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Discharge characteristics of a trench weir
Flow Measurement and Instrumentation 21 (2010) 80–87
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Flow Measurement and Instrumentation journal homepage: www.elsevier.com/locate/flowmeasinst
Discharge characteristics of a trench weir S. Kumar, Z. Ahmad ∗ , Umesh C. Kothyari, M.K. Mittal Department of Civil Engineering, Indian Institute of Technology, Roorkee, Uttarakhand – 247667, India
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Article history: Received 5 June 2009 Received in revised form 7 December 2009 Accepted 1 January 2010 Keywords: Trench weir Boulder stream Rack Discharge Submergence
abstract Trench weirs are commonly adopted in boulder streams for diverting water for use in hydropower, irrigation and water supply schemes etc. Here, a trench is built across the river below its bed level. The top level of this trench is covered with bars to prevent the entry of sediment into the trench. Discharge characteristics of this weir apart from flow conditions also depend on the geometric characteristics of the bars used. Generally round bars are used, however, from a structural consideration, flat bars are preferred over round bars as flat bars have more flexural rigidity. In the present paper, the results of an experimental study on the discharge characteristics of a trench weir consisting of flat bars under free and submerged flow conditions are reported. © 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Qd = Cd ε BLw
Conventional types of raised-crest weir are not suited for boulder streams for diverting water for use in hydro power generation, irrigation, water supply etc. The raised-crest weirs cause changes in the flow conditions on the upstream. As a result sediment deposition occurs on upstream of the crest and the intake also gets choked up. Further, severe erosion occurs downstream of the weir leading to breaches in the weir [1]. The most suitable type of diversion weir adopted in boulder streams therefore is a trench weir, which overcomes the above mentioned problems. It is simply a trench built across the stream below its bed level. The top of the trench weir is covered with bottom rack bars. Water while flowing over it, passes through the bottom racks and enters into the trench and is collected in an intake well located at one of the banks of the trench. The top edge of the trench weir is almost flush with the natural bed surface of the stream. The bottom racks which consist of heavy rounded steel bars or flats are laid on edge and placed parallel with the river flow on the river bed level. This type of weir has a definite advantage as it does not affect the general bed level of the stream. The objective of present study was to investigate in detail the discharge characteristics of trench weirs. Assuming the specific energy of flow to be constant along the longitudinal bottom rack, Mostkow [2] proposed the following equation for the diverted discharge into the trench:
Based on a limited experimental study, Mostkow [2] suggested that Cd varies from 0.435, for a rack sloping as 1 in 5, to 0.497 for a horizontal rack. Noseda [3], with an additional assumption of critical approach flow conditions, analyzed the flow over longitudinal racks and presented a design chart relating the diverted flow to the stream flow. White et al. [4] compared the performance of bottom racks with those predicted by Noseda’s [3] method and indicated the inadequacy of Noseda’s [3] design chart. On the basis of experimental study, Subramanya and Shukla [5] and Subramanya [6,7] related Cd with Vh∗ , the ratio of diameter and clear spacing of bars, rack slope etc. Ghosh and Ahmad [8] found that the Cd for flat bars is lower than that for rounded bars. They also proposed an equation for Cd albeit by using limited data. Brunella et al. [9] performed experiments using rounded bars of 6 mm and 12 mm diameter and found that Cd measured under static conditions indicate a slight dependence on the orifice Reynolds number and a stronger dependence on rack porosity. Righetti and Lanzoni [10] used rectangular bars of length 0.45 m, width 0.035 m and thickness 0.02 m with a rounded upstream edge. They found that the diverted discharge per unit length of the rack decreases along longitudinal direction and the total diverted discharge decreased with decrease in Froude number. Ahmad and Mittal [11] noticed that the optimum length of the bottom rack is obtained when the diverted discharge is equal to the incoming discharge in the stream. From a structural consideration, flat bars are preferred over rounded bars as flat bars have more flexural rigidity. However not many studies are yet available on flow over trench weirs having flat bars as the trash rack. The present work, therefore, deals with an experimental investigation of the discharge characteristics of
∗
Corresponding author. E-mail addresses: [email protected] (S. Kumar), [email protected] (Z. Ahmad), [email protected] (U.C. Kothyari), [email protected] (M.K. Mittal). 0955-5986/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.flowmeasinst.2010.01.002
p
2gE0 .
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
Nomenclature
Table 1 Ranges of data collected in the present study. Parameters
B Cd E0 Fr g H L Lw Ls n Qm Qr Qd R Re s S Ss sr t V0 Vh Vh∗
w
W y0 ys
yr
ρ ε µ λ
Length of the trench perpendicular to the river flow, m Coefficient of diverted discharge Specific energy of approach flow, m Froude number Acceleration due to gravity, m/s2 Depth of trench at its mid point from the lower level of rack, m Length of bottom racks, m Wetted length of bottom rack bars, m Length of vortices in between the bars, m Manning’s rugosity coefficient, s/m1/3 Discharge in main channel upstream of trench, m3 /s Discharge in main channel downstream of trench, m3 /s Diverted discharge into the trench, m3 /s Hydraulic radius, m Reynolds number Clear spacing of rack bars, m Bed slope of main channel Bed slope of trench Slope of rack Thickness of flat bars, m Approach velocity, m/s Velocity head, (V02 /2g ), m Dimensionless velocity head, (V02 /2gE0 ) Width of flat bars, m Width of the trench, m Depth of flow in main channel upstream of rack, m Submergence depth (i.e., depth of water in the intake well above the bed level of main channel upstream of trench), m Depth of flow downstream of main channel, m Mass density of water, kg/m3 Ratio of clear opening area and total area of the rack Dynamic viscosity of water, N s/m2 Qd (submerged flow)/Qd (free flow)
