The minimum flow in the upstream basin of the Timis River

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1 IOP Conference Series: Earth and Environmental Science The minimum flow in the upstream basin of the Timis River To cite this article: Niculae Iulian Teodorescu 28 IOP Conf. Ser.: Earth Environ. Sci View the article online for updates and enhancements. Related content - Numerical Model of Transitory Flood Flow in 25 on River Timis Marie-Alice Ghitescu, Gheorghe Lazar, Albert Titus Constantin et al. - Integrated Hydrographical Basin Management. Study Case Crasna River Basin Mircea Visescu, Erika Beilicci and Robert Beilicci - The necessity of flood risk maps on Timi River Geogr Ctlin Aldescu This content was downloaded from IP address on 7/3/219 at 15:49

2 The minimum flow in the upstream basin of the Timis river Niculae Iulian Teodorescu Ph.d. hydrologist, National Administration Apele Române, Banat Water Directorate Timisoara Abstract. The minimum discharge represents a very important stage in the water flow, especially during the long periods lacking rainfall, both in the cold season, but actually mainly during the dry season. Due to this fact, the present paper aims at an analysis of this stage of the water flow in the upper basin of the Timis River, upstream the Lugoj gauging station. This part of the hydrographical basin presents a major importance due to the fact that downstream this gauging station at about 7 km there is The Costei Hydro technical Knot, through which at low water levels, the entire quantity of water in the Timis river bed is directed towards the Bega river in order to supplement the quantity of water upstream Timisoara, the location of the water supply plant. The water taken from the river is treated there in order to be distributed for use in Timisoara, the capital city of the county. The hot period of the year 27 was characterized in Romania by the presence of some very long periods with high temperatures (the maximum values being of over 39 C in many regions) and lacking rainfall. Under these circumstances very low values were recorded on rivers, drastic drops of underground water reserves having as an effect the appearance of drought in certain hydrographical basins. In the analysed hydrographical basin the values of the minimum water quantities during the summer were situated around the assurance values of 75% - that means they were about 75%. The conclusion we have reached is that this summer wasn t among the driest, lower values being recorded in the years , 1957, 1962, 1965,and so on. Keywords: Timis Upstream Basin, dry period, General presentation The Timis River Danube s tributary on Serbian territory, springs under the Piatra Goznei Peak in the Semenic Mountains Banat s water castle at an altitude of 1,28 m. Banat territory is crossed by the river on 244 km, developing an area of 7,31 km 2 (Figure1). Its course is divided into 3 parts: the first part in the mountain area, where it gathers several short streams and reduced area water streams; the second part gets through the Timis-Cerna gorge, a tectonic scallop that separates the Banat Mountains from the Southern Carpathians Range (Carpati Meridionali). Here it receives several tributaries from the mountain ranges Tarcu-Godeanu and Semenic the first ones more developed and presenting a consisting flow. Finally, the last part after receiving its most important tributary Bistra (F=919km 2, L=6 km) spreads over the Timis dejection cone and Banat s flooding plain. Within the Timis River basin there are several important reservoirs Trei Ape Reservoir (S=52.6 ha, 4.4 mil m 3 at NNR Normal Level of Retention), Rusca Reservoir (S=12.5 ha., volume 18.6 mil m 3 at NNR).As a result, important modifications of the flowing regime are produced, which have to be considered when analysing the minimum flow. c 28 Ltd 1

3 The upper part of the Timis River is the area controlled by the Lugoj gauging station, due to the fact that the flow practically forms in this area (morph metrical elements are presented in Table 1). At the same time, downstream of this station there is the Timis-Bega supply canal (Figure 2) where during dry periods waters are diverted to supply the low discharge on the Bega river. Figure 1. Bega River Basin Figure 2. Timis-Bega double connection 2

