engleski

Influence of the Sedimentation Process on the Raša River Mouth on the Outflow Regime of Coastal Springs

The paper discusses the influence of the sedimentation process at the Raša river mouth on the outflow regime of several coastal springs important for the water supply of Istria, among which some are subject to salination. The reason of existence of a number of high-yielding springs in this area may be explained by the fact that the Raša river valley, whose canyon part is cut deep into the upper Cretaceous limestones of the Istrian karst plain during the Holocene transgression is the lowest drainage base for surface and ground water in the broader part of Istria. The valley bottom is covered by deep impermeable alluvial Holocene sediments, and the above-mentioned ascending karst springs upper in the zone of contact between the karst background and the valley, or the sea. The basic limestone rock mass in the Raša river estuary is found at depths over 80 m, within the reach of intensive development of karst phenomena. The sedimentation process in the river mouth has resulted in building up of sediment layers at the beginning of the estuary where the springs are situated, and these layers reach to the depth of some seventy or more meters. The paper also discusses the process of formation of the valley zone and the effects of this process on the water regime of the springs involved in these changes. Depending on the location-distance of individual sources from the sea and their position in relation to the sediment, the influence of the sea on salination of source water is noted. The paper discusses the influence of the position of the sediment on the hydraulic mechanism of water outflow from the sources. As examples, three lowest lopated important sources in the Raša river catchment area have been selected - the spring Rakonek as the most downstream source in the Raša valley in which the influence of the sea is not felt, the spring Fonte Gaja-Kokoti where the influence of the sea is felt only in extreme hydrologic conditions, and the spring Blaz, in which salination is the regular seasonal problem. As the natural sedimentation processes affect the outflow regime of the sources and protect them from salination, they may, in the upstream part of the Raša river, serve as a model for future measures for protection of downstream springs from salination.

sedimentation of the river mouth; coastal karst springs; salination; the

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