UNDERLYING PRINCIPLES AND CONSEQUENCES OF CAPACITY REDUCTION OF THE RIGHT BANK RIVERS OF PRYPYAT Vasylenko Levgeniia Ukraіnіan Hydrometeorologіcal Research Institute Pr. Nauky 37, Kyіv 03028 Ukraіne [email protected]; [email protected] Abstract Rivers overgrowing is a difficult process, which development is caused by the general influence of natural and anthropogenic factors. The vigorous activity of individual on rivers catchment amends in development of a grassy biomass. Major factors which determine development of water vegetation are the hydrological regime of the river, its thermal mode, natural chemical water compound, anthropogenic influence. The hydrological regime encloses characteristics of liquid and firm runoff, feature of a morphological structure of the river, bottom topography and ground character, movement regime of bed load, etc. Separately are allocated characteristics of the thermal regime and water analysis as they appreciably determine underlying principles of overgrowing. Keywords: overgrowing, river-bed, flood-lands, levels, lag-time, floods. 1 PROBLEM SETTING AND ANALYSIS OF LAST RESEARCHES AND PUBLICATIONS Development of water vegetation often leads to negative consequences: fast siltation and shallowing of the rivers, channels and storage pools, waterlogging of water flood- lands, water deterioration, and complication of water supply. And this is far not the full list of negative consequences. For Verigina's data on the Novomoskovsk hydroelectric power plant, where overgrowing is only 10 % of the catchment-cooler area, has served as a reason of underproduction 576 million kvt/h of the power industry for a year. The extensive damage overgrowing does to a water management and land improvement. At channels overgrowing, owing to capacity reduction, becomes complicated drainage and irrigation. So, for Alieva's data at overgrowing speed of water current in channels, and, accordingly, their capacity, decrease in 3-4 times in comparison with designed. In many cases damage which was done by overgrowing of the flat, marshy rivers, at all does not give in to the full account. Overgrowing is accompanied with head of water level which in natural conditions of the flat rivers conducts to waterlogging of the flood-lands grounds. Alongside with this, the hydrometric account of the runoff becomes complicated also. As a result of river-bed overgrowing decrease in current speed, there are "dead zones", are deformed diagram speeds on depth and width of the stream. Accordingly, overgrowing leads to infringement dependence of water discharge from level (Vekshyna T.,2004). Human activity on the catchment has the big influence on siltation processes and on river-bed overgrowing. Excess of borders of the admissible areas of agricultural crops alongside with ploughing up also is the main reason of erosion and siltation. The analysis of researches has shown that on more mastered small rivers of the Goryn river basins ploughing-up makes 35...65 %. The limited quantity of erosion-preventive and water-protective plantation on the Goryn’s bank and its inflows and agricultural developing predetermine receipt in rivers river-beds and in ponds of a significant amount of uliginous - sand sediment. It is the reason of water vegetation overgrowing of this part of the river river-bed (Statnik I., 2007). 2 STATEMENT OF THE BASIC RESEARCH MATERIALS One of modern major problems of the Western Polisya including a biological variety, in our opinion, there is a problem of river functioning and connected with them water- marsh ecosystems in the Prypyat river basin, in particular the rivers: actually Prypyat, Stokhod, Styr, Turiya, Vyzhivka, Goryn, Sluch, Stvig. For the rivers of Polisya is characteristic significant overgrowing of river-beds and flood-lands of water vegetation and bushes and, accordingly small capacity - from several cubic meter up to tens for a second which is caused by their small depth, small inclination, excessive quantity in the river-bed of hygrophilous vegetation and other factors. Thereof it is created head of water levels in the rivers, decrease in stream speed, i.e. the certain water masses proceeds at higher levels, than it happens under condition of the free waterway. All these facts testify that during floods water masses come out on flood-lands and move on its surface. If the surface of flood-lands has a low roughness parameter so such form of flood passing over, especially proceeding from ecological positions, would be faster positive, than negative. However the modern flood-lands surface, which is imperforated by bushes, cane, and other vegetation, strongly influences on movement speed of flooding water, considerably reducing it and predetermining increase in flooding duration of flood-lands