Numerical Investigation of the Combined Slot Effect on the Erosion Pattern Around a Combination of Spur Dikes in Series

Modifying the river course for flood control, prevention of bed erosion, bank protection, and the regulation of river width are among the goals of spur dikes incorporation. The common spur dikes have simple (I), L and T geometrical shapes. The present research has been conducted to reduce the scour depth in front of the spurs dikes and improve the sedimentation conditions for the LTT combination of spur dikes in series by investigating different combinations of slots in the body of the spur dike; using numerical methods. The slot dimension was taken equal to 10% of the effective area of the spur dike body. Finally, the (LS-W-Wi, TS-W, TS-W-Wi) combination contained the slots in the web and wing of the first and third spur dike also the slot at the web of the middle spur dike was found as the best combination of slots. This combination conducted to reduce the scour depth about 6.8% and increase the deposition about 52% comparing by the spurs dikes without slots. Reducing the scour depth and increasing the sedimentation rate of materials between the spurs dikes. Also, the maximum scour depth decreases up to 20%. The results revealed that the presence of slots in spur dike structures and their different positions have complicated and considerable influences on the form and morphology of the erodible bed which could be the topic for further researches.

Bridge Abutment Protection against Scouring for Unsteady Flow Conditions

The bridge abutment is one of the main parts of a bridge and significantly contributes to bridge stability. This study experimentally investigated the effect of the unsteadiness characteristics of hydrographs on the scouring phenomenon around the bridge abutment under clear water conditions. The ability of the permeable and impermeable spur dikes and their distances from the abutment at its upstream on the control of scouring around the bridge abutment was also investigated. The experimental observations imply that the effect of unsteady flow on the scouring process is relatively similar to the steady flow conditions. The results showed that the base time of hydrographs, the type of spur dikes, and the distance of spur dikes from the bridge abutment were the dominant parameters among the considered parameters in this study on the scouring process around the abutment. The results also revealed that the impermeable spur dike was able to completely eliminate scouring around the bridge abutment for two distances of 2L and 3L (where L is the abutment length) for both steady and unsteady flow conditions.

Experimental investigation of scouring around a single spur under clear water conditions

This study presents the effect of different parameters on scouring process around spur dikes. Our research group's stated objective was to evaluate the effects of sediment gradation, flow depth, spur angle and spur length on scouring process. Since most existing studies generally employed uniform sediment; in this study uniform and non-uniform sediment were selected. Experiments were made in a rectangular open channel in uniform flow conditions. Results showed that the effect of the spur dike length and the orientation angle on sediment scour varies with the type of sediment used. Scour volumes were 40% greater in uniform sediments than in non-uniform sediments. Measured scour depth was maximum at spurs perpendicular to the flow, whereas the scour volume was maximum at spurs directed upstream. The scour depth increased with an increase in the spur length; however, effect of spur length on scouring varied at a contraction rate of 0.29 for uniform sediments and 0.36 for non-uniform sediments. A multiple regression analysis was also performed, and four equations were suggested to predict the scour depth and scour volume. Comparisons were made with the literature equations applicable for clear-water scouring to check the suggested equation. Because of a wide range of contraction ratios considered in this study, the equations which considered the contraction effect yielded better estimates.

Experimental and numerical investigation of flow over a spillway bend with different combinations of permeable spur dikes

In this paper, the effects of different combinations of permeable spur dikes installed in the bend section of spillway on flow characteristics and energy dissipation rate were experimentally and numerically investigated. The results indicate that The permeable spur dikes installed in the spillway bend appreciably contributes to the improvement on the water surface uniformity, and the water surface uniformity can reach 90.13% with three permeable spur dikes installed in the bend. The permeable spur dike can lead to different degrees of decrease in the time-averaged longitudinal velocity in each zone of spillway bend. Different from previous study, no circulation zone is formed upstream and downstream of permeable spur dike due to the presence of permeable holes, and the flow upstream of permeable spur dikes could be divided into three distinctly different flow modes according to dye tracing. The presence of permeable spur dikes causes the concentration of TKE zone at concave bank of the spillway bend, except for TKE zone immediately next to the bottom plate. The TKE first increases and then decreases with the increase in the vertical distance from the bottom plate of the spillway bend, exhibiting a typical parabolic distribution. The energy dissipation rate in the spillway bend with permeable spur dike was calculated using a modified integral method, and the dissipation rate can reach as high as 21.08% with three spur dikes installed in the bend.

