Hidrológiai Közlöny 1977 (57. évfolyam)

2. szám - Puskás Mária: Keresztmetszethálós vízminőség vizsgálatok a Duna Szob–Budapest közötti szakaszán

G6 Hidrológiai Közlöny 1977. 2. sz. Puskás M.: Keresztmetszethálós vízminőség vizsgálatok komponens esetén általában kisebb vízhozamnál több mintavételi ponton kell vizsgálni. Az optimalizált mintavételi program keretében kapott eredmények reprezentálják a keresztszelvényben! vízminőséget. A hirodinamikai mérések alapján elvégezhető az optimális mintavételi pontokhoz tartozó keresztszelvény szegmensek kijelölése, amelyekben az átáramló vízmennyiség is meghatározható. Ily módon a szegmensre jellemző koncentráció-érték ismerete alapján egyszerűen számítható az egész keresztszelvényben szállított anyagmennyiség. Számításaink szerint az ily módon számított keresztszelvénybeni anyagáram jól egyezett a keresztmetszethálóban végzett összes mérés alapján számított értékkel. IRODALOM [1 | Vízminőség-vizsgálatok végzése a Sajó és Duna Vízminőségszabályozási Mintaterületen. V1TUKI témabeszámoló. III. 4.4.24. 1975. Budapest. [2] A Középdunavölgyi Vízügyi Igazgatóság összefoglaló jelentései a KÖVIZIG 1973., 1974. és 1975. évi project tevékenységéről. Budapest. [3] Literáthy Péter—Puskás Mária: Problems in the Representative Determination of Pollution in Major Streams. XVIth 1AHR Congr. Sao Paolo, Brasil, Jul. 27—Aug. 1. 1975. Proceedings Vol. 3. C 67, 564—71. [4] Somlyódy László: A Duna Szob és Budapest közötti szakaszára vonatkozó leíró jellegű vízminőségi (diszperziós) modell kidolgozása. Hidrológiai Közlöny, 1977. 1. sz. p. Transverse-prill water quality analyses over the Szob—Budapest Danube section By Puskás, M. (Mrs) Regular analyses on the quality of I )anube water have been started in the early 1960ies using samples taken from single points in each cross-section. In an attempt to explain some inconsistencies observed in water quality profiles along the stream, samples were taken subsequently from three points in the individual cx'oss-sections. As revealed by some representative data compiled in Table I, the quality of water is far from identical at the different points within a particular cross-section of the Danube. The non-uniform quality of water within a crosssection is obviously due to the fact that transverse mixing of the pollutants introduced by effluent discharges and by the tributaries occurs in large streams such as the Danube, over distances of several 10 km only. In studies on the pollution caused by the communal wastewaters of Budapest, the Water Quality Inspectorate of the district water authority KOVIZlG has applied as early as in 1970 — 71 the transverse-grit 1 method of water analysis of the Budapest Danube section, which has been continued in several crosssections and with greater frequency under the Project activities started in 1972. The objective of these series of investigations was to develop a methodology for selecting the optimal location of sampling points and for describing in a representative manner the quality of water in cross-sections with non-uniform quality, further to provide on the basis thereof the data needed for the reliable estimation of mass currents. For detailed studies over the Szob — Budapest Danube section transverse-grid analyses have been made on 4 occasions annually, in 7 cross-sections on each occasion. In the more advanced phases sampling was accompanied by simultaneous flow-velocity measurements. With due regard to flow-velocity distribution, channel shape and surface width, 3 to 9 verticals have been selected for sampling in the cross-section, while in each vertical the points were spaced at 1 m intervals starting 50 cm below the surface. Parallel to this sampling procedure 5 additional samples have been taken from a particular point in the cross-section, each of which has been analysed for the individual components to determine the error of measurement characterized by the variance C

v. In fact, the standard deviation of water analyses on samples taken simultaneously from several points within the same cross-section is influenced fundamentally by two factors, namely the error of measurement and the variability of the concentration of the component considered in the section. In evaluating the analytical results the water quality in the cross-section is said to be non-uniform if the standard deviation of the results is greater than the error of measurement. The analytical results obtained for the water samples taken from several verticals and dephts have been used for tracing the concentration contour lines representing the non-uniformity of water quality, as shown, in Figs. 1 and 2. The quality of Danube water at Szob, in the entrance cross-section to Hungary is non uniform as regards several components. Pollution was invariably found to be higher in the vicinity of the left-hand bank, which was attributed primarily to the effect of the tributary Vág River. The differences in ammonium ion, COD and UV absorption were especially conspicuous. The quantity of polluting substances transported through the cross-section can be estimated in the most reliable manner by dividing the transverse profile into 10 m wide bands, for each of which the mean concentration is computed by linear interpolation of depth, mean flow velocity. The mass current s are then computed for each 10 m wide vertical band and added up for the cross-section. Transverse-grid investigations are too labour consuming to be performed in greater numbers. They offer, however, the possibility for optimizing the regular data collection work on the Danube, by designating with the help of Eqs. (2), (3) and (4) the necessary sampling points. The optimal number and position of the necessary sampling points for COD are shown in Fig. 3 at three different streamflow rates, while for several other components in Fig. 4 at a particular streamflow. From the results of similar investigations it has been concluded positively that the optimal number of necessary sampling points may depend on the component considered and on the; rate of streamflow. In general, a greater number of sampling points is needed at lower streamflow rates. On the basis of hydraulic measurements the crosssection segments pertaining to the optimal sampling points are found, the rate of flow through them is determined and thus in the knowledge of the concentration representative of the segment, the mass current through the latter is computed. The amount of substances transported through the entire cross section is found by adding the segment values.