RIVER TRAINING STRUCTURES - GROYNES

RIVER TRAINING STRUCTURES: - GROYNESBy Arun Lila Design Engineer Mahendra Chaudhari Design Engineer Maccaferri Environmental Solutions Pvt. Ltd. ABSTRACT River training is the stabilization of the channel in order to maintain the desired cross section and alignment. Training structures are then necessary in order to protect the channel against the changes that occur due to this disturbance. River training has assumed considerable significance in India due to huge annual recurring damage caused by the floods. The paper attempts to highlight the requirement of Groynes, followed by detail design consideration such as planview shape and cross section of Groynes, length and spacing of Groynes, orientation and permeability of the Groynes, as per International and Indian standards. This paper also emphasize on the scour protection work near the Groynes due to localized scour around the Groynes as per Indian standards. A working example of installation of Groynes using Gabion as a construction material is presented to understand the design procedure. The design instructions given in this paper must be used as guide line and not interpreted as a strict code of practice. Key Words: River training work, Groynes, Gabions 1. INTRODUCTION River training is the stabilization of the channel in order to maintain the desired cross section and alignment. The practice of training a river dates back to the sixteenth century where the Yellow River in China was trained by building embankments along its banks so that the flow would be confined to a single deep channel, which would transport the sediment load to the sea. Modern river training practice, however, started in Europe in the nineteenth century, driven by the demands of the industrial revolution for the purpose of maintaining sufficient channel depth and a better course for navigation. In general, the objectives of river training may be summarized as: To increase the safety against flooding by accommodating the flood flow To improve the efficiency of the sediment transport To minimize bank erosion by stabilizing the course of flow To direct the flow to a desired river stretch To reduce the probability of meandering And in most of the cases the primary objective of river training is to improve navigation by maintaining channel depth Natural processes and human interference may disturb the equilibrium between the sediment load contributed to the channel and the transport capacity of the flow. Seasonal variations in the flow, dredging of the river, construction of a reservoir, and deforestation in the catchment area are all examples of causes of disturbance. Training structures are then necessary in order to protect the channel against the changes that occur due to this disturbance. They could be classified into: I. Longitudinal structures II. Transverse structures In this paper, the focus will be only on the Groynes as a transverse structure. Minimol Korulla GM Design Beckstead (1975). or gabions. Classification according to the method and materials of construction: Groynes may be permeable allowing the water to flow through at reduced velocities or impermeable blocking and deflecting the current. L-head. Classification according to the action on the stream flow: Groynes may be classified as attracting. Classification according to their appearance in plan: Groynes may be built with different plan view shapes. orientation to the flow. and Przedwojski et al. action on stream flow and appearance. II. permeable Groynes may be designed owing to the fact that they disturb the flow much less than solid Groynes. (1975). Richardson et al. are constructed using rock. They are made of stone. These effects controlling flow cause a flow to concentrate affect maintenance of the depth of water for navigation and reduce the velocity of a river bank. spacing between Groynes. gravel. Examples are straight Groynes. Attracting Groynes point downstream.2 DESIGN OF GROYNES The most important considerations involved in Groynes design are plan view shape. deflecting or repelling Groynes.There are two main effects controlling flow. Then another is as the strong velocity of a river bank in a bight can be reduced. As a result. 1995) considers the following. They serve to maintain a desirable channel for the purpose of flood control.A Groyne is a protection technique which can protect a bank and improve scenery in environs at the same. IV. They serve to change the direction of flow without repelling it.1 TYPES OF GROYNES Various types of Groynes can be distinguished according to their construction. not only various habitats but also a refuge as a flood for fishes and microorganisms are provided. beginning at the riverbank with a root and ending at the regulation line with a head. Repelling Groynes point upstream. straight Groynes with pier head. III. bamboo or timbers whereas impermeable Groynes also called solid Groynes. crest elevation and slope. Which of the two types will be used is dictated by the design conditions. inverted hockey shaped Groynes.In particular. rock. The main object of installation of Groyne in rivers is to prevent the breaking of a bank caused by sediment erosion as a flood. According to this phenomenon. Usually impermeable Groynes are designed to be non-submerged since flow over the top of solid Groynes may cause severe erosion along the shanks. Alvarez (1989). cross-section. TRANSVERSE STRUCTURES (GROYNES) Groynes are structures constructed at an angle to the flow in order to deflect the flowing water away from critical zones.