REVIEW QUESTIONS INSOIL AND WATER CONSERVATION ENGINEERING Arthur It. Tambong, FPSAE Professor III, MSU - Main Campus INSTRUCTIONS: Select the best answer. Shade the corresponding box of your answer in the answer sheet. Give only one answer for each question. Do not make any unnecessary marking in the answer sheet. 1. Which one is the flattest canal side slope? A. 1:1 B. 1:4 C. 4:1 D. 2:1 Answer: C 2. Determine the side slope angle of an unlined canal with slope ratio z of 2:1 (run: rise)? A. 16.6º B. 26.6º C. 45º D. None of the above Answer: B Solution: Side angle with the horizontal Ө is (Note: Fuid Mech. & Hydraulics by Gillesania uses Ө symbol for side angle w/ the vertical) Ө = arctan (rise /run) = arctan (1/2) = 26.6º Note: In specifying side slope, run is written first, ex. 4:1 means horizontal run is 4. In computing angles whether bed slope or side slope, rise is numerator: tan Ө = rise /run Ө = arctan (rise /run) 577 A = bd + zd2 A-zd2 = bd b = (A-zd2) / d = [50 – 0.12)/2] 50 = 5[10] 50 = 50 C.29 m B.89+7.12 m + [2(5) / 1. 4m C.5) = 2 (5) (0.12)(5) + 0. 9. What is the bottom width for the best hydraulic cross-section (best proportion) of concrete open channel if design depth is 5 meters and side slope is 45º? A. 12.9 m D.6+14. A.89 m Checking 1: A = bd + zd2 50=(7.577(5) 2] / 5 = 7. 5 m D.1 m 3a.12 m Answer: C Solution: Design Criteria: Most Efficient Canal (Ө=60º) Q = AV 100 = A (2) A = 50 m2 tan Ө = 1 / z tan 60 º = 1 / z 1.577(5)2 50=35. What is the top width at water surface level of the most efficient concrete open channel if design depth is 5 meters? Design discharge is 100 m3/s and velocity is 2 m/s. None of the above Answer: B Solution: b = 2 d tan (Ө/2) = 2 (5) tan (45/2) = 2 (5) tan (22.41) = 4.732 = 1 / z z = 0.12 m t = b + (2d / tan Ө) = 7.732] = 12.4 50=50 Checking 2: A = d [(t + b)/2] 50= 5 [(12. 3 m B. None of the above .3. 1. 12)(5) + 0.577(5) 2] / 5 = 7. A.75) / 1.577(5)2 50=35. None of the above .12)/2] 50 = 5[10] 50 = 50 C. 12.8 m Answer: B Solution: Design Criteria: Most Efficient Canal (Ө=60º) Q = AV 100 = A (2) A = 50 m2 tan Ө = 1 / z tan 60 º = 1 / z 1.732] = 12.4 50=50 Checking 2: A = d [(t + b)/2] 50= 5 [(12.8 m Checking 1: A = bd + zd2 50=(7.3b.15(5) = 5.12 m + [2(5) / 1.12 + [2(5.6+14.89+7. 18.89 m D = 1.12 m t = b + (2d / tan Ө) = 7.732] = 7. Use 15% freeboard.64 = 13.732 = 1 / z z = 0.15d = 1. What is the total top width of the most efficient concrete open channel if design depth is 5 meters? Design discharge is 100 m3/s and velocity is 2 m/s.12 + 6.75 m T = b + (2D / tan Ө) = 7.3 m D.577 A = bd + zd2 A-zd2 = bd b = (A-zd2) / d = [50 – 0. 13.9 m B. 7.3c.4 = 6.4)2 50=33. 2.72 m B.732 d2 50/1. What is the base of the most efficient trapezoidal concrete open channel if discharge is 100 m3/s and velocity is 2 m/s.14 m Checking 1: A = bd + zd2 50=(6.732 = d2 d = 5. 3 m B. 4m C.6º b = 4 d tan (Ө/2) C. 4.2+16.577(5.47 m D. None of the above Answer: A Solution: Q = AV 100 = A (2) A = 50 m2 A = 1. B. 7.8 m C. None of the above . What is the bottom width for best hydraulic cross-section of unlined open channel with minimum seepage if design depth is 5 meters and side slope is 2:1? A. What is the bottom width for best hydraulic cross-section of unlined open channel for minimum seepage if design depth is 5 meters and side slope is 45º? A.14)(5. None of the above Answer: C Solution: b = 4 d tan (Ө/2) = 4 (5) tan (22. 