Ivan Franko National University of Lviv

Vul. Doroshenka, 41/65; Lviv 79000, Ukraine

PROBLEM RELEVANCE. TERMINOLOGICAL QUESTIONS.

The designation "small" is generally attributed to a river with a watershed situated in a single geographic zone and having an area of no more than 2000 km², which hydrologic regime is under the significant influence of local factors thus possibly being different from the regime of big zonal rivers.

Small rivers are reasonably considered the most vulnerable link in the global hydrologic cycle. At the same time, they are the most numerous hydrologic entities on Earth, being the components of bigger river systems.

The quantitative parameters of small rivers (length, watershed area, riverbed width and slope angle, water discharge, changes in water levels, etc.) accepted in different countries, are rather provisional and vary considerably in relation to different natural and socioeconomic conditions, historical traditions of nature utilization and studying, and proceeding hydrologic processes. When referring a river to a category “small” one usually takes into consideration its length (up to 100, sometimes 200 km), the area of watershed (up to 2000 km²), the depth of groundwater layers draining into the river, the local landscape and geographical basin properties, and other parameters [Small rivers of Ukraine, 1991].

As small rivers are the initial link of river systems, all the changes in their state, functioning regime, and water quality significantly influence the states of middle-size and large rivers and the processes developing therein. Small rivers are particularly sensitive to anthropogenic influences on watershed landscapes and floodplain-riverbed complexes. Tree cutting, slope ploughing, land surface development, the construction of infrastructure, mining of minerals and building materials, lowering of ground water levels as a result of water usage and melioration, expansion of agriculture and stock raising have provoked the active development of slope denudation processes and the delivery of the very large amount of sediment onto the small river floodplains and riverbeds, together with the dissolved material, the components of organic and mineral fertilizers, the sewage and drainage water discharges. These processes have caused the silting of small river watercourses, their shallowing, the decreased water discharges, the overgrowing of streams by hydrophilic vegetation, their transformation into interim streams or their overall disappearance as rivers.

The complex of processes of the silting of small rivers by the products of soil erosion, delivered by the slope outflow on stream floodplains and riverbeds, which cause decreasing supply and lowering the quality of water resources, shallowing and overgrowing of watercourses by hydrophilic vegetation, the drying out and disappearance of small rivers as perennial streams, is termed the river system degradation [Kovalchuk, Shtoiko, 1982; Kovalchuk, 1987; Velykopolskaya, Kovalchuk, 1988; Chalov, 2000].

Figure 1.The structure of degradation processes developing in small rivers and river systems

Some authors [Golosov, Panin, 1998] propose to regard the degradation and the silting as differing concepts. By degradation they mean the disappearance of constant flow in rivers and streams as a result of a range of natural and anthropogenic causes, including the silting. This process is considered to be a multistadial phenomenon, wherein the total destruction of small river (stream) ensues in its final stage. At the same time, the proper silting of small rivers, according to them, doesn't always lead to river system degradation. We propose the following scheme to depict the structure of degradation processes (Fig. 1).

The main consequence of the development of degradation processes is the decrease of small river number and length, the simplification of river system structure viz. the lowering of their rank, the decrease in water contents, the deterioration of water resources, the reduction of their biological and landscape diversity, the decrease of the durability of basin and river landscapes to anthropogenic stresses.

Besides the degradation processes, river systems are susceptible to the influence of transformation ones. The transformation processes are the consequences of human impacts on basin and river systems, leading to changes in river appearance, emergence of man-made water bodies (mainly under the influence of melioration), increase in stream number and length, increases or decreases of their discharges, flow velocities, transporting capacity, etc. [Kovalchuk, 1997].

High diversity and accessibility of water and biological resources of small rivers, and their continual natural renewal predetermined their big attractiveness for humans. Rivers have been serving as a transportation routs, sources of energy and biological resources, are utilized for the maintenance of water usage, irrigation, the placement of cities and settlements, industrial and agricultural enterprises, recreation facilities, etc. Humans, by the utilization of the natural resources of rivers and river valleys, have caused the active development of transformation and degradation processes therein. These processes encompass practically every small river on Earth. Meanwhile, the deterioration of river ecological state threatens the very existence of humans. Therefore, the study of the degradation processes of small rivers is an urgent problem of modern natural sciences – hydrology, geomorphology, ecology, and landscape ecology. In this connection, let us consider in more detail the essence, distribution, intensity, prerequisites, causes, conditions of manifestation, and consequences of the development of degradation processes in river systems, especially in their upper links –small rivers.

