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ŠUMARSKI LIST 13/2005 str. 110     <-- 110 -->        PDF

V. Ivančević: BIOLOGICAL AND TECHNICAL REGULATION OF THE SENJ TORRENT "TORRENTE" Šumarski lisl - SUPLEMENT (2005). 91-109
maximal capacity of 39.0 1/sec or 1,225,500 m3 per
year. The water system capacity was calculated to meet
the needs of the 5,000 citizens of Senj on the basis of
daily consumption of 900 m3. This equals the capacity
of 10.41 1/sec or 328,500 m3 per annum, which is slightly
higher than the minimal capacity. The reconstruction
of the water supply system ensured sufficient annual
quantities of water, but the increased consumption in
summer months would still cause shortages. Pipes of
cast iron with diameters of 50, 60 and 80 mm were laid
along the water route and pipes with diameters of
50-150 mm were laid in the town network. The total reconstruction
costs were 63,709,926 dinars (Figure 7).


The construction of the hydropower station Senj in
the 1960s ensured undisturbed supply of water for the
wider area of the southern continental and littoral area
and the adjacent islands. The high-capacity water system
was built in the southern part of the Croatian littoral,
as was the new water route from Hrmotin to Senj.
This solved the problem of water supply for the Town
of Senj. The former water supply system from the area
of Senjska Draga currently only serves the downstream
hamlets. The old water route with the springs and other
facilities is in a state of neglect, which is unwise policy.
This old water supply system should always be at the
disposal in case of major breakdowns in the new water
system. Also, its waters could be used to enliven the
formerly regulated torrential channel from the cemetery
to its entry into the sea, thus providing an original
tourist attraction. A constant increase in the number of
springs and their inclusion in the Senj water supply
system is definitely the result of successful biological-
technical operations in the upper slope of the Senj torrent
in Senjska Draga. However, no systematic research
has been conducted and no reliable conclusions can
be drawn. In this case, the only conclusions can be based
on the perceptions of the forestry science on a close
relationship between biological-technical operations
and the intensity of torrents and erosion.


Regrettably, no systematic research has been done
related to the increase in the number of springs with re


lation to vegetation progression. No historical records
have been found for this segment. We have used the
scarce project documentation relating to the water supply
of Senj. However, the documentation does not provide
a key answer that would confirm the correlation
between a higher number of springs and vegetation
progression. The crucial dilemma remains: was a gradual
increase in the number of springs limited by financial
reasons or was there no need to include new
springs? In this case, too, we may stand by the claim
that the number and capacity of the springs increased
in proportion with the intensity of biological-technical
operations, with simultaneous decrease in erosion processes.
The former Senj torrent and the resulting erosions
in Senjska Draga have been consolidated, but a
pilot project designed to further monitor these relations
would be more than welcome and would be of exceptional
importance not only for the forestry and water
management profession but also for other related disciplines.
The existing springs should be regulated and a
permanent experiment of their capacity set up. Some of
them represent highly successful civil engineering solutions,
which deserve to be included in the monuments
of technical culture.


Forestry experts and experts from other related disciplines
should gather to further investigate the water
capacity of Senjska Draga linked with the former water
supply of the Town of Senj. To our knowledge, such
successful and extensive regulation of torrents and erosions
in Senjska Draga with biological-technical measures
has not been accomplished anywhere else in the
Mediterranean area. Senjska Draga has become a compulsory
destination for home and foreign forestry and
other experts, who are invariably impressed by its
grandeur. Senjska Draga is a striking example of an
outstanding achievement of the Croatian karst forestry
profession. It may justifiably rank among the karst forestry
professions of the most developed Mediterranean
countries, while in some segments it even takes up
the leading position.


CONCLUSIONS


The disappearance of forests in the Senjska Draga
valley several centuries ago resulted in devastating
torrents and erosions.


In its total length of 25 km, the Senj torrent brought
an average of 32,000 m3 of sediments annually in
the upper slope in Senjska Draga, which then moved
towards the lower slope, threatening the Town
of Senj.


To remove the danger of torrents in the lower slope,
the torrential channel from the old city centre was


relocated outside the town walls at the end of the
18th century. This partial measure mitigated the danger
of torrents, but did not remove it completely.


The Inspectorate and special torrent regulation services
launched a very successful regulation of the
Senj torrent and erosion in the second half of the
19th century. Combined biological-technical measures
in its upper slope were used for this purpose.


The majority of the work was done at the end of the
19th and the beginning of the 20th century, when 22