(1995). Deflecting Groynes are generally short ones and used for local protection. on the other hand. The first effect is that an existing thalweg can be led to other direction. which brings out problems related to erosion. (2) (3) 2. Functions of Groyne (1) Prevention of river bank erosion:. gravel. In particular. 2. improved navigation and erosion control. or tail Groynes. wing. a strong flow in a bight of a river causes sediment in environs to move. so the direction of flow would be controlled. Improvement of ecological environment and scenery:. as the velocity in a Groynes field would be reduced enough compare to a main stream. they serve to attract the stream flow towards themselves and do not repel the flow towards the opposite bank. hockey shaped. T-head. expected by installation of a bank.2. Permeable Groynes are fabricated from piles. Flow Control:. construction materials and scour. length of the Groynes. . earth. necessary for a full description of Groynes: I. For submerged conditions. a river bank would be protected. Classification according to submergence: Groynes may be designed either as submerged or as nonsubmerged. a flow would be delayed. They serve to repel the flow away from themselves. (as reported by Przedwojski et al. In short Groynes contribute to create ecological environments. or piles. 1 PLANVIEW SHAPE Of the above mentioned types of Groynes according to their appearance in plan view. which stays in the flow.2. The minimum extent of bank protection determined from Figure 1 should be adjusted according to field inspections to determine the limits of active scour. Providing the major principle are recognized and incorporated.3) . L-head. The range of conditions. functions and construction material means that design becomes a judgmental process which must rely heavily on the experience and common sense of the designer. the straight Groynes is set at an angle from the bank and has a rounded head to provide extra volume and area for scour protection at the outer end.The purpose of Groynes design to ensure a set of structures which Are of a length and height to maximize their effectiveness Are located and oriented to maximize their effectiveness Are able to withstand bed scour adjacent to the structures and Have sufficient structural strength to withstand hydraulic and debris forces without failure Firm design rules for Groynes not exist. less scour at their head. The working length is usually kept between the lower and upper limits of the mean depth and a quarter of the mean width of the free . and economics of construction. wing or tail Groynes have larger sediment deposits between Groynes. channel surveys at low flow. and aerial photography and field investigations at high flow.1. Figure:. Flexibility in the design process can be lead to innovative implementations and major cost saving without sacrificing effectiveness. The design instructions given in this paper must be used as guide line and not interpreted as a strict code of practice. Hockey-shaped Groynes have scour holes that are more extensive in area than the T-head Groynes. 2. purpose. The total length of the Groynes includes the anchoring length. spacing. The T-head Groynes is normally set at a right angle from the bank and it has a straight shank with a rectangular guide vane at the outer end. Extent of protection required at a channel bend (after USACE (1981)(11) ) Groynes length depends on the location. and the working length. The length can be established by determining the channel width and depth desired. Figure 1 was developed from USACE(1981)(11) studies of the extent of protection required at meander bends.2 LONGITUDINAL EXTENT & LENGTH OF THE GROYNES The longitudinal extent of channel bank requiring protection is discussed in Brown (1985)(1.2. provide greater protection to the banks and are more effective in channelization for navigation when the length closes 45 to 65 percent of the gap between Groynes. which remains embedded in the bank. 2. is a function of Groynes permeability and the ratio of Groynes length to channel width. and purpose.2. If the Groynes are spaced too close together on the other hand. Thus assuming angle of repose of sand to be 2.5H : 1V & anticipated maximum depth of scour below bed be ds. and cause a hindrance to navigation. Impermeable Groynes are usually installed with lengths of less than 20 percent while permeable Groynes have been successful with lengths up to 25 percent of channel width. If the spacing between Groynes is too long. Figure:. The flow expansion angle. to keep a spacing of 1. In case of wide. permeability. and angle to the bank. Richardson et. It is related