Bridge Scour in Nonuniform Sediment Mixtures and in Cohesive Materials: Synthesis Report

3. EFFECTS OF GRADATION AND COARSE MATERIAL FRACTION ON ABUTMENT SCOUR

3.1 GENERAL

The majority of currently available abutment scour predictors, including some of the methodologies recommended by FHWA, relate abutment scour to a characteristic length (such as flow depth, Y, abutment protrusion length, a, etc.) and the approach flow Froude number. Some of these regression equations include sediment size and gradation as independent variables. However, since these relationships were developed from limited laboratory and field data, they cannot reflect effects due to sediment size properties; therefore they often result in unrealistic scour estimations. As shown in figures 26(a) and 26(b), they provide no guidance when applied to graded sediment mixtures such as those used in the present experimental study.

Figure 26. Variation of dimensionless abutment scour with Froude number: (a) abutment protrusion length, a, as characteristic length; (b) as characteristic length.

This chapter presents results of the experiments to analyze effects of gradation and coarse material fraction on abutment scour. As a result of this study, 384 new abutment scour data points covering a range of selected sediment mixtures have been contributed to the literature. Parameters controlling abutment scour in mixtures have been identified, and two new relationships for estimating abutment scour have been developed. The close agreement of these new relationships with laboratory experiments is encouraging.

3.2 EXPERIMENTAL SETUP AND MEASUREMENTS

This section presents details of the experimental setup, testing procedure, laboratory facilities, and measuring equipment that were utilized in the abutment scour experiments. First, the three laboratory test flumes used to study the effects of gradation on abutment scour are described. Next, individual measurements along with associated instrumentation and their accuracy are discussed. These measurements include initial and final bed topographies and slopes, hydraulic grade line, flow discharge, flow velocity, scour hole topography and its evolution with time, flow visualization, grain size distribution, and sampling of the armor layer. Finally, the experimental procedure followed for the various runs is discussed along with measures taken to ensure the accuracy and reliability of results.

Laboratory Flumes

Three laboratory flumes, designated as the hydrodynamics flume, sedimentation flume, and the river mechanics flume, were simultaneously utilized for conducting the abutment scour experiments in noncohesive sediment mixtures. The former two flumes are sediment recirculating facilities, while the latter does not recirculate sediment. All flumes are housed at the Hydraulics Laboratory of the Engineering Research Center at CSU. The water supply to these flumes is from the nearby Horsetooth Reservoir. The temperature of the water in the laboratory is controlled through a heating pipe system.

Hydrodynamics Flume

The hydrodynamics flume is a tilting, water and sediment recirculating laboratory facility. The flume is 0.6 m wide, 0.75 m deep, and 18 m long and is made of a steel bottom and Plexiglas side walls to facilitate visual observations. The facility is rigidly supported on U-shaped steel frames located every 1.2 m and is equipped with angled upper and lower flange stiffeners. The bottom flanges are supported on two I-beams spanning the full length of the flume and ground supported at the far upstream, middle, and far downstream. Two carefully leveled guide rails are mounted on the top flanges to provide an escorting track for the measuring carriage. The flume can be tilted around its middle lateral axis through the synchronized operation of two mechanical jacks located at the upstream and downstream ends. Flow is supplied to the flume from a ground sump via a 0.3-m diameter steel pipe line, equipped with a 0.15-m diameter bypass for fine tuning of the flow, and a 20-HP centrifugal pump. The flow is first introduced to an upstream head box equipped with a multilayer screen containing gravel at its outlet to serve as a flow guide to provide uniform velocities and turbulence characteristics at the entrance of the flume. A wave suppressor is then introduced to ensure the accomplishment of the previous concerns. The flow depth is controlled by a downstream rotating gate hinged across the bottom of the flume, spanning the full width, and operated by a system of pulleys. Due to the tail gate control and the nature of the flume, a back water effect is sometimes noticed, causing the water depth to increase as the gate is approached. A 23-cm thick uniform sediment layer prepared from the tested mixture is spread along the full length of the flume, with provisions made for a downstream 1.8-m long sediment trap and an upstream 1.8-m long transition zone. The upstream transition zone is composed of coarser sediments, with a sloping profile carefully designed to provide excess friction to ensure the existence of fully developed turbulent flow and with a boundary layer hitting the free surface far upstream of the study reaches for all flow conditions.