HISTORICAL ASPECTS OF STUDY OF SMALL RIVER DEGRADATION PROCESSES

The origin of the study of degradation processes in environment resulting from the environmental influences of human activities and influencing the state of small rivers is associated with the published works of G. Marsh (1864), V. Dokuchaev (1878, 1892), Ye. Oppokov (1890), and A. Voyeikov (1894).

They have pointed to the numerous facts of the increased seasonal and inter-year variations of river flow – the increased flood levels, the decreased low water levels, the drying out of a lot of smallest and small rivers in steppe, forest-steppe, and southern forest zone.

In the ensued discussion on causes and factors of these changes, and the mechanics of the river systems reactions, two opinions were put forward:

1. The main reason of the changes of flow regime and river drying-out is the multiyear climatic oscillations;

2. The most important factor of the drying-out of small rivers and the changes of flow regime is the tree cutting and the expansion of arable lands, which have influenced the ratio of surface and underground components of river flow.

These discussions continued to the beginning and in the first half of XX century, when the intensive construction of ponds, reservoirs, and hydroelectric power stations took place, together with the amelioration of floodplain and basin swamps, accompanied by the significant modifications of rivers flow and the transformations of river systems structure. However, at this time, as well as in 60-70^th of XX century, when studying human influences on rivers the main emphasis was placed on revealing the scales of changes of river water content. To this purpose, the experiments were carried out with the basin clear-cutting and the estimation of its influence on water and sediment flow, and also the parallel studies on forested, deforested, and agriculturally utilized watersheds. It was established that the increase in the watershed forest cover leads to a decrease of flood discharges and an increase of low-water discharges, while the decrease of forest cover leads to an increase of the within-year flow variability and of the intensity of erosion-accumulation processes, that lead to the silting of channels of small rivers and of ponds build on them, the accumulation of silt on floodplains and by the foothills of slopes under arable [Voronkov, 1970; Krestovsky, 1986; Shiklomanov, 1989; Vodogretsky, 1990; Koronkevich, 1990, etc.]

At 1980-th the historico-geographical studies of the river systems of Podilska upland were launched at Lviv University. They were based on the comparative analysis of high-scale maps for different time sections, and the field examination of small rivers [Kovalchuk, Stoiko, 1982, 1989, 1992; Shtoiko, 1986; Kovalchuk, 1987, Velikopolskaya, Kovalchuk, 1988, etc.] As a result of these studies, the charactreristic features of the distribution of transformation and degradation processes in the structure of river systems of left Dnister tributaries, specifically the directionality and intensity of the silting and vanishing of the smallest and small rivers were determined, and the contribution of natural (climatic fluctuations) and anthropogenic (tree cutting, slope ploughing, ameliorative works, construction, etc.) factors was assessed. In following time the geography of these studies has expanded – they have embraced the rivers of Precarpathia, Transcarpathia, Ukrainian Carpathians, Lesser and Volyn Poliss'a, Volyn Upland, Donbass [Kovalchuk, 1987, 1997; Dybis, 1995; Kurhanevych, 2001; Kovalchuk, Volos, Holod'ko, 1992, 1996; Chemerys, 1993; Kiseliov, 2001; Pavlovs'ka, 2006, etc.]

This research direction kindled the interest and was followed in other scientific centres – MGU [Ivanova, 1990; Golosov, Ivanova, Litvin, Sidorchuk, 1992; Golosov, Dobrovols'kaya, Ivanova, 1995; Golosov, Panin, 1997; Chalov, 2000, 2004; Golosov, 2000; Alexeevskiy, Chalov, 2001; Malye reki volzhskogo bassejna (The small rivers of Volga basin), 1998; and many others]., Kazan' university [Priciny i mechanism (Causes and Mechanism), 1996; Dedkov, Kurbanova, Mozzherin, 1995; Kurbanova, Butakov, 1996, etc.], Udmurt university [Yegorov, 2000, 2005; Perevoshchikov, 1993; Petuhova, 2004; Rysin, Petuhova, 2006], Perm university [Nazarov, Yegorkina, 2000], and Bashkir state university [Gareev, Musin, 2006, etc.] in Russian Federation, and also in Poland [G. Marushchak, G. Vachoviak, L. Starkel, A. Lajchak, B. Vizhga, S. Gurzalsky, etc.], Chech republic, Slovakia, France, USA, Japan and other Asian countries, etc.