a trench weir having bottom racks of flat bars under free and submerged flow conditions. 2. Experimental work 2.1. Set-up Experiments were carried out in a rectangular channel of 17.0 m length, 0.50 m width and 0.64 m depth in the Hydraulics Laboratory of Department of Civil Engineering, IIT Roorkee, India (Fig. 1). Water was supplied to the main channel from a 10 m long, 0.75 m width and 0.51 m deep supply channel fitted with sharpcrested rectangular Weir-A. Grid walls and wooden suppressors were provided to break the large size eddies and to dissipate the surface disturbances, respectively. A tail-gate was provided at the end of the main channel to regulate the depth of the flow. A trench of 0.5 m length, 0.3 m width, 0.34 m depth and 1:12.5 bed slope was provided in the bed of the channel at a distance of 10.6 m from the upstream end of the channel. A bottom rack using flat bars was placed over the trench. The trench was opened on its left bank to an intake well of size 1 m length, 1 m width and 0.91 m depth. A diversion channel of 3.9 m length, 0.30 m width and 0.72 m depth was taken from the intake well with a perforated wall and wooden suppressor provided at its entrance as shown in Fig. 1. A gate was provided at the head of
81
S sr s l
w Qm Qd y0 yr ys
Units
– – m m m m3 /s m3 /s m m m
Range of data Free flow
Submerged flow
0.0008–0.002 0.066–0.330 0.002–0.009 0.005 0.0191–0.0508 0.0133–0.0874 0.0129–0.0650 0.0422–0.1515 0.0–0.0491 –
0.0008–0.002 0.066–0.330 0.002–0.009 0.005 0.0254 0.0874 0.0122–0.0357 0.1278–0.1475 0.0508–0.1001 0.0002–0.0924
the diversion channel to increase the depth of water in the intake well for creating submerged flow conditions in the trench weir. A rectangular weir namely Weir-B was provided at the end of the diversion channel to measure the diverted discharge. Weir-A was calibrated by measuring the discharge using an ultrasonic flow meter fitted in the supply pipe, while, Weir-B was calibrated by measuring the velocity distribution in the diversion channel using a digital velocity meter. Levels were measured using a digital point gage of accuracy ±0.01 mm. Five bottom racks consisting of mild steel flat bars of 5 mm thickness; 335 mm length; and 19.1, 25.4, 31.8, 38.1 and 50.8 mm width respectively were used. 2.2. Procedure Experiments were performed for free flow conditions with 1/1250, 1/847 and 1/500 upstream bed slopes; 1/15, 1/5 and 1/3 rack slopes; 5 mm thickness of flat bars; 19.1 mm, 25.4 mm, 31.8 mm, 38.1 mm and 50.8 mm width of flat bars and 2.0 mm, 5.0 mm and a 9.0 mm clear spacing of the rack. Five discharges were used for each set of these parameters. For single values of S , sr , t , w, s and discharge, water was allowed to flow in the main channel. A part of the approach flow gets diverted in the diversion channel while crossing over the trench. The head causing the flow over the crests of weirA and weir-B were measured and the discharges in the main channel Qm and in diversion channel Qd were thereby determined. The discharge in the main channel downstream of trench Qr was calculated as the difference between Qm and Qd , the normal depth of flow yr corresponding to Qr was determined from Manning’s equation and yr was maintained in the main channel by regulating its tail gate. In case the head causing flow over the weirs altered due to tail gate operation, the changed Qr and hence yr were re-adjusted in such a way that during each run the value of Qr becomes equal to the difference between Qm and Qd . For this condition, the approach flow depth, y0 in the main channel at 1.0 m upstream of the trench was measured to calculate V0 and E0 . Two types of flow condition over the rack were examined, one in which incoming discharge is completely diverted into the trench i.e., Qm is equal to Qd while in the second case only a part of incoming discharge is diverted into the trench and the reminder flows downstream to the trench in the main channel. For submerged flow conditions, the water level in the intake was raised using a gate provided at the head of the diversion channel. The water level in the gage well was measured and the submergence defined as ys /E0 was calculated. The vortex shape and size formed in the trench was also visualized for different flow conditions. Ranges of various parameters covered in the data collected in the present study are given in Table 1. 3. Data presentation and analysis Experimental data collected in the present study were analyzed to investigate the discharge characteristics of a trench weir under free and submerged flow conditions.
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87 Y Sump
900
Diversion Channel
Weir - B 3900
Flow Suppresser Weir - A
Grid Walls
Boulders
Flow Suppresser
Grid Wall
Gauge Well
Main Channel
400 1000
1000 400
Intake Well
X
X Sump
500
750
Perforated Plates
Supply Channel
Bottom Rack Tail Gate Glass Panel
Y
300 5900
1200
600
2000
600
300
10000
1100
6000
PLAN Side Wall
580 730
Channel Bed
Weir - A
SECTION - X-X
Bed
Trench Top of Wall
Bed
ALL DIMENSIONS ARE IN mm SECTION - Y-Y Fig. 1. Layout of the experimental set-up.
Fig. 2. Flow pattern in trench for its different aspect ratios (a) H /W = 1.05; (b) H /W = 0.525; (c) H /W = 0.271; and (d) H /W = 0.173.
3.1. Effect of various parameters on the coefficient of discharge 3.1.1. Aspect ratio of trench Experiments were performed for constant Qm , S , w, t , s, sr , Lw with varying depth of the trench H to study the effect of aspect ratio of trench i.e., H /W on the diverted discharge. The vortex size formed in the trench as shown in Fig. 2(a) is of the order of
the width of the trench while the aspect ratio is large. Once the depth of trench H is less than the width of trench W (i.e. while H /W is smaller), the water in the trench pushes the vortex up resulting in an increase of pressure in the trench thereby increasing the depth of flow over the rack and consequently reducing the vortex size tendency of the water jet to enter into the trench as shown in Fig. 2(b). Variation of Qd /Qm with H /W and variation of Cd (determined as per Eq. (1)) with H /W are shown in Fig. 3(a) and
S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
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Fig. 3. Effect of aspect ratio of trench on diverted discharge and coefficient of discharge.
Fig. 4. Variation of Cd with sr for S = 1/1250 and 1/500.
Fig. 5. Variation of Cd with s for S = 1/1250 and 1/500. s
s
Eddies
Flow Separation
Vortex shedding (fully developed)
(a) Coarser spacing.
s Eddies
s Flow Separation
Vortex shedding (partially developed)
(b) Finer spacing.
Fig. 6. Formation of vortices in between bars and behind the bars.
(b), respectively. These figures depict that the diverted discharge and Cd increase with an increase in H /W . As the aspect ratio H /W approached unity, the values of Qd and Cd tend to become constant and any further increase in H /W does not have any effect on Qd and Cd . This indicates that the depth of trench should be equal to or significantly larger than the width of trench for attaining the maximum withdrawal of discharge while the other parameters are constant.
