Currently, due to prolonged soil drought, dehydrated peat soils are particularly exposed to subsidence and, as a consequence, even to disappearance from the natural environment, in which they perform many important functions, e.g. storage of organic carbon and water retention. Therefore, predicting of settlement and disappearance processes of these soils is very important issue. This study was conducted to: (1) determine the degree and rate of subsidence of a drained peatland over 40 years, (2) establish the effect of subsidence on the depth of ditches and a watercourse, (3) verify empirical equations describing the subsidence based on field measurements. The work was carried out on fen in Central Poland which was managed as a grassland until around 2000, and then its use was discontinued. Subsidence rate was estimated from measurements of the peat deposit thickness taken in 11 locations in 1978 and 2018. Fourteen empirical equations used for estimating subsidence rate of drained peatlands were selected to verify the calculations against field data. The average subsidence rate of the studied peatland was relativity low (0.62 cm year−1), which may be associated with abandoning of agricultural use for the last 20 years. Loss of peat thickness varied from 5 to 41% and depended rather on drainage intensity than on its initial depth. In general, six from the verified empirical equations were useful in estimating average subsidence rate. Four equations seemed to be the most useful for deeply drained sites. Estimation of the subsidence solely on the basis of time since drainage may be biased.

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.

Turbulent intensity and scales of turbulence after hydraulic jump in rectangular channel. Experimental research was undertaken to investigate the changes in spatial turbulence intensity and scales of turbulent eddies (macroeddies) in a rectangular channel and the influence of the hydraulic jump on vertical, lateral and streamwise distributions of relative turbulence intensity and scales of turbulent eddies. The results of three tests for different discharges are presented. An intensive turbulent mixing that arises as a result of a hydraulic jump has a significant effect on instantaneous velocity, turbulent intensities and sizes of eddies, as well as their vertical and longitudinal distributions. In the analysed case the most noticeable changes appeared up to 0.5 m downstream the hydraulic jump. In the vertical dimension such an effect was especially seen near the surface. The smallest streamwise sizes of macroeddies were present near the surface, maximum at the depth of z/h = 0.6 and from that point sizes were decreasing towards the bottom. The intensive turbulent mixing within the hydraulic jump generates macroeddies of small sizes.

Szkoła Główna Gospodarstwa Wiejskiego w Warszawie streszczenie. W pracy przedstawiono wpływ procesów osiadania i zanikania gleb organicznych murszowych na 4 profile podłużne rowów odwadniająco-nawadniających, wchodzących w skład systemu nawodnień podsiąkowych obiektu Solec (gm. Góra Kalwaria, pow. piaseczyński, woj. mazowieckie). Analizie poddano zmiany rzędnych brzegów oraz dna rowów w latach 1967-2013, ich głębokości oraz spadków dna. Na podstawie przeprowadzonych badań stwierdzono, że w okresie 46 lat nastąpiło obniżenie się brzegów rowów w pobliżu ich ujścia do rzeki o ok. 80-120 cm, co było skutkiem osiadania i zanikania gleb organicznych na analizowanym obszarze. Średnie roczne tempo obniżania się powierzchni terenu wynosiło 1,7-2,6 cm • rok-1. Powyższe procesy spowodowały znaczne zmniejszenie się głębokości rowów, jak również bardzo duże zmiany spadków dna na poszczególnych odcinkach. słowa kluczowe: gleby organiczne murszowe, osiadanie, zanikanie, profile podłużne rowów odwadniająco-nawadniających. WsTĘp W Polsce w latach 60. i 70. XX wieku na cele rolnicze odwodniono ok. 80% gleb torfowisk niskich, tj. ok. 820 tys. ha [Czaplak i Dembek 2000]. Odwodnienie tych gleb spowodowało rozwój procesu decesji, który wiąże się w pierwszych latach m.in. ze zjawiskiem osiadania powierzchni torfowisk na skutek zaniku siły wyporu wody i zagęszczania materii organicznej. Skala tego zjawiska zależy w głównej mierze od głębokości odwodnienia, rodzaju gleby torfowej i jej pierwotnej miąższości. W lite

The consequences of organic soil subsidence gained considerable importance in a wide range of scientific literature. Since most of the works focused mainly on the subsidence of the land surface, less attention was paid to the effects on hydraulic structures, either to their malfunctioning or to the proper management of the subirrigation systems. For the reasons mentioned above, the paper considers the selected technical parameters (underground pipelines covering thickness and soil subsidence behind inlet and outlet protections) of 37 culverts (communication structures) and 42 culvert-gates (communication and water damming). All the structures were located within the area of a subirrigation system on the previously drained organic soils (Solec system, Mazovian Voivodship, 30 km south of Warsaw). They underwent field measurements of the pipelines covering subsidence and land surface lowering behind their protections on the left and right side of the inlet and outlet section. The achieved results were confronted with the adopted limit and admissible values. Due to the progressing congestion and subsidence of organic soil, the covering thickness of pipelines did not exceed the limit value for 38.5% of the culverts and 36% of culvert-gates. From a long-term perspective (1971-2014) the average subsidence rates in the vicinity of the structures and surrounding peatland surface were found as comparable, ranging from 0.63 to 0.83 cm/year. Particular attention was paid to the influence of water damming that was evident for the inlet sections of culvertgates showing considerably lower subsidence and damage degree.