Vertical canal fall

Design Methodology of Vertical Fall

1. VERTICAL FALL DESIGN Muhammad Fahim Aslam

2. PRESENTATION LAYOUT Fall Structures Purpose of Falls Types of Falls Steps for Design of Fall Structures Literature Review Methodology Results Profile Drawings Conclusion References

3. FALL STRUCTURES A canal fall or drop is an irrigation structure constructed across a canal to lower down its bed level to maintain the designed slope when there is a change of ground level to maintain the designed slope when there is change of ground level. Fall structures are also necessary on canals to provide flatter longitudinal bed slope to the canals when the average natural slope of land is steeper than required longitudinal slope to design stable

4. PURPOSE OF PROVIDING FALLS It conveys water from a higher to a lower elevation Dissipates excess energy Helps to save earthwork Helps to Improve command and regulation of canal

5. Classification of Falls : Meter Falls: Measure the discharge of the canal Non meter Falls Do not measure discharge For a fall to act like meter, it must have broad weir type crest so that the discharge coefficient is constant under variable head . Generally glacis type fall is suitable as a meter whereas vertical drop is not suitable due to formation of partial vacuum under the nappe.

6. Flumed Falls The contracted falls are called flumed falls Unflumed Falls while full channel width falls are the unflumed falls

7. Types of Falls: Vertical Fall Glacis Fall Rapids Trapezoidal notch falls Chute Fall Inglis Fall Montague type fall

8. STEPS INVOLVED IN HYDRAULIC DESIGN OF FALLS

9. LITERATURE REVIEW Masoume et al. (2018) performed a comprehensive set of experiments on grid drop-type dissipators in a rectangular open channel. The adjustment and boundaries of different flow regimes The variation of flow hydraulic characteristics downstream of a grid drop-type dissipator , caused by the gradual alteration of the tail-water depth. Results indicated that two key flow regimes, namely “bubble impinging jet flow regime” and “surface flow regime” arise because of the changes made in the tail-water depth. Jyh-jong et al. (2015) presents failure cases of low-head drop structures in bedrock channel. Three processes include, Local scour in channel bed and bank toe downstream the vertical drop structure. Scour at structure edges of the transition interface between artificial material and natural bedrock. Damage of concrete pavement by impact of large boulders

10. LITERATURE REVIEW (Cont.) Lin et al. (2010) investigated the characteristics of flows over a vertical drop experimentally using laser Doppler velocimetry for detailed quantitative velocity measurements and a flow visualization technique for qualitative study of flow pattern. Ismail et al. (2009) investigated the flow over a drop structure placed in a rectangular channel through an experimental program. Procedures adopted are The first procedure was physically based with an empirical component for the estimation of the depth of the pool formed at the base of the drop. The second resulted in an equation for the direct estimation of the downstream depth.

11. LITERATURE REVIEW (Cont.) Rajaratnam et al. (2010) presented a critical analysis of the energy loss at drops. Mohammad et al. (2008) experimentally studied the energy loss of the vertical drop with subcritical flow in the upstream channel with a physical model of 0.20m drop height. Kabiri et al. (2016) investigated flow characteristics over vertical drops equipped with a grid roof The results indicate that the proposed hydraulic structure eliminates unfavorable flow conditions and forms the basis of a more effective flow control system compared with a plain vertical drop. Xie et al. (1998) developed experimental hardware to perform the experiments of drop Marangoni migration in the case of intermediate Reynolds numbers in a microgravity environment. Experimental results show that Marangoni migration velocity depends on the temperature gradient and the drop diameter for fixed experimental mediums

12. LITERATURE REVIEW (Cont.) Arturo et al. (2010) used computational fluid dynamics (CFD) models to formulate, implement and evaluate junction and drop-shaft boundary conditions (BCs) for one-dimensional modeling of transient flows in single-phase conditions (pure liquid). The results suggest that the junction and drop-shaft BCs can be used for modeling transient free-surface, pressurized, and mixed flow conditions with good accuracy. Roberta et al. (2013 ) made an experimental campaign in order to investigate the hydraulic features of a vertical drop shaft, also considering the influence of a venting system consisting of a coaxial vertical pipe, projecting within the drop shaft with different plunging rates.

