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Abstract

The sediment supply, deltaic deposits and processes of sedimentation in the glacier-fed lake downstream from Tunsberg-dalsbre in western Norway have been investigated. The depositional processes were analyzed by a computer model which is structurally different but of the same type as that of Bonham-Carter and Sutherland (1968). Particle trajectories are computed by numerical integration through the lake flow field and the zones of sedimentation of different particle sizes in the bottomset layers determined. The effect of turbulence was represented by the introduction of a stochastic element causing the particles to move in a random walk. Various test runs showed that the turbulent spread of particle trajectories increased with decreasing particle fall velocity.

Application of the model to Lake Tunsbergdalsvatn involved investigations of the lake flow field during different sediment and water discharge situations. Calculations of the extension of the zones of sedimentation during this latter situation tallied with the results obtained from analysis of grain size distributions of bottomset beds.

A process response model of the long-term delta development is presented. The present lake is a remnant of an 8-km-long and 100-m-deep fjord valley lake that existed after deglaciation 9000 BP. A major part of the volume of the delta sediments was deposited by flow divergence processes at the delta front. The deltaic deposits are regarded as the results of a series of different phases of delta development through time. During each phase, the magnitude and composition of sediment supply, and the basin flow fields, were decisive for delta formation processes. The morphology of former basin conditions, however, influences the flow field in a feedback loop, and future development is dependent upon past history.

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