Sedimentation Flume

The sedimentation flume is an elevated sediment transport testing facility that provides for both longitudinal tilting and sediment recirculation. The flume is 60 m long, 2.4 m wide, and 1.2 m deep and allows for slope adjustments up to 3 percent through a system of hydraulic jacks. The flume is constructed from steel plates at the bottom and sides with provisions for Plexiglas windows along specific locations at its side. The structure's skeleton is composed of U-shaped lateral steel frames with cantilevers for sidewalks and supported on box-sectioned longitudinal girders. The upper flanges house guide rails for an electrically motorized measuring carriage that can virtually move to any point in the flume. Three different pumps (125, 150, and 250 HP), with a maximum combined capacity of 3 m³/s, can be simultaneously operated to supply water to the flume from a reservoir sump via three separate steel pipe lines. The flow is first introduced to the upstream head box, which contains several guide vanes and flow straighteners followed by a honeycomb mesh. The flow then passes through a gravel-filled screen succeeded by a wave suppressor. Rapid development of the fully turbulent boundary layer is achieved through an upstream concrete ramp and/or artificial roughening of the entrance zone. The flow depth is regulated through a manually operated downstream adjustable tail gate. The sediment bed is built to a thickness of about 0.4 m, with provisions made for a downstream sediment trap that extends for 6 m. To facilitate drainage of the flume after the experiments, a perforated 10-cm diameter PVC pipe was embedded in the bed material and spanned the full length of the study reach.

River Mechanics Flume

The river mechanics flume is a fixed-slope facility. The flume is 6 m wide, 0.9 m deep, and around 30 m long. The test section, however, was 24 m long, 5.1 m wide, and 0.9 m deep, providing for two Plexiglas viewing sections along one side of the flume and a large upstream reservoir to create uniform entrance conditions. I-beam rails are mounted on the side walls to provide a track for the huge measuring carriage. A 75-HP axial pump of maximum capacity around 0.6 m³/s supplies water to the flume through a 0.6-m diameter pipeline. The upstream main ends in a similar size diffuser located orthogonal to the main flow direction to distribute the flow uniformly across the flume width. The flow then passes through a gravel-filled screen followed by an artificially coarsened concrete ramp that joins the main sediment bed. The setup also provides for a downstream sediment trap and a downstream sill for depth regulation.

Measurements

A series of measurements are needed in order to define the relationship between local scour at abutments and the various hydraulic, geometric, and sediment parameters, both quantitatively and qualitatively. These measurements are described below.

Flow Discharge

The water discharge in all three test flumes was measured through a system of orifice-meter and a differential manometer. For the hydrodynamics flume, two orifice plates were available: one mounted on the 0.3-m diameter main and the other attached to the 0.15-m diameter bypass line. Both orifice-plates are connected to a dual water-mercury manometer for detecting the pressure drop across the ends of the plate. The flow discharge was then computed from the calibration curves for the orifices. The pressure tapping across the orifice plate is connected to the manometer through hard vinyl tubing provided with bleeding valves for drainage and for ensuring an air-free environment. The sedimentation flume is equipped with three similar setups for measuring the discharge, each attached to a different pump. Extreme care was taken to ensure the release of air bubbles entrapped in all manometer lines. The error in measuring the discharge in the hydrodynamics flume is around 3 percent, in the sedimentation flume around 4 percent, and in the river mechanics flume around 5 percent. These error estimates are due to the calibration errors of orifice plates, unsteadiness in the pump discharge, and fluctuations in manometer readings.

