The influence of morphological changes of small lowland river on discharge rate

Abstract

Abstract The influence of morphological changes of small lowland river on discharge rate. The aim of the study was the comparison of the changes of cross-sections and longitudinal profile of the Mała river at the distance of 600 m. The paper presents the geometry changes of the river from field measurements made in 2013 in comparison with design assumptions from 1967 which were implemented in 1971. The four (available historical) cross-sections (hm 7+700, 7+800, 7+900, 8+000) and longitudinal profile (hm 7+700÷8+300) of the river were analysed and compared. The large scale of subsidence of the land surface on both banks was observed (even to 0.5 m). Probably it is the effect of peat shrinkage and mineralization processes of organic soils. The bottom of the Mała river was still located at the same altitude in sand deposits in the analysed period 1971-2013. The designed slope of bottom of the Mała river equals 0.7‰ (1967) and present slope (2013) was estimated to be around 1‰. The subsidence of peat layers on both river banks, changes in cross-sections’ parameters (present irregular shapes in comparison with designed trapezoidal cross-sections) caused the reduction of cross-sectional area and water discharge of about 40-50% in comparison with parameters designed in 1967 and made in 1971.