16. Role of the hydro-geological system in Issyk-Kul Aqueous basin
A.N. Mandychev Institute of aqueous problems and Hydropowers NAS KR
The hydro-geological system Issyk-Kul of aqueous basin is considerable on sizes by a unit of basin. Its linear boundaries coincide with watersheds of a immediate and underground runoff Terskey - southern and Kungey - northern ranges and pass on a saddle-point Santash in east and Karatash to a threshold in west. The plane twodimensional boundary passes inside Terskey and Kungey ranges, where is determined by a zone of exogenous and deep tectonic fracturing, containing underground water. A substratum of this fracture subsystem are the massive rocks, in main, palaeozoic of age. Through deep tectonic faults in this subsystem the arrival in basin of fluids from a crust and mantle is possible.
The massive rocky fracture subsystem is the basis for younger sedimental cover of basin having mesozoic - neozoic age. This sedimental cover represented by boulder, gravel, sand, clay and half - rocky by the cement clastics such as conglomerates, sandstones, soapstones and siltstones. The sedimental cover occupies a majority Issyk-Kul of a trough and in its limits the lake a Issyk-Kul (fig. 1) is collocate. In a sedimental subsystem of a young cover, the underground porous waters circulate on seams most permeable large – detrital of rocks - headers. Their open porosity 10-20 %, that is much more than common fracture capacity of the system of the massive rocky foundation of basin. The maximal width of a sedimental cover Issyk-Kul of basin in east part reaches 5 km (fig. 2). All this strata is saturated by underground waters of a different mineralization and different age of finding under ground. Majority of these underground waters filtration under ground from a surface, i.e. their source are the surface waters. The youngest underground waters concentrated in a top of a sedimental cover, in quarternary depositions. They have width about 300 m, contain friable rocks, with most coarse wastes, sedimentary stratas and consequently most water-permeable with permeability coefficients 1 - 100 m / day. The main recharge quarternary of the water bearing complex (WC) is carried out at the expense of filtering under ground of fluvial waters in upper submontane parts of their detrital cones. The small part of water infiltrate in quarternary WC from fissures ranges and foundation (up to 15 % from all of natural restored resources of underground waters quarternary WC). The common value of restored resources of underground waters or stream of underground waters on all basin in quarternary WC is estimated in a range 62,8-74,4 m3/sec. These underground waters are completely discharged in lake a Issyk-Kul as springs in an inshore zone, on underwater inclines and at the bottom lakes. These waters have a mineralization about 1g/l and, in main, hydrocarbonate - calcium chemical composition. The natural stores of fresh underground waters quarternary of the water bearing complex, or size of underground waters of quarternary depositions, contained in a pore space, compound 58 km3 [1].
Legends to figure 1.
1. a) Boundary of a sedimental cover of basin. b) Tectonic boundary between interfacing basins.
2. Shore line of lake
3. Boundary of hydro-geological districts
4. Egresses Mesozoic – neozoic of hydro-geological of a sedimental level
5. Egresses of the foundation of basin
6. Quarternary depositions
7. Hole hydro-geological tested and its number
8. Number of hydro-geological district
9.Hydro-geological profile and its number
Thus, the underground waters quarternary of the water bearing complex, in main, determine hydrodynamic and hydrostatic boundary conditions of lake a Issyk-Kul. The concrete allocation of a underground runoff on peripherals of lake depends on a tectonic framework of board parts Issyk-Kul of a trough, introduced low piedmonts formed mesozoic and paleogene - neogene, in main clay and frequently by saliferous rocks, and as presence of the rivers on concrete sites [3,4].
Water exchange between underground waters quarternary WC and lake the Issyk-Kul does not exhaust a complete cycle water exchange.
Legends to figures 2.
