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Variation in Local Scour Profiles of an Embankment Pond
Available online at www.sciencedirect.com
APCBEE Procedia 5 (2013) 323 – 327
ICESD 2013: January 19-20, Dubai, UAE
Variation in Local Scour Profiles of an Embankment Pond Ayesha Ghulam Rasool and Zahiraniza Mustaffa Civil Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar 31750 Tronoh, Perak, Malaysia.
Abstract This paper intents to identify the variation in local scour profiles of an embankment pond under varying pond water depths. The embankment pond was constructed to regulate the water issuing from the tunnel of a hydropower station before releasing it to the river. To avoid the structural collapse of any hydraulic structure, the scour process is one of the primary factors that must be controlled. Sediments (soils and sands) are composed of aggregation of individual grains that have varying density, volume, shape and orientation. Therefore an investigation is quite important on interactions between the fluid and sediment particles in open and pipe channel flows in hydraulics and river engineering. The variation in pond water level has significant effect on the scour that may occur on the bed of the embankment pond. This paper highlights the variations and suggests for maintaining certain pond water level to lessen the scour hazards.
© 2013 2013The Published ElsevierbyB.V. Selection © Authors.by Published Elsevier B.V. and/or peer review under responsibility of Asia-Pacific Chemical, &under Environmental Engineering Society Selection andBiological peer review responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Key words: Embankment pond; Scour; Baffle Blocks.
1. Introduction Flow from the outflow structure of a hydropower station carries an enormous energy which has the capability to erode surfaces placed at the downstream section, for instance a re-regulating pond. Usually the pond is provided as an intermediate structure to discharge the flows in a controlled manner to the downstream river. To alleviate the scour problem from getting worse, the energy from the supercritical flow must be reduced before it is released directly to the river. In a large stilling basin, the flow pattern that occurs is very complex and depends on several factors. The flow structure is also deeply affected by the presence of a
Corresponding author. Tel.: +601-96071341; fax: +605-365 6716. E-mail address: [email protected]
2212-6708 © 2013 The Authors. Published by Elsevier B.V. Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2013.05.055
324
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
mobile bed [1]. Scouring in excess can gradually undermine the foundations of hydraulic structures and cause failure. Because of its frequent occurrence, scour downstream of hydraulic structures constitutes an important field of research. This paper addresses the problems associated with local scouring of a re-regulating storage pond. The storage pond was designed to accept the flow from the penstock of a dam and further release the discharge to the river in a controlled manner. The pond was fully lined to alleviate the geotechnical risks with the site [2]. Despite the adoption of design procedures of stilling basin and provision of energy dissipating structures at the downstream of the flow, the lining ruptured and caused excessive scouring of the pond bed. A physical model of the re-regulating storage pond is designed at a Froude scale model ratio of 1:36. The model is provided with an energy dissipation system comprising of different baffle block arrangements for effective energy dissipation. An experimental approach is applied to study the effects of varying pond water levels on the local scour occurring on the pond bed caused by moderate and high flows. In this paper, the author intents to cover the following objectives (i) investigate the location and depth of scour, (ii) comparison between the effects of pond water level on associated scour depths and (iii) comparison between the scour occurring along different points in the vicinity of flow. This study will be considered useful whenever the topologic layout of a re-regulating pond/stilling basin is expected to sufficiently reduce the local scour, or in rehabilitation of similar hydraulic structures. 2. Literature Review Naturally, scour occurs due to the erosive action of flowing water including the morphological changes in rivers and also because of the construction of various types of water way structures [3]. Local scour is the erosion of bed surface as a result of the impact effect of flowing water over or through hydraulic structures [4]. The sediment particle lying on the equilibrium scoured bed is acted upon by the drag force FD, lift force FL and the submerged weight of that sediment particle FG as shown in Fig. 1. The scour parameters (depth dm and location of maximum scour xm) are also shown in Fig. 1.