3.1.2. Slope of rack From the complete set of observations such data were screened out for which Qm , S , s, w, t are constant and Cd varied with sr only. A decrease in the values of Cd with an increase in slope of rack is noticed (Fig. 4). The separation of flow that occurs over the rack is considered to be the prime cause for this, as for a steeper rack, the separated flow joins the racks at a large distance on the downstream side, which results in a decreased Cd .
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
Fig. 7. Variation of Cd with w for S = 1/1250 and 1/500. s
vortices, which results in more dissipation of energy. An increase in the width of bars beyond this limit decreases the space for the vortex formation resulting in a slight decrease in energy loss and an increase of Cd . However, for a further increase of width (i.e., w is greater than Ls ), the separated flow rejoins the bars and increases the energy loss by energy dissipation due to friction on the face of plate, resulting in a decrease in the Cd value with the increase in w . Fig. 7 also shows that value of Cd is lower for steeper channel slopes as compared to its value while channel slope is flatter. Further, it can also be seen from Fig. 7, that the maximum value of Cd for a given S occurs for w at about 0.026 m.
Ls w
Fig. 8. Flow separation and re-attachment.
3.1.3. Clear spacing of rack Variations of Cd with s while Qm , S , sr , w and t were constant is shown in Fig. 5 and Cd is found to decrease with an increase in s. During experimentation it is noticed that flow separation starts from the upward face of rack bars and subsequently vortices are formed in downstream portion. The separated flow and vortices are not able to develop fully for a smaller (fine) spacing between the bars as the separated flow remains confined to the rack boundary only in such cases, whereas for a larger (coarse) spacing, a fully developed separated flow develops (Fig. 6). Thus, the energy loss is smaller when s is small as compared to case when s is large, which results in high Cd for a lower spacing of bars. 3.1.4. Width (flatness) of rack Data corresponding to a relatively constant value of Qm , S , sr , s and t were screened out from the complete data set to study the variation of Cd with w . This variation is shown in Fig. 7. It is seen from this figure that Cd first increases and then decreases with an increase in w values. It seems that for w about 0.024 m, the separated flow does not rejoin the bars (i.e., w is less than Ls , Fig. 8) and enough space is available behind the bars for the formation of
3.1.5. Specific energy of approach flow The variation of Cd with E0 for the two sets of data wherein the values of other variables are constant is shown in Fig. 9, indicating a decrease in Cd with an increase in the specific energy. 3.1.6. Froude number, Reynolds number and dimensionless velocity head of approach flow The variation of Cd with Fr , Re and Vh∗ of the approach flow is shown in Fig. 10, 11 and 12, as an illustration using two data sets. Note that values of other variables affecting Cd are relatively constant in Figs. 10–12. These figures revealed that Cd values do not have any systematic variation with Fr and Vh∗ . However, Cd is found to decrease with an increase in Re . The value of Fr has varied in a small range which perhaps was not adequate to capture the variation in Cd values. Further data are being collected in the ongoing experimental work covering higher ranges of Fr . 3.2. Dimensional analysis Probable variables affecting the values of Cd are identified as B, L, S , H , W , t , w, s, sr , Lw, V0 , y0 , ys , E0 , µ, ρ, g. The functional relationship for Cd may be thus written as Cd = f1 (B, L, S , H , W , t , w, s, sr , Lw , V0 , y0 , ys , E0 , µ, ρ, g ) .
Fig. 9. Variation of Cd with E0 for the two sets of data.
(2)
S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
85
Fig. 10. Variation of Cd with Fr .
Fig. 11. Variation of Cd with Re .
Fig. 12. Variation of Cd with Vh∗ .
of y0 and V0 only E0 may be considered. Eq. (3) may be modified in terms of the Reynolds number and the Froude number of the approach flow and dimensionless velocity head as
Cd = f3
w s Lw E0 ys V02 ρ V0 (4R) V0 S , , , sr , , , , ,√ t t t t t 2gE0 µ gy0
.
(4)
Analysis of data collected in the present study and those by other investigators [6,12] revealed that the Froude number, Reynolds number and dimensionless velocity head have no discernable effect on Cd . For free flow conditions with partial withdrawal, ys is equal to zero and Lw is equal to L, which is constant for a given rack slope. Therefore, Eq. (4) may be written as Fig. 13. Check on the proposed relationship (Eq. (6)) for Cd .
Taking ρ, V0 and t as the repeating variables, the resulting nondimensional parameters may be written as
Cd = f2
B L
H W w s
t
t
, , S, t
,
t
,
t
Lw y0 ys E0 ρ V0 t t
,
t
,
t
,
t
,
µ
, , sr , t
V0
,√
gt
.
(3)
In the present study, B/t , L/t , H /t, and W /t are constant and thus these are dropped. Since E0 is sum of y0 and Vh , thus in place
Cd = f3
S,
w s E0 , , sr , t
t
t
.
(5)
Graphical plotting of data presented in the previous section also revealed that the variables S , w, s, sr and E0 have a significant effect on Cd . 3.3. Relationship for coefficient of discharge for free flow condition Using 305 data sets collected in the present study for partial withdrawal, the following relationship for Cd has evolved by the
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
Fig. 14. Flow characteristics of partial and complete withdrawal of discharge.
least squares technique. Cd = 0.471 − 0.124 × ln (s/t ) − 0.194 × sr − 0.01
× (w/t ) ;
R2 = 0.83.
(6)
Inclusion of other variables like S, E0 /t in Eq. (6) did not significantly improve the value of R2 . The remaining 114 data sets, not used in the derivation of Eq. (6), were used next to validate the proposed relationship for Cd i.e., Eq. (6). Observed and computed values of Cd using Eq. (6) for the test data are compared graphically in Fig. 13, which revealed that the computed Cd has a maximum error of ±10% which is considered as satisfactory. Under partial withdrawal, the trench is completely filled with water with a core of air in the center of the trench due to vortex flow. This results in non-existence of free water surface in the trench (Fig. 14). However, during complete withdrawal, atmospheric pressure exists on the both sides of the water jet, which results in the high discharge capacity of the bottom racks. 3.4. Relationship for coefficient of discharge for submerged flow condition Under submerged flow conditions, the trench is completely filled with water with no air entrainment due to the higher water level in the intake well. Pressure in the trench is high compared to the free flow condition and it increases with an increase of submergence resulting in a reduced value of the diverted discharge. Using 267 data sets collected in the present study for the submerged flow condition, the following relationship for λ has evolved.
