04- Punjab Barrages, Dr. Zulfiqar Ch

Pakistan Journal of Water Resources, Vol.13(2) July-December 2009/ 29

Punjab Barrages - Hydraulic Deficiencies and Rehabilitation Solutions

Z.A. Chaudhry1

ABSTRACT: The world’s largest irrigation system consisting of barrages, canals, distributaries and watercourses exists in Pakistan. Some of the barrages are facing hydraulic and structural problems due to aging and water induced wear and tear. Irrigation and Power Department, Government of Punjab, has planned to rehabilitate and modernize its barrages. A project entitled as, “Rehabilitation and Modernization of Barrages in Punjab” has been launched with the financial assistance of World Bank under which Taunsa barrage has already been modernized. The major rehabilitation work undertaken is the construction of a subsidiary weir at the downstream of the barrage. Arguments have emerged regarding problems identification and technical/financial rationalities of provision of subsidiary weir, whereas the feasibility/detail design to rehabilitate and modernize some of the remaining barrages are in progress. The paper critically reviews hydraulic/structural deficiencies at the barrages in Punjab and propose solutions/guidelines to optimize rehabilitation works.

KEYWORDS: Subsidiary weir, Two-step weir, concrete block floor, loose stone apron.

INTRODUCTION

Barrages/head regulators may face stability problems such as aging, energy dissipation in stilling basins, piping underneath the floor and malfunctioning of mechanical gates. To optimize quantum of rehabilitation works, precise identification of hydraulic problems is paramount; otherwise huge investment may partially or completely waste as noted by Chaudhry et al. (2008), Chaudhry (2008) and Chaudhry (2009).

Studies such as, Evaluation of Safety of Jinnah Headworks (1998), Feasibility Report of Jinnah Barrage (2005), Hashmi (2003), Sectional Model of Taunsa Barrage (2005), and Appraisal Report on Safety of Jinnah Barrage (2001) noted that the main problem which has posed threats to some of the barrages in Punjab is poor functioning of energy dissipation system causing the baffle/impact blocks to deteriorate. It was further reported that major cause for inefficient energy dissipation mechanism is the drop in water level due to excessive retrogression; consequently

1Professor, Civil Engineering Department, University of Engineering & Technology, Lahore – Pakistan.

giving rise to sweeping of hydraulic jump over the floor. Even if those statements are correct, barrages are low head hydraulic structures and there is hardly a chance of cavitations and consequently the failure of concrete floor. While finding the underlying reasons, Chaudhry (2008) noted that the structural damages to baffle/impact blocks could be due to abrasion and striking of coarse material carried with water. These damages therefore needs be repaired as and when required e.g. in case of Jinnah barrage the baffle/impact blocks and adjacent concrete floor were repaired during 2001-03, first time after the barrage became operational in 1947. At present the repaired/replaced blocks and concrete floor is working properly.

Islam barrage on river Sutlej was rehabilitated by constructing a subsidiary weir at about 400 ft of its downstream. The subsidiary weir was constructed to shift hydraulic jump on the glacis and to dissipate excessive kinetic energy. But the barrage lost its discharging capacity soon after its rehabilitation, implying inefficacy of the subsidiary weirs. Similarly, Taunsa barrage has been recently rehabilitated in the same way i.e. constructing a subsidiary weir across the river. Furthermore, existing concrete floor was

Z.A. Chaudhry


strengthened by overlaying 3 ft thick RCC slab and replenishment of loose stone apron. Rationality of this massive rehabilitation weir becomes questionable as Chaudhry (2009) noted that the prevailing water depth downstream of Taunsa barrage was adequate to form hydraulic jump over the glacis. Hydraulic performance of barrage, under-sluices, silt excluders and subsidiary weir are not yet tested at higher discharges. Furthermore, hydropower development after the construction of subsidiary weir has become very difficult.

