Joint management of Latvian – Lithuanian transboundary river and lake water bodies (TRANSWAT)

Joint Management of Latvian–Lithuanian Transboundary River and Lake Water Bodies (TRANSWAT)


Project leader: Dr. Tomas Virbickas

Division: Laboratory of Fish Ecology

Source of funding: EU/ERDF

Joint Management of Latvian–Lithuanian Transboundary River and Lake Water Bodies (TRANSWAT)

Project programme 

Project duration                      01.10.2020 – 30.09.2022

DB reference     

The purpose of TRANSWAT project is to ensure the general assessment and management of transboundary river and lake water bodies, the hydromorphological and/or ecological quality of which do not possibly satisfy the requirements of the EU  Water Framework Directive (WFD).

The territory of the programme encompasses three Latvian-Lithuanian transboundary river basins (Venta, Lielupė and part of Dauguva), in which the status of most rivers and lakes fails to satisfy the criteria of “good ecological status”. Some rivers are even assigned to severely modified water bodies due to changes in natural conditions, because their water regime is regulated by cascades of hydroelectric power plants (HPPs). To date, the lakes situated on the Latvian–Lithuanian border are most frequently described as water bodies only in Latvia. Consequently, quality monitoring and impact assessment of these lakes are pursued only in Latvia.

The project is divided into two parts: (1) assessment and management of rivers regulated by HPP cascades and (2) assessment and management of the ecological status of transboundary lakes and the health of lake ecosystems.

The first part will focus on determination of the ecological flow (E-flow) in the rivers of the basin of one of the Lithuanian–Latvian transboundary rivers, Venta, which are regulated by HPP cascades, and on amendments to the national water laws related to mitigation of the impact of regulation of such rivers. Fieldwork will be organised to collect hydromorphological and ichthyological data for E-flow modelling in Lithuania (in the Varduva River with 5 HPPs) and Latvia (in the Losis River with 2 HPPs and in the Ciecere with 3 HPPs). Then the most popular model for E-flow calculation (MesoHABSIM), which complies with WFD requirements, will be employed. The TRANSWAT project will employ a harmonized method created under the Interreg Latvia-Lithuania project (ECOFLOW) for E-flow modelling. E-flow calculations will also be performed on the modelling platform online, which will be developed under the recently lunched project “LIFE GoodWater IP project”. Based on the results of E-flow assessment, HPP cascade operation will be modelled applying the HEC-RAS model (software intended for hydraulic modelling of water bodies) to ensure ecological regime downstream of each HPP and sustainable management of water bodies. Based on the results obtained, recommendations on amendments to the national water laws in relation to the mitigation of the impact of river regulation will be proposed.

The second part will focus on assessment of the state of five transboundary lakes in the basins of the Lielupė (Gaiaris/Ilgė) and Dauguva (Galinu/Šalna, Kumpiniskiai/Kampiniškių, Lauceses/Laukesas and Skirnas) rivers. Three lakes (Galinu/Šalna, Kumpinisku/Kampiniškiai, and Lauceses/Laukesas) belong to the NATURA 2000 network. New data collection will base on water quality and quantity monitoring as well as comprehensive biological and ichthyological investigations. New data combined with detailed analysis of lake basins (assessment of surface and ground water interaction and quantitative analysis of pollution sources by mathematical procedures) will allow determination of the ecological status of five lakes. The general methodology for the assessment of the health of lake ecosystems will be developed and tested in a pilot lake Garais/Ilgė. In order to ensure the sustainability of project results and further improvement of water quality, the harmonized Latvian-Lithuanian monitoring programme (MP) and programme of measures (PoM) will be treated.

During implementation of the tasks of the first part of the project, information on the current ecological status of the Varduva River and on the elements describing its quality was collected, and information on diverse human impact on the ecological status of the river was analysed. Downstream of each of five HPPs on the Varduva River, representative river segments were selected for ichthyological investigations, which were performed in hydromorphological units identified in selected river segments. Such units distinguished by specific bottom composition, depth and stream rate, as well as hiding places suitable for fish. Investigations were conducted on fish species distribution in different hydromorphological units, and the rate of deviation of fish-based indices from natural conditions in all studied river segments was estimated. Based on analysis data, the general patterns of changes in fish community status in the gradient of HPP cascades were identified, and the main drivers of such changes were identified. Also, the testing of conditional habitat suitability criteria for different fish species was completed. The criteria are used for further modelling (MesoHABSIM model) of habitat suitability for fish under different flow and for the determination of the optimal E-flow.

During implementation of the tasks of the second part of the project, information on the ecological status of five transboundary lakes: Ilgė/Garais, Šalna/Galinu, Kampiniškiai/Kumpinisku, Laukesas/Lauceses and Skirnas/Skirnas, was collected. Also, information on the type and intensity of anthropogenic activities in the basins of these lakes was collected and identification of potential sources of pollution was pursued.  During the first stage of the project, automated water level measurement devices were installed in Laukesas and Kampiniškiai lakes. The devices were removed after  15 months of uninterrupted measurements. Exhaustive data on changes in water level are used for the assessment of the ecological status of the lakes. Investigations into fish communities were carried out in all five lakes. The data of investigations were analysed and the degree of deviation of fish-based indices from natural conditions was estimated.  Fish-based indices were used to determine the ecological status of studied lakes. Deviations of fish-based indices in the lakes failing to meet the criteria of good ecological status were assessed in the context of possible anthropogenic impact. In addition, project participants are currently engaged in testing a method for comparison of the systems of assessment of ecological status of lakes according to Latvian and Lithuanian fish indices.

Project duration: 01.10.2020 – 30.09.2022

Project number: LLI-533
Project acronym: TRANSWAT
Project budget: EUR 607,466.51 (of which EUR 516,346.53 funded from the ERDF)
Project funding: 2014–2022 Programme for Latvian–Lithuanian Transboundary Cooperation
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