λ=
Qd (submerged flow) Qd (free flow)
+ 0.535;
= 0.685 ×
R2 = 0.65.
ys E0
2
− 1.021 ×
ys
E0 (7)
The remaining 83 data sets, not used in the derivation of Eq. (7), were used next to validate the proposed relationship for λ i.e., Eq. (7). Observed and computed values of λ using Eq. (7) for the test data are compared graphically in Fig. 15, which revealed that the computed λ have a maximum error of ±20%. Thus, for calculating Qd under submerged conditions first the diverted discharge is calculated for free flow conditions. Next Eq. (7) is used to calculate the diverted discharge under the submerged condition. It may be noted that effect of other variables viz: s/t, sr and w/t on Qd (submerged) is accounted for through the use of Eq. (6) for the determination of the Qd (submerged). 4. Conclusions Analysis of collected data reveals that for the maximum discharge capacity of the trench, the aspect ratio of the trench i.e. ratio of its depth to width should be more than unity. The coefficient of
Fig. 15. Check on the proposed relationship (Eq. (7)) for λ.
discharge decreases with an increase of rack slope, width of flat, clear spacing of bars and Reynolds number of the approach flow. However, the Froude number and dimensionless specific energy do not affect the coefficient of discharge. The discharge coefficient of the rack under free flow conditions for partial withdrawal is less than the value corresponding to complete withdrawal due to the existence of atmospheric pressure on both sides of the water jet. The relationship developed for partial withdrawal i.e. Eq. (6) under free flow conditions computes the coefficient of discharge within ±10% of the observed ones. The coefficient of discharge for complete withdrawal depends on the wetted length of the rack. Under submerged flow conditions, the trench gets completely filled with water without air entrainment and it results in a reduced value of the diverted discharge compared to that under free flow conditions. In the absence of other information the proposed relationship i.e. Eq. (7) can be used for the computation of diverted discharge under submerged flow conditions with a maximum error of ±20%. References [1] Paudyal GN, Tawatchai T. Design of a bottom intake structure for mountain streams. In: Proc. int. symp. on design of hydraulic structure. 1987. p. 73–82. [2] Mostkow MA. A theoretical study of bottom type water intake. La Houille Blanche 1957;4:570–80. [3] Noseda G. Operation and design of bottom intake racks. In: Proc. 6th gen. meeting. IAHR, 3(17). 1956. p. 1–11. [4] White JK, Charlton JA, Ramsay CAW. On the design of bottom intakes for diverting stream flows. Proceedings of the Institution of Civil Engineers (London) 1972;51:337–45. [5] Subramanya K, Shukla SK. Discharge diversion characteristics of trench weir. Journal of Civil Engineering Division, The Institution of Engineers (India) 1988; 69(I3):163–8. [6] Subramanya K. Trench intake for mini hydro projects. In: Proc hydromech and water resources conf IISc. 1990. p. 33–41. [7] Subramanya K. Hydraulic characteristics of inclined bottom racks. In: National symp. on design of hydraulic structures. India: Deptt of Civil Eng., Univ of Roorkee; 1994. p. 3–9. [8] Ghosh S, Ahmad Z. Characteristics of flow over bottom racks. Water and Energy International, CBIP 2006;63(2):47–55.
S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87 [9] Brunella S, Hager WH, Minor HE. Hydraulics of bottom rack intake. ASCE Journal of Hydraulic Engineering 2003;129(1):2–10. [10] Righetti M, Lanzoni S. Experimental study of the flow field over bottom intake racks. ASCE Journal of Hydraulic Engineering 2008;134(1):15–22. [11] Ahmad Z, Mittal MK. Hydraulic design of trench weir on Dabka river—A case study. Water and Energy International, CBIP 2004;60(4):28–37. [12] Venkataraman P. Discharge characteristics of an idealised bottom intake. Journal of the Institution of Engineers 1977;58(2–3):99.
S. Kumar is currently research scholar of Civil Engineering at IIT Roorkee, India. He obtained his Diploma (DDC), B.Tech. (Civil) and M.Tech. (Civil) degree from AMU, Aligarh, India. He has published 2 papers in referred national conference proceedings. His area of research is hydro power, computational hydraulics and hydraulic structures. He has been recipient of University medal for standing 1st in M.Tech. Z. Ahmad is currently Associate Professor of Civil Engineering at IIT Roorkee, India. He obtained his B.Tech. (Civil) degree from AMU Aligarh, M.Tech. (Hyd) degree from Univ. of Roorkee and Ph.D. degree from T.I.E.T., Patiala. He has published about 52 papers in referred national and international journals and conference proceedings. His area of research is surface water quality management, computational hydraulics and hydraulic structures. He has written two Monographs on Transport of Pollutants
87
in Open Channels and Control Section in Open Channels for AICTE, New Delhi. He has been recipient of G.N. Nawathe, Jal Vigyan Puraskar (twice); Department of Irrigation Award; and his name appeared in Marquis Who’s Who in the World edition 2005. Umesh C. Kothyari is presently professor of Civil Engineering, IIT Roorkee, did M.E. (Hyd.) and Ph.D. (River Eng.) from University of Roorkee (now IIT) in 1985 and 1990, respectively. He Joined Univ. of Roorkee in 1985 and since then actively engaged in teaching, research and consultancy. Supervised 12 Ph.D. theses, 49 M.Tech. theses, published 61 research papers in international review journals, 57 papers in conference proceedings and completed more than 24 consultancy projects. Recipient of Young Engineer Award awarded by Central Board of Irrigation and Power, India, 1994 and S.N. Gupta Memorial Lecturer award awarded by Indian Society for Hydraulic Engineering, Pune, 2006. M.K. Mittal is presently Emeritus Fellow of Civil Engineering, IIT Roorkee, did B.E. from Gorakhpur University in 1966 and M.E. (Hyd.) from University of Roorkee (now IIT) in 1968. Joined Univ. of Roorkee in 1971 after serving two years as Assistant Engineer in U.P. Irrigation Department. Retired as professor of Civil Engineering, I.I.T. Roorkee in 2007. Actively engaged in teaching, research and consultancy for the last 38 years. Supervised 34 M.Tech. theses, published 38 research papers and associated with more than 100 consultancy projects. Recipient of University Gold Medal and Khosla Research Award. Fellow of ISH and Member of ISTE and ISCMS.
