Vízügyi Közlemények, 1967 (49. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(4 3) The final and most important conclusion of these investigations appears to be that in areas where as a result of human interference a high degree of development has been realized, no considerable inundations are likely to occur even under extreme conditions. In the development of systems care should be taken to increase the density of the canal network, yet at the same time the performance of low-order drainage works should receive equal attention. These latter are mainly the responsibility of agriculture, but are as important as the efficient operation of principal drainage structures, which constitutes the task of water authorities. GENERAL BASIC EQUATION DESCRIBING DISCHARGE THROUGH HYDRAULIC STRUCTURES, WITH SPECIAL REGARD TO DISCHARGE MEASUREMENT By Ö. Starosolszky, Civ. Engr. (For the Hungarian text see pp. 72) No efficient management of water resources meeting contemporary requirements is imaginable without the measurement of discharges, which has by now become indispensable in every branch of water management. In the planned operation of irrigation farming the path of water from the main diversion to the plot can be traced with the help of the discharge measuring network only, and the rate of supply specified, or required by the plant cannot be ensured, unless discharges are measured continuously in various parts of the system. A wide variety of installations and structures has been developed and tested in Hungary for the realization of continuous discharge measurement, keeping mainly interests of irrigation in view. Some of these structures, installations and instruments were found suitable for measuring discharges in natural small watercourses, canals, or pipelines. From among the measuring structures and installations those relying on a hydraulic principle and operating by the measuring head ( Fig. 1 ). have found wide application for continuous measurement in irrigation practice. General relationships relating to discharge through these structures (measuring weirs, venturi flumes, measuring orifices, calibrated structures, water dispensers) and measuring devices (orifices, measuring weirs, venturi tubes, measuring elbows, Pitot probes) are dealt with in this paper. These relationships are demonstrated by results of field and laboratory experiments. For discharge measuring structures and devices operating by the measuring head, the relationship between discharge and measuring (differential) head can be written with the help of the energy equation ( Fig. 2 ) into the form of Eq. (4a). The importance of velocity distribution, pressure distribution, the contraction ratio and the energy loss between cross sections for which the differential head is observed, is reflected by the formula. Upon introduction of the contraction coefficient the expression assumes the form given by Eq. (17). With certain simplifying assumptions the energy loss is given by Eq. (13) in terms of friction and local losses. The general expression may hereafter be rearranged into the form of Eq. (14), wherein k? is the energy loss coefficient. The contraction coefficient may be regarded (in the case of ß[ = ß

2 = l) as the square root from the ratio of two kinds of velocity distribution and the energy loss - see Eq. (19) — wherein the subscript indicates allowance for the contracted section. In the case of ß

1 = ß„ = l, the discharge coefficient may also be related to the coefficients of velocity distribution and energy loss, as well as to the contraction ratio according to Eq. (21), where Fj/F

l=m is the contraction ratio. Correspondingly, the error committed in the discharge coefficient, (or variations of the discharge coefficient) may be determined with the help of Eq. (29) relating to M. For measuring contractions built in open channels (Fig. 3), in the case of free flow through the structure, the criterion may be introduced that critical depth occurs at some point, so that velocity and depth in Section 2 may be expressed in terms of