Vízügyi Közlemények, 1956 (38. évfolyam)
2. füzet - VII. Kisebb közlemények
9 (82) SURVEY OF IRRIGATION WATER RESOURCES E. Kertai (Figures and tables on pp. 355—372. of Hungarian text UDC 626.81 In Hungary in 1947 12 000 ha were irrigated; at present irrigation is provided for 120 000 ha. Long-term projects aim at the irrigation of a multiple of that acreage. For conservative development programs the resources of irrigation water have to be known. In Hungary hydrologists have been engaged in the calculation of irrigation water resources for 20 years. By older methods, in general, irrigation water was determined on hydrological basis. In the course of drafting the General Plan of National Water Economy, completed in 1954, a novel, more precise survey of the irrigation water resources was achieved. The term of irrigation water resources of a country does not mean at all that portion of the total water resources which is available for use after other needs have been met. That is the upper limit, within which economic viewpoints, first of all, will decide how much from the water resources are usable for irrigation. In this sense the following distinctions may be made : 1. Theoretical irrigation water resources. 2. Economically usable irrigation water resources. The own water resources of one system can be increased by diversion of water from another system. The method of calculation applied in the General Plan of National Water Economy can best be presented by factual figures relating to irrigations in the Tisza Valley. On the basis of the contour map of the area and of soil conditions the acreage amenable to irrigation may be set at 550 000 ha (Fig. 1.) The maximum supply needed may be put at 300 m 3/sec. The Tisza River and her tributaries can supply only part of this volume. Some additional supply of water will be needed. To establish the economic measure of this has to be determined the deficit in crop yields against optimum values at different rates of additional water supply to make up for the shortage (Fig. 2. and 3). This is being done on the basis of agronomic considerations with regard to the different seasonal effect of water shortage on crop deficiency. Afterwards the investment cost of additional water supply of different degree <in the case of Fig. 2. by storage, in the case of Fig. 3. by diverting water from the Danube) and therefrom the annual costs were determined, which latter is plotted as a function of the additional water supply. Adding up costs and the value of the crop deficit, the curve of total losses is obtained, the minimum point of which determines the most economical rate of additional water supply. The result of calculations has shown that the maximum amount of water supplement may be annually 500 million eu m. of water from storage and 90 m 3/sec of water diverted from the Danube. At this rate of additional water supply limitations •on water consumption will still be necessary in drought years, but the diminution of crop yield resulting from it will be minimum. Fig. 4. shows I ho development of water requirements and the means of meeting them in an extremely unfavourable and in an average year. Fig. 5. presents how the water economy of the Tisza River would have developed in the last 52 years. Thereby the economically usable water resources of the Tisza Vallev have been determined, which ma> r be increased up to the theoretical maximum, shoidd more new needs turn up, on the basis of similar considerations. Fig. 6. presents the distribution of water among the irrigation systems of the Tisza Valley. The basis of the determination of the irrigation water resources is the survey of the resources of the entire country. The precise determination of this is indispensable for a dependable result. In this respect the publication of the Research Institute for Water Resources entitled "Water resources of Hungary" is a great help to water economy planning.