Contents lists available at ScienceDirect
Flow Measurement and Instrumentation journal homepage: www.elsevier.com/locate/flowmeasinst
Discharge characteristics of a trench weir S. Kumar, Z. Ahmad ∗ , Umesh C. Kothyari, M.K. Mittal Department of Civil Engineering, Indian Institute of Technology, Roorkee, Uttarakhand – 247667, India
article
info
Article history: Received 5 June 2009 Received in revised form 7 December 2009 Accepted 1 January 2010 Keywords: Trench weir Boulder stream Rack Discharge Submergence
abstract Trench weirs are commonly adopted in boulder streams for diverting water for use in hydropower, irrigation and water supply schemes etc. Here, a trench is built across the river below its bed level. The top level of this trench is covered with bars to prevent the entry of sediment into the trench. Discharge characteristics of this weir apart from flow conditions also depend on the geometric characteristics of the bars used. Generally round bars are used, however, from a structural consideration, flat bars are preferred over round bars as flat bars have more flexural rigidity. In the present paper, the results of an experimental study on the discharge characteristics of a trench weir consisting of flat bars under free and submerged flow conditions are reported. © 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Qd = Cd ε BLw
Conventional types of raised-crest weir are not suited for boulder streams for diverting water for use in hydro power generation, irrigation, water supply etc. The raised-crest weirs cause changes in the flow conditions on the upstream. As a result sediment deposition occurs on upstream of the crest and the intake also gets choked up. Further, severe erosion occurs downstream of the weir leading to breaches in the weir [1]. The most suitable type of diversion weir adopted in boulder streams therefore is a trench weir, which overcomes the above mentioned problems. It is simply a trench built across the stream below its bed level. The top of the trench weir is covered with bottom rack bars. Water while flowing over it, passes through the bottom racks and enters into the trench and is collected in an intake well located at one of the banks of the trench. The top edge of the trench weir is almost flush with the natural bed surface of the stream. The bottom racks which consist of heavy rounded steel bars or flats are laid on edge and placed parallel with the river flow on the river bed level. This type of weir has a definite advantage as it does not affect the general bed level of the stream. The objective of present study was to investigate in detail the discharge characteristics of trench weirs. Assuming the specific energy of flow to be constant along the longitudinal bottom rack, Mostkow [2] proposed the following equation for the diverted discharge into the trench:
Based on a limited experimental study, Mostkow [2] suggested that Cd varies from 0.435, for a rack sloping as 1 in 5, to 0.497 for a horizontal rack. Noseda [3], with an additional assumption of critical approach flow conditions, analyzed the flow over longitudinal racks and presented a design chart relating the diverted flow to the stream flow. White et al. [4] compared the performance of bottom racks with those predicted by Noseda’s [3] method and indicated the inadequacy of Noseda’s [3] design chart. On the basis of experimental study, Subramanya and Shukla [5] and Subramanya [6,7] related Cd with Vh∗ , the ratio of diameter and clear spacing of bars, rack slope etc. Ghosh and Ahmad [8] found that the Cd for flat bars is lower than that for rounded bars. They also proposed an equation for Cd albeit by using limited data. Brunella et al. [9] performed experiments using rounded bars of 6 mm and 12 mm diameter and found that Cd measured under static conditions indicate a slight dependence on the orifice Reynolds number and a stronger dependence on rack porosity. Righetti and Lanzoni [10] used rectangular bars of length 0.45 m, width 0.035 m and thickness 0.02 m with a rounded upstream edge. They found that the diverted discharge per unit length of the rack decreases along longitudinal direction and the total diverted discharge decreased with decrease in Froude number. Ahmad and Mittal [11] noticed that the optimum length of the bottom rack is obtained when the diverted discharge is equal to the incoming discharge in the stream. From a structural consideration, flat bars are preferred over rounded bars as flat bars have more flexural rigidity. However not many studies are yet available on flow over trench weirs having flat bars as the trash rack. The present work, therefore, deals with an experimental investigation of the discharge characteristics of
∗
Corresponding author. E-mail addresses: [email protected] (S. Kumar), [email protected] (Z. Ahmad), [email protected] (U.C. Kothyari), [email protected] (M.K. Mittal). 0955-5986/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.flowmeasinst.2010.01.002
p
2gE0 .
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
Nomenclature
Table 1 Ranges of data collected in the present study. Parameters
B Cd E0 Fr g H L Lw Ls n Qm Qr Qd R Re s S Ss sr t V0 Vh Vh∗
w
W y0 ys
yr
ρ ε µ λ
Length of the trench perpendicular to the river flow, m Coefficient of diverted discharge Specific energy of approach flow, m Froude number Acceleration due to gravity, m/s2 Depth of trench at its mid point from the lower level of rack, m Length of bottom racks, m Wetted length of bottom rack bars, m Length of vortices in between the bars, m Manning’s rugosity coefficient, s/m1/3 Discharge in main channel upstream of trench, m3 /s Discharge in main channel downstream of trench, m3 /s Diverted discharge into the trench, m3 /s Hydraulic radius, m Reynolds number Clear spacing of rack bars, m Bed slope of main channel Bed slope of trench Slope of rack Thickness of flat bars, m Approach velocity, m/s Velocity head, (V02 /2g ), m Dimensionless velocity head, (V02 /2gE0 ) Width of flat bars, m Width of the trench, m Depth of flow in main channel upstream of rack, m Submergence depth (i.e., depth of water in the intake well above the bed level of main channel upstream of trench), m Depth of flow downstream of main channel, m Mass density of water, kg/m3 Ratio of clear opening area and total area of the rack Dynamic viscosity of water, N s/m2 Qd (submerged flow)/Qd (free flow)
