Hydrogeomorfologiczne skutki intensywnych opadów na międzyrzeczu Bystrzycy i Giełczwi (Wyżyna Lubelska)

On the 31st July – 6th August 2005 in Lublin surroundings, high and intensive rainfalls appeared (Table 1). The highest one took place at night of 3rd–4th August and its level exceeded 100 mm in two stations (Fig. 1). It was the rain of changeable intensity to 1 mm·min–1, lasting 4–5 hours. In the area of 400 square kilometers enclosed with 100 mm isohyet, an intensive runoff with erosional effects appeared. Its size in rural area was conditioned by land use, crop structure, fi eld pattern and road network. Majority of corn fi elds determined the predominance of dispersed runoff and little rainwash. Concentration of runoff and linear erosion took place only on small area of: roads, fi elds with root plants and fi elds of aerated soil (Fig. 3). The maximum of erosion rate in the fi eld scale reached: 200 t·ha–1 of translocated material and 70 t·ha–1 of carried material, fi eld surface lowering by 5 mm and convex parts of slope by 8 cm. Deposition of material, in form of fans and proluvial covers took place in dry valley fl oors. Concentrated runoff formed here episodic channels: transport and deposition in channels being fl at and erosional channels in crops with uncovered soil. Below roads crossing the channels, potholes with the capacity to 50 m3 and bars of eroded material were formed. Most of moved soil material was left within dry valleys whereas water runoff was the main source of fl ood waters in river valleys. Specifi c outfl ow from dry valley catch ments, with the area of 5 square km, reached 1–2.5 m3·(s·km2)–1. In valleys of small perennial fl ows with catchment area less than 50 square km (for instance: Skrzyniczanka, upper Stawek and Sierotka Streams), located in zone of the highest rainfall, local fl oods appeared. They caused losses in road and hydrotechnical infrastructure. Waves from these catchments, with specifi c outfl ow to 0.8 m3·(s·km2)–1, caused relatively smaller fl ood waters in higher valleys in next days (Fig. 2). Five-times growth of fl ow in Biskupice on the Giełczew River and seven-times one in Sobianowice on the Bystrzyca river occurred. On 4th–11th August period, about 12 mm of water fl owed from these catchments but in the Czerniejówka catchment, level of groundwater raised about 30–70 cm.