unit-2 all notes and questions with answers
- 1. Lecture-1 Canal Drop – Notch Type DESIGN AND DRAWING OF IRRIGATION STRUCTURES 1
- 2. What is Canal Drop (Fall)?? It is a solid masonry or concrete structure constructed on the canal if the natural ground slope is steeper than the designed canal bed slope. If the difference in slope is small single fall can be constructed, otherwise more falls are constructed at regular suitable intervals. 2 DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 3. Types of Canal Fall Depending on the ground level condition and shape of the fall, they are classified as Ogee fall, Stepped fall, Vertical fall, Rapid fall, Straight Glacis fall, Trapezoidal notch fall, Well or Cylindrical notch fall(Syphon well drop), Montague type fall and Inglis or Baffle fall. DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 4. Design a canal drop of 2 meters with the following data Good soil is available for foundations at +8.50. DESIGN AND DRAWING OF IRRIGATION STRUCTURES Hydraulic Particulars Of The Canal Above Drop Below Drop Full supply discharge 4 m3/s 4 m3/s Bed width 6.00 m 6.00 m Bed level +10.00 +8.00 Full supply depth 1.50 m 1.50 m F.S.L +11.50 +9.50 Top of bank 2 m wide at level +12.50 +10..50 Half supply depth 1.00 m.
- 5. Components to be Designed 1. Trapezoidal Notch (Dimensions Of The Notch) 2. Length Of Drop Wall Between Abutments 3. Profile Of Drop Wall 4. The Length Of Horizontal Floor Of The Cushion 5. Notches And The Notch Pier 6. Design Of Protective Works DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 6. Design: 1. Trapezoidal Notch Assume 2 notches. Discharge through each notch = 4/2 = 2 cubic meters/second The discharge through a trapezoidal notch = QRec+ QTri Q = 2/3 LCd 𝟐𝒈 𝒉𝟑/𝟐 + 8/15 Cd Tan (𝜽/𝟐) 𝟐𝒈 𝒉𝟓/𝟐 Assume Cd = 0.7 For full Supply Discharge Q = 2 m3/s h = 1.5 m 2 = 2/3×0.7 𝟐 × 𝟗. 𝟖𝟏 × 𝟏. 𝟓𝟑 /𝟐 + 8/15 × 0.7 × Tan (𝜽/𝟐) 𝟐 × 𝟗. 𝟖𝟏 𝟏. 𝟓𝟓 /𝟐 ------ (I) For Half Supply Discharge Q = 1 m3/s h = 1.0 m 1 = 2/3×0.7 𝟐 × 𝟗. 𝟖𝟏 × 𝟏. 𝟎𝟑/𝟐 + 8/15 × 0.7 × Tan (𝜽/𝟐) 𝟐 × 𝟗. 𝟖𝟏 𝟏. 𝟎𝟓 /𝟐 ------ (II) By solving above Two Equation We will get L = 0.4 m and 𝜽 = 5o – 45’ DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 7. The width of notch at sill +10.00 = 40 cms The width of notch at F S L.i.e., at +11.50 = (0.40 + 1.5 x 2 x tan 50451 ) = 0.70 meter or 70 cms. DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 8. 2. Length Of Drop Wall Between Abutments The length of drop wall = 7/8 x u/s bed width = 7/8 x 6 = 5.25 m 3. Profile Of Drop Wall DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 9. Top thickness of drop wall = h1/2 + (15 to 30 cms) = 1.5/2 + 0.15 = 0.9 m (adopt 1 m) The height of drop wall depends upon the depth of water cushion that is to be allowed in rear. Depth of water cushion can be calculated based on the following formula. (X+h2) = 0.9 x h1 x 𝒉 X = Depth of water cushion h1 = U/s full supply depth = 1.5 m h2 = D/s full supply depth = 1.5 m h = head causing flow = U/s FSL – D/s FSL = 11.50 – 9.50 = 2 m X = 0.4 m = 40 cms DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 10. Hence water cushion may be kept 40 cms below the D/s bed level of channel. D/s bed level of channel = +8.00 Top level of solid apron = 8.00 – 0.40 = +7.60 Top level or sill level of drop wall = +10.00 Bottom level of drop wall = +7.60 Height of drop wall = 10.00 – 7.60 = 2.40 m DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 11. Base width of the drop wall This can be calculated based on the following formula B = 𝑯+𝒉𝟏 