a trench weir having bottom racks of flat bars under free and submerged flow conditions. 2. Experimental work 2.1. Set-up Experiments were carried out in a rectangular channel of 17.0 m length, 0.50 m width and 0.64 m depth in the Hydraulics Laboratory of Department of Civil Engineering, IIT Roorkee, India (Fig. 1). Water was supplied to the main channel from a 10 m long, 0.75 m width and 0.51 m deep supply channel fitted with sharpcrested rectangular Weir-A. Grid walls and wooden suppressors were provided to break the large size eddies and to dissipate the surface disturbances, respectively. A tail-gate was provided at the end of the main channel to regulate the depth of the flow. A trench of 0.5 m length, 0.3 m width, 0.34 m depth and 1:12.5 bed slope was provided in the bed of the channel at a distance of 10.6 m from the upstream end of the channel. A bottom rack using flat bars was placed over the trench. The trench was opened on its left bank to an intake well of size 1 m length, 1 m width and 0.91 m depth. A diversion channel of 3.9 m length, 0.30 m width and 0.72 m depth was taken from the intake well with a perforated wall and wooden suppressor provided at its entrance as shown in Fig. 1. A gate was provided at the head of
81
S sr s l
w Qm Qd y0 yr ys
Units
– – m m m m3 /s m3 /s m m m
Range of data Free flow
Submerged flow
0.0008–0.002 0.066–0.330 0.002–0.009 0.005 0.0191–0.0508 0.0133–0.0874 0.0129–0.0650 0.0422–0.1515 0.0–0.0491 –
0.0008–0.002 0.066–0.330 0.002–0.009 0.005 0.0254 0.0874 0.0122–0.0357 0.1278–0.1475 0.0508–0.1001 0.0002–0.0924
the diversion channel to increase the depth of water in the intake well for creating submerged flow conditions in the trench weir. A rectangular weir namely Weir-B was provided at the end of the diversion channel to measure the diverted discharge. Weir-A was calibrated by measuring the discharge using an ultrasonic flow meter fitted in the supply pipe, while, Weir-B was calibrated by measuring the velocity distribution in the diversion channel using a digital velocity meter. Levels were measured using a digital point gage of accuracy ±0.01 mm. Five bottom racks consisting of mild steel flat bars of 5 mm thickness; 335 mm length; and 19.1, 25.4, 31.8, 38.1 and 50.8 mm width respectively were used. 2.2. Procedure Experiments were performed for free flow conditions with 1/1250, 1/847 and 1/500 upstream bed slopes; 1/15, 1/5 and 1/3 rack slopes; 5 mm thickness of flat bars; 19.1 mm, 25.4 mm, 31.8 mm, 38.1 mm and 50.8 mm width of flat bars and 2.0 mm, 5.0 mm and a 9.0 mm clear spacing of the rack. Five discharges were used for each set of these parameters. For single values of S , sr , t , w, s and discharge, water was allowed to flow in the main channel. A part of the approach flow gets diverted in the diversion channel while crossing over the trench. The head causing the flow over the crests of weirA and weir-B were measured and the discharges in the main channel Qm and in diversion channel Qd were thereby determined. The discharge in the main channel downstream of trench Qr was calculated as the difference between Qm and Qd , the normal depth of flow yr corresponding to Qr was determined from Manning’s equation and yr was maintained in the main channel by regulating its tail gate. In case the head causing flow over the weirs altered due to tail gate operation, the changed Qr and hence yr were re-adjusted in such a way that during each run the value of Qr becomes equal to the difference between Qm and Qd . For this condition, the approach flow depth, y0 in the main channel at 1.0 m upstream of the trench was measured to calculate V0 and E0 . Two types of flow condition over the rack were examined, one in which incoming discharge is completely diverted into the trench i.e., Qm is equal to Qd while in the second case only a part of incoming discharge is diverted into the trench and the reminder flows downstream to the trench in the main channel. For submerged flow conditions, the water level in the intake was raised using a gate provided at the head of the diversion channel. The water level in the gage well was measured and the submergence defined as ys /E0 was calculated. The vortex shape and size formed in the trench was also visualized for different flow conditions. Ranges of various parameters covered in the data collected in the present study are given in Table 1. 3. Data presentation and analysis Experimental data collected in the present study were analyzed to investigate the discharge characteristics of a trench weir under free and submerged flow conditions.
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87 Y Sump
900
Diversion Channel
Weir - B 3900
Flow Suppresser Weir - A
Grid Walls
Boulders
Flow Suppresser
Grid Wall
Gauge Well
Main Channel
400 1000
1000 400
Intake Well
X
X Sump
500
750
Perforated Plates
Supply Channel
Bottom Rack Tail Gate Glass Panel
Y
300 5900
1200
600
2000
600
300
10000
1100
6000
PLAN Side Wall
580 730
Channel Bed
Weir - A
SECTION - X-X
Bed
Trench Top of Wall
Bed
ALL DIMENSIONS ARE IN mm SECTION - Y-Y Fig. 1. Layout of the experimental set-up.
Fig. 2. Flow pattern in trench for its different aspect ratios (a) H /W = 1.05; (b) H /W = 0.525; (c) H /W = 0.271; and (d) H /W = 0.173.
3.1. Effect of various parameters on the coefficient of discharge 3.1.1. Aspect ratio of trench Experiments were performed for constant Qm , S , w, t , s, sr , Lw with varying depth of the trench H to study the effect of aspect ratio of trench i.e., H /W on the diverted discharge. The vortex size formed in the trench as shown in Fig. 2(a) is of the order of
the width of the trench while the aspect ratio is large. Once the depth of trench H is less than the width of trench W (i.e. while H /W is smaller), the water in the trench pushes the vortex up resulting in an increase of pressure in the trench thereby increasing the depth of flow over the rack and consequently reducing the vortex size tendency of the water jet to enter into the trench as shown in Fig. 2(b). Variation of Qd /Qm with H /W and variation of Cd (determined as per Eq. (1)) with H /W are shown in Fig. 3(a) and
S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
83
Fig. 3. Effect of aspect ratio of trench on diverted discharge and coefficient of discharge.
Fig. 4. Variation of Cd with sr for S = 1/1250 and 1/500.
Fig. 5. Variation of Cd with s for S = 1/1250 and 1/500. s
s
Eddies
Flow Separation
Vortex shedding (fully developed)
(a) Coarser spacing.
s Eddies
s Flow Separation
Vortex shedding (partially developed)
(b) Finer spacing.
Fig. 6. Formation of vortices in between bars and behind the bars.
(b), respectively. These figures depict that the diverted discharge and Cd increase with an increase in H /W . As the aspect ratio H /W approached unity, the values of Qd and Cd tend to become constant and any further increase in H /W does not have any effect on Qd and Cd . This indicates that the depth of trench should be equal to or significantly larger than the width of trench for attaining the maximum withdrawal of discharge while the other parameters are constant.
