Tomáš Dostál

Modelling sediment supply to rivers and reservoirs in Eastern Europe during and after the collectivisation period

At present, the landscapes in the former communist countries of Eastern Europe are undergoing a second major change in 50 years. After World War II, collective agricultural systems, such as the United Agricultural Cooperatives and the State Farms, were established. Following the example of the Soviet Union, individual fields were put together in order to enable mass production. This, however, led to an enormous acceleration of erosion and sediment transport processes on arable land. Since the fall of the communist regimes in 1990, farmers, or their successors, can claim back their original property. The large collective fields are split up in smaller spatial units. The land that is not claimed back is abandoned. This new transition has again a huge impact on soil erosion and sediment export to rivers and reservoirs. In order to control and optimize the transition from collective to private farming systems, land arrangement administrations need modeling tools to simulate the geomorphic impact of possible future land use scenarios. In this paper, SEDEM, a spatially distributed sediment delivery model, is calibrated and validated with measured sediment yield data from Czech drainage basins. The results suggest that SEDEM is able to predict the impact of land use changes on the mean annual sediment supply to rivers. Next, SEDEM is applied to assess the impact of a range of possible future landscape scenarios such as the splitting up of large fields in smaller spatial units and conversions from arable land to pasture.

Identification of prevailing storm runoff generation mechanisms in an intensively cultivated catchment

Abstract The fact that flash floods initiated in arable catchments are often accompanied by massive sediment and nutrient loads often leads to the assumption that surface runoff is the principle pathway by which runoff reaches watercourses. On the basis of an evaluation of several rainfall-runoff events in a representative agricultural catchment, we show that runoff from cultivated land may be generated in a way similar to that seen on forested slopes, where shallow subsurface runoff is the predominant pathway by which runoff makes its way to watercourses in most runoff events. To identify the predominant runoff pathway, we employed a combination of turbidity measurements and stream discharge data. Suspended sediment flux, a newly introduced index representing the ratio between precipitation duration and total sediment yield, and direction of the discharge-turbidity hysteresis loops were proposed as reflective indicators of the frequency of runoff via different pathways. In our study, most of the events initiated by rainstorms of various intensities and durations resulted in rapid increases in stream discharge. Although we observed temporal variability of topsoil properties attributable to seasonal weather changes and agricultural activities, e.g. bulk density and porosity, runoff generation was mainly driven by precipitation characteristics and the initial catchment saturation.

Determining the protective effect of agricultural crops on the soil erosion process using a field rainfall simulator.

In this paper the data measured by application of the MDS NZ2 field rainfall simulator have been used to demon strate the effect of vegetation cover on surface runoff generation and soil loss. The results of 15 experiments for two crops (oats and wheat) are presented. Canopy cover and the leaf area index are used to describe the vegetation development. Measured soil loss decreased with growing vegetation significantly from the maximum values 74.7 g/min for oats (38.4 g/min for wheat) to 0.4 g/min (1.5 g/min respectively) from the experimental plot of 16 m 2 . Thus, this work clearly demonstrates the positive effect of canopy development on soil loss. However, the ef fect of the developing cover on the surface runoff generation was not significant.

Floodplain retention capacity assessment for Lužnice river

One of main topics of interdisciplinary project NIVA – Water Retention in Floodplains and Possibilities of Retention Capacity Increase is the assessment of flood wave transformation in the floodplain. The project focuses on broad field of floodplain ecosystem services and flood mitigation is a phenomenon which is researched by the team from Czech Technical University from different points of view and using different methods. Despite the fact that the main influence on flood wave transformation is flow retardation due to the flow velocity decrease, the retention in surface depressions within floodplain has been analyzed to get better overview of whole transformation process. Detailed digital relief model (DRM) has been used for given purposes to be able to analyze terrain depressions volumes. First, the methodology of analysis was prepared and tested on artificial surface. This surface was created using random raster generation, filtration and resampling with final resolution of 1,000 × 1,000 units and height of maximum 10 units above datum. The methodology itself is based on analysis of areas inundated by water at different elevation levels. Volume is then calculated for each depression using extraction of terrain elevations under corresponding water level. The method was then applied on the area of Lužnice River floodplain section to assess the retention capacity of real floodplain with natural character which usually means higher surface retention capacity in comparison to trained rivers. Results obtained from above mentioned analysis applied on Lužnice river are presented in this paper. The importance of floodplain retention capacity for flood transformation is low as results from obtained values.

Sediment transport and water quality in Máchovo Lake (Czech Republic)

Sediment transport and water quality in Máchovo Lake (Czech Republic) Máchovo Lake is a historical reservoir founded by Czech King Charles IV. in 14th century. Located in northern part of central Bohemia it has been widely used for recreation purposes for many decades (or even centuries). Its catchments (ca 100 sq km) consist of intensively used agricultural land (ca 25% of area) and of large forested area under nature protection. Several other lakes (ponds) are chained on the two reservoirs inlets. Irrespective of its great recreation potential Máchovo Lake is one of the Bohemian lakes known for its problems with eutrophication and water quality. The project was set up to point out sources of nutrients and to search for proper solutions. Sediment loads in every lake within the catchments were measured and sampled in order to quantify the nutrients and other pollution. Point and non point sources of phosphorus and other nutrients were searched. Sediment transport within catchments was modelled using WaTEM/SEDEM model. Interestingly, the water quality in the particular ponds varies significantly even though each one of several hundred years old ponds is heavily silted. Soil erosion protection measures within catchments were proposed altogether with flood protection measures in the stream valleys and waste water treatment facilities in surrounding villages. Setting up water quality sampling devices in selected stream profiles was tested and designed. The continual proper management should lead to water quality improvement. Transport sedymentu i jakość wody w Jeziorze Mahovo (Republika Czeska) Położone w północnych Czechach Jezioro Máchovo jest zbiornikiem dla celów rekreacyjnych zbudowanym w XIV wieku przez czeskiego króla Karola IV. Jego zlewnia o powierzchni 100 km2 jest w 25% intensywnie użytkowana rolniczo, a pozostały zalesiony obszar podlega ochronie. Jakość wody i eutrofizacja wód jeziora oraz towarzyszących mu silnie zamulonych stawów stanowi poważny problem ekologiczny. Celem badan było określenie punktowych i powierzchniowych źródeł dostawy składników pokarmowych i rozwiązanie tego problemu. Do oceny dostawy sedymentu zastosowano WaTEM/SEDEM model. Została zaproponowana przeciwpowodziowa i przeciwerozyjna ochrona gleby przed erozją oraz gospodarka ściekami w obrębie zlewni. Działania te powinny doprowadzić do polepszenia jakości wody.