Hydrographic review of Tomsk oblast

According to generally accepted geographical demarcation the territory of the West-Siberian Plain is seen as a large artesian basin. Upper hydrogeological stage is characterized by free water cycle and only its lower part has difficulties. Within the upper stage mainly fresh subsurface waters are present, mineralized waters present to a lesser degree. Waters of the lower hydrogeological stage are characterized by a difficult water exchange and high mineralization degree. These are predominantly thermal and mineral waters.

Lower aquiferous layer is the basement presented by sedimentary, volcanogenic and metamorphic rocks. The underground waters are widely distributed; it is connected with the destruction of basement rock roof and areas of faulting. Loose sediments of the upper aquiferous layer carry bed porous waters.

For public water supply in the most part of the oblast territory Paleogene water deposits are used, and only in the south waters of Proterozoic and Paleozoic deposits. Waters of the neogene-quaternary and cretaceous deposits play the less important role in public water supply.

Neogene-quaternary aquifer system is widespread almost in the whole artesian basin. It comprises quaternary deposits of floodplain bench complex of the modern river network, of Paiduginskaya, Smirnovskaya, Kochkovskaya suites and Miocene. With the Tomsk inlier water-bearing deposits are distributed locally in the form of narrow bands and lentils.

Water-bearing rocks are presented by varigrained sands with lentils and interbeds of clay, loam, sandy loams, and pebble tophaceous deposits.

The aquiferous system receives recharge from the infiltration of precipitations practically in the whole territory of its distribution, on elevated areas of flat interfluvial territories and slopes of river valleys, except for interstreams made by argillaceous deposits of Fedosovskaya, Smirnovskaya and Kochkovskaya suites where the infiltration is obstructed.

On the dividing plateaus, with the exception of areas occupied by ancient stream flow valleys,

Aquifer is strongly protected from surface pollution. In river valleys and within ancient stream flow valleys (mainly the north-eastern part of the oblast) ground aquifer is not protected or protected badly.

Paleogene aquifer system that unites sediments of Lagernotomskaya, Novomikhailovskaya, Altymskaya, Yurkovskaya and sometimes Kuskovskaya suites, is pervasive in the oblast territory except for its southern part. Its section shows multilayer facies changeable thick sands, sand and pebble tophaceous deposits, aleurite, clays with lignite and brown coal lentils.

Within the Tomsk oblast the aquifer system receives main recharge from the infiltration of precipitation, most intensive in open north-east, east and south-east parts of the oblast in the underset current of the rivers Parabel and Chaya.

The upper boundary of the system is presented by sandshale deposits of the Lagernotomskaya suite and Novomikhailovsk clay, the bottom sage comprises clayey and sandy Eocene bodies or of Upper Cretaceous.

The cover thickness of the aquifer system roof varies within the very wide range and increases while moving from the east to the west and from the north-east to the south-west. In the valleys of large rivers the thickness usually doesn’t exceed 30-40 m, in interstreams accounts for 80-90 and more meters. The deepest thickness is in the south of the Kozhevnikovo and Shegarsky regions (110-120 m), and in the interfluve between the rivers Ulu-Yul and Chichka-Yul the thickness increases to 195 m.

The thickness of water storage deposits is increasing in the west-north west direction and is changing from 0-10 m near the borders of paleogene deposits balk in the south part of the oblast to 185 m in the extreme north-west.

Waters are generally pressure. Statistic levels can be traced in the first meters depths in river valleys up to 26-40 m and in the interstream they are deeper. In the valleys of the river Ob and its large tributaries the spouting can be seen and levels are set at 0.5-10 and more meters above the land surface.

Abundance of water of the aquifer system changes regarding both the area and the section depending on lithology and power of water storage deposits. Water-bearing deposits are presented by the sands with different grain-size distribution. The grain size decreases while moving from the south and south-eats to the north and north-west, and regarding the structure section- bottom-upwards.

The value of transmissibility is characterized by the great variability. Areas with the largest transmissibility value (1000-2000 m2/day and more) are located in the southern, central and north-western parts of the oblast, while the areas with the lowest range (less than 200 m2/day) – in the eastern and south-eastern parts; it is connected with the loss of power of water storage deposits and the balk of the most water abundant deposits of the Yurkovskaya suite.

