JWSS - Journal of Water and Soil Science

A labyrinth weir is a nonlinear weir folded in the plan-view which increases the crest length and the flow rate for a given channel width and an upstream flow depth. Nowadays, a labyrinth weir is an attractive alternative for those weirs that have a problem in passing the probable maximum flood. The three-dimensional flow pattern and unlimited geometric parameters provide a major challenge to the designers of these weirs. The present study aimed at determining discharge coefficients of sharp-crested triangular labyrinth weirs using the support vector machine (SVM). The results were compared with the experimental data. For this purpose, 123 laboratory test data including  geometric and hydraulic parameters such as vertex angle (θ), magnification ratio (L/B), head water ratio (h/w), Froude number (Fr), Weber Number (We) and Reynolds number (Re) were used. The results showed that the SVM-based model produced the most accurate results when only three geometric parameters, e.g. (h/w, θ, L/B), were introduced as the input parameters (R² = 0.974, Root mean square error [RMSE] = 0.0118, mean absolute error [MAE] =0.0112 and mean normal error [MNE] =0.017 for the test stage). Also, for these weirs, polynomials linear and nonlinear regression equations were presented. Finally, the discharge coefficient of sharp-crested triangular labyrinth weirs based on the Rehbock equation was evaluated and compared with the SVM using nonlinear and linear regression methods.

Local scour around the foundation of marine and hydraulic structures is one of the most important factors in the instability and destruction of these structures. False prediction of scour depth around bridges has caused financial losses in plasticization and endangered many people's lives. Therefore, an accurate estimation of this complex phenomenon around the bridges is necessary. Also, since the formulas presented by different researchers relate to laboratory conditions, they are less true and less accurate in other situations. Recently, many researchers have tried to introduce new methods and models called soft calculations in predicting this phenomenon. In this research, 146 different laboratory data series (three different laboratory conditions) were analyzed using a backup vector machine to predict scour depth around the bridge head. These data are presented in the form of various combinations of input parameters  which, respectively, represent thickness under the slippery layer, Reynolds number, critical velocity, Shields parameter, velocity Shear, average speed, flow depth, the average diameter of the particles and diameter of the bridge. The parameters in two different scenarios (the mode with dimension and mode) were introduced into the SVM network and the results of this machine were compared with those obtained from the experimental formulas and relations presented in this study. The results showed that in the first scenario, the combination of No. 5 with input parameters () and in the second scenario, the combination No. 5 with input parameters  () for the test stage were selected as the best model. It was also concluded from the results that the scenario two (the state with dimension) in predicting the scour depth around the vertical single-pillar provided a more accurate estimate than the first scenario (barrier state). At the end, the sensitivity analysis was carried out on the parameters and the parameters D, U*, V were selected, respectively, as the most effective parameters

Sand mining from rivers is one of the biggest concerns in the science today. Certain principles and rules for choosing the right place for mining materials and the amount of this mining are missing in the design codes. Therefore, mining of river materials from sites with less potential and near structures has been occasionally seen. In the present study, it has been attempted to reinforce the structure to control the impact of the mining of material, which results in the increased scour by changing the flow pattern around the structure. The experiments were carried out in two simple and armed modes, in sand bed with a grain size of 0.78 mm, with a length of 4.25 meters, inside a canal of 13 meters in length and 1.2 meters in width. The extent of scouring along the longitudinal and transverse directions in different times from the start to the scouring equilibrium was investigated for all substrates under sub-critical flow conditions (range 0.5-0.25). The results showed that the use of a cable-protected method in the upstream pit led to 29.6% reduction in the maximum scour depth at the front and 34% reduction in the back of the pier; also, in the downstream of the pit, it reduced the maximum scour depth by 15% at the front of the pier. Therefore, the cable arrangement used at the piers surface, according to the current research method, resulted in a significant reduction in the depth and extent of scouring in the pier group of the bridge.

Inclined drop is one of the supercritical flow producers used in open channels to reduce slope and elevation of the ground. Given that the application of horizontal and vertical screen in the downstream of this drop as an energy dissipater can be effective in the n energy dissipation of flow, in the present study, 180 different experiments were performed to investigate the energy dissipation of flow. The results showed that the angle of the drop had no marginal impact on energy dissipation and the relative depth of downstream of inclined drop equipped with a vertical screen, but increasing the porosity of screen caused enhancement in both parameters. Also, for the inclined drop equipped with a horizontal screen, by increasing angle and decreasing the porosity of screen, the energy dissipation and relative depth of downstream were raised. Also, for inclined drop equipped with a horizontal screen, by increasing the angle and decreasing the porosity of screen, the energy dissipation and relative depth of downstream were enhanced. For a constant relative critical depth, the relative depth of downstream and the energy dissipation of the inclined drop equipped with a horizontal screen considered the function of the wetted length of screen and length of the drop. For vertical screen, it is only a function of screen porosity.

The scour around the bridge piers is one of the main causes of bridge failure and the extraction of aggregates may aggravate this phenomenon. The present study comprehensively investigated the scour around the groups of bridge piers in the presence of aggregate extraction pits, using different discharges. The bridge piers roughened by gravel had been compared with the simple bridge piers; so, the results showed that the roughening caused the reduction of the scour depth. Scour depth change rate led to an increase in the equilibrium time. The results also showed that the reduction of the scour depth at the downstream groups of piers was more than that in the upstream. For the lowest discharge, the aggregate extraction pits had a considerable effect on the scour depth difference for the groups of piers in the downstream and upstream. On the other hand, the effects were decreased when the rate of discharge was increased. The experimental results obtained by the rough surface models showed that as the discharge was increased, the local scour was increased too; at the same time, the bed profile was posed at the low level. Generally, the scour depth of the groups of piers in the downstream of the extraction pit was more than that in the upstream. The results of the current research, therefore, demonstrated that the surface of the bridge pier roughened by gravel reduced the scour depth.

In the last decade, the use of gabion structures in hydraulic engineering for stabilizing the structure due to its high density and weight has become widespread. Also, the material's roughness and porosity cause it to be used in energy dissipation and drainage projects. This study evaluates the relative energy dissipation of gabion structures downstream of the ogee spillway in the conditions of a submerged hydraulic jump. The evaluated parameters in this study were Froude number, gabion height, gabion thickness, and material diameter. The experiments were performed with three average diameters of 1.5, 2.2, and 3 cm for rock material, three gabion heights of 10 and 20 cm, and Max. The end sill heights were 10, 20, and 30 cm. The operated discharges were regulated from 20 to 40 l/s. The results showed that by decreasing the average diameter of gabion aggregates, the amount of relative energy dissipation increases in all tested models, so that in gabion with a 1.5 cm average diameter of aggregates, the amount of energy dissipation increased by 3.6% in comparison with using the diameter of 3cm for the average diameter of the material. Increasing the height of the gabion to the extent that the flow is entirely inward can have up to 33% more relative energy dissipation than the gabion with a height of 10 cm. Also, by increasing the diameter of the gabion from 10 cm to 30 cm, relative energy dissipation increases up to 15%.