Ocena dokładności odwzorowania wałów i przewałów w numerycznym modelu terenu polderu Majdany

The aim of this study was to assess the accuracy of mapping of embankments and embankments control structure as the most important elements affecting the Majdany polder hydraulic characteristics. The polder was built between 1965 and1969 years as part of the drainage valley Tralalka. Area of the polder is equal to around 580 hectares. Capacity is equal up to 3.7 million m3. The polder is located about 4 km southeast of the city Kolo, in the valleys of the Warta, Ner and Rgilewka river network. The paper presents an analysis of the accuracy of the available digital elevation models (DEM) for Majdany polder in TIN format, which were worked out in 2009 on a scale 1:10 000. DEM worked out in 2011 based up on LIDAR data is presented in a scale 1:2 500. DEM in 2009 was worked out on the basis of aerial photographs in the scale of 1:26 000 and is available in the form of TIN, and LIDAR DTM-made ISOK project was based on airborne laser scanning (LIDAR) and it is available in LAS format. An assessment was carried out in the section embankments about 1.4 kilometers representing 21% of the total length of the embankments on the polder and one of embankment control structure 218 m in length. A total of 651 measurements with Sokkia GPS was done including 496 and 155 measurements on embankment and control structure respectively. DEM accuracy assessment was performed separately for embankments and control structures. Due to the fact that the distribution of errors of embankments was close to a normal distribution, the following statistical measures was used: Root Mean Square Error (RMSE), mean error (ME) average and standard deviation (SD). Due to the fact that the distribution of the error for embankment control structure on DEM significantly deviates from a normal distribution robust statistical methods like: median, Normalized Median Absolute Deviation (NMAD), 68.3% and 95% quartile was applied. The study showed that the data quality obtained from DEM are usually not sufficient for modeling embankment and control structure. Therefore, if the DEM generate the above data source (LIDAR or aerial images) is acceptable – talking only of polder topography, in order to estimate the volume and modeling its work unacceptable due to the relatively large errors in the mapping embankment control structures. It is necessary improve these DEM even by direct measurements of the same terrain such as GPS-RTK devices.