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Antoni Grzywna, Andrzej Bochniak, Kamil Nieścioruk
University of Life Sciences in Lublin, Poland
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Abstract
The analysis of river network density was conducted using ArcGIS and information gathered from cartographic materials. The past state was vectorised using the 1:50 000 topographic map of 1938 by Military Geographical Institute. The modern one was based on the visualisation of VMap L2 topographic database of 2011. Both materials were georeferenced into the WGS. The next step was to create equidistant from the research area central point. The zones covered 4 kilometres in diameter with step every 250 meters and with limitation to the catchments area. Lakes areas were subtracted from the zones. The river network was then intersected with the zones resulting in lengths values in every zone. They were used to calculate river network density. It can be illustrated by means of variogram, presenting a change of network density with growing distance from the given centre point. The largest transformations of hydrographic network took place in the 1960s of the 20th century due to the construction of Wieprz-Krzna Canal, Piwonia regulation, and wetlands drainage. The river length increased by 5.3 km, and its headwater was transferred from Nadrybie Lake to Uściwierzek Lake. Density of hydrographic network increased from 0.98 km·km-2 in 1938 to 2.77 km·km-2 in 2011 with the decrease of area of lakes by 16.5%. On the basis of spatial statistics, the spatial network structure in examined area in both years can be described as clusters of regular size and random distribution. Pearson's correlation coefficient for the 1938 and 2011 is significant and amounts to 0.5 which is the result of new watercourses emergence. Ripley's K test shows the most significant growth of clusters at the distance of about 2.75 km from the centre of the region.

Keywords 
river network, lakes drainage, Ripley’s K test, Pearson's test

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