Hidrológiai Közlöny 1968 (48. évfolyam)

2. szám - Dr. Hankó Zoltán: A Nagymarosi Vízlépcső kisvízmintakísérlete. III. A műtárgy ellenőrző vizsgálata

62 Hidrológiai Közlöny 1968. 2. sz. Hankó Z.: A Nagymarosi Vízlépcső henden Eisfelder über das geöffnete Stauwehr herabzulassen. Bei kleinen und mittleren Abflussmengen kamen wir auch auf die Feststellung, dass Eis nur in dem Fali herabgelassen werden kann, wenn die gesamte Abflussmenge durch das Stauwehr strömt. Unsere, auf die Beibehaltung der allgemeinen Anordnung des Objekts bezüglichen Vorschláge habén wir in der Abb. 1 mit punktiertem Zűgen angeführt. Unsere Feststellungen bezüglich Betrieb des Bauwerkes: Zum Anhalten der Schiffe und für die Schiffzugsmanöver inüssen im Oberwasser stromauf des Profils bei 1697 + 500 Flusskm und im Unterwasser dem Profils des Pegels bei Nagymaros ein Platz bestimmt werden. Es ist zweckmássig, die Maschinen der Wasserkraftanlage in folgender Reihenfolge in Betrieb zu setzen: — zuerst die Maschinen Nr. VII—X., dann die Maschinen Nr. III., IV., nachher die Maschinen Nr. V., VI. und zuletzt die Maschinen Nr. I. und II. Was den Betrieb des Stauwehrs anbelangt: wenn die Wasserkraftanlage mit vollem Betrieb arbeitet und das überflüssige Wasser über das Stauwehr mit Überfall abfliesst, so ist es aus Sicht der Oberwasserströmungsverháltnisse am günstigsten, wenn wir das Wasser in der Mit,te des Stauwehrs überfallen lassen; für das Unterwasser ist die gleichmássige Wasserherablassung am günstigsten, im Falle von Hochwássern werden die Strömungsverhaltnisse durch Korrigierung der Linienführung des Oberwassers am rechten Ufer, die Ausbildung einer Insel neben der Schiffschleuse und der oberen Mole, weiter durch die dem Oberwasser zu nach vorn ragenden Spitze des Trennpfeilers verbessert. An der Unterwasserseite muss für die Sicherung des durch das Hochwasser stark angegriffenen rechten Ufers gesorgt werden. Wenn wir auch die allgemeine Anordnung des Objekts modifizieren, dann muss in erster Reihe untersucht werden, ob es nicht möglich ware, im Falle der planmássigen Anordnung die Mole der Schiffschleuse im Verháltnis zur Schiffschleuse zum linken Ufer zu knieken. Ausserdem muss untersueht werden, ob die Schiffschleuse dem Unterwasser zu nicht um ungefahr 150 m verschoben werden kann. Im weiteren erwáhnen wir auch den Gedanken einer einheitlichen Anordnung mit einer mittleren Kraftanlage und die Anwendbarkeit der Anordnung der Wasserkraftanlage mit geknickter Achse (Cabelkasehe Anordnung). Model Tests on the Nagymaros Barrage III. Study of the Structure By Dr. Hankó, Z. Problems arising in conneetion with the planning of the Nagymaros barrage were studied by model tests. Those assoeiated with preliminary planning, designing and construction, as well as with the identification of the model were reported upon in Part I, while those related to the construction pit enclosure were described in Part II of the present account. Model tests performed for checking the proposed structure will be described subsequently in the concluding Part III. The objective of the hydraulic model test related to the planning of the river barrage was to study the mutual intörference between the proposed structure and the watercourse. The proposed structure is illustrated in Figs. 1 and 2. The resistance to flow created by the structure was determined for the entire rangé of stages, assuming peak flow conditions. Results have been represented by stage differences between representative cross sections and the Nagymaros gage, in terms of stage at Nagymaros, in Fig. 3. The resistance of the structure with the weir gates fully open is about 25 times as high as that of a 1 km long channel, whereas with the navigation lock open as well, the resistance is about 10-fold only. Highest and lowest values were determined approximately (Fig. 4) for the open weir (with the navigation lock and power station in closed condition). Discharges through individual parts of the barrage were alsó examined. The portion of discharge flowing around the structure at a given condition of operation and stage on the Nagymaros gage was alsó determined, assuming again peak flow conditions (Fig. 5). The distribution of discharges among the open navigation lock and weir was found to be QH-QD = 31 :69, and to remain unchanged in the rangé considered, regardless of stage. Similar studies were performed to determine the share of individual weir openings in totál discharge. Conveyance was found to depend on the location of the particular opening and on stage. Flow conditions around the structure were checked for altogether 29 different conditions of operation. On the basis of flow pattern photography significant changes were found to result from the construction of the structure over an about 3 km long river reach between the Nagymaros gaging section and K. St. 1697 + 500 km. Flow approached the structure from an unfavourable oblique direction. Obliqueness was found to increase with increasing river discharge and as a consequence thereof, separation was observed in the extreme openings beside the separation piers, where areas of stagnation and vortices developed. The discharge leaving the weir openings is conveyed under favourable conditions. The initial tangent of flow lines was in eaeh opening perpendieular to the axis of the structure. Concerning the power stat ion, the discharge through two turbines on each side of the weir was found to be higher than through the rest. In the conveyance of flood discharges, the navigation lock was found to play an important role. The upstream pier, which extends adversely into the flow greatly effects the flow approaching the weir and the distribution of discharge among the turbines in the power station. The proposed layout of the bankline on the lefthand side proved to be satisfactory at all operating conditions, whereas that on the right-hand side was found to be inadequate. In the interest of improved approach to the weir the bankline should be shifted towards the river on the upstream side. The bank protection and training works on the downstream side were designed with a too narrow radius. Sedimentation is to be expected: on the upstream side in the large vortex along the upper pier and the navigation lock, as well as in the right-hand forebay of the power station, in the upper entrance to the navigation lock, as long as the gates of the latter are closed; on the downstream side in the downstream entrance of the lock and in the adjacent stagnant area and vortex, down to the Nagymaros gaging section, further in the tailwater of the power stations. Erosion of bed material is likely to occur primarily along the path of hi |h velocity flow through the weir. At times of high tloods similar conditions arise along the path of current flowing through the navigation lock. From studies on flood conditions it could be ascertained that high waters can be diseharged through the barrage without adverse effects. Studying the distribution of discharge through the power station among individual turbine units it was found that the units in the right-hand group (VII—X) diseharged more than their proportionate share, whereas units III and IV in the left-hand group diseharged less than units I, II and V, VI. The evaluation of flow conditions from the point. of view of navigation revealed the necessity of selecting a location with more balanced flow conditions for atten-