– 80 – – 8 – type of structure quantity
consolidation and retention
dams 3.475 pcs
consolidation sills 3.081 pcs vegetative
bank protection works 56 km other bank protection works 146 km.
5,2 % 18,3 %
63,0 % 0
500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 5.000
from year 1955 1955 till 1990 1990 do 2003
Cross-sectional structures [Nr.]
Cross-sectional structures [Nr.] Damaged structures [%]
MAINTENANCE OF TORRENT CONTROL STRUCTURES IN SLOVENIA
Dr. Aleš Horvat1, Jože Papež2 EROSION IN SLOVENIA
Slovenia faces different forms of erosion, among which water erosion is particularly significant. The most significant are torrent outbursts, extreme sediment transport and debris flow events, landslides, rockfall and avalanches. 44% of the area is potentially at risk by erosion, one third of the area is considered as unstable or conditionally stable. Almost one quarter of Slovene territory are torrential watersheds, where the erosion phenomena can obtain larger dimension and cause major damage when precipitations are intensive. In the last 15 years natural disasters have claimed 4% of GDP on the average, a big part of them were caused by torrents. Integrated torrent control, of which maintenance of protection systems and structures are important part, is therefore one of the basic conditions for sustained progress of society and the state respectively.
TORRENT CONTROL
Since the beginning of the organized torrent control in Slovenia in 1884 (1875), quite a lot of work has been done, and safety from erosion and torrents has been substantially improved.
The standard of design and execution of construction torrent control works was continuously improved, by means of new knowledge, new materials and new technology of works.
Tab. 1: Torrential and antierosional works undertaken from 1884 till 2003
The majority of torrent control structures have been actually constructed on proper locations, taking into consideration also the best possible way of their integration in the landscape. Unfortunately, many of these structures are old and damaged. The largest parts of damaged structures (63%) have been constructed before the second world war. 20% of the damaged structures are representing those made between 1955 and 1990. Recently built structures are in better shape. The fact that so many torrent control protection structures are old and damaged should cause great concern, since they are constructed in systems and their destruction could have disastrous consequences, in some cases even worse then in case that there were no protective structures at all.
Fig. 1: Overview of damaged cross-sectional structures in Slovene torrent watersheds
1 Puh d.d. – Torrent And Erosion Control Enterprise, inc., Hajdrihova 28, p.p. 319, SI-1001 Ljubljana, Slovenia;
2 Project Leader; Puh d.d. – Torrent And Erosion Control Enterprise, inc., Hajdrihova 28, p.p. 319, SI-1001 Ljubljana, Slovenia; Tel.: +386-1-47-75-200; Fax: +386-1-25-10-030; email: joze.papez@puh.si;
– 80 – – 8 –
MAINTENANCE OF TORRENTIAL AND ANTIEROSIONAL OBJECTS
Integrated water management begins in torrent catchments. Bedload transport control successfully carried out by correctly positioned and designed consolidation and retention structures (Fig. 2, 3). These structures are generally integrated in a system and therefore their functions are interactively supplementing. (Fig 4, 5).
Fig. 2, 3: Damaged dam; damaged sill
Damaged structures and structures that are not maintained regularly do not protect but offer a deceptive impression of security. In case of their destruction the consequences may be even worse then if there would be no protective structures at all. It is therefore essential that they are well and regularly maintained.
Fig. 4, 5: Damaged consolidation structures in the catchments of torrents Pišenca and Joškov graben
CONCLUSION
Increased number of weather extremes are causing increasing number and frequency of natural disasters, and because of the economical development, the consecutive damages are getting proportionally bigger. The significance of maintenance and modernisation of the existent torrent control structures is therefore getting larger. Only well maintained torrent control structures and systems can perform the required function. We have to pay more attention to systematic measuring and analysing of magnitude and frequency of sediment transporting events in Slovene torrents. Because of the obvious non-maintenance of the larger number of torrent structures, Slovenia will have to assign a larger share of funds to their maintenance and increase the share of funds for prevention measures afterwards, to preserve the balance conditions in torrential catchments. Weather extremes could become even more frequent, and the time for catching up the earlier lack of maintenance measures is running out.
Keywords: Torrent Hazard, Torrent Control Structures, Antierosion Measures, Maintenance Measures, Deceptive Impression of Security
