GATE CE 2025 Set 1 — Question 61
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Water Resources Engineering → Canals & Hydraulic Structures → Canal Losses
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Question
A symmetrical trapezoidal canal is 100 km long. The bottom width is 10 m and the side slope is 1 Horizontal : 1 Vertical. The average flow depth in the canal is 2.5 m throughout the month of April. The measurement from a Class-A evaporimeter in the vicinity of the canal indicated an average evaporation rate of 0.5 cm/day in April. The volume of water evaporated from the canal (in ) in the month of April is close to __________________ (rounded off to 1 decimal place).
Correct answer
120 to 180
Solution
Given:
Length of canal,
Bottom width,
Side slope, (1H:1V)
Flow depth,
Pan evaporation rate,
Number of days in April = 30Step 1: Calculate the top width () of the trapezoidal canal.
Step 2: Calculate the surface area () of the canal.
Step 3: Calculate the total pan evaporation for April.
Total Step 4: Calculate actual lake/canal evaporation ().
Using a standard pan coefficient () for a Class-A pan, typically .
Step 5: Calculate the volume of water evaporated ().
The range provided (120.0 to 180.0) accounts for variations in the pan coefficient (from approx. 0.53 to 0.8).
Length of canal,
Bottom width,
Side slope, (1H:1V)
Flow depth,
Pan evaporation rate,
Number of days in April = 30Step 1: Calculate the top width () of the trapezoidal canal.
Step 2: Calculate the surface area () of the canal.
Step 3: Calculate the total pan evaporation for April.
Total Step 4: Calculate actual lake/canal evaporation ().
Using a standard pan coefficient () for a Class-A pan, typically .
Step 5: Calculate the volume of water evaporated ().
The range provided (120.0 to 180.0) accounts for variations in the pan coefficient (from approx. 0.53 to 0.8).
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