Mahboob (1942 and 1943) reviewed the design of Jinnah barrage and found it acceptable to the requisite hydraulic/structural standards. Feasibility Report of Jinnah Barrage (2005) found excessive retrogression to repel hydraulic jump, whereas Chaudhry (2008) observed that the stilling basin mechanism at Jinnah barrage is impact-jump type, which is not very sensitive to downstream water level. The feasibility report (2005) proposed subsidiary dam as a feasible measure of rehabilitation whereas Chaudhry et al. (2008) and Chaudhry (2008) disagreed and proposed two alternatives to the subsidiary weir.

REVIEW OF LITERATURE

Punjab Barrages

There are 14 barrages/head regulators, constructed in Punjab on five rivers i.e. Indus, Jhelum, Chenab, Ravi and Sulej. Khanki head regulator was the first to be constructed during 1889-1892. However, it suffered from structural and hydraulic problems soon after its construction and was therefore had to be remodeled during 1919-20. After that, a number of barrages were constructed on various rivers to irrigate barren land in Punjab. Structural details/salient features of the barrages/head regulators are summarized in Table 1 and 2.

The barrages on Indus, Jhelum and Chenab rivers are designed for discharge varying from 800,000 to 1100,000 cusec, whereas the design discharge per unit width varies from 204 to 300. Normal flows in river Ravi and Sutlej have significantly been reduced after signing “Indus Water Treaty” with India. However, during summer the possibility of higher discharges still exists.

Table 1: Details, Design Discharges and Maximum Flood Levels of Major Barrages

River Barrage/

Head Regulator

Year of Completion

Waterway (ft)

Design Discharge (cusec) Max Flood Passed

(cusec) Total

Per Unit Width

Indus Jinnah 1946 3353 950000 283

862000

Chashma 1971 3556 950000 267 950000 Taunsa 1959 3862 1000000 259 760784

Jhelum Rasul 1967 2880 850000 295 880000

Chenab

Marala 1968 3960 1100000 278 1100000

Khanki 1920 (Remodeled)

3929 800000 204 1086000

Qadirabad - 3000 900000 300 854000 Trimmu 1938 2220 645000 291 943225 Panjnad - 2820 700000 248 802516

Ravi Balloki 1913 1400 225000 161 275000 Sidhani - 760 150000 197 244348

Sutlej Sulemanki - 1920 325000 169 - Islam 1928 1399 300000 214 492000 Mailsi - 1440 429000 298 160000

Punjab Barrages, Hydraulic/Structural Deficiencies and Rehabilitation Solutions


Table 2: Salient Features and Energy Dissipation Systems of Various Barrages

Barrage

Additional Energy

Dissipation Devices

Concrete Floor (ft) Stone Apron

(ft)

Crest Level - D/S Floor Level (ft)

Impervious Pervious Provided

Value as per USBR

Jinnah Baffle Blocks 70.00 60.58 40 8.0 12

Chashma Baffle Blocks 113.50 40.00 104.0 18.0 12

Taunsa Baffle Blocks 110.00 66.83 80.00 12.0 12

Rasul Baffle Blocks 86.00 65.00 105.00 18.0 13

Marala Baffle Blocks 64.50 22.00 54.00 10.5 12

Khanki Stepped Chute 100.00 55.00 60.00 12.0 11

Qadirabad Baffle Blocks 92.00 77.00 57.00 13.5 13

Trimmu No 64.00 95.00 50.00 9.5 13

Panjnad No 46.50 62.00 48.00 9.0 11.5

Balloki Baffle Blocks 70.00 55.50 55.00 7.0 11.5

Sidhani Baffle Blocks 105.00 103.00 40.00 15.5 11.5

Sulemanki No 35.00 60.00 30.00 11.0 11.5

Mailsi Baffle Blocks 100.00 78.00 - 12.0 13

Data given in Table 2 noted that the barrages constructed even on same river and in similar terrain are having different depth between crest and downstream floor. For example the three barrages on Indus, (Jinnah, Chashma and Taunsa) are having almost same design discharge but the depth between crest and downstream varies. Higher depth for Chashma (18 ft) is understandable as the barrage is designed for storage but why the depth differs between Jinnah (8 ft) and Taunsa barrages (12 ft). Similarly the length of impervious and pervious floor and loose stone apron also considerably vary.