Flow Velocity

In the hydrodynamics flume, velocities were measured utilizing two different size pitot tubes and a two-dimensional magnetic flow meter depending on the desired accuracy. A 3-mm diameter minute pitot tube, tapered to a 1.5-mm diameter total head sensor that is connected to a membrane-type transducer, was first used to detect the flow velocity with an accuracy of ±1.5 percent. However, the problems encountered with air entrainment and blockage of the sensing and conveying tubing led to the replacement of this pitot tube with a larger one. The second pitot tube had a 3-mm diameter sensing stem with a pressure take-off diameter of 3 mm and a probe length of 0.3 m. The pressure transducer that was connected to the pitot tubes contained a 0.7 kilo pascal (kPa) steel membrane and is commercially available as P7D±5 PSID SER. 11534. The output signals from the transducer are amplified, filtered, and analyzed by a data acquisition board and a personal computer. The velocities sensed by this device are in the order of ±2.5 percent of accuracy. The second method for velocity measurements in the hydrodynamics flume utilized the 2-D electromagnetic Marsh McBirney, Model 523 flowmeter. The flowmeter consists of a spherical electromagnetic probe with cable and signal processor powered by 6-V DC externally charged with 110-V AC. The probe has a diameter of 12 mm and is mounted on a 6-mm diameter vertical standing rod. The analog signals corresponding to the two orthogonal velocities sensed by the probe are intercepted by a multichannel data acquisition board connected to a personal computer. The sampling frequency was 50 Hz. Overall accuracy of the latter setup is around 3.5 percent.

In the river mechanics and sedimentation flumes, velocities were measured with a one‑dimensional Marsh McBirney, Model 2000 electromagnetic flowmeter with a 2.54-cm elliptic probe and a digital display conversion voltmeter. The accuracy of the flowmeter is reported to be ±2 percent by the manufacturer, and its operating range is from -0.015 m/s to +6.1 m/s within temperature extremes of 0 ^oC to 71 ^oC. Overall accuracy of the velocity measuring setup is estimated to be 5 percent.

Flow Visualization

Examination of flow field in the vicinity of the abutment was achieved through flow visualization techniques, including:

• Surface and subsurface floats made of hollow glass spheres partially filled with a fluid to maintain neutral buoyancy. These floats were 1 cm in diameter and were used in determining separation, reattachment, and reversed flow zones.
• Lightweight plastic pellets sprayed on the water surface gave a good picture of the surface stream lines, especially at low flows.
• Dye injection of potassium permanganate solution with the same density as water was very indicative of the nature of the horse vortex and other subsurface features. Other chemicals were tried but did not provide further improvement.
• Potassium permanganate crystals sprayed on the sediment bed surface, inside the scour hole or around it, provided visualization of boundary currents.
• Video and still picture cameras for documenting various phenomena.

Free Stream Bed and Scour Hole Topographies

The bed topographies for the scour holes and the free stream approaches are measured using point gauges. In all flumes, the standard topography measurement procedure started with the leveling of instrumentation carriages at each measurement location along and across the flume to account for the potential unevenness of tracks. Choosing an arbitrary fixed level, every location in the flume, as identified by its Cartesian coordinates, was assigned a correction factor reflecting its elevation relative to the fixed level.

In the hydrodynamics flume, three different point gauges were utilized for measuring purposes depending on the location and accuracy desired. The bed topographies at four different approach sections were measured for each abutment model to define the upstream bed elevation. At each cross section, the bed level was considered to be the average of 10 measurements evenly distributed across the flume's width. To define bed topography in the vicinity of local scour requires more intensive measurements. A measuring grid of an average of 17 cross sections, with a minimum of 21 points per section, was adopted to describe the scour hole region for each abutment.