4 2. Annual minimum average monthly flow analysis Analysing the minimum average monthly flows registered in 27, it is noticeable that significantly long periods with high temperatures and lack of rainfall were registered in our country during the summer months. This was reflected in the minimum discharge values registered in several areas. Table 1 offers a comparative presentation of the values at different ensurances of this parameter and those registered in 27. Within the analysed river basin minimum flow values higher than 8% assurance values the limit for hydrologic drought were recorded. If we analyse Figure3 the relationship between the specific flow values calculated for the 2 pairs of values is obvious and it shows 2 different distinctive relations. Thus it is necessary to notice the fact that for watercourses that have their springs in the eastern part of the river basin in the Tarcu-Godeanu mountain range, the minimum flow values are higher. The same tendency can be observed when we monitor the 27 value evolution the distribution is the same on 2 relations the values being higher for the river basin with higher altitudes especially in the mountain areas. This is due to the fact that in the analysed area the 27 rainfalls were higher than the multiannual average values (Figure 4), except for the river basin in its lower part, reflected in the registered values at the Obreja and Lugoj gauging stations. Nr Table 1. Morphometrical and typical discharge elements for the upper part of the Timis river basin River Hydrometric station F km 2 Hm m Multiannual Average flow Annual minimum monthly average discharge Ensurance of Minimum Monthly Average flow 27 8% 1 Timis Teregova ,28,295,378 2 Timis Sadova ,9 1,48 2,2 3 Timis Caransebes ,5 2,25 2,29 4 Timis Lugoj ,4 7, 7,58 5 Raul Rece Rusca ,64,81 1,62 6 Fenes Fenes ,82,495,668 7 Golet Golet ,686,15,24 8 Sebes Turnu Ruieni ,675,65 9 Bistra Bucova 64, ,345,55 1 Bistra Voislova Bucova ,71,545 1,38 11 Bistra Obreja ,1 4,34 3,3 12 Rusca Voislova ,7,54 1, 13 Bistra Poiana Marului Marului ,71,57 1,1 14 Sucu Poana Marului ,,59 1,2 15 Nadrag Nadrag ,374,14,192 There are no significant differences when analysing the seasonal distribution of these values; thus it can be noticed that across the river basin s greatest part that belongs to the main water course Timis river values that presented a module coefficient no higher than 1.37 have been registered (at Teregova hydrometric station) and they were lower within the main tributary river basin Bistra; here the rainfall module coefficients registered values of up to.85 in the lower part of the river basin (Obreja hydrometric station) and slowly exceeded in the mountain area (up to 1.15 at Poiana Marului hydrometric station). 3

5 A similar tendency was preserved during the warm period of the year the time period between June and September, when the module coefficients have exceeded with 7%-16% the normal values on the largest part of the river basin. It can be noted that these values were more reduced in the lower part at altitudes under 25 m, the 27 registered values were 4% (Lugoj)-14% (Obreja hydrometric station) were lower. P mm Teregova Rusca Fenes Sadova Bucova Voislova P. Marului Obreja Lugoj Mean multiannuale values Values from 27 P mm Teregova Rusca Fenes Sadova Bucova Voislova P. Marului Multiannuale values for the hot seasons Values for the seasonal for 27 Obreja Lugoj Figure 3. Comparative analysis of rainfall multiannual average values The analysis of the distribution of the 27 monthly minimum discharge values shows that in the upper part of the river basin the values were much higher compared to the discharge values with the ensurance of 8% and decreased towards the river basin lower part. Thus within the upper part the module coefficient registered values between 5,39 (at Bucova gauging station) and 3,17 (at Golet gauging station), values that decreased till 1,91 at Lugoj gauging station. 4