to river width. the protrusion of the Groynes in the deep channel should not exceed 1/5 th of the width of the channel on which the Groynes is proposed excluding the length over the bank. construction costs will be higher and the system would work less efficiently without making best use of each individual Groynes.2. Groynes length. orientation to the flow.3 SPACING BETWEEN GROYNESS The spacing between Groynes is measured at the riverbank between their starting points. The length of bank protected measured in terms of projected Groynes length is essentially constant up to Groynes lengths of 20 percent of channel width for permeable and impermeable Groynes. Groynes angle. a meander loop may form between Groynes.5ds. Normally the effective length of Groynes should not exceed 1/5th of width of the flow in case of single channel. although there exists successful examples of bank protection with short Groynes spaced apart 10 to 100 times their length where the banks are protected with riprap or vegetation. Long and far apart spaced Groynes may contract the flow resulting in channel degradation and bank erosion..5 to 6 times the upstream projected Groynes length into the flow. Field installations of Groynes have been successful with lengths from 3 to 30 percent of channel width. 2. or the angle at which flow expands toward the bank downstream of a Groynes. Figure 2 indicates . This ratio is susceptible to alteration by excavation on the inside of the bend or by scour caused by the Groynes installation. the length should be more than 2.al. it is often expressed as a multiple of the Groynes length. and the degree of curvature of the bend. The length of both permeable and impermeable Groynes relative to channel width affects local scour depth at the Groynes tip and the length of bank protected. Relationship between Groynes length and expansion angle for Groynes permeability (Brown (1985)(2)) Groynes spacing is a function of Groynes length. The anchoring length on the other hand is recommended to be less than a quarter of the working length. In order to obtain a well defined deep channel navigation. shallow & braided rivers. bank curvature. However.surface respectively. only the most permeable Groynes were effective at greater lengths. As per IS 8408 : 1994 the Groynes length should not be less than required to keep the scour hole formed at the nose away from the bank. (1975) recommends a spacing of 1.5 to 2 times the Groynes length is recommended. whereas for bank protection the ratio of spacing to Groynes length is less and distances from 2 to 6 times the Groynes length are generally used. velocity of flow. Laboratory tests indicate that diminishing returns are realized from Groynes lengths greater than 20 percent of channel width. However. Each orientation affects the stream in a different way and results in different deposition of sediment in the vicinity of the Groynes. Next. and deflecting Groyne. . Therefore.5 times its effective length. Figure:. Groynes may be oriented perpendicular to the flow or be inclined either upstream or downstream. The arc describing the ends of Groynes projecting into the channel will be essentially concentric with the arc describing the desired flow alignment. permeable retarder Groynes or retarder structures may be appropriate. point upstream. The amount of deposition between Groynes is maximized in case of upstream inclination due to their ability to protect bank areas upstream and downstream of themselves. A Groynes pointing downstream is an attracting Groynes. which attracts the stream flow towards itself. This may approximately describe the existing concave bank or a new theoretical bankline which protects the existing bank from further erosion. If the flow alignment must be altered in order to reverse erosion of the bank or to alter the flow alignment significantly.that the expansion angle for impermeable Groynes is an almost constant 17°. depending on whether there is a need to arrest erosion of the concave bank or reverse erosion that has already occurred. The desired flow alignment may differ from existing conditions or represent no change in conditions. which deflect the flow away from the bank. Figure 4 defines the Groynes angle such that an acute Groynes angle means that the Groynes is angled in an downstream direction and an angle greater than 90° indicates that the Groynes is oriented in a upstream direction. The distance from this arc to the arc describing the desired bank line. fixes the spacing between Groynes.4 ORIENTATION OF THE GROYNESS Groynes orientation refers to Groynes alignment with respect to the direction of the main flow current in a channel. This arc will represent the desired extreme location of the thalweg nearest the outside bank in the bend. along with the expansion angle. A Groyne that is oriented upstream causes more deposition than a perpendicular one at the downstream bank and also at the area upstream where a reverse eddy is formed and causes suspended load to settle. Also. deflector Groynes or retarder/deflector Groynes are appropriate. Groynes of this kind are best suited for bank protection and sedimentation purposes. If the need is to arrest erosion. Repelling Groyne. Groynes spacing in a bend can be established by first drawing an arc representing the desired flow alignment (Figure 3). Groynes spacing in a meander bend (Brown (1985)(2)) As per IS 8408 1994 the spacing of the Groynes is normally 2 to 2. Groynes with 35 percent permeability have almost the same expansion angle except where the Groynes length is greater than about 18 percent of the channel width. The arc representing the desired flow alignment may be a compound circular curve or any curve which forms a smooth transition in flow directions. draw an arc representing the desired bankline.3. 