A similar procedure was followed for the other two flumes, with provisions made for measuring the initial as well as the final levels. The raw measurements are adjusted with the leveling correction factors for each location and then regressed together to yield the value of the bed slope. Approximately 400 topography measurements were performed for each abutment model per experiment. Due to the large sampling size, the error in bed measurements is considered to be equal to 0.25 of the D₉₀ grain size.

Hydraulic Grade Line

The water surface elevations were measured using point gauges with a resolution of ±0.3 mm. Water surface elevation measurements were conducted at a minimum of three approach cross sections per abutment and at a minimum of five locations across the flume width at each cross section. At every location in the cross section, the water level was considered to be the average of two minimum and maximum detected values, to account for any residual fluctuations in the supply discharge and any surface waves induced by the setup. This tedious procedure assumes an accuracy of 2 percent in the computed water depth. Again the hydraulic grade line is identified through regressing the measured water surface values after being adjusted with the level correction factors. The regression results in high correlation coefficients (R² = 0.95). The velocity head was then added to the hydraulic grade line to define the total energy line.

Sampling of the Armor Layer

Surface samples representing the armor coat formed at the approach to the abutment and inside the scour hole were carefully collected after the experiments were over and the bed was dried. Various techniques, including molten paraffin wax, sticky polymers, modeling clay, scraping the surface, and pebble counting from still photographs, were tried. Among these, the modeling clay method proved to be the most practical and the most accurate.

Soft modeling clay, sometimes treated with castor oil to make it softer, was used to prepare a thin paste around 5 mm thick. The paste was placed at the desired sampling location and gently stamped down under a uniformly distributed applied pressure. The paste was then carefully lifted up, thus collecting a patch of adhered sediments representing the armor coat. After waiting for a short time to allow the paste to become drier, the collected sediments were removed by scraping the surface. If the clay is left on for a long time (one day or more) it becomes very stiff and the removal process has to be done under warm water. The following step was to wash the sediments to make sure that no residual clays are present, then oven dry them and finally prepare them for sieve analysis.

Grain Size Distribution

The relative size distributions for the various sediment mixtures and samples was determined using the sieve analysis method. The sieve sizes used were those defined by the U.S. Bureau of Standards, which represents the sieve number by the number of openings it has per square inch. An average shaking time of 10 minutes was applied for all tested samples.

Experimental Procedure

The experimental procedure for the abutment scour experiments is summarized as follows:

1. The sediment mixture forming the bed of the flume is naturally compacted in layers. A low flow is then introduced to the flume while raising the downstream gate (for the Hydrodynamics and river mechanics flumes), or lowering the downstream gate (for the sedimentation flume), and is allowed to prevail for long enough to saturate the bed and drive away any entrapped air.
2. The flow is stopped and the bed is leveled to the desired elevation. Initial bed levels are then recorded at the desired sections. The bed around the abutments where local scour is expected to occur is protected with specially prepared shields.
3. The flow is introduced to flumes at a very slow rate in order to avoid disturbing the bed topography, especially around the abutments. A depth of flow greater than the desired depth for the experiment is maintained within the flume. The shields around the abutments are then removed.
4. The required flow depth and discharge are then achieved through simultaneous adjustment of the discharge valve and the downstream gate (or sill) position. Recording of scour development with time is immediately started.
5. Water surface elevations and flow velocities are recorded following the procedure given above.
6. Flow visualization and video recording, if any, are then performed.
7. The shut down process includes raising the depth inside the flume through downstream gate adjustment while decreasing the flow rate in steps. At complete shut down, the flume has to be holding a sizable depth of water that is then allowed to drain very slowly. The current step is crucial for preserving the local scour features produced through the run.
8. After allowing the bed to be completely drained, the final bed topographies are recorded, still camera photography is performed, and sampling of the armor layer is conducted.
9. The local scour areas are then replenished with new sediments and the previous procedure is repeated for the next experiment.

