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ABSTRACT Because of the late withdrawal of the Levantine lake waters and because of low relief the Eastern Romanian Plain was fragmented only by big alochthonous rivers (Ialomi?a, C?lm??ui and Buz?u). The tabular-like, 40–50-km-wide interfluve areas covered by loessoid deposits and eolian sands on the periphery are deprived of surface drainage which accounts for their present evolution. The major relief forms in these interfluves are depressions called in Romanian ‘crov’ (sink-holes) in the central areas and short valleys formed initially by erosion processes and now modelled by mechanical and chemical weathering at their periphery: in these depressions (sink-holes) and in the secondary valleys, peripheral to the interfluve areas, lakes had started to be formed. Because of the semiarid climate sink-hole lakes have an intermittent hydrological regime, whereas those located in the small fluviatile liman-type valleys, enjoy a permanent regime. By the absence of surface drainage, by the loss of significant amounts of water through evaporation and the degree of mineralization, these lakes fall within the group of salt lakes. In the past few years (since 1966 and especially since 1969) the level of these lakes has continually risen and the depressions formerly lacking water started being flooded by the rising of the piezometric level. An analysis was made of the water balance of the Amara-Ialomi?a lake to investigate this phenomenon. Level and evaporation recordings were made in the period 1956–1970. The findings revealed that the supply of underground water to the lake amounts to 47·3 per cent exceeding the water supply produced by the rains that fell on the surface of the lake (46·7 per cent). A close relationship was established (with a lapse of 8–12 months) between the surface supply of the basin (through rainfalls) and the flow of underground water to the lake. Extending the precipitation-induced level changes over a longer period (1896–1915 and 1921–1970) it was found that level increases are cyclic, as a direct consequence of the corresponding precipitation regime. 相似文献
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