3.1.2. Slope of rack From the complete set of observations such data were screened out for which Qm , S , s, w, t are constant and Cd varied with sr only. A decrease in the values of Cd with an increase in slope of rack is noticed (Fig. 4). The separation of flow that occurs over the rack is considered to be the prime cause for this, as for a steeper rack, the separated flow joins the racks at a large distance on the downstream side, which results in a decreased Cd .
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
Fig. 7. Variation of Cd with w for S = 1/1250 and 1/500. s
vortices, which results in more dissipation of energy. An increase in the width of bars beyond this limit decreases the space for the vortex formation resulting in a slight decrease in energy loss and an increase of Cd . However, for a further increase of width (i.e., w is greater than Ls ), the separated flow rejoins the bars and increases the energy loss by energy dissipation due to friction on the face of plate, resulting in a decrease in the Cd value with the increase in w . Fig. 7 also shows that value of Cd is lower for steeper channel slopes as compared to its value while channel slope is flatter. Further, it can also be seen from Fig. 7, that the maximum value of Cd for a given S occurs for w at about 0.026 m.
Ls w
Fig. 8. Flow separation and re-attachment.
3.1.3. Clear spacing of rack Variations of Cd with s while Qm , S , sr , w and t were constant is shown in Fig. 5 and Cd is found to decrease with an increase in s. During experimentation it is noticed that flow separation starts from the upward face of rack bars and subsequently vortices are formed in downstream portion. The separated flow and vortices are not able to develop fully for a smaller (fine) spacing between the bars as the separated flow remains confined to the rack boundary only in such cases, whereas for a larger (coarse) spacing, a fully developed separated flow develops (Fig. 6). Thus, the energy loss is smaller when s is small as compared to case when s is large, which results in high Cd for a lower spacing of bars. 3.1.4. Width (flatness) of rack Data corresponding to a relatively constant value of Qm , S , sr , s and t were screened out from the complete data set to study the variation of Cd with w . This variation is shown in Fig. 7. It is seen from this figure that Cd first increases and then decreases with an increase in w values. It seems that for w about 0.024 m, the separated flow does not rejoin the bars (i.e., w is less than Ls , Fig. 8) and enough space is available behind the bars for the formation of
3.1.5. Specific energy of approach flow The variation of Cd with E0 for the two sets of data wherein the values of other variables are constant is shown in Fig. 9, indicating a decrease in Cd with an increase in the specific energy. 3.1.6. Froude number, Reynolds number and dimensionless velocity head of approach flow The variation of Cd with Fr , Re and Vh∗ of the approach flow is shown in Fig. 10, 11 and 12, as an illustration using two data sets. Note that values of other variables affecting Cd are relatively constant in Figs. 10–12. These figures revealed that Cd values do not have any systematic variation with Fr and Vh∗ . However, Cd is found to decrease with an increase in Re . The value of Fr has varied in a small range which perhaps was not adequate to capture the variation in Cd values. Further data are being collected in the ongoing experimental work covering higher ranges of Fr . 3.2. Dimensional analysis Probable variables affecting the values of Cd are identified as B, L, S , H , W , t , w, s, sr , Lw, V0 , y0 , ys , E0 , µ, ρ, g. The functional relationship for Cd may be thus written as Cd = f1 (B, L, S , H , W , t , w, s, sr , Lw , V0 , y0 , ys , E0 , µ, ρ, g ) .
Fig. 9. Variation of Cd with E0 for the two sets of data.
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
85
Fig. 10. Variation of Cd with Fr .
Fig. 11. Variation of Cd with Re .
Fig. 12. Variation of Cd with Vh∗ .
of y0 and V0 only E0 may be considered. Eq. (3) may be modified in terms of the Reynolds number and the Froude number of the approach flow and dimensionless velocity head as
Cd = f3
w s Lw E0 ys V02 ρ V0 (4R) V0 S , , , sr , , , , ,√ t t t t t 2gE0 µ gy0
.
(4)
Analysis of data collected in the present study and those by other investigators [6,12] revealed that the Froude number, Reynolds number and dimensionless velocity head have no discernable effect on Cd . For free flow conditions with partial withdrawal, ys is equal to zero and Lw is equal to L, which is constant for a given rack slope. Therefore, Eq. (4) may be written as Fig. 13. Check on the proposed relationship (Eq. (6)) for Cd .
Taking ρ, V0 and t as the repeating variables, the resulting nondimensional parameters may be written as
Cd = f2
B L
H W w s
t
t
, , S, t
,
t
,
t
Lw y0 ys E0 ρ V0 t t
,
t
,
t
,
t
,
µ
, , sr , t
V0
,√
gt
.
(3)
In the present study, B/t , L/t , H /t, and W /t are constant and thus these are dropped. Since E0 is sum of y0 and Vh , thus in place
Cd = f3
S,
w s E0 , , sr , t
t
t
.
(5)
Graphical plotting of data presented in the previous section also revealed that the variables S , w, s, sr and E0 have a significant effect on Cd . 3.3. Relationship for coefficient of discharge for free flow condition Using 305 data sets collected in the present study for partial withdrawal, the following relationship for Cd has evolved by the
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S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87
Fig. 14. Flow characteristics of partial and complete withdrawal of discharge.
least squares technique. Cd = 0.471 − 0.124 × ln (s/t ) − 0.194 × sr − 0.01
× (w/t ) ;
R2 = 0.83.
(6)
Inclusion of other variables like S, E0 /t in Eq. (6) did not significantly improve the value of R2 . The remaining 114 data sets, not used in the derivation of Eq. (6), were used next to validate the proposed relationship for Cd i.e., Eq. (6). Observed and computed values of Cd using Eq. (6) for the test data are compared graphically in Fig. 13, which revealed that the computed Cd has a maximum error of ±10% which is considered as satisfactory. Under partial withdrawal, the trench is completely filled with water with a core of air in the center of the trench due to vortex flow. This results in non-existence of free water surface in the trench (Fig. 14). However, during complete withdrawal, atmospheric pressure exists on the both sides of the water jet, which results in the high discharge capacity of the bottom racks. 3.4. Relationship for coefficient of discharge for submerged flow condition Under submerged flow conditions, the trench is completely filled with water with no air entrainment due to the higher water level in the intake well. Pressure in the trench is high compared to the free flow condition and it increases with an increase of submergence resulting in a reduced value of the diverted discharge. Using 267 data sets collected in the present study for the submerged flow condition, the following relationship for λ has evolved.