Sluice Gate
Tail Water Q
Dune
FL
Floor
xdmm
dm
Scour
FD FG
Sediment Bed Fig. 1. Schematic diagram of scour downstream of horizontal apron [5]
In alluvial channels energy dissipating structures are built to prevent excessive channel bed degradation. However, local scour downstream from energy dissipating structures occurs as a result of erosive action of the weir overflow and this additional turbulence may destabilize these structures. Thus, a comprehensive understanding of the mechanics, location and extent of the downstream scour, and sufficient protective provisions must be included in the structural design of the energy dissipating structures to minimize local
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
scour [4]. The scour process downstream of hydraulic structures is experimentally studied by many researchers (for e.g, [6], [7], [8]). The location and depth of maximum scour over erodible bed was `investigated by [6]. Based on the experiments conducted by [6] scour characteristics like the locations of maximum scour depths, peak of dune and the variation of maximum scour depth were correlated with time through the development of empirical expressions. The rate of scour downstream of a rigid apron was studied by [7]. A semi empirical theory based on characteristic mean velocity in the scour hole was proposed by [7] to predict the time rate of scour. The evaluation of scour hole through distinguished phases and the functional design of bed protection downstream of large hydraulic structures was studied by [8]. [9] studied the similarity in the development of scour profiles, controlling of scour mechanism and prediction of scour geometry. The work of [9] concluded that the main parameters that control the scour are relative operating head, sediment size and roughness of the energy dissipating arrangement provided downstream. 3. Methodology The methodology adopted to achieve the objectives of this study is described in this section. 3.1. Experimental Setup A physical model of an embankment pond was constructed within a study area of 27 m x 12 m at the Universiti Teknologi PETRONAS (UTP) Hydraulics laboratory. Fig. 2 illustrates longitudinal section view of the embankment pond with the inclusion of its energy dissipation system (baffle blocks, concrete apron). The inflow Q is released into the pond from the outflow conduit. The discharge flows on the concrete apron and runs into the three rows of baffle blocks that are arranged at a distance of 125 cm, 165 cm and 169 cm respectively from the outflow conduit. The experimental area of about 5 m x 4.25 m was made of loose-bed (sand). The scour depth ys can be observed on the sand bed. The water level ypond was maintained to a specific range of values for each set of experiment. 3.2. Experimentation Experimental data was collected for moderate and high flow conditions. A set of measurements for each experiment involved the discharge (Q), water level in the pond (ypond) and local scour depths (ys). The discharge was maintained in a range of 12 to 15 L/s for moderate flow and 30 L/s for high flow. The water level in the pond was taken under the dry (ypond= 0 cm) and submerged (ypond= 9 cm) conditions. After each experimental run, the whole pond was allowed to drain. Once dried, the measurements for scour depths produced on the sand bed were taken. For instance, the bed topography was observed for each specific Q and ypond. The scours and depositions of the sand bed were measured using point gauge along centreline and centreline as shown in Fig. 3.
Outflow conduit
ypond Q
Baffle blocks
Deposition dm
ys
Scour
Fig. 2. Longitudinal section of the embankment pond
Fig. 3. Scour depth measurement lines along point A, B and C
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Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
4
4
Moderate Flow @ ypond = 0 cm
3
0 -1
10
20
30
40
50
60
70
80
90
100
Scour depth (cm)
Scour depth (cm)
Apron Level Flow
0
High Flow @ ypond = 9 cm
2
2 1
High Flow @ ypond = 0 cm
3
Moderate Flow @ ypond = 9 cm
-2
Apron Level
1 0 -1 0
10
20
30
80
90
100
-6 Distance from Apron (cm)
Fig. 4. (a) Scour profile along Point A for moderate flow;
(d) Scour profile along Point A for high flow 4