To give an example, as early as in 1955 the International symposium on the role of humans in the changing of the Earth’s face was held at Princeton University. Some of its reports [Leopold L., 1956; Tomas H. E., 1956; Strahler A. N., 1956) elucidate the questions of the influence of agriculture on river sediment flow, and the causes of the activated erosion and degradation processes in river systems. In 2006, in connection with the 50-th anniversary of the publication of the materials of this symposium, the geomorphologic symposium on the human role in the changes of fluvial systems was held in Binghamton. Its materials were published in a special issue of “Geomorphology” journal (vol. 79, issues 2-4). In a number of its papers, the interesting results of the researches of the influences of human activities on river systems, channels, riverbed and slope erosion processes were reported (Gregory, 2006; James and Mareus, 2006; Hooke, 2006; Chin, 2006; Kand and Marston, 2006; Wohl, 2006).

In 2006 at Lviv national Ivan Franko university the International seminar was held with a topic “Erosion-accumulation processes and river systems of the developed areas” where the problems of the river systems degradation were discussed.

The main emphasis in the researches on the degradation processes of small rivers presently is placed on: 1) determination of the rates of the silting of small rivers floodplains and channels in different types of environment; 2) study of the intensity and directions of horizontal and vertical channel deformations; 3) determination of the role and relative importance of natural and anthropogenic factors in the changes of the small rivers water flow, the structure of river systems, the alternation of the zones of alluvium erosion and accumulation in the channels of small rivers; 4) solution of the problems of palaeohydrology and palaeogeomorphology – the reconstruction of the history of river valleys formation, determining the intensity of erosion-accumulation processes on different stages of river development, etc.; 5) determination of the relation of watershed and channel constituents of river sediment flow for rivers of different ranks; 6) assessment of the influence of economic activities on the water, sediment and solute flow regimes; 7) assessment of the consequences of the influences of human activities on the functioning regime and ecological state of small rivers, and the systems of ponds and reservoirs constructed on them; 8) the substantiation of the system of water-protection, anti-erosion, and flow-regulating measures.

CHARACTERISTIC FEATURES OF SMALL RIVERS, CONTRIBUTING TO THE DEVELOPMENT OF DEGRADATION PROCESSES.

The conducted studies allowed to define the following characteristic features of small rivers, contributing to the active development of degradation processes therein:

1. Close relationship of the state of riverbeds with the state of a whole catchment area and the erosive-accumulative and other exogenic processes developing therein;

2. Small water content and its significant seasonal variations, caused by climatic factors, local physico-geographical conditions, and economic activity;

3. High sensitivity to sewage runoff pollution (caused by communal, industrial, animal runoff, the runoff from fertilizer, pesticide, fuel and greases storages, solid-waste landfills, filling stations, car-washes, etc.);

4. Rapid reaction to artificial cutoffs, dredging, discharge regulations by ponds and small reservoirs, floodplain meliorations;

5. Rapid silting of riverbed and floodplain water bodies, caused by the active development of slope and riverbed erosive-accumulative processes;

6. Intensive overgrowing of riverbeds and floodplains, blooming of waters, and euthrophication of floodplain water bodies, developing when the anthropogenic stress on rivers exceeds their self-restoration ability;

7. Ploughing the slopes and floodplains of small river basins almost up to the water level, absent bank protection measures, violation of the water protection requirements, causing the erosion of watershed slopes and banks, the silting and overgrowing of riverbeds, the deterioration of water quality, the drying out of small rivers;

8. Active ameliorative influences on floodplain body and law waterlogged terraces, which causes irreversible changes of the state of small rivers and interruption of their functioning (water, sediment, and solute discharge).

These features determine the distribution of degradation and transformation processes in the structure of river systems and riverbeds of small rivers, their specific diversity and the intensity of development, geoecological consequences and the scales of their state changes and the decrease of their biological and landscape diversity.

MECHANISMS OF DEGRADATION PROCESSES DEVELOPMENT IN SMALL RIVER BASINS

The mechanism of degradation process development is a certain combination of factors influencing a small river and the chain of its feedbacks, which manifest themselves in forms of riverbed silting, overgrowing, decrease in water content, deterioration of water quality, partial or complete drying out of watercourse, its transformation into an interim stream (Kovalchuk, 1997).