λ=
Qd (submerged flow) Qd (free flow)
+ 0.535;
= 0.685 ×
R2 = 0.65.
ys E0
2
− 1.021 ×
ys
E0 (7)
The remaining 83 data sets, not used in the derivation of Eq. (7), were used next to validate the proposed relationship for λ i.e., Eq. (7). Observed and computed values of λ using Eq. (7) for the test data are compared graphically in Fig. 15, which revealed that the computed λ have a maximum error of ±20%. Thus, for calculating Qd under submerged conditions first the diverted discharge is calculated for free flow conditions. Next Eq. (7) is used to calculate the diverted discharge under the submerged condition. It may be noted that effect of other variables viz: s/t, sr and w/t on Qd (submerged) is accounted for through the use of Eq. (6) for the determination of the Qd (submerged). 4. Conclusions Analysis of collected data reveals that for the maximum discharge capacity of the trench, the aspect ratio of the trench i.e. ratio of its depth to width should be more than unity. The coefficient of
Fig. 15. Check on the proposed relationship (Eq. (7)) for λ.
discharge decreases with an increase of rack slope, width of flat, clear spacing of bars and Reynolds number of the approach flow. However, the Froude number and dimensionless specific energy do not affect the coefficient of discharge. The discharge coefficient of the rack under free flow conditions for partial withdrawal is less than the value corresponding to complete withdrawal due to the existence of atmospheric pressure on both sides of the water jet. The relationship developed for partial withdrawal i.e. Eq. (6) under free flow conditions computes the coefficient of discharge within ±10% of the observed ones. The coefficient of discharge for complete withdrawal depends on the wetted length of the rack. Under submerged flow conditions, the trench gets completely filled with water without air entrainment and it results in a reduced value of the diverted discharge compared to that under free flow conditions. In the absence of other information the proposed relationship i.e. Eq. (7) can be used for the computation of diverted discharge under submerged flow conditions with a maximum error of ±20%. References [1] Paudyal GN, Tawatchai T. Design of a bottom intake structure for mountain streams. In: Proc. int. symp. on design of hydraulic structure. 1987. p. 73–82. [2] Mostkow MA. A theoretical study of bottom type water intake. La Houille Blanche 1957;4:570–80. [3] Noseda G. Operation and design of bottom intake racks. In: Proc. 6th gen. meeting. IAHR, 3(17). 1956. p. 1–11. [4] White JK, Charlton JA, Ramsay CAW. On the design of bottom intakes for diverting stream flows. Proceedings of the Institution of Civil Engineers (London) 1972;51:337–45. [5] Subramanya K, Shukla SK. Discharge diversion characteristics of trench weir. Journal of Civil Engineering Division, The Institution of Engineers (India) 1988; 69(I3):163–8. [6] Subramanya K. Trench intake for mini hydro projects. In: Proc hydromech and water resources conf IISc. 1990. p. 33–41. [7] Subramanya K. Hydraulic characteristics of inclined bottom racks. In: National symp. on design of hydraulic structures. India: Deptt of Civil Eng., Univ of Roorkee; 1994. p. 3–9. [8] Ghosh S, Ahmad Z. Characteristics of flow over bottom racks. Water and Energy International, CBIP 2006;63(2):47–55.
S. Kumar et al. / Flow Measurement and Instrumentation 21 (2010) 80–87 [9] Brunella S, Hager WH, Minor HE. Hydraulics of bottom rack intake. ASCE Journal of Hydraulic Engineering 2003;129(1):2–10. [10] Righetti M, Lanzoni S. Experimental study of the flow field over bottom intake racks. ASCE Journal of Hydraulic Engineering 2008;134(1):15–22. [11] Ahmad Z, Mittal MK. Hydraulic design of trench weir on Dabka river—A case study. Water and Energy International, CBIP 2004;60(4):28–37. [12] Venkataraman P. Discharge characteristics of an idealised bottom intake. Journal of the Institution of Engineers 1977;58(2–3):99.
S. Kumar is currently research scholar of Civil Engineering at IIT Roorkee, India. He obtained his Diploma (DDC), B.Tech. (Civil) and M.Tech. (Civil) degree from AMU, Aligarh, India. He has published 2 papers in referred national conference proceedings. His area of research is hydro power, computational hydraulics and hydraulic structures. He has been recipient of University medal for standing 1st in M.Tech. Z. Ahmad is currently Associate Professor of Civil Engineering at IIT Roorkee, India. He obtained his B.Tech. (Civil) degree from AMU Aligarh, M.Tech. (Hyd) degree from Univ. of Roorkee and Ph.D. degree from T.I.E.T., Patiala. He has published about 52 papers in referred national and international journals and conference proceedings. His area of research is surface water quality management, computational hydraulics and hydraulic structures. He has written two Monographs on Transport of Pollutants
87
in Open Channels and Control Section in Open Channels for AICTE, New Delhi. He has been recipient of G.N. Nawathe, Jal Vigyan Puraskar (twice); Department of Irrigation Award; and his name appeared in Marquis Who’s Who in the World edition 2005. Umesh C. Kothyari is presently professor of Civil Engineering, IIT Roorkee, did M.E. (Hyd.) and Ph.D. (River Eng.) from University of Roorkee (now IIT) in 1985 and 1990, respectively. He Joined Univ. of Roorkee in 1985 and since then actively engaged in teaching, research and consultancy. Supervised 12 Ph.D. theses, 49 M.Tech. theses, published 61 research papers in international review journals, 57 papers in conference proceedings and completed more than 24 consultancy projects. Recipient of Young Engineer Award awarded by Central Board of Irrigation and Power, India, 1994 and S.N. Gupta Memorial Lecturer award awarded by Indian Society for Hydraulic Engineering, Pune, 2006. M.K. Mittal is presently Emeritus Fellow of Civil Engineering, IIT Roorkee, did B.E. from Gorakhpur University in 1966 and M.E. (Hyd.) from University of Roorkee (now IIT) in 1968. Joined Univ. of Roorkee in 1971 after serving two years as Assistant Engineer in U.P. Irrigation Department. Retired as professor of Civil Engineering, I.I.T. Roorkee in 2007. Actively engaged in teaching, research and consultancy for the last 38 years. Supervised 34 M.Tech. theses, published 38 research papers and associated with more than 100 consultancy projects. Recipient of University Gold Medal and Khosla Research Award. Fellow of ISH and Member of ISTE and ISCMS.