4
High Flow @ ypond = 0 cm
Moderate Flow @ ypond = 0 cm
3
3
Moderate Flow @ ypond = 9 cm
Flow
0 0
10
20
30
40
50
60
70
80
90
100
Scour depth (cm)
Apron Level
1
High Flow @ ypond = 9 cm
2
2 Scour depth (cm)
70
-3
Distance from Apron (cm)
Flow
1
Apron Level
0 -1
-2
-2
-3
-3
0
10
20
30
40
50
60
70
80
90 100
-4
-4
Distance from Apron (cm)
Distance from Apron (cm)
Fig. 4. (b) Scour profile along Point B for moderate flow;
(e) Scour profile along Point B for high flow 4
4
High Flow @ ypond = 0 cm
Moderate Flow @ ypond = 0
3
3
Moderate Flow @ ypond = 9 cm
High Flow @ ypond = 9 cm
2 Apron Level
1
Flow
0 0
10
20
30
40
50
60
70
80
90
100
Scour depth (cm)
2 Scour depth (cm)
60
-5
-4
-1
50
-4
-3
-1
40
Flow
-2
Apron Level
0 -1
-2
-2
-3
-3
-4
Flow
1
0
10
20
30
40
50
60
70
80
90
-4 Distance from Apron (cm)
Fig. 4. (c) Scour profile along Point C for moderate flow;
Distance from Apron (cm)
(f) Scour profile along Point C for high flow
100
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
4. Results and Discussion The scour locations and depths were measured and plotted as illustrated in Fig. 4(a) to (f). The moderate flow condition is presented in Fig. 4(a), (b) and (c), while Fig. 4(d), (e), (f) represent the high flow condition. The apron level is taken at a benchmark elevation of 0 cm. The points lying below the apron level are scouring and points lying below the apron level are deposition of the transported sediments. The experimental results show that the pond water level has significantly affected the scour depths occurring on pond bed. Specifically, for high flow condition and higher pond water level, lesser scour depths have been observed in comparison to the dry pond condition as illustrated in Fig. 4(d), (e) and (f). For moderate flow condition, the effect of pond water level is not as significant as in case of high flow. The extension of scour from the concrete apron can also be observed from the experimental results. The scour length for high flow has extended to almost twice the distance than the scour for moderate flow, especially along the centreline A. The scour depths along point A i.e., centreline of the discharge is greater as compared to the other two lines of observation i.e., B and C. 5. Conclusion The hydraulic characteristics of the flow were studied and scours observed on the pond bed were critically reported. The experimental results show that the pond water level has affected the extent of scour depth occurring on pond bed. Specifically, in high flow condition and higher pond water level, lesser scour depths have been observed in comparison to the dry pond condition. Thus, this study suggests maintaining a certain water level in the pond to lessen the scour hazards. Furthermore, the area most affected by scour is along the centerline of the discharge, proving the hazard to be more vulnerable along the incident flow. References [1] S. Pagliara and M. Palermo, "Effect of Stilling Basin Geometry on Clear Water Scour Morphology Downstream of a Block Ramp," Journal of Irrigation and Drainage Engineering, vol. 137, pp. 593-601, 2011. [2] C.J. Grant, "Reregulation of the Pergau Hydroelectic power station," Proceedings of the ICE - Water Maritime and Energy vol. 136, pp. 81-91, 1999. [3] M. C. Tuna and M. E. Emiroglu, "Scour Profiles at Downstream of Cascades," Scientia Iranica, vol. 18, pp. 338-347, 2011. [4] G. Aytac, "A Multi-Output Descriptive Neural Network for Estimation of Scour Geometry downstream from Hydraulic Structures," Advances in Engineering Software, vol. 42, pp. 85-93, 2011. [5] S. Dey and A. Sarkar, "Scour Downstream of an Apron Due to Submerged Horizontal Jets," Journal of Hydraulic Engineering, vol. 132, pp. 246-257, 2006. [6] S. S. Chatterjee, et al., "Local Scour due to Submerged Horizontal Jet," Journal of Hydraulic Engineering, vol. 120, 1994. [7] N. M. K. N. Hassan and R. Narayanan, "Local Sour Downstream of an Apron," Journal of Hydraulic Engineering, vol. 111, 1985. [8] G. J. C. M. Hoffmans and K. W. Pilarczyk, "Local Scour Downstream of Hydraulic Structures," Journal of Hydraulic Engineering, vol. 121, 1995. [9] D. BijaN, "Scour Development Downstream of a Spillway," Journal of Hydraulic Research, vol. 41, pp. 417-426, 2003.