2. which repel the flow away. For site specific cases model studies may be conducted.2. draw an arc connecting the nose (tip) of Groynes in the installation. 4. . Figure:. Groynes that are perpendicular to the flow have protection over a smaller area.5. result in greater scour depth at the tip. The flow towards the root of the downstream Groynes threatens the surrounding bank area as well as the Groynes itself. Therefore. best performance is obtained by perpendicular or downstream pointed Groynes. (2001)) No consensus exists regarding the orientation of permeable retarder/deflector Groynes and impermeable deflector Groynes. and they perform this function equally as well without respect to the Groynes angle. all retarder Groynes should be constructed at 90° with the bank for reasons of economy. and have a greater tendency to accumulate debris. Downstream facing Groynes are not suitable for bank protection purposes due to their attracting effect on the flow. Permeable retarders Groynes are usually designed to provide flow retardance near the streambank. Groynes orientation at approximately 90° has the effect of forcing the main flow current (thalweg) farther from the concave bank than Groynes oriented in an upstream or downstream direction.al. Scour adjustment for Groynes orientation (Richardson et. There is some agreement that Groynes oriented in an upstream direction do not protect as great a length of channel bank downstream of the Groynes tip. Since Groynes oriented normal to the bank and projecting a given length into the channel are shorter than those at any other orientation.Figure:. Definition sketch for Groynes angle (Karaki (1959)). For the purpose of maintaining a deep channel to improve navigation on the other hand. while Groynes with permeability of 35 percent or less caused bank erosion similar to the effect of impermeable Groynes. i. the degree of flow retardance and velocity reduction required. Richardson et. al (2001) Figure:. A method to adjust scour depth for permeability is presented in the following section. Impermeable Groynes. Subsequent Groynes downstream should all be set normal to the bank line to minimize construction costs. and the severity of the channel bend.5 GROYNES PERMEABILITY The permeability of the Groynes depends on stream characteristics. 2.. flow passes over the crest of the Groynes generally perpendicular to the Groynes as illustrated in Figure 6. can create erosion of the stream bank at the Groynes root. Under submerged conditions. Where bends are mild and only small reductions in velocity are necessary. Impermeable Groynes can be used on sharp bends to divert flow away from the outer bank. Above a permeability of 35 percent. The lateral extent of scour can be determined from the depth of scour and the natural angle of repose of the bed material the expansion angle downstream of Groynes. This can occur if the crests of impermeable Groynes are lower than the height of the bank.more positive flow control is achieved with Groynes oriented approximately normal to the channel bank. Groynes oriented in an upstream direction cause greater scour than if oriented normal to the bank. in particular. The implication is that Groynes orientation affects the length of bank protected only because of the projected length of the Groynes along the channel bank.e. highly permeable Groynes can also provide required bank protection under more severe conditions where vegetation and debris will reduce the permeability of the Groynes without destroying the Groynes. Figure 5 can be used to adjust scour depth for orientation.6. However. and Groynes oriented in a downstream direction cause less scour. It is recommended that the Groynes furthest upstream be angled downstream to provide a smoother transition of the flow lines near the bank and to minimize scour at the nose of the leading Groynes. the length of bank protected decreases with increasing permeability. It should be noted that permeability also affects scour depth. highly permeable retarders Groynes can be used successfully. Laboratory studies of Groynes with permeability greater than about 70 percent were observed to cause very little bank erosion. Figure 7 shows the results of laboratory tests of the effects of permeability and orientation on the expansion angle of flow downstream . This is acceptable provided the bed load transport is high.2. Flow components in the vicinity of spurs when