1. Rocky palaeozoic the foundation of basin
2. Tectonic faults.
3. Isotherms
4. Boundaries of geologic complexes of different age
5. Drill hole: at the top of its number, below - depth. Black rectangle - interval of sampling. Arrow - value of head of underground waters, digit for arrow an absolute benchmark of underground waters, reduced to density of sweet water with temperature 200C
In lake, as alone base of a surface and underground runoff, the underground waters of more deep water bearing complexes are discharged as also: Sharpyldak - pliocene - quarternary, Issykkul and Kirghiz, having paleogene - neogene age and mesozoic water bearing complex. First has width about 500 m, on the filtrational parameters it on the order is lower than quarternary WC, contains as fresh cold waters of hydrocarbonate - calcium composition and inappreciable natural restored resources because of little permeability, about several cubic meters per one second, but the static capacity stores are commensurable with those quarternary WC. The underground waters Issykkul WC, at width up to 1500 - 2000 m, according to the author, have natural restored resources about 4-5 ì3/sec [3]. Here capacity stores are on a rate stores quarternary WC, lower porosity of rocks, is cancelled by big width. These waters are thermal because of a natural geotermal gradient (on the average 30Ñ/100m), their hydrodynamic mode can be active and passive, depending on a tectonic framework of separate blocks of a sedimental cover in limits of a zone of low piedmonts. Depending on a type of the hydrodynamic mode these underground waters are or fresh hydrocarbonate -calcium, at active water exchange, or high mineralization up to 60 g/l and more, chloride - sodic, calcium, at passive water exchange (fig. 3). Most vivid example passive water exchange is the case of detection retrieval on naphtha by a well, in limits of anticline frame Big Orgochor anomalously of high formation pressures in the Kirghiz water bearing complex and chloride -calcium pickles with a mineralization up to 475 g/l (fig. 3). These waters as will be discharged, at the end, in lake at seismic exposure of the isolated system. It is possible, that with unloading of thermal underground waters on a water area of lake, are interlinked residual thermal anomaly, captured by geophysical researches in districts Toruaigyr, Karabulun. In the Kirghiz and Mesozoic water bearing complexes dominates passive water exchange, that is the modern recharge them surface and atmospheric by waters practically misses, and there are no natural restored resources. Ancient waters here contain, the age which one can be calculated in hundreds and thousand years. Owing to lowering with depth of a porosity, at the expense of compaction and cementation containing water of rocks, the capacity stores of these water bearing complexes on the order are lower than those Issykkul WC. Thus, the complete cycle water exchange in Issyk-Kul aqueous basin starts with fallout in its limits of atmospheric precipitation, which one are partially accumulated on inclines ranges in solid phase, and liquid phase infiltrate into the fracture system ranges, circulates in it including diving on zone of fractures on depthes about 3000 m, with derivation of natural egresses of thermal mineral waters (field Djety - Oguz, Chon-Kysylsu, Teplokljuchenka etc., with cooperative natural resources 0,049 m3/sec [1]). The ground mass of fracture underground waters in limits of inclines mountain ranges again is transformed to a surface runoff of the rivers and only about 15 % a sedimental cover of basin on sistems of flaws immediately feeds.
The following stage of recharge of underground waters of a sedimental cover happens at an output of the rivers for limits of mountain inclines, in main, in headers of detrital cones of the rivers and further along channels. Here there are main losses of a surface runoff. The filtering compounds of chennels of the rivers about 50 m3/sec, from irrigation channels approximately 18 m3/sec. The role of atmospheric precipitation in immediate recharge of underground waters is extremely inappreciable, only in a zone of non deep of a level last, in an inshore zone of lake (about 1,5 m3/sec) and in limits of the hydro-geological sistem of ranges. Thus, the main recharge in limits of a trough is provided with a concentrated long-time surface runoff. In this case, non perennial water stream do not render essential feeding effect, as infiltration the moisture hangs up in a zone of aeration not reaching uderground water level. Transpiration immediately from a surface of underground waters in a zone of their non deep of a level (less than 3 m.) Is estimated at a rate of several cubic meters per one second [2].
Paleogene – neogene WC as gain main recharge from the rivers in a zone of low piedmonts, where they egress on a surface, and the explicit link of character water exchange in these water bearing complexes from character tectonic of frames tectonic of blocks in a submontane zone is collocate [3]. In that case, when the frames represented little dislocated by monoclines fall in a direction of a central part of basin, in the block is observed active modern water exchange, if the frames are difficultly dislocated or have opposite direction fall of seam, in the side of the hydro-geological sistem of ranges, in the block is observed passive water exchange, absence of restored resources of underground waters, which one have a high mineralization, as a rule.
In hydro-geological districts 1,2,3,5,6,7,8,9,10,11,14 (fig. 1) is observed active water exchange in deep levels Issykkul of the water bearing complex. In 4,12,13 hydro-geological districts takes place passive water exchange. The different types water exchange differ by a mineralization and value of head of underground waters. At active water exchange a mineralization of underground waters in Issykkul the water bearing complex about 1 - 2 g/l, the hydrostatic heads correspond to potential areas of recharge and creation of head. At passive water exchange the mineralization of underground waters from 20 g/l and is higher, the hydrostatic heads are less, than at effect of possiblearea of recharge.