327
APCBEE Procedia 5 (2013) 323 – 327
ICESD 2013: January 19-20, Dubai, UAE
Variation in Local Scour Profiles of an Embankment Pond Ayesha Ghulam Rasool and Zahiraniza Mustaffa Civil Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar 31750 Tronoh, Perak, Malaysia.
Abstract This paper intents to identify the variation in local scour profiles of an embankment pond under varying pond water depths. The embankment pond was constructed to regulate the water issuing from the tunnel of a hydropower station before releasing it to the river. To avoid the structural collapse of any hydraulic structure, the scour process is one of the primary factors that must be controlled. Sediments (soils and sands) are composed of aggregation of individual grains that have varying density, volume, shape and orientation. Therefore an investigation is quite important on interactions between the fluid and sediment particles in open and pipe channel flows in hydraulics and river engineering. The variation in pond water level has significant effect on the scour that may occur on the bed of the embankment pond. This paper highlights the variations and suggests for maintaining certain pond water level to lessen the scour hazards.
© 2013 2013The Published ElsevierbyB.V. Selection © Authors.by Published Elsevier B.V. and/or peer review under responsibility of Asia-Pacific Chemical, &under Environmental Engineering Society Selection andBiological peer review responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Key words: Embankment pond; Scour; Baffle Blocks.
1. Introduction Flow from the outflow structure of a hydropower station carries an enormous energy which has the capability to erode surfaces placed at the downstream section, for instance a re-regulating pond. Usually the pond is provided as an intermediate structure to discharge the flows in a controlled manner to the downstream river. To alleviate the scour problem from getting worse, the energy from the supercritical flow must be reduced before it is released directly to the river. In a large stilling basin, the flow pattern that occurs is very complex and depends on several factors. The flow structure is also deeply affected by the presence of a
Corresponding author. Tel.: +601-96071341; fax: +605-365 6716. E-mail address: [email protected]
2212-6708 © 2013 The Authors. Published by Elsevier B.V. Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2013.05.055
324
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
mobile bed [1]. Scouring in excess can gradually undermine the foundations of hydraulic structures and cause failure. Because of its frequent occurrence, scour downstream of hydraulic structures constitutes an important field of research. This paper addresses the problems associated with local scouring of a re-regulating storage pond. The storage pond was designed to accept the flow from the penstock of a dam and further release the discharge to the river in a controlled manner. The pond was fully lined to alleviate the geotechnical risks with the site [2]. Despite the adoption of design procedures of stilling basin and provision of energy dissipating structures at the downstream of the flow, the lining ruptured and caused excessive scouring of the pond bed. A physical model of the re-regulating storage pond is designed at a Froude scale model ratio of 1:36. The model is provided with an energy dissipation system comprising of different baffle block arrangements for effective energy dissipation. An experimental approach is applied to study the effects of varying pond water levels on the local scour occurring on the pond bed caused by moderate and high flows. In this paper, the author intents to cover the following objectives (i) investigate the location and depth of scour, (ii) comparison between the effects of pond water level on associated scour depths and (iii) comparison between the scour occurring along different points in the vicinity of flow. This study will be considered useful whenever the topologic layout of a re-regulating pond/stilling basin is expected to sufficiently reduce the local scour, or in rehabilitation of similar hydraulic structures. 2. Literature Review Naturally, scour occurs due to the erosive action of flowing water including the morphological changes in rivers and also because of the construction of various types of water way structures [3]. Local scour is the erosion of bed surface as a result of the impact effect of flowing water over or through hydraulic structures [4]. The sediment particle lying on the equilibrium scoured bed is acted upon by the drag force FD, lift force FL and the submerged weight of that sediment particle FG as shown in Fig. 1. The scour parameters (depth dm and location of maximum scour xm) are also shown in Fig. 1.