𝜌 Where H = height of the drop wall = 2.40 m h1 = water flowing depth = 1.50 m 𝜌 = masonry density = 2.25 B = bottom width of the drop wall = 2.60 m DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 12. Design of horizontal floor of the cushion 1) Length Length of solid apron from the toe of the drop wall Maximum length = 2ℎ1 + 2 ℎ1ℎ = 2 × 1.50 + 2 1.5 × 2.0 = 6.46 m Minimum length = 1.50 + 2 ℎ1ℎ = 1.50 + 2 1.5 × 2.0 = 4.96 m Adopt length of solid apron = 5.0 m 2) Thickness The thickness of the solid apron should be sufficient to resist the uplift. The uplift is maximum at the toe of the body wall (i.e., at point D) when the canal is running full. DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 13. Head causing flow = 11.5 - 9.5 = 2.0 m Assuming thickness of the apron 1m And hydraulic gradient of 1 in 4. Length of the creep up to point D = AB+BC+CD= 2.4+1.0+0.3+2.6 = 6.30 Head lost between A & D = 6.3/4 = 1.6 m Residual head at point D (hD) = 2 – 1.6 = 0.4 m Thickness required at point D = hD/(G – 1) = 0.4/(2.25 – 1) = 0.35 m But minimum thickness is usually provided to withstand the impact of the falling water = 0.5 ℎ1 + 𝑑 = 0.5 1.5 + 2.0 = 0.94 𝑚 However, provide 1 m thick of concrete. DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 14. Notches & Notch Pier The sills of the notches = U/S bed level of canal Two notches are arranged in the notch Pier over the body wall. Top of the notch pier = U/S F.S.L = 11.50 Width of the notch = (h1/2) = 1.5/2 = 0.75 m. but in this case 0.85 m proided This type of arrangements reduces the – eddies around the body wall DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 15. Protective works Abutment(BC) Length of the abutment = base width of the drop wall = 2.6 m Top width of the abutment = 0.5 m Top level of the abutment = T.B.L of U/S canal = +12.50 Bottom level of the abutment = foundation of the drop wall = +7.60 Height of the abutment = 12.50 – 7.60 = 4.90 m Base width of the abutment = 0.4 × 4.90 = 1.96 ≈ 2.0 m DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 16. U/S wing wall(AB) Providing a splay 1 in 1 Top width = 0.50 m Top level = T.B.L of U/S canal = +12.50 Bottom level = good soil for foundation = +8.50 Height of wing wall = 12.50 – 8.50 = 4.0 m Bottom width = 0.4 × 4 = 1.60 m Provide a foundation concrete of 60 cm thick Provide a front batter of 1 in 8 DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 17. D/S wing wall (CD) It is sloping from C to D Section at C = section of abutment But foundation concrete is 60 cm thick Section at D Top width = 0.50 m Top level = T.B.L of D/S canal = +10.50 Bottom level = the top of water cushion = +7.60 Height of wing wall = 10.50 – 7.60 = 2.90 m Bottom width = 0.4 × 2.9 = 1.16 m ≈ 1.20 m Provide a foundation concrete of 60 cm thick D/S return(DE) It is a level return wall Section at E = Section at D DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 18. U/S revetment and apron Length of the revetment = 3h1 or min of 3 m = 3 × 1.5 = 4.50 m Length of the revetment = 4.50 m from the drop wall towards the U/S Length of the apron = 0.5 × Length of the revetment = 0.5 × 4.50 = 2.25 m D/S revetment and apron Length of the revetment = 4(h1+d) or min of 6 m = 4(1.5 + 2) = 14 m Length of the revetment = 14 m from the end of the cistern Length of the apron = 0.5 × Length of the revetment = 0.5 × 14 = 7.00 m DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 19. DESIGN AND DRAWING OF IRRIGATION STRUCTURES
- 20. DESIGN AND DRAWING OF IRRIGATION STRUCTURES