Summary:

In the paper is presented the procedure of calculation of the water flow parameters and bedload transport in the small lowland river-bed with a sandy bottom, in which the bank slopes will change roughness by restoration process. In calculation the results of field investigation of flow resistances and bedload transport were used, which were carried out in the natural Zagożdżonka River, located in research catchment of Dept. Hydraulic Engineering and Environment Recultivation Warsaw Agricultural University. The river-bed on investigated reach have following parameters: width of bed at bankfull level – 3 ÷ 4m, bottom width – 2 ÷ 3m, maximal depth – 0.6 ÷ 0.7m, longitudinal slope – about 1‰, bed material – sand with medium size d₅₀ = 0.41mm. Based on results of field investigations the bedload function was established, in which bedload specific rate q_r depends on average flow velocity V in river cross-section. The comparison’s calculation of bedload transport show good agreement of results obtained from Bagnold’s and own bedload functions. For prognostic calculations of bedload transport in regulated river-bed both functions were used. In calculation assumption was made that flow conditions in natural Zagożdżonka River can characterize final state of regulated river-bed after restoration process. It was found that in river-bed with the some dimensions and flow regime the restoration process will cause increasing of bedload rate and erosion of river bottom. In order to not allow river-bed erosion the compound cross-section should be used in restorated river-bed or single cross but with wider bottom then in regulated one.