Sluice Gate
Tail Water Q
Dune
FL
Floor
xdmm
dm
Scour
FD FG
Sediment Bed Fig. 1. Schematic diagram of scour downstream of horizontal apron [5]
In alluvial channels energy dissipating structures are built to prevent excessive channel bed degradation. However, local scour downstream from energy dissipating structures occurs as a result of erosive action of the weir overflow and this additional turbulence may destabilize these structures. Thus, a comprehensive understanding of the mechanics, location and extent of the downstream scour, and sufficient protective provisions must be included in the structural design of the energy dissipating structures to minimize local
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
scour [4]. The scour process downstream of hydraulic structures is experimentally studied by many researchers (for e.g, [6], [7], [8]). The location and depth of maximum scour over erodible bed was `investigated by [6]. Based on the experiments conducted by [6] scour characteristics like the locations of maximum scour depths, peak of dune and the variation of maximum scour depth were correlated with time through the development of empirical expressions. The rate of scour downstream of a rigid apron was studied by [7]. A semi empirical theory based on characteristic mean velocity in the scour hole was proposed by [7] to predict the time rate of scour. The evaluation of scour hole through distinguished phases and the functional design of bed protection downstream of large hydraulic structures was studied by [8]. [9] studied the similarity in the development of scour profiles, controlling of scour mechanism and prediction of scour geometry. The work of [9] concluded that the main parameters that control the scour are relative operating head, sediment size and roughness of the energy dissipating arrangement provided downstream. 3. Methodology The methodology adopted to achieve the objectives of this study is described in this section. 3.1. Experimental Setup A physical model of an embankment pond was constructed within a study area of 27 m x 12 m at the Universiti Teknologi PETRONAS (UTP) Hydraulics laboratory. Fig. 2 illustrates longitudinal section view of the embankment pond with the inclusion of its energy dissipation system (baffle blocks, concrete apron). The inflow Q is released into the pond from the outflow conduit. The discharge flows on the concrete apron and runs into the three rows of baffle blocks that are arranged at a distance of 125 cm, 165 cm and 169 cm respectively from the outflow conduit. The experimental area of about 5 m x 4.25 m was made of loose-bed (sand). The scour depth ys can be observed on the sand bed. The water level ypond was maintained to a specific range of values for each set of experiment. 3.2. Experimentation Experimental data was collected for moderate and high flow conditions. A set of measurements for each experiment involved the discharge (Q), water level in the pond (ypond) and local scour depths (ys). The discharge was maintained in a range of 12 to 15 L/s for moderate flow and 30 L/s for high flow. The water level in the pond was taken under the dry (ypond= 0 cm) and submerged (ypond= 9 cm) conditions. After each experimental run, the whole pond was allowed to drain. Once dried, the measurements for scour depths produced on the sand bed were taken. For instance, the bed topography was observed for each specific Q and ypond. The scours and depositions of the sand bed were measured using point gauge along centreline and centreline as shown in Fig. 3.
Outflow conduit
ypond Q
Baffle blocks
Deposition dm
ys
Scour
Fig. 2. Longitudinal section of the embankment pond
Fig. 3. Scour depth measurement lines along point A, B and C
325
326
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
4
4
Moderate Flow @ ypond = 0 cm
3
0 -1
10
20
30
40
50
60
70
80
90
100
Scour depth (cm)
Scour depth (cm)
Apron Level Flow
0
High Flow @ ypond = 9 cm
2
2 1
High Flow @ ypond = 0 cm
3
Moderate Flow @ ypond = 9 cm
-2
Apron Level
1 0 -1 0
10
20
30
80
90
100
-6 Distance from Apron (cm)
Fig. 4. (a) Scour profile along Point A for moderate flow;
(d) Scour profile along Point A for high flow 4
4
High Flow @ ypond = 0 cm
