Dorota Mirosław-Świątek

A hydrodynamic model coupled with GIS for flood characteristics analysis in the Biebrza riparian wetland

A hydrodynamic model coupled with GIS for flood characteristics analysis in the Biebrza riparian wetland The paper presents the application of the hydrodynamic 1D unsteady model for calculating hydro-ecological flood characteristics in the Lower Biebrza River Basin located in northeastern Poland. The 1D model is combined with the Digital Elevation Model for determining of flood extent. The model was calibrated using measurements of flood extent and verified comparing calculated flood extent to satellite images. Consequently, the flood characteristics important for plant communities of the riparian wetland were calculated for vegetation season (February-September) daily time series (1961-1996). Then, their relations to particular generalized groups of vegetation were analyzed. The results show a significant congruity between the type of vegetation and calculated flood characteristics. The hydrodynamic model was confirmed to be a useful tool for calculating flood characteristics.

Scenarios of the spread of a waste heat discharge in a river — Vistula River case study

The problem of two-dimensional mathematical modelling of heated cooling water discharges into running waters is considered in the paper. Two models — one for the evaluation of 2D turbulent velocity field and the other, developed by authors of the study, for 2D heat transport in open-channels — were used in the calculations. Relevant scenarios of the spread of heated water discharged from a designed gas-stem power plant to be constructed at the Vistula River were presented. Environmentally most friendly variant of the discharge of the thermal pollution was selected from among four various variants.

Groundwater Modelling and Hydrological System Analysis of Wetlands in the Middle Biebrza Basin

In the presented approach, a three dimensional finite-difference steady-state groundwater model was applied to analyze the groundwater flow system of the Middle Biebrza Basin. Study contains analysis of hydrogeological and morphological outline of the area, as well as the description of developed groundwater model including conceptual model description, model calibration and sensitivity analysis of parameters. Analysis of volumetric water budget of the model within assumed boundary conditions indicated that groundwater resources of the analyzed part of the Middle Biebrza Basin in approximately 80% come from lateral inflow from the adjacent plateaus. Analysis of spatial distribution of groundwater discharge indicated that the most intensive groundwater inflow to the top peat layer is concentrated within the “Czerwone Bagno”, where the peatlands are not degraded and wetland habitats develop naturally, not being directly impacted by drainage ditches and canals.

Temporal variability of the selected flood parameters in the Biebrza River valley

