Will HPP Ulog operate in peak-load regime?
HPP Ulog will operate in run of the water regime only. HPP Ulog will not operate in peak-load regime, which can cause changes in water flows downstream from the power plant. When water levels are low and the necessary conditions for the main generators to operate do not exist, power production will be taken over by the small HPP power plant located next to the Nedavići Dam. The small plant processes the biological minimum of water, as regulated by law.
Why does the HPP Ulog project not include the construction of a compensation dam?
Work on the conceptual design of the HPP Ulog project included consideration of a compensation basin and dam. It was concluded that a compensation basin, made up essentially of a dam about 30 metres high, was an environmental problem in itself. The construction of such a facility would obstruct fish migration patterns and sediment flows. The analysis of the construction of a compensation basin focused on two effects. Firstly, the height of the compensation dam would reduce the available height difference by about 25%, in turn reducing by 25% the rated power and total output of HPP Ulog. Secondly, construction of a compensation dam would make possible a different operational regime of HPP Ulog – a higher percentage of peak-load power production. The market price of the peak-load energy produced in this way is about 25% higher. Viewed from an economic aspect, the economic effect of building a compensation dam would be roughly equal to that of the solution ultimately chosen. In view of the aforementioned environmental implications, the construction of a compensation basin would not be justified.
Will construction and operation increase water temperatures in the river Neretva downstream of the power plant?
The upper reaches of the Neretva are characterised by high water levels in the spring and autumn and a long period of low water in the summer. HPP Ulog’s reservoir is relatively small, with a total volume of about 6.44 million cubic metres, and takes three days to fill at average water flow rates. When natural flow is high and when the power plant works at full capacity the replacement of water in the reservoir takes place at a fast rate (daily). Such an operational regime cannot change water temperatures downstream of the power plant. When water levels are low, an ecologically acceptable quantity of water is processed and released (a biological minimum), which also cannot change water temperatures downstream, all the more so as the hydrological and temperature status of the river is dominated by the karst spring at Krupac, located a short distance downstream from HPP Ulog’s powerhouse.
How will the construction and operation of HPP Ulog affect fish migrations and the survival of fish species?
Research and ichthyologic studies performed by the Norwegian University of Life Sciences (UMB) and the Faculty of Agriculture and Food Production in Sarajevo have formed a clear picture of the presence of fish species in the upper reaches of the Neretva. It was determined that the softmouth trout and the marble trout, dominant in the Neretva downstream from the village of Ljusići (the location of the powerhouse), do not migrate upstream because of two natural obstacles: the rapids near Ljusići, and a shallow section of the river upstream from Nedavići (the location of the Nedavići dam). Furthermore, the Ulog brown trout cannot be found downstream from Ljusići, as its natural habitat is further upstream. The said natural circumstances indicate that the construction of the Nedavići dam will not substantially obstruct the migratory patterns and survival of fish species. For that reason the Study about the Estimated Environmental Impact of HPP Ulog envisages stocking the river with appropriate indigenous fish species, upstream of the future dam. This activity will help to restore normal levels of fish stocks, which have already been reduced, in the reservoir, and also further upstream.
Will the construction and operation of HPP Ulog adversely affect the production and flow of sediments downstream from the dam?
An analysis of the morphological and geological characteristics of the drainage basin of the river Neretva, which will be controlled by the Nedavići dam indicates that the dominant type of rock in the basin is marlstone, producing sediment in the form of round stones and pebbles originating from the marlstone. A natural inversion is also evident when one follows the course of the river Neretva. Upstream from Ulog (the upstream end of the reservoir) the riverbed’s gradient is extremely shallow, up to one-tenth of that in the gorge section downstream. That part of the river contains major deposits of pebbles and larger round stones, but not sand. Calculations of the production and flow of sediment performed in the Conceptual Design indicate a need for very modest measures of protecting the reservoir from the deposition of sediment. For that reason the project envisages mainly biological measures in the form of planting trees on bare ground prone to erosion. Due to its relatively small volume, the Ulog reservoir certainly does not inhibit the downstream flow of sediments which are suspended in the water.
The Nedavići Dam is located at the upstream end of a limestone gorge, in whose section downstream of the dam a white limestone and quartz sand is formed. This white Neretva sand is formed by fluvial erosion of limestone boulders which fall into the river from the canyon’s cliffs. The catchment basin of the river upstream of the Nedavići dam is only 290 sq. km, and that to the town of Konjic is much bigger – 1,390 sq. km, which means that the dam and reservoir of HPP Ulog cannot disrupt the production and natural transport of the river-borne sediments which are important for depositing roe and preserving fish populations downstream of the project’s location.
The task given to the teams which drafted Environmental Impact Assessment Study for the Ulog HPP was to define measures which will eliminate the effects of the construction of HPP Ulog up to the project’s boundary lines - the Spatial Plan. The Study has precisely defined the measures which eliminate all adverse effects by the boundary line of the Spatial Plan.