the crest is submerged (Brown (1985)(2)) Permeability up to about 35 percent does not affect the length of channel bank protected by the Groynes. Scour along the stream bank and at the Groynes tip are also influenced by the permeability of the Groynes. the angle of flow expansion downstream of the contraction at the Groynes is about 17° for impermeable Groynes for all Groynes angles. Figure:. Groynes with permeability up to about 35 percent can be used in severe conditions but permeable Groynes may be susceptible to damage from large debris and ice. To avoid overtopping the crest elevation should be higher than the expected levels of water. the crest should be at least as high as the bank. less material needed for construction. when submerged. expansion angle (Brown (1985)(2)) 2.2. High permeability Groynes are suitable for use where only small reductions in flow velocities are necessary as on mild bends but can be used for more positive flow control where it can be assumed that clogging with small debris will occur and bed load transport is large.25 due to their advantages of reducing scour at the Groynes end. sloping crested Groynes work best normal or angled upstream. For this figure. SLOPE & CROSS SECTION OF GROYNES The crest elevation of Groynes depends on the purpose and possible problems due to overbank flow. sloping-crested Groynes are recommended by Alvarez (1989) with a slope of 0. Impermeable Groynes provide more positive flow control but cause more scour at the toe of the Groynes and. Richardson et al . Groynes lengths were 20 percent of the channel width projected normal to the bank. Figure:. whereas.7 Groynes permeability and spur orientation vs. For bank protection. faster deposits of sediment between Groynes. level crested Groynes work best normal to the flow or angled downstream. cause erosion of the stream bank. For navigation channel control.1 to 0.of Groyness. (Brown (1985)(2)) From the above discussion.6 CREST ELEVATION.8 Groynes Crest Sloping and Level (Courtesy of Maccaferri ) For bank protection. Crests may be either level or sloping downwards from the bank towards the end of the Groynes (Figure 8). it is apparent that Groynes of varying permeability will provide protection against meander migration. ------------------------------Eqn 2 . For permeable Groynes. Most failures of the river training structures result from an underestimation of depth of scour. impermeable Groynes should be designed so that overtopping will not occur at the bank. The minimum crest width of 1m is controlled by the equipment placing the Groynes and wider crests make placing easier. Permeable Groynes. impermeable Groynes should be equal to the bank height. Less permeable retarder/deflector Groynes which consist of a soil or sand embankment should be straight with a round nose.(1975). Q = discharge in cum/sec. However. However. The depth of scour for different portions of Groynes can be adopted as per IS 8408: 1994 o Nose 2. The crest of impermeable Groynes should slope downward away from the bank line. straight Groynes should be used for most bank protection. The top width of embankment Groynes should be a minimum of 1 m (3 ft.25 to 1:5. 2. highly permeable Groynes consisting of jacks or tetrahedrons are dependent on light debris collecting on the Groynes to make them less permeable. in particular erosion of the bed adjacent to the river training structure. Impermeable Groynes are generally designed not to exceed the bank height because erosion at the end of the Groynes in the overbank area could increase the probability of outflanking at high stream stages. In general. Straight Groynes are more easily installed and maintained and require less material. Groynes permeability and Groynes orientation vs. In general a top width equal to the width of a dump truck can be used.2. q=intensity of discharge in cum/sec/m. As per IS 8408 1994: the top width of Groynes should be 3 to 6m as per requirement the slopes of the side & nose the Groynes would be 2:1 to 3:1 depending upon the material used.5 D o Transition from nose to shank and first 30 to 60m in upstream 1. in many cases the top width will be dictated by the width of any earth moving equipment used to construct the Groynes.0 D o Transition from nose to shank and first 15 to 30m in downstream 1. the width depends on the type of permeable Groynes being used. which could cause damage by particle erosion or damage to the stream bank. expansion angle (Brown (1985)(2)). The crest width ranges from 1to 6m and side slopes from 1:1.76 d1/2. general or a combination of both. should be designed to a height that will allow heavy debris to pass over the top. The expected scour near the structure during the construction and during the service is one of the most important aspects to consider during design.). If flood stages are lower than the bank height.0 D to 2. and in particular those constructed of light wire fence. following formula may preferably used D = 1. In which D = 0.0 D Where. D = The depth of scour below HFL estimated using Lacey’s formula. When the discharge intensity is known.5D o Next 30 to 