Charakterystyka wodonośności fliszu karpackiego na podstawie wydatku studzien

Henryk Niedzielski


Characteristics of water capacity of the carpathian Flysch on the basis of well discharges

The paper evaluates fresh water resources in Flysch deposits of th e External Carpathians with respect to the discharge of an individual drilled well. A hundred wells were chosen out of the 245 wells drilled in the Flysch Carpathians region of Poland; the chosen wells had complete hydrogeological characteristics and correct results of pumping, tests. Localization of these wells is shown in Figure 1. The discharge of a well at a depression of 5 m was accepted as. a comparative value (Q5). The choice of this criterion was justified by a poorly diversified depth of an active water exchange zone, on an average amounting to 30—40 m, according to special studies of Niedzielski (1974, 1976), as well as by poorly diversified bore-hole diameters (Fig. 3), similar construction of wells and most commonly found depressions (Fig. 4). It has been fond, on the bases of a detailed analysis of hydrogeological conditions and localization of each well, that 62 of the 100 chosen wells are non-infiltration of Flysch intakes, whereas the remaining 38 — infiltration ones, i.e. alimented to a considerable extent by water from Quaternary aquifers or from rivers. On the whole, it may be assumed that intakes with a comparative discharge bigger than 3 m3/h, at a depression of 5 m (Fig. 5), are infiltration ones, and are characterized by a frequently irregular shape of the function Q = f(s) curve (Fig. 2 and 6). The comparative walues Q5 of non-infiltration intakes formed two sets of data. Each set was divided into 6 sub-sets, depending upon the character of water table and the kind of infiltration (laminar, transient and turbulent). The Student t-test was used to assess significant differences between means of 12 respective samples. The above mentioned test demonstrated that the values Q5 of non-infiltration intakes do not differ from one another in a significant way, irrespective of the water table conditions and the kind of infiltration. Similarly, no significant differences were found between samples belonging to infiltration intakes. On the other hand, however, the tests used pointed to significant differences between the two sets: one (n = 62) — representative of non- -infiltration wells, and the other (n = 38)— characteristic of infiltration ones. Thus evidence is accumulating that each of the two samples comes from different population. The set consisting of 62 data is of primary importance for the characteristics of underground water resources in the Flysch of the External Carpathians. The frequency distribution Q5 is J-shaped (Fig. 7) and may be approximated with the exponential function of density distribution. In this way, a possible discharge that can be obtained from one well at a depression of 5 m was determined (Fig. 8). Discharges of the Flysch webls were also plotted on the function Q=f (s). They formed two sub-sets of data (Fig. 9): one, comprising the majority of data (71%), was approximated with the straight line s = 8.3 Q, obtaining weak but significant correlation with the coefficient r = 0.5678. This straight line represents mean discharges of wells with an error of ± 44.52% in the Flysch Carpathians region. The other sub-set of data (29%) was approximated with the straight line s = 2.28 Q with strong correlation r = 0.946. The la tte r straight line is characteristic of discharges in particularly favourable hydrogeological conditions. Both straight lines do not include a decrease in well discharge, taking place during prolonged exploitation (Fig. 10). The set composed of discharges of inflitration intakes differs from the sets discussed above. It is represented by a parabolic curve s = 3.07 Q°-47S, which was used to approximate this set of data. The small capacity of the Flysch is characterized by the mean permeability coefficient 2.10“6 m/s. The above mentioned parameters are characteristic of a sandy Flysch sub-facies of the External Carpathians, found not only in the territo ry of Poland but also beyond its borders, as it can be assumed on the basis of Hynie’s study (1961). Despite оf a considerable differentiation of the lithology, tectonics and geomorphology of this region, the hydrogeological conditions are poorly diversified. The alternate occurrence of sandstones and shales results in division of relatively thick sandstone series into many poorly aquiferous horizons. A steep dipping of beds and their tectonic breaking into smaller blocks, isolated by impermeable layers, limits surfaces of precipitation infiltration. A rapid, depth-related constriction of fissures limits the range of a olive water exchange to a shallow surface zone; moreover, large differences in elevation of the area makes drainage easier. All these factors, mentioned above, cause small capacity of underground waters in the Flysch Carpathians.

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