Temporal variability of the selected flood parameters in the Biebrza River valley The paper presents the application of the hydrodynamic one-dimensional model of river flow based on St Venant equations for calculation of annual floods characteristics in the Lower Biebrza River Basin situated in the Northeast of Poland. This model was combined with the Digital Elevation Model (DEM) for determining of area of flooding, its mean depth and flood volume. The model was calibrated using measurements of flood extent and verified comparing calculated flood extent to satellite images. The water level values calculated with the numerical model of flood-flow for cross-sections were next used to determine the digital model of the floodwater table in the valley. Then, inundation extent maps and water depth maps were calculated for whole area of the valley by overlaying the DEM and water table layers. This procedure, flood simulations with the hydrodynamic model and GIS analysis for determinations of inundation extent, was repeated for each day of the analyzed period of 1966-2000. A set of each year maximum calculated areas of flooding with related mean water depths and flood volumes was created and it was submitted to the trend analysis in order to determine possible change tendencies. Statistical analysis of three above described time series of annual flood characteristics was conducted with the use of moving average technique and linear regression method. Moving averages were calculate in two variants: with time step of 5 years and of 10 years. Next, linear trends were calculated by linear regression method. The results indicate that the developed hydrodynamic model of river flow combined with the DEM was useful for the calculation of annual maximum floods in the Lower Biebrza Valley and their parameters. Analysis of calculated flood parameters variability within the analyzed time period of 1961-2000 show decreasing trends for investigated area. This means that results of climate changes are perceptible in investigated area and they form serious danger to riparian wetlands. Czasowa zmienność wybranych parametrów wezbrań w dolinie rzeki Biebrzy W artykule przedstawiono zastosowanie jednowymiarowego hydrodynamicznego modelu przepływu w rzece bazującego na równaniach Saint Venanta do obliczenia charakterystyk maksymalnych rocznych zalewów rzecznych w basenie dolnej Biebrzy, usytuowanym w północno-zachodniej Polsce. Model ten został połączony z Numerycznym Modelem Terenu (NMT) dla wyznaczenia zasięgu zalewu, jego średniej głębokości i objętości. Model został skalibrowany z wykorzystaniem pomiarów zasięgu zalewu i zweryfikowany poprzez porównanie obliczonego zasięgu zalewu ze zdjęciami satelitarnymi. Rzędne zwierciadła wody obliczone modelem numerycznym przepływu dla przekroi poprzecznych były dalej użyte do wyznaczenia cyfrowego modelu zwierciadła wody w dolinie. Następnie mapy zasięgu zalewu i mapy jego głębokości zostały obliczone dla całego obszaru doliny poprzez nałożenie NMT i warstw zwierciadła wody. Ta procedura, obliczanie wezbrań przy pomocy modelu hydrodynamicznego i analiza GIS dla określenia zasięgu zalewu, została powtórzona dla każdego dnia w analizowanym okresie 1961-2000. Utworzony został zbiór maksymalnych rocznych zasięgów zalewu wraz z odpowiadającymi im średnimi głębokościami i objętościami wezbrania, który został poddany analizie trendów w celu określenia możliwych tendencji zmian. Przeprowadzona została analiza statystyczna trzech powyżej opisanych serii czasowych charakterystyk rocznych wezbrań z zastosowaniem techniki średnich ruchomych i analizy regresji. Średnie ruchome obliczono dla dwóch wariantów: z krokiem czasowym 5 lat i 10 lat. Następnie obliczono trendy liniowe metodą regresji liniowej. Uzyskane rezultaty wykazały, że opracowany hydrodynamiczny model przepływu w rzece połączony z NMT był przydatny do obliczania maksymalnych rocznych zalewów rzecznych w basenie dolnej Biebrzy i ich charakterystyk. Analiza zmienności obliczonych parametrów wezbrania dla okresu 1961-2000 wykazała istnienie trendów malejących dla badanego obszaru. Oznacza to, że rezultaty zmian klimatycznych są zauważalne w badanym obszarze i stanowią one poważne zagrożenie dla mokradeł przybrzeżnych.

The flood extent in the lower Biebrza basin calculated by the 1D flow model for different land use scenarios

The flood extent in the lower Biebrza basin calculated by the 1D flow model for different land use scenarios The flood extent in the lower Biebrza basin calculated by the 1D flow model for different land use scenarios. An application of an steady 1D flow model for determination of a flood extent in the natural river valley is discussed in this paper. The Pasche method was used to calculate the total Darcy-Weisbach friction factor for each cross section according to the type of vegetation and flow interaction between the main channel and vegetated areas. In this approach friction caused by interaction between the main channel and vegetated areas are taken into account. The model was applied to the Biebrza Valley, fairly undisturbed river-marginal peatland, located in the north-east of Poland. Actual land use carried out in the National Park was analyzed to determine the influence of changes in the vegetation structure on the flood extent in the river valley. The obtained results show variation of a flooded area in relation to the vegetation of the floodplain. Zastosowanie jednowymiarowego modelu hydrodynamicznego do wyznaczania zasięgu zalewu w Basenie Dolnym Biebrzy przy różnym sposobie użytkowania. W artykule przedstawiono jak różny sposób użytkowania doliny Basenu Dolnego Biebrzy wpływa na zasięg zalewów oraz ich średnią głębokość. Obliczenia przeprowadzono dla przepływu maksymalnego oraz średniej wartości zaobserwowanych przepływów maksymalnych z wielolecia, obejmującego okres 1965-1996. Obliczone jednowymiarowym modelem hydrodynamicznym rzędne zwierciadła wody wykorzystano za pomocą technik GIS i Numerycznego Modelu Terenu do określenia zasięgu oraz średniej głębokości zalewów. Zastosowany model hydrodynamiczny na podstawie ogólnego prawa przepływu Darcy-Weisbacha oraz procesy wymiany pędu i masy pomiędzy korytem głównym a terenami zalewowymi w ujęciu zaproponowanym przez Pasche, pozwala na uwzględnienie w obliczeniach wpływu porastającej tereny zalewowe roślinności. Cztery scenariusze użytkowania doliny realizowane są w modelu obliczeniowym poprzez przestrzenną zmienność chropowatości absolutnej roślinności porastającej dolinę rzeki. Scenariusze obejmują działania w zakresie ekstensywnego użytkowania terenów podmokłych, jak koszenie, karczowanie i wypasanie rozległych obszarów łąk. Przeanalizowano również scenariusz, w którym rozległe obszary torfowisk nie są objęte użytkowaniem, lecz są pozostawione do naturalnej sukcesji.