60M in upstream 1. Therefore the expected scour depth should be taken into consideration in the determination of the base depth of the Groynes. and f = silt factor = 1. Scour Apron should be placed on the upstream and downstream faces as well as on the nose of the Groynes to inhibit erosion of the Groynes.7 SCOUR PROTECTION FOR THE GROYNES River training works should be designed to resist scour. Bank erosion is more severe if the Groynes are oriented in the downstream direction. Where d is the mean diameter of river bed material in mm.473 (Q/f)1/3 ------------------------------Eqn 1 Where. Use of a sloping crest will avoid the possibility of overtopping at a low point in the Groynes profile.33 (q2/f)1/3 Where. The side slopes of the Groynes should be 1V:2H or flatter. because it is difficult to construct and maintain a level Groynes. Where stream stages are greater than or equal to the bank height. The crest profile of permeable Groynes is generally level except where bank height requires the use of a sloping profile. For Groynes scour can be localized. V – Velocity on m/s.5 Dmax Nominal or No Apron 1.0 Dmax Nominal or No Apron Detailed plan & Sections drawings of straight Groynes as per IS 8408:1994 is shown in Appendix:-1 Thickness of Loose stone Pitching as per IS 8408: 1994 Thickness of pitching should be equal to two layers of stones determined for velocity from equation given below in the case of free dumping stone W= Where 0. Ss – Specific gravity of stones.Angle of repose of Thickness of protection layer should be checked for negative head created due to velocity from the following formula T= V2 2 g (S s − 1) ------------------------------Eqn 5 Where. the shape of the crates as far as possible cubical.02323S s 6 V 3 K (S s − 1) 1 ------------------------------Eqn 3  sin 2 θ  K = 1 −  sin 2 φ     2 ------------------------------Eqn 4 .5 Dmax 1. should be PVC coated as per International standards.I wire of adequate strength and should be with double knots.5 Dmax 1.21 ------------------------------Eqn 6 D50 – Mean diameter of stone used in crates in mm. φ . θ . W – Weight of stone in Kg.Angle of sloping bank.Shape and Size of Launching Apron as per IS 8408: 1994 o o o o o o Nose at upstream Transition from nose to shank and first 30 to 60m in upstream Next up to upstream bank line Nose at downstream Transition from nose to shank and first 15 to 30m in downstream Next up to downstream bank line 1. T – Thickness in m. The stone size should be larger than opening of the crates. Crates should be of made of G. The thickness of crates or Gabions is decided on the basis of the Eqn 5 the condition that the mass of each crate should not be less than that determined on the basis of velocity consideration in Eqn 3 for Gabions or crates.245 + 0.864 (D50 ) 0. protection material. For estimating it an empirical relation between void ratio and mean diameter of stone in mm is as follows: e = 0. V – Velocity in m/sec. the mass specific gravity of the crate is required to be worked out to account for the porosity. Ss – Specific gravity of stones Thickness of Wire Crates or Gabion as per IS 8408: 1994 In case of crates. . The mass specific gravity of the crates can be worked out from the formula given below Sm = (1-e)Ss ------------------------------Eqn 7 For working out the volume of crates Sm should be used instead of Ss in Eqn 3. indeed will allow the water to pass through it and will help in protecting downstream bed. Step 1. To reduce scour at the bridge abutment & piers by aligning flow in the channel with the bridge opening. For the present scenario as per plan view appearance the straight Groynes is set an angle from the bank and has a rounded head to provide extra volume and area for scour protection at the other end.8 DESIGN EXAMPLE OF GROYNE INSTALLATION We have assumed a location at which a migrating bend threatens an existing bridge as shown in Figure. Type of Groynes Impermeable deflector Groynes are suitable to accomplish these objectives and the stream regime is favorable for the use of this type of countermeasure. as indicated in Figure 2. seven Groynes will be required. Therefore for the present example the effective length of Groyne is = 1/5 x 50 = 10 m. To stop migration of the meander before it damages the highway stream crossing. The expansion angle for this Groyne type is approximately 17° for a Groyne length of about 20 percent of the desired channel width. It has been assumed that for this particular site the conditions are favorable for the use of Gabions as a construction material. Ultimately. It has been desired to achieve the 30% porosity of the Gabions. Length and Expansion angle of Groynes As per IS 8408:1994 the effective length of Groyne should not exceed the 1/5th (20 percent) of the desired river width.2. Although the number of Groynes is not known in advance. Figure 9. 