Vízügyi Közlemények, 2001 (83. évfolyam)

2. füzet - Rövidebb tanulmányok, közlemények, beszámolók

332 Jolánkai C.-Biró I. Somlyódy L.-van Straten G. (editors): Modeling and Managing Shallow Lake Eutrophication; with application to Lake Balaton. Springer Verlag, 1986. Streeter H.W.-Phelps E.B.: A Study of the Pollutions and Natural Purification of the Ohio River. Public Health Bulletin No. 146. U.S. Public Health Service, 1925. VITUKI(TAS-Balaton): Overall Evaluation and Priority Ranking of the Water-environment Control Projects of Lake Balaton. Phare Framework Contract-Environment No. OSS HU 9513, final report, (VITUKI, Budapest), 1999. Thornton J. A.-Rast W.-Holland M.M.-Jolánkai G.-Ryding S.O. (editors): Assessment and Control of Non-point Source Pollution of Aquatic Systems. A Practical Approach. Man and the Biosphere Series Volume 23. UNESCO, Paris and Parthenon Publishing, Camforth, 1999. * # * On the determination of water quality targets and the allowable pollution loads by Dr. Géza JOLANKAI Doctor of Science and István BIRO civil engineers It is stated that the setting of water quality objectives (criteria, targets) and the determination of allowable pollution discharges (loads), defining the former, cannot be done for a given water system and its pollution discharges, without a water quality model of that water system. More precisely, water quality target conditions could (probably) be set, but the pollution load, which would define the former, cannot. This statement follows from the fact that the allowable pollution load, which defines the water quality state of the recipient water bodies, can only be determined on the basis of cause-and-effect relationships. Here, the causes are the pollution loads (of point and non-point sources) and the effect is the state of the quality of water of the recipient (changing both in time and space). Since the number of causes (pollution sources) is high and the effect, the state of the quality of water, is defined by a large number of transport and transformation processes, the only means of defining this relationship is the construction and calibration of a water quality model of the water system concerned. The authors made an attempt for the professionally accurate definition of water quality target conditions. It was found very important to make this definition from the point of view of sustainability. Nevertheless, sustainability has not yet been defined by numerical values, but basic principles only, by very important principles, but only by general ones. It follows from this statement that (at our present level of knowledge) water quality target conditions can only be defined by an arbitrarily set system of parameter and index values. Thus the present system of criteria shall be modified (generally strengthened) later. It was also found that no scientifically supported definition of the term "allowable load" exists (because the scientifically based system of criteria of sustainability does not exist either). Consequently at the present one must define the allowable load in other way: It is the load at which the criteria of "target water quality conditions", the immission limit values, can be complied with. As stated before this load can only be determined by using water quality models. Next, starting with the very basics of water quality models, those stream and lake models were reviewed, which could form the basis of a practice oriented determination of "allowable loads". The modelled water quality stream profile is illustrated by Figure I, while the oxygen sag curve (as the basic example of coupled reactions) is shown in Figure 2. Reviewing the possibilities and limitations of the use of these very simple models the following conclusions have been drawn: — The allowable pollution load of a stream can only be defined on the basis of an appropriately selected water quality model, which was calibrated against the data of detailed field measurements (of emission discharges and in-stream immission values, following the time of travel);