Effects of water course management on the monthly mean discharges in the Tarnava river basin

A high degree of flow modification is noticed in 1986 in the Tarnava Mica basin, at Báláujeri and Tarnáveni hydro stations, where the correction discharges exceeded 5% in 10 months, except for March and April. The natural discharge reconstructed at Báláu^eri in September was 2.14 m3/s as compared to 4.64 m3/s (the multiannual average value of September) and in December Qnat =1.99 m3/s as compared to 5.94 m3/s (the multiannual average value of December). At the hydrometric station of Tarnaveni the natural discharges reconstructed in November were 2.56 m3/s compared to 5.84 m3/s (the multiannual average value of November) and in December Qnat =2.38 m3/s compared to 7.06 m3/s (the multiannual average value of December). In March and April, the K values reflect a reduced value of flow change, but they remain low in the other months of the year, reaching a peak in September and December at the hydrometric station of Báláu^eri, namely in November and December at Tarnaveni.

In 1990, the water management works had a great influence on the discharges in the Tárnava river basin. At Mihalt, the volumes stored in this year were 34.7 Mm3, a value similar to the one in 1988 in which the discharge was higher, reaching its peak. The highest rates of flow stored were also recorded in August and September, months which presented the lowest monthly rate of flow in 1990 and also the highest correction discharges (Fig. 35.1). The reconstruction correction works were necessary beginning with April (6.88%) till the end of December (15.47%). The highest correction discharges are in August (26.81%) and September (24.16%). In the river basin of Tárnava Mica, at the hydrometric station of Tarnaveni, the highest rate of runoff was recorded in August 1990 (Fig. 35.2).

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Fig. 35.1 The average natural and reconstructed monthly discharges variation at Mihalt hydrometric station in 1990.

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Fig. 35.1 The average natural and reconstructed monthly discharges variation at Mihalt hydrometric station in 1990.

The highest runoff from the whole period analyzed was recorded in 1998. The annual average discharges were 51.6 m3/s at the hydrometric station Mihalt. The discharges of water stored in the basin were 22.1 m3/s. Analyzing the variation of the average rate of flow measured and reconstructed as well as the share of correction discharges in 1998 at Mihalt, we observe the positive role of the storage reservoirs in the Tarnava basin, put in use after 1990. The mitigation of maximum discharges is illustrated by the Q natural > Q measured > Q annual average meas ured values of the following months: January, April, June, and July. The accumulations regulated the flow by storing extra volumes, redistributed gradually in time. In some of the months of 1998 important flows were registered (Sorocovschi and Haidu, 2004). A positive influence of water training works is noticed in the basin due to the perennial storage reservoir Zetea and Bezid.

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Fig. 35.2 Modification of the monthly average discharges in 1990 at Tarnaveni.

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