Study - Determining Environmental Flow at Seven Profiles of the Neretva and Trebisnjica


Investor: Federal Ministry of Agriculture, Water Management and Forestry, Agency for the Adriatic Sea Basin, Republika Srpska’s Ministry of Agriculture, Forestry and Water Management, Agency for the Trebisnjica River Basin District and Croatian Waters

Implementation Period: 2014

Consortium: ‘Elektroprojekt’ Zagreb – Consortium Leader, Institute for Water Management (IWM) Bijeljina and Institute for Water Management (IWM) Sarajevo


This study is a part of the ‘Neretva and Trebisnjica Management Project’, Component 2 ‘Improved Management and Use of Wetland Ecosystems and Biodiversity’, item 2.3. ‘Improvement of the Operation of Reservoirs, Hydroelectric Power Stations and Dams’, sub-item ‘Conducting a Study which will Determine the Environmental Flow (EF)’.

The goal of this component is to maintain, preserve and, where possible, restore water-dependent ecological systems and their biodiversity in the riparian area of the Neretva and Trebisnjica river basins. The Transboundary Diagnostic Analysis for Mediterranean Sea and Strategic Action Programmes identified this issue as crucial for health of the Adriatic-Mediterranean ecosystem.

Given the hydraulic structures and their mode of operation in the Neretva and Trebisnjica basins, and the numerous requirements for the use of water in the basins, it was necessary to consider the positive and negative impacts that they may have on the flow regime.

The immediate goal of this study is the contribution to the development of the Neretva and Trebisnjica Management Plan, through the establishment of the EF in accordance with the requirements of relevant Water Acts (FB&H; RS and the Republic of Croatia), other relevant regulations, and the proposed Code, all in accordance with professional and scientific criteria.

Environmental flow was determined for selected and hydrologically gauged profiles on the Neretva and Trebisnjica:

      • Mostar GS /The Carinski Bridge (Neretva River);
      • Do / upstream from Stolac (Bregava River);
      • Zitomislici GS (Neretva River);
      • The Arslanagic Bridge /Trebinje (Trebisnjica River);
      • Dobromani (Trebisnjica River);
      • Gorani (Neretvica River);
      • Jablanica GS (Neretva River).

The Project Team was organised territorially, so that the IWM from Bijeljina completely processed three profiles in the Republika Srpska (RS): the Arslanagic Bridge and Dobromani on the river Trebisnjica, and Do on the river Bregava. The IWM from Sarajevo processed the Gorani profile on the Neretvica and the Jablanica profile on the Neretva, while ‘Elektroprojekt’ from Zagreb processed the Carinski Bridge and Zitomislici profiles on the Neretva, and as the Project Leader, coordinated applied methodologies and processing.

In accordance with the Terms of Reference, the environmental flow (EF) on all seven profiles (regardless of whether they are in the FB&H or RS) was determined following the provisions of the Water Acts of the FB&H and RS, the Code proposed in the ToR, the relevant Code of Determining the Environmental Flow in FB&H (FB&H Official Gazette No. 4/13), as well as the Guaranteed Environmental Flow method (GEF) which was tested in the RS. The EF was determined depending on the water body, the availability of data and resources, and considering all aspects of the river (environmental, economic, social, and cultural values).

The adequacy of the environmental flow, which was determined by the hydrological method, was verified using a holistic approach. Due to the lack of an elaborate universal holistic approach, different and still insufficiently verified holistic approaches are used in the world, similarly as with hydrological approaches. Therefore, only some of these experiences were used in this study. Currently we lack conditions to use complex methods of biological response in the main watercourse downstream of the water intake and a special database of spatial and temporal dynamics of ecological indicators (all biological elements of water quality). Until we have this, in order to ensure the adequacy of environmental flow determined by hydrological method, we are verifying this method with the following:

      • A combined approach using available legally defined indicators (saprobic index (SI)) and other indicators of bio-ecological balance of watercourses (e.g. fish);
      • An expert assessment of conditions which, at certain flows and their corresponding hydraulic and morphological indicators, are sufficient to enable a normal development of certain species of fish and benthic invertebrates in their habitats at a single analysed site or a section of the watercourse.

For each profile we assessed the environmental flow and provided a comparison of the results obtained by different methods, including a recommendation for the EF. The following figure shows an example of the Do GS on the river Bregava and the results of the EF assessment according to the draft Code and the GEF method.

Comparative diagram of calculating EF using different methods


General Conclusion
The analyses carried out within this study to determine the EF are only a first step in a comprehensive understanding of the conditions for coordinated water management of the Neretva and Trebisnjica. It is important to note that all results obtained using different methods are for local/individual conditions at the profiles. Therefore, the complexity of interactions between different users must be taken into account and the agreed EF may be further reconsidered on the basis of new scientific knowledge and specific conditions of different areas.