8 m D.4) 2] / 5.5) = 8.12 m B.8 50=50 4. 7. 12.4 m A = bd + zd2 b = (A-zd2) / d = [50 – 0.577(5.21 m D. 42 m Answer: A Solution: Ө = arctan (rise /run) = arctan (1/2) = 26.2 m 5.4) + 0. 2 m. The estimated width and depth of concrete-lined rectangular open channel for water velocity of 2 m/s and discharge of 10 m3/s. 1.58 m b = 2 (1.72 m 6.6/2) = 4 (5) tan (13.236) = 4.6m C. 3. 6.3m B. A.= 4 (5) tan (26.3) = 4 (5) (0.16 m 7.1 m.1m Ө = 45º . A = d2 50 = d2 d = 7. What should be the depth and side angle with the horizontal of concrete-lined triangular open channel for a cross-sectional area of 50 m2. None of the above Answer: B Solution: Expressing b in terms of d: b =2d Determining A: A = Q/V = 10/2 = 5 m2 Solving for b and d: A = bd 5 = (2d)d d2 = 5/2 d = 1. 2.5m. What should be the base and depth of concrete-lined rectangular open channel for a cross-sectional area of 50 m2. A = 2 d2 50 =2 d2 d=5m b = 2d b = 2(5) b = 10 m Checking: A = bd 50 = (10)(5) 50 = 50 8. 5.58) = 3. Design for efficiency over proportion.0m D. 2. 5 m D.732 d2 d = 3. 31. If a unlined trapezoidal canal with best hydraulic cross-section can be used. 2. 2. If the most efficient of all trapezoidal cross-sections can be used. 3. 1. what design depth of open channel would you recommend to carry 100 cumecs with a velocity of 5 mps? (No. 1. MSU-GSC Preboard on Hydrology and SWCE.2 m D.12 m B.4 m D.3 m Answer: C Solution: A = Q/V = 100/5 = 20 m2 A = 1.12 m Answer: B Solution: A = Q/V = 10/1 = 10 m2 Ө = arctan (rise /run) = arctan (1/2) Ө = 26. what actual depth of open channel would you recommend to carry 100 cumecs with a velocity of 5 mps? Use 15% freeboard.4 m D = 1. what actual depth of open channel would you recommend to carry 10 cumecs with a velocity of 1 mps? Use 2:1 side slope and 15% freeboard. A.4 m C.4) = 3.9. 21.91 m 11. Part II) A.4 m 10. A.21 m .4 m B. 3.15 d = 1.732 d2 20 = 1. 3. page 64.4 m C. 3. If the most efficient of all trapezoidal cross-sections can be used.9 m B.732 d2 20 = 1. 1.3 m Answer: A Solution: A = Q/V = 100/5 = 20 m2 A = 1. 1. 2.732 d2 d = 3.15 (3.565º C. 15 d = 1.8 4) / 0.84 [(9.15 (1.944d + 2d2 but z = 2 10 = 2.944 d = 0.b = 4 d tan (Ө/2) b = 0.84 m) = 2.944d2 d = 1.74 + [2(1.944d + zd2 but z = 2 10 = 0.12m Checking: tan (26.944 (1.11 m A = d [(t + b)/2] 10 = 1.565º) = 0.11+1.944 d A = bd + zd2.5] t = 9.84m) = 1.84 m D = 1.5 b = 0.74 m t = b + (2d / tan Ө) t = 1. 10 = 0.74)/2] 10 = 10 . OPEN CHANNEL DESIGN CRITERIA DESIGN CRITERIA: EFFICIENT CANAL (For Concrete Only) “Efficient” means maximum discharge for a given volume of reinforced concrete a) Trapezoidal Canal. & Hydraulics by Gillesania uses Ө symbol for side angle w/ vertical) A = 1. Ө = 45º (best angle w/ the horizontal for triangular canals) A = d2 . Ө=60º (MOST EFFICIENT among trapezoidal & rectangular) Ө is the side angle with the horizontal (Note: Fuid Mech. Ө=90º A = 2 d2 b = 2d R = d/2 c) Triangular Canal.732 d2 R = d/2 b) Rectangular Canal. DESIGN CRITERIA: BEST HYDRAULIC CROSS-SECTION (or best b-d proportion) a) Concrete Canals Base b relative to depth d at side angle with the horizontal Ө: b = 2 d tan (Ө/2) b) Unlined Canals (No Concrete) Base b: b = 4 d tan (Ө/2) Top Width t at water surface level: t = b + (2d / tan Ө) Total Top Width T at total depth D level: T = b + (2D / tan Ө) .
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