TIME-LAG OF DUNES FOR UNSTEADY FLOW CONDITIONS

Horst Nasner

Abstract


Many publications based on theoretical considerations or model tests, give utterance to the demand that there should be unequivocal relations between hydraulic conditions and bed form characteristics which should be generally applicable. These relationships determined for steady conditions and limited water depths should be handled with care when being applied to natural rivers. The bed configurations do not immediately fit themselves to the varying flow conditions. The bed forms need a certain reconstruction time in case of a changing discharge. The time-lag of dunes was observed on numerous rivers, in the past. A general review of investigations made in this field is given by ALLEN (1976 b). In the following contribution, an attempt is made to describe the magnitude of the time lag of bed forms for unsteady flow conditions.

Keywords


unsteady flow; dune; time-lag; dune time-lag

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