Barrages such as Chashma, Rasul, Marala, Khanki, Qadirabad, Trimmu, Panjnad, Islam and Balloki, the water depth over the loose stone apron is further raised by depressing concrete block floor and placing loose stone apron at slope. Two rows of baffle/impact blocks and two rows of friction blocks are provided at almost all the barrages to stabilize hydraulic jump and to ensure its termination over paved floor.

Hydraulics

On the basis of surface flow hydraulics and energy dissipation system the Punjab barrages can be placed into two categories. Category 1 barrages are having enough water depth to form hydraulic jump over the glacis and to satisfy USBR requirements for the design of low Froude number stilling basins whereas otherwise are to be considered in Category 2 (Table 2). Stilling basins for barrages such as Chashma, Taunsa, Rasul, Marala, Khanki, Qadirabad, Sidhani, Sulemanki and Mailsi may be considered as jump type as the floor is placed as per USBR guidelines to form hydraulic jump over the glacis. However, due to excessive retrogression if water level goes down, the impact blocks divert flow up and energy dissipation take place partly in air and partly in water. Furthermore, friction blocks help to stabilize and terminate hydraulic jump over paved floor.

It is already stated that the depth between crest and downstream floor is 8 ft for the Jinnah

Z.A. Chaudhry


barrage whereas the minimum value as per USBR guidelines is 12 ft (Table 2). As shown in Figure 1 the jump sweeps, but baffle/impact blocks helps to develop and terminate the jump within paved floor. Chaudhry (2008) noted that the energy dissipation takes place partly in air and partly in water and no structural damages occur at paved floor, whereas the damages to baffle/impact blocks could be due to abrasion and striking of gravely material travelled alongwith water. However, relatively higher downstream velocity will displace loose stone apron more frequently at Jinnah barrage.

Displacement of loose stone apron can be controlled by placing stone either at stable slope or at lower level by depressing concrete block floor. This concept is being applied at number of barrages such as Chashma, Rasul, Marala, Khanki, Qadirabad, Trimmu, Panjnad, Islam and Balloki.

It is stated that the barrages placed in Category 1, are having enough water depth, therefore the provision of subsidiary weir/second stilling basin, downstream of such barrages has no technical justification. Furthermore if existing downstream floor is overlaid by concrete slab, the block floor and loose stone elevation may keep at same elevation. Otherwise, stone apron will be more susceptible to displacement as compared with the condition before rehabilitation. Data given in Table 2 reveal that the stilling basins floor length looks adequate for all the barrages in Punjab.

Structural Concrete at Downstream Floor and Glacis

In general higher grade concrete is being used over glacises and part stilling basins. The structural performance of barrages remained adequate except Taunsa barrage, where ripping of floor slab and uprooting of impact blocks occurred, repeatedly. Feasibility Report Taunsa Barrage (2005) noted that structural and mass concrete is of poor quality. It was mentioned in the report that rate of drilling in skin concrete was fast, i.e. 12 inches in 55 minutes and core recovery was only 45% in broken pieces with maximum of 4 inches.

Chaudhry (2009) noted that structural concrete 1 ft thick (top layer) is insufficient in situations where repeated loads act; consequently the mass and structural concrete separated. In this scenario the uplift pressure may directly act underneath the structural concrete and lift it up. However, at Taunsa barrage, 2 ft top layer of downstream glacis and stilling basin was removed and 3 ft thick reinforced concrete of 4000 psi overlaid. Impact and friction blocks were replaced by chute blocks and end sill.

Some minor damages to downstream floor and impact blocks may have occurred at the other barrages. These damages may be due to abrasion and striking of course material traveled along with water. Such damages are natural and can be repaired as and when required.

