DEVELOPMENT OF ORCHARD IRRIGATION SYSTEM IN POTKOZARJE, MUNICIPALITY OF GRADISKA

 

  • The Terms of Reference included the development of the Preliminary Design for the irrigation of orchards in Potkozarje and the Detailed Design for the selected two subsystems together with 30km of transportation pipelines. The initial irrigation area of 1,500ha has been extended to 6,000ha where it is possible to intensively cultivate fruit and vegetable crops;
  • The project is financed by the World Bank's loan in accordance with the terms of the World Bank. It is also planned to implement the Detailed Design by the end of November 2019;
  • The concept plans the water supply through reservoirs and dams in the upper course of the Vrbaska, Bukovica and Lubina rivers as the main sources of water and reservoirs on the Jablanica and Borkovici. The Preliminary Design elaborated 8 dam sites (Terms of Reference required 6);
  • On the basis of the geodetic data (layout, longitudinal and cross sections) and hydrological data, different types and structure of the dams were considered, including the normal water surface, reservoir storage and release of flood waters;
  • Geological composition of the land is favourable for dam construction using materials for embankment dams;
  • Due to the exceptionally high levels of 10,000-year flood flows and maximum probable flood, which were used to verify the spillways for the Bukovica and Vrbaska embankment dams, there is a significant backwater effect of 3-5m in the reservoir.
  • Hydrological analyses have shown that these rivers have high levels of hydrographs for 1,000 and 10,000-year flood flows (steep channel gradients and significant runoff coefficients), which were used for dimensioning the spillways for concrete and embankment dams;
  • Detailed analyses were carried out for these parameters, including the possible dam structures and heights that would provide sufficient quantities of water for irrigation;
  • It was proposed to construct higher dams on some sites in Phase II to mitigate flood waves. The Ministry commissioned the development of an optimum technical solution;
  • The selected types and structures of dams for development Phases I and II will provide irrigation water for an area of 6,000ha;
  • The calculation showed that specific consumption in a dry year of 5-year return period is 3.15mm/day, which corresponds to the average daily specific consumption in the design period (duty of water consumption) of qs=0.37 [l/(s ha)];
  • The complexity of the project requires phased construction. It is planned to have two phases, where Phase I is divided into three stages which will provide irrigation across 2,500ha. Completion of Phase II will provide irrigation of all 6,000ha;
  • Most of the irrigation system is gravity-fed, while pumping stations and tanks will be constructed for the supply of higher areas (in total 3 pumping stations with 3 tanks);
  • In order to maximize the use of rivers, it is planned to heighten dams in later phases of construction;
  • The Preliminary Design proposes further design for heightening the embankment dams by 15m (Bukovica and Lubina), which would be followed by the construction of the key dam in the system, the 30m high Vrbaska gravity concrete dam and its connecting pipelines. These dams will be multipurpose structures providing water for irrigation and controlling floods;
  • Types and structures of dams on 8 sites were decided by technical / economic analyses and optimisation (Bukovica, Lubina and Jablanica embankment dams, Vrbaska concrete dam). It is also proposed to further elaborate in a detailed design two low height dams, so they can be financed by the WB loan;
  • Economic analyses obtained extremely satisfactory economic indicators for Phases I and II (B/C, EIRR). The Sensitivity Analysis also obtained positive results;
  • Detailed Designs will be developed for the Bukovica and Lubina sites and 30km of transportation pipelines leading to the three irrigation sites, in accordance with the WB loan.