surface by water, river-beds and flood-lands siltation with sand-loam silt. All this leads to efficiency reduction of bottomland meadows and opportunities of their economic use (Alekseevskiy V., 2000; Lukjanets O., 1999). The reason of capacity deterioration of the Prypyat river-bed is a number of factors caused both economic activities, and development of natural climatic processes: - channeling (Prypyat, Stokhod, Turiya, Vyzhivka), or their stretches (Ustya, Chornoguzka, Lypa); - total drainage of bottomland meadows and bogs, and creation on their place of a network of drainage systems (open or closed type); - practically uncontrolled functioning of Vyzhivka water supply point which water gets from Prypyat close with v. Pochapy Ratnivskyy district of the Volyn area for needs of functioning of Dnipro-Bug river-bed in the territory of Belarus (diversion capacity is carried out by the Belarus side in the territory of Ukraine) in this connection there is as river-bed drying up of Prypyat in the low-flow period, and its overgrowing on stretches below this diversion capacity, an occurrence of stretches of secondary bogging in flood- lands, degradation from drying up of some lakes. - artificial narrowing of flood-lands width as a result of construction of dams and construction of roads-dams which creates head of water, in particular, during spring flooding in bridge transitions with water difference up to 40 sm; - cover up old river-beds in connection with economy of means for construction of additional bridges, or old liquidation, that create head of water, in particular, during spring floods; - device of bridges of boats through the river and flood-lands, which, also creates head of water during spring flood; - one of the reasons of river-bed degradation of the Prypyat, Stokhid, Tsyr rivers is mass construction of the ponds equipped by local population for fish poaching (on the average along the river they meet through 600 m, and on some stretches - through 150- 200 m). As a result of this strongly degrades the river-bed, decrease in fish stocks, especially during the spawning period. This problem is not new, it exists not one decade. Nevertheless till 80th years of the last century ponds were under construction only for the winter period and it is very rare - for all width of the river river-bed, and in the spring they necessarily striped, so practically did not harm to the nature. For last 20 years the quantity of ponds has considerably increased; they are under construction, basically, through all river-bed and stand during all year. As a result there is an intensive sedimentation of organic parts before the pond and gradual overgrowing, and then river- bed waterlogging, especially lateral branches. Thus the hydrological cycle completely changes. Marsh massifs are impoverished that corresponding process occurs without participation of characteristic flora representatives. They do not carry out characteristic for bogs moisture accumulators function. And it is one of the reasons of that valley of the Prypyat river in its upper part gradually, but stable, turns in huge waste bog which loses two extremely important hydrological functions - capacity and moisture accumulative (Veremchuk V.,2004). In long-term aspect (1947-1999) on the right bank rivers of Prypyat is observed the increase tendency of levels and increase in terms of flood-lands flooding. For example, increase of an annual water level in the river-bed and flood-lands of Prypyat in Ljubashovskyy district of the Volyn area in 1987-1997 in comparison with 1947-1956 has made 60-64 sm for the vegetative period, and maximal during summer-autumn floods – 81 sm. Duration of flood-lands flooding has increased from 43 till 165 days. These phenomena happen at constant water discharges during the vegetative period and at reduction of discharges during floods (Shchach V., 2000). During summer floods influence of the river-bed overgrowing and flood-lands on their capacity changes, as receipt of significant water masses lead to relative reduction in course obstacles. Nevertheless it concerns mainly river-beds whereas flood-lands capacity during the warm period of year sensitively decreases. If in overgrown river-bed water discharges at the same levels in 1,3 - 1,5 times less rather with free from vegetation. In some cases flood-lands can be flooded by water, and current on it absolutely is absent (Upper Prypyat, Vyzhivka, Turiya, Stokhod, Styr, Goryn). Owing to reduction in current speed in the rivers it is created head of water levels. Therefore during floods water is kept during 2-3 and more months at high levels, which on 1,5 - 4,5 m above for usual low, flooding of flood-lands and interfering with decrease in levels of ground water in nearby territory. Also capacity