Rzeźba Pogórza Wielickiego ze szczególnym uwzględnieniem współczesnych procesów stokowych w otoczeniu zbiornika wodnego w Dobczycach

Abstract

Dobczyce water reservoir is situated on Pogórze Wielickie which is flysch upland. It consists of wide hummocks of 350 – 420 m.a.s.l. The lowest point is in the Raba valley in Dobczyce (243 m.a.s.l.) and the highest is in the southern part reaching 400,4 m.a.s.l. Relative heights difference is 157,4 m. Fragments of 2 planation surfaces are very well preserved in Pogórze Wielickie. The higher one, makes plateaus about 110 - 140 m above the Raba valley bottom, the fragments of the lower one can be noticed along the valley at heigth 50 – 80 m. Dobczyce dam was built in the Raba valley in structural gorge between Góra Zamkowa and Góra Jałowcowa. The gorge is about 600 m wide. The Raba dissected Pogórze Wielickie which is built of folded flysch deposits belonging to the silesian overthrust. The valley in this part is an insequent valley with wide terraced bottom. There are many valleys with flat often wet bottoms in Pogórze Wielickie. The slopes of the Raba valley are covered with weathering covers mainly with clays from the Pleistocene. They are often cut by young valleys and they are overgrown by forests. There are many landslides and their surfaces are areas which can be hardly used by agriculture Landslides cover an area of about 450 ha what makes 22,5%. of slope area. There is a great concentration of them in the marginal zone of the reservoir. There are mainly frontal landslides and they appeared in places wher high waters of the Raba undercut the banks. They cover about 26,2%. of the Raba banks. Width of frontal landslide complex varies from 40 - 300 m but they are usually 100 - 110 m wide. On other areas landslide can be noticed in spring depressions and they are incisioned by V-shaped valleys. The V-shaped valleys cut in rocky landslides some others are in clayey and loamy colluvium. The most frequent landslides are in lower Istebna layers and their niches are on the contact of spotted shales and godulskie or istebniahskie layers. On the right slope of the Raba valley subsequent landslides (Przedmieście landslide) or consequent-sliding (Gaik-Brzezowa) predominate. On the left slope of the valley insequent (Borzęta), obsequent (Kasperówka and Przylasek) predominante. Thickness of landslide colluvium is different and varies from 1,5 to 19 m. Deep landslides appear in the marginal zone. Slopes shaped by creeping cover an area of 45 ha (2,2%) of slope area. Weathering creeping takes place on slopes with loamy covers overgrown by turf. Great areas of this kind are in the marginal zone of the Wolnica. Slope inclination is about 10° and thickness of weathered material is about 0,4 m. Creeping is active during thawing season and long lasting summer or autumn rains.