Vízrajzi Évkönyv 92., 1987 (Budapest, 1988)

Tartalomjegyzék

dicated by the symbols used in the tables of stages. At the bottom of the daily data monthly and annual typical data of the current year and the reference period have been grouped separately, indicating alsö the extreme values.

Some of the stage-discharge cun’es have been modified on the basis of more recent, or a larger number of measurement data, but such modification has not been extended to the previous years. The bivariate stage-discharge curves apply to the streamflow rates passing at peak stage conditions.

In some gaging cross sections, such as the reaches influence*! by dams and tributaries on the Tisza River and in the Tisza Valley, the streamflow rate is influenced significantly by the surface slope as well. For such gages the relationship between the streamflow rate, the stage and the surface slope has been determined from the results of streamflow measurements. The daily mean discharges have been estimated using the relationship determined. For such calculations the I0 and Q0 values pertaining to the particular stage have been obtained from the tabulation containing the corresponding values of the stages (h, cm), the surface slope under steady flow contitions (Io, cm/km) and the streamflow rate (Qo, m3/s) under similar conditions. Hereafter, in the knowledge of the simultaneous stage data on the auxiliary gage also indicated in the table, the actual surface slope (I, cm/km) for the given instant over the reach included by the two gages has been determined. These data have then been entered into the formula Q = Q0 V(l/I0)to find the actual streamflow rate Q/m3/s/ passing the gaging cross section under consideration.

For estimating the streamflow rates through the Szeged gaging cross section on the Tisza River, allowance had to be made, besides the stages on the Mindszent gage, also for the stages on the Makó gage on the Maros River. Consequently, the value of I0 had to be found from the auxiliary table in terms of the stages at Szeged and at Makó. The streamflow rates through the cross sections, for which three-, or multi-variate relationships are published can be calculated only by taking the other two (or three) variables simultaneously into consideration (no variable must be omitted, or neglected in the calculations).

Typical water temperature data are given for the gages which are representative for longer river sections controlling the variations in water temperature. Where the water temperatures are observed but once, in the morning only, the extreme values are the data selected from the readings taken in the morning. The water temperatures are measured at 10 to 40 cm depth below the water surface.

The hydrological particulars (stages, streamflow rates etc.) over some streams, or sections of streams, such as the Sió Canal, some sections in the Tisza River System, are influenced by human activites, such as the operation of weirs, diversions, discharges. The extend of these influences varies with time, and the length of the river section affected depends on stage. The duration in time and range of these effects can be indentified by a detailed analysis of the observation data alone.

The data on sediment transport - both for the current year and the longer period - are values estimated from observation data. The values corresponding to the highest stages on record and observed during the year of report have been entered as extreme values.

The concentration of suspended sediment is estimated on the basis of samples taken from 7 to 9 verticals in a cross section. Sample of one litre volume are taken at ten points evenly spaced over each vertical. The mean concentration in the vertical is found from the ten samples combined. The extreme values have been calculated by extrapolating the correlations between the quantities describing sediment transport, and should therefore be regarded as approximate values only.

3. The chapter containing the data on subsurface waters has been completed with the water levels in the key deep wells (on artesian- and karstic waters), and with the hydrographs of three artesian-water observation wells.

The elevations of the springs above the Baltic level have in some instances been obtained from maps, in others by geodetical surveying.

4. In the chapter on hydrometeorological data, in the tabulation of monthly and annual precipitation depths, the stations reporting daily have been indicated by underlining.

The water equivalents of the snow cover have been calculated from the results of 20 samples taken along a straight line (2 samples taken at 10 points along a distance of round 100 m).

Evaporation from the open water surface has been estimated from the data of pans comprised in the network operated by the National Meteorological Service. Evaporation from natural water bodies may be from 0.7 to 1.1 times of pan evaporation, depending on local particulars (area of the water surface, depth of and vegetation in, the water body, wind exposure etc.).

THE MAPS OF THE DATA COLLECTION NETWORK indicate the gages, springs, wells and meteorological stations, which were operated over the year of report, or over a part thereof.- 23 -