RESEARCH FOR

REGULATED STREAMS REHABILITATION
USING BIOENGINEERING METHODS
experience of foreign countries, ways and methods
of rehabilitation of regulated rivers are analysed
and summarized (Conservation…, 2007; Danish…,
1995; Florineth, 2008; Freshwater..., 2001; Jormola,
2006, 2008; Living…, 2006; Longinojan…, 2006;
River..., 1996; The river …, 1998). Natural means
of naturalization are being reviewed and grouped
according to origin and possibilities of use (Chanson,
2000; Christensen 2000; Cokgor, 2004; Danish, 1995;
Fischer and Fischenich 2000; Florineth, 2008).
Having summarized material gathered in literature,
5 groups of rehabilitation by bioengineering methods
have been highlighted. These groups are composed
according to slope (0.7 m km -1 )
and natural environment (field, forest, field-forest) for
which are suggested bioengineering packets. Finally,
an example for partial naturalization method for
regulated rivers is proposed.
results and discussion
Consequences of rivers regulation
Melioration basically changed the environment,
hydrography, morphology and hydrology of rivers
and streams. It gave a new meaning to engineering
building with the purpose of accumulating and freeing
water in time from the drained areas (Lamsodis, 2001).
When performing melioration works, bands of forests
and scrublands, through which migrated animals were
destroyed. After having drained some swamps, the
regime of ground water changed, processes of bend
formation stopped, wind erosion increased, but the
level of ground water decreased (Vilkevičiūtė, 2003).
Drainage of grounds has changed network of
Lithuanian rivers and streams as well as processes
occurring in their channels. Morphological,
hydrological, and hydromorphological changes of
hydrographical network in channels of regulated
streams and influence of those changes on flora and
fauna are being introduced.
Changes of hydrographic network. Channels of
rivers and streams of intensive ground drainage to
the extent of all country shortened for 2.5 km or
8.2% on average, and areas of river-basins changed
correspondingly – 7.5 km 2 (12%) (Gailiušis and
Kriaučiūnienė, 2001). It is calculated that after having
drained 46.6% of country territory, the length of river
channels increased from the mentioned above 63.4
thousand km to 76.8 thousand km, i.e. approximately
20.6%, and the number of rivers reduced from 29.1
thousand to 22.2 thousand, i.e. 23.7% (Gailiušis and
Kriaučiūnienė, 2001).
Morphological changes. After having straightened
the streamways, their morphology has changed: limits
and the shape of the streamway, structure of slopes,
shape of coastline, substrate of the bottom, also
hydraulic conditions of the current have changed.
Antanas Maziliauskas,
Raimundas Baublys, Ramūnas Gegužis
After having straightened streamways, it obtained
a shape of regular trapeze in leading trenches. After
having straightened streamways, their longitudinal
slopes have increased even up to 1.5–2.0 times, and
simultaneously water speed and outwash discharge
have changed. In the upper reaches of the straightened
rivers and streams due to high speed of the current,
as washing force of water increased, intensive erosion
processes, which influence widening and sinking of
streamways occur. Meanwhile, in the lower reaches
of the straightened rivers and streams, the streamway
silts up, due to the satiation of current with the outwash
(Vaikasas, 2007). Thus, in the straightened streams
and rivers with a monotonous, fast current and with
the silted streamway bad conditions for settlement and
living of fishes and other ichthyofauna form.
Hydrological changes: After having straightened
the rivers, their hydrological parameters – the speed of
the current, debit, module of run-off, and slope have
changed. Since the module of run-off best evaluates
changes of hydrological regime, for this reason
changes of natural hydrological regime of rivers have
been evaluated according to the changes of quantity of
natural yearly run-off. As the run-off has changed, i.e.
water quantity in the river-basin, river discharges have
changed as well. According to the researches of A.
Dumbrauskas, A. Povilaitis and others (Dumbrauskas
et al., 1998; Kutra et al., 2006), changes of the run-off
are related with intensified after rivers’ straightening,
land usage and with changes of water balance. It is
identified that the impact of stream straightening
on decrease of run-off may be not more than 2-3%.
Greater influence on discharge of the straightened
river is felt in a small river-basin, but in bigger rivers
only deviant balance of surface - ground discharge is
felt more.
Hydromorphological conditions strongly influence
the change of physical - chemical parameters of the
streamway. After having straightened the rivers, a water
current starts running faster in the streamway, while
the possibility of water self-depuration decreases. As
nourishment accumulates, favourable conditions for
water plants development appear. In water, saturated
with nourishment, the usage of oxygen consumption
which is harmful for water animals increases. Thus,
as values of physical - chemical parameters change,
conditions of water animals’ existence in basin change
as well.
Impact on flora and fauna. During the period of
straightening of rivers and streams, water and riverside
fauna and ichthyofauna which until that moment
was present was destroyed. Its rehabilitation was
blocked by later performed works of maintenance of
drainage systems (Freshwater..., 2001). After having
straightened the streams, shrubbery and trees have
been cut, grass flora has changed them. Haymaking of
110 ReseaRch foR RuRal Development 2012