Vízügyi Közlemények, 1966 (48. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(12) The prerequisites for arriving at weil founded conclusions from data on past events on those anticipated in the future, are a

) the availability of a records*extending over an adequately long period, and b

) that there have accurred no significant changes in the conditions under which events have developed over the period of study. The first of these prerequisites implies, that the collection of hydrologie data must — depending on economic significance — precede the birth of practical demands by several years, or even decades. Otherwise the information cannot be regarded as representative. The second prerequisite expresses the condition that hydrological computations — just as other computations — must be based on a homogeneous set of data. Surface water resources and particularly the quantity aspects thereof are only considered in this paper. Chapter 1. is devoted to some of the problems arising in connection with the collection of hydrologie data and is concerned with the representativeness of data recorded. In Hungarian hydrographie and hydrologie practice, which is continued over a century, requirements to be met by hydrographie stations have been established. On small watercourses discharge measurements, performed once monthly in natural cross sections, are but rarely sufficient for satisfying these requirements. In the interest of producing a continuous discharge hydrographs, permanent gaging sections are being established in ever increasing numbers. In Chapter 2 the necessity and possibility of homogenizing hydrological data is discussed. The knowledge of regime conditions over an extended period in any particular gaging section is of no avail, if eventual changes in factors which modify gathering and runoff conditions over the catchment area pertaining to, or in the bed above, the section are unknown. As revealed by Fig. 1., given as an illustrative example, water resources of a river supplied by a vast catchment area w

Tere also reduced by 5 to 30% as a result of irrigation. Homogenization of records can be effected by a survey of water uses and hydraulic construction activity. Such a survey is aimed at the compilation of the water resources balance. Results of the annually repeated survey are entered on the filing card illustrated in Fig. 2. Chapter 3 is concerned with the accuracy limits of the survey and it is pointed out that the reliability of determining natural regime conditions depends, besides the reliability of hydrological data collecting, also on the reliable knowledge of artificial interference. In Chapter 4 the processing of discharge data is analysed in detail, extending the discussion to frequency-, duration- and probability calculations. These are exemplified in Fig. 3. In the low-water range durations are used, rather than probabilities, for the reason that instead of a single value, individual groups of values are obtained for each period, which affords the following advantages: — these are less likely to be biased than a single value, — the result (information) obtained is more significant, since a single extreme value (a single day, or a fraction thereof)'is not likely to cause significant damages in resources management (in contrast with floods). In Chapter 5 it is pointed out that water resources management — to be successful — must obtain reliable and detailed information on quality aspects of waters as well. Beyond values determined at the time of observation, inter- and extrapolated values in time and space are necessary. By extrapolation in time, the objective is to forecast probable changes in the quality of surface water, if new sources of pollution are admitted, or if the present regime is modified by artificial interference. The determination of numerical values is the objective of research all over the World.