Possibilities for active flood control management with the application of mathematical models - the case study of reservoir Bočac on Vrbas river

Sistemi zaštite od poplava spadaju u klasu najvažnijih, najvitalnijih sistema koje čovek gradi, jer su vezani za ciljeve opstanka, rasta i razvoja ljudskog društva. Zato su ti sistemi u stalnom razvoju, kako sa stanovišta dograđivanja i rekonstrukcije objekata, tako i sa gledišta neprekidnog usavršavanja mera operativnog upravljanja tokom perioda velikih voda. Sistemi zaštite od poplava daju najveće efekte kada se spregnuto, integralno koriste sve tri grupe mera: (a) pasivne mere zaštite linijskim sistemima zaštite (nasipi, prateći sistemi odvođenja unutrašnjih voda), (b) aktivne mere zaštite primenom akumulacija i retenzija, kojima se smanjuju vršni delovi talasa velikih voda, (c) neinvesticine mere planskog uređenja teritorije kojima se sprečava građanje neprikladnih objekata u plavnim zonama, kako bi se zaustavio porast potencijalnih šteta od poplava. Povećanje operativnosti i tačnosti hidrometeoroloških prognoza i razvoj informaciono-računarske tehnologije, stvorio je mogućnosti da se znatno operativnije i uspešnije koriste akumulacije za aktivnu zaštitu – smanjivanjem vršnih delova talasa velikih voda. U radu se prikazuju mogućnosti primene upravljačkih matematičkih modela za ublažavanje poplavnih talasa. Model je razmatran na akumulaciji Bočac na Vrbasu sa nedeljnim regulisanjem protoka. Pokazalo se da se namenskim upravljanjem samo radom hidroelektrane mogu uz odgovarajuću prognozu vrlo uspešno ublažiti talasi češćih povratnih perioda (2, 5 i 10 godina). Ukoliko su prognoze nailaska velikih padavinskih ciklona operativne, sa prognozom od par dana unapred (savremene metode meteoroloških osmatranja i prognoziranja to već omogućavaju), primenom upravljačkog modela, koji omogućava fleksibilno upravljanje radom agregata HE, preliva sa ustavama i temeljnog ispusta, moguće je blagovremenim obaranjem nivoa vode u akumulaciji uspešno ublažiti i talase ređih verovatnoća sa povratnim periodima 50 i 100 godina (na Bočcu stogodišnja velika voda se smanjuje za preko 200 m3/s). Akumulacija je mala da bi mogla da utiče na talase veoma retkih pojava (0,2% i ređe). Vrlo bitna su tri opšta zaključka: (1) pri projektovanju brana čije će se akumulacije koristiti i za zaštitu od poplava, veoma je važno da se predvide snažni evakuatori (temeljni i srednji ispusti) čiji kapaciteti omogućavaju elastičnu kontrolu nivoa, obaranjem nivoa pre nailaska poplavnog talasa, (2) tendencija povećavanja instalisanosti pribranskih HE sa godišnjim regulisanjem (odnos Qinst/Qsr do oko 6) pogoduje aktivnoj zaštiti od poplava; (3) simulacioni i optimizacioni matematički modeli, uz dobre meteorološke prognoze velikih padavinskih ciklona, mogu se uspešno primenjivati za aktivnu odbranu od poplava čak i akumulacije manjih relativnih zapremina, u slučaju Bočca sa nedeljnim regulisanjem protoka. Akumulacije sa godišnjim regulisanjam u tom pogledu daju znatno povoljnije rezultate.Flood protection systems are one of the most important, most vital systems that man builds because they are related to the goals of survival, growth and development of human society. That is why these systems are in constant development, from the aspect of upgrading and reconstruction of facilities, as well as from the aspect of continuous improvement of management measures during the period of high flows. Flood protection systems have the greatest effects when coupled using all three groups of measures: (a) passive protection measures with line protection systems (levees with inland drainage systems), (b) active protection measures by the use of reservoirs and retention to reduce pik flows (c) non-investment measures of landscaping that prevent the construction of inappropriate structures in floodplains that can increase potential flood damage. Accurate hydro-meteorological forecasts and the development of computer technology enabled using reservoirs for active protection more efficiently and successfully (by reducing the peak flows of the flood waves). The paper presents the possibilities of mathematical models for flood wave mitigation. The model was applied at the Bočac reservoir (reservoir with weekly flow regulation) on Vrbas river. It has been shown that the waves of frequent return periods (2, 5 and 10 years) can be very successfully mitigated using only the discharge through the hydroelectric power plant. If high precipitations are predicted several days in advance (modern methods of meteorological observation and forecasting allow it), and with flexible management of HPP units, spillways controled with gates and bottom outlets, water levels in the reservoir can be properly decreased and the waves of rarer probabilities (with return periods of 50 and 100 years) can be successfully mitigated. At Bočac reservoir 100-year high water can be decreased for over 200 m3/s. The Bočac reservior is to small to significantly decrease flood waves of very rare occurrences (0.2% and less). Three general conclusions can be driven out: (1) When designing dams whose reservoirs will be used for flood protection, it is very important to have strong evacuators (bottom outlets, spillways with gates) with discharge capacities large enough for efficient decrease of water level before the flood occurs, (2) the trend of increasing the installed capacity of HPPs with annual regulation (ratio Qinst / Qsr round 6) is also favourable in periods of active flood protection; (3) Simulation and optimization mathematical models, with acurate meteorological forecasts of high precipitation, can be successfully applied for active flood protection, even with the reservoirs with relatively smaller storage volumes (in the case of Bočac reservoir - the weekly flow regulation). Reservoirs with bigger relative water storage volumes (reservoirs with annual flow regulation) are more favorable in that aspect