Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Kolin László: A vízminőség szerepe és változásai tározókban

58 Hidrológiai Közlöny 1971. 1. sz. Special Conference Number, Szebellédy, L. the development of basin types ensuring correct flow conditions, further improvement in this field in still desirable. It should be noted in this context that in the storage basins designed, constructed and operated so far in Hungary, shafts provided with protecting screens are the only means of ventillation for the space above the water surface. Neither adequate cleaning, nor satisfactory flow of air can be aehieved in this manner. Special attention should be devoted to the design of overflow- and bottom outiét conduits. There are very few operating basins in Hungary, where suitable sanitary protection (overflow, svphon) is provided for these two conduits. 4.2. Solutions und experiences abroad Very interesting papers have been submitted to the Conference, in which experiments concerned with flow conditions in storage basins, with the satisfactory arrangement of inlet and outflow ports, as well as with the ventillation of the air space within the basin, are deseribed. Flow conditions developing in basins having different lavouts in plan are subject to a very detailed and thorough study by W. Langer. The results of his studies may be summarized as follows: — Care should be taken not to concentrate inflow and withdrawal to single points, but to distribute them evenly over the entire depth of water in the basin. For this purpose the inlet and outflow pipes are provided with verticai end pieces slotted in a definite pattern. — In basins over a rectangular plan smallest stagnation areas and optimum flow conditions are obtained at a length to widtli ratio of 4: 1. Basins of different geometry should be divided by baffle walls into compartments of the above side ratio. — In circular basins the preferable solution appears to be tangential inflow and withdrawal at the center through a device resembling a stationary turbine. In this manner continuous spirál flow is created in the basin. At the inlet care should be taken again to ensure three-dimensional flow. In the paper by A. Lohr a storage basin in Munich, the experiments preceding its design and operating experiences gained with the completed basin are deseribed. Water into the basin providing 65 000 cu.m live storage volume is admitted through the slotted wall of a r.c. flume running parallel to the basin and ensuring uniform distribution of inflow over the entire height and length of the basin. The two side walls of the largelv square basin form hvperbolae and the flow pattern created by this boundary is such to guide water towards the intake. A special feature of this basin is that great care has been devoted to the cleaning and disinfection of air above the watersurface and to ensuring adequate circulation. Subsequent operating experience has demonstrated the care and throughness devoted to this problem to be fullv warranted. As reported by Lohr, as long as the air-cleaning and disinfecting equipment functioned regularly, in water that was uncontaminated at the inflow, no germs could be detected at withdrawal. For purposes of checking, the cleaning and recirculation of air was stopped. The germ count in the originaly germfree water rose in two days to 300 and in a weekto 700 per millilitre. This example should be regarded as striking evidence for the importance of ensuring adequate ventillation to storage basins and of passing this air through a cleaning system. A special type of basin is deseribed in the paper by 1. Schmit. This type of basin was developed in response to the desire of ensuring under all conditions uniform flow and complete water exchange in the basin. The resulting design features a spirál labvrinth, realized with the help of a guide wall. Water is admitted at the center of the spirál, whence it passes through the labvrinth towards the withdrawal at the extreme end thereof. Besides ensuring perfect flow conditions, this type of design is claimed to permit considerable savings in construction costs. In the past years more than 20 storage basins of this type have been built in Austria, with live storage capacities ranging from 500 to 5000 cu.m. 5. Conclusions, recommendations Concerning the future design of storage basins it is concluded that the organizing committee was fully justified in incuding this subject among the agenda. It would be mistaken to claim that the present situation is entirely satisfactory, but it is encouraging to observe that the theoretical, scientific background required for the sound design of future basins is available and that there exist a few successfuly practical solutions that can be utilized for improvement in this field. Concerning the future storage basins the following principles may be established: — The design of major storage basin projects should be based on model tests for obtaining a clear picture on flow conditions and for determining the most favourable flow pattern. — Special attention should be devoted in each case to the spatial arrangement of inlet and withdrawal. considering verticai standpipes in smaller basins and slotted-wall inlets in major ones. In circular basins withdrawal through a standing turbine located at the center appears to be preferable. — It is considered essential to provide adequate ventillation in storage basins, cleaning and disinfection of the air admitted, as well as uniform air circulation is the space above the watersurface. — Suitable weirs and syphons should be provided in order to prevent contaminating matter from entering the basin through the overflow, or bottom outiét conduit. It should be noted finally that none of the papers submitted dealt with the hydraulie problems in elevated tanks. It was thus rewarding to consider the influenee of basin design on the quaüty of stored water, and the wealth of information precented in the papers is expected to contribute, already in the near future, to the improvement of storage basins.