(Fig. 1a) (Fig. 1b)

Figure 1: Shows Functioning of Energy Dissipation System at the Jinnah Barrage



REHABILITATION SOLUTIONS

It is already stated that the excessive kinetic energy is dissipated with the provision of submerged or submerge cum impact jumps. In either case a structurally adequate concrete floor remains safe. At higher discharges the loose stone apron is more susceptible to displacement as the velocity remains higher than the limiting velocity noted by Chaudhry (2009). Launching of loose stone apron will be pronounced at barrages where loose stone is deficient in size and placed at shallow depth.

A barrage usually consists of weir and undersluices sections, separated by divide walls. To ensure flushing, undersluices crest and floor levels are kept low as compared with weir section of the barrage. The rehabilitation works downstream of a barrage should be self-governing for weir and undersluices sections. Furthermore, the detailed structural assessment and river survey has to be carried out to finalize the scope of rehabilitations works. The downstream water levels, at different discharges, should be computed with caution otherwise, reliability of numerical solutions and model study results will be questionable noted by Chaudhry (2009).

Three feet additional retrogression was considered while designing rehabilitation works at Taunsa and Jinnah barrages. A barrage functioning perfectly alright if checked with additional retrogression show jump sweeping and high downstream velocity. This has already been demonstrated during model studies of Taunsa

and Jinnah barrage rehabilitation scenarios. Chaudhry (2008) and Chaudhry (2009) noted that no further retrogression occurred and water level has been stabilized at the Jinnah barrage since last sixteen years. Design of rehabilitation works on the basis of anticipated/additional retrogression is therefore not a realistic assumption.

Hydropower development option within the barrage should be kept in mind while designing rehabilitation works. Dismantling of permanent structures would be highly difficult if power generation option is considered later on. Following sections discuss salient features of possible rehabilitation scenarios to address energy dissipation problems and consequently the launching of loose stone apron.

Subsidiary Weir

A subsidiary weir has already been constructed downstream of the Taunsa barrage. A similar structure has been proposed downstream of Jinnah barrage as rehabilitation structure, narrated in Feasibility Report, Jinnah Barrage (2005). Data given in Table 2 reveal that hydraulic design of Taunsa barrage is adequate indicating that a rehabilitation structure like subsidiary may not needed.

Subsidiary weir arrangement at 600 ft from the barrage crest was tested during physical model studies of Jinnah barrage rehabilitation scenarios. The subsidiary weir crest level varied from EL674 to EL676. Chute blocks and end sill were also

Fig. 2a Fig. 2b

Figure 2: Downstream of the Barrage the Scour Pits Developed and Stone Apron Launched (Subsidiary Weir at 600ft and Crest at EL676)

Z.A. Chaudhry


tested in the model study. The rise in water level upstream of subsidiary weir with crest level at EL676 was just satisfactory to shift the hydraulic jump over the glacis. Subsidiary weir crest level was 2 ft lower and 1 ft higher as compared with crest level of weir (EL678) and undersluices (EL685) sections of the barrage, respectively.

Table 3 indicates that the decrease in velocity upstream of subsidiary weir, especially at higher discharges is not promising. Furthermore, the velocity remained higher and fluctuating near the bed, which developed deep scour pits and loose stone apron was completely washed away. Experimental results indicate that the subsidiary weir is an isolated structure and not showing any structural support to the barrage.

Extension of Concrete Block Floor and Placing Loose Stone Apron at Stable Slope

Hydraulic jump if not terminate over paved floor and velocity remain fluctuating and higher near the bed; consequently the displacement of loose

stone apron will be more. In such cases the concrete block floor can be extended to ensure jump termination over paved floor. Extended floor can be depressed by few feet to ensure acceptable velocity over loose stone apron. Depressed concrete block floor has already been provided on barrages such as Chashma, Rasul, Marala, Balloki, etc.

Water depth along loose stone apron can further be increased by placing stone at slope. Stone apron can be extended up to the anticipated retrogression level both at weir and undersluices sections of a barrage. This arrangement works as protective measure and make barrage safe from ill effects of further retrogression and local scour. The stone apron at 1:15 slope and extended up to the anticipated retrogression level has been proposed at Jinnah barrage as Alternative 1 to the subsidiary weir Chaudhry (2008). Figure 3 show that the arrangement worked well even at the discharge 950000 cusec when tested on physical model.

