JOURNAL OF HYDRAULICS
Year:2005 | Volume:1 | Issue:1|Papers Count:6

Radial gates are used widely as a kind of control gates, worldwide. Although they are used widely, discharge estimation is not easy and few studies have been cited in the literature. In the present study, new relationships for estimation of discharge coefficients under free flow and submerged conditions are obtained. In these relationships, the discharge coefficient was related to the gate lip angle and the ratio of the water head to the gate opening height. By using these relationships, the accuracy of estimated discharge is increased. For this purpose, nonlinear multiple regression analysis and a set of laboratory data were used. Some statistical parameters such as maximum error, average error and standard error and three sets of field observed data were also used for evaluation of the relationships.One set of these data was collected in the present study and the others from previously published studies. The ranges of used observed discharge data were 0.030 to 0.320 and 0.010 to 0.180 m3s-1 in laboratory under free flow and submerge conditions, respectively. For the field observed data, these ranges were 0.11 to 239.6 and 0.05 to 209.02 under free flow and submerged conditions.Results showed that the relationships obtained could be appropriate for estimation of discharge coefficients in free flow and submerged radial gates. Relationships including gate lip angle, gate opening and upstream water depth are more reliable than the ones using only gate opening and upstream water depth. The average values of discharge estimation error could be about 2 and 1 percent under submerged and free flow conditions, respectively.

Bed load in curved rivers usually move from outer to inner curve as a result of helical flows due to curvature. Hence, there will be a chance to have flows with lower sediment around outer curves which will result in water flow diversion. Moreover, water depth will increase around the outer curve of the river following erosion occurring at this part and bed load will consequently move at a higher depth than of the entrance of intake. Therefore, impoundment condition will grow at the part of the curve at which helical flow reaches its maximum intensity and makes a more appropriate section as intake location.The present research deals with the process of locating such a point in some model with a trapezoidal section through continuous injection of sediment (bed load) in a sinuous channel form. The results show that the place of pothole formation as well as some other relevant parameters is a function of Froud number of the approach flow in up the curve. The location of helical flow maturity or the part at which the most rate of scouring and deepest part occurs, moves from downstream to upstream of the flow in curve with the increase in Froud number.

The occurrence of transcriticalor mixed flow, i.e., supercritical and sub critical flow regimes, is considered as a special case of unsteady flow in a channel reach, which can clearly be exemplified by a moving hydraulic jump. Some complexity is inherent in the numerical analysis of transcritical flow and published experimental data regarding this kind of flow are rarely available. In this research an experimental setup was prepared to compile the hydraulic characteristics of transcritical flow in a rectangular flume. The flume was equipped with a sluice gate at the upstream boundary. Each inflow hydro graph generated unsteady supercritical flow regime at the downstream side of the sluice gate and formed a moving hydraulic jump along the channel. During each run, the water surface profile was continuously recorded using a pressure transducer. Based on the recorded data, some flow parameters such as flow depth, pressure head and energy head were determined. The result reveals specific relations between the discharge and moving hydraulic jump parameters. Also, by applying proper assumptions and employing steady state momentum and energy equations simple yet reasonable (and time independent) relations were obtained, that determines the pressure head in subcritical region of unsteady mixed flow. Consequently, having the discharge variation as a boundary condition, one may reliably determine the unsteady transcritical flow parameter based on time independent relations.

Uncertainty is always an element in the design process of flood control systems. Hence, efficient flood management needs uncertainty analysis. Computation of water levels at different floods magnitudes is a main task in flood management studies such as flood plain delineation for flood insurance studies, flood hazard mapping, and project planning for flood damage reduction investigations, design of levees, and design of bridges at stream crossings. Two of the sources of uncertainty associated with the computation of water levels, those of hydrologic uncertainty of estimation of design discharge and hydraulic uncertainty of channel capacity, are examined in this paper. The uncertainty of the channel capacity is determined by first-order uncertainty of the Manning's equation using Mean First-Order Second-Moment (MFOSM) method. The uncertainty of flow area, wetted perimeter, and the friction slope, as the parameters of Manning's equation, are expressed in terms of the variance of vertical, lateral, and longitudinal measurements performed with land surveying instruments. The uncertainty of Manning's n is characterized by the equation of standard deviation of n developed by Hydrologic Engineering Center, US Army Corps of Engineers. The uncertainty of design discharge, as hydrologic uncertainty, is investigated considering the parameters uncertainty and different probability distributions.The uncertainty information is used to derive confidence limits for the water surface elevation of 100 year return period and to analyze the reliability of levees via direct integration method of solving the joint probability of design discharge and channel capacity as the system's loading and resistance respectively. In a case study application to the Sistan River, Sistan and Balouchistan Province, results show that ignoring the hydraulic uncertainties, the water level would be underestimated and the reliability overestimated.

The role of unsaturated drainage layer and hydraulic control systems in sanitary-engineered solid waste landfills were simulated using -three-layer one-dimensional laboratory models. In the models, from top to bottom, a sodium chloride solution as a contaminant source reservoir, a first compacted silt layer as a primary liner, a coarse sand layer as a secondary leachate collection system or a hydraulic control layer, a second compacted silt layer as a secondary liner, and a bottom water reservoir as a groundwater aquifer, were used. In the first two tests, the model simulated the secondary leachate collection system and natural hydraulic trap system (upward flow through the second clayey silt layer). In this case, the contaminant transport mechanisms through the first silt layer were downward advection and diffusion, and through the second silt layer, diffusion was downward and advection was upward. The results showed that the implementation of the natural hydraulic control system could effectively reduce the contaminant transport to the underlying groundwater reservoir. In the third test, the natural and engineered hydraulic trap systems were simulated (upward flow from the bottom reservoir to the upper reservoir). In the fourth test, the model simulated the engineered hydraulic trap system (downward flow through the first silt layer and upward flow through the second silt layer). The results showed that natural and engineered hydraulic trap systems have important effects on reducing the contaminant transport toward the underlying aquifer. In all experiments the chloride concentration in silt and coarse sand layers and top and bottom reservoirs were measured and the observed concentrations were compared with theoretical concentrations calculated by computer code POLLUTE V6. The results showed that there is good agreement between theoretical and observed data.

Due to large differences in hydraulic characteristics of main channel and floodplains, unsteady flow mechanisms in compound open channels is very complex. In these types of channel sections, the main channel velocity is considerably higher than that of floodplains and this leads to high momentum transfers from main channel to floodplains. Available unsteady mathematical models for compound channels have such limitations that need to be modified. In this paper, to take this interaction effect into account in the flood routing computations, the combined depth-averaged Shiono and Knight model (1991) with Saint-Venant equations in diffusion form, have been solved numerically using the finite difference method. For evaluating the accuracy of this model, the results have been compared with two benchmark unsteady mathematical models for the homogeneous and heterogeneous compound channels. The finite element DAMBRK and RFMFEM models selected in this paper are based on full dynamic and diffusion wave solutions, respectively. The results showed that in comparison to the selected models, the present proposed model have considerably shorter execution time, i.e. about 10% that of DAMBRK model. Furthermore, compared to the experimental data of Treske (1988) in a straight compound open channel, the results showed that the computed peak outflow discharge differs from the observed one by a factor of 3.5%. Generally, the most important features of the proposed model are the small execution time and good performance in both homo and heterogeneous compound channels.