Developing an algorithm for enhancement of a digital terrain model for a densely vegetated floodplain wetland

Abstract. Airborne laser scanning survey data were conducted with a scanning density of 4  points/m2 to accurately map the surface of a unique central European complex of wetlands: the lower Biebrza River valley (Poland). A method to correct a degrading effect of vegetation (so-called “vegetation effect”) on digital terrain models (DTMs) was applied utilizing remotely sensed images, real-time kinematic global positioning system elevation measurements, topographical surveys, and vegetation height measurements. Geographic object-based image analysis (GEOBIA) was performed to map vegetation within the study area that was used as categories from which vegetation height information was derived for the DTM correction. The final DTM was compared with a model obtained, where additional correction of the “vegetation effect” was neglected. A comparison between corrected and uncorrected DTMs demonstrated the importance of accurate topography through a simple presentation of the discrepancies arising in features of the flood using various DTM products. An overall map classification accuracy of 80% was attained with the use of GEOBIA. Correction factors developed for various types of the vegetation reached values from 0.08 up to 0.92 m and were dependent on the vegetation type.

Modelling of hydrological processes in the Narew catchment

Operational Rainfall/Snowmelt-runoff Model for Upper Narew River.- Multi-site Calibration and Validation of the Hydrological Component of SWAT in a large Lowland Catchment.- Automatic Calibration of the WetSpa Distributed Hydrological Model for small Lowland Catchments.- Modelling Hydrological Flow Paths during Snowmelt induced high flow event

Processing of airborne laser scanning data to generate accurate DTM for floodplain wetland

Structure of the floodplain, especially its topography and vegetation, influences the overland flow and dynamics of floods which are key factors shaping ecosystems in surface water-fed wetlands. Therefore elaboration of the digital terrain model (DTM) of a high spatial accuracy is crucial in hydrodynamic flow modelling in river valleys. In this study the research was conducted in the unique Central European complex of fens and marshes - the Lower Biebrza river valley. The area is represented mainly by peat ecosystems which according to EU Water Framework Directive (WFD) are called “water-dependent ecosystems”. Development of accurate DTM in these areas which are overgrown by dense wetland vegetation consisting of alder forest, willow shrubs, reed, sedges and grass is very difficult, therefore to represent terrain in high accuracy the airborne laser scanning data (ALS) with scanning density of 4 points/m2 was used and the correction of the “vegetation effect” on DTM was executed. This correction was performed utilizing remotely sensed images, topographical survey using the Real Time Kinematic positioning and vegetation height measurements. In order to classify different types of vegetation within research area the object based image analysis (OBIA) was used. OBIA allowed partitioning remotely sensed imagery into meaningful image-objects, and assessing their characteristics through spatial and spectral scale. The final maps of vegetation patches that include attributes of vegetation height and vegetation spectral properties, utilized both the laser scanning data and the vegetation indices developed on the basis of airborne and satellite imagery. This data was used in process of segmentation, attribution and classification. Several different vegetation indices were tested to distinguish different types of vegetation in wetland area. The OBIA classification allowed correction of the “vegetation effect” on DTM. The final digital terrain model was compared and examined within distinguished land cover classes (formed mainly by natural vegetation of the river valley) with archival height models developed through interpolation of ground points measured with GPS RTK and also with elevation models from the ASTER-GDEM and SRTM programs. The research presented in this paper allowed improving quality of hydrodynamic modelling in the surface water-fed wetlands protected within Biebrza National Park. Additionally, the comparison with other digital terrain models allowed to demonstrate the importance of accurate topography products in such modelling. The ALS data also significantly improved the accuracy and actuality of the river Biebrza course, its tributaries and location of numerous oxbows typical in this part of the river valley in comparison to previously available data. This type of data also helped to refine the river valley cross-sections, designate river banks and to develop the slope map of the research area.

