The Cetina River Catchment Hydropower System, HEP Croatia

The Cetina River Catchment Hydropower System, HEP Croatia

The Cetina River has highly pronounced karst characteristics. Due to its topographic location and avail-able quantity of water, including the streams from its wider catchment, it has enormous power generation potential. The Cetina River rises from a number of karst springs at the foothill of the Dinaric Alps in the northern part of the CetinjskoPolje near the town of Vrlika. Along its course, the Vrličko, Koljansko, Ribaričko, Hrvatačko i SinjskoPolje fields open. In the SinjskoPolje, upstream the town of Trilj, the Cetina is joined by the Ruda River. The Cetina length from its spring to the town of Omiš where it joins the Adriatic sea is 100.5 km. Total head from the spring to the river mouth is about 380 m, wherefrom one third is concentrated at the Gubavica waterfalls.
The Cetina catchment also encompasses the karst fields (polje) of the north-west Bosnia - the LivanjskoPolje with BuškoBlato, Duvanjsko, Šujičko, Kupreško i Glamočko, at altitudes from 700 to 1,200 ma.s.l. The Cetina catchment area is about 4,160 km , average annual rainfall about 1,400 mm. The Cetina is a torrential river. The karst region it runs through is characteristic for underground retentions and a wide-spread network of underground flows causing the water to retard in the underground and thus alleviate its torrential character. However, the unfavorable distribution of precipitations under the original conditions caused occasional flooding of parts of these karst fields, when the inflow used to be in excess of the through-put capacity of the underground conduits.
The Cetina flow rate increases between its spring and Trilj, where it reaches its mean annual value of 107.5 m3/s. In its downstream stretch, towards the sea, the Cetina does not receive any major tributaries. The Cetina flow rate fluctuations throughout the year are large, from the minimum 7.4 m3/s to the maxi-mum 415.4 m3/s.
After the comprehensive hydrologic, geologic and hydrogeologic analyses had been completed within the Framework Multipurpose River Basin Development Study, the basic concept was set up for the water resources management and power generation utilization of the Cetina River catchment including the karst fields flood control and irrigation, and harnessing of water for power generation at the power facilities located towards the Adriatic sea.
The majority of the Cetina power generating potential is concentrated in its downstream stretch. That is where the Kraljevac Hydroelectric Power Plant (HPP) was built in 1912 using the Gubavica waterfall head. This facility has used the greatest individual head of the Cetina riverbed; however, care was not taken either of utilization of the entire stream or of the water regulation. The consequence of such approach was uneven power generation caused by irregular Cetina flow rates throughout the year. Such situation was unacceptable regarding the power supply to the consumers. For that reason, and considering the power generation and cost-effectiveness aspect, it was determined that the most favorable solution would be construction of a number of remote reservoirs in the upstream Cetina course, namely in the karst fields of its greater catchment, which would provide for the Cetina catchment inflows regulation and their uniform utilization in power generation throughout a year.
The first reservoir created in the karst terrain was the one impounded by the Peruća Dam in the Cetinacanyon upstream the HrvatačkoPolje. The reservoir active storage of about 37 % of the mean annual inflow volume had considerably affected the Cetina flow regulation at the downstream power facilities between the SinjskoPolje and Adriatic Sea. The head concentration realized by construction of the PerućaDam was used by the Peruća Hydroelectric Power Plant with installed discharge of 120 m3/s, installed capacity 41.6 MW and average annual output 120 GWh.
In the upper horizon of the LivanjskoPolje and BuškoBlato, the BuškoBlato Reservoir was impounded with active storage of about 782.0 mil. m3. The water stored in the BuškoBlato Reservoir is conveyed through canals into the Lipa Reservoir with active storage of 1.38 mil. m3, which is a compensation reser¬voir for the Orlovac Diversion Type Hydroelectric Power Plant. The water for the Orlovac Hydroelectric Power Plant has been impounded in the Lipa Reservoir. The water from the reservoir is conveyed through a 12.1 kmpressure headrace tunnel and 1,577 m penstock to the Orlovac Hydroelectric Power Plant turbines. The Orlovac HPP installed discharge is 70 m3/s, installed capacity 237 MVV and average annual output is 440 GWh.
The water used for power generation in the Orlovac Hydroelectric Power Plant is discharged thought an open canal into the Ruda River, which is the left tributary of the Cetina in the SinjskoPolje near Trilj.
