Abstract:The paper presents a method for the correction of low quality DEMs, based on aerial photographs, for use in 2D flood modeling. The proposed method was developed and tested on the example of the floodplain of the Warta River, which is the third biggest river in Poland. The correction of DEM is based on a series of a small number of measurements using GPS-RTK, which enable calculations of the global statistics like mean error (ME), root mean square error (RMSE) and standard deviation (SD). The impact of DEM accuracy was estimated by using a 2D numerical model. The calculated values of flow velocities, inundation area and volume of floodplain for each tested DEM were compared. The analyses indicate that, after the correction procedure, the predictions of corrected DEM based on poor quality data is in good quantitative and qualitative agreement with the referenced LIDAR DEM. The proposed method may be applied in the areas for which high resolution DEMs based on LIDAR data are not available.
This study compares four digital elevation models (DEMs), based on various data sources, to define polder retention capacities. Two commercial and two publically available, free of charge data sources were used. Commercial sources are DEMs based on aerial images and LIDAR (Light Detection and Ranging) data. Free data source DEMs generated are based on: SRTM (Shuttle Radar Topography Mission) and ASTER GDEM (ASTER Global Digital Elevation Model). In addition, the impact of the spatial resolution of the numerical terrain model on the calculated polder volume was evaluated. A DEM based on LIDAR data was used as the reference model and was supplemented with our own geodetic GPS (Global Positioning System) measurements. In flood modeling and management, including retention of river valleys and polders, it is necessary to properly estimate their capacity and the relation between capacity and water level. The study showed the impact of quantitative and qualitative data sources in determining the retention capacity of a polder.
This paper presents an analysis of the effectiveness of variants of the reconstruction of a polder, which is part of the flood protection system of a large urban agglomeration. The Golina polder, located in the floodplain of the Warta River, was selected as the case study. The multi-criteria decision support methods AHP and Fuzzy AHP were used to assess the effectiveness of individual variants. Information on the floods from 1997 and 2010, data on land cover, land development, nature and historical objects were used to estimate the value of the coefficients for the multi-criteria decision methods. It was shown that the planned deep modernization of the hydrotechnical infrastructure and the purchase of land in the polder area is less effective than maintaining the current state of development of the polder.
Reinforced concrete structures are frequently designed and executed in such facilities as: halls, warehouses, factories, multi-family buildings, single-family buildings, tanks, silos and many others. For this type of structures, it is particularly relevant to provide an appropriate thickness of concrete lagging, which aims at protecting reinforcement against corrosion, and to design it with appropriate spacing allowing the in-between space to be filled with a concrete mix. A frequent problem met while making reinforced concrete structures is such a density of reinforcing bars, particularly within structural nodes, that there is no possibility of filling the space between them with a concrete mix or it is not possible to vibrate the concrete mix in order to prevent segregation of mixture components. Structural nodes are points where special attention should be paid to careful compaction of concrete mixes and application of measures that prevent concrete from adhering to molds. The case study illustrates two structural nodes connecting a column with a bolt, located in a wall with a column-transom structure. During the modernisation works carried out in the production hall there were exposed two structural nodes completely unfilled with a concrete mix and with visible reinforcing bars that showed little buckling and the onset of corrosion. The columns, due to their location in the general static scheme of the wall, were subjected to compression or locally compressed and affected by bending. Particularly unfavourable was the fact that the columns did not feature the concrete lagging in the compression zone of the element. Removal of concrete lagging in the compression zone always results in decrease in the bearing capacity of a structure. It can be concluded that due to faulty workmanship the columns had a lower load bearing capacity than anticipated in the building permit design. The paper provides software-derived guidelines for repairing reinforced concrete columns so as to obtain the value of load bearing capacity equal or higher than expected in the design and on the assumption that repair works would be carried out on columns subjected to loading.
As climate changes progress we are dealing with violent and excessive environmental actions. However, the impacts of loads acting on a building object caused by unlikely phenomena such as: fire, explosion, flood, vehicle impact, plane impact, excessive snowfall, and excess wind gusts are still being ignored when analyzing the structure of building objects in the combinatorics of loads. The paper presents a multi-criteria approach to accidental actions and analyzes design situations and load combinations in relation to accidental actions. The existing legal acts were used to define the concept of a construction disaster. The authors verified, on the basis of applicable legal acts and design guidelines, individual analysis strategies for ensuring the safety of building objects and divided them into consequence classes of structural damage. They collected and analyzed the number of construction disasters which occurred in Poland between 1995–2019 (25 years) based on the data from the General Office of Building Control. The number of disasters was divided by voivodeships and causes and supplemented with the data on the number of people injured. The article presents the direction of research development that could be undertaken in order to eliminate future catastrophes caused by the omission of the analysis of the impact of accidental actions at the design stage. Statistical analyses were carried out to show whether land use, population density, and weather factors (wind) affect the number of recorded disasters. It has been shown that regions that have preserved the sustainable development of their territories are less vulnerable to disasters resulting from extreme weather events.
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