Research, Monitoring and Data Processing to Determine Environmental Flow Downstream of the HET 2 Dam

The aim of this Study is to adapt to the needs of the population in the region through the use of water for electricity production and the provision of clean water for water supply with maximum care for the environment. In particular, water related projects should improve ecological status (through the improvement of flow regimes and enhancement of biological diversity).

In this particular case, the goal of determining the environmental flow (EF) is to provide an adequate flow regime in terms of quantity, quality and timing, to ensure the health of the Trebisnjica River and other aquatic ecosystems downstream from the Gorica dam, through the city of Trebinje, and further downstream. The appropriate environmental flow for a particular river depends on the values for which the river system is to be managed. Those values will determine the decisions about how to balance environmental, economic and social aspirations, and the uses of the river's waters. This means that environmental benefits will not necessarily be the only or even primary results of establishing an environmental flow but it is required to balance needs between water distribution to meet environmental requirements and other water use needs, such as hydropower, irrigation, water supply and recreation.

The Study provides an overview of approaches and methods for determining an EF used in the world, such as hydrological methods (methods related to some characteristic flow rate), hydraulic methods (wetted perimeter method), habitat quality conservation methods (fish habitat simulation methods), and holistic method, that combines hydrological and hydraulic methods, as well as analyses of the impact on the river as an ecological system.

A certain difficulty in defining the methodological approach to determine the EF is the fact that so far, no EU country has defined a law-based methodology for calculating the EF, especially not in karst regions, as our project area. Therefore, following a thorough analysis of the world's most relevant approaches and the application of some of them, it was decided to use existing approaches that have been, to some extent, tested in nearby areas.

Following a thorough analysis, two basic methods were selected: Guaranteed Environmental Flow Method (GEF) and Method of Abiotic and Biotic Parameters and Saprobic Index (MABPS). They are developed using two different but complementary methodological approaches that were tested on the available data. It is important to emphasize that both methods complement the environment of ecosystems and the health of the river.

Guaranteed Environmental Flow Method (GEF)

The GEF method was developed on the basis of numerous hydrological, morphological and biological analyses of watercourses in the former SFRY. It is increasingly used in the countries of the region, because it is relevant for climate and hydrological regimes in the Balkans. Hydrological analyses were especially focused on the analysis of monthly low flows to obtain regional low flow relationships for different return periods. Morphological analyses included the morphological relations of the main river channels to observe the regularities of the morphology of the structure and geometric relations in the main river channels of environmentally completely stable watercourses. In this respect, this method also included the wetted perimeter method, which is often used in the world. On the basis of all these analyses, a methodology was produced which is deliberately reduced to quite simple rules to allow its universal applicability. It was tested on a number of watercourses of various characteristics in Serbia, Bosnia and Herzegovina, Macedonia and Montenegro. It produced logical results in terms of the possibility of maintaining stable relations between rivers as a biotope and biocoenosis living in those habitats.

The diagram below shows how to determine the guaranteed environmental flow using previously defined relations. It clearly shows the flows in the warm and cold part of the year, in standard non-typical conditions.

Determining guaranteed environmental flow


Method of Abiotic and Biotic Parameters and Saprobic Index (MABPS)

The MABPS method was developed specifically for river systems in B&H which were included in the monitoring of abiotic and biotic parameters. Quality parameters have been measured since 1965 in the HET system within the project ‘Testing the quality of watercourses in SR B&H’. The analyses carried out within this Study showed that this way of analysing a river as an ecosystem is methodologically good approach. It is imperative to measure in the future quality parameters simultaneously with the flows to enable multidimensional correlation analysis of the relationship between the flow, water quality indicators, and air temperature. Therefore, the MABPS method produced an adaptive model structure which will be increasingly improved as more observation results are available and their quality is better.

The EF was also analysed using methods recommended by ESHA (the European Small Hydropower Association) which give a wider range of results. The results of these most commonly used methods matched the results obtained by the two previous much more detailed and studious methods which combine both abiotic and biotic parameters.

Providing EF, as one of the important conditions for the protection of aquatic ecosystems, will not be sufficient if other measures are not taken, especially those referred to in the Proposal of Measures for the Improvement of the Quality and Ecological Status of the Trebisnjica. All entities that affect flow regimes of the Trebisnjica must participate in the provision of the EF, especially in relation to the water quality.

Given that the entire course of the Trebisnjica is a heavily modified and artificial water body (result of alterations by human activity), determining the environmental flow is extremely complex. In case of heavily modified water bodies, it is necessary to provide a high ecological potential (the best possible conditions in given circumstances, i.e. certain biological, physical-chemical and hydromorphological elements). So far, none of the EU countries has defined a methodology for calculating ecological potential. This study is a pioneering and extremely important step forward in this area, due to the HET expert teams’ attention to environmental protection.