Moderate Flow @ ypond = 0 cm
3
3
Moderate Flow @ ypond = 9 cm
Flow
0 0
10
20
30
40
50
60
70
80
90
100
Scour depth (cm)
Apron Level
1
High Flow @ ypond = 9 cm
2
2 Scour depth (cm)
70
-3
Distance from Apron (cm)
Flow
1
Apron Level
0 -1
-2
-2
-3
-3
0
10
20
30
40
50
60
70
80
90 100
-4
-4
Distance from Apron (cm)
Distance from Apron (cm)
Fig. 4. (b) Scour profile along Point B for moderate flow;
(e) Scour profile along Point B for high flow 4
4
High Flow @ ypond = 0 cm
Moderate Flow @ ypond = 0
3
3
Moderate Flow @ ypond = 9 cm
High Flow @ ypond = 9 cm
2 Apron Level
1
Flow
0 0
10
20
30
40
50
60
70
80
90
100
Scour depth (cm)
2 Scour depth (cm)
60
-5
-4
-1
50
-4
-3
-1
40
Flow
-2
Apron Level
0 -1
-2
-2
-3
-3
-4
Flow
1
0
10
20
30
40
50
60
70
80
90
-4 Distance from Apron (cm)
Fig. 4. (c) Scour profile along Point C for moderate flow;
Distance from Apron (cm)
(f) Scour profile along Point C for high flow
100
Ayesha Ghulam Rasool and Zahiraniza Mustaffa / APCBEE Procedia 5 (2013) 323 – 327
4. Results and Discussion The scour locations and depths were measured and plotted as illustrated in Fig. 4(a) to (f). The moderate flow condition is presented in Fig. 4(a), (b) and (c), while Fig. 4(d), (e), (f) represent the high flow condition. The apron level is taken at a benchmark elevation of 0 cm. The points lying below the apron level are scouring and points lying below the apron level are deposition of the transported sediments. The experimental results show that the pond water level has significantly affected the scour depths occurring on pond bed. Specifically, for high flow condition and higher pond water level, lesser scour depths have been observed in comparison to the dry pond condition as illustrated in Fig. 4(d), (e) and (f). For moderate flow condition, the effect of pond water level is not as significant as in case of high flow. The extension of scour from the concrete apron can also be observed from the experimental results. The scour length for high flow has extended to almost twice the distance than the scour for moderate flow, especially along the centreline A. The scour depths along point A i.e., centreline of the discharge is greater as compared to the other two lines of observation i.e., B and C. 5. Conclusion The hydraulic characteristics of the flow were studied and scours observed on the pond bed were critically reported. The experimental results show that the pond water level has affected the extent of scour depth occurring on pond bed. Specifically, in high flow condition and higher pond water level, lesser scour depths have been observed in comparison to the dry pond condition. Thus, this study suggests maintaining a certain water level in the pond to lessen the scour hazards. Furthermore, the area most affected by scour is along the centerline of the discharge, proving the hazard to be more vulnerable along the incident flow. References [1] S. Pagliara and M. Palermo, "Effect of Stilling Basin Geometry on Clear Water Scour Morphology Downstream of a Block Ramp," Journal of Irrigation and Drainage Engineering, vol. 137, pp. 593-601, 2011. [2] C.J. Grant, "Reregulation of the Pergau Hydroelectic power station," Proceedings of the ICE - Water Maritime and Energy vol. 136, pp. 81-91, 1999. [3] M. C. Tuna and M. E. Emiroglu, "Scour Profiles at Downstream of Cascades," Scientia Iranica, vol. 18, pp. 338-347, 2011. [4] G. Aytac, "A Multi-Output Descriptive Neural Network for Estimation of Scour Geometry downstream from Hydraulic Structures," Advances in Engineering Software, vol. 42, pp. 85-93, 2011. [5] S. Dey and A. Sarkar, "Scour Downstream of an Apron Due to Submerged Horizontal Jets," Journal of Hydraulic Engineering, vol. 132, pp. 246-257, 2006. [6] S. S. Chatterjee, et al., "Local Scour due to Submerged Horizontal Jet," Journal of Hydraulic Engineering, vol. 120, 1994. [7] N. M. K. N. Hassan and R. Narayanan, "Local Sour Downstream of an Apron," Journal of Hydraulic Engineering, vol. 111, 1985. [8] G. J. C. M. Hoffmans and K. W. Pilarczyk, "Local Scour Downstream of Hydraulic Structures," Journal of Hydraulic Engineering, vol. 121, 1995. [9] D. BijaN, "Scour Development Downstream of a Spillway," Journal of Hydraulic Research, vol. 41, pp. 417-426, 2003.
327