Too wet and too dry? Uncertainty of DEM as a potential source of significant errors in a model-based water level assessment in riparian and mire ecosystems

Modelling groundwater depths in floodplains and peatlands remains a basic approach to assessing hydrological conditions of habitats. Groundwater flow models used to compute groundwater heads are known for their uncertainties, and the calibration of these models and the uncertainty assessments of parameters remain fundamental steps in providing reliable data. However, the elevation data used to determine the geometry of model domains are frequently considered deterministic and hence are seldom considered a source of uncertainty in model-based groundwater level estimations. Knowing that even the cutting-edge laser-scanning-based digital elevation models have errors due to vegetation effects and scanning procedure failures, we provide an assessment of uncertainty of water level estimations that remain basic data for wetland ecosystem assessment and management. We found that the uncertainty of the digital elevation model (DEM) significantly influenced the results of the assessment of the habitat’s hydrological conditions expressed as groundwater depths. In extreme cases, although the average habitat suitability index (HSI) assessed in a deterministic manner was defined as ‘unsuitable’, in a probabilistic approach (grid-cell-scale estimation), it reached a value of 40% probability, signifying ‘optimum’ or ‘tolerant’. For the 24 habitats analysed, we revealed vast differences between HSI scores calculated for individual grid cells of the model and HSI scores computed as average values from the set of grid cells located within the habitat patches. We conclude that groundwater-modelling-based decision support approaches to wetland assessment can result in incorrect management if the quality of DEM has not been addressed in studies referring to groundwater depths.

Application of the Bayesian Belief Nets in dam safety monitoring

Application of the Bayesian Belief Nets in dam safety monitoring The systems for earth dam monitoring should enable measurements of basic physical parameters describing the behavior of the structure, including: soil water pressure, soil stress, displacements, leaks, and drainage discharges. In the case of earth dam safety assessment, the monitoring data are used to detect any anomalies in dam behavior. In this paper, the dam safety has been analyzed using the Bayesian Nets. Two types of information: water pressure measurements and drainage discharge measurements are used in analyses. The seepage anomalies in the Klimkówka Dam were considered in demonstrate the practical advantages of using the Bayesian Nets for monitoring data interpretation. Presented examples of the Bayesian Nets applications (forward and backward propagation) in analysis of seepage through earth dams show that this method can be an effective tool supporting an assessment of dams technical condition and monitoring of the dam safety. Zastosowanie sieci Bayesa w monitoringu bezpieczeństwa zapór wodnych Systemy monitorowania zapór ziemnych powinny umożliwiać pomiar podstawowych parametrów fizycznych opisujących zachowanie się konstrukcji. Do podstawowego monitoringu należą pomiary piezometryczne, pomiar przemieszczeń, wydatki w drenażach, obserwacje przecieków. W przypadku zapór ziemnych dane z monitoringu stosowane są w celu wykrycia anomalii w zachowaniu się obiektu. W niniejszej pracy w ogólny sposób zaprezentowano możliwosść wykorzystania sieci Bayesowskich do analizy bezpieczeństwa zapory wodnej w oparciu o monitoring piezometryczny i obserwacje wydatków w drenażu. Na przykładzie zapory Klimkówka pokazano możliwość zastosowania wnioskowania w przód i wstecz w celu poznania przyczyn nieprawidłowości w przebiegu filtracji. Omówione przykłady analizy wskazują że sieci Bayesowskie mogą być skutecznym narzędziem wspomagającym ocenę stanu technicznego zapór.