Table 3: Water Depth and Velocity Variations, with and Without Subsidiary Weir

Discharge (cusec) (prototype values)

Water depth downstream of barrage (ft)

Velocity downstream of barrage (ft/sec)

Total Per unit width

With subsidiary weir

Prevailing value

With subsidiary weir

Prevailing value

50000 15 8.45 3.70 1.78 4.05 100000 30 9.90 5.30 3.03 5.66 300000 90 13.50 10.10 6.67 8.91 500000 150 16.35 13.70 9.17 10.95 750000 225 19.60 17.70 11.48 12.71 850000 255 20.70 18.20 12.32 14.01 950000 285 21.65 20.00 13.16 14.25

Fig. 3a: Existing Condition Fig 3a: Proper Sized Stone Placed at 1:15 Slope

Figure 3: Physical Model of Jinnah Barrage, Showing Loose Stone Apron Displacement



CONCLUSIONS

Except Taunsa, the barrages in Punjab are structurally adequate and there is a little chance of cavitations, along glacis and horizontal floor. Damages to baffle/impact blocks and adjacent concrete are customary and shall be repaired as and when required. While repairing baffle blocks and adjacent concrete floor, erosion resistance lining may be provided.

Hydraulic jump if not terminate over paved floor, velocity remain fluctuating and higher near the bed; consequently displacement of loose stone apron could be more. In such cases concrete block floor can be extended to ensure jump termination over paved floor. Furthermore, the extended floor can be depressed by few feet to ensure acceptable velocity over loose stone apron. A rational, viable and economical solution is the placing of loose stone at stable slope in proper size.

ACKNOWLEDGEMENT

The author is thankful to Mr. Shakoor, Senior Model Expert for technical discussions and valuable suggestions.

REFERENCES

Chaudhry. Z.A., S.H. Nasim., A. Shakoor (2008). Alternative Report to Subsidiary Weir, Rehabilitation and Modernization of Jinnah Barrage Project, Submitted to Irrigation & Power Department, Government of Punjab.

Chaudhry. Z.A. (2008). “Energy Dissipation Problems Downstream of the Jinnah Barrage”. Pakistan Journal of Engineering and Applied Sciences, 3: 19-25.

Chaudhry. Z.A., (2008). “Hydraulics of Jinnah Barrage; Existing Structure and Rehabilitation

Alternatives”. Pakistan Journal of Engineering and Applied Sciences, 4: 66-73.

Chaudhry. Z.A. (2009). “Surface Flow Hydraulics of Taunsa Barrage (Before and after Rehabilitation)” Accepted Publication in Pakistan Journal Science, 61(3).

Evaluation of Safety of Jinnah Headworks (1998). Report Submitted by Associated Consulting Engineers ACE (Pvt.) Ltd to Irrigation & Power Department, Government of Punjab.

Feasibility Report, Jinnah Barrage (2005). Submitted by Joint Venture of Associated Consulting Engineers (ACE) to Irrigation and Power Department.

Hashmi, M.Z. (2003). Analysis of Hydraulic Jump and Effectiveness of Energy Dissipation Devices at Jinnah Barrage. Water Resources Engineering, CRE, UET, Lahore.

Sectional Model of Taunsa Barrage (2005). Irrigation & Power Department, Government of the Punjab, IRR-1172.

Appraisal Report on Safety on Jinnah Barrage (2001). Submitted by National Development Consultants (NDC) to Irrigation & Power Department, Government of Punjab.

Mahboob. S.I (1942). The Kalabagh Barrage, Punjab Engineering Congress, Paper No.251. 66p.

Mahboob. S.I. (1943). Design and Construction of Kalabagh Barrage, Punjab Engineering Congress, Paper No.34.

Chaudhry, Z.A. (2009). Physical Model Study of Jinnah Barrage Rehabilitation Alternatives, Submitted for Publication in Pakistan Journal of Engineering and Applied Sciences.

Documents

04- Punjab Barrages, Dr. Zulfiqar Ch