Aim of the study:
The aim of the study was to 1) compare and assess the accuracy of the results of sediment deposition calculations made on the basis of the determined isobaths and cross-sections, and 2) develop a forecast of the capacity reduction of a small dam reservoir together with a forecast of the sediment deposits distribution.

Material and methods:
The volume of accumulated sediment was calculated based on the developed cross-sections and isobaths. The calculation results were compared with the predicted volume of sediment deposition, calculated using the Gončarov formula. The sediment distribution in the reservoir was also developed based on the results of surveying and compared with the predicted distribution of sediment developed according to the Annandale method and the modification of this method proposed by Michalec.

Results and conclusions:
The volume of sediment deposited in the reservoir, calculated using the isobath method based on the results of surveying, is 15,205 m3. It is burdened with the smallest error in relation to the result obtained from the forecast developed according to the Gončarov formula. This error is only -0.4%. Calculations of the silted volume using the cross-section method are burdened with an error of -3.6%. The modification of the Annandale method proposed by Michalec, developed based on the results of studies of eight small water reservoirs, allowed for the correct determination of the predicted distribution of sediment in the Niedźwiadek reservoir. The predicted distribution of these sediments corresponded to their distribution determined on the basis of measurements.