The mechanisms of the development of degradation process in river systems (in the first place in small rivers) can be represented in a scheme (fig. 2).

As a result of aggregate influence of natural and anthropogenic factors the small river passes several stages during its development, the combination of which forms a succession series. The study of the degradation processes of the small rivers in lowlands, uplands, foothills, and mountains allows distinguishing the following succession series of degrading small rivers:

I. Evolution succession series of degrading upland river systems:

A. River system consisting of a branching network of typical affluent small rivers of different ranks → B. River system having in its structure some rivers regulated by ponds, and rivers with cutoffs → C. River system with small rivers regulated by ponds, with cutoffs and some streams suffering silting, decreased discharge, and deterioration of water quality → D. River system with numerous small rivers suffering the impact of degradation and transformation processes, with silted ponds, overgrown watercourses, ploughed floodplains.

Figure 2. The mechanisms of the development of degradation process in river systems

II. Evolution succession series of degrading lowland river systems:

A. River system consisting of branching network of different-rank, meandering small rivers, nurturing springs and swamp basins → B. River system containing small rivers, regulated by floodplain and riverbed ponds, and small rivers with straightened channels and ameliorated floodplains → C. River system with dominating small rivers, regulated by ponds, and rivers with straightened channels, experiencing silting and overgrowing by hydrophilic vegetation → D. River system with dominating canalized small rivers, channels, canals and ponds experiencing overflowing and overgrowing by hydrophilic vegetation, with the dried-out springs, arable watershed and floodplain → E. Silted small rivers, transformed into interim streams.

III. Evolution succession series of degrading mountain and foothills river systems:

A. River system consisting of branching network of different-rank small rivers, with a substantial variation in flow → B. River system with a few small rivers having gravel quarries in their riverbeds, with banks strengthened by bearing walls → C. River system with 10 to 30% of tributaries with technogenically transformed riverbeds and clear-cut watersheds, the active development of erosion processes, the deterioration in water quality caused by sediment inflow, wood decay, and sewage discharges → D. River system with more than 30% of small rivers experiencing technogenic transformation and channel silting, pollution of water resources, with watershed lands extensively developed by agriculture, industry, housing, and transportation → E. River system with completely silted small rivers and rivers regulated by ponds and reservoirs, with bank-maintaining constructions, bridges, recreation facilities, spans with timber floating, etc.

The experience in studying small rivers in different regions suggests that the tendency of changes in the state of small rivers can both be negative (deterioration of state) and positive (state improvement, the return to previous phases). Usually the latter situation occurs with the abatement or cease of economic influences on rivers and their watersheds, and with the implementation of water-protective measures and reforestation.

THE SCALE AND INTENSITY OF SMALL RIVERS DEGRADATION

The degradation of small rivers is actively developing in industrial areas, urban and rural settlements. Here rivers are being polluted by sewage waters, domestic and constructional solid waste is accumulated, untreated rain and snowmelt waters are released into rivers, the euthrophication of water reservoirs is taking place, the river channel morphology is being changed by cutoffs, the flow direction is being changed, the engineering structures are being constructed, the streams are often canalized (confined into pipes).

In regions where mining industry is developed (producing open mines, riverbed and floodplain quarries where minerals and construction materials are being extracted) watercourses are disappearing or unrecognizably changing being excavated, engulfed by landfills, replaced elsewhere. Where underground mines prevail, land surface often subsides, causing the waterlogging of floodplains and water pollution.

In places with prevailing agriculture and stock rising, numerous ponds are created on rivers, their water being used for irrigation and animal watering, while the watercourses of small rivers being utilized for drainage water discharge. The active development of slope erosive processes leads to a silting of ponds, their euthrophication, and overgrowing by hydrophilic vegetation, contributing to small rivers degradation. Besides, earthen dams build on small rivers are susceptible to destruction, the products of their erosion being deposited in channel and on floodplain downstream, leading to silting of small rivers [Kovalchuk, 1997; Chalov, 2004]. On lowlands small river degradation is facilitated by amelioration and cutoff works that increase channel slope, flow velocity, and sediment traffic, together with water intake from channels, which causes sediment accumulation and channel overgrowth.