9. Step 2. based upon the following design example. . Example of Groynes design. Existing bank line conditions are shown with a solid line. the Groynes (and other design steps) are shown as dashed lines on Figure 9 as they will be specified after completing the following design example. We have assumed that the width of the river from the desired (North) bank line to the existing bank line is 50m and the other river flow parameters are assumed and given in appendix 2.2. Objectives of Groynes installation:• • • To establish a different flow alignment & to reverse erosion of concave (outer side) bank. smoothly joining the left bank at the upstream extremity of eroded bank . and been shorter and more economical.2. Detailed plan of the Groyne as per design is shown in appendix 3.2. For an actual location.5 times of its effective length . It may be desirable to place gabion mattress protection on the stream bank at the abutment. Groynes are set at 90° to a tangent with the arc for economy of construction. Visualize both the high-flow and low-flow thalwegs. up to the existing bed elevation at the pier at the angle of repose. from the desired bankline to the Groyne tips (Figure 9) would be: The effective length of Groynes = 1/5 x 50 = 10 m Step 5. but might have caused excessive local scour. The calculation & supported assumed data for the presented working example is shown in appendix 2.Step 3. The seventh and last Groyne upstream is shown oriented in a downstream direction to provide a smooth transition of the flow approaching the Groyne field. Locate First Groyne Step number five is to locate Groyne number 1 so that flow expansion from the nose of the Groyne will intersect the stream bank downstream of the abutment. If the extent of scour at this Groyne overlaps local scour at the pier. the Groyne spacing. the first Groyne could be considered to be either the upstream end of the abutment or guide bank if the Groyne field is being installed upstream of a bridge. and decreases scour at the nose of the Groyne. Last Groynes should be anchored well into the bank to prevent outflanking. Design of Scour protection work using Gabions as per IS 8408:1994 Scour depth & scour apron length for different parts of Groynes is calculated as per section 2. deposition will be encouraged between the desired bank line and the existing eroded bank. determined in Step 5). This is accomplished by projecting an angle of 17° from the abutment alignment to an intersection with the arc describing the nose of Groynes in the installation or by Eqn 8. Thus.7. Using this Groyne spacing. This Groyne could have been oriented normal to the existing bank. therefore Minimum S = 10 x 2. The thickness of the Gabion mattress is calculated on the Groynes slope on river bed. Step 4. S. total scour depth at the pier may be increased. using dimensions as illustrated in Figure 3 (i. Sketch Desired Thalweg The third step is to sketch the desired thalweg location (flow alignment) with a smooth transition from the upstream flow direction through the curve to an approach straight through the bridge waterway (Figure 9).. concentric with the desired bankline alignment. L.e. the spacing. would be: S=L x cot θ=10 x cot17° = 33m ---. also three alternatives of Groynes cross section using Gabions has been shown in the appendix 3. Alternatively. it would be necessary to examine a greater length of stream to establish the most desirable flow alignment. Hence 33m spacing is ok. the size of the scour hole at the Groyne directly upstream of the bridge should be estimated. Furthermore. This can be determined by extending the maximum scour depth at the Groyne tip. Then draw an arc representing the desired bank line in relation to thalweg locations.5 = 25 m. Step 6. Step 6.Eqn 8 As per IS 8408: 1994 the minimum spacing of Groyne should be 2 to 2. The . S. The theoretical or desired left bank line is established as a continuation of the bridge abutment and left bank downstream through the curve. Sketch Alignment of Groyne Tips The forth step is to sketch a smooth curve through the nose (tip) locations of the Groynes. Using a guideline of 1/5th (20%) of the desired channel width for impermeable Groynes (see Section 2. Orienting the furthest upstream Groyne at an angle in the downstream direction provides a smoother transition into the Groyne field.2) the distance. Locate Remaining Groynes Groynes upstream of Groyne number 1 are then located by use of Eqn 8. Vegetation growth and prevents scouring of downstream bank. “The design of Groyness for river training. D. Vol. “Flow near groyne-dike structures. Stevens. Federal Highway Administration. HY3. and then the river itself should follow the nature system to create topography formation. 382-388. 1985. construction. “Bed topography and local scour in rivers with banks protected by groynes. Report CER59SSK36. Washington. V. D. J. Washington.C. and Simons. Alvarez.F. 6. D. B.. Lagasse. Washington. construction viability. 4. ASCE. 2.11.2. pp. 7. Hydraulic Design Series No.A.A. Brown.. Przedwojski.S. R. 4. IAHR congress. 2. Rajaratnam. 8. which make them popular worldwide. IS 8408:1994 Planning and Design of Groynes in alluvial river Guidelines. 6." Report No. McLean. Brown. B. N. Prepared for the Federal Highway Administration. and Nwachukwu. 296-301. Army Corps of Engineers. Federal Highway Administration. 