摘要：Investigations within the channel zone of the Middle Vistula River have shown the presence of protrusions of the alluvial basement composed of deposits resistant to erosion. On their surface, and in the basal part of the present-day channel facies, occur residual lags composed of gravels and pebbles. These lags indicate exposure of the surface of the alluvial basement in the channel bottom during high-water stages. Protrusions of the resistant alluvial basement often show a complex morphology which influences the course of the thalweg, particularly during floods. The constant trend to concentrate the high-water stream may be the reason for the damage to regulation and flood control system structures. The concentration of the high-water flow causes the formation of specific erosional and depositional forms on the terrace surface. Such forms can thus serve as indicators of the zones of alluvial basement protrusions. The paper presents examples of three reaches of the Middle Vistula River Valley (The Mid-Polish Lowlands).