The degradation processes are most active in the forest-steppe and steppe zones. The dominant processes that cause here the degradation of small rivers and transformation of river systems, are: the intensive erosion of slope arable lands, supplying 20-64% of the products of slope erosion on floodplains and watercourses [Kovalchuk, 1997]; increased unsteadiness of river flow on account of increasing surface flow constituent and decreasing underground constituent; disappearance of springs that nurture the heads of small rivers (caused by ameliorative and cutoff works, water intake, decreased replenishment of underground water sources); increased arable areas on watersheds, and reduction in forest cover.

In the forest zone owing to a humid climate and high flow-regulating role of forests the small river degradation is less manifested and has mostly local character. Here the silting of small rivers is often connected with timber floating. Trunks are intercepted on meanders, shallows, and bars, which reduce the channel carrying capacity, create artificial "dams", bring about waterlogging of upstream areas of watercourses and floodplains, sediment accumulation therein, while the products of wood decay – tannins, tars, and organic acids – negatively affect the physical and chemical properties of water and biochemical processes.

In mountainous areas the small rivers are influenced by a number of factors, like the washout from slopes of upper soil layer, dislocated by timber haul (together with tree brunches and other by-products of lumbering), which fill up the watercourses; the creation of small water bodies (clausers) by the river heads designed for timber floating during floods, which are silted to a big extent; and also the destruction of banks by floating logs. As a result, the small rivers get overgrown by hydrophilic vegetation and are being transformed into interim streams flowing through waterlogged floodplain valley.

In the first place, degradation processes pervade higher links of river systems, represented by the smallest (with a length of less than 10 km), very small (10-25 km), rather small (25-50 km), and small (50-100 km) rivers. The geography of degradation processes and their intensity have a pronounced zonal character: in forest zone the intensity of small rivers degradation is small, and their extent is local (associated with developed areas); in forest-steppe zone the intensity of degradation processes is high, they usually embrace rivers of orders I-III, sometimes of higher orders (by Strahler classification scheme); in steppe zone their intensity is high as well, yet here, apart from anthropogenic causes, a substantial influence on the deterioration of the small rivers state exert the climatic conditions – insufficient precipitation, small river discharges, intensive evaporation, low ground water levels, etc.

The specific researches of the extent of the distribution and intensity of small rivers degradation in different regions [Kovalchuk, Shtoiko, 1982, 1989, 1992; Velikopolskaya, Kovalchuk, 1988; Kovalchuk, 1997; Golosov, Ivanova, Litvin, Sydorchuk, 1992; Golosov, Dobrovolskaya, Ivanova, 1995; Wachoviak, 1981; Holod’ko, 1996; Boyko, Butakov, Kurbanova, 1993; Dedkov, Mozzherin, 1993; Brylev, Shugayev, Agarkov, Svechnikova, 1996; Chernov, 1994; Chalov, 2000, 2004; Alekseevsky, Chalov, 2001; Kurhanevych, 2001; Kiseliov, 2001; Dedkov, Kolesnik, Kuznetsov, et al., 2003; Miskovets, 2003; Yegorov, 2005, etc.] allow to distinguish five zones in Northern Eurasia by the intensity and character of small river silting [Kovalchuk, 1997; Alexeevskiy, Chalov, 2001]. These zones are characterized by different intensity and directionality of the development of degradation processes:

1. With the prevalence of rivers in their natural state (tundra and taiga);

2. With the alternation of rivers remaining in natural state and being in different stages of silting and degradation (zone of broadleaf forests);

3. With an active silting of rivers of I and II ranks and partial silting of rivers of higher ranks (forest-steppe);

4. With a total silting of the majority of rivers of I and II ranks and partial silting of middle-sized rivers (steppe and semi-desert zones);

5. Mountain and highland rivers, which are mostly in natural state and are partially degraded in the regions of long-lasting forestry, water management and agriculture.

The scales of the development of degradation processes in Ukraine are envisaged in a number of the results of regional researches [Kovalchuk, Shtoiko, 1992; Chemerys, 1993; Dubis, 1995; Kovalchuk, Volos, Holod'ko, 1996; Kovalchuk, 1997; Kurhanevych, 2001; Kiselev, 2001; Pavlovs’ka, 2006].

