engleski

Stability Assessment Of the River Channel Bedform

This paper presents the results of monitoring of meander cute cut-off in send-bed river. Hydrologic-hydraulic data were collected on 24 control cross-sections on ten occasions during one year. The water levels were recorded using RTK- GPS, and data on the bedform, velocity profiles and discharges were collected using 4 beam broadband ADCP with frequency of 1200 kHz. Measurements were performed during low, medium and high flows. On a section somewhat longer than the cut-off itself, a 1-d morphodynamic model was constructed by using HEC-RAS 4.0 software. The paper gives an overview of the methodology of data collection and the results of estimated bedforms by using various methods of sediment transport calculation. The calculated bedforms were compared to the measured data. Parameters used for the evaluation of different methods of bedform prediction are hydraulic depth , river channel level and width of the water surface B. The calculation of river bedforms was made through the quasi-dynamic 1-d morphodynamic model for a period of one year. There were also surveys of the river bed on cut-off in this period, and thus calculated and measured bedforms could be compared. The dynamic boundary conditions were recorded discharges at the upstream boundary and recorded water levels on the downstream boundary, and estimated incoming sediment load on the basis of the existing sediment load curve. The bedforms were calculated for several methods of sediment transport calculation: Ackers-White, Engelund- Hansen, Laursen, Meyer- Peter-Muller, Toffaleti and Yang. Hydrologic and hydraulic characteristics of the monitored watercourse are in the range of validity of all mentioned methods, but it should be emphasized that the Meyer-Peter-Muller method is valid predominantly for gravel river bed material. The paper also presents a sensitivity analysis for a certain morphological parameter in the numerical model. The sensitivity analysis was performed for: incoming sediment load, river bed material, sediment specific gravity, particle settling velocity and water temperature.

river channel ; morphodynamics ; 1-d model

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