Hydrologic regime restoration in the Dovinė river basin, Lithuania: Modelling scenario approach

Abstract

Therefore, partial naturalization of the flow might be achieved by reconstructing the sluice gates and installing specially designed overflow spill weirs along with fishways. Also, a good measure for improving the hydrological conditions is to block drainage ditches and remove bushes and trees from the wetlands. The effect of the measures on the river flow is that the blocking of ditches decreases the flow whereas the other measures increase the flow. For all the measures considered, the flow in the river was compared with the reference situation. In this way the measures were also evaluated for the change in river flow: the average, high, low and peak flows. Based on the results of modelling scenario relevant measures were proposed to the Dovine river basin management plan and subsequently implemented into practice. Their effectiveness on the improvement of hydrological conditions has been monitored. More details on the implemented measures and their usefulness will be shown and discussed in the presentation. Flow regime is generally considered to be the primary process driving the river ecosystem. However, during the second half of the 20th century, large-scale agricultural expansion posed a threat to the natural water conditions in the Dovine River basin, Lithuania. The water regime of this river has been altered significantly: sluice gates have been built at the outlets of some lakes, and natural peatlands have been reclaimed for agriculture. To improve the situation, an integrated project was carried out at basin level with the aim of producing a management and restoration plan for the basin. The Dovine River basin covers an area of 588 km2. The basin consists of a network of streams and a number of through-flowing lakes (Dusia 23 km2, Zuvintas 9 km2, Simnas 2.4 km2, and Amalvas 2 km2). It holds one of the most important and currently most threatened nature reserves of Lithuania: the Zuvintas Lake. Before river regulation took place, the river valley flooded each spring. During the floods, organic and inorganic material accumulated on the flood plain, which was used as meadows. Since the regulation, the flood plain has become much smaller and most of the transported sediments and nutrients now accumulate in the lakes. Obviously, the change in the hydrological regime has had a negative impact on the biodiversity of the Dovine River basin and on Lake Zuvintas in particular. To analyse the complex Dovine basin with its wetlands and lakes the physically-based spatially distributed hydrological model SIMGRO (SIMulation of GROundwater and surface water levels) was used. It simulates the flow of water in the saturated zone, the unsaturated zone and the surface water. The model gave a proper basis for making decisions about feasible measures.