It was determined that for the last 200 years 973 perennial streams in the basins of left Dnister tributaries have ceased to exist, and 35 new rivers – the amelioration canals – have originated [Kovalchuk, Shtoiko, 1992]. The index of the transformation of the total river number amounts to 29.5%, and its basin amplitude – to
–30%...+89%. The fraction of degraded or transformed first-order streams is 71%. The total length of perennial streams decreased on 1071 km or 15.4%, while in some basins – up to 64%. The indexes of stream length transformation for the period between 1772 and 1855 were less than 1.8%, for the period between 1855 and 1925 they rose to 5.5-15.0%, while for the period from 1925 to 1955 they amounted to 7-22%. The total shrinkage of stream lengths by individual basins varied from 7% to 31%. The indexes of stream number transformation in river systems for the same periods amounted to, accordingly, 2-3.7%, 14-23%, and 23-56%, and also 36-65% for the total time span of observations [Kovalchuk, 1993]. The most intensely have degraded the upper links of river systems – the I-II order streams, which signify mostly anthropogenic causes for these processes.

In Poliss’a region, characterized by lowland relief, the abundance of swamps, and redundant humidification, for the last 75-100 years versatile changes took place in the structure of river systems: the degradation of small rivers (silting, decrease in water content, overgrowing, drying out, transformation into interim streams) and the transformation of river systems structure (increase in a number of I-III order streams as a result of the construction of the network of amelioration canals). For instance, in the basin of Goryn’ (a right tributary of Prypiat’), 81.3% of river systems showed the increase in river number (on account of canals), while other river systems mostly showed the degradation of I-II order rivers and the reduction of order of bigger rivers [Pavlovs’ka, 2006]. The similar results were obtained for other basins of Ukrainian Poliss’a [Chemerys, 1993; Kurhanevych, 2001].

In many other countries the silting of small rivers has manifested as a result of the agricultural development of lands. These happened as early as in mediaeval times (for instance, in Germany in XIII – XIV centuries [Bork, 1989]), and also in 20-30-th of XX century (for instance, in USA in Corn Belt, as shown in a special study [Simon, 1994].

In humid conditions, the density of river network may slightly increase of decrease (±5%). In steppe and forest-steppe the decrease in river network density for the studied period varied from 35% to 50% and more of its total length [Golosov, Panin, 1998]. In upper Don basin the most intensive degradation of small rivers occurred in late XVIII – middle and second half of XIX centuries.

In the mixed and broadleaf forests zone and the northern forest-steppe zone the most intensive decrease in the length of hydrographic network and the number of small rivers have been taking place up to 80-90-th of XX century, when, as a result of the rise in precipitation and the decrease of the intensity of agricultural practices the rise of river flow and the local renewal of perennial flow in small rivers have began to appear.

CONCLUSION

1. The analysis of the present opinions regarding the causes and prerequisites of the silting of small rivers and the degradation of river systems, allows to infer that the main factors in the development of these processes are:

· The destruction of natural vegetation, leading to the drying out of upper aquifers, the lowering of ground water levels, the reduction of spring discharges, the downslope drifting of riverheads [Kovalchuk, Shtoiko, 1992; Dedkov et al., 1995];

· The silting of river upper courses by the slope sediments eroding from arable [Kovalchuk, Shtoiko, 1992; Kovalchuk, 1997; Golosov, Ivanova, 1993];

· The long-term and multiyear oscillations in humidification, differently manifested in steppe, forest-steppe and forest zones, which influence the depth of ground water level, as well as the river flow, the intensity of slope and channel erosion-accumulation processes, the sediment transportation, and the silting of small river watercourses;

· The discharges of agricultural, industrial, communal, and other sewages into rivers, that cause the euthrophication of water bodies, the deterioration of water quality, the decrease in self-restoring capabilities of river ecosystems.

2. The small river degradation reduces the water resources available for regional economy and population, increases waterlogged areas and areas unsuitable for utilization, curtails the recreational and economical values of rivers, brings about a chain of negative environmental consequences for the population, and regional biological and landscape diversity.

3. The remaining urgent problems (tasks) of the study of degradation processes are:

· The assessment of the intensity and directionality of the degradation processes of small rivers in different natural and socio-economical environment;

· The application of GIS-technology to the modeling of scenarios of the future climate changes and the impacts of these on the states of small rivers and the functioning of river systems.

· The generalization of the available regional data on the distribution of degradation processes, the causes and consequences of their development in river systems;

· The substantiation of the measures directed to the restoration of small rivers flow, the improvement of their ecological state, the optimization of the utilization of water resources.

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