Experimental Study on Flow Structure around Spur Dikes of Different Types

As water damage phenomenon of spur dike exists generally, spur dike must be maintained in order to ensure its regulation function, but its structure changed in the process of maintenance. In order to find out flow structure around the spur dike of different pattens, through generalized flume model tests, variation characteristics of water surface profile and flow velocity around the spur dike of five different pattens were analysed. The results show that the straight head had a greater influence than hook head spur dike on the water surface profile, circular cross-section had smaller effects than trapezoidal cross-section spur dike on the water surface profile; Velocity of Choke area and contraction order from large to small is trapezoidal cross-section and fan straight head dike, trapezoidal cross-section and arc straight head dike, arc section and arc straight head dam, trapezoidal cross-section and fan hook head dike, trapezoidal cross-section arc hook head dike; Cross section vertical velocity distribution from large to small is trapezoidal cross-section and fan hook head dam, trapezoidal cross-section and circular straight head dike, arc cross-section and circular straight head dam, trapezoidal cross-section and circular hook head dike.

Velocity Field and Turbulence Structure around Spur Dikes with Different Angles of Orientation under Ice Covered Flow Conditions

Spur dikes are well-known structures that are widely used in rivers and coastal regions. Depending on their types, sizes, and orientation angles, spur dikes can substantially change flow characteristics. Results of previous studies indicate that the presence of an ice cover in rivers can cause complicated flow structures. The present experimental study investigates velocity fields and turbulence structures in the vicinity of spur dikes under ice cover with different roughness coefficients. The spur dikes were set up at the following three angles of orientation, 90°, 60°, and 45°. Our results show that the strongest velocity fluctuation occurs immediately above the scour hole surface and very close to the dike tip. The increase in the dike angle toward upstream, the velocity component values increase, leads to a larger scour hole. Results show that an increase in dike angle of each 10° (from 45° to 90°) increases the scour depth between 5% and 10%, depending on flow conditions. Furthermore, the increase in the cover roughness coefficient and the blockage ratio of a spur dike leads to a further increase in turbulence kinetic energy and 3D velocity components values. The findings of this study imply that the appearance of an ice cover can increase turbulence intensities up to nearly 30%.

Effects of permeable groins on river regime in the lower Yellow River

<p><strong>Abstract</strong>: To control the river regime in the wandering river channels is an important work of ecological protection and high-quality development in the Yellow River Basin. Using MIKE21, this study compared and analyzed the control effects of the spur dike group on the river regime under different oriented angles, layout methods, and dam types. The results show that: (1) A optimal oriented angle existed that can efficiently control the river regime. Among the dikes with three oriented angles designed in this study, the spur dam of 45° has the strongest effect blocking the flow, and the corresponding uniformity coefficient of the flow velocity CV reached the lowest value, 0.44, at this time. Under this condition, the flow-velocity distribution was more stable than that of other angles, dynamic pressure on the bank foundation was relatively small, and thus the groins could play a relatively effective influence on the protection of the river bend. (2) The effect on the river regime of a spur-dike group was more than the total amount of all single spur dikes. If only a single spur dike were arranged, the spur dike would keep the high-speed flow away from the concave bank and protect the riparian line with a length of about 80 m. In contrast, if the spur dikes worked as a group, a single spur dike would protect the riparian line with a length of about 100 m. (3) The diversion effect of the permeable groin in the lower Yellow River is the same as that of the solid groin with the same layout. Both the flow reduction rates of the permeable and solid groins are all close to 80%. It is concluded that the impermeable groins can be widely used in the lower Yellow River for it is able to achieve the expected control effect and relatively safe operation condition in virtue of permeability.</p><p><strong>Keywords</strong>: wandering river channel; permeable groins; flow characteristics; MIKE21</p>

Effect of T-shaped spur dike length on mean flow characteristics along a 180-degree sharp bend

An open channel flume with a central 180-degree bend with a rigid bed is designed to obtain a better understanding of the complex flow pattern around a T-shaped spur dike located in a sharp bend. The 3-dimensional velocities are measured by using an acoustic Doppler velocimetry under clear-water conditions. This study’s primary objective is to compare variations of the mean flow pattern along a 180-degree bend with a variety of T-shaped spur dike lengths. In order to do so, parameters such as streamlines, the maximum velocity distribution, and the secondary flow strength under the influence of three T-shaped spur dike lengths will be analyzed and then compared with the case where no spur dikes are implemented. The results show that with the spur dike placed at the bend apex, the mean secondary flow strength at that range increases by approximately 2.5 times. In addition, a 67% increase in the length of the wing and web of the spur dike leads to a 27% growth in the mean secondary flow strength along the bend.