The Dale Dam was built in the Cetina canyon downstream Trilj to create the reservoir with active stor¬age of about 2.6 mil. m3. The head concentration achieved by the dam construction is used by the Dale Hydroelectric Power Plant, the adjacent-to-the-dam facility with a power house which is the part of the impoundment structure. The Dale Hydroelectric Power Plant installed discharge is 220 m3/s, installed capacity 40 MVV, and the average annual output 157 GWh.
Immediately downstream the Dale Dam, the Prančevići Reservoir begins with active storage of 6.8 mil. m3. The Prančevići Reservoir was formed by construction of the Prančevići Dam, and it is a compensation reservoir for the Zakučac Hydroelectric Power Plant. The water from the Prančevići Reservoir is conveyed to the Zakučac Hydroelectric Power Plant turbines by two pressure headrace tunnels 9,876 m(right tunnel) and 9,894 m (left tunnel) long, and through two penstocks, 289 m long each. The ZakučacHydroelectric Power Plant installed discharge is 220 m3/s, installed capacity 486 MW, and the average annual output 1,640 GWh.
The Kraljevac Hydroelectric Power Plant is located downstream the Prančevići Dam. The KraljevacHydroelectric Power Plant is the oldest power generating in Croatia facility in the region which lost its importance due to the construction of the Zakučac HPP Presentlv, in povver generation it uses only the biological minimum water discharged from the Prančevići Dam and the dam overflows. The Kraljevac HPP installed discharge is 80 m3/s, installed capacity 67.2 MVV, and the average annual output 40 GWh.
The hydropower system located in the Cetina River Croatia catchment is planned for extension in the future.
In the north-west part of the LivanjskoPolje, the Čaprazlije Reservoir is planned with active storage of abut30 mil. m3, which would receive the excessive water from the north-east part of the LivanjskoPoljedelivered through a system of canals and weirs. The water would be used in the Orlovac HPP and other downstream power plants. Construction of this system would result in additional Orlovac HPP average annual output of 135.2 GWh.
The upper horizon of the Cetina catchment is planned for construction of the Kablić and Vrilo HPPs.
The Kablić HPP would harness the water from the smaller reservoirs at the upstream streams in the GlamočkoPolje (the Hozići i Buleklagija) conveyed through trained watercourses and canals to the Pučineretention and further by a penstock to the Kablić HPP power house. The Kablić HPP installed discharge would be 15 m3/s at the gross head of 160 m, installed capacity 20 MVV, and anticipated annual output 67 GWh.
The Vrilo HPP would harness the water from thereservoirs in the KupreškoPolje (the Milač and Mrtvicareservoirs), at the Šujica River in ŠujičkoPolje (the Šujica Reservoir) and temporary winter retentions in the DuvanjskoPolje. The Vrilo HPP installed discharge would be 40 m3/s at the gross head of 140 m, installed capacity 48 MVV, and anticipated annual output 120 GWh.
Construction of the above mentioned multipurpose facilities would help to meet the basic water management requirements in the region with harnessing of water for power generation at the concentrated heads, which resolves the flood control and drainage issues and enables irrigation of the farm land, as well as water captation for water supply, water protection and the like.
Construction of the small Peruća Hydroelectric Power Plant (SHPP), Prančevići SHPR and Tisne Stine HPP is planned in the narrow Cetina catchment, along with the series of small hydroelectric power plants (ČikotinaLađa, Voloder, Plejići, Bartulovići, Koštanje) at the RuminVeliki, RudaVelika i Grab streams.
The Peruća SHPP would use the potential of the biological minimum water released from the PerućaReservoir past the main generating units (6 m3/s), and would be located by the Peruća HPP power house. The installed discharge would be 5 m3/s, installed capacity 2.6 MVV, and average annual output 3 GWh.
The Prančevići SHPP would be constructed in order to harness the biological minimum discharged from the Prančevići Reservoir, located at the left Cetina bank with water intake at the Prančevići Dam. The installed discharge would be 8 m3/s, installed capacity 1  MW, and possible annual output 10.74 GWh.
The Tisne Stine SHPP would be located in the Cetina Canyon downstream the Prančevići Dam. The hydroelectric power plant with two generating units would use the head of 41 m, installed discharge would be 2x10 m3/s, installed capacity 2x3.7 MVV.
The average possible annual output from the Cetina Hydropower System is about 2,500 GWh. Construction of new facilities would increase it by approximately 12%.