The aquiferous system of upper cretaceous deposits of the Symskaya and Simonovskaya suites is pervasive in the territory of the oblast except for the extreme south part (the Tomsk inlier), but used for water supply of only Asino, Pevomaisky and Zyryansky regions. Water storage deposits are presented by varigrain sands (usually from close- to medium sand with predominance of fine sands) with lentils, clay interbeds, aleurites. Sands are often politic, kaolinized, what deteriorates their filtration qualities. The continental sandstone deposits of the symsk suite on the right bank of the river Ob have the highest kaolinization that is why they belong to the rocks with low permeability and water return. However among thick kaolinized sands the lentils of the relatively wash gravel can be seen, which are of interest as possible water supply sources.

The depth to the aquiferous system roof amounts to 80-140 m in the southern and south-eastern parts of the oblast and while moving to the north-west it increases up to 420 and more meters.

The thickness of the water-bearing deposits varies in the very wide ranges: from the first meters near the border of cretaceous deposits bulk to 200 and more meters in the northern part of the oblast. Thickness less than 100 m. can be noted in the south-eastern part of the oblast.

Waters are mainly of the pressure type. In the extreme south-east the pressure amounts to 70-100 m and in the north it increases to 446 m.

Abundance of water in sands is low and determined not only by their grain texture but by the degree of kaolinization. Minimal specific yield (0,002-0,024 l/s) received from the deposits of the Symskaya suite in the southern and central parts of the oblast. Meanwhile in this very area the specific yields of 0,1-0,5 l/s were received.

The abundance of water-bearing deposits of the Simonovskaya suite is also very low. The specific yields of wells usually doesn’t exceed 0,08-0,1 l/s and make up the thousandth of l/s. Maximum specific yield (0,88 l/s) was received while pumpdowning from the sands of the Simonovskaya suite near the town of Asino.

Water transmissibility of the water storage deposits is characterized by the rapid variability. Its minimal values can be received near the Tomsk inlier (3-12 m 2/day), and maximal (600-900 m 2/day) – in the Kolpashevo and Bakchar regions. During the exploration of the Sosnovskoye underground water deposit near the town of Asino the value of water transmissibility of the Simonovskaya suite was set in the range from 60 to 339 m2/day.

The water of Proterozoic and Paleozoic deposits is the only source for water supply within the borders of the Tomsk inlier, because aquifers of loose sediments have low water abundance, insignificant distribution and are often drained by deep narrows and river valleys. Underground waters are located in the upper part of the Paleozoic basement, subjected to the processes of exogenetic fissure, or in the faulting areas. The depth of fractured zone varies from the first meters to 107-111 m. The fissure is overlapped by faulting processes, which lead to the localization of underground waters along the faulting areas and attendant crushed zones.

Water bearing bodies in the western and central parts of the Tomsk oblast are presented by crumbled sandstones, clay slates, argillites and siltstones.

Almost all lithologic rocks varieties are water-cut but to a different extent. The fissure type of reservoir rocks is characterized by a large watercut in river valleys or low areas of relief if compared to interstreams.

In the eastern part of the Tomsk inlier, in the area of the Upper Riphean and the Upper Devonian bodies presented by amphibolites, marbles, limestones, conglomerates, etc the watercut areas are usually situated in the places with karst marbles and limestones.

Piezometric surface of underground waters lies in the depths from the first meters to 40.5 m within the borders of elevated interstreams and in river valleys its levels are closing the day surface and even exceed it. Watercut sediments pressure head above the roof changes from 145 m in the area of the basement plunging in the north-western part of the Tomsk inlier to 40 m within the limits of elevated interstreams and drops to zero in places of Paleozoic rocks outcrop.

The abundance of water of the exogenetic fissure areas is highly uneven and changes from 0,006-0,4 l/s in the interstreams to 0,01-3,83 l/s in the river valleys. Sufficiently watercut areas are located in the junction zones of Paleozoic rocks (limestones and clay slates) and dyke rocks and in tectonic fractures. Specific yields of the well in these zones increase to 0, 59-1, 71 l/s.

Material is prepared by OJSC "Tomskgeomonitoring"