Summary:

In result of considerably diminished retention abilities of catchment area as well of river and stream inundation areas, increased high water flows occurred, particularly in the watercourse mouth sections. It poses a considerable flood hazard for the urbanized areas. Registered flood of July 1977 and June 2001 caused by high waters confirmed significant flood hazard in the areas of Carpathian tributaries of the Vistula River. In the Carpathian Foothills area, because of high water culmination times are shorter, watercourse regulation in closely built-up areas is necessary. Strong urbanization of the riverbank terrains resulting from historical location of towns gives no possibility to design riverbed in character close to natural. One of the main solutions, which is the most frequently applied and guarantees conducting high water flows is heavy consolidation of bed constructed in a shape of a trough. An example of this type of regulation is applied the mouth section of the Naściszówka stream. The Naściszówka inflow to the Łubinka river is situated in the Nowy Sącz city area. The streambed runs along Barska street. The adjacent terrain is characterised by a close urban building. The trough discharge capacity was assessed. According to the design guidelines in „Mountain stream consolidation”, the reliable flow Q1% was assumed for computing the trough bed discharge capacity. Because of the lack of hydrological observations the computations of probable flows were conducted using empirical formula. A reliable flow of 34.1 m³s^-1 was assumed, established by Punzet formula for the Carpathian catchments. The results of computations of stream mouth section discharge capacity show no possibility of conducting reliable flow in the streambed trough. The places which pose a hazard of water overflowing the trough are arcs and the lower section of the trough. Water overflowing the bank onto Barska street running along the trough, floods the buildings along the street. The bridges and foot-bridges above the trough let through the designed computational flow. A protection against the Naściszówka stream overflowing involves raising the trough banks by 6.0 m and by 5.0 in the vicinity of buildings. According to the European Union Framework Water Directive 2000/60/WE concerning the surface waters protection, their maintenance and restoration or reconstruction of water ecosystem values, a possible replacement of concrete trough by a channel close to natural was analysed, following the rule of watercourse regeneration.