13. Methodology Basic Hydraulic and geometric Data of the Canal was available comprising of. Discharge Full Supply Level (FSL) of canal Bed Levels of Canal Berm Widths Free Board Flow velocity Longitudinal Slope Side Slope Lacey’s Silt Factor

14. Methodology (Cont.) First of all crest level, crest height and crest width were calculated in order to check the discharge carrying capacity of structure, with the help of following formulas CL = Q/(CW) 0.667 Where CL= Crest Level Q= Discharge in canal C= Co-efficient of Discharge W= Width of structure   Measured the Lacey’s scour depth (R ) R’ =FOS × R Three criteria’s were used to decide the level of cutoff length. Minimum Level from following three was decided as the cutoff level. U/S and D/S cutoff levels have been calculated through this method R’-(FSL- Bed Level) (FSL-Bed Level)/2 (NSL- 1ft)

15. Methodology (Cont.) Basin design of the fall( Length of Cistern and sill height) has been done with the help of two approaches Bahadarbad Irrigation Research Institute Formula (Ref. Iqbal Ali)   Eichvery Formula

16. Methodology (Cont.) Calculation of uplift pressures was done with the help of Khosla’s Theory and accordingly the structural lengths have been calculated ἀ =b/d  λ = (1 + √(1+α2))/2 φ E =(1/π)(Cos -1 (λ-2)/λ) φ D =(1/π)(Cos -1 (λ-1)/λ) Stone protection works(Length and Thickness) on U/S and D/S side have been calculated by using the scour levels and structural lengths  Computation of exit gradient was done   Exit Gradient value must be below the permissible values of Exit Gradient.

17. Methodology (Cont.) Structural Lengths of the structure are calculated according to the canal cross section   Length of Wing Wall =   Hz. Length of Splay of Wing Wall =   Computation of U/S, D/S Tail energy levels(TEL) were calculated with the help of levels and losses.   Energy values were read from the Blench Curves (Plates 10.1, 10.2, 10.3a, 10.3b and 11) Froude no. was calculated to check the type of flow over the fall.   Levels of the Hydraulic Grade line were calculated by using the uplift pressures calculated earlier. Profile of the vertical fall before and after the jump was drawn by using the dimensions of the floor lengths, hydraulic grade line and unbalance head before and after the vertical fall.

18. GENERAL PROFILE OF FALL

19. DRAWINGS (General Arrangement Plan)

20. Longitudinal Cross Section

21. CONCLUSION Literature review on Vertical Fall has been done Most optimum design has been carried out using different theories and criteria’s so that the best hydraulic results are achieved from the structure without affecting the economy and life. Check for exit gradient and uplift pressures by Khosla’s Theory The structure is safe against piping and uplift. Also, the heel of the walls of the fall has been extended so that the weight of soil shall also help to increase the weight of the structure Accordingly the structure lengths have been calculated. Hydraulic grade line and Hydraulic Profile of the vertical fall has been drawn by calculating the energy levels and pre/post fall unbalance heads.

22. REFERENCES Masoume Sharif,  Abdorreza Kabiri-Samani . (2018)  Flow regimes at grid drop-type dissipators caused by changes in tail-water depth .  Journal of Hydraulic Research  0:0, pages 1-12.  C. Lin, W.-Y. Hwung , S.-C. Hsieh, K.-A. Chang. (2007)  Experimental study on mean velocity characteristics of flow over vertical drop .  Journal of Hydraulic Research  45:1, pages 33-42.  Ismail I. Esen ,  Jasem M. Alhumoud ,  Khoanddkar A. Hannan . (2004)  Energy Loss at a Drop Structure with a Step at the Base .  Water International  29:4, pages 523-529.  N. Rajaratnam , M.R. Chamani . (1995)  Energy loss at drops .  Journal of Hydraulic Research  33:3, pages 373-384.  Mohammad R. Chamani , N. Rajaratnam , M. K. Beirami . (2008) Turbulent Jet Energy Dissipation at Vertical Drops.  Journal of Hydraulic Engineering  134:10, pages 1532-1535.  A.R. Kabiri-Samani , E. Bakhshian , M.R. Chamani . (2017) Flow characteristics of grid drop-type dissipators .  Flow Measurement and Instrumentation  54, pages 298-306.  Xie J., Lin H., Han J., Dong X., Hu W., Hirata A. and Sakurai M. (1998). Experimental investigation on Marangoni drop migrations using drop shaft facility. International Journal of Heat and Mass Transfer , 41(14), pp.2077-2081. Naib S.K.A. (1984) Hydraulic Research on Irrigation Canal Falls. In: Smith K.V.H. ( eds ) Channels and Channel Control Structures. Springer, Berlin, Heidelberg. Padulano , Roberta & Del Giudice , Giuseppe & Carravetta , Armando. (2013). Experimental Analysis of a Vertical Drop Shaft. Water. 5. 1380-1392. 10.3390/w5031380. Garg , Santosh . Irrigation Engineering and Hydraulic Structures. 16 th ed. Delhi: Khanna Publishers, 2002. Chow, Ven. Open Channel Hyraulics . Singapore: McGraw-Hill International, 1959. Ali, Iqbal . Irrigation and Hydraulic Structures. 2nd ed. Karachi: Farhat Iqbal , 2003.

23. Thank you