A flow net is drawn for a weir. The total head loss is 6 m, number of potential drops is 10 and length of flow path for the last square is 1m. The exit gradient is
- A0.6Correct
- B0.7
- C1.0
- D1.6
Solution
Concept
Exit gradient
Formula
iexit = (Δh per equipotential drop) / (length of flow path in the last square) = (H/Nd)/l
Step-by-step solution
1. Head loss per drop = 6 / 10 = 0.6 m. 2. Length of last square = 1 m. 3. iexit = 0.6 / 1 = 0.6.
Explanation
In a flow net the hydraulic gradient across an element is the head drop across it divided by the length of the flow path. The exit gradient is the gradient across the last element at the downstream end.
Shortcut
iexit = H / (Nd × l).
Common mistake
Using the total head loss (6) without dividing by the number of drops.
Correct answer: A) 0.6