Summary:

The small retention program for the Lower Silesian Voivodeship anticipates among others the construction of a retention reservoir in Maleszów on Mała Ślęza river with the total volume of 5,60 mln m3. The length of designed dam will amount to 338 m with the maximum height of H=11,11 m.
The geotechnical documentation, made for drawing up the conception of the dam, shows that the top layer of the ground up to about 3,0 m depth is made of loess alike heavy loam in soft state (IL = 0,40), which overlay heavy loam in firm state (IL = 0,17). Based on these findings authors of the geotechnical documentation have come to the conclusion that founding of the dam on the Quaternary loess alike deposits is not recommended.
From the research presented in the geotechnical documentation worked out by the authors of this paper, it appears that Holocene loamy aggradate mud con-taining organic mater (Iom= 5÷10 %) are deposited on the bottom of the valley. Maximum thickness of these deposits is 9,0 meters. The calculation of dam stability with the Fellenius and Bishop's method have been made using author's computer program. The results of slope stability and deformation calculations indicate that the dam foundation is possible in the designed cross section of Mała Ślęza.
To keep consolidation of the foundation ground, the dam embankment should be constructed in two phases in minimum two years period and the vertical drainage should be made in aggradate mud foundation in the form of sand piles.