian zones. The soil at Liz is developed on biotite paragneiss bedrock. The basic comparison of hydrological time series reveals that the event-related stream discharge variations at the Uhlirska catchment are bigger and significantly more frequent than at Liz. The analysis of isotope concentration data revealed different behavior of the two catchments during the major rainfall-runoff events. At Uhlirska, the percentage of the direct runoff formed by the event water reaches its maximum on the falling limb of the hydrograph. At Liz, the event water related fraction of the direct outflow is maximal on the rising limb of the hydrograph and then lowers. The hydraulic functioning of the Uhlirska catchment is determined by communication between hillslope and riparian zone compartments.
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.
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.
Soil hydraulic conductivity is a key parameter to predict water flow through the soil profile. We have developed an automatic minidisk infiltrometer (AMI) to enable easy measurement of unsaturated hydraulic conductivity using the tension infiltrometer method in the field. AMI senses the cumulative infiltration by recording change in buoyancy force acting on a vertical solid bar fixed in the reservoir tube of the infiltrometer. Performance of the instrument was tested in the laboratory and in two contrasting catchments at three sites with different land use. Hydraulic conductivities determined using AMI were compared with earlier manually taken readings. The results of laboratory testing demonstrated high accuracy and robustness of the AMI measurement. Field testing of AMI proved the suitability of the instrument for use in the determination of sorptivity and near saturated hydraulic conductivity.
The interception was recognized as an important part of the catchment water balance in temperate climate. The mountainous forest ecosystem at experimental headwater catchment Liz has been subject of long-term monitoring. Unique dataset in terms of time resolution serves to determine canopy storage capacity and free throughfall. Spatial variability of throughfall was studied using one weighing and five tipping bucket rain gauges. The basic characteristics of forest affecting interception process were determined for the Norway spruce stand at the experimental area - the leaf area index was 5.66 - 6.00 m2 m-2, the basal area was 55.7 m2 ha-1, and the crown closure above individual rain gauges was between 19 and 95%. The total interception loss in both growing seasons analyzed was 34.5%. The mean value of the interception capacity determined was about 2 mm. Throughfall exhibited high variability from place to place and it was strongly affected by character of rainfall. On the other hand, spatial pattern of throughfall in average showed low variability.
The main objective of this study is to assess the effect of hysteresis of soil hydraulic properties on model predictions of soil water movement in a variably saturated soil. The model predictions are generated by the S1D model, which is based on numerical solution of one-dimensional Richards’ equation. The analysis is made for a loamy sand soil located in a small headwater catchment. The model is used to simulate the development of soil water pressure during three successive vegetation seasons. Three major simulation scenarios are formulated: the first scenario assumes no hysteresis in soil hydraulic properties, the second scenario involves a predefined hypothetical hysteresis, while the third scenario is based on optimized hysteresis, determined through the inverse modeling procedure. The analysis of the simulation results suggests that, in our case, ignoring hysteresis does not lead to any significant deviation of the model predictions from the observed soil water system responses. and Možnosti efektivně matematicky modelovat proudění vody v přirozených půdních formacích omezuje komplikovanost určení půdních hydraulických charakteristik, a to nejen s ohledem na jejich prostorovou a časovou variabilitu, ale také hysterezi. Příspěvek je zaměřen na testování vlivu hystereze na výsledky simulací proudění půdní vody v podmínkách malého horského povodí. Numerický model S1D, řešící Richardsovu rovnici v jednorozměrném tvaru, byl použit k výpočtu sezónního vývoje tlaku půdní vody. V simulacích byla alternativně uvažována hystereze retenční křivky. Odchylky mezi odezvami modelu a měřeními byly minimalizovány optimalizací scaling faktorů. Rozsáhlý srovnávací soubor uskutečněných optimalizací umožnil posoudit rozdíly modelové odezvy dvou hysterezních a jedné nehysterezní varianty a kvantifikovat dopad zanedbání hystereze na přesnost předpovědi modelu. Neuvažování hystereze v našem případě nezhoršuje schopnost modelu popsat změny půdní vlhkosti.
A one-dimensional dual-continuum model (also known as dual-permeability model) was used to simulate the lateral component of subsurface runoff and variations in the natural 18O content in hillslope discharge. Model predictions were analyzed using the GLUE generalized likelihood uncertainty estimation procedure. Model sensitivity was evaluated by varying two separate triplets of parameters. The first triplet consisted of key parameters determining the preferential flow regime, i.e., the volumetric proportion of the preferential flow domain, a first-order transfer coefficient characterizing soil water exchange between the two flow domains of the dual-continuum system, and the saturated hydraulic conductivity of the preferential flow domain. The second triplet involved parameters controlling exclusively the soil hydraulic properties of the preferential flow domain, i.e., its retention curve and hydraulic conductivity function. Results of the analysis suggest high sensitivity to all parameters of the first triplet, and large differences in sensitivity to the parameters of the second triplet. The sensitivity analysis also confirmed a significant improvement in the identifiability of preferential flow parameters when 18O content was added to the objective function. and K simulacím laterální složky podpovrchového proudění a změn koncentrace izotopu kyslíku 18O ve vodě vytékající ze svahu byl použit jednorozměrný model využívající přístupu duálního kontinua. Nejistota modelových předpovědí byla odhadnuta s využitím metody zobecněné věrohodnosti (GLUE). Citlivost modelu byla zjišťována pomocí variací dvou samostatných trojic parametrů. První trojice sestávala z klíčových parametrů pro určení režimu preferenčního proudění, tj. objemového podílu preferenční domény proudění, přenosového koeficientu charakterizujícího výměnu vody mezi oběma doménami duálního systému a nasycené hydraulické vodivosti preferenční domény. Druhá trojice zahrnovala výhradně parametry určující hydraulické charakteristiky preferenční domény proudění, tj. retenční křivku a funkci hydraulické vodivosti. Z výsledků analýzy vyplývá vysoká citlivost modelu na všechny parametry z první trojice a velké rozdíly v citlivostech parametrů druhé trojice. Analýza dále potvrdila významné zlepšení zjistitelnosti parametrů preferenční domény v případě, kdy je do cílové funkce přidána koncentrace izotopu kyslíku 18O.