Grzegorz Janicki

Changeability of Movable Bed-Surface Particles in Natural, Gravel-Bed Channels and Its Relation to Bedload Grain Size Distribution (Scott River, Svalbard)

Abstract The presented paper analyses the variability of grain size distribution parameters of bedload transported by the gravel‐bed cott iver (valbard) draining a glacier catchment with an area of 10 km2. The grain size distribution analysis is one of the basic elements of identification of the fluvial transport mechanisms in gravel‐bed rivers. It is used for the determination of threshold values for bedload movement. It is also treated as an important indicator of the origin, routes of distribution, and conditions of transport and deposition of fluvial bedload. The field study in a natural proglacial gravel‐bed channel was carried out at two reaches in the mouth section of cott iver. The study revealed relatively high temporal variability and similar mean parameters of grain size distribution in conditions of low discharges. Bedload transport rates reached a mean of 71.9–76.0 kg d−1 in channel cross‐section. Bedload texture was dominated by gravels with a proportional contribution of the fine‐grained fraction along with very fine‐grained gravels (8‐2 mm) of 38.8%. The medium‐grained fraction (16‐8 mm) constituted 33.7%, with a lower contribution from the coarse‐grained fraction (32‐16 mm) of 23.2%, and the very coarse‐grained fraction (64‐32 mm) of 4.4%. Two periods in the course of bedload transport and distribution of grain size distribution parameters were distinguished based on variation of hydro‐meteorological conditions. The first half of the measurement period was distinguished by significantly higher values of daily loads and increased contribution of the coarse‐grained and very coarse‐grained fraction (28–31% and 6.2–6.6%, respectively). During this time, the river discharged up to 94% of bedload. This resulted in a clear tendency for riverbed scouring. The second half was distinguished by generally low daily bedload transport rates (<10 kg d−1), an increase in contribution of fine‐ and very fine‐grained gravels (42–55.6%), and a change in the tendency to aggradation. Grain size indices were more varied, and grains were usually finer and better sorted. Selective transport processes, often related to redeposition, were dominant in the channel. Along with an increase in flow velocity, conditions for material deposition became more variable. This was manifested in weaker sorting and an increase in grain diameter.

VARIABILITY OF SEDIMENT TRANSPORT IN THE SCOTT RIVER CATCHMENT (SVALBARD) DURING THE HYDROLOGICALLY ACTIVE SEASON OF 2009

Abstract Investigations of fluvial transport in the glacial river catchment (Scott River, Spitsbergen) were conducted in the melt season of 2009. A special attention was given to dynamics and distribution of bedload transport − the major component of fluvial transport in a proglacial gravel-bed river. Bed-load transport rate was determined using the River Bedload Traps (RBT) constructed for the project’s need. The obtained results indicate high diversity of bedload transport, the amount of which reached up to 220 kg m-1 day-1 for twenty-four hours in particular measurement sites. The results confirmed also great variability of local intensity fluvial processes in polar zone.

Precipitation‐free periods and water resources in the Lublin region, SE Poland

Purpose – The moist periods with high precipitation and periods of atmospheric droughts are a potential great hazard to the functioning of ecosystems and different sectors of the national economy in the Lublin region. Therefore, a recognition of time variability of these atmospheric phenomena and the conditions of their occurrence are the main aims of this paper.Design/methodology/approach – The analysis of the precipitation‐free periods was based on the meteorological data from the years 1951‐2009 recorded in the Meteorological Observatory of the Maria Curie‐Sklodowska University in Lublin. Main hydrological data concerning dynamics of groundwater table and surface water table came from the measurement network of the Institute of Meteorology and Water Management.Findings – Very long precipitation‐free periods, lasting over 20 days, appeared only seven times – once a year in 1953, 1956, 1959, 1971, 1983, and twice in 2000. Since the 1980s, the number of precipitation‐free periods has been decreasing paral...