3.3 EXPERIMENTAL RESULTS

A comprehensive experimental program was designed to investigate the different aspects of gradation and coarse material fraction effects on local abutment scour. These experiments are categorized into 14 different sets of runs labeled set A through set N. The experimental program was carried out concurrently in three different laboratory facilities. Sets A, B, C, G, H, I, J, K, L, M, and N were performed in the hydrodynamics flume, while sets D and E were conducted in the sedimentation flume. The river mechanics flume was assigned to set F experiments. Sixteen different sediment mixtures and 10 different abutment models were subjected to a range of flow conditions, resulting in a total of 384 different abutment case studies. Tables 8 through 21 present these cases. A summary table of the sediment characteristics associated with the different mixtures utilized in the study is given in table 22.

In the abutment scour experiments presented in this section, the effects of the following parameters on local abutment scour were investigated:

• Effect of mean sediment size, D₅₀ (in sets I, G, and L).
• Effect of sediment gradation, _g (in sets A, B, and C, D-M1, E-M1, and E-M3).
• Effect of the coarsest tenth percentile of the sediment size gradation (sets I, K, and L, M, N, D-M1, D-M2, D-M3, E-M1, E-M2).
• Effect of flow depth, Y (sets H, I, and J).
• Effect of abutment protrusion length, a (all sets).

The following sections present details of each set of experiments and references to related summary tables whenever applicable.

Hydrodynamics Flume Experiments

The majority of the experiments (304 different abutment case studies) were carried out in the hydrodynamics flume. The details of each set of experiments are given below.

Set A Experiments

Set A consisted of 18 different runs (A-1 through A-18). Four abutment models were tested in each of the runs A-1, A-2, and A-3. All the four abutment models had the same length of 11.4 cm in the direction of flow; however, their protrusion lengths (length orthogonal to flow) varied. The abutment with a protrusion length of 2.54 cm was identified as M1, that with a protrusion length of 5.08 cm was identified as M2, that with a protrusion length of 7.62 cm was identified as M3, and that with a protrusion length of 10.16 cm was identified as M4. In runs A-4 through A-18, the 2.54-cm model (M1) was dismantled, since its small size could introduce undesirable scale effects with the selected sediment sizes and therefore could influence the validity of the results. The bed material tested (sediment Type IV) was coarse graded sand with a D₅₀ of 1.8 mm and a _g of 2.1, with an approximate log-normal size fraction distribution. The flow depth to abutment protrusion length (Y/a) varied between 0.5 and 2.0, the average velocity was between 18 cm/s and 40 cm/s, and the mean Froude number ranged from 0.2 to 0.5. Table 8 shows a summary of the experimental conditions for set A runs. It should be noted that flow depth (Y) and flow velocities were all measured at an approach section located at a distance of (10a) upstream from each abutment, where a is the abutment protrusion length.

Set B Experiments

Set B included 16 different runs (B-1 through B-16). Three abutment models (M2, M3, and M4) were tested in each of the runs except for runs B-12 and B-13 where only M2 and M4 were examined. Sediment of Type III, which is a coarse uniform sand with a D₅₀ of 1.8 mm and a _g of 1.17, was used throughout this set. The flow depth to abutment protrusion length (Y/a) varied between 0.3 and 2.3, the average velocity ranged between 0.21 m/s and 0.45 m/s, and the mean Froude number was between 0.25 and 0.6. Table 9 presents a summary of the experimental conditions for set B runs.

Set C Experiments

As shown in table 10, 21 case studies were included in set C (C-2 through C-8). Throughout this series and in the remaining sets that were conducted in the 0.61-m-wide flume, only abutment models M2, M3, and M4 were used. The bed material selected for this set was a coarse graded sand with a D₅₀ of 1.8 mm, a _g of 3.9, and an approximate log-normal size fraction distribution (Type V sediment). The flow depth to abutment protrusion length (Y/a) varied between 0.38 and 1.7, the average velocity (V_u) was between 0.21 m/s and 0.44 m/s, and the mean Froude number ranged from 0.3 to 0.5. A summary of the experimental conditions for set C runs is presented in table 10.

