ИСТИНА

Use of water resources is inevitably accompanied by augmentation of risk of influence of hydrological processes at safety of the population, social and industrial structures located on flood plains of the rivers. Features of the analysis of the dangerous hydrological phenomena and accordingly an assessment of connatural risk depends on dimensional scale of research. It defines composition of the initial information, methods of its processing, a choice of the conforming indexes and features of display of the phenomenon on a map. Depending on the scale of considered terrain for an assessment of hazard of inundations two approaches can be applied. Firstly this is the complex procedures of mark assessments considering the most various factors of connatural hazard and social and economic vulnerability, being components of connatural risk, and secondly the detailed hydrological, cartographical and social and economic research of formation of dangerous processes and a damage arising from it. Integrated assessments of hazard of the hydrological phenomena allow to compare regions among themselves, however at transferring to local level more detailed methods of the research are required, allowing to consider features of water, ice and channel regime of a certain reach of a river. This sort of researches are made by the authors for the reaches of the rivers Severnaja Dvina (from confluence of the Sukhona and Ug to the mouth of Vychegda where the cities of Velikiy Ustyug, Krasavino, Kotlas are located) and the Tom' (near Mezhdurechensk at confluence of the rivers of Tom' and Usa) to assess a hazard of inundations induced by ice dams. Purpose of research. To develop and test various methods of a quantitative assessment of a connatural component of risk of the dangerous and unfavorable hydrological phenomena bound to water and ice regime of the rivers, such as inundations and ice phenomena. Methods. For regional level the complex assessment of hazard is expedient for carrying out on the basis of the indirect indexes characterizing probability of occurrence of dangerous process and degree of vulnerability of terrain. The sense of this procedure consists in building of the thematic cartographical generalizations characterizing dimensional change of quantity indicators of dangerous connatural processes in a certain terrain. They reflect conditions and factors of the dangerous hydrological phenomena, probability of their occurrence, the characteristic of vulnerability of the population, social and industrial objects, assessments of a possible average damage from their influence. The two-dimensional equations of Saint-Venant are put in a basis of a mathematical model of flooding on local reaches of the rivers. The set of equations of Saint-Venant is most applicable for the given class of problems as it considers real bathymetry of channels and topography of flood plains, allows to receive distribution of water discharges between branches of a channel, to define water velocity and depth of a stream at any point of the plan. Modelling was carried out on the basis of a program complex "STREAM-2D" (by V.V.Belikov). Digitization of the two-dimensional equations is effected on the triangle-quadrangular grid adapted to river channel network. The initial data were: results of field surveys, measurements of depth; slopes of water surface; the measured water discharges and flow velocities, morphometric cross sections through valleys of the rivers, location and altitude of road dams, presence of water pass holes through the dams, topographic maps of scale 1: 100000, 1:25000, 1:50000, the long term record data of water regime ; space pictures during high water and low water seasons, the social and economic information about a damage and cost of protective structiors. Based on the available records of 1896-2013 period, maximum water levels of water flow and of ice dam were calculated together with water discharges of 1 and 5 % of occurrence. For calibration of the model, calculations for the various scenarios bound to transit of peak discharges of water and formation of ice dams, including the most catastrophic inundation of 1998 on the Severnaja Dvina and of 1977 on the Tom' have been carried out. In those cases when formation of ice dams took place, the model considered a place of formation of an ice dam, its duration; the roughness coefficient of ice on the ice dam reach of the river; reduction of average depth of the stream dew to filling of the channel with ice. Results. For the terrain of The Russian Federation the total index of hazard of the inundations is estimated, considering both as hydrological indexes (the area, duration and depth of flooding during the transit of the maximum flow, probability of these events), and intensity of impact on the population and economy. Efficiency of geographical demarcation of the territory of the country on this index is confirmed with the statistical data. The calculations carried out for local reaches of the Severnaja Dvina, Tom', Lena and the Amur have shown that the used model of water motion adequately reflects a real pattern of flooding and can be applied to an assessment of possible flooding of investigated terrain at various hydrological situations. For the evaluation of modelling the procedures of verification of model on the basis of space pictures of various types and accuracy, developed by the author, have been used. As a result of modelling for each of scenarios (for the present conditions and possible construction of bank protection dams in future), the altitudes of water surface, stream velocities in each point of the plan of the area under consideration , duration and depth of flooding have been received. Modelling has shown that water levels formed by river flow in spring high water period of 1 % of occurrence, can exceed low water levels by 6-7 m. In case of formation of ice dams maximum levels can increase even by 2-3 m more. At calculations, the economic damage of the terrain from flooding has been subdivided into direct and indirect. The procedure of an assessment of an economic damage from flooding used in the Russian practice has been corrected depending on the available statistical information and economic-geographical features of terrain. Calculations have allowed to estimate the general potential damage in a region of possible flooding. For example, for a case of inundation of 5 % occurrence around Velikiy Ustyug it was estimated that 70 % of all expenses - the cost of restoration of dwellings and compensation of losses to the population; 20 % - expenses for restoration of objects of industrial sphere; 10 % - expenses for restoration of objects of a social infrastructure. However, comparison of expenses for liquidation of consequences of inundation and expenses for construction of protective dams shows that civil-engineering projects of protection dams for the cities located, for example, on the banks of the Severnaja Dvina, are effective enough only at very high inundations (1 % of occurrence). The effectiveness ratio (the ratio of an annual damage to the cost of protective constructions) is equal in this case approximately 4-5. Conclusions. The careful analysis of modern trends of change of ice, water and channel regime, application of GIS-Technologies and methods of mathematical modelling of flooding of flood plains and cannel areas has allowed to update approaches to prevention of flooding of settlements and to make a critical assessment of these approaches, to develop recommendations on variety of the directions which at competent combination allow to prepare a uniform program on a decrease of negative influence of high waters on the population and economy.