Effects of water course management on floods in the Tarnava river basin

In the Tarnava river basin most of the floods are generated by rain. Thus, at Odor-hei hydrometric station the highest floods recorded before 1970 were the floods caused by the rainfalls in August 1955, July 1957 and 1959 with peak discharges of 80—90 m3/s. After 1970, the highest discharges of 205 m3/s were recorded on March 13, 1981. At Blaj hydrometric station the most important floods were caused by rainfalls, for example, those in 1953, April—May 1956, and July-August 1960. The peak discharges of 851 m3/s were recorded on July 4, 1975. Because of the significant increase of the basin's storage surface, the mixed floods, with a frequency comparatively inferior to the frequency characteristic to floods caused by rainfalls, could present peak discharges and huge volumes of water.

In 1970, between May 12 and 16 peak discharges of 700 m3/s (May 15, 1970) were recorded at the hydrometrical station from Topa on the Tarnava Mare river and 323 m3/s at the hydrometrical station from Sarateni on the Tarnava Mica river. The flood was formed because of heavy rainfalls and melting snow in the upper basin. In 1975, they registered the most increased discharges at Simonejti, Medias, Blaj, Tarnaveni, and Mihalt stations. Heavy rainfalls on a highly saturated soil caused severe floods on the Tarnava Mica and Tarnava Mare rivers. Peak discharges of 135 m3/s were registered at Simonejti on Feernic on July 2, 1975; 900 m3/s at Medias on Tarnava Mare on July 3, 1975; 851 m3/s at Blaj on Tarnava Mare, 1 day later and 830 m3/s on July 3, 1975, at Tarnaveni on the Tarnava Mica river. At Mihalt hydrometric stations 1350 m3/s were registered. In 1998, two periods of substantial precipitations were recorded in the same month, June. The first between June 11-15, 1998 and the second between June 16-20, 1998. Peak discharges recorded on Tarnava Mica were of 335 m3/s at Balaujeri and of 196 m3/s at Tarnaveni.

The flood analyses from the period of 1972-2004 at the hydrometric post in Tarnaveni show a major flood in July 1975, when, at 5:00 A.M. on July 3, 630 m3/s were registered, a value 60 times higher than the average discharges characteristic of July at this post. Analyzing the flood routing between Sarateni and Tarnaveni, we can observe the increasing speed of the flood wave, from 1.5 to 4 km/h, because of the hydrotechnical works done after 1977. The rainfalls in December 1995 caused peak flows on the Tarnava Mica river in the Tarnava Mica river basin with high water overrun and serious damages. Serious damages were recorded in the following villages: Suplac: 528 hectares of arable terrain flooded, right river bank eroded in the outskirts; Adamuj: 82 flooded households, 22 houses, and 380 hectares of arable terrain destroyed (Voda, 2007). Consequently, it is absolutely necessary to start flood protection works in the area of Suplac, Adamuj, Cornejti, and Craiejti.

g 300

g 300

0S/23/05

08/24/05

0S/23/05

08/24/05

Fig. 35.3 Feernic flood wave hydrograph in 2005 at Simonejti.

In August 2005, the flood wave recorded at the Simonejti hydrometric station was very strong (Fig. 35.3), the water level grew rapidly, starting at 06:00 A.M. (H - 10, Q - 2.16 m3/s) on August 23 2005, with 70 cm until 17:00 h (H - 80, Q -18.1 m3/s). This way at 18:00 h (H - 140, Q - 48 m3/s) in one single hour the water level grew by 60 cm, while at 19:00h (H-200, Q - 104 m3/s) by another 60 cm. The highest level of the flood is reached a half an hour later at 19:30 h (H-367, Q-480 m3/s). In an only 30 min spell the water level raised by 1.67m and the water discharge of the Feernic grew by 460%. Practically in 2V h, between 17:00 and 19:30, the Feernic's water level rose by almost 3m! The danger- quote was exceeded by 217 cm in the evening of August 23, 2005, the water level remained high until 2:00 in the night (H - 180, Q - 82 m3/s), after that it started to lower until the morning of August 24, 2005 at 09:00 A.M. (H - 120, Q - 38 m3/s). It rose again until 10 o'clock (H - 180, Q - 82 m3/s), receding then at 14:00 h below the danger quote (H - 130, Q - 42 m3/s). In 2 h eight localities - Odorheiu Secuiesc, Lupeni, Porumbeni, Simonejti, Mugeni, Corund, Feliceni, and Dealu - were covered by the floods started on the surrounding hills and the swollen creeks, which had outran 100 mm in less than an hour. The peak flows killed 13 people in Lupeni, Feliceni, and Simonejti, another 3 people were reported missing in these places, probably swallowed by the peak flows that destroyed 55 houses in only a few minutes.

Was this article helpful?

0 0
Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

Get My Free Ebook


Post a comment