Set G Experiments

This set was designed to test a second uniform medium sand mixture with a D₅₀ of 0.78 mm, and a _g of 1.3 identified as Type II sediment. The set consisted of seven runs, which provided 21 data points as indicated in table 11. The experiments were conducted using a constant flow depth of 0.075 m for M2, 0.08 m for M3, and 0.09 m for M4. Mean velocity in set G experiments varied between 0.13 m/s and 0.3 m/s, and mean Froude number varied between 0.14 and 0.35.

Sets H, I, and J Experiments

Sets H, I, and J were all conducted with fine silica sand with a D₅₀ of 0.1 mm and _g of 1.4 (Type I sediment). Set H consisted of 24 cases, all of which were run for a constant depth of 0.10 m. Set I included 18 study cases, all being tested at a constant depth of 0.075 m, and similarly, set J consisted of 18 tests conducted at a constant depth of 0.05 m. Tables 12 through 14 demonstrate the experimental conditions associated with each set. In each of these sets the most severe flow condition resulted in live bed scour, whereas the rest of the experiments were all conducted under clear-water conditions. For set H, velocities and Froude numbers ranged between 0.01 m/s and 0.33 m/s and between 0.09 and 0.3, respectively; for set I, velocities and Froude numbers ranged between 0.075 m/s and 0.40 m/s and between 0.13 and 0.46, respectively; and for set J velocities and Froude numbers ranged between 0.11 m/s and 0.31 m/s and between 0.15 and 0.44, respectively.

Set K Experiments

Table 15 lists test conditions for the seven runs in the set K experiments using Type VII sediment. The Type VII sediment resembles the Type I sediment in all of its features except that the coarsest 15 percent fraction matches that of sediment Type III. All experiments were conducted at an almost constant flow depth of 0.075 m, while the flow velocity varied from conditions which initiated local scour at the abutments to conditions that resulted in the initiation of live-bed scour (clear-water scour limit).

Set L Experiments

This set of experiments is similar to set B in which Type III sediment with a D₅₀ of 1.8 mm and a _g of 1.17 was used. However, in this set the flow depth was maintained at a constant value of about 0.08 m. Flow conditions for the 24 cases considered in set L are given in table 16.

Set M Experiments

As shown in table 17, 10 different experiments were performed in set M using a constant depth of 0.075 m. The bed material tested was Type VI sediment, which basically had the same D₅₀ and _g as uniform coarse sand of Type III (1.8 mm and 1.17, respectively), while having the D₉₀ (i.e. the same coarsest fraction) of the graded sediment mixture of Type IV. Flow conditions in this set of experiments varied from conditions that initiated scour to conditions that initiated bed forms.

Set N Experiments

This set of experiments is similar to set A, which used Type IV graded coarse sand. However, in these experiments the flow depth was kept at a constant value of 0.075 m. Flow conditions pertaining to set N experiments (27 cases) are given in table 18.

Sedimentation Flume Experiments

Sixty-eight different abutment case studies were tested in the sedimentation flume; these studies constituted about 17 percent of the total number of abutment scour cases involved in this research. All the tests performed in the 2.44-m wide flume were conducted at a constant depth of 0.3 m. A total of eight different sediment mixtures were tested. Five different sand types, all having the same D₅₀ of 0.78 mm but with varying gradation coefficients and ninety-percentile diameters, were selected to study sensitivity to various sediment size characteristics. The experiments are divided into two major sets: D and E.