The water resources in limits Issyk-Kul of aqueous basin represented by static and dynamic components, first is accumulated as glaciers and snows, and as as water of lake and capacity stores of underground waters. The dynamic component represented by a surface and underground runoff, finite base of accumulation of all sorts of resources is the lake. Alone account section is the transpiration and atmospheric offset of a moisture for boundaries of aqueous basin. The research of a problem about geohydrological boundaries has shown, that Issyk-Kul the aqueous basin is hydraulic the isolated system, the underground outflow for its limits does not happen, neither in east, nor in western closure of a trough. Western closure is most problematic in this respect, as it is formally possible to guess possibility of a underground runoff in hypsometric below collocated Chu a trough. But, runoff of lake water and underground waters quarternary of the water bearing complex in Boom the canyon, on valley of the river Chu, hinders Kutemaldy a threshold of a underground runoff, form infiltration the arbor of water, filtered from the river Chu on sub - meridional a segment of its channel, up to turn in Boom canyon. A threshold of a runoff for paleogene - neogene of underground waters is Karatash a threshold collocate to the west Kutemaldy threshold, and in limits which one there is pinch paleogene – neogene of a cover to an egress palaeozoic of the foundation.
Generally, the considerable filtering of underground waters through fracture zone of faults in massive rocks Boom canyon during 40 km practically is impossible [5].
Existing on today estimates making of aqueous balance concern immediately to lake and underground waters quarternary of the water bearing complex of a trough, the estimate of complete aqueous balance all Issyk-Kul of aqueous basin while misses.
Matching of estimates of parts of aqueous balance for lake fulfilled Z.A. Vikulina in 1946, I.D. Cigelnay in 1960, M.N. Bolshakov in 1969, on which one the inflow in lake compounds 86,3 - 112 m3/sec [1, 2] and similar estimates of parts of balance of underground waters quarternary of the water bearing complex on operations VNIIKAMS (1971, 1984), GIDROINGEO (1979), to the Kirghiz hydro-geological expedition (1978) at a rate of 62,8-74,4 m3/sec[ 6 ], demonstrates, that basically estimation of parts of balance is objective and in further, at an improvement, will not undergo considerable changes.
Thus, a further direction of research of common aqueous balance Issyk-Kul of aqueous basin will be in main detailing and detection of separate parts of balance, that in the total will allow to improve and common complete balance.
Outputs
As a result of research aqueous balance Issyk-Kul of aqueous basin as integrated geohydrological system the part of aqueous balance, bound with underground waters of deep levels paleogene - neogene and mesozoic age is improved. Is rotined, that the main recharge of lake a Issyk-Kul is carried out at the expense of underground fresh cold waters quarternary of the water bearing complex (more than 70 %) and thermal - mineral water. This fact underlines the relevant role of underground waters in creation of hydrochemical conditions in lake a Èññûê-sack and in particular in anthropogenous chemical contamination.
Is educe, that quarternary the water bearing complex sets hydrostatic and hydrodynamic boundary conditions for lake.
The analysis of a geological feature has shown east and western of closures Issyk-Kul of a trough, that there are premises for underground crossflow from lake a Issyk-Kul and from aquifers Issyk-Kul of basin in a direction Boom canyon and further in Chu basin.
It is necessary to allow for all these features at research hydrochemical and hydrodynamic processes in lake a Issyk-Kul. The balance estimates are necessary for utillizing at planning economic-potable and recreational usage cold fresh and thermal - mineral underground waters with the purpose of protection them from exhausting and contamination. It is specially actual in a light explicating in limits of the large occupied items, such as Balykchi, Karakol, anthropogenous contamination of underground waters, which one requires carrying out of appropriate measures on warning contamination. Besides, it is necessary to realize a control behind maintenance of thermal -mineral underground waters, for preventing, on separate sites, exhausting of their resources. In the long term, in a light possible drought of a climate, role of underground waters, concentrated in underground water storages Issyk-Kul of basin, will increase.
Literature
1. Hydrogeology USSR. Kirghiz SSR. Tome 40. Ì., Nedra, 1971
2. Lake a Issyk-Kul (Sketches on physiography). Frunze, Ilim, 1978
3. Mandychev A.N. " Resources of underground waters of deep levels East Chu and Issyk-Kul of artesian basins. " In digest High-mountainous Researches: change and perspective in 21 century, Bishkek, 1996, p. 136-137.
4. Mandychev A.N." Normalization of hydro-geological conditions upper hydro - geological level Issyk-Kul of artesian basin " Materials 8-th Interrepublican conf. the scientists AS Kirgiz SSR, Frunze, "Ilim", 1986, p.129-131, co - author: Mandycheva V.N.
5. Mandychev A.N." About possibility of unloading of underground waters of western part Issyk-Kul of artesian basin in a direction Boom canyon" Thesis of report 1-th of Republican scientific and technical conference. Frunze, 1981, p. 44-46, co - author: Suyunbaev M.N.
6. Mangeldin R.S.Resources of underground waters of internal mountains of troughs Tian-Shan. Bishkek. “ Ilim”, 1991, p.149.
