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The rectangular broad crested weirs are widely used to measure the water dischargewhich is one of the most popular tools in the irrigation canals particularly, in developingcountries.The present article is trying to demonstrate the results of an experimental work carriedout on rectangular broad crested weir with sloped upstream face to investigate the effect ofupstream slope on discharge efficiency. The upstream slope was varying from 90 to 23 degreeswhile incoming discharge was ranging from 14 to 75 lit/ sec. The experiments were conducted in aflume with a weir of fixed height under the normal downstream water depth .It is revealed that theslope of upstream face in rectangular broad crested weir would smoothen the flow profile havingthe critical depth on the weir crest adjacent and upstream of downstream edge of the weir . Theresults also lead to a novel achievement showing that the weir discharge efficiency is dependenton the slope of upstream face of the weir. As the slope of upstream face of the rectangular broadcrested weir is decreasing from 90 to 23 the weir discharge efficiency is increasing and reachingto its maximum through a parabola function at slope angle of 25 degrees(i.e. 1:2.15). Theinvestigation also showed that the depth of flow over the weir crest, the specific energy head ofthe approaching flow relative to chanel bed and the critical depth would be a pertinent similarityscales to asses the flow behavior over different sloped rectangular broad crested weirs betweenmodel and prototype. However, some broad investigation is recommended to endorse theachievements.

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ABSTRACT

Induced total pressure by flow, including mean and fluctuating components, around a selected chute block in SAF stilling basins downstream of an ogee spillway was studied. Several pressure holes were selected on various faces of a selected chute block to get enough information regarding the total pressure field. This paper reports the results of an experimental work and measurement of mean and fluctuation pressures around chute blocks of SAF stilling basins. The observations showed that the maximum total pressure varies inversely with Froude number of incoming flow while its position of occurrence follows a quadratic polynomial relation ship. Statistical analysis also showed that the peak instantaneous pressure fluctuations could be as large as ±4.5times the RMS value.It is concluded that pressure fluctuation around the chute blocks may double the magnitude of pressure field around the chute blocks and can not be overlooked in designing such appurtenances.

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Because of the complexity of the physical processes in the vicinity of the hydraulic structures due to the separation of the flow, traditional methods for for prediction of maximum scour depth downstream of hydraulic structures are mostly based on empirical approaches. Hence, only a few theoretical works have been reported to study this phenomenon. The present paper describes a new approach based on the momentum principles to estimate the maximum local scour depth downstream of a submerged sluice gate flowing over horizontal or adverse stilling basin. A control volume of the fluid in the equilibrium state of the scour hole was considered and based on momentum principles, some equations are derived to estimate the scour depth at equilibrium state. To verify the proposed equations, large numbers of experiments were planned and conducted under wide range of characteristic parameters such as, incoming Froude number, sediment size, tailwater depth, length and slope of the apron. It was found that the proposed equations fall in a good agreement with experimental results. It was also observed that, in the case of horizontal apron, a specific tailwater depth exists with which the local scour depth attains a minimum value. However, in the case of adverse basins when the tailwater depth takes a specific value, the maximum depth of the scour hole reaches to its maximum and then decreases to a constant value as the tailwater depth increases. This critical tailwater depth was formulated using a semi-theoretical equation.

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Local scour downstream of hydraulic structures is one of the critical phenomena which has absorbed a vast amount of interests by researchers. The designers of hydraulic structures, particularly, spillways try to utilize proper means to minimize the consequences of excess energies downstream of such structures which usually tend the erosion at their immediate downstream reaches. The stepped spillway is designed to create a large amount of energy dissipation by means of steps and would decrease the amount of scour evolution at its downstream. This article presents the results of 67 experiments conducted at two different scales of stepped spillways, to study the local scour downstream the structure. The experiments were planned to consider a wide range of geometrical factors, flow characteristics, and sediment properties. The time length of experiments was ranged from 6 to 24 hours which produced more than 80000 data points for analytical considerations. The results were used to render a regression equation to define the similarity among the scour hole profiles. It was observed that, a long term observation would be needed to reach the equilibrium state. However, semi-equilibrium conditions will be achieved after 24 hours. It was also noted that the depth of scour hole adjacent to channel walls was bigger than that at centerline.