Set D Experiments

Set D consisted of eight different runs. As shown in table 19, four abutment models were tested in each of these runs. All the abutment models were 0.46 m long (in direction of flow) and were identified as M1, M2, M3, and M4. Abutments M1, M2, and M3 had a protrusion length of 0.22 m, while the protrusion length of M4 was 0.18 m. Abutment models M1 and M4 were used for testing an approximate log-normally graded medium sand mixture of D₅₀ equal to 0.78 mm and _g equal to 2.43 (Type VIII sediment). Abutment M2 was designated for testing a mixture similar to that at M1, but with a coarser upper ten-percentile fraction (Type XI sediment). Similarly, a third mixture (Type X sediment), that was basically Type VIII sediment but with a coarser upper five-percentile fraction, was introduced at abutment M3.

Set E Experiments

Table 20 summarizes the 36 test conditions for the set E experiments. Four abutment models, which were also identified as M1, M2, M3, and M4, with protrusion lengths of 0.22 m and 0.45 m, were used in these experiments. In runs E-1 through E-8, abutment M1 was used for testing a graded medium sand mixture of D₅₀ equal to 0.78 mm and _g equal to 3.4 (sediment Type IX). Abutment M2 was for testing a mixture similar to that at M1, but with a coarser upper ten-percentile fraction (sediment Type XII). A uniform medium sand with a D₅₀ of 0.78 mm and _g of 1.3 (Type II ) was utilized at M3. For comparison purposes, a mixture of sand and clay (70 percent sand and 30 percent clay) was introduced at M4. Runs E-9 and E-10 were conducted using a gravel mixture to examine potential variations due to median sediment size.

River Mechanics Flume Experiments

In the set F experiments, which were conducted in the 5.2-m wide river mechanics flume, a sediment mixture with mean diameter of 0.55 mm, a gradation coefficient of 2.1, and a D₉₀ of 1.3 mm (sediment Type XV) was used. Table 21 summarizes the experimental conditions for this series. Set F experiments were conducted for the qualitative description of the scour hole and related geometric features.

Table 8. Experimental conditions for set A runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Velocity measured along the longitudinal passing through the abutment nose at the approach section.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion
4. All experiments are performed in a 0.61‑m wide flume measured at the approach section.
5. Bed slope is set to a value of 0.0037.

Table 9. Experimental conditions for set B runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Velocity measured along the longitudinal passing through the abutment nose at the approach section.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion.
4. All experiments are performed in a 0.61‑m wide flume measured at the approach section.
5. Bed slope is set to a value of 0.0037.

Table 10. Experimental conditions for set C runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Approach velocity measured along the longitudinal passing through the abutment nose.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion measured at the approach section.
4. All experiments are performed in a 0.61‑m wide flume.

Table 11. Experimental conditions for set G runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Approach velocity measured along the longitudinal passing through the abutment nose.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion measured at the approach section.
4. All experiments are performed in a 0.61-m wide flume.

Table 12. Experimental conditions for set H runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Approach velocity measured along the longitudinal passing through the abutment nose.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion measured at the approach section.
4. All experiments are performed in a 0.61-m wide flume.

Table 13. Experimental conditions for set I runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Approach velocity measured along the longitudinal passing through the abutment nose.
3. Diverted Velocity: Integrated mean velocity across the deflected flow portion measured at the approach section.
4. All experiments are performed in a 0.61‑m wide flume.
5. Bed slope is set to a value of 0.0017.

Table 14. Experimental conditions for set J runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Velocity measured along the longitudinal passing through the abutment nose at the approach section.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion.
4. All experiments are performed in a 0.61‑m wide flume measured at the approach section.
5. Bed slope is set to a value of 0.0017.

Table 15. Experimental conditions for set K runs for abutment scour.

Notes:

1. Average Velocity: Mean velocity prevailing at the approach cross section.
2. Abutment Velocity: Velocity measured along the longitudinal passing through the abutment nose at the approach section.
3. Diverted Velocity: Integrated mean velocity prevailing across the deflected flow portion.
4. All experiments are performed in a 0.61‑m wide flume measured at the approach section.
5. Bed slope is set to a value of 0.0017.

Table 16. Experimental conditions for set L runs for abutment scour.