6 Hm q 8% Figure 4. Relation between the multiannual minimum monthly average minimum flow with 8 % ensurance ( --) and the one in 27 ( --) 3. Daily minimum average flow analysis In order to be successful in our attempt, annual minimum daily flows were processed, which allowed us to establish the values on different ensurances for this element of the minimum flow. Values are presented in Table 2. The role of the rainfall upon the minimum flow in this river basin area is considered not to be relevant, mainly due to the fact that the upper part has received during this very time spell a relatively permanent supply of the flow, but also due to the distribution of the water volumes from the abovementioned reservoirs. This is very well reflected if we consider the daily average flow graphic for the time period June 1- September 3 27 at Lugoj gauging station (Figure 5), where no permanent decrease can be noticed due to exclusive supply from the underground water. This happened because of the frequent turbinations upstream and then evacuations from the Zervesti reservoirs the buffer lake that sloop the flows into the Sebes and then Timis River. We appreciate that in the absence of these conditions the flow would have registered more drastic decreases (marked with red line in Figure 5) than those represented in the figure, which could have led to lower flow values. This fact allows us to appreciate the positive role of the hydro technical works that redistribute the flow in time, category where the existing reservoirs in this part of the river basin can be included. Otherwise this fact is more obvious if we notice the yearly minimum flow evolution registered between at Lugoj gauging station the station that controls the entire river basin area. As it can be noticed (Figure 6) the 27 registered value, of 7.58 m 3 /s (8.3% higher than the value for the 8% assurances) is the 15 th value in a 58-year range. This proves that in this part of Banat area we cannot speak about a hydrological drought, even if for agriculture it has been such. The not very low minimum flows value has also reflected into the ground waters level, which at fall end registered values close to multiannual average values. If we consider the number of days with permanent decreasing or equal values this was of 4 to 6 and was registered several times in August and only once in September and October. 5

7 Nr. Table 2. Morphological elements and characteristic flows for the upper part of the Timis River Annual minimum average daily flow River. With ensurances Gauging station F km 2 Hm m Multiannual average flow 8% Minimum daily average flow 27 1 Timis Teregova ,28,298,378 2 Timis Sadova ,9 1,49,88 3 Timis Caransebes ,5 2, Timis Lugoj ,4 4,7 7,58 5 Raul Rece Rusca ,64,785,668 6 Fenes Fenes ,82,491 2,2 7 Golet Golet ,686,22 2,29 8 Sebes Tr. Ruieni ,65 9 Bistra Bucova 64, , Bistra Voislova Bucova ,71,51 1,38 11 Bistra Obreja ,1 2, Rusca Voislova , Bistra Poiana ,71,65 Marului Marului Sucu Poiana ,,593 Marului Nadrag Nadrag ,374, Figure 5. The evolution of the daily average flow values at Lugoj gauging station on the Timis River between June-September 27 6

8 Figure 6. The annual minimum flow evolution between Hm q l/s.sqkm Figure 7.The relation between the multiannual minimum daily average specific flow with ensurance of 8% ( --) and that in 27 ( --) The interruptions were caused by some increases either due to sloops into the reservoirs, or of some flows increasing due to rainfall, the most important being the period 4 to 1 August. If we analyse these values, considering the registered multiannual daily average values, we notice this was approx. 12% higher. In what concerns their repartition over a time period, we can notice the fact that the lowest values occurred at the beginning of the 5s and mid 6s and as never before 4 years in a row with decreasing values were registered. (e.g and ). 7

9 If we consider the last 1 years, we can notice that we have to deal in 4 cases with low values for the daily average values, 2 of them being lower than the values with the assurance of 8%. 4. Conclusions Within the Timis river upper river basin we cannot speak about a hydrological drought, although there were periods with low water. These were interrupted by periods with rainfall (the number of rainy days during summer-fall was 37), which determined a good supply of the underground waters as well as the river- beds. In the mean time we consider it led to a certain supply of the ground levels with positive effects on minimum flow values. In this paper we did not present the reconstituted flow values due to the fact that these would have been lower (errors from 1.2% to 5.4%). In order to register drought periods within the Timis River basin upper part it is necessary to register a major rainfall deficit (several months one after another as it was the case in 2, when the deficit of rainfalls was present during May-November); otherwise the minimum flow values will not fit into very high value assurances. References [1] Diaconu C and Serban P 1994 Sinteze si regionalizari hidrologice E.T. Bucuresti [2] Stanciu P 27 Caracteristicile secetelor hidrologice Hidrotehnica Bucharest [3] Topor N 1964 Ani ploiosi si secetosi in Republica Populara Romana (Bucharest: Meteorological Institute) p 34 [4] * * * 197 Raurile Romaniei (IMH Bucharest) [5] * * * Banat Water Branch Archive 8