Hidrológiai Közlöny 1950 (30. évfolyam)

1-2. szám - Kivonatok

Sediment transportation of the Sajó river and the subsidence of silty water. By J. Bogárdi, D. Eng(Hungárián text with figs. and tables on p. 15.) U. D. C. 628 .16 : 627 .157 : 532 . 3/5 The actual sediment measurements began in Hungary in 1935 and siuce that lime according to tho requiremen'.s the importance of these meaí,u'cements increased s'.eadily. -Among the "many prclilems in engieneeriug practiee involving the sediment transpor'.ation one is the subsidence of cooling wa'.er taken out from silt-laden river courses. The present paper is deal'ing with a problem of this nature. As a part of the Hungárián five years plán a coal-energy plánt is projec'eid in the Sajó valley where for the purpose of cooling will be necersary the subsidence of the silt-laden „Sajówater". When the problem arose there haven't- been any data referring to the sediment transportation of the Sajó river. The first problem was therefore to de.ermine the variation aud alsó the extreme values of the sediment concentration in the Sajó river. In december 1948 we measured four times the Midim Mit transportation 'at relative'y low stages. Fig. 1. reprcsents two characteristic concentration curves. According to these . measuremen s the lowest sed ment concentrations in the Sajó river are around 10 gr/m

3. In oriler to predict Ihe daily silt transportation we applied Prof. Lanes and Shulitsh' G [tonris/day] = 21. J

3 equation. [See Fig. 2.J The result is 200000 tonns/day, which is inexpeetedly high value and :s round ten times greater than the eempu'ed 21000 tónus daily silt transportation of the Tisza river- The only eonclusion drown from this fact is that the Sajó carries probably more suspended sediment than the Tisza. Fig 2. was suppltmented by the aulhor with 16 poin's, based on Prof. Parde's datia and with two values fixed for 'the Tisza river. Based 011 the sediment measurements on the Tisza at Záhony and Rázompuszta an effort was raade to determine the probable maximum sediment concentration of the Sajó river. There are a number of measured mean concentration (c) and mean veloci'ty (v) value-pairs on the Tisza. To each value of the measured concentrations and velocities l rlongs a sd'.urcrtion reJori'v (vt) respestively a satumtton concentration (ct) according to equation (1) and (2). Taking the ratios — vt and — and the mean depfh of the observation Cí section H it was found that the relation of these values (See Fig. 3. and 4.) was fairly constarit tor a uumber of different observation sections on 'be Tisza. Now if we assume that the sediment on the Sajó watenshed originates under sim'lar conditions as it does on the Tisza watershed, presu mably the ratio — on the Sajó will be nearly ct equal to that on the Tisza- Near to the observation section at. he Bánréve gage on the Sajó we have ilischarge, e. i. veloci'y measurements at flood stages too. Üsing for flood stages 'the Bánréve H and v values, from Fig. 3. the — ratio, and fr'om vt Fig. í. the — ratio were determined. et for the ct Sajó sediment for given H was computed according to equation (2). and s'o f ina Ily c = 2000 gr/m

3 concentration wasobtained for a mean flood stage. The mean diameter of the Sajó sediment in December 1948 was d=0.1 mm. We expected finer sediment, e. i. smalleer mean diameter in spring tinié at flood staiies, which will increaise the sediment concentration. Taking in account the forgoing statement in the end of 1948 the expected highest concentration at extreme floods was determined in 10.000 gr/m

3, e. i. in 10 'kg/m

3. In Apri'l an>d May 1949 we succeded to measure at more higher stages, which made it possible to extrapolate tho sediment concentration — stage relation. (See Fig. 5-) Knowing 'the discharge we determined the silt load — stage relation too. (See Fig. 6'.) The two relation are expressed by equations (3) and (4). According- to Fig. 5. at 406 cm. tho most highest Bánréve stage, the expected extreme concentration should be 24,5 :kg/m

3. This is an exlremely high concentration but it seems anyway exceptable. The bed load increased proportionally with the stages and was in average 1000 times smaller than the suspended load. The mean diameter of the bed load varies between 0,2—0 5 mm. Finally the paper comprises the theory of sedimen tation. The channel velocity required to start suspension, respeetively scour is given by equations (5) and (10). Equation (10) was introduced by Professor Camp and gives a relatively higher limit of channel velocity Ihan equation (5). Now in the simple theory of sedimen'tation tho first requirement is tihat the channel velocity should be less than the suspension, respeetively the scouring velocity for Ihe given suspended matériái, determined by equati'cms (5) and (10). The second requirement is that the leng^íh of the S'ettling zone should be great enough to settleout the suspended matériái in question 1 r'ough the totál depth H of the set'.ling zone. In the simple theory the lenth ol' -the settling zone is therefore fixöd by the settling velocity of the matériái. H depth, and by the channel velocity. Taking brsius with different depths and channel velocities it is evident how important factors are the demensions of the basins and the channel velocities. It is worth while to recapiíuliate the theory of sedimentation in detail. Equiation (11) is the basic principle of the late Allén Hazen. Professor Slade introduced the distribution function and in determining the phenomenon of sedimenta fon takes intő considleration the turbulence of flow too. According to his statements the turbu'lent flow is eiiher incomplete, complete or eritical. Equation (21) is the basic formula and equation (23) is his so called working formula, where the distribution function is broken intő a number of parts to avoid the inconvinient integrations. Slacle's assumptions are very remarkable but knowing the interpretations of the turbulent sediment suspension his statements should be consillered as out of date. In theory cf sedimentation should be mentioned Professor Camp's research work pubüsheil in 1937. Camp's statements ai-c fully reoapulated in the present paper (See Fiu-. 7.). The next to be mentioned is E. Dobbins' ivork. who applied the turbulent suspension theory suecesfully on the phenomenon of sedi 78