1989. "Hydraulic Model Study of Groynes Dikes for Highway Bridge Openings. 1959. New Orleans. B. Brazil. Federal Highway Administration. Brown. Blazejewski.A.S... "River Engineering for Highway Encroachments Highways in the River Environment. S. (1995).9 SUMMARY AND CONCLUSION 1. cost. E. 109. E. A. (1983). Przedwojski. D. K. 9. 1985. 1985. model experiments for a relevant river. S. M. 1981.selection of suitable alternative depends upon important of structure. 100 Federal Highway Administration." Final Report to Congress.. The ecological connectivity of Gabion Groynes increases through the opening in the Gabion Groynes. (1995). 33(2). 5.” Journal of Hydraulic Div.. 2001. 3. and P. Karaki. REFERENCE 1.V.C. and Pilarczyk. (1975). "Streambank Stabilization Measures for Highway Engineers. River training techniques fundamentals. availability of stone & other geotechnical. FHWA-IP-89-016. 257-273. 2. Brown." Colorado State University.” Proceedings 1989 National Conference On Hydraulic Engineering. Clyde. No. 3. (1989)...." FHWA/RD84-101.C. and E. Final Report. "The Streambank Erosion Control Evaluation and Demonstration Act of 1974." FHWA/RD-84. 12. A.S. The opening allows the better migration of species. Simons. Final Report. September.A. Sao Paulo. 47 pp. 13. . S. D. VA. 10. 11. 463-480.A. W.C. U.” XVIth . "Design of Spur-Type Streambank Stabilization Structures. A. FHWA NHI 01-004." FHWA/RD-84101. "Design of Groynes-Type Streambank Stabilization Structures. S. B. "Design of Riprap Revetment." Hydraulic Engineering Circular No. environmental & hydraulics stability. pp. D. Firm design rules for Groynes not exist. Balkema. Rotterdam. To install Groynes properly it is required to take four-steps: the fundamental design. Richardson. Civil Engineering Section. Washington.. The design instructions given in this paper must be used as guide line and not interpreted as a strict code of practice. M.. Executive Summary and Conclusions. S.” Journal of Hydraulic Research. Among the different types of structures for river Groynes are most nature friendly. design and application. “Design of groins and Groynes dikes. Richardson.B. APPENDIX:-1 PLAN AND SECTION OF GROYNES (As per IS 8408:1994) . 3 Weight of Stone W= 150 0.5 942. 3 Weight of Stone W= 26.5 m thickness with diaphragms at every 1 m Volume of Gabion (1 x 1 x 0.6 m/s cum/sec m cum/s/m Degree m m Thickness of Gabion From Eqn. 6 The mass specific gravity of Gabions (Sm) From Eqn.44753 425.446 0.5 )= Mass of Stone Weight of Stone in each gabion is higher than that computed by Eqn. 5 Assume Gabion Mattress of 0. 5 Assume Gabion Mattress of 0. 3 0.56 0. 3 0.5 )= Mass of Stone Weight of Stone in each gabion is higher than that computed by Eqn.7 ASSUMED DATA Velocity of Water (V) Discharge (Q) Desired Width of River (W) Discharge Intensity (q) Angle of Repose of Fill Material ( Ф ) HFL Free Board Specific gravity of stones (Ss) Thickness of Gabion Protection work on Bed for Scour Protection Assumed Opening of Gabions 100mm x 120 mm Assumed D50 of stones in Gabions Void ratio (e) From Eqn.27517 1.551 0.5 942.46 Kg m Degree Thickness of Gabion From Eqn.5 1 2.2.APPENDIX:-2 PROTECTION WORK CALCULATION FOR WORKING EXAMPLE AS PER SECTION 2.5 m thick Gabion Mattress can be adopted for the Launching apron on Bed Thickness of Gabion Protection work on Side Slope of Groynes Assumed Side slope of Groynes is 2H:1V Slope Factor K From Eqn. 7 From Eqn.282 cum Kg Hence 0.282 cum Kg . 4 From Eqn.88457 190.5 m thickness with diaphragms at every 1 m Volume of Gabion (1 x 1 x 0.8 2000 50 40 30 4.46 Kg m mm 3. 0558 5.5 times of Effective length than Spacing S = 25 m 5.1673 24.5837 11.5558 11.5 m thick Gabion Mattress can be adopted for the Launching apron on Bed Calculation For Depth of Scour Assumed Silt Factor f = Lacey's Scour Depth (D) From Eqn.1115 16.5 m 3 to 6 3 m m 10 27.5279 m m m m m m 1 15.0558 11.0558 11. 1 Maximum Scour Depth For Nose Portion consider Dmax = 2 D Transition from nose to shank and first 30 to 60m (Assumed up to Scour Depth) in upstream Next up to upstream River Bank Transition from nose to shank and first 15 to 30m (Assumed up to 50 % of scour Depth ) in downstream Next up to downstream River Bank Calculation For Length of Scour Apron Nose at upstream Transition from nose to shank and first 30 to 60m(Assumed up to Scour Depth) in upstream Next up to upstream (Assumed up to Scour Depth) River Bank line Nose at downstream Transition from nose to shank and first 15 to 30m (Assumed up to 50 % of scour Depth ) in downstream Next up to downstream (Assumed up to Scour Depth) bank line (50% of Maximum Scour Depth ) Check For Length of Groynes As per Desired Width of River Effective Length Total Length of Groynes should be Greater than 2.6394 m m 33.Hence 0.0558 33.5 times Scour depth Calculation For Top Width of Groynes Top Width of Groyne Assumed Width of Groynes Calculation For Height of Groynes Top level of Groyne Spacing of Groynes Minimum Spacing of Groyne should be 2 to 2.0558 22.5 times of its effective length Assumed 2.1673 11.0558 m m m m m m m .8755 11. APPENDIX:-3 PLAN VIEW AND SECTION OF WORKING EXAMPLE .